Responses of hypothalamic paraventricular neurons in vitro to norepinephrine and other feeding-relevant agents

To investigate paraventricular hypothalamic neuronal actions responsible for the effects of neurotransmitters on feeding, and to test the notion that a single population of cells there could account for feeding effects, hypothalamic slices containing the paraventricular nucleus (PVN) were prepared from rats. Electrophysiological responses of individual PVN neurons to feeding-inducing agents norepinephrine (NE) and gamma-aminobutyric acid (GABA), and to anorexic agents serotonin (5-HT) and histamine (Hist) were examined. NE inhibited neuronal activity through alpha 2-adrenergic receptors, and excited through alpha 1-receptors. alpha 2-receptors are known to mediate the behavioral effect of NE. NE inhibited most clearly those neurons that otherwise fired continuously in this type of in vitro preparation. GABA affected the activity of 37% of the neurons tested, primarily by inhibition. The inhibitory action of GABA can be related to its feeding-inducing effect. GABA in PVN can also attenuate excitatory responses and enhance inhibitory responses to NE or 5-HT. 5-HT caused excitatory and inhibitory responses with the former action outnumbering the latter by approximately 3 to 1. Since this would result in a net excitation, it appears that 5-HT in PVN inhibits feeding mainly by exciting neuronal activity. Hist excited 72% and inhibited only 2% of PVN neurons. The excitation was blocked by H1-antagonists, which have been shown to mediate Hist effect on feeding. Comparing across neurons, the inhibitory response to NE was correlated with that to GABA, but not with any responses to 5-HT or Hist. The excitatory responses to Hist correlated with 5-HT responses.(ABSTRACT TRUNCATED AT 250 WORDS)