christian alberto - Academia.edu (original) (raw)
Uploads
Papers by christian alberto
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 27, 2006
Orexin neurons in the lateral hypothalamus (LH)/perifornical area (PFA) are known to promote food... more Orexin neurons in the lateral hypothalamus (LH)/perifornical area (PFA) are known to promote food intake as well as provide excitatory influence on the dopaminergic reward pathway. Dopamine (DA), in turn, inhibits the reward pathway and food intake through its action in the LH/PFA. However, the cellular mechanism by which DA modulates orexin neurons remains largely unknown. Therefore, we examined the effect of DA on the excitatory neurotransmission to orexin neurons. Whole-cell patch-clamp recordings were performed using acute rat hypothalamic slices, and orexin neurons were identified by their electrophysiological and immunohistochemical characteristics. Pharmacologically isolated action potential-independent miniature EPSCs (mEPSCs) were monitored. Bath application of DA induced a bidirectional effect on the excitatory synaptic transmission dose dependently. A low dose of DA (1 microM) increased mEPSC frequency, which was blocked by the D1-like receptor antagonist SCH 23390, and m...
The Journal of Physiology, 2008
The glutamatergic synapses of the supraoptic nucleus display a unique activity-dependent plastici... more The glutamatergic synapses of the supraoptic nucleus display a unique activity-dependent plasticity characterized by a barrage of tetrodotoxin-resistant miniature EPSCs (mEPSCs) persisting for 5-20 min, causing postsynaptic excitation. We investigated how this short-term synaptic potentiation (STP) induced by a brief high-frequency stimulation (HFS) of afferents was initiated and maintained without lingering presynaptic firing, using in vitro patch-clamp recording on rat brain slices. We found that following the immediate rise in mEPSC frequency, STP decayed with two-exponential functions indicative of two discrete phases. STP depends entirely on extracellular Ca 2+ which enters the presynaptic terminals through voltage-gated Ca 2+ channels but also, to a much lesser degree, through a pathway independent of these channels or reverse mode of the plasma membrane Na + -Ca 2+ exchanger. Initiation of STP is largely mediated by any of the N-, P/Q-or L-type channels, and only a simultaneous application of specific blockers for all these channels attenuates STP. Furthermore, the second phase of STP is curtailed by the inhibition of mitochondrial Ca 2+ uptake or mitochondrial Na + -Ca 2+ exchanger. mEPSCs amplitude is also potentiated by HFS which requires extracellular Ca 2+ . In conclusion, induction of mEPSC-STP is redundantly mediated by presynaptic N-, P/Q-and L-type Ca 2+ channels while the second phase depends on mitochondrial Ca 2+ sequestration and release. Since glutamate influences unique firing patterns that optimize hormone release by supraoptic magnocellular neurons, a prolonged barrage of spontaneous excitatory transmission may aid in the induction of respective firing activities.
Journal of Neuroscience, 2011
Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide that promotes positive energy ... more Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide that promotes positive energy balance and anxiety. Since dopamine (DA) is also closely implicated in these functions, the present study investigated the effect of DA on MCH neurons. Using whole-cell patch-clamp recordings in rat brain slices, we found that DA hyperpolarizes MCH neurons by activating G-protein-activated inwardly rectifying K(+) (GIRK) channels. Pharmacological study indicated that the effect was mediated by α2A adrenoceptors, not DA receptors. DA-induced outward current was also observed in the presence of tetrodotoxin or the dopamine β-hydroxylase inhibitor fusaric acid, suggesting that DA directly binds to α2A receptors on MCH neurons, rather than acting presynaptically or being transformed into norepinephrine (NE) in the slice preparation. The effects of NE and DA were concentration-dependent with EC(50) of 5.9 and 23.7 μm, respectively, and a maximal effect of 106.6 and 57.2 pA, respectively, suggesting that DA functions as a partial agonist. Prolonged (5 min) activation of α2A receptors by either DA or NE attenuated the subsequent response to DA or NE, while 5 s applications were not sufficient to induce desensitization. Therefore, a history of α2A receptor activation by DA or NE can have a lasting inhibitory effect on the catecholaminergic transmission to MCH neurons. Our study suggests that α2A receptors expressed by MCH neurons may be one of the pathways by which DA and NE can interact and modulate mood and energy homeostasis, and this cross talk may have functional implications in mood disorders and obesity.
PLoS ONE, 2012
Nociceptin/orphanin FQ (N/OFQ) is known to induce food intake when administered into the lateral ... more Nociceptin/orphanin FQ (N/OFQ) is known to induce food intake when administered into the lateral ventricle or certain brain areas. This is somewhat contradictory to its reward-suppressing role, as food is a strong rewarding stimulus. This discrepancy may be due to the functional diversity of N/OFQ's target brain areas. N/OFQ has been shown to inhibit orexin and melanin-concentrating hormone (MCH) neurons, both of which are appetite-inducing cells. As the expression of these neurons is largely confined to the lateral hypothalamus/perifornical area (LH/PFA), we hypothesized that N/OFQ inhibits food intake by acting in this area. To test this hypothesis, we examined the effect of local N/OFQ infusion within the LH/PFA on food intake in the rat and found that N/OFQ decreased sugar pellet as well as chow intake. This effect was not seen when the injection site was outside of the LH/PFA, suggesting a site-specific effect. Next, to determine a possible cellular mechanism of N/OFQ action on food intake, whole cell patch clamp recordings were performed on rat orexin neurons. As previously reported in mice, N/OFQ induced a strong and long lasting hyperpolarization. Pharmacological study indicated that N/OFQ directly inhibited orexin neurons by activating ATP-sensitive potassium (KATP) channels. This effect was partially but significantly attenuated by the inhibitors of PI3K, PKC and PKA, suggesting that the N/OFQ signaling is mediated by these protein kinases. In summary, our results demonstrate a KATP channel-dependent N/OFQ signaling and that N/OFQ is a site-specific anorexic peptide.
Glutamate plays a predominant role in regulating the activity of orexin neurons that coordinate m... more Glutamate plays a predominant role in regulating the activity of orexin neurons that coordinate motivated behaviors, sleep-wake cycle and autonomic functions. To gain more insight into the properties of excitatory transmission to orexin neurons, whole cell patch clamp recordings were made in rat brain slices and quantal analysis of pharmacologically isolated miniature excitatory postsynaptic currents (mEPSCs) was performed. In more than half the orexin neurons examined, mEPSCs showed heterogeneous time course: some mEPSCs had fast rise and decay (fast mEPSC), while some had longer kinetics, smaller amplitude but larger integrated area (slow mEPSC). Other orexin neurons showed low frequency mEPSCs with uniform, fast kinetics. In the former, distribution histogram of 10-90% rise time displayed two peaks, indicating that fast and slow mEPSCs are distinct subgroups. Occasionally fast and slow EPSCs would summate, suggesting that they arise from different pairs of active zones and postsynaptic receptor clusters. A large majority of mEPSCs were mediated by AMPA receptors that are sensitive to GYKI 52466 and DNQX. To determine whether synapses that give rise to fast and slow mEPSCs are differentially modulated, the D1-and D2-like agonists were tested on various parameters of mEPSCs. The agonists altered the frequency as previously reported, but had no effect on the rise, decay or area of mEPSC, suggesting that dopamine affects fast and slow mEPSCs equally. Given the potential physiological impact of EPSC time course on synaptic integration, our study raises an interesting possibility that distinct subset of excitatory synaptic inputs are processed differently by orexin neurons. j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / y b b r c
R e c e p c i ó n : 1 0 d e o c t u b r e d e 2 0 0 4 I A c e p t a c i ó n : 2 0 d e a g o s t o... more R e c e p c i ó n : 1 0 d e o c t u b r e d e 2 0 0 4 I A c e p t a c i ó n : 2 0 d e a g o s t o d e 2 0 0 5
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 27, 2006
Orexin neurons in the lateral hypothalamus (LH)/perifornical area (PFA) are known to promote food... more Orexin neurons in the lateral hypothalamus (LH)/perifornical area (PFA) are known to promote food intake as well as provide excitatory influence on the dopaminergic reward pathway. Dopamine (DA), in turn, inhibits the reward pathway and food intake through its action in the LH/PFA. However, the cellular mechanism by which DA modulates orexin neurons remains largely unknown. Therefore, we examined the effect of DA on the excitatory neurotransmission to orexin neurons. Whole-cell patch-clamp recordings were performed using acute rat hypothalamic slices, and orexin neurons were identified by their electrophysiological and immunohistochemical characteristics. Pharmacologically isolated action potential-independent miniature EPSCs (mEPSCs) were monitored. Bath application of DA induced a bidirectional effect on the excitatory synaptic transmission dose dependently. A low dose of DA (1 microM) increased mEPSC frequency, which was blocked by the D1-like receptor antagonist SCH 23390, and m...
The Journal of Physiology, 2008
The glutamatergic synapses of the supraoptic nucleus display a unique activity-dependent plastici... more The glutamatergic synapses of the supraoptic nucleus display a unique activity-dependent plasticity characterized by a barrage of tetrodotoxin-resistant miniature EPSCs (mEPSCs) persisting for 5-20 min, causing postsynaptic excitation. We investigated how this short-term synaptic potentiation (STP) induced by a brief high-frequency stimulation (HFS) of afferents was initiated and maintained without lingering presynaptic firing, using in vitro patch-clamp recording on rat brain slices. We found that following the immediate rise in mEPSC frequency, STP decayed with two-exponential functions indicative of two discrete phases. STP depends entirely on extracellular Ca 2+ which enters the presynaptic terminals through voltage-gated Ca 2+ channels but also, to a much lesser degree, through a pathway independent of these channels or reverse mode of the plasma membrane Na + -Ca 2+ exchanger. Initiation of STP is largely mediated by any of the N-, P/Q-or L-type channels, and only a simultaneous application of specific blockers for all these channels attenuates STP. Furthermore, the second phase of STP is curtailed by the inhibition of mitochondrial Ca 2+ uptake or mitochondrial Na + -Ca 2+ exchanger. mEPSCs amplitude is also potentiated by HFS which requires extracellular Ca 2+ . In conclusion, induction of mEPSC-STP is redundantly mediated by presynaptic N-, P/Q-and L-type Ca 2+ channels while the second phase depends on mitochondrial Ca 2+ sequestration and release. Since glutamate influences unique firing patterns that optimize hormone release by supraoptic magnocellular neurons, a prolonged barrage of spontaneous excitatory transmission may aid in the induction of respective firing activities.
Journal of Neuroscience, 2011
Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide that promotes positive energy ... more Melanin-concentrating hormone (MCH) is a hypothalamic neuropeptide that promotes positive energy balance and anxiety. Since dopamine (DA) is also closely implicated in these functions, the present study investigated the effect of DA on MCH neurons. Using whole-cell patch-clamp recordings in rat brain slices, we found that DA hyperpolarizes MCH neurons by activating G-protein-activated inwardly rectifying K(+) (GIRK) channels. Pharmacological study indicated that the effect was mediated by α2A adrenoceptors, not DA receptors. DA-induced outward current was also observed in the presence of tetrodotoxin or the dopamine β-hydroxylase inhibitor fusaric acid, suggesting that DA directly binds to α2A receptors on MCH neurons, rather than acting presynaptically or being transformed into norepinephrine (NE) in the slice preparation. The effects of NE and DA were concentration-dependent with EC(50) of 5.9 and 23.7 μm, respectively, and a maximal effect of 106.6 and 57.2 pA, respectively, suggesting that DA functions as a partial agonist. Prolonged (5 min) activation of α2A receptors by either DA or NE attenuated the subsequent response to DA or NE, while 5 s applications were not sufficient to induce desensitization. Therefore, a history of α2A receptor activation by DA or NE can have a lasting inhibitory effect on the catecholaminergic transmission to MCH neurons. Our study suggests that α2A receptors expressed by MCH neurons may be one of the pathways by which DA and NE can interact and modulate mood and energy homeostasis, and this cross talk may have functional implications in mood disorders and obesity.
PLoS ONE, 2012
Nociceptin/orphanin FQ (N/OFQ) is known to induce food intake when administered into the lateral ... more Nociceptin/orphanin FQ (N/OFQ) is known to induce food intake when administered into the lateral ventricle or certain brain areas. This is somewhat contradictory to its reward-suppressing role, as food is a strong rewarding stimulus. This discrepancy may be due to the functional diversity of N/OFQ's target brain areas. N/OFQ has been shown to inhibit orexin and melanin-concentrating hormone (MCH) neurons, both of which are appetite-inducing cells. As the expression of these neurons is largely confined to the lateral hypothalamus/perifornical area (LH/PFA), we hypothesized that N/OFQ inhibits food intake by acting in this area. To test this hypothesis, we examined the effect of local N/OFQ infusion within the LH/PFA on food intake in the rat and found that N/OFQ decreased sugar pellet as well as chow intake. This effect was not seen when the injection site was outside of the LH/PFA, suggesting a site-specific effect. Next, to determine a possible cellular mechanism of N/OFQ action on food intake, whole cell patch clamp recordings were performed on rat orexin neurons. As previously reported in mice, N/OFQ induced a strong and long lasting hyperpolarization. Pharmacological study indicated that N/OFQ directly inhibited orexin neurons by activating ATP-sensitive potassium (KATP) channels. This effect was partially but significantly attenuated by the inhibitors of PI3K, PKC and PKA, suggesting that the N/OFQ signaling is mediated by these protein kinases. In summary, our results demonstrate a KATP channel-dependent N/OFQ signaling and that N/OFQ is a site-specific anorexic peptide.
Glutamate plays a predominant role in regulating the activity of orexin neurons that coordinate m... more Glutamate plays a predominant role in regulating the activity of orexin neurons that coordinate motivated behaviors, sleep-wake cycle and autonomic functions. To gain more insight into the properties of excitatory transmission to orexin neurons, whole cell patch clamp recordings were made in rat brain slices and quantal analysis of pharmacologically isolated miniature excitatory postsynaptic currents (mEPSCs) was performed. In more than half the orexin neurons examined, mEPSCs showed heterogeneous time course: some mEPSCs had fast rise and decay (fast mEPSC), while some had longer kinetics, smaller amplitude but larger integrated area (slow mEPSC). Other orexin neurons showed low frequency mEPSCs with uniform, fast kinetics. In the former, distribution histogram of 10-90% rise time displayed two peaks, indicating that fast and slow mEPSCs are distinct subgroups. Occasionally fast and slow EPSCs would summate, suggesting that they arise from different pairs of active zones and postsynaptic receptor clusters. A large majority of mEPSCs were mediated by AMPA receptors that are sensitive to GYKI 52466 and DNQX. To determine whether synapses that give rise to fast and slow mEPSCs are differentially modulated, the D1-and D2-like agonists were tested on various parameters of mEPSCs. The agonists altered the frequency as previously reported, but had no effect on the rise, decay or area of mEPSC, suggesting that dopamine affects fast and slow mEPSCs equally. Given the potential physiological impact of EPSC time course on synaptic integration, our study raises an interesting possibility that distinct subset of excitatory synaptic inputs are processed differently by orexin neurons. j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / y b b r c
R e c e p c i ó n : 1 0 d e o c t u b r e d e 2 0 0 4 I A c e p t a c i ó n : 2 0 d e a g o s t o... more R e c e p c i ó n : 1 0 d e o c t u b r e d e 2 0 0 4 I A c e p t a c i ó n : 2 0 d e a g o s t o d e 2 0 0 5