Fig. 1.

Photoperiod effects on locomotor and cardiovascular parameters in Siberian hamsters. Gray and black bars represent lights out for long- and short-photoperiod hamsters, respectively. Home cage locomotor activity across the day (A) and broken up across early and late active and inactive periods (D). HP in milliseconds (60,000/heart rate) across the day (B) and divided across the early and late active and inactive periods (E). Respiratory sinus arrhythmia (RSA) plotted around the clock (C) and broken up across early and late active and inactive periods (F). Data are presented as mean ± SEM and mean differences were considered statistically significant when P < 0.05; *, significantly different from long days.