Muscarinic modulation of GABAergic transmission to neurons in the rat subfornical organ.
Cholinergic actions on subfornical organ (SFO) neurons in rat slice preparations were studied by using whole cell voltage- and current-clamp recordings. In the voltage-clamp recordings, carbachol and muscarine decreased the frequency of GABAergic inhibitory postsynaptic currents (IPSCs) in a dose-dependent manner, with no effect on the amplitudes or the time constants of miniature IPSCs. Meanwhile, carbachol did not influence the amplitude of the outward currents induced by GABA. Furthermore, carbachol and muscarine also elicited inward currents in a TTX-containing solution. From the current-voltage relationship, the reversal potential was estimated to be -7.1 mV. These carbachol-induced responses were antagonized by atropine. In the current-clamp recordings, carbachol depolarized the membrane with increased frequency of action potentials. These observations suggest that acetylcholine suppresses GABA release through muscarinic receptors located on the presynaptic terminals. Acetylcholine also directly affects the postsynaptic membrane through muscarinic receptors, by opening nonselective cation channels. A combination of these presynaptic and postsynaptic actions may enhance activation of SFO neurons by acetylcholine.
Xu
S H
SH
Department of Physiology, Kyushu Dental College, Kokurakitaku, Kitakyushu 803-8580 Japan.
Honda
E
E
Ono
K
K
Inenaga
K
K
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D004553:Electric Conductivity; D018698:Glutamic Acid / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009116:Muscarine / Q000378:metabolism*; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013356:Subfornical Organ / Q000166:cytology / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D018679:Cholinergic Agonists; D018727:Muscarinic Antagonists; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D001285:Atropine; D009116:Muscarine; D002217:Carbachol