Muscarinic control of intracortical connections to layer II in rat entorhinal cortex slice

The cholinergic system is critically involved in oscillatory network activity and synaptic plasticity in the entorhinal cortex (EC) hippocampal formation. Here we demonstrate robust inhibition of field potentials in layer II of the medial EC evoked by stimulation in the deep EC or in the lateral layer II by carbachol (CCh, 0.1-100 microM, K(D) approximately 1 microM). This effect appears not to be mediated by suppression of presynaptic Ca(2+)-signals since paired pulse facilitation was increased by CCh. Blockade of the effect by the muscarinic antagonists atropine and pirenzepine demonstrates mediation by muscarinic receptors, most likely of the M1 subtype. The effect is characterized by absence of desensitization and should be important for laminar shaping of oscillatory activity and synaptic plasticity during acetylcholine-dependent theta-rhythmic activity.