Baroreflexes of the rat. III. Open-loop gain and electroencephalographic arousal

Abstract

In early studies of humans, baroreflex sensitivity was found to be higher during sleep; however, subsequent observations in several species, including humans, have been at variance with the original reports. Sleep and arousal are behavioral states, and it is difficult to accurately and repeatedly measure baroreflex sensitivity in behaving animals. However, pharmacologically immobilized (neuromuscularly blocked) rats have apparently normal sleep-wakefulness cycles, and baroreflex gain can be measured directly in this preparation. Using the delta band of the EEG (EEG(delta)) as an index of sleep and arousal and open-loop aortic depressor nerve (ADN) stimulation as a baroreflex input, we found that blood pressure (BP) level depended on arousal (r = -0.416; P < 0.0001), and BP baroreflex gain depended on BP level (r = 0.496; P < 0.0001), but that BP baroreflex gain was independent of arousal (r = 0.001; NS). Heart period (HP) was different; although HP level depended on arousal (r = 0.352; P < 0.0001), HP baroreflex gain did not depend on HP level (r = 0.029; NS), and HP baroreflex gain increased with arousal (r = 0.315; P < 0.0001). A partial-correlations analysis showed that the presence of the relationship between BP level and BP baroreflex gain probably attenuated the relationship between arousal and BP gain. The results are consistent 1) with physiological findings showing that arousal attenuates afferent transmission through the nucleus of the solitary tract and enhances sympathoinhibition at the rostral ventrolateral medulla; and 2) with observations in humans and animals showing increased cardiac baroreflex sensitivity during sleep, but little if any effect of sleep on BP baroreflex sensitivity. The findings are relevant to all methods of baroreflex gain estimation that use HP as the index of baroreflex activation.

Baroreflexes of the rat. VI. Sleep and responses to aortic nerve stimulation in the dmNTS

“…4, which compares the neural ERs of the present study with the cardiovascular ERs in an earlier study (4). Because in the earlier study we did not classify the sleep state, using all four quarters for Fig.…”

“…The post-dmNTS divergence provides ample opportunity for modulating influences from sleep and arousal to have separate effects on the baroreceptor parasympathetic and sympathetic reflexes; however, our partial-correlations analysis indicated that the effects were, in fact, quite similar (see discussion in Ref. 4 for details and references). In the present study, we extend the NMB rat preparation to enable direct measurement of the magnitude of single-pulse ADN stimulation-elicited evoked responses (ERs) from second-or higher-order baroreflex neurons in the dmNTS.…”

“…For example, in chronic dog studies, implanted carotid sinus nerve stimulators elicit 12-22% greater bradycardia during sleep, but sleep produces no change in the net BP depressor effect (20); in baboons, during sleep, compared with the awake resting state, although the carotid occlusion (baroreceptor inhibition) effect on heart period (HP) is increased, lower abdominal conductance is unaffected, and the renal conductance response to occlusion is attenuated (1). In an earlier study (4), using chronically neuromuscular-blocked (NMB) rats, which have distinct diurnal and sleep-wakefulness cycles, we compared the effects of EEG arousal on the open-loop HP and BP baroreflex gains. Using the power of the ␦-band of the EEG (EEG ␦ ) as an index of sleep and arousal and aortic depressor nerve (ADN) electrical stimulation as a baroreflex input, we observed that although the HP baroreflex gain increased with sleep, the open-loop BP baroreflex gain (the decrease in BP in response to the ADN test stimulus) did not.…”

The Effect of Nutritional Status in the Pathogenesis of Critical Illness Myopathy (CIM)

“…A total of four rats were euthanized after a period of 0 days (serving as controls (C), no mechanical ventilation). Five animals underwent surgery to induce the experimental ICU condition (see below) [29,30] and remained in the mimicked ICU setting; anaesthetized, mechanically ventilated and treated with α-cobrotoxin (post‑synaptic neuromuscular blockade) for a 10–14 day period. Two animals were administered with the required caloric nutrition (eucaloric EC) and three with low caloric nutrition (low calorie (LC)).…”

Neural control of arterial pressure variability in the neuromuscularly blocked rat

“…Over the past 30 years, our laboratory has developed and utilized a unique chronic NMB rat preparation (Dworkin and Dworkin 1990, 2004Dworkin et al 2000a, b;Dworkin 2007a, b, 2009) that largely constrains peripheral influences and significantly limits the complex interactions between the central and peripheral nervous systems. As such, this model provides a platform to clarify the CNS's contribution to a specific physiological phenomenon because of minimal interference from peripheral influences.…”