The biological clock mechanism in non-insulin-dependent and insulin-dependent diabetic rats

The biological clock mechanism was studied in both non-insulin-dependent and insulin-dependent diabetic model rats. Otsuka Long Evans Tokushima Fatty (OLETF) rats were used as a non-insulin-dependent model. Streptozotocin (STZ, 100 mg/kg, i.p.) was administered to 8- to 10-week-old Wistar rats for an insulin-dependent diabetic model. Both young non-diabetic OLETF and STZ-induced diabetic rats needed more days for re-entrainment to a new light-dark cycle than control rats on activity rhythm. In young OLETF rats, dim-light-induced Fos expression (50 and 100 lux) was significantly decreased in the suprachiasmatic nucleus. In diabetic OLETF rats, Fos expression was decreased by the exposure of light at 300 lux. In STZ-induced diabetic rats, Fos expression was also decreased by 300 lux of light. In OLETF rats, the phase delay by glutamate application was significantly smaller than that in control rats on the suprachiasmatic nucleus neuronal (SCN) activity rhythms. On the other hand, the same level of phase delay was observed between control and STZ-induced diabetic rats by glutamate application. These results suggest that entrainment function is disordered in OLETF rats before the onset of hyperglycemia. To clarify the entrainment function of STZ-induced diabetic rats, however, further study is necessary.