GABAergic and glutaminergic modulation of centrally evoked arrhythmias in rats

A standard electrical stimulus applied to the posterior hypothalamus evoked cardiac arrhythmogenic responses in the spontaneously hypertensive rat. Isolated premature ventricular beats or doublets and nonsustained ventricular tachycardic salves were observed. This effect was associated with a large rise in blood pressure (79+/3 mm Hg). The same stimulus in normotensive Wistar-Kyoto rats produced no significant cardiac arrhythmias, and the rise in blood pressure was smaller (36+/-2 mm Hg). We investigated the influence of baclofen, a GABA(B) receptor agonist, and two N-methyl-D-spartate receptor antagonists on the arrhythmogenic response to hypothalamic stimulation. Intravenous baclofen (3 mg/kg) had no effect in the normotensive Wistar-Kyoto rats, but in the spontaneously hypertensive rats it enhanced the adjusted mean value of the number of extrasystoles from 0.5+/-0.5 to 18+/-1 (P<.001). This value was also increased (from 3+/-1 to 17+/-1, P<.001) by an intracisternal injection of baclofen (1 mu g/kg). This facilitatory effect of baclofen was prevented by treatment with atenolol (0.,5 mg/kg). Two glutamate receptor antagonists, ketamine (7.5 mg/kg IV) and kynurenic acid (200 mu g/kg intracerebroventricularly), prevented both the arrhythmogenic response to the hypothalamic stimulation and its facilitation by baclofen. The study confirms that hypothalamic stimulation facilitates the development of arrhythmias through a sympathetic drive and that these arrhythmias are easier to induce in spontaneously hypertensive rats than in normotensive Wistar-Kyoto rats. Both the central GABAergic and the glutamatergic systems are implicated in the development of these ventricular arrhythmias, since baclofen could disinhibit the glutamatergic central pathway. These results could account for the ability of the spontaneously hypertensive rats to develop ventricular arrhythmias of central origin.