Lateral hypothalamus and local stimulation induced postsynaptic responses in zona incerta neurons in an in vitro slice preparation of the rat.

Postsynaptic potentials evoked in the zona incerta (ZI) neurons were studied in in vitro slice preparations. Lateral hypothalamus (LH) and local stimulation evoked fast IPSPs, fast EPSPs, and slow EPSPs. The amplitude of the slow EPSPs increased when the neuron was hyperpolarized by a low intensity current injection but was blocked when it was hyperpolarized with a strong current. The slow EPSPs were reversibly suppressed by an application of 50 microM DL-2-amino-5-phosphonovaleric acid (APV) and 20 microM 3-[(+/-)-2-carboxypiperazine-4-yl-]-propyl-1-phosphonic acid (CPP). The slow EPSPs were augmented in Mg-free medium and by train pulse stimulation. Pressure application of NMDA induced a depolarization similar to the slow EPSP. On the other hand, the fast EPSPs showed a conventional voltage dependency and were antagonized by kynurenic acid but not by APV or CPP. The fast IPSPs were completely blocked by 10 microM bicuculline methiodide. The results indicate that LH and local stimulation evoked monosynaptic fast EPSPs and slow EPSPs mediated by N-methyl-D-aspartate (NMDA) and non-NMDA receptors, respectively. The IPSPs appear to be mediated by GABAA receptors and regulate the expression of NMDA receptor-mediated slow EPSPs.