RESUMEN
Male Wistar rats were decerebrated at precollicular level, by aspiration, under ether anaesthesia. The experiments employed rats instrumented for chronic electrocardiogram (ECG) recordings or mean blood pressure (MBP) and heart rate (HR) determination. Immediately after surgery, decerebrate (D) and sham operated (SO) animals presented a small and similar increase in their HR. Three and a half hours after surgery, SO group presented a normal HR, whilst D animals continued to show an increase in their HR up to 4.5 h, when it stabilized. Twenty four hours after surgery both groups presented similar MBP (D:110 +/- 6; SO:108 +/- 1 mmHg) but displayed marked differences on their HR (D:550 +/- 11; SO:335 +/- 5 beats/min). The blockade of parasympathetic tonus induced significant increases in the HR of both groups, without major changes in their MBP. Beta-adrenergic blockade reduced HR of both groups, bringing HR of D almost to control level. Simultaneously there was a reduction in MBP of D but not of SO animals. When parasympathetic blockade was superimposed to beta-adrenergic blockade, there was a significant increase in HR of SO, but not of D or in MBP of both groups. Thus we conclude that the decerebrate rat presents normal MBP with simultaneous tachycardia mainly caused by increased sympathetic outflow to the heart.
RESUMEN
The medullary raphe nuclei are involved in central autonomic regulation. In all species investigated, electrical stimulation of the raphe nuclei causes cardiovascular responses, although, these changes vary between species. The present study was designed to investigate the participation of these nuclei in cardiovascular regulation in the guinea pig. We studied the effect on arterial blood pressure (BP) and heart rate (HR) of electrical stimulation (isolated cathodal square wave pulses for 10 s at 100 Hz, 40-100 muA and 1-ms pulse duration) within the medullary raphe nuclei in urethane-anesthetized (1.2g/kg, i.p.) guinea pigs (400-600g. either sex). Electrical stimulation of the same sites was performed on a group of paralyzed (Flaxedil½, 1 mg/kg, i.v.) and artificially ventilated animals. Stimulation sites were histologically defined and maps of the stimuli were obtained for the effect of electrical stimulation on arterial blood pressure. In another series of experiments, L-glutamate (0.2 M) was microinjected (75 to 150 nl) into the nucleus raphe obscurus. Electrical stimulation of the raphe nuclei produced predominantly pressor responses (delta= +15 to +100 mmHg: 43 percent of the stimulated sites). Hypotension (delta= -10 to -25 mmHg, 24 percent of the stimulated sites), biphasic responses (2 percent) or no change in BP (31 percent) were evoked from fewer stimulation sites. Pressor responses were also predominant in paralyzed animals (delta= +15 to +95 mmHg; 47 percent of the stimulates sites), and after microinjection of L-glutamate into the raphe obscurus (A= +20 to +45 mmHg). The present results demonstrate that in the guinea pig the stimulation of these nuclei evokes mainly pressor responses. These responses are similar to those obtained in the rat and hamster but opposite to those observed in the cat and rabbit. (AU)