Enhancement of NMDA receptor mediated synaptic potentials of rat hippocampal neurones in vitro by thyrotropin releasing hormone.

The effects of thyrotropin releasing hormone (TRH) on excitatory postsynaptic potentials (EPSPs) evoked by electrical stimulation of Schaffer collaterals on CA1 neurones of the adult rat hippocampal slice preparation were investigated using intracellular recording under current clamp conditions. At resting membrane potential and in the presence of extracellular Mg2+, TRH (10-20 microM) largely potentiated NMDA receptor-mediated EPSPs while leaving those mediated by non-NMDA receptors unaffected. This phenomenon had a brief duration (approximately 2 min) and was not accompanied by changes in resting membrane potential or input conductance. It is suggested that TRH provided a transient upregulation of synaptic responses due to NMDA receptor activation.