Neurons often contain, and probably release, more than one neuroactive substance that may have diverse or opposite actions on the postsynaptic cell. It remains unexplained how these neurons utilize their multiple neuroactive substances while maintaining appropriate resolution of neurotransmitter functions. Here, we have examined the ultrastructural localization of glycine receptors by using a monoclonal antibody directed to the intracellular domain of the strychnine-sensitive glycine receptor. We have found that glycine receptors are only localized to 56% of the synapses made by presumed 'glycinergic' (more accurately, glycine-utilizing) amacrine cells in the turtle retina. The remaining synapses made by these same boutons show no evidence of glycine receptors. As there is no evidence to suggest the presence of a second type of glycine receptor, these data indicate that only a portion of the postsynaptic sites contacted by the glycine-utilizing neurons can respond to glycine. They also suggest that a neuron containing multiple neuroactive substances can selectively affect postsynaptic elements by means of heterogeneous receptor localization.

There has been a rapid growth in research focused on retinal transplantation as a strategy for restoration of or rescue of function in retinas rendered afunctional by disease or trauma. This strategy has been partially stimulated by recent transplantation efforts in brain related to neurodegenerative diseases such as Parkinson’s, Huntington’s, and Alzheimer’s. These latter efforts have been hindered by a dearth of information regarding the specific properties of the inputs, intrinsic processing and outputs within the brain underlying these diseases. This is especially significant when attempting to study correlated functional and structural properties of the implanted tissue. In contrast to such studies, this research utilizes the retina, of which there is greater knowledge about the inputs (complex light patterns), intra-retinal processing and anatomical micro-circuitry, and the output (patterns of ganglion cell activity). Our research demonstrates, for the first time, organized, complex physiological function and its underlying neuronal microcircuitry in mammalian subretinal transplants.

Embryonic rabbit retina can be transplanted to the subretinal space of adult rabbit with a new method, which gives a high rate of successful short-term transplants. Embryonic (stage E 15) neural retina cells were injected through an incision just behind the sclerocorneal border with a thin (inner diameter 0·15 – 0·4 mm, outer diameter 0·3 – 0·5 mm) plastic tube attached to a specially designed instrument, by which the length of the protruding plastic tip could be controlled. The retina was penetrated from the vitreous side and the donor tissue was injected into the subretinal space. The cells survived in the host for at least 5 months, although the long-term survival rate tended to decrease. The transplanted cells matured and differentiated, forming an approximation of the layered, retinal structure with some anomalies (e.g. rosettes). The subretinal location offers an interesting and convenient way of studying the development of retinal cell transplants in rabbits. Large transplants can be produced, and the risk for failures due to erroneous vitreous placement is small.