Fig 3.

Diminished T₄ uptake in the hypothalamus of photorefractory hamsters. (A) Mean ETV (±SEM) over the 44-week experiment for hamsters that had been exposed to short or long day lengths for 32 weeks (SDR and LD, respectively), and in hamsters exposed to short day lengths for 32 weeks followed by long day lengths for 12 weeks (SDR+LD; a photoperiod treatment that restores photosensitivity in photorefractory hamsters) (6). (B and C) Tissue/plasma ratios (+SEM) of ¹²⁵I-L-T₄ uptake in the hypothalamus and neocortex of photosensitive (LD and SDR+LD) and photorefractory (SDR) hamsters. SDR hamsters exhibited lower T₄ uptake relative to LD hamsters; breaking of refractoriness by exposure to LD restored elevated hypothalamic T₄ uptake. (*, P < 0.05 vs. all other groups.)