Lack of sensorial innervation in the newborn female rats affects the activity of hypothalamic monoaminergic system and steroid hormone secretion during puberty

There is evidence that sensory innervation plays a role regulating ovarian functions, including fertility. Since sensory denervation by means of capsaicin in newborn female rats results in a lower response to gonadotropins, the present study analyzed the effects that sensory denervation by means of capsaicin in neonatal rats has on the concentration of monoamines in the anterior (AH) and medium (MH) hypothalamus, and on steroid hormone levels in serum. Groups of newborn female rats were injected subcutaneously with capsaicin and killed at 10, 20, and 30 days of age and on the first vaginal estrous. The concentrations of noradrenaline, dopamine, serotonin (5-HT), and their metabolites in the AH and MH were measured using HPLC, and the levels of estradiol (E), progesterone (P), testosterone (T), FSH, and luteinizing hormone using radioimmunoanalysis. The results show that at 20 days of age, capsaicin-treated rats have lower noradrenergic and serotonergic activities in the AH, and that the dopaminergic activity was lower in the MH. These results suggest that the sensorial system connections within the monoaminergic systems of the AH and MH are different. Capsaicin-treated animals had lower T, E, and P levels than in the control group, suggesting that the lower activity in the AH monoaminergic system and lower hormone secretion could be explained by the blockade of information mediated by the sensory innervation (probably substance P), mainly between the ovary and the AH.