Serotonergic stimulation of prolactin and corticosterone secretion is mediated by different pathways from the mediobasal hypothalamus.
In previous studies we obtained evidence that serotonin release by p-chloroamphetamine (PCA) causes an increase in corticosterone secretion but that this effect is not mediated via the raphe nuclei in the midbrain. In contrast, PCA-induced prolactin secretion was abolished by dorsal raphe lesions. In the present study, posterolateral cuts which interrupted caudal inputs to the hypothalamus attenuated the effect of PCA on plasma prolactin but did not block the PCA-induced increase in plasma corticosterone levels. Large lesions of the mediobasal hypothalamus produced a significant reduction of plasma corticosterone concentration but did not completely prevent the effect of PCA on corticosterone secretion. Hypophysectomy performed 24 h before sacrifice caused a marked decrease in plasma corticosterone levels but did not completely abolish the effect of PCA. These results suggest that PCA also stimulates corticosterone secretion via a direct action on the adrenal gland. The lesions in the mediobasal hypothalamus caused an increase in plasma prolactin concentration, and in these rats, PCA suppressed rather than stimulated prolactin secretion. This suggests that the known weak dopamine agonist activity of PCA is exposed when the effects of serotonin release in the brain are eliminated.