Journal of Applied Physiology, Vol 70, Issue 5 2181-2187, Copyright © 1991 by American Physiological Society
Effect of preexisting brain ischemia on sympathetic nerve response to intracranial hypertension
B. Kocsis, L. Fedina and E. Pasztor
Department of Physiology, National Institute of Neurosurgery, Budapest, Hungary.
The performance of the sympathetic nervous system during sustained moderate
cerebral ischemia (CI) was examined in the present study. For this purpose,
a Cushing response was elicited repeatedly during incomplete global CI in
anesthetized artificially ventilated cats after vagotomy and baroreceptor
denervation. In control animals without CI, sympathetic activity in
response to brief elevation of intracranial pressure (ICP) showed a
well-repeatable two-phase reaction. During CI there was a progressive
deterioration of background sympathetic nerve discharge (SND) over a period
of 30 min. SND response to repeated elevation of ICP was initially similar
to control response but later with progression of CI was seriously changed.
1) Instead of the usual hyperactivation, sympathetic nerve activity was
depressed during intracranial hypertension. 2) The characteristic
desynchronized activity either appeared later during the reperfusion period
or remained absent. The progressive loss of SND response to raised ICP in
developed CI was compared with the changes seen in experiments in which
repeated ICP elevations were superimposed on asphyxia. These findings
suggest that the sympathetic component of the Cushing reaction strongly
depends on the actual state of brain stem autonomic circuits and may be
seriously altered in pathological situations involving ischemic brain
injury.
