Socially-related and spontaneous circadian thermo-acrophase shifts in Rhabdomys pumilio.

Abstract

The reportedly diurnally-active African four-striped field mouse, Rhabdomys pumilio (Sparrmann, 1784; Rodentia: Muridae), studied with food freely available singly-caged at 24 ± I°C by the use of an intraperitoneal transensor for telemetry, exhibits a prominent circadian rhythm in core temperature. A reliably diurnally-active rodent is a potential tool for pharmacologists interested in the possibility of extrapolating data from their experimental animals to diurnally active human beings. Spontaneous and socially-induced shifts in timing of temperature pattern along the 24-h scale, gauged by the fit of a 24-h cosine for acrophase computation, occur and lead to drastic inter-individual differences in timing of core temperature rhythm for singly-housed Rhabdomys kept in different cages, yet in the same experimental environment (same isolation chamber). The importance of individualized monitoring of a marker rhythm such as core temperature before drawing conclusions as to the diurna!ity or nocturnality of metabolism emerges from these findings. Drug responses related to any marker rhythm are best individualized while the monitoring of a few individuals from a larger socially synchronized group is a second, yet practicable and cost-effective choice, as also documented herein for Rhabdomys.