Immunohistochemical characterization of the sheep suprachiasmatic nucleus

Using 19 antisera raised against neuropeptides, amines or enzymes of amine biosynthesis, an immunohistochemical characterization of the sheep suprachiasmatic nucleus was performed. The most distinguishing characteristic of the sheep suprachiasmatic nucleus was the low density of serotonin- and neuropeptide Y-immunoreactive fibres; their concentration was similar to that in surrounding areas. This is different from observations in rodents but similar to those in primates. Moreover, the sheep suprachiasmatic nucleus is also characterized by a dense plexus of methionine-enkephalin-immunoreactive fibres. This has not been observed in other species. As in other species, such as rodents, the sheep suprachiasmatic nucleus contains numerous neurophysin-immunoreactive neurons and a few tyrosine hydroxylase-immunoreactive neurons. After colchicine pretreatment, many intensely stained vasoactive intestinal peptide-, vasopressin- and somatostatin-immunoreactive perikarya appeared, and more neurophysin-immunoreactive cell bodies were observed. Thus, although similarities exist among species, there are distinct differences in the neuro-chemical organization of the suprachiasmatic nucleus in the sheep and other species.