The cholinergic agonist carbachol increases the frequency of spontaneous GABAergic synaptic currents in dorsal raphe serotonergic neurons in the mouse.
Dorsal raphe nucleus (DRN) serotonin (5-HT) neurons play an important role in feeding, mood control and stress responses. One important feature of their activity across the sleep-wake cycle is their reduced firing during rapid-eye-movement (REM) sleep which stands in stark contrast to the wake/REM-on discharge pattern of brainstem cholinergic neurons. A prominent model of REM sleep control posits a reciprocal interaction between these cell groups. 5-HT inhibits cholinergic neurons, and activation of nicotinic receptors can excite DRN 5-HT neurons but the cholinergic effect on inhibitory inputs is incompletely understood. Here, in vitro, in DRN brain slices prepared from GAD67-GFP knock-in mice, a brief (3 min) bath application of carbachol (50 μM) increased the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) in GFP-negative, putative 5-HT neurons but did not affect miniature (tetrodotoxin-insensitive) IPSCs. Carbachol had no direct postsynaptic effect. Thus, carbachol likely increases the activity of local GABAergic neurons which synapse on 5-HT neurons. Removal of dorsal regions of the slice including the ventrolateral periaqueductal gray (vlPAG) region where GABAergic neurons projecting to the DRN have been identified, abolished the effect of carbachol on sIPSCs whereas the removal of ventral regions containing the oral region of the pontine reticular nucleus (PnO) did not. In addition, carbachol directly excited GFP-positive, GABAergic vlPAG neurons. Antagonism of both muscarinic and nicotinic receptors completely abolished the effects of carbachol. We suggest cholinergic neurons inhibit DRN 5-HT neurons when acetylcholine levels are lower i.e. during quiet wakefulness and the beginning of REM sleep periods, in part via excitation of muscarinic and nicotinic receptors located on local vlPAG and DRN GABAergic neurons. Higher firing rates or burst firing of cholinergic neurons associated with attentive wakefulness or phasic REM sleep periods leads to excitation of 5-HT neurons via the activation of nicotinic receptors located postsynaptically and presynaptically on excitatory afferents.
Laboratory of Neuroscience, Department of Psychiatry, VA Boston Healthcare System and Harvard Medical School, Brockton, MA, USA.
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Laboratory of Neuroscience, Department of Psychiatry, VA Boston Healthcare System and Harvard Medical School, Brockton, MA, USA. Electronic address: Ritchie_Brown@hms.harvard.edu.
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D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D018679:Cholinergic Agonists / Q000494:pharmacology*; D005260:Female; D059330:GABAergic Neurons / Q000187:drug effects* / Q000502:physiology; D055879:Gene Knock-In Techniques; D066298:In Vitro Techniques; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D018727:Muscarinic Antagonists / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000494:pharmacology; D010487:Periaqueductal Gray / Q000187:drug effects / Q000502:physiology; D011903:Raphe Nuclei / Q000187:drug effects / Q000502:physiology; D011976:Receptors, Muscarinic / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000378:metabolism; D059326:Serotonergic Neurons / Q000187:drug effects* / Q000502:physiology; D013569:Synapses / Q000187:drug effects* / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D018679:Cholinergic Agonists; D018727:Muscarinic Antagonists; D018733:Nicotinic Antagonists; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D002217:Carbachol
(2R)-amino-5-phosphonovaleric acid; 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid; 5-HT; 6,7-dinitroquinoxaline-2,3-dione; ACSF; AHP; ANOVA; AP; AP5; DNQX; DRN; EGTA; GAD67-GFP knock-in mice; HEPES; LDT; N-methyl-d-aspartate; NMDA; PGO; PPT; PnO; Ponto-geniculo-occipital; REM; RMP; SubC; TTX; action potential; afterhyperpolarization; analysis of variance; artificial cerebrospinal fluid; decussation of the superior cerebellar peduncle; dorsal raphe nucleus; ethylene glycol tetraacetic acid; laterodorsal tegmentum; mIPSCs; miniature inhibitory postsynaptic currents; patch-clamp; pedunculopontine tegmentum; pontine nucleus, pars oralis; presynaptic modulation; rapid-eye-movement; resting membrane potential; sIPSCs; serotonin; sleep; spontaneous inhibitory postsynaptic currents; subcoeruleus; tetrodotoxin; ventrolateral periaqueductal gray; vlPAG; xscp