Immunocytochemical localization of the catecholamine-synthesizing enzymes, tyrosine hydroxylase and dopamine-beta-hydroxylase, in the hypothalamus of cattle

Immunocytochemical staining for the presence of catecholamine synthesizing enzymes, tyrosine hydroxylase and dopamine beta-hydroxylase, was used to characterize the regional distribution of catecholaminergic neurons in the hypothalamus and adjacent areas of domestic cattle, Bos taurus. In steers, heifers and cows, tyrosine hydroxylase-immunoreactive perikarya was located throughout periventricular regions of the third cerebral ventricle, in both anterior and retrochiasmatic divisions of the supraoptic nucleus, suprachiasmatic nucleus, and ventral and dorsolateral regions of the paraventricular nucleus, dorsal hypothalamus, ventrolateral aspects of the arcuate nucleus, along the ventral hypothalamic surface between the median eminence and optic tract, and in the posterior hypothalamus. Immunostained perikarya ranged from small (10-20 microns, parvicellular) to large (30-50 microns, magnocellular) and were of multiple shapes: round, triangular, fusiform or multipolar, often with 2-5 processes of branched arborization. There were no dopamine-beta-hydroxylase immunoreactive perikarya observed within the hypothalamus and adjacent structures. However, both tyrosine hydroxylase and dopamine-beta-hydroxylase immunoreactive fibers and punctate varicosities were observed throughout regions of tyrosine hydroxylase immunoreactivity perikarya. Generally, the location and pattern of hypothalamic tyrosine hydroxylase immunoreactivity and dopamine-beta-hydroxylase immunoreactive were similar to those reported for most other large brain mammalian species, however, there were several differences with commonly used small laboratory animals. These included intense tyrosine hydroxylase immunoreactivity of perikarya within the retrochiasmatic division of the supraoptic nucleus (ventral A15 region), the absence of tyrosine hydroxylase immunoreactive perikarya below the anterior commissure or within the bed nucleus of stria terminalis (absence of the dorsal A15 region), an abundance of tyrosine hydroxylase immunoreactive perikarya within the ependymal layer of the median eminence, heavy innervation of the arcuate nucleus with dopamine-beta-hydroxylase immunoreactive fibers and varicosities, and the paucity of dopamine-beta-hydroxylase immunoreactive throughout the median eminence.