Microinjections of glutamate within trigeminal subnucleus interpolaris alters adrenal and autonomic function in the cat

The influence of rostral portions of the trigeminal sensory complex on adrenal and autonomic function was assessed by microinjections of l-glutamate (500 or 5 mM, 100 nl) directed at subnucleus interpolaris (Vi) or at the nucleus principalis/subnucleus oralis level (Vp/Vo) in chloralose-anesthetized cats. Microinjections of glutamate (500 mM) within Vi evoked prompt (by + 1 min) dose-related increases in the adrenal secretion of epinephrine (+11.4±2.5 ng/min, P < 0.001), adrenal blood flow (+0.19±0.06 ml/min, P |s 0.05), mean arterial pressure (+6.6±3.0 mmHg, P < 0.025) and heart rate (+8.0±2.7 beats/min, P < 0.01, n = 16). Microinjections of lower doses of l-glutamate (5 mM, n = 7) within Vi had no effect. Microinjections of 500 mM glutamate within Vp/Vo (n = 15) or within the spinal trigeminal tract (n = 13) had no consistent effect on adrenal or autonomic function. Plasma concentrations of ACTH were not altered significantly by glutamate regardless of dose or of the site of injection. The results suggest that local release of glutamate within Vi, but not within Vp/Vo, influences adrenal and autonomic function. Together with previous results obtained after injections of glutamate within subnucleus caudalis, these data indicate that glutaminergic input to both Vi and to more caudal portions of the spinal trigeminal nucleus contribute to the control of autonomic function such as that which often accompanies trigeminal nociception.