Morphological study of neurotransmitter receptors in the rat brain.

1. We performed light and electron microscopic autoradiography of GABA and opiate receptors using 3H-muscimol and 3H-DAMA. 2. Selection of development method is important for electron microscopic autoradiography. The authors obtained silver grains in a pattern precisely localized to the cytoplasmic membrane, i.e., the receptor site by means of EAA development. 3. 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 are 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 are noticed on the plasma membranes of the axons, dendrites, and nerve cell somas, some corresponding to synapses, others not. There are still problems to be solved in the autoradiographical observation of neurotransmitter receptors. Nevertheless, this technique is very important in observing the morphological relationship between transmitters and their receptor sites.