Octopamine release at two points along lobster nerve trunks.

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Abstract
Nerve cells in the proximal regions of 2nd thoracic roots in lobsters were injected with fluorescent dye Procion Yellow. Examination of the roots revealed an elaborate array of cell branches in a superficial layer of the root in the vicinity of the cell bodies. Large varicosities, up to 10 .mu.m in diameter, were seen lined up along fine nerve branches. In these same regions, EM examination showed the presence of large profiles filled with 0.1-0.2 .mu.m dense cored granules, having the appearance of nerve endings. These profiles probably corresponded to the varicosities seen in the Procion Yellow injections. The dense cored granules within the endings had a crystalline substructure. All the endings were found within 7 .mu.m of the surface of the root and no obvious physiological target tissue exists in their surroundings. Endings were not traced directly to root cell bodies. Granules of similar dimensions to those seen in endings were found in cell bodies, axon-hillock regions and numerous axonal profiles in the superficial root regions near cell bodies. The morphological studies suggested that the root neurons had the typical appearance of neurosecretory cells. Octopamine pools in cell body regions of 2nd thoracic roots could be isotopically labeled by incubation with either [3H]tyramine or [3H]-tyrosine. After labeling, pulsing with 100 mM K+ caused an increase in the rate of release of radioactive material. Upon return to normal media background rates of release were re-established. The enhanced efflux had the properties: repeated pulses of K+ released less radioactive material each time; a prolonged K+ pulse produced first a peak of release, then a decline to a plateau, and the plateau level of release was maintained for the duration of the K pulse; release was dependent on the presence of Ca2+ in the bathing fluid and 40 mM CoI+ prevented release; release was selective for octopamine. With tyrosine as a presursor compound, as much radioactive tyrosine as octopamine was found in tissues after incubation, yet pulsing with K+ caused an enhanced efflux only of octopamine from preparations. Release of octopamine was demonstrated from pericardial organs near the ends of lateral branches of the roots and the properties of the release were identical to those seen with cell body regions. Physiological studies in which root cells were antidromically activated while recording from cell bodies, suggested that the distal endings of at least some of the root cells were at the pericardial organs. Root cell neurons were probably neurosecretory cells capable of releasing octopamine at 2 points: 1 near cell bodies, the other at the pericardial organs near the distal ends of the roots. Release near cell bodies was into hemolymph on its way to the gills, while release at pericardial organs is into hemolymph that has just passed through the gills on its way to the pericardial sinus surrounding the heart. The significance of the two points of release of octopamine is not known at the present time.