Aldemar Degroot - Academia.edu (original) (raw)

Papers by Aldemar Degroot

Research paper thumbnail of Biomarker-Guided Drug Development for Better Defined Early Patient Studies and Clinical Trial Efficiency

Translational Medicine in CNS Drug Development

Research paper thumbnail of CB 1 Receptor Antagonism Increases Hippocampal Acetylcholine Release : Site and Mechanism of Action

Evidence indicates that blockade of cannabinoid receptors increases acetylcholine (ACh) release i... more Evidence indicates that blockade of cannabinoid receptors increases acetylcholine (ACh) release in brain cortical regions. Although it is assumed that this type of effect is mediated through CB1 receptor (CB1R) antagonism, several in vitro functional studies recently have suggested non-CB1R involvement. In addition, neither the precise neuroanatomical site nor the exact mechanisms underlying this effect are known. We thoroughly examined these issues using a combination of systemic and local administration of CB1R antagonists, different methods of in vivo microdialysis, CB1R knockout (KO) mice, tissue measurements of ACh, and immunochemistry. First, we showed that systemic injections of the CB1R antagonists N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4methyl-1H-pyrazole-3-carboximide hydrochloride (SR141716A) and N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251) dose-dependently increased hippocampal ACh efflux. Li...

Research paper thumbnail of Evaluation of 5-HT7 receptor antagonism for the treatment of anxiety, depression, and schizophrenia through the use of receptor-deficient mice

Behavioural Brain Research

Research paper thumbnail of Genetic deletion of CB1 receptors improves non-associative learning

Behavioural Brain Research, 2005

Habituation (a form of non-associative learning) was measured by assessing locomotion in novel ac... more Habituation (a form of non-associative learning) was measured by assessing locomotion in novel activity monitors in CB1 receptor knockout mice and juxtaposed to habituation measured in muscarinic M2, M4, and double M2/M4 receptor knockout mice. M2 and M2/M4, but not M4, receptor knockout mice appeared to have an impaired ability to habituate, whereas CB1 receptor knockout mice showed enhanced habituation compared to wild-type animals. We conclude that CB1 receptor gene invalidation improves habituation tentatively through an increase in cholinergic neurotransmission.

Research paper thumbnail of Classification and definition of misuse, abuse, and related events in clinical trials: ACTTION systematic review and recommendations

PAIN®, 2013

As the nontherapeutic use of prescription medications escalates, serious associated consequences ... more As the nontherapeutic use of prescription medications escalates, serious associated consequences have also increased. This makes it essential to estimate misuse, abuse, and related events (MAREs) in the development and postmarketing adverse event surveillance and monitoring of prescription drugs accurately. However, classifications and definitions to describe prescription drug MAREs differ depending on the purpose of the classification system, may apply to single events or ongoing patterns of inappropriate use, and are not standardized or systematically employed, thereby complicating the ability to assess MARE occurrence adequately. In a systematic review of existing prescription drug MARE terminology and definitions from consensus efforts, review articles, and major institutions and agencies, MARE terms were often defined inconsistently or idiosyncratically, or had definitions that overlapped with other MARE terms. The Analgesic, Anesthetic, and Addiction Clinical Trials, Translations, Innovations, Opportunities, and Networks (ACTTION) public-private partnership convened an expert panel to develop mutually exclusive and exhaustive consensus classifications and definitions of MAREs occurring in clinical trials of analgesic medications to increase accuracy and consistency in characterizing their occurrence and prevalence in clinical trials. The proposed ACTTION classifications and definitions are designed as a first step in a system to adjudicate MAREs that occur in analgesic clinical trials and postmarketing adverse event surveillance and monitoring, which can be used in conjunction with other methods of assessing a treatment's abuse potential.

Research paper thumbnail of Increasing Acetylcholine Levels in the Hippocampus or Entorhinal Cortex Reverses the Impairing Effects of Septal GABA Receptor Activation on Spontaneous Alternation

Learning & Memory, 2000

Intra-septal infusions of the ␥-aminobutyric acid (GABA) agonist muscimol impair learning and mem... more Intra-septal infusions of the ␥-aminobutyric acid (GABA) agonist muscimol impair learning and memory in a variety of tasks. This experiment determined whether hippocampal or entorhinal infusions of the acetylcholinesterase inhibitor physostigmine would reverse such impairing effects on spontaneous alternation performance, a measure of spatial working memory. Male Sprague-Dawley rats were given intra-septal infusions of vehicle or muscimol (1 nmole/0.5 µL) combined with unilateral intra-hippocampal or intraentorhinal infusions of vehicle or physostigmine (10 µg/µL for the hippocampus; 7.5 µg/µL or 1.875 µg/0.25 µL for the entorhinal cortex). Fifteen minutes later, spontaneous alternation performance was assessed. The results indicated that intra-septal infusions of muscimol significantly decreased percentage-of-alternation scores, whereas intra-hippocampal or intra-entorhinal infusions of physostigmine had no effect. More importantly, intra-hippocampal or intra-entorhinal infusions of physostigmine, at doses that did not influence performance when administered alone, completely reversed the impairing effects of the muscimol infusions. These findings indicate that increasing cholinergic levels in the hippocampus or entorhinal cortex is sufficient to reverse the impairing effects of septal GABA receptor activation and support the hypothesis that the impairing effects of septal GABAergic activity involve cholinergic processes in the hippocampus and the entorhinal cortex.

Research paper thumbnail of Role of Cannabinoid Receptors in Anxiety Disorders

Cannabinoid agents modulate anxiety, although their effects vary and depend on regional endogenou... more Cannabinoid agents modulate anxiety, although their effects vary and depend on regional endogenous tone, basal anxiety levels, environmental context, species differences, type of anxiety, prior exposure, and dose. Cannabinoid receptors are densely located in brain areas that are involved in the regulation of emotional states and induce neurochemical responses that are congruent with anxiolyt ic/anxiogenic effects. The effects on emotion mediated by cannabinoid compounds are believed to be due to a regulation of activity at the cannabinoid CB1 receptors although there is some limited evidence implicating the cannabinoid CB2 and a putative novel cannabinoid receptor (GPR55?) in some of the observed emotional responses. Effects on emotion are likely the result of a net effect of the summated neurochemical responses. Compounds that indirectly regulate activity at the cannabinoid receptors more consistently reduce anxiety both in preclinical and clinical models. Consequently, these compounds may be the focus of future pharmaceutical development of anxiolytic compounds.

Research paper thumbnail of Infusions of physostigmine into the hippocampus or the entorhinal cortex attenuate avoidance retention deficits produced by intra-septal infusions of the GABA agonist muscimol

Brain Research, 2001

Septal gamma-aminobutyric acid (GABA) receptor activation is known to disrupt memory formation, a... more Septal gamma-aminobutyric acid (GABA) receptor activation is known to disrupt memory formation, although the mechanisms underlying this impairment remain unclear. The present study explored the possibility that high levels of septal GABA receptor activity might impair memory by down-regulating acetylcholine (ACh) function in archicortex and entorhinal cortex. To test this possibility, rats were trained on an avoidance task 15 min after receiving intra-septal infusions of vehicle or muscimol (5 nmol/0.5 microl) combined with unilateral intra-hippocampal (10 microl/1 microl) or intra-entorhinal cortex (1.875 microg/0.25 microl) infusions of vehicle or the acetylcholinesterase inhibitor physostigmine. We demonstrate that these infusions do not alter acquisition performance on a continuous multiple trial inhibitory avoidance task. However, intra-septal infusions of muscimol dramatically impair retention performance 48 h later. More importantly, infusions of physostigmine into the hippocampus or the entorhinal cortex, at doses that do not influence acquisition or retention performance when infused alone, attenuate the impairing effects of the muscimol infusions on retention. We suggest that high levels of septal GABA receptor activity might impair memory by down-regulating ACh levels in the hippocampal region, and that such memory impairments can be ameliorated by increasing ACh levels in the hippocampus or entorhinal cortex.

Research paper thumbnail of Glucose increases hippocampal extracellular acetylcholine levels upon activation of septal GABA receptors

Brain Research, 2003

Activation of septal GABA receptors impairs learning and memory and this effect likely involves a... more Activation of septal GABA receptors impairs learning and memory and this effect likely involves an influence on the hippocampus. We found previously that the memory-impairing effects of septal infusions of the GABA agonist muscimol are reversed by hippocampal infusions of glucose and suggested that glucose reverses these deficits by increasing hippocampal acetylcholine (ACh). In this study, we report that septal infusions of muscimol produce dose-dependent decreases in ACh levels in hippocampal dialysates. Importantly, increasing glucose levels in the hippocampus elevates hippocampal extracellular ACh levels in rats given septal infusions of muscimol, but not in rats given vehicle. Thus, glucose increases hippocampal extracellular ACh levels when the ACh system is inhibited, an effect that likely contributes to the effects of glucose on memory.

Research paper thumbnail of Systemic EMD 68843 injections reduce anxiety in the shock-probe, but not the plus-maze test

European Journal of Pharmacology, 2001

Selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors and 5-HT1A receptor agonists ... more Selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors and 5-HT1A receptor agonists are believed to reduce anxiety. In the present study we examined the effects of injections of 5-{4-[4-(5-cyano-3-indolyl)-butyl]-1-piperazinyl}-benzofuran-2-carboxamide hydrochloride salt (EMD 68843), a 5-HT1A receptor agonist and selective 5-HT reuptake inhibitor, in two animal models of anxiety, plus-maze and shock-probe. Rats received intraperitoneal injections of vehicle, diazepam (2.5 mg/kg), or EMD

Research paper thumbnail of Dorsal and ventral hippocampal cholinergic systems modulate anxiety in the plus-maze and shock-probe tests

Brain Research, 2002

There is emerging evidence that increased acetylcholine levels in brain reduce anxiety. More spec... more There is emerging evidence that increased acetylcholine levels in brain reduce anxiety. More specifically there is evidence that some of these anxiolytic effects of acetylcholine are modulated by the hippocampus. In the present study we examined the roles of the cholinergic systems in the dorsal and ventral hippocampus in two animal models of anxiety: the elevated plus-maze and the shock-probe burying tests. We found that microinfusions (10 microg/0.5 microl) of the acetylcholinesterase inhibitor physostigmine in either the dorsal or the ventral hippocampus increased rats' open arm exploration in the plus-maze test, and decreased burying behavior in the shock-probe test. Interestingly, infusions in the ventral, but not the dorsal hippocampus also increased the number of contacts rats made with the shock-probe. Overall, the results suggest that cholinergic stimulation in the dorsal and ventral hippocampus modulate anxiety, but that only the ventral hippocampal cholinergic system is involved in the passive avoidance of painful stimuli.

Research paper thumbnail of Anxiety is functionally segregated within the septo-hippocampal system

Brain Research, 2004

Previous lesion studies have suggested that the septal -hippocampal system is involved in fear an... more Previous lesion studies have suggested that the septal -hippocampal system is involved in fear and anxiety. In this study we examined the effects on anxiety of temporary neuronal inhibition of various aspects of the septo-hippocampal system in rats. Infusions of tetrodotoxin (TTX) were used to induce reversible lesions in the fimbria fornix, medial septum, dorsal hippocampus, and ventral hippocampus. To assess anxiety we used the elevated plus-maze and the shock-probe burying tests. A reduction in anxiety in the elevated plus-maze is indicated by increased open arm exploration, whereas a reduction in anxiety in the shock-probe burying test is indicated by decreased burying behavior or increased contacts with the shock-probe. The results suggested that inhibition of the septal -hippocampal system induced site-specific anxiolytic effects that vary in nature. Tetrodotoxin lesions of the fimbria fornix increased both open arm exploration and the number of shocks taken by the rats, while having no effect on burying behavior. Both septal and ventral hippocampal lesions increased open arm exploration and decreased burying behavior, but had no effect on the number of probe shocks. Finally, TTX lesions of the dorsal hippocampus increased the number of shocks taken by the rats, but did not affect open arm activity or burying behavior. Neuroanatomical studies indicated that the effect on the number of shocks induced by dorsal hippocampal TTX lesions was not likely mediated by the amygdala. Collectively, the data suggest that the control of specific anxiety reactions is functionally segregated within different aspects of the septo-hippocampal system. D

Research paper thumbnail of Septal GABAergic and hippocampal cholinergic systems modulate anxiety in the plus-maze and shock-probe tests

Pharmacology Biochemistry and Behavior, 2001

According to Gray [(1982) The neuropsychology of anxiety: an enquiry into the function of the sep... more According to Gray [(1982) The neuropsychology of anxiety: an enquiry into the function of the septo-hippocampal system. Oxford: Oxford University Press; (1991) Neural systems, emotion and personality. In: Neurobiology of learning, emotion, and affect (Madden J, ed), pp 273-306. New York: Raven Press; Gray JA, McNaughton N (2000) The neuropsychology of anxiety. Oxford: Oxford University Press], the septum and the hippocampus act in concert to control anxiety.

Research paper thumbnail of Septal gabaergic and hippocampal cholinergic systems interact in the modulation of anxiety

Neuroscience, 2003

According to Gray [(1982) The neuropsychology of anxiety: an enquiry into the function of the sep... more According to Gray [(1982) The neuropsychology of anxiety: an enquiry into the function of the septo-hippocampal system. Oxford: Oxford University Press; (1991) Neural systems, emotion and personality. In: Neurobiology of learning, emotion, and affect (Madden J, ed), pp 273-306. New York: Raven Press; Gray JA, McNaughton N (2000) The neuropsychology of anxiety. Oxford: Oxford University Press], the septum and the hippocampus act in concert to control anxiety.

Research paper thumbnail of Genetic deletion and pharmacological blockade of CB1 receptors modulates anxiety in the shock-probe burying test

European Journal of Neuroscience, 2004

Cannabinoids affect various behavioral processes, including emotion, learning and memory, which m... more Cannabinoids affect various behavioral processes, including emotion, learning and memory, which may be specifically regulated through the CB1 receptors. The exact role CB1 receptors play in anxiety remains unclear. Both genetic and pharmacological blockade of CB1 receptors have produced inconsistent effects on anxiety. However, these studies examined passive avoidance as an index of anxiety. In the present study, both active and passive avoidance were examined using the shock-probe burying test while CB1 receptors were blocked genetically or pharmacologically. In the shock-probe burying test, anxiety is reflected by increased burying (increased active avoidance) and increased freezing (increased passive avoidance). In addition, probe-contacts may reflect cognitive performance and/or passive avoidance. As there have been few studies examining mouse behavior in the shock-probe burying test, experiment 1 was designed to pharmacologically validate this model in mice. Our results indicated that administration (i.p.) of chlordiazepoxide (4 mg/kg) or FG7412 (5 mg/kg) decreased and increased burying behavior, respectively, without affecting freezing or the number of probe contacts. Experiments 2 and 3 showed that both CB1 knockout mice and mice injected (i.p.) with 3 or 10 mg/kg, but not 1 mg/kg, of the CB1 receptor antagonist SR141716A had lower burying scores, fewer contacts with the probe and similar freezing times compared with wild-type mice and mice injected with vehicle (experiments 2 and 3). Collectively, these results suggest that CB1 receptor blockade reduces some, but not all, aspects of anxiety. The decrease in probe contacts induced by CB1 receptor blockade may be due to enhanced cognition.

Research paper thumbnail of Genetic deletion of muscarinic M 4 receptors is anxiolytic in the shock-probe burying model

European Journal of Pharmacology, 2006

We used muscarinic M 2 and M 4 receptor knockout (KO) mice to further explore the role of the cho... more We used muscarinic M 2 and M 4 receptor knockout (KO) mice to further explore the role of the cholinergic system in anxiety. Using the shockprobe burying model we were able to both assess anxiety and cognition. In this paradigm, an anxiolytic response is reflected by decreased burying behavior. In addition, retention latency depicts long-term memory performance. Whereas muscarinic M 2 receptor KO mice did not differ behaviorally from wild-type mice, muscarinic M 4 receptor KO mice showed increased anxiolysis, but normal long-term memory compared to wild-type mice. Therefore, muscarinic M 4 receptors are of particular significance in anxiety modulation that seems dissociated from changes in long-term memory.

Research paper thumbnail of Exposure to an elevated platform increases plasma corticosterone and hippocampal acetylcholine in the rat: reversal by chlordiazepoxide

European Journal of Pharmacology, 2004

There is evidence that the septohippocampal cholinergic system is activated in response to stress... more There is evidence that the septohippocampal cholinergic system is activated in response to stressful stimuli. In addition, prior studies indicate that stimulating the hippocampal cholinergic neurotransmission increases open arm exploration in the elevated plus-maze. This raises the possibility that exposing the rat to an elevated platform, which would be similar to confining the animal to the open arms of the plus-maze, would alter hippocampal acetylcholine levels. Results from the present study suggest that an elevated platform can be used as an animal model of stress in that exposure to the platform significantly increased plasma corticosterone levels. Importantly, exposure to a platform significantly increased hippocampal acetylcholine efflux. Interestingly, the increase in plasma corticosterone and hippocampal acetylcholine levels upon exposure to an elevated platform could be prevented by chlordiazepoxide at a dose that had no effect on basal hippocampal acetylcholine or plasma corticosterone levels. However, the elevated platform-induced increase in hippocampal acetylcholine could not be blocked by prior administration of buspirone. These results provide direct evidence for the importance of the hippocampal cholinergic system in stress and provide validation for the elevated platform as a model of stress.

Research paper thumbnail of Fluoxetine Disrupts the Integration of Anxiety and Aversive Memories

Neuropsychopharmacology, 2005

Anxiety disorders may result from an overexpression of aversive memories. Evidence suggests that ... more Anxiety disorders may result from an overexpression of aversive memories. Evidence suggests that the hippocampal cholinergic system could be the point of convergence of anxiety and memory. We propose that clinically effective anxiolytics may exert their effect by interfering with this integration mechanism. To assess anxiety and aversive memory, we used the shock-probe burying test. A reduction in anxiety in this test is indicated by decreased burying, whereas impaired cognition is reflected by an increased number of probe-contacts and/or reduced retention latency. Both an aversive stimulus and the memory of that stimulus significantly increased hippocampal acetylcholine (ACh) levels (Experiment 1). In fact, the memory of the event seemed to be more important than the event itself since the aversive memory induced a greater increase in hippocampal ACh. Injections (i.p.) of fluoxetine (Prozac s ) reduced burying behavior, while not affecting probe contacts or retention latency (Experiment 2). Although injections of fluoxetine did not affect basal hippocampal ACh efflux (Experiment 3), fluoxetine abolished the increase in ACh induced by the aversive stimulus and the memory of that stimulus (Experiment 4), emphasizing the significance of aversive memories in anxiety disorders. These actions may be mediated by a decrease in the event-related enhancement in cholinergic neurotransmission through M1 cholinergic receptors (Experiment 5). Therefore, anxiety disorders may stem from an unopposed formation of aversive memories and clinically effective anxiolytics hinder the association between emotional and cognitive processing. This reduces the emotional impact of aversive memories, thereby opposing consequent anxiety.

Research paper thumbnail of In vivo neurochemical effects induced by changes in endocannabinoid neurotransmission

Current Opinion in Pharmacology, 2007

Research paper thumbnail of Genetic deletion of CB1 receptors improves non-associative learning

Behavioural Brain Research, 2005

Habituation (a form of non-associative learning) was measured by assessing locomotion in novel ac... more Habituation (a form of non-associative learning) was measured by assessing locomotion in novel activity monitors in CB1 receptor knockout mice and juxtaposed to habituation measured in muscarinic M2, M4, and double M2/M4 receptor knockout mice. M2 and M2/M4, but not M4, receptor knockout mice appeared to have an impaired ability to habituate, whereas CB1 receptor knockout mice showed enhanced habituation compared to wild-type animals. We conclude that CB1 receptor gene invalidation improves habituation tentatively through an increase in cholinergic neurotransmission.

Research paper thumbnail of Biomarker-Guided Drug Development for Better Defined Early Patient Studies and Clinical Trial Efficiency

Translational Medicine in CNS Drug Development

Research paper thumbnail of CB 1 Receptor Antagonism Increases Hippocampal Acetylcholine Release : Site and Mechanism of Action

Evidence indicates that blockade of cannabinoid receptors increases acetylcholine (ACh) release i... more Evidence indicates that blockade of cannabinoid receptors increases acetylcholine (ACh) release in brain cortical regions. Although it is assumed that this type of effect is mediated through CB1 receptor (CB1R) antagonism, several in vitro functional studies recently have suggested non-CB1R involvement. In addition, neither the precise neuroanatomical site nor the exact mechanisms underlying this effect are known. We thoroughly examined these issues using a combination of systemic and local administration of CB1R antagonists, different methods of in vivo microdialysis, CB1R knockout (KO) mice, tissue measurements of ACh, and immunochemistry. First, we showed that systemic injections of the CB1R antagonists N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4methyl-1H-pyrazole-3-carboximide hydrochloride (SR141716A) and N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251) dose-dependently increased hippocampal ACh efflux. Li...

Research paper thumbnail of Evaluation of 5-HT7 receptor antagonism for the treatment of anxiety, depression, and schizophrenia through the use of receptor-deficient mice

Behavioural Brain Research

Research paper thumbnail of Genetic deletion of CB1 receptors improves non-associative learning

Behavioural Brain Research, 2005

Habituation (a form of non-associative learning) was measured by assessing locomotion in novel ac... more Habituation (a form of non-associative learning) was measured by assessing locomotion in novel activity monitors in CB1 receptor knockout mice and juxtaposed to habituation measured in muscarinic M2, M4, and double M2/M4 receptor knockout mice. M2 and M2/M4, but not M4, receptor knockout mice appeared to have an impaired ability to habituate, whereas CB1 receptor knockout mice showed enhanced habituation compared to wild-type animals. We conclude that CB1 receptor gene invalidation improves habituation tentatively through an increase in cholinergic neurotransmission.

Research paper thumbnail of Classification and definition of misuse, abuse, and related events in clinical trials: ACTTION systematic review and recommendations

PAIN®, 2013

As the nontherapeutic use of prescription medications escalates, serious associated consequences ... more As the nontherapeutic use of prescription medications escalates, serious associated consequences have also increased. This makes it essential to estimate misuse, abuse, and related events (MAREs) in the development and postmarketing adverse event surveillance and monitoring of prescription drugs accurately. However, classifications and definitions to describe prescription drug MAREs differ depending on the purpose of the classification system, may apply to single events or ongoing patterns of inappropriate use, and are not standardized or systematically employed, thereby complicating the ability to assess MARE occurrence adequately. In a systematic review of existing prescription drug MARE terminology and definitions from consensus efforts, review articles, and major institutions and agencies, MARE terms were often defined inconsistently or idiosyncratically, or had definitions that overlapped with other MARE terms. The Analgesic, Anesthetic, and Addiction Clinical Trials, Translations, Innovations, Opportunities, and Networks (ACTTION) public-private partnership convened an expert panel to develop mutually exclusive and exhaustive consensus classifications and definitions of MAREs occurring in clinical trials of analgesic medications to increase accuracy and consistency in characterizing their occurrence and prevalence in clinical trials. The proposed ACTTION classifications and definitions are designed as a first step in a system to adjudicate MAREs that occur in analgesic clinical trials and postmarketing adverse event surveillance and monitoring, which can be used in conjunction with other methods of assessing a treatment's abuse potential.

Research paper thumbnail of Increasing Acetylcholine Levels in the Hippocampus or Entorhinal Cortex Reverses the Impairing Effects of Septal GABA Receptor Activation on Spontaneous Alternation

Learning & Memory, 2000

Intra-septal infusions of the ␥-aminobutyric acid (GABA) agonist muscimol impair learning and mem... more Intra-septal infusions of the ␥-aminobutyric acid (GABA) agonist muscimol impair learning and memory in a variety of tasks. This experiment determined whether hippocampal or entorhinal infusions of the acetylcholinesterase inhibitor physostigmine would reverse such impairing effects on spontaneous alternation performance, a measure of spatial working memory. Male Sprague-Dawley rats were given intra-septal infusions of vehicle or muscimol (1 nmole/0.5 µL) combined with unilateral intra-hippocampal or intraentorhinal infusions of vehicle or physostigmine (10 µg/µL for the hippocampus; 7.5 µg/µL or 1.875 µg/0.25 µL for the entorhinal cortex). Fifteen minutes later, spontaneous alternation performance was assessed. The results indicated that intra-septal infusions of muscimol significantly decreased percentage-of-alternation scores, whereas intra-hippocampal or intra-entorhinal infusions of physostigmine had no effect. More importantly, intra-hippocampal or intra-entorhinal infusions of physostigmine, at doses that did not influence performance when administered alone, completely reversed the impairing effects of the muscimol infusions. These findings indicate that increasing cholinergic levels in the hippocampus or entorhinal cortex is sufficient to reverse the impairing effects of septal GABA receptor activation and support the hypothesis that the impairing effects of septal GABAergic activity involve cholinergic processes in the hippocampus and the entorhinal cortex.

Research paper thumbnail of Role of Cannabinoid Receptors in Anxiety Disorders

Cannabinoid agents modulate anxiety, although their effects vary and depend on regional endogenou... more Cannabinoid agents modulate anxiety, although their effects vary and depend on regional endogenous tone, basal anxiety levels, environmental context, species differences, type of anxiety, prior exposure, and dose. Cannabinoid receptors are densely located in brain areas that are involved in the regulation of emotional states and induce neurochemical responses that are congruent with anxiolyt ic/anxiogenic effects. The effects on emotion mediated by cannabinoid compounds are believed to be due to a regulation of activity at the cannabinoid CB1 receptors although there is some limited evidence implicating the cannabinoid CB2 and a putative novel cannabinoid receptor (GPR55?) in some of the observed emotional responses. Effects on emotion are likely the result of a net effect of the summated neurochemical responses. Compounds that indirectly regulate activity at the cannabinoid receptors more consistently reduce anxiety both in preclinical and clinical models. Consequently, these compounds may be the focus of future pharmaceutical development of anxiolytic compounds.

Research paper thumbnail of Infusions of physostigmine into the hippocampus or the entorhinal cortex attenuate avoidance retention deficits produced by intra-septal infusions of the GABA agonist muscimol

Brain Research, 2001

Septal gamma-aminobutyric acid (GABA) receptor activation is known to disrupt memory formation, a... more Septal gamma-aminobutyric acid (GABA) receptor activation is known to disrupt memory formation, although the mechanisms underlying this impairment remain unclear. The present study explored the possibility that high levels of septal GABA receptor activity might impair memory by down-regulating acetylcholine (ACh) function in archicortex and entorhinal cortex. To test this possibility, rats were trained on an avoidance task 15 min after receiving intra-septal infusions of vehicle or muscimol (5 nmol/0.5 microl) combined with unilateral intra-hippocampal (10 microl/1 microl) or intra-entorhinal cortex (1.875 microg/0.25 microl) infusions of vehicle or the acetylcholinesterase inhibitor physostigmine. We demonstrate that these infusions do not alter acquisition performance on a continuous multiple trial inhibitory avoidance task. However, intra-septal infusions of muscimol dramatically impair retention performance 48 h later. More importantly, infusions of physostigmine into the hippocampus or the entorhinal cortex, at doses that do not influence acquisition or retention performance when infused alone, attenuate the impairing effects of the muscimol infusions on retention. We suggest that high levels of septal GABA receptor activity might impair memory by down-regulating ACh levels in the hippocampal region, and that such memory impairments can be ameliorated by increasing ACh levels in the hippocampus or entorhinal cortex.

Research paper thumbnail of Glucose increases hippocampal extracellular acetylcholine levels upon activation of septal GABA receptors

Brain Research, 2003

Activation of septal GABA receptors impairs learning and memory and this effect likely involves a... more Activation of septal GABA receptors impairs learning and memory and this effect likely involves an influence on the hippocampus. We found previously that the memory-impairing effects of septal infusions of the GABA agonist muscimol are reversed by hippocampal infusions of glucose and suggested that glucose reverses these deficits by increasing hippocampal acetylcholine (ACh). In this study, we report that septal infusions of muscimol produce dose-dependent decreases in ACh levels in hippocampal dialysates. Importantly, increasing glucose levels in the hippocampus elevates hippocampal extracellular ACh levels in rats given septal infusions of muscimol, but not in rats given vehicle. Thus, glucose increases hippocampal extracellular ACh levels when the ACh system is inhibited, an effect that likely contributes to the effects of glucose on memory.

Research paper thumbnail of Systemic EMD 68843 injections reduce anxiety in the shock-probe, but not the plus-maze test

European Journal of Pharmacology, 2001

Selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors and 5-HT1A receptor agonists ... more Selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors and 5-HT1A receptor agonists are believed to reduce anxiety. In the present study we examined the effects of injections of 5-{4-[4-(5-cyano-3-indolyl)-butyl]-1-piperazinyl}-benzofuran-2-carboxamide hydrochloride salt (EMD 68843), a 5-HT1A receptor agonist and selective 5-HT reuptake inhibitor, in two animal models of anxiety, plus-maze and shock-probe. Rats received intraperitoneal injections of vehicle, diazepam (2.5 mg/kg), or EMD

Research paper thumbnail of Dorsal and ventral hippocampal cholinergic systems modulate anxiety in the plus-maze and shock-probe tests

Brain Research, 2002

There is emerging evidence that increased acetylcholine levels in brain reduce anxiety. More spec... more There is emerging evidence that increased acetylcholine levels in brain reduce anxiety. More specifically there is evidence that some of these anxiolytic effects of acetylcholine are modulated by the hippocampus. In the present study we examined the roles of the cholinergic systems in the dorsal and ventral hippocampus in two animal models of anxiety: the elevated plus-maze and the shock-probe burying tests. We found that microinfusions (10 microg/0.5 microl) of the acetylcholinesterase inhibitor physostigmine in either the dorsal or the ventral hippocampus increased rats' open arm exploration in the plus-maze test, and decreased burying behavior in the shock-probe test. Interestingly, infusions in the ventral, but not the dorsal hippocampus also increased the number of contacts rats made with the shock-probe. Overall, the results suggest that cholinergic stimulation in the dorsal and ventral hippocampus modulate anxiety, but that only the ventral hippocampal cholinergic system is involved in the passive avoidance of painful stimuli.

Research paper thumbnail of Anxiety is functionally segregated within the septo-hippocampal system

Brain Research, 2004

Previous lesion studies have suggested that the septal -hippocampal system is involved in fear an... more Previous lesion studies have suggested that the septal -hippocampal system is involved in fear and anxiety. In this study we examined the effects on anxiety of temporary neuronal inhibition of various aspects of the septo-hippocampal system in rats. Infusions of tetrodotoxin (TTX) were used to induce reversible lesions in the fimbria fornix, medial septum, dorsal hippocampus, and ventral hippocampus. To assess anxiety we used the elevated plus-maze and the shock-probe burying tests. A reduction in anxiety in the elevated plus-maze is indicated by increased open arm exploration, whereas a reduction in anxiety in the shock-probe burying test is indicated by decreased burying behavior or increased contacts with the shock-probe. The results suggested that inhibition of the septal -hippocampal system induced site-specific anxiolytic effects that vary in nature. Tetrodotoxin lesions of the fimbria fornix increased both open arm exploration and the number of shocks taken by the rats, while having no effect on burying behavior. Both septal and ventral hippocampal lesions increased open arm exploration and decreased burying behavior, but had no effect on the number of probe shocks. Finally, TTX lesions of the dorsal hippocampus increased the number of shocks taken by the rats, but did not affect open arm activity or burying behavior. Neuroanatomical studies indicated that the effect on the number of shocks induced by dorsal hippocampal TTX lesions was not likely mediated by the amygdala. Collectively, the data suggest that the control of specific anxiety reactions is functionally segregated within different aspects of the septo-hippocampal system. D

Research paper thumbnail of Septal GABAergic and hippocampal cholinergic systems modulate anxiety in the plus-maze and shock-probe tests

Pharmacology Biochemistry and Behavior, 2001

According to Gray [(1982) The neuropsychology of anxiety: an enquiry into the function of the sep... more According to Gray [(1982) The neuropsychology of anxiety: an enquiry into the function of the septo-hippocampal system. Oxford: Oxford University Press; (1991) Neural systems, emotion and personality. In: Neurobiology of learning, emotion, and affect (Madden J, ed), pp 273-306. New York: Raven Press; Gray JA, McNaughton N (2000) The neuropsychology of anxiety. Oxford: Oxford University Press], the septum and the hippocampus act in concert to control anxiety.

Research paper thumbnail of Septal gabaergic and hippocampal cholinergic systems interact in the modulation of anxiety

Neuroscience, 2003

According to Gray [(1982) The neuropsychology of anxiety: an enquiry into the function of the sep... more According to Gray [(1982) The neuropsychology of anxiety: an enquiry into the function of the septo-hippocampal system. Oxford: Oxford University Press; (1991) Neural systems, emotion and personality. In: Neurobiology of learning, emotion, and affect (Madden J, ed), pp 273-306. New York: Raven Press; Gray JA, McNaughton N (2000) The neuropsychology of anxiety. Oxford: Oxford University Press], the septum and the hippocampus act in concert to control anxiety.

Research paper thumbnail of Genetic deletion and pharmacological blockade of CB1 receptors modulates anxiety in the shock-probe burying test

European Journal of Neuroscience, 2004

Cannabinoids affect various behavioral processes, including emotion, learning and memory, which m... more Cannabinoids affect various behavioral processes, including emotion, learning and memory, which may be specifically regulated through the CB1 receptors. The exact role CB1 receptors play in anxiety remains unclear. Both genetic and pharmacological blockade of CB1 receptors have produced inconsistent effects on anxiety. However, these studies examined passive avoidance as an index of anxiety. In the present study, both active and passive avoidance were examined using the shock-probe burying test while CB1 receptors were blocked genetically or pharmacologically. In the shock-probe burying test, anxiety is reflected by increased burying (increased active avoidance) and increased freezing (increased passive avoidance). In addition, probe-contacts may reflect cognitive performance and/or passive avoidance. As there have been few studies examining mouse behavior in the shock-probe burying test, experiment 1 was designed to pharmacologically validate this model in mice. Our results indicated that administration (i.p.) of chlordiazepoxide (4 mg/kg) or FG7412 (5 mg/kg) decreased and increased burying behavior, respectively, without affecting freezing or the number of probe contacts. Experiments 2 and 3 showed that both CB1 knockout mice and mice injected (i.p.) with 3 or 10 mg/kg, but not 1 mg/kg, of the CB1 receptor antagonist SR141716A had lower burying scores, fewer contacts with the probe and similar freezing times compared with wild-type mice and mice injected with vehicle (experiments 2 and 3). Collectively, these results suggest that CB1 receptor blockade reduces some, but not all, aspects of anxiety. The decrease in probe contacts induced by CB1 receptor blockade may be due to enhanced cognition.

Research paper thumbnail of Genetic deletion of muscarinic M 4 receptors is anxiolytic in the shock-probe burying model

European Journal of Pharmacology, 2006

We used muscarinic M 2 and M 4 receptor knockout (KO) mice to further explore the role of the cho... more We used muscarinic M 2 and M 4 receptor knockout (KO) mice to further explore the role of the cholinergic system in anxiety. Using the shockprobe burying model we were able to both assess anxiety and cognition. In this paradigm, an anxiolytic response is reflected by decreased burying behavior. In addition, retention latency depicts long-term memory performance. Whereas muscarinic M 2 receptor KO mice did not differ behaviorally from wild-type mice, muscarinic M 4 receptor KO mice showed increased anxiolysis, but normal long-term memory compared to wild-type mice. Therefore, muscarinic M 4 receptors are of particular significance in anxiety modulation that seems dissociated from changes in long-term memory.

Research paper thumbnail of Exposure to an elevated platform increases plasma corticosterone and hippocampal acetylcholine in the rat: reversal by chlordiazepoxide

European Journal of Pharmacology, 2004

There is evidence that the septohippocampal cholinergic system is activated in response to stress... more There is evidence that the septohippocampal cholinergic system is activated in response to stressful stimuli. In addition, prior studies indicate that stimulating the hippocampal cholinergic neurotransmission increases open arm exploration in the elevated plus-maze. This raises the possibility that exposing the rat to an elevated platform, which would be similar to confining the animal to the open arms of the plus-maze, would alter hippocampal acetylcholine levels. Results from the present study suggest that an elevated platform can be used as an animal model of stress in that exposure to the platform significantly increased plasma corticosterone levels. Importantly, exposure to a platform significantly increased hippocampal acetylcholine efflux. Interestingly, the increase in plasma corticosterone and hippocampal acetylcholine levels upon exposure to an elevated platform could be prevented by chlordiazepoxide at a dose that had no effect on basal hippocampal acetylcholine or plasma corticosterone levels. However, the elevated platform-induced increase in hippocampal acetylcholine could not be blocked by prior administration of buspirone. These results provide direct evidence for the importance of the hippocampal cholinergic system in stress and provide validation for the elevated platform as a model of stress.

Research paper thumbnail of Fluoxetine Disrupts the Integration of Anxiety and Aversive Memories

Neuropsychopharmacology, 2005

Anxiety disorders may result from an overexpression of aversive memories. Evidence suggests that ... more Anxiety disorders may result from an overexpression of aversive memories. Evidence suggests that the hippocampal cholinergic system could be the point of convergence of anxiety and memory. We propose that clinically effective anxiolytics may exert their effect by interfering with this integration mechanism. To assess anxiety and aversive memory, we used the shock-probe burying test. A reduction in anxiety in this test is indicated by decreased burying, whereas impaired cognition is reflected by an increased number of probe-contacts and/or reduced retention latency. Both an aversive stimulus and the memory of that stimulus significantly increased hippocampal acetylcholine (ACh) levels (Experiment 1). In fact, the memory of the event seemed to be more important than the event itself since the aversive memory induced a greater increase in hippocampal ACh. Injections (i.p.) of fluoxetine (Prozac s ) reduced burying behavior, while not affecting probe contacts or retention latency (Experiment 2). Although injections of fluoxetine did not affect basal hippocampal ACh efflux (Experiment 3), fluoxetine abolished the increase in ACh induced by the aversive stimulus and the memory of that stimulus (Experiment 4), emphasizing the significance of aversive memories in anxiety disorders. These actions may be mediated by a decrease in the event-related enhancement in cholinergic neurotransmission through M1 cholinergic receptors (Experiment 5). Therefore, anxiety disorders may stem from an unopposed formation of aversive memories and clinically effective anxiolytics hinder the association between emotional and cognitive processing. This reduces the emotional impact of aversive memories, thereby opposing consequent anxiety.

Research paper thumbnail of In vivo neurochemical effects induced by changes in endocannabinoid neurotransmission

Current Opinion in Pharmacology, 2007

Research paper thumbnail of Genetic deletion of CB1 receptors improves non-associative learning

Behavioural Brain Research, 2005

Habituation (a form of non-associative learning) was measured by assessing locomotion in novel ac... more Habituation (a form of non-associative learning) was measured by assessing locomotion in novel activity monitors in CB1 receptor knockout mice and juxtaposed to habituation measured in muscarinic M2, M4, and double M2/M4 receptor knockout mice. M2 and M2/M4, but not M4, receptor knockout mice appeared to have an impaired ability to habituate, whereas CB1 receptor knockout mice showed enhanced habituation compared to wild-type animals. We conclude that CB1 receptor gene invalidation improves habituation tentatively through an increase in cholinergic neurotransmission.