Autonomic interactions in the control of heart rate in the monkey

Effect of different anesthetic mixtures-ketamine-xylazine, ketamine-acepromazine and tiletamine-zolazepam-on the physiological and blood biochemistry parameters of male rhesus monkeys (Macaca mulatta) at different ages

BACKGROUND

Anesthetic agents are commonly utilized in the handling of non-human primates for prevent the stress caused in physical exploration or physical restrain. For this reason, the objective of this work was to describe the effect of age and dissociative anesthetics (ketamine and tiletamine), and their combinations with acepromazine, xylazine and zolazepam, on the physiological and blood biochemical parameters in Macaca mulatta.

METHODS

Eighty male Macaca mulatta were divided into four experimental groups depending on the anesthetic mixture applied. Each group of 20 males was divided into five sub-groups according to age. Physiological parameters were recorded every 5 minutes during a 30-minute period. A blood sample was drawn to analyze blood biochemistry.

RESULTS

Statistical analyses revealed significant differences in the physiological parameters between the ketamine-acepromazine and ketamine-xylazine groups compared to the control group. The analysis of blood biochemistry found significant differences by age and by anesthetic mixture among all groups.

CONCLUSION

These findings contribute to standardizing this animal model in biological research.

An essay on the circulation as behavior

Most conceptual models of the organization of the cardiovascular system begin with the premise that the nervous system regulates the metabolic and nonmetabolic reflex adjustments of the circulation. These models assume that all the neurally mediated responses of the circulation are reactive, i.e., reflexes elicited by adequate stimuli. This target article suggests that the responses of the circulation are conditional in three senses. First, as Sherrington argued, reflexes are conditional in that they never operate in a vacuum but in a context together with other reflexes. Guided by functional utility, they interact rather than add. Second, as Pavlov argued, stimuli acquire meanings as a result of experience. This notion of stimulus effect plus the Sherringtonian notion of conditionality suggest that association is one of the ways stimuli eliciting cardiovascular reflexes acquire their meanings and thus their relative strengths. Finally, as Skinner and others have argued, operants are responses that act upon the environment to obtain consequences – that is, stimuli. As operants, cardiovascular responses fulfill a major biological need, functioning proactively. The cardiovascular response is an integral component of the animal's behavior regardless of whether it is an elicited reflex or the eliciting stimulus acquired its properties as a result of the genetic inheritance of the animal or through experience, or the cardiovascular response is emitted in anticipation of an environmental consequence. The main theses of this essay are: (1) behavior is an integrated set of responses and the circulation is one of the response systems comprising behavior; (2) behavior is, in part, determined by its functional significance within a context; (3) the contextual factors operative at the time of the behavior have a major role in determining which of the set of possible responses will determine the final act, that is, which behavior will be the effective response and which other behaviors will be concomitants.

Parasympathetic nervous system control of heart rate responses to stress in offspring of hypertensives

The elevated heart rate response to stress in normotensive offspring of hypertensives (PH+) has been suggested to be a function of sympathetic nervous system activity. This study examined whether parasympathetic nervous system activity may also underlie familial differences in the heart rate response. Twenty-four subjects, half of whom were PH+, were exposed to four stressor tasks administered in counterbalanced order. Stressors were chosen based on previous research that suggested vagal contributions to the heart rate response. Stressors were a cold pack to the forehead, isometric hand grip, a noxious film, and a shock-avoidance video game task. Physiological measures included heart rate (HR), respiration rate (RR), and respiratory sinus arrhythmia (RSA). RSA values were corrected for corresponding RR by analysis of covariance. Familial differences in HR were observed in response to the hand grip and video game tasks. However, in both cases analyses suggest that familial differences in reactivity were a function of primarily sympathetic as opposed to parasympathetic influences. Familial differences in RSA were not observed for rest or tasks. This study found no evidence for parasympathetic mediation of familial differences in the heart rate response to the stressors employed.

Cardiac sympathetic and parasympathetic activity during self-regulation of heart period

Fourteen subjects attempted to increase and 15 attempted to decrease cardiac interbeat interval (IBI) while being provided with biofeedback of IBI, T-wave vector magnitude (TWVM), or respiratory sinus arrhythmia (RSA). Subjects in both groups showed directional change in IBI relative to a tracking control task, but the three types of feedback did not differentially affect performance. Voluntary IBI increases were associated with significant increases in TWVM and RSA, and voluntary IBI decreases were associated with significant reductions in RSA and nonsignificant reductions in TWVM. This pattern of results suggests that alterations in cardiac vagal tone are involved in voluntary IBI increase and decrease tasks. The results also suggest a role for cardiac sympathetic nervous activity in voluntary IBI increase. The role of changing respiration cycle period was also investigated.

Autonomic blockade does not prevent learned heart rate attenuation during exercise

Each of three monkeys was operantly conditioned to slow its heart, to exercise (lift weights) and to attenuate the tachycardia of exercise by combining these two skills. Each was further tested during beta-adrenergic blockade (atenolol), combined alpha-adrenergic blockade (prazosin) and beta-adrenergic blockade, or cholinergic blockade (methylatropine). During all experiments heart rate, stroke volume, intraarterial blood pressure, O2 consumption, and CO2 production were recorded on a beat-to-beat basis. Each animal was able to attenuate the tachycardia of exercise under each of the drug conditions, indicating that "central command" is not the expression of fixed, cardiovascular and pulmonary reflexes elicited by somato-motor commands, but rather is an adaptive behavior, determined by environmental contingencies and mediated by cardiovascular and pulmonary as well as somato-motor commands. The ability of the animals to perform with greater cardiac efficiency during the combined exercise and heart rate slowing task relative to the exercise-only task was not affected by sympathetic blockade; however, parasympathetic blockade did reduce cardiac efficiency.

Cardiopulmonary adjustments during operant heart rate control

Twenty-three healthy men and women participated in a 5-session experiment in which they attempted to increase and decrease their heart rate with the assistance of visual analogue biofeedback. As a group subjects did successfully raise and lower heart rate from resting baseline. These changes in heart rate were closely paralleled by changes in V, a measure of cardiac vagal tone. Heart rate slowing was associated with increases in V, and heart rate speeding was associated with decreases in V. Respiration rate and amplitude did not differ significantly between heart rate slowing and speeding trials, and covariance analysis indicated that respiratory changes did not account for the heart rate or V effects. The weighted coherence between respiration and heart rate showed that cardiopulmonary coupling increased during heart rate slowing and decreased during heart rate speeding. Individual differences in cardiac vagal tone and cardiopulmonary coupling were unrelated to heart rate speeding and slowing performance.

Cardiovascular reactivity as behavior

The word, behavior, means action or reaction. Thus, all physiologic responses meet this definition and are behavior. Furthermore, if the response is neurally mediated, then there are only 3 possible behavioral mechanisms that can be operating to determine it: (1) The response is part of a reflex, elicited by an adequate stimulus. In this case, in an intact animal the expression of the response will be modulated by a variety of situational factors. (2) The response is part of a reflex. However, the capacity of the stimulus to elicit the response is acquired through association with an adequate stimulus. Thus, the reflex is learned rather than innate. (3) The response is part of a "central command" and is emitted in anticipation of a consequence whose likelihood of occurrence has been learned. Neurally mediated responses of the circulation meet all these criteria. Thus, circulatory responses not only are passive reflexes, they also are reactive and proactive behaviors, which permit animals to interact effectively with their environments, and which change with practice. These principles explain a variety of cardiovascular effects observed in experimental or clinical settings. Furthermore, by applying well-established behavioral principles to circulatory responses, it is possible to achieve clinically significant effects. This presentation will characterize the way in which behavioral mechanisms are expressed in the circulation, it will describe a number of clinically significant findings that illustrate the importance of these mechanisms, and it will propose a number of applications of behavioral principles that can be used in clinical practice.

Beta-adrenergic blockade may prolong life in post-infarction patients in part by increasing vagal cardiac inhibition

Beta-adrenergic blocking drugs prolong lives of post-infarction patients primarily by preventing sudden cardiac death. The mechanisms responsible for this beneficial effect are not understood clearly, since beta-blockers, in doses used in most clinical trials, are only weakly effective against stable ventricular arrhythmias. Arrhythmias during myocardial ischemia may differ from arrhythmias in other clinical settings in that they depend importantly upon autonomic neural factors, including the balance between levels of sympathetic cardiac stimulation and parasympathetic cardiac inhibition. Beta-blockers reduce sympathetic cardiac stimulation, and they may influence this balance favorably in another important way: a well documented, but not generally appreciated property of beta-blocking drugs is that they also increase levels of vagal cardiac inhibition. I propose that beta-blockade prevents arrhythmic deaths in post-infarction patients in part by increasing levels of vagal cardiac inhibition.