Indirect evidence for an association of 5-HT1B binding sites with retinal and geniculate axon terminals in the rat suprachiasmatic nucleus
✍ Scribed by C. Manrique; F. HÉRY; M. Faudon;; A.M. François-Bellan
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 276 KB
- Volume
- 33
- Category
- Article
- ISSN
- 0887-4476
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✦ Synopsis
The purpose of the present study was to investigate the possible cellular location of 5-HT 1B receptors on retinal and geniculate afferents in the rat suprachiasmatic nucleus (SCN). Biocular enucleation significantly decreased 5-HT 1B binding site labeling (35%), specifically in the ventral part of the SCN, while monocular enucleation produced a decrease of smaller magnitude (12%), limited to the ventral part of the contralateral SCN, these results being consistent with the known distribution of retinal afferents in the nucleus. By contrast, bilateral geniculate lesion did not induce any significant variation of 5-HT 1B binding site labeling in the SCN. Previously, we reported that serotonin (5-HT) synthesis inhibition by parachlorophenylalanine increases 5-HT 1B binding site labeling in the SCN. Using saturation studies, we have now demonstrated that this upregulation reflected an increase in the total number of 5-HT 1B binding sites (ϩ41% in the dorsal and ϩ67% in the ventral part of the SCN). Furthermore, we evaluated the effects of bilateral geniculate lesion after 5-HT stores depletion in order to overcome problems of technical resolution limits. The magnitude of upregulation was significantly decreased (27%) after bilateral geniculate lesion, suggesting that part of the 5-HT 1B receptor population was located on geniculate axon terminals within the SCN. The possible involvement of 5-HT 1B receptors, according to their cellular locations evidenced in the present study, in photic and nonphotic entrainment of the circadian clock is discussed.