Differential sympathetic reactions during cerebral ischaemia in cats: the role of desynchronized nerve discharge.

Abstract

SUMMARY1. Sympathetic nerve discharge (SND) of three postganglionic nerves with different functions and anatomical locations was simultaneously recorded at rest and during severe cerebral ischaemia (Cushing reaction). The three nerves, controlling the heart (inferior cardiac nerve), visceral (renal nerve) and skeletal muscle circulation (vertebral nerve), were selected with the assumption that their activity pattern will represent the differential central autonomic command to the major players of the circulatory response to cerebral ischaemia.2. Changes in the power density spectra of the nerve signals, and in the pairwise coherence functions, elicited by the cerebral ischaemia, were evaluated separately for the rhythmic (R-SND, i.e. between 0 and 6 Hz) and high-frequency (HF-SND, i.e. between 12 and 100 Hz) components of the nerve signals.3. The sympathetic nerve response to cerebral ischaemia developed in two phases. Phase 1 was a massive R-SND reaction and phase 2 was characterized by SND desynchronization and by the emergence of HF-SND. The power of HF-SND occupied a wide band between 12 and 80 Hz with maximum between 20 and 30 Hz. All three nerves were involved in the Cushing response but the magnitude and character of the reactions were specific for each nerve. In the cardiac nerve, the power of the rhythmic component of the discharge increased almost twice the control and remained dominant during the whole reaction, strongly modulating HF-SND during the second phase. In the vasomotor nerves, R-SND was suppressed during phase 2 and HF-SND occupied 65 % of the total power of the signal. Near equal Rto HF-SND proportions, however, were reached on different activity levels in renal and vertebral nerves. Whereas total renal SND did not change, the power of the vertebral SND increased more than twice. In addition, desynchronization in the vertebral SND was preceded by a massive R-SND reaction during phase 1, which was missing in the renal nerve.4. For all possible nerve pairs, R-SND was highly coherent before the reaction and remained so during intracranial pressure elevation, regardless of the direction and magnitude of the changes in absolute and/or relative power of this component in different nerves. On the other hand, HF-SND never correlated between any of the MS 1149 B. KOCSIS AND OTHERS nerve pairs indicating that this component in each nerve originated from specific sources of regional sympathetic activity.5. We conclude that the sympathetic nervous system is capable of generating different types of activity, including rhythmic and desynchronized discharges, and these activity patterns play an important role in generating differential sympathetic nerve response to cerebral ischaemia. Different sympathetic networks controlling different cardiovascular effectors, due to their specific properties (i.e. unequal capability of synchronization or desynchronization of the discharge), may convert the general excitatory effect of the cerebral ischaemia into specific discharge patterns with characteristic involvem...

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.…”

“…The power in the autospectra is usually concentrated in a narrow band around the heart rate (Barman, Gebber & Zhong, 1992; Kocsis, Fedina, Gyimesi-Pelczer, Ladocsi & Pasztor, 1993) and the peak coherence between the nerves is higher 687 2710 (Barman et al 1992). Furthermore, there is a significant linear component of the baroreceptor effect on the activity of different sympathetic nerves, which can be quantified by measuring the value of the coherence function between the nerve signal and the arterial blood pressure, at the heart rate (Barman et al 1992;Kocsis et al 1993). Thus, it is reasonable to expect that, in baroreceptor-intact cats, the nerve-to-nerve coherence.can, to some extent, be explained by the influence of the common periodic input from the baroreceptors.…”

The sympathetic nervous system's role in regulating blood pressure variability

“…In contrast to the activity present in motor nerves, sympathetic nerves are continuously active, meaning that all innervated blood vessels remain under some degree of continuous constriction. Since its first description in the 1930s [1,2], SNA has engendered itself to researchers in two camps; neurophysiologists have seen its inherent properties as an opportunity to understand how areas of the central nervous system may be connected to generate and control such activity [3][4][5], while cardiovascular physiologists have viewed its regulation of blood flow as a direct index of circulatory control in response to different stimuli, drugs, and pathological conditions [6][7][8].…”