The neuroanatomical distribution and the physiological role of the biogenic amine octopamine was investigated in the prosomal central nervous system (CNS) of the horseshoe crab, Limulus polyphemus. Perfusion of octopamine onto the isolated CNS elicited the rhythmic feeding motor pattern in the entocoxal motor nerves which innervate the feeding musculature. The specific effects of octopamine on the CNS and the pharmacology of its action are described. The stimulation of the feeding motor program at concentrations comparable to that of octopamine by the octopamine agonists NC-5, NC-7, and NC-13, the diterpene adenylate cyclase activator forskolin and the cyclic AMP analogue, 8-bromo cyclic AMP indicated that octopamine's effects may be mediated by a second messenger. The putative octopamine antagonists tested were ineffective or weakly blocked the effects of octopamine. The distribution and localization of octopamine in the prosomal CNS was determined by light and electron microscopic immunocytochemistry. Sixteen discrete clusters of octopamine-like immunoreactive (Oct-LIR) neurons were found in the circumesophageal ring (CER) of fused thoracic ganglia. The distribution of these immunoreactive cells are described. The immunoreactive somata are 40 to 100 $\mu$m in size and are found in clusters of 12-24 cells. There is extensive distribution of Oct-LIR nerve fibers in Limulus; the wide distribution of Oct-LIR provides an anatomical basis for the several effects of octopamine in Limulus. The subcellular localization of octopamine in Oct-LIR terminals in the CER was determined by postembedding immunoelectron microscopy with a 5 nm immunogold label. Labelled terminals are morphologically unique; they contain large, dense-core granules of a distinct shape, typically cylindrical with an indentation or depression in one end. These large granules are typically 100-150 nm in diameter and 150-400 nm in length. The dense labelling of these unusual granules with the gold particles indicates that octopamine is sequestered in or associated with these granules.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-4552 |
| Date | 01 January 1989 |
| Creators | Lee, Helen M |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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