Fig. 3.

Effects of intrahypothalamic microimplants releasing tri-iodothyronine (T3) on body weight (top) and pelage score (bottom) in male Siberian hamsters in short days (SD). All hamsters were initially maintained on SD for 10 weeks, then received T3 (SD + T3, n = 8) or sham implants (SD sham, n = 8). A third group of hamsters previously exposed to short days for 10 weeks received sham implants but were transferred to long days (LD sham, n = 9). Note that SD initially induced weight loss and a molt to winter pelage (score 1) in all hamsters, and that in those hamsters maintained in SD with sham implants there was then a very gradual increase in body weight reflecting the underlying circannual rhythmicity/photorefractoriness. Implantation of T3 after 10 weeks in SD significantly increased body weight, and the response was more rapid than in sham-implanted hamsters transferred to LD, but the T3 implants did not affect pelage.

Modified from Murphy et al. (2012).