EFFECTS OF PHOTOPERIOD ON HYPOTHALAMIC AND ANTERIOR-PITUITARY TACHYKININS OF MALE SIBERIAN HAMSTERS DURING DEVELOPMENT

In previous reports from our laboratory we showed that the hypothalamu s and especially the anterior pituitary gland of the Siberian hamster contain very high concentrations of substance P- and neurokinin A-like immunoreactive substances, as compared with other common laboratory r odents. It was thought, therefore, that a study of the developmental c hanges of these two tachykinins in the hypothalamus and anterior pitui tary of male Siberian hamsters would be of interest. In addition, as t his species is very sensitive to changes in environmental light, these studies were carried out in animals kept under short or long daily ph otoperiods. The results of this investigation show that in male Siberi an hamsters, photoperiod did not markedly influence the hypothalamic c oncentrations of substance P- and neurokinin A-like immunoreactive sub stances, which steadily increased from prepuberty up to 40-50 days of age. The influence of photoperiod, however, was much more marked on ta chykinin levels in the anterior pituitary gland, because the developme ntal increase of tachykinins in this gland was significantly more evid ent in animals kept under short daily photoperiods than in animals und er long daily exposure to light. These results are similar to those pr eviously obtained in female Siberian hamsters, in spite of the fact th at estradiol and testosterone seem to have opposite effects on anterio r pituitary tachykinin concentrations. It seems, therefore, that, in a ddition to gonadal steroids, other factors may be important mediators of the tachykinin response to photoperiods in the anterior pituitary o f the male Siberian hamster. Copyright (C) 1996 Elsevier Science Inc.