Effects of neurotropin on regional brain noradrenaline metabolism in rats.

By measuring levels of noradrenaline (NA) and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), in various rat brain regions, we investigated the effects of an extract isolated from vaccinia virus-inoculated and inflamed skin or tissue of rabbits (Neurotropin, NSP), administered acutely or chronically, on regional NA metabolism in stressed and nonstressed rats. An acute administration of NSP at 50 mg/kg significantly elevated MHPG-SO4 levels in the amygdala and cerebral cortex; and 100 mg/kg of the drug significantly increased the metabolite levels in the hypothalamus, amygdala, thalamus, midbrain, cerebral cortex and pons plus medulla oblongata without affecting NA levels. This suggests that acutely injected NSP slightly increases NA release in these brain regions. One hour immobilization stress caused significant increases in MHPG-SO4 levels, which were not affected by pretreatment with either 50 mg/kg or 100 mg/kg of NSP. Chronic injection with NSP daily at either 50 mg/kg or 100 mg/kg for 7 days was without effect on NA metabolism in all brain regions examined. However, increases in MHPG-SO4 levels caused by stress were significantly attenuated in some regions including the hypothalamus, amygdala and midbrain in chronic NSP-treated rats. This indicates that although an acute administration of NSP slightly increases brain NA release, a chronic treatment with NSP rather attenuates increases in NA release caused by immobilization stress in brain regions such as the hypothalamus, amygdala and midbrain. This suggests a possibility that these attenuating effects on stress-induced increases in brain NA release caused by chronic administration of NSP might be related to the stress-reducing or anti-stress properties of NSP.