Fos expression in the sleep-active cell group of the ventrolateral preoptic area in the diurnal murid rodent, Arvicanthis niloticus

The ventrolateral preoptic area (VLPO) of the nocturnal laboratory rat rece ives direct input from the retina and is active during sleep; however, noth ing is known about VLPO function in day-active (diurnal) species. In the fi rst study, we used 24-h Videotaping of Arvicanthis niloticus, a diurnal mur id rodent, to estimate the distribution of sleep and wakefulness across a 1 2:12 light-dark cycle. Based on behavioral data, A. niloticus were perfused at a time when the animals are inactive (zeitgeber time (ZT) 20) or at a t ime when they are awake and active (ZT 23). The brains were processed for i mmunocytochemistry for Fos, an immediate early gene product used as an inde x of neural activity. Animals had more Fos-immunoreactive (Fos +) cells in the VLPO at ZT 20 than at ZT 23. The pattern of change in Fos expression se en in this area suggest that the VLPO serves the same function in A. niloti cus as in rats. Eye injections of cholera toxin (beta subunit) were used to identify the retinal inputs to the VLPO of A. niloticus. In these animals, the VLPO had only very sparse retinal inputs compared to the rat. Together , these results raise the possibility that inputs from the suprachiasmatic nucleus (SCN) or the retina affect neuronal activity in the VLPO differentl y in rats and A. niloticus, thereby, contributing to differences in their s leep/wake patterns. (C) 1999 Elsevier Science B.V. All rights reserved.