Sexual receptivity after destruction of serotonergic terminals in hypothalamus or amygdala

In order to localize the sites in the brain where serotonergic (5-HT) input may affect the performance of lordotic responses, the serotonin neurotoxin 5-7-dihydroxytryptamine was injected in the ventromedial hypothalamic nucleus (VMN) or in the medial amygdala (AM) in ovariectomized rats. Estrogen induced receptivity as measured by the lordotic quotient was significantly greater in animals injected in AM, but it was smaller in animals injected in the VMN, as compared to controls or animals injected with the vehicle. No differences were found when the same animals were injected with progesterone. It is proposed that serotonergic afferents exert facilitatory influences in the hypothalamus and inhibitory influences in the amygdala, as concerns estrogen-induced sexual receptivity. The integrity of 5-HT terminals in VMN and AM is not necessary for progesterone to exert its potentiating effects.