ACTIVATION OF NEURONS IN CARDIOVASCULAR AREAS OF CAT BRAIN-STEM AFFECTS SPINAL REFLEXES

In 65 cats anesthetized with chloralose (40 mg/kg) and urethane (400 m g/kg), the effects of electrical stimulation and microinjection of sod ium glutamate (0.2-5 M, 100-200 nl) in the pressor areas in the rostra l brain stem on the evoked L5 ventral root response (EVRR) due to inte rmittent stimulation of sciatic afferents were compared to stimulating the dorsomedial (DM) and ventrolateral (VLM) medulla. In general, sti mulating these rostral brain stem pressor areas including the dienceph alon (DIC) and rostral pons (RP) produced increases in systemic arteri al pressure (SAP). In most of the cases (85%) there were associated ch anges in the EVRR, predominantly a decrease in EVRR (72%). Stimulation of the midbrain (MB, principally in the periaqueductal grey) produced decreases in SAP and EVRR. Decreases in EVRR was observed in 91% of t he DM and VLM stimulations in which an increase in SAP was produced. T his EVRR inhibition was essentially unaltered after acute midcollicula r decerebration. Increases in EVRR were also observed and occurred mor e often in the rostral brain stem than in the medulla. Since changes o f both EVRR and SAP could be reproduced by microinjection of Glu into the cardiovascular-reactive areas of the brain stem, this suggests tha t neuronal perikarya in these areas are responsible for both actions. On some occasions, Glu induced changes in EVRR but not in SAP. This ef fect occurred more frequently in the rostral brain stem than in the me dulla. The present data suggest that separate neuron population exist in the brain stem for the integration of SAP and spinal reflexes. Thes e neurons are relatively dispersed from DIC to RP but are in close pro ximity to one another in the medulla. Rostral structures also contain more neurons responsible for augmenting spinal reflexes.