Effects of Antisense Oligodeoxynucleotide Targeting of the α _2B -Adrenergic Receptor Messenger RNA in the Central Nervous System

Abstract

Abstract-The results of previous studies with genetically engineered mice have suggested that an intact central ␣ 2B -adrenergic receptor (␣ 2B -AR) subtype mediates the development and maintenance of salt-induced hypertension. In the present study, we sought to further define the role of this receptor by injecting antisense oligodeoxynucleotides (AS-ODNs), targeting a selected sequence of the ␣ 2B -AR mRNA, into the lateral cerebral ventricle of rats that had undergone prior subtotal nephrectomy and dietary salt loading. Cell culture studies showed that these AS-ODNs could block ␣ 2B -AR protein generation. Before AS-ODN injection, blood pressure (BP) averaged 133Ϯ5 mm Hg during the daytime and rose to 165Ϯ4 mm Hg during the nighttime activity hours (PϽ0.001 versus baseline average of 120Ϯ2 mm Hg). The injection of AS-ODNs during the early afternoon prevented the BP rise and was associated with a significant fall in heart rate (from 385Ϯ12 to 306Ϯ15 bpm, PϽ0.05) and symptoms of sedation that lasted for several hours, with a peak at 3 to 6 hours and full recovery by 24 hours. At that time, a second injection produced identical effects in all rats (nϭ9). Control rats (nϭ10) that received scrambled ODN injections had no changes in BP or heart rate patterns, and neither group had evidence of neurotoxicity, indicating that these effects are specifically due to translational inhibition of central ␣ 2B -AR. We conclude that a fully functional central ␣ 2B -AR is necessary for the induction of salt-dependent hypertension.

Autonomic control of blood pressure in mice: basic physiology and effects of genetic modification

“…This hypothesis is supported by the finding that acute hypertensive responses to an intravenous infusion of hypertonic saline were absent in anephric (to exclude renal effects) ␣ 2B -AR (ϩ/Ϫ) mice, whereas in wild-type mice, pressure rose by 15 mmHg (127). This hypothesis is supported by recent findings in rats, in which local injection of antisense oligodeoxynucleotides targeted to ␣ 2B -ARs inhibited the induction of salt-induced hypertension (100). Thus the increased susceptibility of ␣ 2A -AR-knockout mice to homeostatic challenges may, in part, be mediated by compensatory actions of central ␣ 2B -ARs.…”

Gender Differences in Hypothalamic Tyrosine Hydroxylase and α2-Adrenoceptor Subtype Gene Expression in Cafeteria Diet-Induced Hypertension and Consequences of Neonatal Androgenization

“…Moreover, various experiments on salt-induced hypertension in mice deficient in one of the three ␣ 2 -adrenoceptor subtypes (Makaritsis et al, 1999a(Makaritsis et al, ,b, 2000 allowed the suggestion that adrenergically mediated hypertension depends on the central ␣ 2B -adrenoceptors. The validity of this hypothesis is further supported by a recent study showing that intracerebroventricular microinjection of antisense-oligonucleotides targeting a specific sequence of the ␣ 2B -adrenoceptor gene in salt-sensitive rats lowered blood pressure (Kintsurashvili et al, 2001). Therefore, it seems likely that the up-regulation of hypothalamic ␣ 2B -adrenoceptor gene expression that we observed only in the hypertensive cafeteria diet-fed rats participates in the maintenance of the hypertensive state.…”

“…In contrast, the ␣ 2B -adrenoceptor mediates the ␣ 2 -agonist-induced increase in blood pressure (Link et al, 1996). Moreover, from a subsequent series of studies on salt-induced hypertension in ␣ 2 -adrenoceptor subtype-deficient mice (Makaritsis et al, 1999a,b), or by using the antisense strategy (Kintsurashvili et al, 2001), it has been suggested that the adrenergically mediated hypertension depends on the central ␣ 2B -adrenoceptor subtype. In contrast with other brain structures, hypothalamus is the area in which the ␣ 2B -adrenoceptor gene is the subtype most expressed (Tavares et al, 1996).…”

α2-Adrenergic receptor signalling in hypertension

“…However, activation of both α 2B -and α 2C -ARs also elicit central effects. Mice with targeted inactivation of the α 2B -AR are resistant to the development of salt-sensitive hypertension [10,11] and α 2B -AR antisense lowers BP in hypertensive rats [12,13]. Mice deficient in α 2C -AR have an augmented startle response and sensorimotor gating deficits, whereas overexpression of the α 2C -AR increases the latency to the startle reflex and improves learning and memory [14,15].…”