Gonadal steroids in the amygdala--differential effects on LH

The direct participation of sexual steroids in the amygdala (AMY)-dependent modulation of LH secretion was investigated by means of a combination of microinjectons into the AMY and electrical stimulation of the AMY. Adult castrated male miniature pigs provided with bilateral 'electro-tubes' into the AMY were used. Electrical stimulation of the AMY without any prior steroid microinjection or with solvent microinjection decreased plasma LH levels. In contrast, electrical stimulation, 3.5 h after microinjection of 60 ng testosterone, resulted in an increase in LH levels. However, prior microinjection of estradiol-17 beta (6 ng) or 5 alpha-dihydrotestosterone (60 ng) abolished the effects of electrical stimulation. Four out of 7 of the animals responded to microinjection of 2-hydroxyestradiol-17 beta (60 ng) with a fall in plasma LH levels. Electrical stimulation increased the LH levels up to those before microinjection in these animals. In the other half of the animals, with no response to catecholestradiol microinjection, the response to electrical stimulation was depression. The results suggest a direct and differentiated effect of steroids on the AMY; the action of testosterone is independent of its aromatization or reduction and steroids could act on the AMY to inhibit or stimulate the inhibitory role of the amygdala in the control of pituitary LH secretion.