Lorenzo Diaz-Mataix - Academia.edu (original) (raw)

Papers by Lorenzo Diaz-Mataix

Journal of Neuroscience, 2011

This new finding suggests that sensory-specific associations are stored in the lateral amygdala, ... more This new finding suggests that sensory-specific associations are stored in the lateral amygdala, allowing for their selective alteration by either element of the association.

Learning & Memory, 2013

In reconsolidation studies, memories are typically retrieved by an exposure to a single condition... more In reconsolidation studies, memories are typically retrieved by an exposure to a single conditioned stimulus (CS). We have previously demonstrated that reconsolidation processes are CS-selective, suggesting that memories retrieved by the CS exposure are discrete and reconsolidate separately. Here, using a compound stimulus in which two distinct CSs are concomitantly paired with the same aversive unconditioned stimulus (US), we show in rats that reexposure to one of the components of the compound CS triggers extinction or reconsolidation of the other component. This suggests that the original training conditions play a critical role in memory retrieval and reconsolidation. 7 These authors equally contributed to this work.

Updating memories is critical for adaptive behaviors, but the rules and mechanisms governing that... more Updating memories is critical for adaptive behaviors, but the rules and mechanisms governing that process are still not well defined. During a limited time window, the reactivation of consolidated aversive memories triggers memory lability and induces a plasticity-dependent reconsolidation process in the lateral nucleus of amygdala (LA) . However, whether new information is necessary for initiating reconsolidation is not known. Here we show that changing the temporal relationship between the conditioned stimulus (CS) and unconditioned stimulus (US) during reactivation is sufficient to trigger synaptic plasticity and reconsolidation of an aversive memory in the LA. These findings demonstrate that time is a core part of the CS-US association and that new information must be presented during reactivation in order to trigger LA-dependent reconsolidation processes. In sum, this study provides new basic knowledge about the precise rules governing memory reconsolidation of aversive memories that might be used to treat traumatic memories.

Recognizing predictive relationships is critical for survival, but an understanding of the underl... more Recognizing predictive relationships is critical for survival, but an understanding of the underlying neural mechanisms remains elusive. In particular, it is unclear how the brain distinguishes predictive relationships from spurious ones when evidence about a relationship is ambiguous, or how it computes predictions given such uncertainty. To better understand this process, we introduced ambiguity into an associative learning task by presenting aversive outcomes both in the presence and in the absence of a predictive cue. Electrophysiological and optogenetic approaches revealed that amygdala neurons directly regulated and tracked the effects of ambiguity on learning. Contrary to established accounts of associative learning, however, interference from competing associations was not required to assess an ambiguous cue-outcome contingency. Instead, animals' behavior was explained by a normative account that evaluates different models of the environment's statistical structure. These findings suggest an alternative view of amygdala circuits in resolving ambiguity during aversive learning. advance online publication nature neurOSCIenCe

Pavlovian conditioning is the reference paradigm for the study of associative learning based on t... more Pavlovian conditioning is the reference paradigm for the study of associative learning based on the programmed relation of two stimuli, the conditioned stimulus (CS) and the unconditioned stimulus (US). Some authors believe that learning the CS-US interval is a co-requisite of or a pre-requisite to learning the CS-US association. There is a substantial literature showing that the amygdala is a critical player in Pavlovian conditioning, with both aversive and appetitive USs. We review a sparse but growing body of literature suggesting that the amygdala may also participate in processing the timing of the CS-US interval. We discuss whether the amygdala, in particular its central, basal and lateral nuclei, in concert with the network it belongs to, may play a role in learning the CS-US interval. We also suggest new and dedicated strategies that would result in better knowledge of the neural mechanisms underlying the learning of the CS-US time interval in isolation from the CS-US association.

This new finding suggests that sensory-specific associations are stored in the lateral amygdala, ... more This new finding suggests that sensory-specific associations are stored in the lateral amygdala, allowing for their selective alteration by either element of the association.

The updating of a memory is triggered whenever it is reactivated and a mismatch from what is expe... more The updating of a memory is triggered whenever it is reactivated and a mismatch from what is expected (i.e., prediction error) is detected, a process that can be unraveled through the memory's sensitivity to protein synthesis inhibitors (i.e., reconsolidation). As noted in previous studies, in Pavlovian threat/aversive conditioning in adult rats, prediction error detection and its associated protein synthesis-dependent reconsolidation can be triggered by reactivating the memory with the conditioned stimulus (CS), but without the unconditioned stimulus (US), or by presenting a CS-US pairing with a different CS-US interval than during the initial learning. Whether similar mechanisms underlie memory updating in the young is not known. Using similar paradigms with rapamycin (an mTORC1 inhibitor), we show that preweaning rats (PN18-20) do form a long-term memory of the CS -US interval, and detect a 10-sec versus 30-sec temporal prediction error. However, the resulting updating/reconsolidation processes become adult-like after adolescence (PN30-40). Our results thus show that while temporal prediction error detection exists in preweaning rats, specific infant-type mechanisms are at play for associative learning and memory.

5-HT 1A receptor agonists increase the activity of dopamine (DA) neurons in the ventral tegmental... more 5-HT 1A receptor agonists increase the activity of dopamine (DA) neurons in the ventral tegmental area (VTA) and DA release in medial prefrontal cortex (mPFC). The mPFC is enriched in 5-HT 1A receptors and projects to the VTA, where mesocortical dopaminergic neurons originate. We examined whether 5-HT 1A receptor activation can modulate the activity of mPFC pyramidal neurons projecting to VTA. These were identified by antidromic stimulation from the VTA and were recorded extracellularly in anesthetized rats. The selective 5-HT 1A agonist BAY Â 3702 (10-80 Ag/kg i.v.) increased the firing rate in 14/19 neurons (283 F 79%) and reduced the activity of 5/19 neurons (22 F 11%), resulting in an overall 2.2-fold increase of the firing rate. Both effects were blocked by the selective 5-HT 1A antagonist WAY-100635. These results suggest that the increase in dopaminergic activity produced by 5-HT 1A receptor activation can be driven by an increase in the activity of projection neurons in mPFC. D

Atypical antipsychotics increase dopamine (DA) release in the medial prefrontal cortex (mPFC), an... more Atypical antipsychotics increase dopamine (DA) release in the medial prefrontal cortex (mPFC), an effect possibly involved in the superior effects of atypical versus classical antipsychotics on cognitive/negative symptoms. We examined the role of 5-HT 1A receptors in the mPFC on the modulation of dopaminergic activity and the mesocortical DA release in vivo. The highly selective 5-HT 1A agonist BAY x 3702 (BAY; 10 -40 g/kg, i.v.) increased the firing rate and burst firing of DA neurons in the ventral tegmental area (VTA) and DA release in the VTA and mPFC. The increase in DA release in both areas was potentiated by nomifensine coperfusion. The selective 5-HT 1A antagonist WAY-100635 reversed the effects of BAY in both areas, and the changes in the VTA were prevented by frontocortical transection.

Fear extinction, which involves learning to suppress the expression of previously learned fear, r... more Fear extinction, which involves learning to suppress the expression of previously learned fear, requires N-methyl-D-aspartate receptors (NMDARs) and is mediated by the amygdala and ventromedial prefrontal cortex (vmPFC). Like other types of learning, extinction involves acquisition and consolidation phases. We recently demonstrated that NR2B-containing NMDARs (NR2Bs) in the lateral amygdala (LA) are required for extinction acquisition, but whether they are involved in consolidation is not known. Further, although it has been shown that NMDARs in the vmPFC are required for extinction consolidation, whether NR2Bs in vmPFC are involved in consolidation is not known. In this report, we investigated the possible role of LA and vmPFC NR2Bs in the consolidation of fear extinction using the NR2B-selective antagonist ifenprodil. We show that systemic treatment with ifenprodil immediately after extinction training disrupts extinction consolidation. Ifenprodil infusion into vmPFC, but not the LA, immediately after extinction training also disrupts extinction consolidation. In contrast, we also show pre-extinction training infusions into vmPFC has no effect. These results, together with our previous findings showing that LA NR2Bs are required during the acquisition phase in extinction, indicate a double dissociation for the phase-dependent role of NR2Bs in the LA (acquisition, not consolidation) and vmPFC (consolidation, not acquisition).

The activation of 5-HT 2A receptors in medial prefrontal cortex (mPFC) by the hallucinogen DOI in... more The activation of 5-HT 2A receptors in medial prefrontal cortex (mPFC) by the hallucinogen DOI increases the firing activity of dorsal raphe (DR) 5-HT neurons and prefrontal 5-HT release. Here we show that the i.v. administration of DOI markedly affected the firing rate of identified pyramidal neurons recorded extracellularly. DOI excited (481%) 21/56 neurons, inhibited (11%) 17/56 neurons and left the rest unaffected (overall 2.4-fold increase in firing rate). Both effects were antagonized by 5-HT 2A receptor blockade. 5-HT 2A -mediated orthodromic excitations were recorded in pyramidal neurons projecting to DR after electrical stimulation of this nucleus. We also examined whether the effects of DOI in mPFC involve thalamic excitatory inputs. The disinhibition of the mediodorsal and centromedial nuclei of the thalamus by local bicuculline resembled the effects of DOI as it increased pyramidal cell firing and 5-HT release in mPFC. However, the selective activation of prefrontal µ-opioid and mGlu II receptors counteracted the effects of the thalamic disinhibition but not those of DOI. Moreover, extensive thalamic lesions did not alter the effect of DOI on pyramidal cell firing and 5-HT release. We conclude that DOI increases the activity of the mPFC-DR circuit by an action on postsynaptic 5-HT 2A receptors unrelated to thalamocortical afferents.

Atypical antipsychotic drugs (APDs) increase dopamine (DA) release in prefrontal cortex (PFC), an... more Atypical antipsychotic drugs (APDs) increase dopamine (DA) release in prefrontal cortex (PFC), an effect probably mediated by the direct or indirect activation of the 5-HT 1A receptor (5-HT 1A R). Given the very low in-vitro affinity of most APDs for 5-HT 1A Rs and the large co-expression of 5-HT 1A Rs and 5-HT 2A receptors (5-HT 2A Rs) in the PFC, this effect might result from the imbalance of 5-HT 1A R and 5-HT 2A R activation after blockade of these receptors by APDs, for which they show high affinity. Here we tested this hypothesis by examining the dependence of the APD-induced DA release in medial PFC (mPFC) on each receptor by using in-vivo microdialysis in wild-type (WT) and 5-HT 1A R and 5-HT 2A R knockout (KO) mice. Local APDs (clozapine, olanzapine, risperidone) administered by reverse dialysis induced a dosedependent increase in mPFC DA output equally in WT and 5-HT 2A R KO mice whereas the DA increase was absent in 5-HT 1A R KO mice. To examine the relative contribution of both receptors to the clozapineinduced DA release in rat mPFC, we silenced G-protein-coupled receptors (GPCRs) in vivo with N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) while 5-HT 1A Rs or 5-HT 2A/2C Rs in the mPFC were selectively protected with the respective antagonists WAY-100635 or ritanserin. The inactivation of GPCRs while preserving y70 % of 5-HT 2A/2C Rs prevented the clozapine-induced DA rise in mPFC. In contrast, clozapine increased DA in mPFC of EEDQ-treated rats whose 5-HT 1A Rs were protected (y50 % of control rats). These results indicate that (1) 5-HT 1A Rs are necessary for the APDs-induced elevation in cortical DA transmission, and (2) this effect does not require 5-HT 2A R blockade by APDs.

Background: Perceptual and psychic alterations and thought disorder are fundamental elements of s... more Background: Perceptual and psychic alterations and thought disorder are fundamental elements of schizophrenia symptoms, a pathology associated with an abnormal macro-and microcircuitry of several brain areas including the prefrontal cortex (PFC). Alterations in information processing in PFC may partly underlie schizophrenia symptoms.

The creation of auditory threat Pavlovian memory requires an initial learning stage in which a ne... more The creation of auditory threat Pavlovian memory requires an initial learning stage in which a neutral conditioned stimulus (CS), such as a tone, is paired with an aversive one (US), such as a shock. In this phase, the CS acquires the capacity of predicting the occurrence of the US and therefore elicits conditioned defense responses. Norepinephrine (NE), through β-adrenergic receptors in the amygdala, enhances threat memory by facilitating the acquisition of the CS-US association, but the nature of this effect has not been described. Here we show that NE release, induced by the footshock of the first conditioning trial, promotes the subsequent enhancement of learning. Consequently, blocking NE transmission disrupts multitrial but not one-trial conditioning. We further found that increasing the time between the conditioning trials eliminates the amplificatory effect of NE. Similarly, an unsignaled footshock delivered in a separate context immediately before conditioning can enhance learning. These results help define the conditions under which NE should and should not be expected to alter threat processing and fill an important gap in the understanding of the neural processes relevant to the pathophysiology of stress and anxiety disorders. 4 These authors contributed equally to this work.

Pavlovian aversive conditioning requires learning of the association between a conditioned stimul... more Pavlovian aversive conditioning requires learning of the association between a conditioned stimulus (CS) and an unconditioned, aversive stimulus (US) but also involves encoding the time interval between the two stimuli. The neurobiological bases of this time interval learning are unknown. Here, we show that in rats, the dorsal striatum and basal amygdala belong to a common functional network underlying temporal expectancy and learning of a CS-US interval. Importantly, changes in coherence between striatum and amygdala local field potentials (LFPs) were found to couple these structures during interval estimation within the lower range of the theta rhythm (3-6 Hz). Strikingly, we also show that a change to the CS-US time interval results in long-term changes in cortico-striatal synaptic efficacy under the control of the amygdala. Collectively, this study reveals physiological correlates of plasticity mechanisms of interval timing that take place in the striatum and are regulated by the amygdala.

A long-standing hypothesis termed "Hebbian plasticity" suggests that memories are formed through ... more A long-standing hypothesis termed "Hebbian plasticity" suggests that memories are formed through strengthening of synaptic connections between neurons with correlated activity. In contrast, other theories propose that coactivation of Hebbian and neuro-modulatory processes produce the synaptic strengthening that underlies memory formation. Using optogenetics we directly tested whether Hebbian plasticity alone is both necessary and sufficient to produce physiological changes mediating actual memory formation in behaving animals. Our previous work with this method suggested that Hebbian mechanisms are sufficient to produce aversive associative learning under artificial conditions involving strong, iterative training. Here we systematically tested whether Hebbian mechanisms are necessary and sufficient to produce associative learning under more moderate training conditions that are similar to those that occur in daily life. We measured neural plasticity in the lateral amygdala, a brain region important for associative memory storage about danger. Our findings provide evidence that Hebbian mechanisms are necessary to produce neural plasticity in the lateral amygdala and behavioral memory formation. However, under these conditions Hebbian mechanisms alone were not sufficient to produce these physiological and behavioral effects unless neuromodu-latory systems were coactivated. These results provide insight into how aversive experiences trigger memories and suggest that combined Hebbian and neuromodulatory processes interact to engage associative aversive learning. Hebbian plasticity | amygdala | neuromodulation | instructive signals | associative learning H ebbian plasticity refers to the strengthening of a presynaptic input onto a postsynaptic neuron when both pre-and post-synaptic neurons are coactive (1). This was originally proposed as a mechanism for memory formation. Findings from in vitro and in vivo physiological studies suggest that Hebbian processes control synaptic strengthening (2-10). However, other results and theories suggest that Hebbian mechanisms alone are not normally sufficient for producing synaptic plasticity and that syn-aptic strengthening mediating memory formation involves interactions between Hebbian and neuromodulatory mechanisms (3, 4, 7, 11-19). Although molecules that may mediate Hebbian processes in memory formation have been identified (3, 11, 16, 17, 20-22), it has been difficult to directly test whether Hebbian plasticity alone or in combination with neuromodulation is necessary and sufficient to produce neural plasticity and memories in behaving animals (especially in mammals). This is because of technical limitations in controlling correlated activity between pre-and postsynaptic neurons involved in memory storage in a temporally/spatially precise manner while measuring behavioral memory formation and neural plasticity. To overcome these problems, we used optogenetic techniques to directly manipulate Hebbian mechanisms in pyramidal neu-rons in the lateral nucleus of the amygdala (LA), a cell population important for storing aversive memories. Pavlovian auditory threat (fear) conditioning (23, 24) is a form of asso-ciative learning during which a neutral auditory conditioned stimulus (CS) is temporally paired with an aversive unconditioned stimulus (US), often a mild electric shock (17, 20, 21, 25-27). Following training, the auditory CS comes to elicit behavioral defense responses (such as freezing) and supporting physiological changes controlled by the autonomic nervous and endocrine systems. These conditioned responses can be used to measure the associative memory created by CS-US pairing. This form of aversive Pavlovian conditioning is a particularly useful model for testing the Hebbian hypothesis because a critical site of associative plasticity underlying the learning has been identified in the LA (17, 22, 28). LA neurons receive convergent input from the auditory system and from aversive nociceptive circuits (29, 30). Auditory inputs to LA neurons are potentiated during threat conditioning (31-34), possibly as a result of auditory evoked presynaptic activity occurring convergently and contemporaneously with strong activation of postsynaptic LA pyramidal neurons by the aversive shock US (i.e., a Hebbian mechanism). If these neural and behavioral changes are the result of Hebbian plasticity, then activity in LA pyramidal neurons specifically during the aversive US period (when both pre-synaptic inputs and postsynaptic neurons may be active) should be necessary for aversive memory formation and learning-related plasticity of auditory input synapses in the LA to occur. Reducing Significance The influential Hebbian plasticity hypothesis suggests that an increase in the strength of connections between neurons whose activity is correlated produces memories. Other theories , however, propose that neuromodulatory systems need to be activated together with Hebbian plasticity mechanisms to engage memory formation. The present work provides direct in vivo evidence supporting the idea that a parallel mechanism involving neuromodulation and Hebbian processes is both necessary and sufficient to trigger synaptic strengthening and behavioral associative memory formation. This parallel process may represent a general mechanism used by many learning systems in the brain.

Rationale Aripiprazole is an atypical antipsychotic drug with high in vitro affinity for 5-HT 1A ... more Rationale Aripiprazole is an atypical antipsychotic drug with high in vitro affinity for 5-HT 1A , 5-HT 2A and dopamine (DA) D2 receptors. However, its in vivo actions in the brain are still poorly characterized. Objective The aim was to study the in vivo actions of aripiprazole in the rat and mouse brain. Methods Brain microdialysis and single-unit extracellular recordings were performed. Results The systemic administration of aripiprazole reduced 5-HT output in the medial prefrontal cortex (mPFC) and dorsal raphe nucleus of the rat. Aripiprazole also reduced extracellular 5-HT in the mPFC of wild-type (WT) but not of 5-HT 1A (−/−) knockout (KO) mice. Aripiprazole reversed the elevation in extracellular 5-HT output produced by the local application of the 5-HT 2A/2C receptor agonist DOI in mPFC. Aripiprazole also increased the DA output in mPFC of WT but not of 5-HT 1A KO mice, as observed for atypical antipsychotic drugs, in contrast to haloperidol. Contrary to haloperidol, which increases the firing rate of DA neurons in the ventral tegmental area (VTA), aripiprazole induced a very moderate reduction in dopaminergic activity. Haloperidol fully reversed the inhibition in dopaminergic firing rate induced by apomor-phine, whereas aripiprazole evoked a partial reversal that was significantly different from that evoked by haloperidol and from the spontaneous reversal of dopaminergic activity in rats treated with apomorphine. Conclusions These results indicate that aripiprazole modulates the in vivo 5-HT and DA release in mPFC through the activation of 5-HT 1A receptors. Moreover, aripiprazole behaves as a partial agonist at DA D2 autoreceptors in vivo, an action which clearly distinguishes it from haloperidol.

Journal of Neuroscience, 2011

This new finding suggests that sensory-specific associations are stored in the lateral amygdala, ... more This new finding suggests that sensory-specific associations are stored in the lateral amygdala, allowing for their selective alteration by either element of the association.

Learning & Memory, 2013

In reconsolidation studies, memories are typically retrieved by an exposure to a single condition... more In reconsolidation studies, memories are typically retrieved by an exposure to a single conditioned stimulus (CS). We have previously demonstrated that reconsolidation processes are CS-selective, suggesting that memories retrieved by the CS exposure are discrete and reconsolidate separately. Here, using a compound stimulus in which two distinct CSs are concomitantly paired with the same aversive unconditioned stimulus (US), we show in rats that reexposure to one of the components of the compound CS triggers extinction or reconsolidation of the other component. This suggests that the original training conditions play a critical role in memory retrieval and reconsolidation. 7 These authors equally contributed to this work.

Updating memories is critical for adaptive behaviors, but the rules and mechanisms governing that... more Updating memories is critical for adaptive behaviors, but the rules and mechanisms governing that process are still not well defined. During a limited time window, the reactivation of consolidated aversive memories triggers memory lability and induces a plasticity-dependent reconsolidation process in the lateral nucleus of amygdala (LA) . However, whether new information is necessary for initiating reconsolidation is not known. Here we show that changing the temporal relationship between the conditioned stimulus (CS) and unconditioned stimulus (US) during reactivation is sufficient to trigger synaptic plasticity and reconsolidation of an aversive memory in the LA. These findings demonstrate that time is a core part of the CS-US association and that new information must be presented during reactivation in order to trigger LA-dependent reconsolidation processes. In sum, this study provides new basic knowledge about the precise rules governing memory reconsolidation of aversive memories that might be used to treat traumatic memories.

Recognizing predictive relationships is critical for survival, but an understanding of the underl... more Recognizing predictive relationships is critical for survival, but an understanding of the underlying neural mechanisms remains elusive. In particular, it is unclear how the brain distinguishes predictive relationships from spurious ones when evidence about a relationship is ambiguous, or how it computes predictions given such uncertainty. To better understand this process, we introduced ambiguity into an associative learning task by presenting aversive outcomes both in the presence and in the absence of a predictive cue. Electrophysiological and optogenetic approaches revealed that amygdala neurons directly regulated and tracked the effects of ambiguity on learning. Contrary to established accounts of associative learning, however, interference from competing associations was not required to assess an ambiguous cue-outcome contingency. Instead, animals' behavior was explained by a normative account that evaluates different models of the environment's statistical structure. These findings suggest an alternative view of amygdala circuits in resolving ambiguity during aversive learning. advance online publication nature neurOSCIenCe

Pavlovian conditioning is the reference paradigm for the study of associative learning based on t... more Pavlovian conditioning is the reference paradigm for the study of associative learning based on the programmed relation of two stimuli, the conditioned stimulus (CS) and the unconditioned stimulus (US). Some authors believe that learning the CS-US interval is a co-requisite of or a pre-requisite to learning the CS-US association. There is a substantial literature showing that the amygdala is a critical player in Pavlovian conditioning, with both aversive and appetitive USs. We review a sparse but growing body of literature suggesting that the amygdala may also participate in processing the timing of the CS-US interval. We discuss whether the amygdala, in particular its central, basal and lateral nuclei, in concert with the network it belongs to, may play a role in learning the CS-US interval. We also suggest new and dedicated strategies that would result in better knowledge of the neural mechanisms underlying the learning of the CS-US time interval in isolation from the CS-US association.

This new finding suggests that sensory-specific associations are stored in the lateral amygdala, ... more This new finding suggests that sensory-specific associations are stored in the lateral amygdala, allowing for their selective alteration by either element of the association.

The updating of a memory is triggered whenever it is reactivated and a mismatch from what is expe... more The updating of a memory is triggered whenever it is reactivated and a mismatch from what is expected (i.e., prediction error) is detected, a process that can be unraveled through the memory's sensitivity to protein synthesis inhibitors (i.e., reconsolidation). As noted in previous studies, in Pavlovian threat/aversive conditioning in adult rats, prediction error detection and its associated protein synthesis-dependent reconsolidation can be triggered by reactivating the memory with the conditioned stimulus (CS), but without the unconditioned stimulus (US), or by presenting a CS-US pairing with a different CS-US interval than during the initial learning. Whether similar mechanisms underlie memory updating in the young is not known. Using similar paradigms with rapamycin (an mTORC1 inhibitor), we show that preweaning rats (PN18-20) do form a long-term memory of the CS -US interval, and detect a 10-sec versus 30-sec temporal prediction error. However, the resulting updating/reconsolidation processes become adult-like after adolescence (PN30-40). Our results thus show that while temporal prediction error detection exists in preweaning rats, specific infant-type mechanisms are at play for associative learning and memory.

5-HT 1A receptor agonists increase the activity of dopamine (DA) neurons in the ventral tegmental... more 5-HT 1A receptor agonists increase the activity of dopamine (DA) neurons in the ventral tegmental area (VTA) and DA release in medial prefrontal cortex (mPFC). The mPFC is enriched in 5-HT 1A receptors and projects to the VTA, where mesocortical dopaminergic neurons originate. We examined whether 5-HT 1A receptor activation can modulate the activity of mPFC pyramidal neurons projecting to VTA. These were identified by antidromic stimulation from the VTA and were recorded extracellularly in anesthetized rats. The selective 5-HT 1A agonist BAY Â 3702 (10-80 Ag/kg i.v.) increased the firing rate in 14/19 neurons (283 F 79%) and reduced the activity of 5/19 neurons (22 F 11%), resulting in an overall 2.2-fold increase of the firing rate. Both effects were blocked by the selective 5-HT 1A antagonist WAY-100635. These results suggest that the increase in dopaminergic activity produced by 5-HT 1A receptor activation can be driven by an increase in the activity of projection neurons in mPFC. D

Atypical antipsychotics increase dopamine (DA) release in the medial prefrontal cortex (mPFC), an... more Atypical antipsychotics increase dopamine (DA) release in the medial prefrontal cortex (mPFC), an effect possibly involved in the superior effects of atypical versus classical antipsychotics on cognitive/negative symptoms. We examined the role of 5-HT 1A receptors in the mPFC on the modulation of dopaminergic activity and the mesocortical DA release in vivo. The highly selective 5-HT 1A agonist BAY x 3702 (BAY; 10 -40 g/kg, i.v.) increased the firing rate and burst firing of DA neurons in the ventral tegmental area (VTA) and DA release in the VTA and mPFC. The increase in DA release in both areas was potentiated by nomifensine coperfusion. The selective 5-HT 1A antagonist WAY-100635 reversed the effects of BAY in both areas, and the changes in the VTA were prevented by frontocortical transection.

Fear extinction, which involves learning to suppress the expression of previously learned fear, r... more Fear extinction, which involves learning to suppress the expression of previously learned fear, requires N-methyl-D-aspartate receptors (NMDARs) and is mediated by the amygdala and ventromedial prefrontal cortex (vmPFC). Like other types of learning, extinction involves acquisition and consolidation phases. We recently demonstrated that NR2B-containing NMDARs (NR2Bs) in the lateral amygdala (LA) are required for extinction acquisition, but whether they are involved in consolidation is not known. Further, although it has been shown that NMDARs in the vmPFC are required for extinction consolidation, whether NR2Bs in vmPFC are involved in consolidation is not known. In this report, we investigated the possible role of LA and vmPFC NR2Bs in the consolidation of fear extinction using the NR2B-selective antagonist ifenprodil. We show that systemic treatment with ifenprodil immediately after extinction training disrupts extinction consolidation. Ifenprodil infusion into vmPFC, but not the LA, immediately after extinction training also disrupts extinction consolidation. In contrast, we also show pre-extinction training infusions into vmPFC has no effect. These results, together with our previous findings showing that LA NR2Bs are required during the acquisition phase in extinction, indicate a double dissociation for the phase-dependent role of NR2Bs in the LA (acquisition, not consolidation) and vmPFC (consolidation, not acquisition).

The activation of 5-HT 2A receptors in medial prefrontal cortex (mPFC) by the hallucinogen DOI in... more The activation of 5-HT 2A receptors in medial prefrontal cortex (mPFC) by the hallucinogen DOI increases the firing activity of dorsal raphe (DR) 5-HT neurons and prefrontal 5-HT release. Here we show that the i.v. administration of DOI markedly affected the firing rate of identified pyramidal neurons recorded extracellularly. DOI excited (481%) 21/56 neurons, inhibited (11%) 17/56 neurons and left the rest unaffected (overall 2.4-fold increase in firing rate). Both effects were antagonized by 5-HT 2A receptor blockade. 5-HT 2A -mediated orthodromic excitations were recorded in pyramidal neurons projecting to DR after electrical stimulation of this nucleus. We also examined whether the effects of DOI in mPFC involve thalamic excitatory inputs. The disinhibition of the mediodorsal and centromedial nuclei of the thalamus by local bicuculline resembled the effects of DOI as it increased pyramidal cell firing and 5-HT release in mPFC. However, the selective activation of prefrontal µ-opioid and mGlu II receptors counteracted the effects of the thalamic disinhibition but not those of DOI. Moreover, extensive thalamic lesions did not alter the effect of DOI on pyramidal cell firing and 5-HT release. We conclude that DOI increases the activity of the mPFC-DR circuit by an action on postsynaptic 5-HT 2A receptors unrelated to thalamocortical afferents.

Atypical antipsychotic drugs (APDs) increase dopamine (DA) release in prefrontal cortex (PFC), an... more Atypical antipsychotic drugs (APDs) increase dopamine (DA) release in prefrontal cortex (PFC), an effect probably mediated by the direct or indirect activation of the 5-HT 1A receptor (5-HT 1A R). Given the very low in-vitro affinity of most APDs for 5-HT 1A Rs and the large co-expression of 5-HT 1A Rs and 5-HT 2A receptors (5-HT 2A Rs) in the PFC, this effect might result from the imbalance of 5-HT 1A R and 5-HT 2A R activation after blockade of these receptors by APDs, for which they show high affinity. Here we tested this hypothesis by examining the dependence of the APD-induced DA release in medial PFC (mPFC) on each receptor by using in-vivo microdialysis in wild-type (WT) and 5-HT 1A R and 5-HT 2A R knockout (KO) mice. Local APDs (clozapine, olanzapine, risperidone) administered by reverse dialysis induced a dosedependent increase in mPFC DA output equally in WT and 5-HT 2A R KO mice whereas the DA increase was absent in 5-HT 1A R KO mice. To examine the relative contribution of both receptors to the clozapineinduced DA release in rat mPFC, we silenced G-protein-coupled receptors (GPCRs) in vivo with N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) while 5-HT 1A Rs or 5-HT 2A/2C Rs in the mPFC were selectively protected with the respective antagonists WAY-100635 or ritanserin. The inactivation of GPCRs while preserving y70 % of 5-HT 2A/2C Rs prevented the clozapine-induced DA rise in mPFC. In contrast, clozapine increased DA in mPFC of EEDQ-treated rats whose 5-HT 1A Rs were protected (y50 % of control rats). These results indicate that (1) 5-HT 1A Rs are necessary for the APDs-induced elevation in cortical DA transmission, and (2) this effect does not require 5-HT 2A R blockade by APDs.

Background: Perceptual and psychic alterations and thought disorder are fundamental elements of s... more Background: Perceptual and psychic alterations and thought disorder are fundamental elements of schizophrenia symptoms, a pathology associated with an abnormal macro-and microcircuitry of several brain areas including the prefrontal cortex (PFC). Alterations in information processing in PFC may partly underlie schizophrenia symptoms.

The creation of auditory threat Pavlovian memory requires an initial learning stage in which a ne... more The creation of auditory threat Pavlovian memory requires an initial learning stage in which a neutral conditioned stimulus (CS), such as a tone, is paired with an aversive one (US), such as a shock. In this phase, the CS acquires the capacity of predicting the occurrence of the US and therefore elicits conditioned defense responses. Norepinephrine (NE), through β-adrenergic receptors in the amygdala, enhances threat memory by facilitating the acquisition of the CS-US association, but the nature of this effect has not been described. Here we show that NE release, induced by the footshock of the first conditioning trial, promotes the subsequent enhancement of learning. Consequently, blocking NE transmission disrupts multitrial but not one-trial conditioning. We further found that increasing the time between the conditioning trials eliminates the amplificatory effect of NE. Similarly, an unsignaled footshock delivered in a separate context immediately before conditioning can enhance learning. These results help define the conditions under which NE should and should not be expected to alter threat processing and fill an important gap in the understanding of the neural processes relevant to the pathophysiology of stress and anxiety disorders. 4 These authors contributed equally to this work.

Pavlovian aversive conditioning requires learning of the association between a conditioned stimul... more Pavlovian aversive conditioning requires learning of the association between a conditioned stimulus (CS) and an unconditioned, aversive stimulus (US) but also involves encoding the time interval between the two stimuli. The neurobiological bases of this time interval learning are unknown. Here, we show that in rats, the dorsal striatum and basal amygdala belong to a common functional network underlying temporal expectancy and learning of a CS-US interval. Importantly, changes in coherence between striatum and amygdala local field potentials (LFPs) were found to couple these structures during interval estimation within the lower range of the theta rhythm (3-6 Hz). Strikingly, we also show that a change to the CS-US time interval results in long-term changes in cortico-striatal synaptic efficacy under the control of the amygdala. Collectively, this study reveals physiological correlates of plasticity mechanisms of interval timing that take place in the striatum and are regulated by the amygdala.

A long-standing hypothesis termed "Hebbian plasticity" suggests that memories are formed through ... more A long-standing hypothesis termed "Hebbian plasticity" suggests that memories are formed through strengthening of synaptic connections between neurons with correlated activity. In contrast, other theories propose that coactivation of Hebbian and neuro-modulatory processes produce the synaptic strengthening that underlies memory formation. Using optogenetics we directly tested whether Hebbian plasticity alone is both necessary and sufficient to produce physiological changes mediating actual memory formation in behaving animals. Our previous work with this method suggested that Hebbian mechanisms are sufficient to produce aversive associative learning under artificial conditions involving strong, iterative training. Here we systematically tested whether Hebbian mechanisms are necessary and sufficient to produce associative learning under more moderate training conditions that are similar to those that occur in daily life. We measured neural plasticity in the lateral amygdala, a brain region important for associative memory storage about danger. Our findings provide evidence that Hebbian mechanisms are necessary to produce neural plasticity in the lateral amygdala and behavioral memory formation. However, under these conditions Hebbian mechanisms alone were not sufficient to produce these physiological and behavioral effects unless neuromodu-latory systems were coactivated. These results provide insight into how aversive experiences trigger memories and suggest that combined Hebbian and neuromodulatory processes interact to engage associative aversive learning. Hebbian plasticity | amygdala | neuromodulation | instructive signals | associative learning H ebbian plasticity refers to the strengthening of a presynaptic input onto a postsynaptic neuron when both pre-and post-synaptic neurons are coactive (1). This was originally proposed as a mechanism for memory formation. Findings from in vitro and in vivo physiological studies suggest that Hebbian processes control synaptic strengthening (2-10). However, other results and theories suggest that Hebbian mechanisms alone are not normally sufficient for producing synaptic plasticity and that syn-aptic strengthening mediating memory formation involves interactions between Hebbian and neuromodulatory mechanisms (3, 4, 7, 11-19). Although molecules that may mediate Hebbian processes in memory formation have been identified (3, 11, 16, 17, 20-22), it has been difficult to directly test whether Hebbian plasticity alone or in combination with neuromodulation is necessary and sufficient to produce neural plasticity and memories in behaving animals (especially in mammals). This is because of technical limitations in controlling correlated activity between pre-and postsynaptic neurons involved in memory storage in a temporally/spatially precise manner while measuring behavioral memory formation and neural plasticity. To overcome these problems, we used optogenetic techniques to directly manipulate Hebbian mechanisms in pyramidal neu-rons in the lateral nucleus of the amygdala (LA), a cell population important for storing aversive memories. Pavlovian auditory threat (fear) conditioning (23, 24) is a form of asso-ciative learning during which a neutral auditory conditioned stimulus (CS) is temporally paired with an aversive unconditioned stimulus (US), often a mild electric shock (17, 20, 21, 25-27). Following training, the auditory CS comes to elicit behavioral defense responses (such as freezing) and supporting physiological changes controlled by the autonomic nervous and endocrine systems. These conditioned responses can be used to measure the associative memory created by CS-US pairing. This form of aversive Pavlovian conditioning is a particularly useful model for testing the Hebbian hypothesis because a critical site of associative plasticity underlying the learning has been identified in the LA (17, 22, 28). LA neurons receive convergent input from the auditory system and from aversive nociceptive circuits (29, 30). Auditory inputs to LA neurons are potentiated during threat conditioning (31-34), possibly as a result of auditory evoked presynaptic activity occurring convergently and contemporaneously with strong activation of postsynaptic LA pyramidal neurons by the aversive shock US (i.e., a Hebbian mechanism). If these neural and behavioral changes are the result of Hebbian plasticity, then activity in LA pyramidal neurons specifically during the aversive US period (when both pre-synaptic inputs and postsynaptic neurons may be active) should be necessary for aversive memory formation and learning-related plasticity of auditory input synapses in the LA to occur. Reducing Significance The influential Hebbian plasticity hypothesis suggests that an increase in the strength of connections between neurons whose activity is correlated produces memories. Other theories , however, propose that neuromodulatory systems need to be activated together with Hebbian plasticity mechanisms to engage memory formation. The present work provides direct in vivo evidence supporting the idea that a parallel mechanism involving neuromodulation and Hebbian processes is both necessary and sufficient to trigger synaptic strengthening and behavioral associative memory formation. This parallel process may represent a general mechanism used by many learning systems in the brain.

Rationale Aripiprazole is an atypical antipsychotic drug with high in vitro affinity for 5-HT 1A ... more Rationale Aripiprazole is an atypical antipsychotic drug with high in vitro affinity for 5-HT 1A , 5-HT 2A and dopamine (DA) D2 receptors. However, its in vivo actions in the brain are still poorly characterized. Objective The aim was to study the in vivo actions of aripiprazole in the rat and mouse brain. Methods Brain microdialysis and single-unit extracellular recordings were performed. Results The systemic administration of aripiprazole reduced 5-HT output in the medial prefrontal cortex (mPFC) and dorsal raphe nucleus of the rat. Aripiprazole also reduced extracellular 5-HT in the mPFC of wild-type (WT) but not of 5-HT 1A (−/−) knockout (KO) mice. Aripiprazole reversed the elevation in extracellular 5-HT output produced by the local application of the 5-HT 2A/2C receptor agonist DOI in mPFC. Aripiprazole also increased the DA output in mPFC of WT but not of 5-HT 1A KO mice, as observed for atypical antipsychotic drugs, in contrast to haloperidol. Contrary to haloperidol, which increases the firing rate of DA neurons in the ventral tegmental area (VTA), aripiprazole induced a very moderate reduction in dopaminergic activity. Haloperidol fully reversed the inhibition in dopaminergic firing rate induced by apomor-phine, whereas aripiprazole evoked a partial reversal that was significantly different from that evoked by haloperidol and from the spontaneous reversal of dopaminergic activity in rats treated with apomorphine. Conclusions These results indicate that aripiprazole modulates the in vivo 5-HT and DA release in mPFC through the activation of 5-HT 1A receptors. Moreover, aripiprazole behaves as a partial agonist at DA D2 autoreceptors in vivo, an action which clearly distinguishes it from haloperidol.