TSH restores a summer phenotype in photoinhibited mammals via the RF-amides RFRP3 and kisspeptin.

In mammals, melatonin is the pivotal messenger synchronizing biological functions, notably reproductive activity, with annual daylength changes. Recently, two major findings clarified melatonin's mode of action. First, melatonin controls the production of thyroid stimulating hormone (TSH) by the pars tuberalis of the adenohypophysis.

Melatonin controls photoperiodic changes in tanycyte vimentin and neural cell adhesion molecule expression in the Djungarian hamster (Phodopus sungorus).

The Djungarian hamster displays photoperiodic variations in gonadal size synchronized to the seasons by the nightly secretion of the pineal hormone melatonin. In short photoperiod (SP), the gonads regress in size, and circulating sex steroids levels decline. Thus, the brain is subject to seasonal variations of both melatonin and sex steroids.