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

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 agglutinin-horseradish 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 area, 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; neurophysin-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.

Retinohypothalamic projections in the common marmoset (Callithrix jacchus): A study using cholera toxin subunit B

“…Our results also indicate a direct retinal projection to the subparaventricular zone, similar to data from previous studies in the hamster (Johnson et al, 1988b;Youngstrom et al, 1991), rat (Levine et al, 1991), and sheep (Tessoneaud et al, 1994). The subparaventricular zone receives the most dense projection from the SCN and projects back to the SCN and also to SCN targets, as observed in the rat and hamster (Kalsbeek et al, 1993;Morin et al, 1994;Orpen and Steiner, 1994).…”

“…The lateral hypothalamic area, according to the results of this study and to previous data in the rat (Mai, 1979;Johnson et al, 1988b;Levine et al, 1991), hamster (Johnson et al, 1988b), and sheep (Tessoneaud et al, 1994), receives a direct projection from the retina. The functional significance of this projection is unknown.…”

“…A retinal projection to the medial preoptic area has also been described in the hamster with HRP (Pickard and Silverman, 1981) and CT-HRP (Youngstrom et al, 1991), in the rat with CT-HRP (Levine et al, 1991), and in the sheep with WGA-HRP (Tessoneaud et al, 1994). In the rat this area receives inputs from limbic regions, including the amygdala, ventral subiculum, and ventral lateral septal nucleus, the encapsulated part of the bed nucleus of the stria terminalis, infralimbic and insular cortical areas, the nucleus accumbens, and the substantia innominata, serotonergic projections from the raphe nuclei, and projections from noradrenergic cell groups, ventral tegmental area, central tegmental field, periaqueductal gray, pedunculopontine nucleus, and the peripeduncular nucleus (Simerly and Swanson, 1986).…”

Chicken suprachiasmatic nuclei: II. Autoradiographic and immunohistochemical analysis

“…The vSCN, on the other hand, is less densely packed with large and small cells. Therefore, in terms of cytoarchitecture, both the mSCN and vSCN display similarity to the SCN of mammalian species such as humans and macaque monkeys (Moore, 1993), rats (Smale and Boverhof, 1999;Moore et al, 2002), ground squirrels (Smale et al, 1991), degus (Goel et al, 1999), and sheep (Tessonneaud et al, 1994).…”

“…This organization is shared by the SCN of the laboratory rat (Moore et al, 2002), grass rat (Smale and Boverhof, 1999), Syrian hamster , degu (Goel et al, 1999), pig, cat, guinea pig (Cassone et al, 1988), macaque monkey (Moore, 1993), and humans (Moore, 1993;Hofman et al, 1996). Other eutherian species appear to lack SCN subdivisions; these include the laboratory mouse (Cassone et al, 1988;Magnin et al, 1999), ground squirrel (Smale et al, 1991), domestic sheep (Tillet et al, 1989;Tessonneaud et al, 1994), and mink (Martinet et al, 1995). In these species, antigen distribution is highly variable and, in the mink, AVP is completely absent (Martinet et al, 1995).…”