Effects of the Medullary Hormones on the Somatic Nervous System in the Cat

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Abstract
Intravenous epinephrine and norepinephrine produce like effects on cortically evoked movements and on the patellar reflex, but higher doses of norepinephrine are required. Two epinephrine response patterns are obtained: a) an augmentation, of 10-50% starting in 30-50 seconds and lasting 1-3 minutes, occurs in the lightly anesthetized animal. This is also elicited by stimulation of the splanchnic nerve and of the posterior hypothalamus. The hypothalamic response includes an immediate part, involving direct action on cord neurones of descending reticulospinal tracts, and a late part, dependent on release, via splanchnic nerves, of adrenomedullary hormones. Interference with the sympathetico adrenal system abolishes the late augmentation and that produced by injection of epinephrine. The late responses fade rapidly on repeated hypothalamus stimulation. Barbiturates reduce augmentation. Large lesions in the retromammillary region decerebration, or spinal trans-section diminish the augmenting action of epinephrine. b) A depression of 10 to 70% and lasting 5-7 minutes, and occasionally preceded by a slight facilitation, is obtained under moderate anesthesia and with larger epinephrine doses. Decerebration and spinalization do not significantly alter depression.