Effects of intiaventricular infusions of LH-RH and norepinephrine (NE) on the electrical activity of the arcuate nucleus were investigated in normally cycling proestrous rats. Under urethane anesthesia, recordings were made of amplitude-discriminated multiple unit spike activity and integrated multiunit activity (MUA) in parallel with cortical EEC Control infusions of saline (2 µ l, isotonic, pH 5.5) were ineffectual, but LH-RH (0.5 µ g) induced a significant increase in both multiunit spike activity and integrated MUA. While the response appeared to be continuous, statistical analysis revealed 2 phases: a quick rise which persisted for approximately 5 min, followed 15 min later by a longer-lasting elevation in activity. The onset of the 2nd increase corresponded with the attainment of peak values of pituitary LH output. Subsequent treatment with 20 µ g NE, on the other hand, resulted in a marked depression of activity. The fact that NE depresses arcuate neuronal activity at dose levels which cause the release of LH and that LH-RH increases activity within the same population of neurons, while possibly mediating an ‘ultrashort-loop’ negative feedback effect, suggests that this responsive component of the arcuate nucleus, perhaps the tuberoinfundibular dopaminergic system of neurons, is inhibitory to LH release.

Keywords:
LH-RH, Norepinephrine, Hypothalamus, Multiple unit activity, Arcuate nucleus
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© 1976 S. Karger AG, Basel
1976
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