Electron microscopic autoradiography of the uptake of [ 3H]GABA in dispersed cell cultures of rat cerebellums. II. The development of gabaergic synapses

Abstract

The formation of GABAergic synapses in dispersed cell cultures of the rat cerebellum was followed from 7 to 21 days in vitro (DIV). The majority of GABAergic synapses appeared between 10 and 14 DIV, and apparently no additional GABAergic synapses formed after 14 DIV. The first step in the development of a GABAergic synapse appeared to be the formation of a large diameter swelling in a GABAergic neuronal process. After the initial contact between the pre- and postsynaptic elements was established, both the number of synaptic vesicles and the thickness of the postsynaptic density increased, while the cross-sectional area of the presynaptic element decreased. The length of the postsynaptic density showed some increase, but no changes were noted in the synaptic cleft thickness, size of the synaptic vesicles or the shape of the synaptic vesicles. Our findings indicate that the formation of GABAergic synapses was not preceded by the formation of other types of junctions or preformed synaptic elements. In addition, the timing and the rate of formation of GABAergic synapses appears not to depend on contact with a single type of postsynaptic neuron, but rather to depend upon intrinsic properties of the development of the GABAergic neuron.