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Bilateral Lesions of the Suprachiasmatic Nuclei Alter the Nocturnal Melatonin Secretion in Sheep (1995)

Tessonneaud, A. ; Locatelli, A. ; Caldani, M. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Journal of neuroendocrinology 7 (1995), S. 0

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ISSN: 1365-2826

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Medicine

Notes: 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 (16L:8D). Lesioned rams were compared to 4 sham and 2 control animals. Blood samples were collected 8 days before, 8 days after, and one month after surgery. Plasma MEL levels were estimated using direct radioimmunoassay. At the end of the experiment, histology and immunohistochemistry of the suprachiasmatic area were performed, and the extent of lesions was evaluated using a computerized image analysis system. Six rams exhibited a complete lesion of the SCN, and in the four remaining animals, the lesions were restricted to the anterior part of the SCN. For all animals, the nocturnal melatonin secretion was altered, but depending on the extent of the lesion, two types of results were observed:Eight days after surgery, in 3 of the 4 rams bearing anterior lesions of the SCN (SCNJ, a nocturnal increase in melatonin secretion still occurred at dusk, but the duration of this secretion extended beyond the end of the night. One month after surgery, melatonin profiles were once again normal, as compared to sham animals. The fourth SCN, ram exhibited a cyclic MEL secretion not synchronized with the light cycle 8 days after surgery, and synchronized with dusk but not dawn one month after surgery.Eight days after surgery, all the rams bearing complete lesions of the SCN (SCNZ) showed strongly altered MEL secretion. This secretion was continuous during the period of sampling, without any characteristic nocturnal peak. Nevertheless, one month after surgery, a nocturnal increase in melatonin secretion synchronized with the dusk was again observed, but the duration of the melatonin secretion was longer than the duration of the night.These results confirm that the SCN mediates the nocturnal pineal gland activity, demonstrate that the anterior part of the sheep SCN is the main drive for the inhibition of the melatonin secretion at dawn and suggest that a positive input to the pineal gland may stimulate MEL secretion at dusk. The partial recovery of the cyclic secretion of melatonin after complete lesioning of the SCN suggests the existence of other structure(s) involved in this rhythmic function.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2826.1995.tb00677.x

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The suprachiasmatic nucleus in the sheep: retinal projections and cytoarchitectural organization (1994)

Tessonneaud, A. ; Cooper, H. M. ; Caldani, M. ; [et al.]

Springer

Cell & tissue research 278 (1994), S. 65-84

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ISSN: 1432-0878

Keywords: Suprachiasmatic nucleus ; Retinohypothalamic tract ; Immunohistochemistry ; Neuropeptides ; Cytochrome oxidase ; Acetylcholinesterase ; Circadian system ; Domestic sheep

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine

Notes: Abstract 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. Following intraocular injection of wheat-germ agglutininhorseradish peroxidase or tritiated amino acids, anterograde label is distributed throughout the SCN. Retinal innervation of the SCN is bilaterally symmetric or predominantly ipsilateral. Quantitative image analysis demonstrates that, although the amount of autoradiographic label is greatest in the ventral and central parts of the nucleus, density varies progressively between different regions. In addition to the SCN, retinal fibers are also seen in the medial preoptic area, the anterior and lateral hypothalamic areas, the dorsomedial hypothalamus, the retrochiasmatic area, and the basal telencephalon. Whereas the SCN can be identified using several techniques, complete delineation of the nucleus requires combined tract tracing, cytoarchitectural, and histochemical criteria. Compared with the surrounding hypothalamic regions, the SCN contains smaller, more densely packed neurons, and is largely devoid of myelinated fibers. Cell soma sizes are smaller in the ventral SCN than in the dorsal or lateral parts, but an obvious regional transition is lacking. Using Nissl, myelin, acetylcholinesterase, and cytochrome oxidase staining, the SCN can be clearly distinguished in the rostral and medial regions, but is less differentiated toward the caudal pole. Immunohistochemical demonstration of several neuropeptides shows that the neurochemical organization of the sheep SCN is heterogeneous, but that it lacks a distinct compartmental organization. Populations of different neuropeptide-containing cells are found throughout the nucleus, although perikarya positive for vasoactive intestinal polypeptide and fibers labeled for methionine-enkephalin are predominant ventrally; neurophysine-immunoreactive cells are more prominent in the dorsal region and toward the caudal pole. The results suggest that the intrinsic organization of the sheep SCN is characterized by gradual regional transitions between different zones.