Effects of partial destruction of the suprachiasmatic nuclei on two circadian parameters: wheel-running activity and short-day induced testicular regression

Many circadian rhythms in mammals are regulated by the suprachiasmatic nuclei located in the anterior hypothalamus. The suprachiasmatic nuclei are a heterogeneous population of neurons loosely segregated into regions. In an effort to determine if a regional specificity of control of different circadian rhythms exists within the SCN, the effect of small electrolytic lesions of the suprachiasmatic nuclei was examined on two parameters which are known to depend on the circadian system for their normal expression: wheel-running activity and short-day induced testicular regression. While some SCN lesions altered both the circadian rhythm of locomotor activity and the normal temporal pattern of gonadal regression on short-days, other partial lesions of the suprachiasmatic nuclei were found to effect one parameter without effecting the other. Detailed histological analysis of the neural damage sustained by the suprachiasmatic nuclei did not indicate an obvious regional specificity of function within the nuclei. However, the results do suggest that functionally specific neural pathways emerging from the suprachiasmatic nuclei carry circadian information to independent neural circuits responsible for locomotor activity and neuroendocrine-gonadal function.