Responses of brain and behavior to changing day-length in the diurnal grass rat (Arvicanthis niloticus)

► Diurnal grass rats develop depression-like behaviors in short days. ► Grass rats show longer duration of elevated PER1 and PER2 in the SCN and expansion in their active phase in long days. ► Grass rats are less responsive to short days in the daily rhythm of PER1 and of behavior.