Application of the 2-deoxy-(1-14C) glucose method to the study of suprachiasmatic nucleus activity and functions: phasic luteinizing hormone secretion and serotonin innervation.

A semi-quantitative analysis of 2-deoxy-(1-14C) glucose (2 DG) incorporation in the suprachiasmatic nucleus (SCN) was performed in male, castrated female, and castrated oestradiol treated female rats (OVX-E2) during the light period (from 9.00 h to 18.00 h). Unilateral orbital enucleation was carried out on each group. In males and castrated females the 2 DG incorporation in the rostral and caudal SCN was constant throughout the studied period. On the contrary, in OVX-E2 rats, which display a clear cut circadian rhythm of LH secretion, the 2 DG incorporation in the rostral SCN was higher in the afternoon than in the morning. After serotonin (5 HT) depletion, the level of morning labelling reached that of the afternoon. These results suggest the existence of a steroid-linked rhythm of SCN metabolic activity during the light period which might be related to the LH surge and dependent on 5 HT innervation.