Photic regulation of c-fos gene expression in the suprachiasmatic nucleus and the circadian rhythm of photosensitivity in the mink.

The relationship between the photic stimulation of the c-fos gene product in cells of the suprachiasmatic nuclei and the photoperiodic control of testicular activity were examined in mink. Mink were kept in a short photoperiod (control, LD4:20), or in 'asymmetric skeleton photoperiods' (groups A and B). The light period for groups A and B was divided into two fractions (3 h 30 min and 30 min); the shorter fraction occurred in the night, 4 h (group A) or 8 h (group B) after the end of the main light period.

Temperature and water conditions mediate the effects of day length on the breeding cycle of a Sahelian rodent, Arvicanthis niloticus.

Laboratory studies of variations in testicular activity (testicular weight and plasma testosterone concentration) were carried out on two populations of Arvicanthis niloticus, a Sahelian rodent that displays the particularity of being able to breed in the dry season. The animals were captured during phases of sexual activity or inactivity and were maintained in the laboratory for 50 days under humid conditions (water-rich diet, 90% atmospheric relative humidity) or dry conditions (water-deficit diet, 20% atmosphere relative humidity) and at low temperatures (20-25 degrees C) or high temperatures (30-35 degrees C). The results show that humid conditions or low temperatures stimulate testicular activity in Arvicanthis niloticus whereas dry conditions or high temperatures inhibit breeding.

Seasonal changes in the hypothalamic vasopressinergic system of a wild Sahelian rodent, Taterillus petteri.

Seasonal variations in the immunoreactivity of vasopressinergic perikarya in the paraventricular (PVN), supraoptic (SON) and suprachiasmatic nuclei (SCN), and in the labelling of vasopressinergic fibres in the internal zone of the median eminence were studied in Taterillus petteri, a rodent that is found in the north Burkina Faso (formerly Upper Volta). In this region, there are four seasonal climatic combinations: the humid and hot, humid and cold, dry and cold, and dry and hot seasons. In the dry hot season, the rodents experience phases of torpor (adaptation to dryness).

Circadian rhythm of photosensitivity and the adaptation of reproductive function to the environment in two populations of Arvicanthis niloticus from Mali and Burkina Faso.

Previous studies have shown that there is a circadian rhythm of photosensitivity in different rodent species of the Sahel (Burkina Faso) and that, despite the low amplitude of seasonal variations in daylength, the photoperiod may control reproductive function. The present investigation of Arvicanthis niloticus provides additional support for this hypothesis. Populations of Arvicanthis niloticus from two regions at the same latitude 1000 km apart but with different climates were studied.