ELECTRON-MICROSCOPIC DEMONSTRATION OF TYROSINE HYDROXYLASE-IMMUNOREACTIVE INTERPLEXIFORM CELLS IN THE LAMPREY RETINA

To clarify the controversies about the existence (or not) of dopaminer gic interplexiform cells in the lamprey retina, we have performed an i mmunocytochemical electron microscopic study of the retina of the rive r lamprey Lampetra fluviatilis, using anti-tyrosine hydroxylase antibo dy. We demonstrate the presence of immunoreactive processes in both in ner (IPL) and outer (OPL) plexiform layers. The external processes are in close contact with horizontal cell processes and photoreceptor ter minals in the OPL, but do not make classical synapses. Some of them ar e ensheathed within Muller cell cytoplasm. Thus, dopaminergic interple xiform cells do exist in Lampetra fluviatilis, but the absence of syna pses rather supports a paracrine action of dopamine in the outer retin a.