Thanks for the responses, everyone.
Some interesting stuff on PubMed. A couple articles mention what you posted, Varanid, about pineal-hypothalamic changes induced by lack of light.
I thought this one was kind of interesting.
Horm Metab Res. 2006 Jun;38(6):434.
Plasma leptin in men and women with seasonal affective disorder and in healthy matched controls.
Cizza G, Romagni P, Lotsikas A, Lam G, Rosenthal NE, Chrousos GP.
Pediatric and Reproductive Endocrinology Branch, Clinical Psychobiology Branch, National Institute of Child Health and Human Development, NIMH/NIH, Bethesda, MD 20892, USA. CizzaG@mail.nih.gov
Seasonal affective disorder (SAD) is a specific clinical entity characterized by recurrent episodes of depression, which typically occur during the winter with periods of remission during the spring and summer. These depression episodes are accompanied by hyperphagia with cravings for carbohydrates and moderate weight gain, and usually respond to light therapy.
We examined potential relationships between leptin, a hormone known to affect appetite and weight regulation, and seasonal changes in mood and appetite by measuring plasma leptin, clinical severity of depression, appetite scores, and body mass index (BMI) in 19 women and 8 men with SAD and matched controls (20 women and 8 men) in the summer and winter.
Plasma leptin was positively correlated with BMI in patients and controls during both seasons. Women and men with SAD both experienced depression in the winter, which was associated with increased appetite, caloric intake, and carbohydrate craving.
Increased body weight during the winter in subjects with SAD was paralleled by a lack of concomitant changes in plasma leptin, which suggests that leptin sensitivity to changes in body weight may be influenced by seasons in subjects with SAD, similar to seasonal mammals.