Glutamate-induced fastigial pressor response in the dog

This study indicates that orthodromic pathways emanating from the fastigial nucleus are responsible for the pressor/tachycardia response observed with electrical stimulation of the nucleus. The fastigial presser response was obtained electrically using bipolar electrodes. l-glutamate, which activates only cell bodies, was then injected into the nucleus through the hollow electrode. A slowly-rising pressor response and vagal-mediated bradycardia resulted. On the basis of: (1) dye diffusion studies; (2) the time course of events and similarity to the electrical response;(3) comparison with direct injections into the fourth ventricle; and (4) glutamate injections into adjacent cerebellar tissue, it was concluded that the response emanated from the fastigial nucleus. Electrophysiological studies on cat spinal cord confirmed that the technique of injecting relatively large amounts of glutamate into nuclei activates cell bodies and not axons.