Angiotensin II AT1 receptors mediate neuronal sensitization and sustained blood pressure response induced by a single injection of amphetamine

Abstract

A single exposure to amphetamine induces neurochemical sensitization in striatal areas. The neuropeptide angiotensin II, through AT1 receptors (AT1-R) activation, is involved in these responses. However, amphetamineinduced alterations can be extended to extra-striatal areas involved in blood pressure control and their physiological outcomes. Our aim for the present study was to analyze the possible role for AT1-R in these events using a twoinjection protocol and to further characterize the proposed AT1-R antagonism protocol. Central effect of orally administered AT1-R blocker (Candesartan, 3 mg/kg p.o. 5 days) in male Wistar rats was analyzed by spontaneous activity of neurons within locus coeruleus. In another group of animals pretreated with the AT1-R blocker or vehicle, sensitization was achieved by a single administration of amphetamine (5 mg/kg i.p. – day 6) followed by a 3-week period off drug. On day 27, after receiving an amphetamine challenge (0.5 mg/kg i.p.), we evaluated: (1) the sensitized c-Fos expression in locus coeruleus (LC), nucleus of the solitary tract (NTS), caudal ventrolateral medulla (A1) and central amygdala (CeAmy); and (2) the blood pressure response. AT1-R blockade decreased LC neurons’ spontaneous firing rate. Moreover, sensitized c-Fos immunoreactivity in TH + neurons was found in LC and NTS; and both responses were blunted by the AT1-R blocker pretreatment. Meanwhile, no differences were found neither in CeAmy nor A1. Sensitized blood pressure response was observed as sustained changes in mean arterial pressure and was effectively prevented by AT1-R blockade. Our results extend AT1-R role in amphetamine-induced sensitization over noradrenergic nuclei and their cardiovascular output.