Truly opportunistic breeders, such as the tropical cane mouse, show neither photoperiodic inhibition of reproduction nor interactions between photoperiod and neonatal androgen treatment or FR. In contrast, seasonal breeders such as the deer mouse (Peromyscus maniculatus) show strongly inhibited reproduction in SD, with greater inhibition when FR and SD are combined. Deer mice have both phenotypic and genetic variation in the magnitude of their response to SD alone. In F344 rats, the pathway regulating reproduction is intermediate to that of purely opportunistic breeders such as the cane mouse and classic seasonal breeders such as deer mice or hamsters. buy asthma inhalers
FR alone has almost no effect on reproductive development in F344 rats, while SD produces a delay of approximately 4 wk in testicular growth. The combination of SD and FR extends the delay in testicular growth, such that FR animals in SD had reproductive growth delayed by an additional 2-4 wk; this total of 6-8 wk represents a large delay for an animal whose wild relatives have a life expectancy that is generally on the order of a few months.