Changes In Autonomic Activity Research Articles

Effects of sino-aortic denervation on the acute circulatory responses to centrally administered 6-hydroxydopamine and of clonidine in conscious rabbits.

In intact animals the circulatory responses evoked by transmitter released from specific neurons of the central nervous system (CNS), or by centrally administered drugs, depend on the direct effects initiated in the CNS plus secondary reflex changes in autonomic activity. We have studied the contribution of the arterial baroreceptor reflexes to the mean arterial pressure (MAP) and heart rate responses produced by intracisternal (i.c.) clonidine and during the first few hours after i.c. 6-hydroxydopamine (6-OHDA), which releases transmitter from noradrenergic neurons. The direct and reflex components were assessed from the differences in responses between intact and sino-aortic denervated (SAD) rabbits, with the latter's responses taken to approximate the direct CNS-induced effects. The direct effects of transmitter release were (a) an early fall in MAP followed by a late pressor effect; and (b) an early bradycardia followed by a late tachycardia. The early responses were similar to the direct effects of i.c. clonidine and to the findings observed in pontine rabbits with intact baroreceptors. In intact rabbits, feedback through the arterial baroreceptors reduced the fall in MAP with clonidine, but had no effect on the heart rate changes. Similarly, it eliminated the early depressor response to 6-OHDA but had little effect on the early bradycardia; however, the late pressor response was little affected, and the late tachycardia was masked by a reflex bradycardia. Our findings suggest that arterial baroreceptor reflexes can modify some effects initiated in the CNS, but some of the pathways are not involved in this interaction.

Cardiac beta adrenoceptors and adenylate cyclase in normotensive and renal hypertensive rabbits during changes in autonomic activity.

The effects of hypertrophy and alterations in cardiac autonomic activity on left ventricular (LV) beta adrenoceptors and adenylate cyclase were measured in rabbits. Normotensive and renal hypertensive animals were exposed to three levels of chronic sympathetic activity: (i) "normal" activity; (ii) reduced activity after 2 weeks treatment with guanethidine; (iii) 2 weeks increased sympathetic activity following sino-aortic denervation. In hypertensive animals with "normal" activity LV beta receptor sarcolemma concentration was reduced by 36+ compared with the normotensive subgroup whilst total LV receptor numbers were unaltered. Isoprenaline activated adenylate cyclase was similarly affected whilst other sarcolemma marker enzymes were unaffected. Chronic guanethidine administration to normotensive rabbits increased beta receptor concentration (16%, P less than 0.05), basal and isoprenaline activated meters were unaffected. Sino-aortic denervation did not significantly affect beta receptor concentration in either group. The small changes in beta receptor concentration during alterations in sympathetic activity suggest that only a small proportion of LV beta receptors appear to be innervated. The reduction in sarcolemma beta receptor concentration in hypertensive animals appears to be a specific effect due to hypertrophy of the cardiocyte.

The central nervous system and its operation in cardiovascular control.

In the intact organism environmental disturbances affecting the circulation often result in simultaneous changes of several groups of peripheral afferents. These elicit characteristic patterns of autonomic activity with distinctive patterns of vagal activity, of regional sympathetic neural activity and of adrenal catecholamine secretion. During simultaneous changes in several groups of afferents the autonomic responses are often non-linear, with the response to one input markedly influenced by the level of the others. When these non-linear interactions involve the central arterial baroreflex pathways the properties of the body's blood pressure system can become greatly altered. With certain combinations of afferents these interactions make it possible for the organism to better withstand large perturbations than it could do through the normal properties of the arterial baroreceptor reflex. The different neuron groups contributing to the CNS autonomic pathways release many different transmitters including noradrenaline or serotonin and changes in reflex properties result from alterations in transmitter release in one or other of the pathways of the particular network. The peripheral arterial baroreceptors become rapidly reset during sustained alterations in blood pressure. Their 'memory' for any given absolute blood pressure is only a few minutes duration. Hence sustained changes in autonomic activity depend on the properties of the CNS either through signals arising from other groups of peripheral receptors, from central 'command' or owing to changes in transmitter release in a given pathway.

Relationship of cerebral blood flow to cardiac output, mean arterial pressure, blood volume, and alpha and beta blockade in cats.

The relationship among cerebral blood flow (CBF), blood volume, cardiac output (CO), and mean arterial blood pressure (MABP) at varying levels of arterial CO2 tensions (PaCO2) were studied in 70 normal cats. The CBF was measured from the clearance curve of xenon-133 and CO with a thermal dilution catheter placed in the pulmonary artery. The CBF, CO, and MABP values varied appropriately with changes in PaCO2, confirming the reliability of the preparations and the presence of normal autoregulatory responses. Moderate hypovolemia that did not change MABP did, nevertheless, significantly decrease CO and CBF. In an effort to determine if this decrease in CO and CBF were coupled responses, the effects of beta stimulation, hypervolemia, and alpha and beta blockade were investigated. Propranolol, in a dosage insufficient to change MABP, decreased both CO and CBF. This agent abolished the CO response to elevations in PaCO2 but not the CBF response, making it unlikely that this CBF reduction resulted from impaired cerebral autoregulation. Isoproterenol, which, in contrast to propranolol, does not cross the normal blood-brain barrier, alone or in combination with phenoxybenzamine, produced a 38% and 72% increase in CO, respectively, without a change in CBF. Alpha blockade (no major change in CO) and beta blockage (major decrease in CO) did not significantly effect cerebral autoregulation to changes in MABP from angiotensin. The ability of the brain to resist increases in MABP and CO and maintain normal CBF is explained by normal cerebral autoregulation. However, its vulnerability to modest decreases in blood volume, which cannot be attributed to variations in perfusion pressure, is unexplained but obviously has important therapeutic implications. This may be related to reduction in CO, changes in autonomic activity, or a decrease in the size of the perfused capillary bed.

The Comfort Behaviour of Adélie and Other Penguins

[Comfort movements include the behaviours of shaking, stretching, cleaning, preening, and washing. These were described and analyzed for Adelie Penguins. The function for some movements such as oil-preening was difficult to determine and could only be hypothesized. Cleaning, preening, washing, head-shaking, and sneezing function in the care of body surfaces and are responses to the presence of irritants or foreign material on surfaces. Stretching and other shaking movements may function to help prepare muscles and peripheral circulation for activity. Ruffle-shakes may function to dissipate heat and arrange plumage. Some movements of oil-preening and some areas of the body preened are performed in a predictable sequence ordered according to functional relationships among the different movements. Some movements are normally performed only after certain others have been performed. Bathing in penguins is a socially facillitated behaviour. The pattern of Adelie bathing is determined largely as an anti-predator strategy. Adelie, African, and Humboldt Penguins perform the same repertoire of comfort movements. The one exception is that both spheniscids allopreen but Adelies do not. The motor patterns of all other movements except for two are the same for the three species. The two spheniscids perform the jaw-stretch and the both-wings-stretch differently than does the pygoscelid. The comfort movement repertoires of several other penguin species were compared to these. Their repertoires were all very similar. Head-shaking is performed in Adelies during disturbance as a response to an increase in secretion rate of the salt gland. The increase in salt fluid secretion is probably a result of a change in autonomic activity. Head-shaking and social displays which include a form of head-shaking have been reported for several seabird species during disturbance or social interaction. In Adelie Penguins and albatrosses the increased head-shaking during these circumstances is a response to increased salt gland secretion. It is hypothesized that some of the head-shaking and head-shaking displays of other seabirds are caused in the same way. Head-shakes and other vigorous shakes and stretch movements probably have signal function during social interaction., Comfort movements include the behaviours of shaking, stretching, cleaning, preening, and washing. These were described and analyzed for Adelie Penguins. The function for some movements such as oil-preening was difficult to determine and could only be hypothesized. Cleaning, preening, washing, head-shaking, and sneezing function in the care of body surfaces and are responses to the presence of irritants or foreign material on surfaces. Stretching and other shaking movements may function to help prepare muscles and peripheral circulation for activity. Ruffle-shakes may function to dissipate heat and arrange plumage. Some movements of oil-preening and some areas of the body preened are performed in a predictable sequence ordered according to functional relationships among the different movements. Some movements are normally performed only after certain others have been performed. Bathing in penguins is a socially facillitated behaviour. The pattern of Adelie bathing is determined largely as an anti-predator strategy. Adelie, African, and Humboldt Penguins perform the same repertoire of comfort movements. The one exception is that both spheniscids allopreen but Adelies do not. The motor patterns of all other movements except for two are the same for the three species. The two spheniscids perform the jaw-stretch and the both-wings-stretch differently than does the pygoscelid. The comfort movement repertoires of several other penguin species were compared to these. Their repertoires were all very similar. Head-shaking is performed in Adelies during disturbance as a response to an increase in secretion rate of the salt gland. The increase in salt fluid secretion is probably a result of a change in autonomic activity. Head-shaking and social displays which include a form of head-shaking have been reported for several seabird species during disturbance or social interaction. In Adelie Penguins and albatrosses the increased head-shaking during these circumstances is a response to increased salt gland secretion. It is hypothesized that some of the head-shaking and head-shaking displays of other seabirds are caused in the same way. Head-shakes and other vigorous shakes and stretch movements probably have signal function during social interaction.]

Effects of hyperventilation on the circulatory response of the rabbit to arterial hypoxia.

1. The circulatory effects of artificial hyperventilation with air and low oxygen mixtures were studied in rabbits anaesthetized with chloralose-urethane and given decamethonium iodide. The role of vagal afferents in the response to hypoxia was also assessed in spontaneously breathing unanaesthetized and anaesthetized animals.2. In the anaesthetized rabbit artificial hyperventilation inhibited all the changes in autonomic activity to the heart and peripheral circulation resulting from stimulation of the arterial chemoreceptors, and also reduced vagal efferent tone. In animals with section of the carotid sinus and aortic nerves the changes in autonomic activity observed during hypoxia and hyperventilation were much smaller than in normal animals and affected only cardiac autonomic activity.3. The effects of hyperventilation during hypoxia were mediated chiefly through vagal afferents rather than through the effects of hypocapnia. In the absence of changes in autonomic activity (e.g. during artificial hyperventilation with air) the circulatory effects were small and less clearly related to afferent vagal activity.4. In the spontaneously breathing anaesthetized and unanaesthetized rabbit vagal afferent activity resulting from the respiratory response to hypoxia inhibits sympatho-adrenal activity in the same way as during hypoxia with artificial hyperventilation.5. The importance of the vagal afferent input in the rabbit is discussed in relation to the qualitative differences in circulatory response with increasing severity of hypoxia, and in relation to the effects of anaesthesia.

The effects of chloralose-urethane and sodium pentobarbitone anaesthesia on the local and autonomic components of the circulatory response to arterial hypoxia.

1. The circulatory and respiratory responses to severe arterial hypoxia were studied in normal rabbits, ;de-efferented' rabbits without functioning autonomic effectors, and atropinized animals before anaesthesia and during chloralose-urethane and sodium pentobarbitone anaesthesia. Net systemic autonomic activity and autonomic activity to the heart was assessed from a comparison of the responses of the various preparations.2. In the normal spontaneously breathing animal each anaesthetic had a similar mode of action, and modified qualitatively the circulatory response present before anaesthesia. In the ;de-efferented' animal the circulatory response was determined by the local effects of hypoxia, and was altered only quantitatively during anaesthesia.3. In the normal unanaesthetized animal the reflex changes in autonomic activity during hypoxia consisted of a large increase in vagal efferent activity, a decrease in cardiac sympatho-adrenal activity, and an increase in total sympatho-adrenal constrictor activity.4 In hypoxia during anaesthesia the vagal efferent activity no longer increased, but the change in sympatho-adrenal activity to heart and systemic circulation was the same as before anaesthesia in the spontaneously breathing animal. During anaesthesia with controlled ventilation systemic sympatho-adrenal activity increased further, and bradycardia again developed. The bradycardia was now due exclusively to reduction in cardiac sympathetic activity and not to an increase in vagal efferent activity.

Auditory Responsivity in the Human Neonate

ELECTROMYOGRAPHIC, autonomic and electroencephalographic responses were recorded from human neonates during stimulation with sine and square wave tones and with human voices. This communication will concentrate on the analysis of the electromyograms, both because of their importance in reflecting behavioural changes, and because changes in autonomic activity, such as heart rate acceleration, are associated with movements. The “artificial” sounds were chosen so as to have certain structural similarities to the “biological” sound: they were either sine wave components of it or selected fundamentals with superimposed high frequencies. Sine wave and square wave tones of the following frequencies, rising by octaves, were selected: 125, 250, 500, 1,000 and 2,000 Hz. Further sine and square wave tones at 70 Hz were added because preliminary studies had suggested that responses to sound frequencies lower than 100 Hz may have especially interesting properties. Recordings of a male and of a female voice saying “baby” were also included.