title: Hemodynamic regulation of tyrosine hydroxylase messenger RNA in medullary catecholamine neurons: a c-fos-guided hybridization histochemical study.
abstract: Medullary catecholamine cell groups are involved in multiple modes of cardiovascular regulation and display indices of functional activation, including widespread c-fos expression, in response to hypotensive hemorrhage. Assessments of the impact of such challenges on transmitter-related gene expression are complicated by the biochemical and connectional heterogeneity that characterize these cell groups. Quantitative hybridization histochemical methods were used to follow the effects of 15% hemorrhage on levels of messenger RNA encoding tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, in medullary aminergic neurons; concurrent staining for nuclear Fos-immunoreactivity permitted comparisons between cells that ostensibly were and were not targeted by the challenge. Increased levels of tyrosine hydroxylase messenger RNA were detected in Fos-immunoreactive neurons in all cell groups examined. Mean maximal increases ranged between 133 and 192% of control values, and were attained within 0.5-1 h post-hemorrhage in noradrenergic (A1 and A2) cell groups, and at 2 h in adrenergic ones (C1, C2, and C2d or dorsal strip). By 4 h after the challenge, tyrosine hydroxylase messenger RNA levels in Fos-immunoreactive neurons in all cell groups had returned to control values. By contrast, tyrosine hydroxylase messenger RNA in non-Fos-immunoreactive cells either did not change significantly over the course of the experiment (C2 and C2d), or showed a rapid and transient increase, whose magnitude tended to be less than that seen in Fos-immunoreactive cells. c-fos messenger RNA was prominently induced in catecholaminergic neurons in each of the medullary cell groups examined at 0.5 h after hemorrhage, suggesting that the early tyrosine hydroxylase messenger RNA response to hemorrhage in non-Fos-immunoreactive cells preceded the capacity of responsive neurons to manifest detectable Fos protein expression. These findings indicate that hemorrhage up-regulates tyrosine hydroxylase messenger RNA levels in medullary catecholaminergic cell groups which have access to adaptive neuroendocrine and/or autonomic control systems. The approach employed here should prove of general utility in assessing the impact of environmental events on messenger RNA expression in connectionally heterogeneous cell groups that share a common biochemical phenotype.
mesh_terms: D000320:Adrenergic Fibers / Q000201:enzymology; D000818:Animals; D015152:Blotting, Northern; D002395:Catecholamines / Q000032:analysis; D018076:DNA, Complementary; D015870:Gene Expression / Q000502:physiology; D006439:Hemodynamics / Q000235:genetics; D006470:Hemorrhage / Q000201:enzymology; D007124:Immunoenzyme Techniques; D017403:In Situ Hybridization; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology* / Q000378:metabolism; D009474:Neurons / Q000737:chemistry / Q000201:enzymology*; D016760:Proto-Oncogene Proteins c-fos / Q000276:immunology / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012680:Sensitivity and Specificity; D013997:Time Factors; D014158:Transcription, Genetic / Q000502:physiology; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics*
chemical_list: D002395:Catecholamines; D018076:DNA, Complementary; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D014446:Tyrosine 3-Monooxygenase