Subcellular distribution of 5-hydroxytryptamine in the rabbit brain.

It was demonstrated by BAKER(1958,1959)that a large fraction of 5-hydroxytryptamine(5-HT)in duodenal mucosa was present in intracellular store granuels denser than the mitochondria.On the other hand,WHITTAKER(1959) reported that the brain 5-HT was chiefly found as a bound form in subcellular fractions less dense than the typical mitochondrial one,suggesting the difference between the brain and intestinal 5-HT.He also described release and inactivation of this particulate 5-HT.Using the fraction action and bioassay method similar to those used by WHITTAKER,his result could be confirmed in our laboratory.But KATAOKA(1962)found that substance P of rabbit brain showed the subcellular distribution and properties quite similar to those of 5-HT. Stating the Vane's rat fundus preparation(1957)used for bioassay for 5-HT in Whittaker's work was also sensitive to substance P,he cast some doubts on the nature of particulate 5-HT described by this investigator,since he omitted the acetone extraction of 5-HT prior to its bioassay.It seemed necessary, therefore,to re-examine whether or not neuronal 5-HT is mainly present in the so-called synaptic vesicle fraction.Then,using the acetone treatment, subcellular distribution and some properties of such a bound 5-HT in brain were re-investigated.This paper is chiefly concerned with this problem.A brief account of the results described has already been submitted to the publication(INOUYE,KATAOKA and SHINAGAWA,1962).