Neuronal uptake of [3H]GABA and [3H]glycine in laminae I-III (substantia gelatinosa Rolandi) of the rat spinal cord. An autoradiographic study

[3H]GABA or [3H]glycine were injected into the subarachnoidal space of adult rats at C4-C5 level. After 10-60 min, the animals were perfused with 4% paraformaldehyde-0.5% glutaraldehyde and thick sections of the cervical spinal cord were postosmicated and Epon embedded. Light microscope autoradiographs of transverse cord sections showed numerous silver grains over the dorsal column and laminae I-III, higher grain densities occurring over lamina I for GABA and lamina III for glycine. In [3H]GABA-injected animals nerve cell bodies in lamina I or at the transition to lamina II appeared strongly labeled in light and electron microscope autoradiographs. These cells were smaller and less rich in RER than marginal cells and poor in axosomatic synaptic contacts. High grain densities appeared over axon terminals synapsing with dendrites in laminae I-II and over the light peripheral axon endings of synaptic glomeruli of laminae II-III. After [3H]glycine treatment, a number of nerve cell bodies were labeled in lamina III. It is suggested that two types of inhibitory interneurons occur in the rat gelatinosa, one GABAergic with cell body in lamina I, and another glycinergic in lamina III.