Distribution of α2-adrenergic receptor subtype gene expression in rat brain

Treatment with the Noradrenergic Alpha-2 Agonist Clonidine, But Not Diazepam, Improves Spatial Working Memory in Normal Young Rhesus Monkeys

“…However, it is now apparent that there are plentiful post-synaptic ␣-2 receptors (U' Prichard et al 1980;Dausse et al 1982;Dooley et al 1983). ␣-2 Receptor mRNA is enriched throughout the rat brain (Nicholas et al 1993;Scheinin et al 1994) and electron microscopic studies of antibodies directed to- Figure 6. Shown is a comparison of the effects of clonidine in the animals in the current study and young reserpinetreated animals.…”

Modulation of the baroreceptor reflex by α2A‐adrenoceptors: a study in α2A knockout mice

“…Selective lesion of catecholaminergic terminals in the NTS or RVLM of rats impairs the baroreceptor reflex function (Snyder et al, 1978;Granata et al, 1983). Also, a 2A -adrenoceptors are densely expressed in both nuclei (Scheinin et al, 1994;Tavares et al, 1996), and activation of these receptors seems to represent the main mechanism of the cardioinhibitory and hypotensive effect of clonidine-like a 2 -adrenoceptor agonists (Guyenet et al, 1995;Vayssettes-Courchay et al, 2002;Szabo, 2002). Finally, chronic impairment of baroreflexes leads to an upregulation of a 2 -adrenoceptors in the NTS and the RVLM, although the study did not discriminate between the different subtypes (El-Mas & Abdel-Rahman, 1997).…”

“…Finally, chronic impairment of baroreflexes leads to an upregulation of a 2 -adrenoceptors in the NTS and the RVLM, although the study did not discriminate between the different subtypes (El-Mas & Abdel-Rahman, 1997). However, in addition to the NTS and the RVLM, a 2A -adrenoceptors are also expressed in the two parasympathetic motor nuclei, the dorsal motor nucleus of the vagus and the nucleus ambiguus, and in the caudal ventrolateral medulla, the relay between NTS and RVLM in the medullary baroreflex loop (Scheinin et al, 1994;Tavares et al, 1996), suggesting that the receptors may also operate there to modulate the baroreceptor reflex.…”

“…Since then, several studies have supported Haeusler's hypothesis. a 2 -Adrenoceptors occur in all cardiovascular brain stem nuclei at high density (Scheinin et al, 1994;Tavares et al, 1996), and their expression in the NTS and the RVLM is increased following chronic impairment of the baroreflex by surgical denervation of the aortic baroreceptors (El-Mas & Abdel-Rahman, 1997). Reflex heart rate responses to baroreceptor loading and unloading are enhanced when the a 2 -adrenoceptor agonists clonidine and a-methylnoradrenaline (or its precursor, a-methyldopa) are injected into the cisterna cerebellomedullaris or microinjected into the NTS (Badoer et al, 1983;Kubo et al, 1990).…”

“…Second, no previous study discriminated between the different a 2 -adrenoceptor subtypes. Experiments using autoradiography, immunohistochemistry or in situ hybridization indicate that, although the main a 2 -adrenoceptor subtype in the cardiovascular nuclei of the brain stem is a 2A , the two other subtypes a 2B and a 2C are also present (Boyajian et al, 1987;Scheinin et al, 1994;Rosin et al, 1996;Tavares et al, 1996). Third, the exact role of a 2 -adrenoceptors within the baroreflex loop -whether a necessary link or only facilitatory -has not been firmly established.…”