Ultrastructure of cultured rat neostriatum

Abstract

Four different types of neurons were identified in cultures of newborn rat neostriatum. Small and medium-sized neurons were most numerous. A few large neurons and some very small ‘microneurons’ were observed. The morphology of medium-sized neurons varied, and this group may contain more than one functional subgroup. Axosomatic synapses were associated with all types of neurons, but most of them made contacts with medium-sized neurons. All axodendritic synapses made symmetrical contacts, with or without synaptic membrane thickenings. A great majority of terminal boutons contained small, round, clear vesicles. A few terminals with large pleomorphic clear vesicles were seen. Large granular vesicles were found in the peripheral cytoplasm of some medium-sized neurons, dendrites and axon terminals. No terminals contained exclusively large granular vesicles, but in some terminals they were more numerous than the small clear vesicles. The dense core of the large granular vesicles was resistant to reserpine treatment. Kainic acid did not cause specific degenerative changes. The presence of several morphologically distinct populations of neurons renders it possible to study the nature of these cells in different experimental conditions. Intrinsic neostriatal synaptic contacts appeared to be symmetrical, although it is possible that some of them have the capacity to develop asymmetrical contacts. The lack of effect of kainic acid may be explained by the early maturational stage of the cells or by the lack of extrinsic contacts. More functional studies are necessary before the usefulness of these cultures for investigating neostriatal function can be assessed.