Hypothalamic aggression area under serotonergic control in mouse-killing behaviour of rats

The serotonergic system participates in the modulation of aggressive behaviour. We examined the neuronal substrate underlying serotonergic control of aggressive behaviour in rats using a transplantation technique. Fetal serotonergic neurons transplanted into the hypothalamus restored inhibition of mouse-killing behaviour (muricide), in rats with raphe lesions induced by a serotonergic neurotoxin, 5,7-dihydroxytryptamine. Immunohistochemical and neurochemical studies indicated that the recovery of serotonergic innervation in the lateral hypothalamic area by the raphe grafts brought about the inhibition of muricide. The extension of serotonergic fibres into the lateral hypothalamic area from the grafted serotonergic neurons is strongly related to inhibition of muricide. These results indicate the possibility that serotonergic neurons regulate muricide through the inhibition of the activity of the lateral hypothalamic area neurons.