Photoperiod-dependent response to androgen in the medial amygdala of the Siberian hamster, Phodopus sungorus.
The medial nucleus of the amygdala (MeA) is a steroid-sensitive region that has been implicated in the expression of behaviors such as mating and aggression. The male Siberian hamster (Phodopus sungorus) uses light cues to regulate its reproductive neuroendocrine system, reducing androgen synthesis in the autumn and increasing it in the spring. There is also evidence that short photoperiods reduce the sensitivity of the brain to the behavioral effects of androgen. The authors tested the hypothesis that MeA neurons are less responsive to androgen in short photoperiods by comparing the regional volume and average soma size of the four MeA subnuclei (anterodorsal [MeAD], anteroventral [MeAV], posterodorsal [MePD], and posteroventral) in adult male hamsters that had been castrated and then implanted with capsules containing either testosterone (T) or nothing. Animals from each group were housed in either long or short photoperiods for 15 weeks. MeAD and MeAV somata displayed photoperiod-dependent responses to androgen, increasing in size after T treatment only in long days. In contrast, the average soma size and the regional volume of the MePD subnucleus were significantly larger in T-treated males regardless of photoperiod. The authors conclude that photoperiod influences the sensitivity of the MeA to androgen.
Cooke
Bradley M
BM
Oregon Regional Primate Research Center, Beaverton 97006-3499, USA.
Hegstrom
Carol D
CD
Breedlove
S Marc
SM
D000679:Amygdala / Q000166:cytology / Q000187:drug effects*; D000728:Androgens / Q000494:pharmacology*; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D048429:Cell Size; D004396:Coloring Agents; D006224:Cricetinae; D008297:Male; D009919:Orchiectomy; D009929:Organ Size / Q000187:drug effects; D017111:Phodopus; D017440:Photoperiod; D012669:Seminal Vesicles / Q000187:drug effects / Q000254:growth & development; D013739:Testosterone / Q000494:pharmacology; D016707:Tissue Fixation
D000728:Androgens; D004396:Coloring Agents; D013739:Testosterone