GABA axon terminals in synaptic contact with enkephalin neurons in the hypothalamus of the guinea pig. Demonstration by double immunocytochemistry.

By using a method combining pre-embedding immunoperoxidase staining for enkephalin and postembedding immunocolloidal gold labeling for gamma-aminobutyric acid (GABA) it has been demonstrate that many GABAergic boutons made synapses on enkephalin-reacting soma in the magnocellular dorsal nucleus of the guinea pig hypothalamus. The gold particles revealing the presence of GABA were essentially located over the small clear vesicles and mitochondria present in these GABAergic nerve endings. All the synapses observed were symmetrical. Taking into account the great number of these nerve endings, we conclude for a strong regulatory role of GABA on enkephalin-containing cells of the magnocellular dorsal nucleus.