Some aspects of the role of the central nervous system in controlling the reproductive cycle of the female amphipod Gammarus setosus Dementieva

MacPherson, Brian Roger (1974) Some aspects of the role of the central nervous system in controlling the reproductive cycle of the female amphipod Gammarus setosus Dementieva. Masters thesis, Memorial University of Newfoundland.

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Abstract

The various neuropiles and cellular glomeruli of the brain, suboesophageal ganglion and ventral ganglion chain were identified in Gammarus setosus Dementieva. Two types of neurosecretory cells, A and B, were present in the brain glomeruli, two in the glomeruli of the suboesophageal ganglion, A and A', and four in the glomeruli of the ventral ganglia, A, A', B and C, all based on perikaryon size. There were two types of neurosecretory granules in the cells of the brain glomeruli, type I were small, dense spheres 98-160 nm in diameter found only in the A cells, while the larger type II vesicles ranged from 195-815 nm, resembled mitochondria and were found in both A and B cells. The type I granules were Golgi-formed but the origin of the type II vesicles is uncertain, the possibilities being transformation of Golgi-formed multivesicular bodies (MVB), or mitochondrial fission and alteration of conformation. Accessory cephalic structures present in the anterior head region were the sinus gland, paired statocysts and a dorsal, medial, unpaired frontal organ. Production and release of neurosecretory material (NSM), was observed in the frontal organ neurons and they were divided into two types, I and II, based on the size of their secretory granules. Those of type I ranged from 1000-4500 nm in diameter, similar in morphology to the type II vesicles of the brain but larger, while the type II vesicles of the frontal organ neurons were 300-900 nm and Golgi-formed. The frontal organ appears to be a neurohemal organ with the NSM liberated through rupture of the cell membrane. The sinus gland contained variable amounts of NSM but release was not observed and no X organ was found. Morphological alteration of the follicular epithelium was noted before vitellogenesis begins and the hepatopancreas was indicated as a probable source of the vitellogenic materials. Decrease in photoperiod stimulates vitellogenesis in late summer and long photoperiods (14 hours light) prolong the ovarian cycle, while shorter ones (12 and 8 hours light) accelerate it respectively. Complete darkness resulted in successive cycles after resorption of the oocytes. The type I frontal organ neurons appear to release an ovary-inhibiting hormone while the role of the type II neurons is unknown. The secretions of the neurosecretory cells of the brain and ganglia also have an uncertain effect upon reproduction with evidence to support either a stimulatory or inhibitory effect dependent upon the type of release exhibited.

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