ABSTRACT
Stress-induced analgesia (SIA) is a key component of the defensive behavioral "fight-or-flight" response. Although the neural substrates of SIA are incompletely understood, previous studies have implicated the hypocretin/orexin (Hcrt) and nociceptin/orphanin FQ (N/OFQ) peptidergic systems in the regulation of SIA. Using immunohistochemistry in brain tissue from wild-type mice, we identified N/OFQ-containing fibers forming synaptic contacts with Hcrt neurons at both the light and electron microscopic levels. Patch clamp recordings in GFP-tagged mouse Hcrt neurons revealed that N/OFQ hyperpolarized, decreased input resistance, and blocked the firing of action potentials in Hcrt neurons. N/OFQ postsynaptic effects were consistent with opening of a G protein-regulated inwardly rectifying K+ (GIRK) channel. N/OFQ also modulated presynaptic release of GABA and glutamate onto Hcrt neurons in mouse hypothalamic slices. Orexin/ataxin-3 mice, in which the Hcrt neurons degenerate, did not exhibit SIA, although analgesia was induced by i.c.v. administration of Hcrt-1. N/OFQ blocked SIA in wild-type mice, while coadministration of Hcrt-1 overcame N/OFQ inhibition of SIA. These results establish what is, to our knowledge, a novel interaction between the N/OFQ and Hcrt systems in which the corticotropin-releasing factor and N/OFQ systems coordinately modulate the Hcrt neurons to regulate SIA.
Subject(s)
Analgesia , Intracellular Signaling Peptides and Proteins/metabolism , Neuropeptides/metabolism , Opioid Peptides/metabolism , Stress, Physiological/physiopathology , Animals , Ataxin-3 , Behavior, Animal/drug effects , Behavior, Animal/physiology , Brain/cytology , Brain/drug effects , Brain/metabolism , Calcium/metabolism , Cytoplasm/metabolism , Electrophysiology , Female , Hypothalamus, Posterior/cytology , Hypothalamus, Posterior/metabolism , Hypothalamus, Posterior/ultrastructure , Immunohistochemistry , Intracellular Signaling Peptides and Proteins/genetics , Intracellular Signaling Peptides and Proteins/pharmacology , Male , Membrane Potentials/drug effects , Membrane Potentials/physiology , Mice , Mice, Inbred C57BL , Mice, Transgenic , Narcotic Antagonists , Neurons/cytology , Neurons/drug effects , Neurons/physiology , Neuropeptides/genetics , Neuropeptides/pharmacology , Nuclear Proteins/genetics , Opioid Peptides/genetics , Opioid Peptides/pharmacology , Orexins , Pain Threshold/drug effects , Pain Threshold/physiology , Presynaptic Terminals/physiology , Reaction Time/drug effects , Reaction Time/physiology , Receptors, Opioid , Tetrodotoxin/pharmacology , Transcription Factors/genetics , Nociceptin Receptor , NociceptinABSTRACT
Hypocretin/orexin (Hcrt) is a critical neurotransmitter for the maintenance of wakefulness and has been implicated in several other functions, including energy metabolism and reward. Using whole-cell patch-clamp recordings from transgenic mice in which enhanced green fluorescent protein was linked to the Hcrt promoter, we investigated GABAergic control of the Hcrt neurones in hypothalamic slices. Bath application of GABA or muscimol caused an early hyperpolarization mediated by Cl(-) and a late depolarization mediated by the efflux of bicarbonate. These GABA(A) receptor-mediated responses were blocked by picrotoxin and bicuculline. Under the GABA(A) blockade condition, GABA produced consistent hyperpolarization, decreased firing rate and input resistance. The selective GABA(B) agonist (R)-baclofen caused a similar response with an EC(50) of 7.1 mum. The effects of (R)-baclofen were blocked by the GABA(B) antagonist CGP 52432 but persisted in the presence of tetrodotoxin, suggesting direct postsynaptic effects. The existence of GABA(B) modulation was supported by GABA(B(1)) subunit immunoreactivity on Hcrt cells colabelled with antisera to the Hcrt-2 peptide. Furthermore, GABA(B) receptor activation inhibited the presynaptic release of both glutamate and GABA. (R)-Baclofen depressed the amplitude of evoked excitatory postsynaptic currents (EPSCs) and inhibitory synaptic currents (IPSCs), and also decreased the frequency of both spontaneous and miniature EPSCs and IPSCs with a modest effect on their amplitudes. These data suggest that GABA(B) receptors modulate Hcrt neuronal activity via both pre- and postsynaptic mechanisms, which may underlie the promotion of non-rapid eye movement sleep and have implications for the use of GABA(B) agonists in the treatment of substance addiction through direct interaction with the Hcrt system.
Subject(s)
Hypothalamus/physiology , Intracellular Signaling Peptides and Proteins/analysis , Neurons/chemistry , Neurons/physiology , Neuropeptides/analysis , Receptors, GABA-B/physiology , Action Potentials/physiology , Animals , GABA Agonists/pharmacology , GABA Antagonists/pharmacology , GABA-A Receptor Antagonists , GABA-B Receptor Antagonists , Male , Mice , Mice, Inbred C57BL , Orexin Receptors , Orexins , Receptors, G-Protein-Coupled , Receptors, GABA-A/drug effects , Receptors, GABA-A/physiology , Receptors, GABA-B/drug effects , Receptors, Neuropeptide , Sleep/physiology , Synapses/drug effects , Synapses/physiology , Wakefulness/physiologyABSTRACT
Inhibitory synaptic transmission plays an important role in regulating the activity of medium spiny neurons (MSNs) in the nucleus accumbens (NAcc). The kainate (KA) subtype of ionotropic glutamate receptor has been shown to potently modulate GABAergic synaptic transmission in several brain regions. Although KA receptor subunits are expressed in the NAcc, KA receptor modulation of GABAergic synaptic transmission in this brain region has not been previously examined. In the current study, we sought to determine if KA receptor activation could alter inhibitory synaptic transmission in the NAcc as it has been shown to do in other brain regions. Using the whole cell patch-clamp technique, we demonstrate that KA receptor activation potentiates evoked GABAergic synaptic transmission and increases the frequency of spontaneous, but not miniature, GABA(A)-receptor-mediated IPSCs in the NAcc. In contrast, KA has no effect on currents evoked by exogenous application of GABA onto MSNs. Taken together, these data suggest that activation of KA receptors in the NAcc core potently facilitates action-potential-dependent GABAergic synaptic transmission, likely via an excitation of presynaptic GABAergic interneurons.
Subject(s)
Neurons/physiology , Nucleus Accumbens/cytology , Receptors, Kainic Acid/metabolism , Synaptic Transmission/physiology , gamma-Aminobutyric Acid/metabolism , Animals , Animals, Newborn , Bicuculline/pharmacology , Calcium/pharmacology , Dose-Response Relationship, Drug , Drug Interactions , Excitatory Amino Acid Agonists/pharmacology , Excitatory Amino Acid Antagonists/pharmacology , GABA Antagonists/pharmacology , In Vitro Techniques , Kainic Acid/pharmacology , Male , Neural Inhibition/drug effects , Neural Inhibition/physiology , Neurons/drug effects , Patch-Clamp Techniques/methods , Rats , Rats, Sprague-Dawley , Synaptic Transmission/drug effects , Synaptic Transmission/radiation effects , gamma-Aminobutyric Acid/pharmacologyABSTRACT
Stress increases addictive behaviors and is a common cause of relapse. Corticotropin-releasing factor (CRF) plays a key role in the modulation of drug taking by stress. However, the mechanism by which CRF modulates neuronal activity in circuits involved in drug addiction is poorly understood. Here we show that CRF induces a potentiation of NMDAR (N-methyl-D-aspartate receptor)-mediated synaptic transmission in dopamine neurons of the ventral tegmental area (VTA). This effect involves CRF receptor 2 (CRF-R2) and activation of the phospholipase C (PLC)-protein kinase C (PKC) pathway. We also find that this potentiation requires CRF binding protein (CRF-BP). Accordingly, CRF-like peptides, which do not bind the CRF-BP with high affinity, do not potentiate NMDARs. These results provide evidence of the first specific roles for CRF-R2 and CRF-BP in the modulation of neuronal activity and suggest that NMDARs in the VTA may be a target for both drugs of abuse and stress.
Subject(s)
Carrier Proteins/physiology , Corticotropin-Releasing Hormone/physiology , Dopamine/metabolism , Neurons/metabolism , Receptors, Corticotropin-Releasing Hormone/physiology , Receptors, N-Methyl-D-Aspartate/metabolism , Animals , Corticotropin-Releasing Hormone/pharmacology , In Vitro Techniques , Male , Mice , Mice, Inbred C57BL , Neurons/drug effects , Patch-Clamp TechniquesABSTRACT
The nucleus accumbens, a brain region involved in motivation, attention, and reward, receives substantial glutamatergic innervation from many limbic structures. This excitatory glutamatergic input plays an integral role in both normal and pathophysiological states. Despite the importance of glutamatergic transmission in the nucleus accumbens, the specific receptor subtypes that mediate glutamatergic signaling in this brain region have not been fully characterized. The current study sought to examine the possible role of the kainate subclass of glutamate receptor in the nucleus accumbens. Kainate receptors are relatively poorly understood members of the ionotropic glutamate receptor family and are highly expressed in the nucleus accumbens. Recent studies have highlighted a number of novel pre- and postsynaptic functions of kainate receptors in several other brain regions. Using the whole cell patch-clamp technique, we report the first demonstration of functional kainate receptors on neurons within the core region of the nucleus accumbens. In addition, we present evidence that activation of kainate receptors in this brain region inhibits excitatory synaptic transmission via a presynaptic mechanism.
