The Stimulatory Effect of 5HT and the Role of the Paraventricular Nucleus on PMS Induced Ovulation in the Immature Rat

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Abstract
Immature rats weighing > 60 g can be induced to ovulate with pregnant mare serum (PMS). In rats weighing < 60 g, 5-hydroxytryptamine (5HT)-60 .mu.g/rat intraventricularly or 2 .mu.g/rat in the paraventricular nucleus (PVN) stimulated ovulation. Injections into several other hypothalamic nuclei were ineffective. In rats weighing > 60 g, lesions of the PVN or injection of 10 .mu.g/rat p-chlorophenylalanine into the PVN inhibited ovulation. The hypothalamic levels of 5HT and 5-hydroxyindoleacetic acid (5HIAA) were generally lower in the afternoon and evening in the < 60 g when compared with the > 60 g rats. Increased 5HT activity may be required to stimulate ovulation and that its site of action is the PVN.