Expression of Tgfα in the suprachiasiviatic nuclei of nocturnal and diurnal rodents

Transforming growth factor alpha (TGF alpha) in the suprachiasmatic nuclei (SCN) has been proposed as an inhibitory signal involved in the control of daily locomotor activity. This assumption is based mainly on studies performed in nocturnal hamsters. To test whether the transcriptional regulation of Tgf alpha can be correlated with the timing of overt activity in other species, we compared Tgfa expression in the SCN of nocturnal Swiss mice and of diurnal Arvicanthis housed under a light/dark cycle (LD) or transferred to constant darkness (DD). In agreement with data on hamsters, Tgfa mRNA levels in the mouse SCN showed peak and trough levels around (subjective) dawn and dusk, respectively, roughly corresponding to the period of rest and activity in this species. In contrast, in Arvicanthis housed in DD, the circadian rhythm of SCN Tgfa was similar to that of the mice in spite of opposite phasing of locomotor activity. Furthermore, in Arvicanthis exposed to LD, Tgfa mRNA levels were constitutively high throughout the day. A tonic role of light in the regulation of Tgfa in Arvicanthis was confirmed by an increased expression of Tgfa in response to a 6-h exposure to light during daytime in animals otherwise kept in DD. In conclusion, this study shows that, contrary to what is observed in mice, Tgfa mRNA levels in the SCN of Arvicanthis do not match timing of locomotor activity and are modulated by light. (c) 2006 IBRO. Published by Elsevier Ltd. All rights reserved.