Response of medial preoptic neurons to electrical stimulation of the mediobasal hypothalamus, amygdala and mesencephalon in normal, serotonin or catecholamine deprived female rats.

Single cell activity from preoptic neurons was extracellularly recorded in normal female rats and the effects of electrical stimulation of the mediocortical amygdala (AMY), the N. med. raphes (MES) and the mediobasal hypothalamus (MBH) was tested. 1. One type of preoptic neurons (55%) reacted with primary excitation to a single electrical stimulus of AMY, MES or MBH, which was usually followed by a period of postexcitatory inhibition. Another type of neurons (29%) were first inhibited after stimulation of AMY, MES or MBH and then showed a period of postinhibitory excitation. The discharge rate of a third type was not affected by electrical stimulation of these structures (16%). If a neuron was affected by a stimulus in a given area it predictably reacted in the same fashion to stimulation of the other areas. 2. The postexcitatory inhibition of the majority of the primarily excited neurons was strong enough to prevent the stimulus response to a second stimulus. Occasional recordings from two neighboured cells simultaneously indicate that they can be inhibitory to each other. 3. By pulse train stimulation of the AMY or MES with varying frequencies it could be demonstrated that low frequencies (10 Hz) had a facilitatory action whereas higher frequencies (100 Hz) were inhibitory to preoptic discharge rates. 4. No obvious alteration of neuronal properties we found neither in rats treated intraventricularly with 5,6-dihydroxytryptamine, which strongly reduces central nervous system serotonin content, nor in 6-hydroxydopamine treated rats, which had low central nervous system catecholamine levels.