A comparison of the effects of stimulation within the raphe nuclei on arterial blood pressure in the anaesthetized rabbit and rat

Blood pressure changes were evoked in the anaesthetized rabbit and rat by stimulating electrically within the caudal raphe nuclei. The responses evoked in the two species were very different, mainly pressor in the rat (85% pressor, 5% depressor) compared with approximately similar proportions of depressor and pressor in the rabbit (29% and 27%, respectively). The responses evoked from a particular site could not be reversed by changing the stimulus strength. It is proposed that the haemodynamic responses evoked in the rabbit and the rat, in response to stimulation within raphe, are related to differences in the central organization of these nuclei and/or their connexions. These results are then discussed in relation to the observation that the tonic phase of desynchronized sleep is accompanied by hypotension in the rabbit and hypertension in the rat. Finally, it is suggested that the haemodynamic differences observed during desynchronized sleep in these two species are caused by differences in central nervous regulation which involve the caudal raphe nuclei, magnus, pallidus and obscurus

Cardiovascular regulation in the acute decerebrate rat

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 ismilar increase in their HR. Three and a half hours after surgery, SO group presented a normal HR, whilst D animals continued to show an increas ein their HR up to 4.5 h, when it stabilized. Twenty four hours after surgery both groups presented similar MBP (D:110ñ6; SO:108ñ11; SO:335ñ5 beats/min). The blockade of parasympathetic tonus induced significant increases in the HR of both groups, withou major changes in their MBP. Beta-adrenergic blockade reduced HR of both groups, bringin 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