MORPHOLOGICAL STUDY ON γ-AMINOBUTYRIC ACID AND MET-ENKEPHALIN RECEPTORS IN THE RAT BRAIN

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We performed light and electron microscopic autoradiography of GABA and opiate receptors using ³H-muscimol and ³H-DAMA.
Light microscopically, distribution of muscimol and DAMA binding sites was demonstrated by means of Texture Analysing System (Leitz).
For electron microscopic autoradiography, selection of development method is important. The authors obtained silver grains in a pattern precisely localized to the cytoplasmic membrane, i.e, the receptor site by means of EAA development.
We observed ³H-muscimol binding site in the neuropiles of the cerebellar molecular layer and the substantia nigra ultrastructurally. Receptor sites labeled with silver grains were located not only on the synaptic regions but also on the plasma membranes of the dendrites and axons not corresponding to synaptic sites. ³H-DAMA binding sites in the caudate nucleus and the amygdaloid nucleus were noted on the plasma membranes of the axons, dendrites and nerve cell somas, some corresponding to synapses, others not. Autoradiographical observation of neurotransmitter receptors has still problems to be solved. Nevertheless, this technique is very important to observe the morphological relationship between transmitters and their receptor sites.