Fig. 3.

Basal autonomic tone in long- and short-day hamsters. Short photoperiods augment both sympathetic and parasympathetic tone; that is, when considered independently from the other branch, the parasympathetic branch would increase heart period and the sympathetic branch decrease HP more in short than in long days. Data are presented as mean (milliseconds of heart period) ± SEM, and mean differences were considered statistically significant when P < 0.05; *, significantly different from long days.