IMMUNOHISTOCHEMICAL DEMONSTRATION OF [D-ALA(2)]DELTORPHIN-I IN AMACRINE CELLS OF RAT RETINA

In an immunohistochemical study, a specific antiserum raised against [D-Ala(2)]deltorphin-I (DADTI), a highly selective ligand for delta opioid receptors, was used to demonstrate immunoreactive structures in the rat retina. [D-Ala(2)]Deltorphin-I immunoreactivity occurred in a subpopulation of the retinal amacrine cells situated in the inner nuclear layer. Their stained professes were mainly distributed in the sublaminae 1 and 3 of the inner plexiform layer. A few positive cells, probably displaced amacrine cells, were also seen in the ganglion cell layer. Double immunostaining revealed that 12.8% of DADTI-immunoreactive cells costored GABA and 27.7% costored neuropeptide Y, whereas only few DADTI-positive cells colocalized tyrosine hydroxylase (0.3%) and almost no other peptides. These findings suggest that some retinal amacrine cells possess DADTI-like molecule(s), possibly acting as neurotransmitter(s) or neuromodulator(s).