Abstract
We found that two inbred strains of Hatano rats bred selectively for shuttlebox avoidance responses, had different characteristics of responses to stress and adrenal function. The characteristics of male puberty, including preputial separation, sperm number, and plasma hormone levels during development, were investigated and compared between the two strains. Body weight in high-avoidance (HAA) rats was consistently heavier than that in low-avoidance (LAA) rats. Although the absolute testicular weight was heavier in HAA rats than in LAA rats during the juvenile period, after the peripubertal period the inverse finding was observed. Preputial separation occurred about 7 days earlier in HAA rats than in LAA rats. The testicular and epididymal sperm head number in HAA rats was greater than that in LAA rats during the peripubertal period, but there were no differences after sexual maturation. A steep increment of plasma gonadotropin levels was observed in HAA rats, and the levels were higher in HAA rats than in LAA rats during the peripubertal period. Plasma testosterone levels began to rise at a younger age in HAA rats than in LAA rats. It was concluded that HAA males sexually mature earlier than LAA males, and that these apparent strain differences in puberty are primarily dependent on gonadotropin levels during sexual maturation.
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