In an effort to determine if sex differences exist in the morphologic characteristics of pyramidal cells and granule cells of the hippocampal formation and whether sex plays a role in determining thyroid hormone sensitivity of these neuronal populations, we used single-section Golgi impregnation to examine the effects of neonatal thyroid hormone administration on hippocampal cells from the brains of adult rats of both sexes. Quantitative analyses of control brains revealed sex differences in the number of primary dendrites and the number of spines on the apical dendritic shaft of CA3 pyramidal cells. These differences showed opposite trends; females possessed more primary dendrites, whereas males showed more apical excrescences. Neonatal treatment with thyroid hormone resulted in long-lasting and dramatic changes of the entire CA3 pyramidal cell. CA3 pyramidal cells from thyroid hormone-treated animals showed significantly larger cell body areas, greater numbers of dendritic branchpoints, and longer dendrites. In addition, CA3 pyramidal cells from thyroid hormone-treated animals showed changes in the morphological characteristics which were shown to be sexually dimorphic; treatment resulted in significantly greater numbers of both primary dendrites and apical excrescences. These treatment differences occurred in both sexes and were of equal magnitude, regardless of sex. On the other hand, no sex differences in the morphologic parameters examined were detected for pyramidal cells in the CA1 region. Moreover, neonatal thyroid hormone treatment did not affect the cell body area, dendritic branch points, or the length of dendrites of these cells. However, neonatal thyroid hormone treatment resulted in a significant increase in dendritic spine density of both the apical and basal dendritic trees. No significant sex differences or thyroid hormone effects were observed for granule cells of the dentate gyrus. These observations suggest that developing hippocampal pyramidal cells of the CA3 region are dramatically affected by excess thyroid hormone and that the resultant effects are persistent well into adulthood. Furthermore, sex differences exist in this neuronal population, but both sexes respond in an equal manner to thyroid hormone. Within the hippocampal formation, these effects appear to be somewhat specific to CA3 pyramidal cells as no sex differences were observed in CA1 pyramidal cells and granule cells.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Neuroscience|
|State||Published - 1990|
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