Distribution of [3H]MK-801 binding in the turtle retina: an autoradiographical study

Frozen sections (15 microns) of the turtle (Pseudemys scripta elegans) retina were incubated in 1.6 nM [3H]MK-801. Autoradiograms were generated using dry autoradiographical techniques. A band of [3H]MK-801 labelling was observed in the outer plexiform layer and cells were occasionally labelled in the inner nuclear and ganglion cell layers. This pattern of labelling was enhanced by preincubation in 1.0 mM glycine but not affected by pre-incubation in 3.0 mM N-methyl-D-aspartate (NMDA). We did not observe labelling associated with somata of bipolar cells and photoreceptors, or in the inner plexiform layer. The distribution of label suggests that [3H]MK-801 was bound to horizontal cells and occasional ganglion and/or amacrine cells. We have previously reported that exposure of L-type horizontal cells to MK-801 irreversibly altered the intracellular response of the cell to exogenous NMDA. The present finding strongly suggests that these physiological effects of MK-801 were due to specific binding of MK-801 to the NMDA receptor complex on the horizontal cell membrane.