Development of synaptic transmission by cholinergic neurons in culture

We examined the development of cholinergic transmission at synapses formed in culture by retinal neurons derived from the embryonic chick. In our experimental system, striated muscle cells served as postsynaptic targets for cholinergic retinal neurons. Functional retina-muscle synapses could be formed in cultures containing either retinal explants or dissociated retinal cells. Plating a low density of dissociated cells permitted the study of relatively isolated, visually identifiable, cholinergic neurons. We found that, early in the functional maturation of retina-muscle synapses, the release of acetylcholine occurs spontaneously, but cannot be evoked by the putative excitatory transmitter, glutamate. This stage is followed by the emergence of transmitter release that is evocable by glutamate in a receptor-mediated and calcium-dependent manner. This ability to transmit excitatory information across a synapse is expressed in culture by neurons derived from retinas that are at an early stage of morphogenesis.