BIOLOGY OF REPRODUCTION 28, 878-882 (1983) 878 Photoperiodic Modification of Opiate But Not i3-Adrenergic or Benzodiazepine Binding Sites in Hamster Brain M. WILKINSON,1’23 R. BHANOT,2 DIANE A. WILKINSON,2 GAIL ESKES2 and W. H. MOGER23 Departments of Physiology and Biophysics2 and Obstetrics and Gynaecology3 Daihousie University Halifax, Nova Scotia, Canada B3H 4H7 ABSTRACT Exposure to short photoperiods induces gonadal regression in the golden hamster. This is accompanied by a fall in serum gonadotropins and changes in hypothalamic neurotransmitter turnover. We have attempted to correlate these changes with alterations in neurotransmitter receptor binding parameters. Compared to hamsters held in long photoperiods, opiate ([3 HI nab- xone) binding in hamsters exposed to short photoperiods is elevated in whole brain and in cerebral cortex but not in hypothalamus. However, $3-adrenergic ((3 H] dihydroalprenolol) and benzodia- zepine ((3 HI flunitrazepam) binding are unaffected in whole brain, cerebral cortex or hypothal- amus. Thus, changes in hypothalamic noradrenaline turnover rate previously reported may not be correlated with changes in 9-adrenergic binding. INTRODUCTION The golden hamster is a seasonal breeder when exposed to changes in day length. Ham- sters maintained in photoperiods with less than 12.5 h of light per day exhibit significant testicular involution accompanied by a decline in spermatogenesis and androgen production, as well as a decrease in serum gonadotro- pins, prolactin and testosterone concentrations (Berndtson and Desjardins, 1974; Turek et al., 1975; Reiter and Johnson, 1974). Precise data on changes in the neurochemistry of the hypothalamo-pituitary system accompanying gonadal regression are singularly lacking, partic- ularly since a large amount of data is available on the role of brain catecholamines and opiate peptides in reproductive function in the rat (Barraclough and Wise, 1982; VanVugt and Meites, 1980). Recently, changes in monoamine levels and turnover rates in the hypothalamus of hamsters exposed to long or short photo- Accepted December 9, 1982. Received October 6, 1982. Reprint requests: Dr. Michael Wilkinson, Dept. of Physiology and Biophysics, Tupper Med. Bldg., Dalhousie University, Ualifax, Nova Scotia, Canada B3H 4H7. periods have been measured (Steger et al., 1982). An alternative and complementary approach is to quantify changes in neuro- transmitter binding sites with the use of radio- ligand binding assays. The relationship between gonadal steroids and changes in brain neuro- transmitter binding sites has been extensively studied in the rat using this technique. For example, we have previously shown that estrogens can elevate central 13-adrenergic binding sites (Wilkinson et al., 1979, 1981). Biegon and McEwen (1982) have reported a biphasic influence of estradiol on central serotonin binding sites. In the castrate male rat, Vacas et al. (1982) reported that testosterone can reduce 13-adrenergic binding. Also in the male, castration elevates opiate sites (Hahn and Fishman, 1979), whereas testosterone readily reverses this change. On the other hand, under a variety of conditions (e.g., ovariectomy, steroid injection, estrous cycle) we have never oberved changes in benzodiazepine binding in the female rat (unpublished observations). In the male rat, however, we have demonstrated a stimulatory effect of castration on benzodia- zepine ([3 HI flunitrazepam) binding (Wilkinson et al., 1980). We describe here the results of experiments conducted to determine whether changes in photoperiod affect neurotransmitter receptor binding in hamster brain. Downloaded from https://academic.oup.com/biolreprod/article-abstract/28/4/878/2766282 by guest on 22 May 2020