Distribution of arginine-vasopressin and vasoactive intestinal peptide messenger RNA in the suprachiasmatic nucleus of the sheep.

The distribution of mRNAs for vasoactive intestinal peptide (VIP) and arginine-vasopressin (VP) was studied in the hypothalamus of the sheep by in situ hybridization. VIP mRNA was detected in the supraoptic nucleus (SON) and in the median part of the suprachiasmatic nucleus (SCN). VP mRNA was observed in the magnocellular system of the hypothalamus and in the dorso-lateral part of the SCN.

Bilateral lesions of the suprachiasmatic nuclei alter the nocturnal melatonin secretion in sheep.

The hypothalamic suprachiasmatic nuclei (SCN) constitute both the biological clock of many circadian rhythms, and the first relay in the transmission of light cues from the retina to the pineal gland, which releases, via nocturnal melatonin secretion, an endocrine expression of the daylength. The aim of the present work was to investigate the precise role of the SCN in the entrainment of the nocturnal rhythm of melatonin (MEL) in sheep. Bilateral lesions of the SCN were performed via a transsinusal surgical approach in 10 adult rams submitted to a constant photoperiod (16:8D).

The suprachiasmatic nucleus in the sheep: retinal projections and cytoarchitectural organization.

The retinal innervation, cytoarchitectural, and immunohistochemical organization of the suprachiasmatic nucleus (SCN) was studied in the domestic sheep. The SCN is a large elongated nucleus extending rostrocaudally for roughly 3 mm in the hypothalamus. The morphology is unusual in that the rostral part of the nucleus extends out of the main mass of the hypothalamus onto the dorsal aspect of the optic chiasm.

A new surgical approach to the ram suprachiasmatic nuclei.

In mammals, lesions of the suprachiasmatic nuclei (SCN) cause alterations in several biological rhythms. Investigation of the role of the ovine SCN requires complete bilateral lesions of the nuclei. However, the elongated shape, location and horizontal orientation of this hypothalamic structure prohibit a classical stereotaxic vertical approach.