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Orexins, also called hypocretins, are newly discovered hypothalamic peptides that are thought to be involved in various physiological functions. In spite of the fact that orexin receptors, especially orexin receptor 2, are abundant in the hypothalamic paraventricular nucleus (PVN), the effects of orexins on PVN neurons remain unknown. Using a whole cell patch-clamp recording technique, we investigated the effects of orexin-B on PVN neurons of rat brain slices. Bath application of orexin-B (0.01-1.0 [micro] M) depolarized 80.8% of type I (n = 26) and 79.2% of type 2 neurons tested (n = 24) in the PVN in a concentration-dependent manner. The effects of orexin-B persisted in the presence of TTX (1 [micro] M), indicating that these depolarizing effects were generated postsynaptically. Addition of [Cd.sup.2+] (1 mM) to artificial cerebrospinal fluid containing TTX (1 [micro] M) significantly reduced the depolarizing effect in type 2 neurons. These results suggest that orexin-B has excitatory effects on the PVN neurons mediated via a depolarization of the membrane potential. hypocretin; magnocellular neuron; parvocellular neuron; electrophysiology

Examines the association of cardiovascular changes due to central hypertonic saline and glutamate release in awake rats. Neurochemical mechanisms underlying cardiovascular responses; Effect of saline perfusion on heart rate; Involvement of glutamate in cardiac responses.