In JoVE (1)

Other Publications (2)

Articles by Ari L. Mendell in JoVE

Other articles by Ari L. Mendell on PubMed

Orchidectomy Does Not Significantly Affect Spine Synapse Density in the CA3 Hippocampal Subfield in St. Kitts Vervet Monkeys (Chlorocebus Aethiops Sabaeus)

Neuroscience Letters. Jan, 2014  |  Pubmed ID: 24269983

Gonadal hormones induce significant changes in cognitive function, associated with alterations in the structure of the hippocampus. We have previously shown that androgens increase the number of spine synapses in the CA1 stratum radiatum of the monkey hippocampus. Recent evidence, however, suggests that loss of testicular hormone production may have variable effects on neuroplasticity in different regions of the hippocampus. To test this hypothesis, we examined the effects of orchidectomy in the dentate gyrus and CA3 subfield of the hippocampus in male St. Kitts vervet monkeys (Chlorocebus aethiops sabaeus). Spine synapse density was significantly reduced (39%) after orchidectomy in the dentate gyrus, consistent with previously published reports in CA1 (40%). However, in CA3 orchidectomy induced a much smaller (22%) reduction in synapse density, which did not reach the limits of statistical significance. These results suggest that orchidectomy exerts heterogeneous effects on hippocampal spine synapse density, the CA3 subfield being relatively spared compared to CA1 and the dentate gyrus. This heterogeneity may contribute to the mixed functional responses observed in males following loss of testicular hormone secretions.

Expansion of Mossy Fibers and CA3 Apical Dendritic Length Accompanies the Fall in Dendritic Spine Density After Gonadectomy in Male, but Not Female, Rats

Brain Structure & Function. Jan, 2017  |  Pubmed ID: 27283589

Androgen loss is an important clinical concern because of its cognitive and behavioral effects. Changes in androgen levels are also suspected to contribute to neurological disease. However, the available data on the effects of androgen deprivation in areas of the brain that are central to cognition, like the hippocampus, are mixed. In this study, morphological analysis of pyramidal cells was used to investigate if structural changes could potentially contribute to the mixed cognitive effects that have been observed after androgen loss in males. Male Sprague-Dawley rats were orchidectomized or sham-operated. Two months later, their brains were Golgi-impregnated for morphological analysis. Morphological endpoints were studied in areas CA3 and CA1, with comparisons to females either intact or 2 months after ovariectomy. CA3 pyramidal neurons of orchidectomized rats exhibited marked increases in apical dendritic arborization. There were increases in mossy fiber afferent density in area CA3, as well as robust enhancements to dendritic structure in area CA3 of orchidectomized males, but not in CA1. Remarkably, apical dendritic length of CA3 pyramidal cells increased, while spine density declined. By contrast, in females overall dendritic structure was minimally affected by ovariectomy, while dendritic spine density was greatly reduced. Sex differences and subfield-specific effects of gonadal hormone deprivation on the hippocampal circuitry may help explain the different behavioral effects reported in males and females after gonadectomy, or other conditions associated with declining gonadal hormone secretion.

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