OCTOPAMINE IMMUNOREACTIVE NEURONS IN THE FUSED CENTRAL-NERVOUS-SYSTEMOF SPIDERS

Using antisera directed against octopamine (OA), we identified and map ped octopamine-immunoreactive (OA-ir) neurons and their projections in the fused, central ganglion complex of wandering spiders, Cupiennius salei. Labeled cell bodies are concentrated in the subesophageal gangl ion complex (SEG) where they are arranged serially in ventral, midline clusters. OA-ir processes from these cells project dorsally. Some neu rites end close to segmental septa; others merge into longitudinal tra cts connecting the neuromeres. Labeled collaterals leaving these tract s project into peripheral neuropil. In the brain, OA-ir somata were fo und only in the two cheliceral hemiganglia, where a cluster of 4-5 rel atively large cells (soma diameter 25 mum) lies next to a group of sma ll somata (diameter < 10 mum). Neurites originating from the large som ata descend into the SEG and merge into longitudinal tracts. The centr al body of the brain contains profuse ascending projections. Except fo r fine varicosities that are confined to the roots of nerves, we found no OA-ir fibers leaving the central nervous system (CNS). Within the CNS, however, OA-ir varicosities are concentrated in neuropil and near hemolymph spaces. This distribution suggests that OA acts as a neurot ransmitter and/or local neuromodulator at central synapses, while it i s also released into the hemolymph and presumably acts hormonally at p eripheral sites. Using high-pressure liquid chromatography measurement s, the hemolymph was in fact found to contain 12-40 nM of free octopam ine.