Effect of light entrainment and temperature on the reproductive cycle in the male hedgehog (Erinaceus europaeus).

The role of photoperiod in the entrainment and synchronization of the reproductive cycle of male hedgehogs, seasonal breeders and hibernating mammals, was investigated. Groups of adult hedgehogs were either maintained outdoors (controls, n = 6) or submitted to accelerated 6-month artificial light regimens under constant ambient temperatures (20 +/- 2 degrees C versus 5 +/- 1 degrees C) in light-proofed rooms. The daily duration of light was varied sinusoidally to produce an amplitude change from 8 h (winter solstice) to 16 h (summer solstice) during the 6-month light cycle. Animals were transferred from outdoors to a high ambient temperature (20 +/- 2 degrees C) and submitted to accelerated 6-month light regimens at two times of the year: from winter solstice (Group 1, n = 14) with increasing daylengths (from 8 to 16 h) and from summer solstice (Group 2, n = 8) with decreasing daylengths (from 16 to 8 h). The light regimens were then reversed for Groups 1 and 2. After the first 6-month cycle, the animals in Group 1 were allocated to two groups and maintained under the same initial light regimen but submitted to two ambient temperatures: Group 1 (n = 7) was maintained at 20 +/- 2 degrees C and Group 3 (n = 7) was transferred to a cold environment (5 +/- 1 degrees C). In control and experimental animals, testicular volume was estimated and blood samples were obtained twice a month to measure plasma testosterone and LH concentrations by radioimmunoassay.(ABSTRACT TRUNCATED AT 250 WORDS)