NEUROPEPTIDE-Y-IMMUNOREACTIVE NEURONS IN THE RETINA OF 2 AUSTRALIAN LIZARDS

Wholemounts and sectioned retina from adults of two lizard species, Po gona vitticeps and Varanus gouldii, were studied by immunohistochemist ry for neuropeptide Y(NPY)-like immunoreactivity. In both species the morphology of two classes of amacrine cells (types A and B) were descr ibed. Cell somata were located mostly in the inner nuclear layer (INL) but were occasionally displaced into the ganglion cell layer (GCL). I n the Pogona retina, type A cells had large somata and dendritic arbor that branched in sublamina (S) 1 and 2/3 of the inner plexiform layer (IPL). Type B amacrine cells had smaller somata and dendritic arbor b ranching mostly in S5 of the IPL. In the Varanus retina, the levels of dendritic branching of types A and B amacrine cells in the IPL were s imilar to those in Pogona although branching in the middle of the IPL occurred at S3. NPY-immunoreactive cells with small somata and narrow to medium sized dendritic fields were predominant. Unclassified cells also displayed NPY-like immunoreactivity; however, their dendritic mor phology could not be determined due to the faint and inconsistent stai ning. In transverse retinal sections three bands of NPY-like immunorea ctivity were evident in the IPL of both species, to which the unclassi fied cells also contributed. In both species type A cells were most nu merous. Total NPY-immunoreactive cells were estimated to be 8,600 in P ogona and 32,860 in Varanus. In both species types A and B cells were non-uniformly distributed across the retina. The most apparent non-uni formity in distribution was observed in type A cells in Varanus. Peak cell density was found across the horizontal meridian of the retina fr om where cell density decreased towards the dorsal and ventral retinal margins. The results of this study provide evidence for the presence of NPY-immunoreactive amacrine cells in the lizard retina of which two types were morphologically characterized. Cross-species comparisons w ere also made among NPY-immunoreactive amacrine cells, and their possi ble function/s discussed.