Reproductive Photoresponsiveness in Unmanipulated Male Fischer 344 Laboratory Rats1

Abstract

Laboratory rats are considered to be reproductively unresponsive to photoperiod because photoperiod treatments do not induce robust reproductive responses. Groups of 15 young male Fischer 344 (F344) rats were tested for effects of long (16L:8D) and short (8L:16D) photoperiods on testicular development and body mass. Two weeks of short photoperiod inhibited testicular growth, spermatogenesis, and increases in body weight. Testis size became refractory to short photoperiod after 8 wk, but the body weight was lower in short photoperiod for the full 10 wk of the study. In young Harlan Sprague-Dawley rats, in contrast, long and short photoperiod had no effect on either body weight or testis size. Pinealectomized F344 rats had significantly higher body weights and larger testes than did sham-operated controls, suggesting that the effects of photoperiod are mediated, at least in part, by the pineal gland. The F344 strain of laboratory rats is the first in which unmanipulated animals have been found to be robustly affected by photoperiod, indicating that this strain could be a valuable new model for the study of reproductive regulation by photoperiod.

Winter day lengths enhance T lymphocyte phenotypes, inhibit cytokine responses, and attenuate behavioral symptoms of infection in laboratory rats

“…Although reproductive photoperiodic responses have been reported in several inbred and outbred laboratory rats (Francisco et al, 2004;Heideman and Sylvester, 1997;Leadem, 1988;Lorincz et al, 2001;Shoemaker and Heideman, 2002); this is not the case for Wistar rats (Fig. 7;Vanecek and Illnerova, 1982;Wallen et al, 1987).…”

“…Nocturnal melatonin secretion reliably tracks seasonal changes in photoperiod (Illnerova and Vanecek, 1980), and pinealectomy abolishes photoperiodic gonadal responses in reproductively photoresponsive rodents (including select rat strains: [Heideman and Sylvester, 1997;Prendergast et al, 2002a]). Pineal melatonin may figure prominently in the transduction of day length information into the immune system of rats, as is the case in hamsters (Wen et al, 2007).…”

“…Rats remained pair-housed for the next 8 weeks. At two week intervals between weeks 0 and 8, rats were weighed and their reproductive condition was assessed by measuring the length and width of the left testis, the product of which provides an estimated testis volume (ETV) which is highly (R 2 >0.9) correlated with testis mass (Gorman & Zucker, 1995) and provides a reliable, non-invasive indicator of hypothalamic-pituitary-gonadal axis activity (Heideman & Sylvester, 1997). On week 8 rats were individually-housed, and on week 9 rats were injected i.p.…”

Behavioral neuroendocrinology in nontraditional species of mammals: Things the ‘knockout’ mouse CAN'T tell us

“…An important point here is that this is a link that would be difficult to make in a traditional model, and even harder to extend to natural populations. For example, there are rat strains that differ in reproductive responses to photoperiod as well as in voluntary food intake, but these strains differ in so many other characteristics, including body mass (Heideman and Sylvester, 1997;Lorincz et al, 2001), that a connection between food intake and reproductive responses to photoperiod has never been proposed. It is not surprising that low voluntary food intake might be linked to lower reproductive performance, but it is intriguing that this might be an important source of natural variation in seasonal reproduction, and that selection on seasonal reproductive traits might cause changes in food intake.…”

Effects of photoperiod on testicular functions in male sprague-dawley rats

“…Variation in reproductive status and body mass in response to short photoperiod has been observed in laboratory rats (Leadem, 1988;Heideman and Sylvester, 1997). Studies have shown that the Fischer 344 (F344) and Brown Norway (BN) inbred rat strains exhibit robust obligate photoresponsiveness, repressing reproduction, food intake, and somatic growth in the absence of light (Leadem, 1988).…”