A comparison of the muscarinic response and morphological properties of identified cells in the guinea-pig olfactory cortex in vitro

Abstract The electrophysiological and morphological characteristics of neurons in the guinea-pig olfactory cortex brain slice were investigated using a combined intracellular recording and neurobiotin-dye filling technique, in an attempt to show whether a clear relation existed between cell morphology and excitatory muscarinic response profile. Out of 46 sampled neurons, 25 (termed type 1), responded to bath-application of the muscarinic agonist oxotremorine-M (10 μM, 2–3 min) with a strong and persistent excitation coupled with the appearance of a slow depolarizing afterpotential (10–20 mV amplitude) following a large depolarizing stimulus. These neurons were identified as deep pyramidal cells located in cortical layer III, with characteristic pyramidal/ovoid shaped cell bodies, prominent apical dendrites with branches extending to the surface, and extensive basal dendritic trees. The cells showed a regular spiking pattern in response to injected depolarizing current, with no evidence of bursting behaviour. Nine cells (termed type 2), were strongly excited by oxotremorine-M, but only generated a weak depolarizing afterpotential ( It is proposed that the selective muscarinic induction of the slow depolarizing afterpotential phenomenon in deep pyramidal cells may be important in olfactory cortical learning and memory processes.