The perirhinal cortex (PRC) works as a gateway between associative cortical areas and the hippocampus. The muscarinic modulation of this area is mandatory for several learning and memory processes.

In this study we investigated the effects of muscarinic modulation on GABAergic interneurons (INs) and pyramidal neurons (Pyr) of the PRC, using the whole-cell patch-clamp technique in mouse brain slices. Both gropus showed very heterogeneous firing patterns. Moreover, in Pyr the application of carbachol (CCh 30 mM), a muscarinic receptor agonist, induced a pure depolarization. By contrast, CCh induced three types of effect in GABAergic INs: i) a pure depolarization; ii) a biphasic hyper/depolarizing response; iii) a pure hyperpolarization. Furthermore, in all cells the signal noise increased significantly during the CCh-induced depolarization. Finally, the co-application of CCh, CPP (30 mM) and NBQX (10 mM), antagonists of the fast glutamatergic transmission, evoked in Pyr synchronous IPSPs at 0.1 Hz. This frequency represents the resonance frequency for these neurons, whereas no resonance property was observed in GABAergic INs.

Altogether these data suggest that muscarinic modulation could i) increase the excitability of both INs and Pyr, ii) increase the paramount excitability of the PRC itself and iii) elicit in Pyr synchronized and periodic IPSP in a resonance frequency that has been strictly correlated with some form of synaptic plasticity during specific learning task.