A possible inhibitory feedback control, by testicular sterooids, of gonadotropin release from the adenohypophysis was tested in adult breeding Japanese quail. Implantation of small pellets of testosterone propionate:charcoal (1:1) into medial or paramedial position in the ventral hypothalamus or adenohypophysis results in (a) testicular regression, (b) regression of the cloacal gland, and (c) a very low level of assayable pituitary gonadotropins. Implants located more anteriorly in the ventral hypothalamus in general result in a greater reduction of testicular weight and diameter of the seminiferous tubules than implants located in more posterior regions of the ventral hypothalamus; implants in both regions are equally effective in causing regression of the cloacal gland. That these effects are specific actions of testosterone, not indirect effects of a physical lesion in the ventral hypothalamus is supported by the findings that (a) implants of cholesterol:charcoal (1:1) in similar locations in the ventral infundibular region have no demonstrable effect on the testes or the cloacal gland, and (b) implants of testosterone propionate:charcoal or glass capillaries filled with crystalline testosterone propionate have only a temporary inhibitory effect on testicular and cloacal gland function; the activities of both these organs return (within 34 days) to near-normal levels despite the persistence of the implant in the brain. Implants in more dorsal regions of the infundibular nuclear complex, in the preoptic and/or supraoptic regions of the hypothalamus, in other regions of the hypothalamus, in the epithalamus and in the forebrain have no effect on testicular weight or functional activity of the cloacal gland; implants of testosterone cause in every bird, a slight reduction in diameter of the seminiferous tubules and in assayable pituitary gonadotropins. © 1972.
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