RELATIVE ENRICHMENT OF THE LIGHTER 59-KDA FORM OF GLUTAMIC-ACID DECARBOXYLASE IN NERVE-ENDINGS - AN IMMUNOBLOTTING STUDY IN PITUITARY NEUROINTERMEDIATE LOBE

Previous studies established that glutamate decarboxylase (GAD) is present in the brain of higher vertebrates in two forms composed of the homodimeric association of two subunits 59 and 63 kDa, respectively, that were found to be structurally related. We have performed quantitative comparative immunoblotting of whole brain and pituitary neurointermediate lobe (NIL) extracts. While GAD in the brain is present in cell bodies and nerve endings, it is known to be contained in the NIL exclusively in nerve endings that belong to a relatively long gamma-aminobutyric acid (GABA)ergic pathway of central origin. The relative immunolabelling ratio of the 59 kDa to the 63 kDa subunit was at least 10-fold higher in the NIL when compared to whole brain extracts. Accordingly we suggest that the GAD composed of the 59 kDa subunits, which appears to be greatly enriched in GABAergic nerve endings, might represent the form of GAD on which short term activity regulation is exerted in relation to neuronal activity. It might result from the post-translational processing of the GAD formed from the 63 kDa subunits during the axonal transport.