Descending spinal pathways mediating the responses of adrenal tyrosine hydroxylase and catecholamines to insulin and 2-deoxyglucose

Abstract

We investigated the bilateral organization of the descending spinal sympathetic projections that subserve adrenomedullary stimulation caused by insulin hypoglycemia or 2-deoxyglucose (2DG) cellular glucopenia in adult rats with right-sided hemisection of the cord at C6–C7 (i.e. above the site of origin of the adrenal innervation). Cord hemisection alone caused a minor rise of adrenal tyrosine hydroxylase activity (ATHA) on the intact side as compared to sham-operated animals, but there was no change on the operated side. Catecholamine levels were marginally affected. In rats with hemisection the drugs elevated ATHA significantly in both glands; the response on the intact side was similar to that in sham-operated rats, but the effect on the sectioned side was reduced by one-half. 2DG affected the adrenaline content differently in the two glands: on the intact side it provoked a decrease comparable with that in non-lesioned rats, but had no significant effect on the lesioned side. 2DG acts through higher CNS structures, for complete transection of the cord at T2–T3 prevents the effects of 2DG on ATHA and adrenal adrenaline. We conclude that adrenal tyrosine hydroxylase induction by insulin and 2DG in hemisectioned rats, just as in the case of immobilization stress, is mediated by ipsilateral and, to a lesser degree, contralateral pathways generating net excitatory effects on ATHA; the latter fibers decussate below the low cervical level. The same organization may prevail for control of the concentration of adrenaline.