Catecholamine‐containing neurons in the sheep brainstem and diencephalon: Immunohistochemical study with tyrosine hydroxylase (TH) and dopamine‐β‐hydroxylase (DBH) antibodies

Abstract

The present study describes the distribution and morphological characteristics of neurons and nerve fibers containing the catecholamine-synthesizing enzymes, tyrosine hydroxylase and dopamine-beta-hydroxylase, in the sheep brainstem and diencephalon on the basis of immunohistochemical procedures. Neurons and fibers were considered to be dopaminergic if they showed anti-tyrosine hydroxylase immunoreactivity, without corresponding anti-dopamine-beta-hydroxylase immunoreactivity. The structures labeled with both antisera were considered noradrenergic or adrenergic. The distribution of catecholaminergic neurons corresponds to that described by other authors with similar methods in the rat and in primates. The noradrenergic neurons belong to cell groups A1 to A7 and the dopaminergic neurons to cell groups A8 to A15. In almost all studied areas, the catecholaminergic innervation is similar to that observed in the other species. However, the central catecholaminergic systems of the sheep showed some specific characteristics: (1) groups A3 and A4, described in the rat, were not found, (2) group A14 contains fewer neurons than in the rat, (3) group A15 does not contain a dorsal but only a ventral portion, (4) there is a larger dispersion of neurons within each group, especially A6 and A7, than in rodents, and (5) there is a larger noradrenergic innervation of the catecholaminergic groups than in the other species.

Estrogen Receptor Expression in Brainstem Noradrenergic Neurons of the Sheep

“…Neurons immunoreactive for DBH were identified throughout medulla and pons as described previously in the sheep [25]. Within the medulla, the numbers of DBH-immunoreactive cells per section in NTS and VLM were low in the most caudal sections analyzed and found to peak just caudal to the obex (level G; fig.…”

“…In all 5 ewes, brainstem sections containing the medulla were divided on a cytoarchitectural basis into seven rostrocaudal regions approximately 1 mm apart. These seven regions correspond exactly to brain sections F–L of figure 10 in the Tillet and Thibault [25] paper which first described the noradrenergic neurons of the ovine brainstem. Levels L, J, H, and F are shown in figure 1.…”

Implication of D2-like dopaminergic receptors in the median eminence during the establishment of long-day inhibition of LH secretion in the ewe

“…The ME dopaminergic terminals, which are located in the external layer of the ME (Tillet & Thibault 1989), establish synaptic contacts with LHRH terminals, suggesting the possibility of a presynaptic control of LHRH secretion by dopamine (Kuljis & Advis 1989). Several arguments suggest that these terminals are implicated in one of the final steps of the long-day-induced inhibition of LH secretion.…”

Mechanisms for gonadotropin-releasing hormone potentiation of growth hormone rebound following norepinephrine inhibition in goldfish pituitary cells

“…The functionality of these GH regulators, in turn, is under the modulation of neurotransmitters acting within the central nervous system (CNS). Adrenergic nerve fibers, presumably originated from the A 1 to A 7 groups in the brain stem (51), innervate the cell bodies of GHRH and SRIF neurons in the medial basal (47) and preoptic hypothalamus (32), respectively. Through activation of ␣ 2 -adrenoreceptors (14), adrenergic stimulation can elevate GH levels by inducing GHRH secretion from the arcuate nucleus (12) with simultaneous inhibition of SRIF release from the periventricular nucleus (31).…”