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). Immunoreactivity of the PVN and SON is highest during the dry cold season. Labelling is intense during the dry hot and humid hot seasons, and is at its lowest during the humid cold season. In the SCN, labelling of the perikarya is only dense during the dry hot season, whereas for the rest of the year, the immunoreactivity is weak or undetectable. The pattern of immunoreactive variations of vasopressin-positive fibres located in the internal zone of the median eminence is similar to those of vasopressinergic perikarya in the PVN and SON. These results suggest that there is an association between: (1) seasonal modifications in the immunoreactivity of PVN and SON vasopressinergic perikarya and vasopressinergic fibres of the internal median eminence, and (2) climatic conditions, water metabolism, behavioural activity and diet. It is not possible to establish a correlation between seasonal variations in water availability and fluctuations in the labelling of vasopressinergic perikarya in the SCN. However, labelling is intense when the animals are in torpor during the dry hot season.