Slow cholinergic excitation of guinea pig hippocampal neurons is mediated by two muscarinic receptor subtypes.
Stimulation of cholinergic fibers or bath application of carbachol (0.1-10 microM) induced a slow excitability increase in CA3 neurons and dentate granule cells of hippocampal slices. This effect which was antagonized by atropine (1 microM) was mediated by two receptor subtypes: a pirenzepine (10 microM)-insensitive receptor, 'M2', and a pirenzepine (1 microM)-sensitive receptor, 'M1'. The M2-receptor activation led to a blockade of slow afterhyperpolarizations following trains of action potentials and to the occurrence of threshold-activated plateau-depolarizations associated with a conductance increase. The M1-receptor mediated a membrane depolarization sometimes associated with a conductance decrease which reversed its polarity at membrane potentials negative to -80 mV. The 'slow excitatory postsynaptic potential' which results from activation of cholinergic fibers is thus caused by the activation of two receptor subtypes.
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001570:Benzodiazepinones / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002799:Cholinergic Fibers / Q000502:physiology; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D006168:Guinea Pigs; D006624:Hippocampus / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D010890:Pirenzepine; D011976:Receptors, Muscarinic / Q000502:physiology*; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects
D001570:Benzodiazepinones; D011976:Receptors, Muscarinic; D010890:Pirenzepine; D001285:Atropine; D002217:Carbachol