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ABSTRACT Neurofactors released from neurosecretory cells associated with the ganglia of the central nervous system are known to participate in the endocrine mediation of osmotic and ionic regulation in decapod Crustacea. The present study examines the effects of differential exposure (3, 6, 12, or 24 h) to high salinity media (HSM, sea water of 14, 21, or 28‰ salinity) on the ultrastructure of the anteromedial cells located within the protocerebral region of the supraesophagcal ganglion of Macrobrachium olfersii (Wiegmann), a euryhaline, fresh-water shrimp. Analysis of thin sections and freeze-fracture replicas reveals that the cells of the anteromedial group are typically neurosecretory in nature, exhibiting a large nucleus, a prominent, single nucleolus, well-developed, rough endoplasmic reticulum, numerous, large Golgi complexes, abundant mitochondria, and free and polyribosomes. In shrimps maintained in river water (0‰ salinity), this cellular machinery, specific for the production and packaging of polypeptides, does not appear to be activated, as indicated by the virtual absence of neurosecretory granules. After exposure of the shrimps to HSM, particularly to 21‰ salinity, for up to 6 h, there is a conspicuous increase in the number of dense-cored, neurosecretory granules of 72.4 ± 6.7 nm diameter, both in the cytoplasm and around the Golgi complexes of these cells. Multivesicular and multilamellar bodies also increase in number, indicating membrane recycling. In shrimps exposed to HSM for longer periods (12 h or more), the ultrastructure of the anteromedial cells is essentially similar to that of control shrimps maintained in fresh water. These data demonstrate that exposure to high salinity media activates a neurosecretory process in the anteromedial cells of the protocerebrum of M. olfersii. The release of these neurosecretory products may be involved in osmotic and ionic regulation in this fresh-water shrimp.

Affiliations: 1: Departamento de Biologia, FFCL, Universidade de São Paulo, Ribeirao Preto 14049 SP, Brasil.


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