Two-phase change of sympathetic rhythms in brain ischemia, Cushing reaction, and asphyxia

Abstract

The present study was designed to determine the extent to which the brain stem neural networks, normally capable of synchronizing the sympathetic nerve discharge (SND) into 2- to 6- and 10-Hz rhythmic fluctuations, contribute to the control of autonomic reactions during brain hypoxia and/or hypercapnia. Vertebral, cardiac, and renal nerve discharges were recorded electrophysiologically in 34 anesthetized, curarized, and artificially ventilated cats. The sympathetic nerve responses to cerebral ischemia (elicited by reducing the blood supply to the brain), intracranial pressure elevation (Cushing reaction), and systemic asphyxia were tested with special focus on the rhythmic structure of the SND. It has been found that there are two phases of SND changes during cerebral ischemia differing mainly in the frequency content of the signals and less in the compound action potential amplitude. During the first phase the rhythmic generators controlling the tonic sympathetic outflow are more strongly activated, which is reflected in a stronger, more regular, and more widespread manifestation of these rhythms on the efferent neurograms. After some time the normal SND structure abruptly changes to a desynchronized activity with loss of the three main sympathetic rhythms and responsiveness to baroreceptor reflex activation. The same stereotyped changes can be observed regardless of the way in which the brain hypoxia and/or hypercapnia has been produced. Nor does the denervation of peripheral baro- and chemoreceptors substantially alter the general pattern of the responses.

Vagal and Sympathetic Nerve Activities Influenced by Posterior Cerebral Circulation in Rabbits

“…Other investigators also showed that SN activity increases under different circumstances such as hypoxia, high intracranial pressure and hemor- Fig. 4 rhagic hypotension (13)(14)(15). These reports parallel our finding of increased SN activities.…”

Baroreceptor influence on the relationships between discharges of different sympathetic nerves of the cat.

“…Systems having both linear and non-linear functions and exhibiting transitions between different states are not infrequent in the nervous system (Freeman, 1975). In the sympathetic networks, functionally relevant phase transitions were described during cerebral ischaemia when the rhythmic SND turned into high-frequency desynchronized discharge (Kocsis et al 1989(Kocsis et al , 1993 and in the awake cat, where a switch between the 2-6 Hz random activity and a stable 10 Hz oscillation occurs, associated with specific behaviours (Ninomiya et al 1989). This latter transition also occurred spontaneously in decerebrate cats (Cohen & Gootman, 1970;Barman et al 1992) and under the effect of anaesthetics (Gootman & Cohen, 1983).…”

“…Postganglionic sympathetic nerve activity was recorded from the central ends of the cut left vertebral (VN), inferior cardiac (CN) and renal nerves (RN) simultaneously, as described earlier (Kocsis, Fedina & Pasztor, 1989; Kocsis et al 1993). The nerve signals were amplified with differential amplifiers with a bandpass of 1P5 Hz to 1P5 kHz and, together with the arterial blood pressure, were stored on magnetic tape for off-line computer analysis.…”

“…The nerve signals were amplified with differential amplifiers with a bandpass of 1P5 Hz to 1P5 kHz and, together with the arterial blood pressure, were stored on magnetic tape for off-line computer analysis. The data from previously published studies (Kocsis et al 1989(Kocsis et al , 1993, in which we examined the effect of cerebral ischaemia on the activity of these nerves, were available on magnetic tape for the present analysis. Only the first control record (i.e.…”

Neonatal blood pressure waves are associated with surges of systemic noradrenaline

“…We have also previously described that such hypertensive BP waves were associated with more severe neonatal illness 2. Many of the neural and endocrine controls of the cardiovascular system have intrinsic rhythms which may be exaggerated by hypoxia 3. Repeated measurements of neonatal endocrine function are scarce due to technical and ethical difficulties; however arginine vasopressin has previously been demonstrated to induce BP waves 4…”