SUBCELLULAR DISTRIBUTION OF 5-HYDROXYTRYPTAMINE IN THE RABBIT BRAIN

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Abstract
Employing the centrifugal fractionation method, the particulate 5-HT of rabbit brain was chiefly found in the heavier granules of crude mitochondrial fraction as well as in the microsomal particles. The higher 5-HT content of microvesicle fraction reported by Whittaker is attributable to his omitting the acetone extraction procedure, the activity observed by him being mainly that of substance P. Such a particulate 5-HT was released by raising temperature, lowering pH, lowering osmotic pressure and by treating with ether, acetone or with higher concentration of KC1, while other cations such as Na+ , Ca++ and Mg++ showed hardly any effect up to 200 m[image]. Reserpine caused loss of particulate 5-HT in about 40% for 4 hours. The particulate 5-HT is susceptible to monoamine oxidase, which seems to destroy it nearly completely when incubated at 37[degree]C. The 5-HT containing granules show hardly any uptake of 5-HT added to the suspension media at 4[degree]C. In the microsomal fraction, a 5-HT-inactivating action is proved, which disappears after boiling and is inhibited by iproniazid, but not so activated with ether as reported by Whittaker.