Sources of axon terminals supplying the sinus gland of the fiddler crab, Uca pugilator
Description
Light and electron microscopic study of the medulla terminalis X-organ (MTXO), medulla terminalis (MT), and the sinus gland (SG) of the fiddler crab, Uca pugilator, showed the SG to be supplied by a distinct nerve tract which originated from 36-40 type 1 cells of the MTXO. At the base of the SG, the sinus gland nerve (SGN) contained 67 (SD = 5.5, n = 3) axons. As it originated from the X-organ, the SGN contained 41 (SD = 3.5, n = 6) axons. The SG, SGN, type 1 cells of the MTXO, and three or four cells near the SG in the MT neuropil were the only organs or cells to stain significantly with paraldehyde fuchsin In the neuropil adjacent to the MTXO, X-organ-sinus gland (XO-SG) tract axons contained NSG 50-200 nm in diameter. Near these axons, other axons contained smaller diameter (50-70 nm) granular vesicles which synapsed on neurosecretory axons, thus providing a source of central nervous system control of the XO-SG tract via aminergic neurotransmitters Treatment of medulla terminalis neuropil (MTN) with the modified chromaffin reaction (MC reaction) (a cytochemical technique to demonstrate aminergic vesicles) preserved granular vesicles (50-75 nm in diameter) with electron-dense reaction product. Other axons in the MTN adjacent to the X-organ contained uniformally dense granular vesicles 35-70 nm after fixation by the MC reaction. Approximately 5% of the granular vesicles were 90-100 nm in diameter MT tissue treated with reserpine and fixed for the demonstration of amines (MC reaction) contained axons with electron-dense reaction product. However, granular vesicles with reaction product were distorted or the quantity of reaction product in vesicles was reduced. Other axons showed an increase in clear synaptic vesicles along with a decrease in reaction product. Therefore because the reaction product in granular vesicles could be modified by reserpine treatment, the method of Tranzer and Richards (1976)--the modified chromaffin reaction--was selective for amines in the MT of U. pugilator