Effect of suprachiasmatic nucleus lesion on circadian dentin increment in rats

Mammalian dentin universally shows circadian increments. However, little is known about the mechanism of this phenomenon. The purpose of the present s tudy was to investigate the role of the suprachiasmatic nucleus (SCN) in th e generation of circadian rhythm in dentin increment. Rats underwent lesion of the SCN by electrodes and were maintained under constant light to exami ne whether the circadian increment free runs. The rats were injected with n itrilotriacetato lead to chronologically label the growing dentin. Two week s after the operation, maxillary incisors and the locations of lesions in t he brain were examined histologically. A harmonic (Fourier) analysis was pe rformed to examine the densitometric pattern of the dentin increments to de termine their periodicity. In rats with a completely lesioned SCN, ultradia n increments, but no circadian increments, were observed in the dentin. Alt ernatively, in rats with an intact or only partially lesioned SCN, circadia n increments persisted or were only temporarily disturbed. These results su ggest that the SCN plays an important role in the generation of the circadi an dentin increment in rats.