Short photoperiod inhibition of growth in body mass and reproduction in ACI, BUF, and PVG inbred rats

Abstract

Laboratory rats have been generally considered non-photoresponsive, but strains of laboratory rats have been found to be variable for this trait. Young males of both the Fischer (F344) and Brown Norway strains (BN) suppress reproductive development, food intake and body mass in short winter photoperiod (short days (SD); 8 h light:16 h darkness), and food restriction interacts with SD to enhance the effect of SD alone. Conversely, young male Harlan Sprague Dawley outbred rats, along with other outbred laboratory rats tested, have little or no response to SD except when unmasked by food restriction or other treatments, and have generally been considered nonphotoperiodic. In order to assess how widespread this trait might be among rat strains, and to test for uncoupling of reproductive and nonreproductive responses, we tested 3 additional inbred strains, including ACI, PVG and BUF rats, for photoresponsiveness and for unmasking of photoperiodic responses by food restriction. Young males of all three inbred strains exhibited photoresponsiveness in testis mass (5 -20% lower in SD), seminal vesicle mass (20-50% lower in SD), and body mass (5-10% lower in SD). Food restriction also suppressed reproduction, but there was little or no interaction with the effects of photoperiod. The results are consistent with the hypothesis that laboratory rats are genetically variable for photoperiodism, and that photoresponsiveness may be widespread among inbred rat strains, as all five inbred strains tested have shown photoperiodic responses. The results are particularly important because standard research protocols may unknowingly manipulate this pathway in rats, causing unsuspected variability among or within studies.

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).…”

Negative energy balance and leptin regulate neuromedin-U expression in the rat pars tuberalis

“…As such, the pars tuberalis is influential in controlling the annual cycles of reproduction, pelage growth and moulting and appetite and body weight in seasonal animals (Lincoln et al 2003). The laboratory rat maintains highly dampened seasonal cycles in reproduction and energy balance, which appear to be straindependent, but may be unmasked by food restriction (Francisco et al 2004).…”

Effect of Short Photoperiod on Some Growth Traits in Sprague Dawley Rats

“…Before puberta, F344 rats, subjected to short (8 h) had similar reproduction organ weight when compared to the ones, kept in long photoperiod regime (16 h) [8] . Presents results stated that, weights of testis and ovary in Sprague Dawley rats were not impressed by 9 h photoperiod, however, some of the strains of Harlan Sprague dawleys, like ACI, BUF and PVG males had lower (5-20%) testis weight than those kept in long photoperiod lighting [3] . When compared to previous results, it is noticed that reaction of the rodents to photoperiod may significantly differ, according to the species, breed, strain, family of the animals.…”

“…Some rodent strains were recorded not to be very sensitive to photoperiod [18] , however, some researchers declared that the photoperiod had a significant effect on growth of the laboratory rodents [19] . F344 and Brown Norway rats reacted to 8 h lighting by reducing feed intake and body weight, where as body weight of Harlan Sprague dawleys decreased about 5-10% [3] .…”

“…However, in natural conditions, it is known that, even the light period is less than 9 h, rats continue their biological activities, including reproduction [1] . Photoperiod regulates melatonin level, epiphysis gland and organ development [2] and the respond varies according to breed, family and strain of the rats [3] . In Fischer (F344) rats, which are exposed to short photoperiod, puberta longened, feed intake and cellular growth decreased [4] .…”