Presynaptic short‐term depression is maintained during regulation of transmitter release at a GABAergic synapse in rat hippocampus

• DOI: 10.1113/jphysiol.2001.013455
• Publication Date: 2002-07-27T12:45:57Z
• Authors: Stefan Hefft; Udo Kraushaar; Jörg R. P. Geiger; Peter Jonas
• Keywords: Baclofen; Neurotransmitter Agents; 0303 health sciences; Time Factors; Presynaptic Terminals; Neural Inhibition; Cholinergic Agonists; Hippocampus; Synaptic Transmission; Electric Stimulation; Rats; 03 medical and health sciences; Synapses; Animals; Calcium Channels; Rats, Wistar; GABA Agonists; gamma-Aminobutyric Acid; Cadmium

To examine possible interactions between fast depression and modulation of inhibitory synaptic transmission in the hippocampus, we recorded from pairs of synaptically connected basket cells (BCs) and granule cells (GCs) in the dentate gyrus of rat brain slices at 34 °C. Multiple‐pulse depression (MPD) was examined in trains of 5 or 10 inhibitory postsynaptic currents (IPSCs) evoked at frequencies of 10–00 Hz under several conditions that inhibit transmitter release: block of voltage‐dependent Ca2+ channels by Cd2+ (10 μm), activation of γ‐amino‐butyric acid type B receptors (GABABRs) by baclofen (10 μm) and activation of muscarinic acetylcholine receptors (mAchRs) by carbachol (2 μm). All manipulations led to a substantial inhibition of synaptic transmission, reducing the amplitude of the first IPSC in the train (IPSC1) by 72 %, 61 % and 29 %, respectively. However, MPD was largely preserved under these conditions (0.34 in control versus 0.31, 0.50 and 0.47 in the respective conditions at 50 Hz). Similarly, a theta burst stimulation (TBS) protocol reduced IPSC1 by 54 %, but left MPD unchanged (0.40 in control and 0.39 during TBS). Analysis of both fractions of transmission failures and coefficients of variation (CV) of IPSC peak amplitudes suggested that MPD had a presynaptic expression site, independent of release probability. In conclusion, different types of presynaptic modulation of inhibitory synaptic transmission converge on a reduction of synaptic strength, while short‐term dynamics are largely unchanged.