Narcotic Drugs: Effects on the Serotonin Biosynthetic Systems of the Brain

Abstract

The effects of short- and long-term administration of morphine on the activity of two measurable forms of rat brain tryptophan hydroxylase were studied. Morphine administration produced an immediate decrease and a longterm increase in the nerve ending (particulate) enzyme activity but did not change the cell body (soluble) enzyme activity. Cocaine administration demnonstrated a short-term decrcease in measurable nerve eniding enzyme activity that was due to the inhibition of the high affinity uptake (the Michaelis constant, K_m is 10-⁵ molar) of trytophan, the serotonin precursor. Cocaine did not aflect the low affinity uptake K_m = 10-⁵ molar) of tryptophan. Both the uptake of the precursor and the enizymiie activity appeared to be drug-sensitive regullatory processes in the biosynthlesis of serotonin.