MUSCARINIC RECEPTOR CONTROL OF PYRAMIDAL NEURON MEMBRANE POTENTIAL IN THE MEDIAL PREFRONTAL CORTEX (MPFC) IN RATS

Damage to the cholinergic input to the prefrontal cortex has been implicated in neuropsychiatric disorders. Cholinergic endings release acetylcholine, which activates nicotinic and/or G-protein-coupled muscarinic receptors. Muscarinic receptors activate transduction systems, which control cellular effectors that regulate the membrane potential in medial prefrontal cortex (mPFC) neurons. The mechanisms responsible for the cholinergic-dependent depolarization of mPFC layer V pyramidal neurons in slices obtained from young rats were elucidated in this study. Glutamatergic and GABAergic transmission as well as tetrodotoxin (TTX)-sensitive Na+ and voltage-dependent Ca++ currents were eliminated. Cholinergic receptor stimulation by carbamoylcholine chloride (CCh; 100 mu M) evoked depolarization (10.0 +/- 1.3 mV), which was blocked by M1/M4 (pirenzepine dihydrochloride, 2 mu M) and M1 (VU 0255035, 5 mu M) muscarinic receptor antagonists and was not affected by a nicotinic receptor antagonist (mecamylamine hydrochloride, 10 mu M). CCh-dependent depolarization was attenuated by extra- (20 mu M) or intracellular (50 mu M) application of an inhibitor of the beta gamma-subunit-dependent transduction system (gallein). It was also inhibited by intracellular application of a beta gamma-subunit-binding peptide (GRK2i, 10 mu M). mPFC pyramidal neurons express Nav1.9 channels. CCh-dependent depolarization was abolished in the presence of antibodies against Nav1.9 channels in the intracellular solution and augmented by the presence of ProTx-I toxin (100 nM) in the extracellular solution. CCh-induced depolarization was not affected by the following reagents: intracellular transduction system blockers, including U-73122 (10 mu M), chelerythrine chloride (5 mu M), SQ 22536 (100 mu M) and H-89 (2 mu M); channel blockers, including Ba++ ions (200 mu M), apamin (100 nM), flufenamic acid (200 mu M), 2-APB (200 mu M), SKF 96365 (50 mu M), and ZD 7288 (50 mu M); and a Na+/Ca++ exchanger blocker, benzamil (20 mu M). We conclude that muscarinic M1 receptor-dependent depolarization in mPFC pyramidal neurons is evoked by the activation of Nav1.9 channels and that the signal transduction pathway involves G-protein beta gamma subunits. (C) 2015 IBRO. Published by Elsevier Ltd. All rights reserved.