Circadian and Photoperiodic Effects of Brief Light Pulses in Male Djungarian Hamsters

OF BIOLOGY 35, 327-3 REPRODUCTION Circadian 35 (1986) and Photoperiodic Effects of Brief in Male Djungarian Hamsters’ JILL J. MILETTE2 Department and of Neuro Northwestern FRED Illinois Pulses W. TUREK biology and University Evanston, Light Physiology 60201 The the effects of brief light pulses neuroendocrine-gonadal running in constant locomotor night, darkness activity. animals; phase-delays and Animals exposed in increased levels of light (but two of phase-advances 1 -mm the during pulses) for testicular weight gains and serum FSH apart, some animals showed a short-day 10 the circadian Djungarian induced induced by of light testicular days light subjective rhythm of locomotor hamsters. day curve” was pulses delivered induced phase similar little resulted in stable entrainment two 10-mm pattern (i.e., did- not in which result trainment increase productive the activity in testicular rhythm growth showed in any of a long-day the animals The annual variation or photoperiod, avian and to bong days several (e.g., has the amount species sparrows, of light per activity manipulation that of breed voles, mice during and only hamsters) Accepted January 27, 1986. Received November 25, 1985. ‘Preliminary reports of this work were presented at the 17th and 18th Annual Meetings of the Society for the Study of Reproduction in Laramie, Wyoming, July 1984, and Montreal, Quebec, July 1985. This work was supported by a National Science Foundation Fellowship to J.J.M., the Whitehall Foundation and NIH Research Grant HD-09885. 2Reprint requests. subjective rhythm presented confined exposure rhythm activity as well 8 and to the activity that to the confined rhythm of in all the same showed light measuring but instead between clock been carried (Gaston Stetson Zucker, and Menaker, et al., 1975; 1978; Matt variety of collegues coincident absolute is dependent bight and (Menaker out and using length of the upon the the animal’s Eskin, 1967; Clarke, 1980; et al., 1974; Darrow 1985). of a circadian clock in in mammals have the golden 1967; Elliott et Elliott, 1976, 1981; and Stetson, 1980). experimental have with measurement the Grocock and and Zucker, Underwood ena rapid on re- time studies on the robe time measurement cycle a short-day photoperiodic circadian as 16 h long neuroendocrine-gonadal and the circadian testicular growth activity of other exposed to 6L:18D or two 10-mm pulses locomotor pattern, revealed Detailed photoperiodic exposure late in the of the activity Follett et a!., 1974; Elliott, 1976; Johnston and Goldman, 1985; short days the photo- and in that short pulses of light can induce hamster and that the effects of light the light and the circadian system. internal appropriate time 1979). In many days stimulate while the does not involve day (or night), phase-relationship as the primary signal for species to synchronize activities to the and Campbell, species, long neuroendocrine-gonadal inhibit it. Experimental of in serves mammalian their reproductive of the year (Turek seasonally breeding period entrainment in which pattern. Taken together, these results demonstrate in neuroendocrine-gonadal function in the Djungarian function depend upon the phase-relationship between INTRODUCTION day, many early on free- observed phase-shift pulses of light were locomotor activity and/or hamsters in the rhythm that in the period of darkness) while other animals showed a long-day entrainment pattern (i.e., to the short period of darkness). Importantly, the stimulatory effects of light activity were clearly dependent on the phase-relationship between the light pulses locomotor activity. While exposure to two 10-mm pulses of light per day induced hamsters shifts to or no of during the night in animals otherwise weight. Daily exposure to two 1-b increases. When entrainment activity Exposure phase-dependent “phase-response the to 1-mm FSH and on male of light were pulses for 7 days of serum in 1-h pulse shape light in duration) investigated to a single while rhythm. resulted mm was general The respectively, not (1-60 axis demonstrated the active bight cycles, hamster a!., 1972; Eskes and Using a Elliott cycle of the golden hamster, stimulation neuroendocrine-gonadab axis occurs. This inducible phase” begins at about the time 327 and that when light phase of the activity/rest his is of the “photoof the ABSTRACT 328 MILETTE onset of locomotor activity and lasts for AND about TUREK transferred to of h) the about 3 wk exposure to 6L:18D, and each animal was categorized into one of four stages according to the method of Hoffmann (1978). Only those animals with testes in the smallest class (Stage N, direct methods of the clock are available itself. The be an excellent model perties of the circadian difficulty release in daylength (Berndtson In for examining clock involved a robust change and/or gonadal is usually not and contrast, the has phase proved to the formal in photoperiodic pro- nonpabpabbe) However, use of this species for inneural and cellular events underlying time measurement presents a major in that tropin measuring hamster in pituitary activity Desjardins, 1974; photostimulation for the a change many Turek of gonado- after observed size weeks et ab., 1975). juvenile Djung- induces a clear Activity To was were assessed used by in these regression. palpation experiments. Recording record locomotor activity, animals were the running wheel an Esterline-Angus activated a microswitch that led to (Indianapolis, IN) event recorder. records for individual animals and pasted onto a board to rise in serum FSH levels within 3 days and an increase in testicular weight within 5 days (Simpson et ab., 1982). Furthermore, as it can in the golden hamster visualization of (Rudeen activity hamster 1984; and Ellis during the photoperiod activity 1982). Reiter, and 1980; Foblett, night can Earnest 1983), of an stimulate Turek, pulse 1983, of light was 5-10 Djungarian hamster an excellent model the relationship between the circadian systems. The present study examines for and the state of light as well testicular MATERIALS on the circadian as on pituitary weight AND in the rhythm gonadoDjungarian Animals Djungarian hamsters (Phodo pus sungorus sungorus) were born and raised in our laboratory breeding colony under a 16L:8D photoperiod (bights on from 0500-02100 h). The colony was derived from animals (Worcester Shrewsbury, hamster received kindly provided Foundation MA). The by for Dr. Bruce Experimental animals chow (Winfield, IA) a weekly supplement were Goldman Biology, fed and water ad of sunflower The young remained with their parents unti (...truncated)