Differential time‐ and dose‐related effects of haemorrhage on tyrosine hydroxylase and neuropeptide Y mRNA expression in medullary catecholamine neurons

Abstract

Hypotensive haemorrhage induces nuclear Fos expression and upregulates tyrosine hydroxylase (TH) mRNA in catecholamine-containing cell groups of the rat medulla oblongata. To shed light on the significance of the coexistence of neuropeptide Y (NPY) in aminergic neurons, the impact of graded levels of haemorrhage on temporal changes in the expression of TH and NPY mRNAs was compared; concurrent staining for Fos permitted comparisons between cells that ostensibly were and were not targeted by the stimulus. A 15% haemorrhage provoked increased NPY expression in all medullary catecholamine cell groups except the A2; these changes were detected predominantly in Fos-immunoreactive neurons (Fos-ir) at later (2-4 h) time points. Upregulation of TH and NPY mRNAs in Fos-ir neurons followed distinct time courses, with NPY responses peaking more rapidly, particularly in the C1 and C2 cell groups. Adrenergic cell groups displayed greater maximal increases in NPY expression than the A1 noradrenergic cell group while the converse was true of TH mRNA response. Increasing the severity of haemorrhage resulted in more pronounced increases in both mRNA responses in each aminergic region. These findings indicate that haemorrhage differentially affects TH and NPY expression in medullary catecholamine cell groups that participate in the maintenance of cardiovascular homeostasis. The differential nature of these responses suggests them not to be a simple consequence of metabolic alterations pursuant to increased synaptic activity. The prompt and robust NPY mRNA responses in adrenergic neurons suggests a mechanism by which peptide content of these cell groups' terminal projections is defended.

Differential effects of intrastriatal 6-hydroxydopamine on cell number and morphology in midbrain dopaminergic subregions of the rat

“…The antibody was specific for a 60 kDa band on Western blots of rat striatal lysates (Haycock, 1989). The immunostaining pattern observed was also consistent with the reported distribution of tyrosine hydroxylase and its mRNA in rat brain (Chan and Sawchenko, 1998). …”

Comparison of the spatial distribution of seven types of neuroendocrine neurons in the rat paraventricular nucleus: Toward a global 3D model

“…The immunostaining pattern observed with the tyrosine hydroxylase antiserum was consistent with the pattern reported previously in the rat brain for this enzyme (Chan and Sawchenko, 1995). The immunostaining pattern observed with the tyrosine hydroxylase monoclonal antibody was also entirely consistent with those reported for the enzyme and its mRNA in rat brain (Chan and Sawchenko, 1998). When the two antibodies were cocktailed, complete co-localization was observed in the colchicine-treated rat PVH.…”

Subcellular localization of nicotinamide adenine dinucleotide phosphate oxidase subunits in neurons and astroglia of the rat medial nucleus tractus solitarius: Relationship with tyrosine hydroxylase immunoreactive neurons

“…It is known that TH is sensitive to cardiorespiratory and other forms of stress Sawchenko, 1995, Chan andSawchenko, 1998). In addition, free radicals can modulate the activity of TH , while the oxidation of catecholamines, such as norepinephrine, results in reactive molecules that impact a variety of intracellular processes including mitochondrial respiration and regulation of metabolic enzymes (Xin et al, 2000).…”