GLUTAMATE-EVOKED CURRENTS IN ACUTELY DISSOCIATED NEURONS FROM THE RATMEDIAL PREOPTIC NUCLEUS

Membrane currents evoked by glutamate were investigated in acutely dis sociated neurons from the medial preoptic nucleus (MPN) of rat. Rapid application of glutamate induced a fast current component in all neuro ns studied. In addition, in >50% of the neurons, a slow current compon ent was elicited. The fast and the slow current components were select ively blocked by the AMPA-receptor antagonist NBQX and by the NMDA-rec eptor channel blocker MK-801, respectively. Rapid application of AMPA induced, in all neurons tested, currents with properties similar to th e fast component of the glutamate-evoked currents whereas rapid applic ation of NMDA induced, in approximate to 75% of the neurons, currents similar to the slow component of the glutamate-evoked currents. The NM DA-evoked currents showed a marked outward rectification that was attr ibuted to a potential-dependent block by extracellular Mg2+. The NMDA- evoked currents also required the presence of extracellular glycine in the micromolar range. In conclusion, the results show that MPN neuron s respond to glutamate with currents that can be attributed to activat ion of ionotropic glutamate receptors of the AMPA-receptor type as wel l as of the NMDA-receptor type.