Temporal organization of the 24-h corticosterone rhythm in the diurnal murid rodent Arvicanthis ansorgei Thomas 1910.

Arvicanthis ansorgei is a diurnal murid rodent from sub-Saharan Africa. The present study reports on the temporal organization of one of the major hormonal rhythms, i.e. the adrenal steroid hormone corticosterone, in an attempt to characterize further the diurnal nature of this species. The data were obtained by means of two different physiological methods: blood sampling and intracerebral microdialysis. The results show a 12-h rhythm of corticosterone release with peak values close to the light-dark (ZT10) and dark-light transition (ZT22-24), which is clearly different from that in a nocturnal animal. Both corticosterone peaks are closely correlated with the occurrence of two major bouts of running wheel activity. As far as we are aware, this is the first demonstration of a hormonal rhythm with a clear crepuscular appearance (peak values around dusk and dawn). In conclusion, these data show that also in a rodent with a diurnal/crepuscular activity pattern, the tight association between the daily corticosterone peak and the onset of activity is maintained. In addition, intracerebral microdialysis is a suitable technique to measure hormonal rhythms when repeated blood sampling is not possible.