Effect of focal cooling of central chemosensitive areas on cerebral ischemic response

The ventrolateral medullary surface (VMS) has been shown to have chemosensitive areas that can alter blood pressure and respiration. It has also been shown that lesions near the VMS can affect the intensity of the cerebral ischemic response (CIR). To determine which regions of the central chemosensitive areas of the ventral medullary surface contribute to the pressor response caused by cerebral ischemia, we used focal cooling of the caudal Loescheke's (CL), intermediate Schlaefke's (IS), and rostral Mitchell's (RM) areas of VMS during ischemia of the brain. Experiments were performed on 17 pentobarbital sodium-anesthetized, paralyzed, and artificially ventilated cats after denervation of the vagi and sinoaortic nerves. Bilateral occlusion of the external carotid and vertebral arteries resulted in a significant increase of arterial pressure (from 129 +/- 4 to 174 +/- 8 mmHg, P less than 0.01) and an increase in splanchnic sympathetic activity. However, heart rate and cervical sympathetic activities were not appreciably affected by cerebral ischemia. Bilateral cooling of the IS area to as low as 10 degrees C led to a decrease or disappearance of phrenic activity but failed to affect the magnitude of the pressor response. Also cooling of the CL and RM areas and application of Gelfoam pledgets soaked in lidocaine (4%) to these areas did not affect the CIR. However, covering the whole VMS with 0.2 ml of 4% lidocaine or cold cerebrospinal fluid (10 degrees C) abolished the ischemic reflex.(ABSTRACT TRUNCATED AT 250 WORDS)