Weaker synaptic inhibition in CA1 region of ventral compared to dorsal rat hippocampal slices.

Extracellular and intracellular recordings were made from slices taken from the dorsal (DH) and ventral (VH) part of rat hippocampus. Using paired-pulse stimulation of Schaffer collaterals, at different interpulse intervals (IPIs), and records of the population spike (PS) we found that the strength and duration of paired-pulse inhibition was much weaker in VH compared to DH slices: at the IPI of 10 ms the decrease of PS in VH (40%) was significantly smaller compared to that in DH slices (76%), while at 20 ms the decrease of PS in DH slices (60%) corresponded to facilitation in VH slices. Moreover, the amplitude and duration of intracellularly recorded fast inhibitory postsynaptic potentials (fast-IPSPs) were found significantly smaller in VH (5.2+/-0.6 mV, 54.8+/-5.8 ms) than in DH (11.2+/-1.1 mV, 105+/-10 ms) neurons. The smaller and shorter fast-IPSP recorded in VH neurons may at least in part explain the results in paired-pulse inhibition. The demonstrated weaker inhibition may underlie the higher propensity of the ventral hippocampus for epileptiform activity. Copyright 2002 Elsevier Science B.V.