A glycoprotein fraction "modulator" of norepinephrine effects in vivo.

The effects of a fraction (Part A of Fraction 8) of a glycoprotein isolated by Lee on the physiological effects of norepinephrine have been studied by measuring the spontaneous activity of Purkinje cells of rats. Fraction A appears to be a "modulator" of norepinephrine because (1) it potentiated the effects of exogenous and endogenous norepinephrine by increasing the amplitude of the response, (2) it significantly prolonged those effects beyond average duration, (3) its effects disappeared only gradually, (4) in the concentrations tested (physiologically available concentrations and up to 20 times greater), it lacked neurotransmitter effects of its own. The effects of Fraction A on endogenous norepinephrine were concluded from (a) its effects on the intact Purkinje cell, (b) its effects on Purkinje cells deprived of norepinephrine content by 6-OH-dopamine or alpha-methyl-paratyrosine, and (c) its effects on Purkinje cell activities induced by stimulation with rectangular pulses of the afferent noradrenergic inhibitory neurons.