Rat hypothalamic noradrenaline levels following midbrain raphé nuclei lesions.

Electrolytic lesions of the median and dorsal raphé nuclei resulted in statistically significant reductions in rat hypothalamic noradrenaline which were observed 1 or 2 days after lesioning, while no changes were observed 7 or 14 days after lesioning. The short term (1-2 days) raphé nuclei lesions produced no changes in hypothalamic 5-hydroxytryptamine or a small reduction in 5-hydroxyindole acetic acid while the expected marked reductions were observed after 7 days. The reduction in hypothalamic noradrenaline observed after short term raphé nuclei lesions suggests the existence of a positive feedback loop between 5-hydroxytryptamine neurons and noradrenaline terminals in the hypothalamus.