On GABA metabolism in the gliocyte cells of the rat pineal gland.

The uptake of the inhibitory transmitter substance gamma-aminobutyric acid (GABA) into the adult rat pineal gland was studied autoradiographically using both light and electron microscopy. The sites of GABA uptake were shown to be exclusively present in the gliocyte cells of the gland following both in vitro incubation with tritiated GABA and after in vivo administration of the amino acid by intra-arterial injection. Both the pinealocyte cells and the numerous sympathetic axons in the gland were devoid of silver grains. Preliminary biochemical studies indicated that the gliocyte uptake process for GABA resembles that in the satellite glia of the sensory ganglia but differed from that in slices of the cerebral cortex. Evidence is also presented which shows the pineal gland to contain endogenous GABA and the enzymes directly associated with its in vivo metabolism, L-glutamate-1-carboxylase (EC 4.1.1.15) (GAD) and GABA-2-oxoglutarate aminotransferase (EC 2.6.1.19) (GABA-T). Furthermore, a 3-fold rise in endogenous GABA occurred in the pineal after inhibition of GABA-catabolism as would be expected if the GABA-shunt pathway was functionally active in the oxidative metabolism of the pineal gland.