Perisympathetic neurosecretion in the American cockroach: an electron microscopic study.

Abstract

An electron microscope study of the ultrastruotural changes due to dehydration and starvation in the cockroach abdominal perisympathetic organs was conduced. The main purpose of the study was to determine the meohanisms of release of the neurosecretory product stored in the perisympathetic organs. The perisympathetic organ's general profile reveals three types of axon endings oontaining three mutually exolusive types of neurosecretion. Type I contains large classical electron-dense granules. Type II contains small electron-dense granules and electron-translucent vesicles. Type III contains only intermediately sized electron-translucent vesicles. Stressing the cockroach by dehydration and starvation causes ultrastruotural changes in Type II terminals. During normal conditions and early stages of stress, the mechanism of neuroseoretory release is exocytosis. As stress continues, the preferred meohanism of neurosecretory release shifts to molecular dispersion. These conclusions are based on changes in the granule to vesiole ratio, ohanges in the frequenoy of release sites, paling of granules, and variations in the distribution of microvesioles. When nutrient reserves are apparently dissipated, autolytic aotivity begins and is denoted by the presence of multivesioular and multilamellar bodies. A secondary purpose of this study was to describe previously undesoribed phenomena in the fine struoture supportive of the neurohemal function of the perisympathetio organs. The perineurium, a barrier to large diffusing molecules, is missing. The glial struotural integrity is maintained by desmosomes and septate desmosomes which allOW neurohormone to pass freely through mesaxons and glial extracellular spaces. No tight junotions, whioh restrict the passage of large diffusable molecules, are found. The neurosecretory release struotures referred to as "synaptic sites" and omega-shaped profiles are present. The traoheal supply is sparse which would be expected in tissue where the main function 1s storage and release of neurohormone.