Developmental changes of hypothalamic, pituitary and striatal tachykinins in response to testosterone: influence of prenatal melatonin

Substance P (SP) and neurokinin A (NKA), members of the family of mammalian tachykinins, are involved in the regulation of many physiological function s and are widely distributed in mammalian tissues. In this report, the effe cts of prenatal melatonin on the postnatal developmental pattern of NKA, an d SP, and on testosterone secretion were investigated. Also, tachykinin res ponse to the administration of testosterone propionate (TP) was studied. Th e brain areas studied were medio-basal-hypothalamus, pituitary gland and st riatum. Male rat offspring of control or melatonin treated mother rats were studied at different ages of the sexual development: infantile, juvenile o r prepubertal periods, and pubertal period. Both groups received exogenous TP (control-offspring+TP and MEL-offspring+TP), or the vehicle (control-off spring+placebo and MEL-offspring+placebo). Hypothalamic concentrations of a ll peptides studied in control offspring+placebo remained at low levels unt il the juvenile period, days 30-31 of age. After this age, increasing conce ntrations of these peptides were found, with peak values at puberty, 40-41 days of age, then declining until adulthood. In the MEL-offspring+placebo a different pattern of development was observed; hypothalamic concentrations of NKA and SP from the infantile period until the end of juvenile period w ere significantly higher than in control-offspring+placebo. TP administrati on exerted a more marked influence on MEL-offspring than on control-offspri ng and prevented the elevation in tachykinin concentrations associated with prenatal melatonin treatment. TP administration to control-offspring resul ted in significantly reduced (P < 0.05) tachykinin concentration only at 40 -41 days of age, and increased (P < 0.01) during infantile period as compar ed to control-offspring+placebo. Pituitary NKA concentrations were lower th an in the hypothalamus. In control-offspring+placebo pituitary NKA levels d id not show significant changes throughout sexual development. A different developmental pattern was observed in MEL-offspring+placebo, with significa ntly increased (P < 0.05) pituitary NKA concentrations at 35-36 days of age than in control-offspring+placebo. TP administration to control-offspring influenced pituitary NKA levels at the end of the infantile and pubertal pe riods, showing at both stages significantly higher (P < 0.05) NKA levels as compared to control-offspring+placebo. NKA levels in MEL-offspring+TP were only affected at 21-22 days of age, showing significantly increased (P < 0 .01) values as compared to MEL-offspring+placebo. Striatal tachykinin conce ntrations in control-offspring did not undergo important modifications thro ughout sexual development, but during the prepubertal period they started t o increase. Maternal melatonin and TP injections produced short-lived alter ations during the infantile period. The results showed that prenatal melato nin delayed the postnatal testosterone secretion pattern until the end of t he pubertal period and postnatal peptide secretion in brain structures. Con sequently, all functions depending of the affected areas will in turn, be a ffected. (C) 1999 Elsevier Science Inc. All rights reserved.