Cholinergic synaptic potentials in the supragranular layers of auditory cortex

Receptive-field plasticity within the auditory neocortex is associated with learning, memory, and acetylcholine (ACh). However, the interplay of eleme nts involved in changing receptive-fields remains unclear. Herein, we descr ibe a depolarizing and a hyperpolarizing potential elicited by repetitive s timulation (20-100 Hz, 0.5-2 sec) and dependent on ACh, which may be involv ed in modifying receptive-fields. These potentials were recorded, using who le cell techniques, in layer II/III pyramidal cells in the rat auditory cor tex in vitro. Stimulation at low stimulus intensities can give rise to a hy perpolarizing response and stimulation at higher stimulus intensities can e licit a depolarizing response. The depolarizing response had a reversal pot ential of -35 mV, and was reduced by the combination of AMPA/kainate and NM DA glutamate receptor antagonists (AMPA/kainate: CNQX, DNQX, and GYKI 52466 ; NMDA: APV, MK-801) and by the muscarinic ACh receptor antagonist atropine . The hyperpolarizing response had a reversal potential of -73 mV and could be reduced by atropine, GABAA receptor antagonists (bicuculline and a Cl- channel blocker picrotoxin), and to a small, extent a GABAB receptor antago nist (saclofen). This suggests that the hyperpolarizing response is likely to be mediated by ACh acting on GABAergic interneurons. Extracellular recor dings, also made from layer II/III of cortical slices, yielded a negative-g oing potential which was reduced by ionotropic glutamate receptor antagonis ts (same as above) and by the ACh receptor antagonists atropine and scopola mine, suggesting that this potential was the extracellular representation o f the depolarizing response. (C) 2001 Wiley-Liss, Inc.