Proceedings of The Physiological Society

University of Cambridge (2004) J Physiol 555P, C23

Communications

Cardiovascular and respiratory regulation through brainstem adenosine receptors in acute ethanol microinjection into NTS

I. Rocha*, G. Postolache† and L.S. Carvalho*

* Instituto de Fisiologia, Faculdade de Medicina de Lisboa, Lisbon, Portugal and † Faculty of Biology, Al.I.Cuza University, Iasi, Romania


Previous studies have suggested that adenosine may be an important mediator of ethanol effects in the brain. In the present study, the cardiovascular and respiratory effects of acute ethanol microinjection into nucleus tractus solitarius (NTS), before and after dipropilsulfophenilxanthine (DPSPX), an adenosine antagonist, were investigated.

Experiments were performed in male Wistar rats (n = 7), anaesthetized (α chloralose, 100 mg/kg), treated with a neuromuscular blocker (pancuronium, 4 mg/kg/h) and artificially ventilated. The depth of the anaesthesia was maintain by ensuring the absence of a withdrawal reflex before paralysing the animal and changes on arterial blood pressure and heart rate to pinching a paw after the administration of a muscle blocker. Arterial blood pressure (BP), electrocardiogram (ECG), phrenic nerve activity and heart rate were monitored. A craniotomy was carried out to allow the insertion of multi-barrelled microelectrodes for electrical stimulation (50 Hz, 1 ms, 20-40 mA), and for unilateral microinjections of ethanol (50 mM, 50 nl) and DPSPX (0.1 mM, 50 nl) into NTS. The baroreflex function was evaluated by peripheral injection of phenylephrine (4 µg/kg) in basal conditions and after microinjection of ethanol into the NTS. The slope of the regression line between beat-to-beat values of RR-interval plotted against the systolic blood pressure values of the preceding cardiac cycles [RRI(i+1) vs. SAP(i)] was considered to be index of baroreflex sensitivity. All the experimental procedures were performed according to Portuguese and EU laws on animal research. At the end of the experiments, animals were humanely killed.

Our results show a decrease of mean blood pressure (29.58 ± 4.9 mmHg, paired t test P < 0.0001) and heart rate (30.833 ± 9.6 bpm, P < 0.01, t test) accompanied by a decrease in nerve phrenic activity, both in frequency and amplitude (duration of response from 1 to 2 min) as result of ethanol microinjection in the NTS. This was accompanied by a markedly decreased of baroreflex slope (from 0.189 ± 0.038 to 0.1346 ± 0.031 ms/mmHg, P < 0.05, t test). Following the treatment with DPSPX, the effects of ethanol microinjection on BP, HR and phrenic nerve activity are greatly attenuated and to a lesser extent baroreflex function.

In conclusion, hypotension, bradycardia and respiratory depression produced by acute ethanol microinjection are at least in part mediated by adenosine receptors. The significantly change of baroreceptor reflex sensitivity observed on ethanol microinjection into NTS underlines centrally neurons implication on reported decreased baroreflex function to peripherally alcohol administration

Where applicable, experiments conform with Society ethical requirements