Cholinergic modulation of synaptic physiology in deep layer entorhinal cortex of the rat

We have recently shown that cholinergic effects on synaptic transmission an d plasticity in the superficial (II/III) layers of the rat medial entorhina l cortex (EC) are similar, but not identical, to those in the hippocampus ( Yun et al. [2000] Neuroscience 97:671-676). Because the superficial and dee p layers of the EC preferentially convey afferent and efferent hippocampal projections, respectively, it is of interest to compare cholinergic effects between the two regions. We therefore investigated the physiological effec ts of cholinergic agents in the layer V of medial EC slices under experimen tal conditions identical to those in the previous study. Bath application o f carbachol (0.5 muM) induced transient depression of field potential respo nses in all cases tested (30 of 30; 18.5% +/- 2.3%) and rarely induced long -lasting potentiation (only 3 of 30; 20.4% +/- 3.2% in successful cases). A t 5 muM, carbachol induced transient depression only (20 of 20, 48.9% +/- 2 .8%), which was blocked by atropine (10 muM). Paired-pulse facilitation was enhanced during carbachol-induced depression, suggesting presynaptic actio n of carbachol. Long-term potentiation (LTP) could be induced in the presen ce of 10 muM atropine by theta burst stimulation, but its magnitude was sig nificantly lower (9.1% +/- 4.7%, n = 15) compared to LTP in control slices (22.4% +/- 3.9%, n = 20). These results, combined with our previous finding s, demonstrate remarkably similar cholinergic modulation of synaptic transm ission and plasticity across the superficial and deep layers of EC. (C) 200 1 Wiley-Liss, Inc.