ENHANCEMENT OF NMDA RECEPTOR-MEDIATED SYNAPTIC POTENTIALS OF RAT HIPPOCAMPAL-NEURONS IN-VITRO BY THYROTROPIN-RELEASING-HORMONE

The effects of thyrotropin releasing hormone (TRH) on excitatory posts ynaptic potentials (EPSPs) evoked by electrical stimulation of Schaffe r collaterals on CA1 neurones of the adult rat hippocampal slice prepa ration were investigated using intracellular recording under current c lamp conditions. At resting membrane potential and in the presence of extracellular Mg2+, TRH (10-20 mu M) largely potentiated NMDA receptor -mediated EPSPs while leaving those mediated by non-NMDA receptors una ffected. This phenomenon had a brief duration (approximately 2 min) an d was not accompanied by changes in resting membrane potential or inpu t conductance. It is suggested that TRH provided a transient upregulat ion of synaptic responses due to NMDA receptor activation.