EXTRACELLULAR AND ASYMMETRIC FORMS OF ACETYLCHOLINESTERASE ARE EXPRESSED ON CHOLINERGIC AND NONCHOLINERGIC TERMINAL NEUROPIL OF THE DEVELOPING CHICK RETINA

Only two out of four major acetylcholinesterase (AChE) subbands in the inner plexiform layer (IPL) of vertebrate retinae correspond to sites of cholinergic synaptic transmission, as has been shown by the co-dis tribution of AChE and choline acetyltransferase (ChAT) staining. The f unction and molecular identity of AChE in non-cholinergic subbands is unknown. We have used immunocytochemical methods to compare the develo pment of asymmetric or extracellularly localized AChE with that of tot al AChE and ChAT in embryonic and adult chicken retinae. After injecti on of the AChE-specific monoclonal antibody 3D10 into the vitreous bod y of live embryos, a method that labels only extracellular AChE, five subbands in the IPL were labelled, whereas cell somata or their radial processes remained unstained. In contrast, the entire cell including processes was immunoreactive, when the 3D10 antibody was applied to pe rmeabilized cryosections, suggesting that in cell bodies the enzyme is exclusively localized intracellularly. Compared with total AChE, dete ction of asymmetric AChE with the monoclonal antibody 6B6 was delayed, first being seen in cells of the inner nuclear layer and finally appe aring on all subbands, reflecting more closely the course of synaptoge nesis. Thus, extracellular and asymmetric forms of AChE are predominan tly found on the terminal arbor neuropil of both cholinergic and nonch olinergic IPL subbands. These data show a differential distribution of extra- and intracellular AChE and suggest novel roles for the AChE in non-cholinergic IPL subbands.