Immunohistochemical studies of the GABA system in the pancreas.

gamma-Amino butyric acid (GABA) is a major inhibitory neurotransmitter in the mammalian brain. In the present study the indirect immunofluorescence technique was employed to localize the GABA-synthesizing enzyme glutamate decarboxylase, and the GABA-metabolizing enzyme GABA-transaminase within the rat pancreas. Both enzymes were found to occur only in the beta-cells of the islets of Langerhans. The other endocrine cell types, the exocrine tissue and the nervous elements in the pancreas did not contain either enzyme. Animals treated with the beta-cell toxins streptozotocin or alloxan showed a loss of immunoreactive cells in the islets. The results provide morphological evidence of the coexistence of GABA and insulin in the beta-cells of the endocrine pancreas.