IMMUNOHISTOCHEMICAL LOCALIZATION OF A LIGAND-BINDING AND A STRUCTURALSUBUNIT OF NICOTINIC ACETYLCHOLINE-RECEPTORS IN THE CENTRAL-NERVOUS-SYSTEM OF DROSOPHILA-MELANOGASTER

The distribution of two subunits of nicotinic acetylcholine receptors in the developing and the differentiated central nervous system of Dro sophila melanogaster was studied. With subunit-specific antibodies rai sed against the ligand-binding alpha-like subunit ALS and the putative non-ligand-binding subunit ARD, we find both ALS-like and ARD-like im munoreactivity widely distributed in most neuropiles of the optic lobe s, the protocerebrum, the deutocerebrum and the thoracic ganglion of t he adult fly. With a single exception, namely in the lamina of the vis ual system, the antigens recognized by the two types of antibodies are colocalized. This observation is consistent with previous immunopreci pitation data indicating that the ALS and ARD proteins are integral co mponents of the same hetero-oligomeric receptor that binds the nicotin ic antagonist alpha-bungarotoxin with high affinity. During embryonic development A-RD-like immunoreactivity is first detectable in almost-e qual-to 10 hour old embryos. Both subunits are consistently detected i n the central nervous system of the late embryo, the three larval stag es, and all prepupal and pupal stages. During metamorphosis the optic stalk is transiently immunoreactive with anti-ARD, but not with anti-A LS antiserum. Although in larvae and adults, immunoreactivity with bot h types of antibodies is most abundant in synaptic regions, in embryos and pupae strong staining of cortical cell body layers is observed, i n particular with anti-ARD antisera. As these developmental periods co incide with strong accumulation of ARD transcripts, the cell body stai ning may reflect newly synthesized and assembled receptors, while the functional ARD- and ALS-containing receptor may be destined for synaps es. (C) 1993 Wiley-Liss, Inc.