Distributions of mRNAs for alpha‐2 adrenergic receptor subtypes in rat brain: An in situ hybridization study

TLDR

Alpha‑2 adrenoreceptor mRNAs are expressed in noradrenergic and possibly adrenergic neurons throughout the rat brain. The authors employed 35S‑labeled oligonucleotide probes specific for rat alpha‑2A, alpha‑2B, and alpha‑2C mRNAs to perform in situ hybridization on unfixed rat brain, spinal cord, and kidney sections. The probes produced distinct, subtype‑specific patterns: alpha‑2A mRNA was abundant in cortical layer six, hypothalamic nuclei, brainstem nuclei, and spinal cord; alpha‑2B mRNA was largely confined to kidney with only faint CNS signal; alpha‑2C mRNA was prominent in olfactory bulb, cortex, striatum, hippocampus, cerebellum, and dorsal root ganglia; specificity was confirmed by competition and sense controls. © 1993 Wiley‑Liss, Inc.

Abstract

Abstract Selective 35 S‐labeled oligonucleotide probes were designed to sequences of the rat alpha‐2A (RG20), alpha‐2B (RNG), and alpha‐2C (RG10) adrenoreceptor mRNAs for use in in situ hybridization experiments on sections of unfixed rat brain, spinal cord and kidney. After hybridized sections were exposed to film or dipped in autoradiographic emulsion, specific and selective labeling patterns characteristic for each probe and region of the central nervous system were observed. Alpha‐2A mRNA labeling was most pronounced in neurons in layer six of the cerebral cortex, hypothalamic paraventricular nucleus, reticular thalamic nucleus, pontine nuclei, locus coeruleus, vestibular nuclei, trapezoid nuclei, deep cerebellar nuclei, nucleus tractus solitarii, ventrolateral medullary reticular formation, and the intermediolateral cell column of the thoracic spinal cord. In some of these locations, the receptor mRNA, in all probability, is present in noradrenaline and perhaps adrenaline neurons. The alpha‐2B probe, which primarily labels the kidney, gave only a very light signal in the thalamus in the central nervous system after extended exposure times. Alpha‐2C mRNA labeling was primarily observed in the olfactory bulb, cerebral cortex, islands of Calleja, striatum, hippocampal formation, cerebellar cortex, and dorsal root ganglia. Labeling patterns disappeared when excess unlabeled probes were added to their respective radiolabeled probes, or when sense probes were employed. When a hybrid antisense probe homologous to all three alpha‐2 probes was used, labeling patterns also disappeared. The present study therefore justifies the pharmacological subclassification of alpha‐2 receptors by providing anatomical evidence for specific and selective cell groups in the rat central nervous system containing mRNA for three alpha‐2 receptor subtypes. © 1993 Wiley‐Liss, Inc.