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

The cholinergic system is critically involved in oscillatory network activi ty and synaptic plasticity in the entorhinal cortex (EC) hippocampal format ion. 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 lay er II by carbachol (CCh, 0.1-100 mu M, K-D similar to 1 mu M). This effect appears not to be mediated by suppression of presynaptic Ca2+-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 chara cterized by absence of desensitization and should be important for laminar shaping of oscillatory activity and synaptic plasticity during acetylcholin e-dependent theta-rhythmic activity. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.