Lowered entrainment function in the suprachiasmatic nucleus of Otsuka LongEvans Tokushima Fatty (OLETF) rats

The entrainment function,ia the suprachiasmatic nucleus (SCN) of young non- diabetic Otsuka Long Evans Tokushima Fatty (OLETF) rats was studied. OLETF rats significantly needed more days for re-entrainment to a new light-dark cycle than control Long Evans Tokushima Otsuka (LETO) rats. We also assesse d Fos expression in the SCN induced by dim light exposure. The number of Fo s-immunoreactive cells was significantly decreased in 5- to 13-week-old OLE TF rats compared with LETO rats. Moreover, the effect of glutamate on neuro nal activity in the SCN of OLETF rats were investigated. In young non-diabe tic OLETF rats, the phase delay in the SCN neuronal firing rhythm induced b y 1 mu M glutamate was significantly less than that in LETO rats. These res ults suggested that the entrainment function is reduced in OLETF rats befor e the onset of diabetes.