HOW DO THE SUPRACHIASMATIC NUCLEI OF THE HYPOTHALAMUS INTEGRATE PHOTOPERIODIC INFORMATION

The suprachiasmatic nucleus of the hypothalamus (SCN) plays an essenti al role in the generation and maintenance of circadian rhythms in mamm als. The SCN activity is also dependent upon the photoperiod. The dura tion of the SCN sensitive phase to light, in term of Fos induction, is variable and tied to the length of the night. The question is how and by which pathways can photoperiod influence SCN? It is possible follo wing the theoretical model of evening and morning component of the clo ck that the SCN build itself the photoperiodic signal. That the SCN in tegrate the photoperiodic information through indirect neural or neuro endocrine pathways is also to consider. Data in favor of these differe nt interpretations are presented. ((C) Elsevier, Paris).