Thus, it is possible that the combined obligate and facultative responses to SD might induce reproductive inhibition in some rats to a degree similar to that in highly photoresponsive rodents such as hamsters, white-footed mice, or voles. In the young of nonphotoperiodic strains of rats, photoperiod-dependent reproductive suppression can be induced by neonatal T injection or food restriction. However, the degree of suppression of the reproductive system is similar to that of young F344 rats treated with SD alone, suggesting that stronger seasonal inhibition is not possible in these strains.
This study tested the hypothesis that F344 rats, which clearly have an obligate inhibition of reproduction in SD, also have an additional, facultative inhibition of reproduction in SD. Two treatments were chosen. The first, 30% food restriction (FR), was chosen to mimic the biologically reasonable condition of low food availability during maturation. The second, delivery of exogenous testosterone propionate (TP) to neonatal males, is a biologically unrealistic pharmacological treatment that we presume alters organizational events in the development of the reproductive axis. The latter treatment does not mimic any biologically realistic challenge, but it was chosen to test whether F344 rats had the potential for stronger responses to inhibitory photoperiod than occur in SD alone. buy ortho tri-cyclen
We predicted that, if F344 rats have the capacity to be fully reproductively inhibited in SD by a combination of obligate and facultative responses to SD, then both FR and TP would enhance the effects of SD. Alternatively, if F344 rats have the capacity for only modest inhibition of the reproductive axis, then SD alone would fully inhibit the reproductive axis, and other treatments would have no additional effect.