Circadian timekeeping in narcoleptic dogs.

Anatomical and functional aspects of the circadian timekeeping system containing the suprachiasmatic nucleus (SCN) were compared in normal and genetically narcoleptic dogs. The retinohypothalamic tract was delineated by tritiated amino acid autoradiography, the SCN was identified and examined by morphological techniques, and the circadian rhythm of melatonin concentrations in cerebrospinal fluid was measured by radioimmunoassay. Results suggest that the retinal input, cytoarchitecture, and essential timekeeping function of the SCN are intact in narcoleptic dogs.