Role of brainstem adenosine A_1 receptors in the cardiovascular response to hypothalamic defence area stimulation in the anaesthetized rat

摘要

1 The role of centrally located adenosine A_1 receptors in the cardiovascular changes associated with the hypothalamic defence response has been investigated by in vitro autoradiography and the intraventricular application of an A_1 receptor antagonist. 2 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX), a highly selective adenosine A_1 antagonist and its vehicle, ethanol, were administered directly into the posterior portion of the fourth ventricle of α-chloralose anaesthetized, paralysed and artificially ventilated rats. 3 DPCPX (0.01 to 0.3 mg kg~(-1)) caused a dose-dependent decrease in the magnitude of the evoked pressor response (from —13 to —23 mmHg) elicited on hypothalamic defence area stimulation at a dose 10 fold lower than that required to produce an equivalent effect following systemic administration whilst ethanol, the vehicle, had no effect. 4 In vitro autoradiography revealed a heterogeneous distribution of adenosine A_1 binding sites in the lower brainstem of rats. Image analysis showed the ventrolateral medulla to have the highest density of A_1 receptors. Intermediate levels of binding were seen in caudal regions of the nucleus tractus solitarii and the hypoglossal nucleus. 5 These data imply that a proportion of the cardiovascular response to hypothalamic defence area stimulation are produced by the activation of adenosine A_1 receptors localized close to the surface of, or adjacent to, the fourth ventricle in the immediate vicinity of the injection site.