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J. N. PASLEY

Summary.

Reproductive organ weights and histology were examined in male and female voles, Microtus pennsylvanicus, which had received daily injections of metyrapone (100 mg/kg) or saline for 21 days from 30 days of age. In females receiving metyrapone, body weight and weights of ovaries and uteri were significantly decreased. In metyrapone-treated males, seminal vesicles were 70% lighter than in saline-injected controls. Histological examination of the reproductive organs confirmed inhibition of reproductive development and maturation in metyrapone-treated voles. The results with metyrapone lend further support to the hypothesis that increased pituitary-adrenal activity may impair reproductive function in rodents.

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J. N. PASLEY and T. D. McKINNEY

Summary.

Female voles, Microtus pennsylvanicus, were caged singly or in groups from weaning to 60 days of age, when they were paired for 72 hr with males. The incidence of coitus and ovulation during pairing was independent of prior housing conditions, but adrenal glands, ovaries and uteri were lighter and fewer CL were formed among previously grouped females. Stimuli associated with all-female groups, therefore, may inhibit coital induction of ovulation and development of reproductive organs in this species.

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T. D. McKINNEY and J. N. PASLEY

Division of Earth and Life Sciences, University of Texas, San Antonio, Texas 78285, and University of Arkansas Medical Center, Little Rock, Arkansas 72201, U.S.A.

(Received 16th April 1974)

Impaired reproductive function among adults and delayed sexual maturation in juveniles are associated with high population densities in a variety of small rodent species (Christian, 1968, 1971). Increased activity of the pituitary adrenocortical axis is postulated as a mechanism regulating population growth (Christian, Lloyd & Davis, 1965). Evidence linking increases in ACTH and plasma corticoids with gonadal dysfunction under laboratory conditions has been obtained for Mus musculus (Christian, 1964), Peromyscus leucopus (Pasley & Christian, 1972), Microtus pennsylvanicus (Pasley & Christian, 1971) and Rattus norvegicus (Desjardins & Ewing, 1971). The present study was initiated to examine the effects of ACTH on the reproductive organs of female northern grasshopper mice (Onychomys leucogaster), a predatory species characterized by low population densities under natural conditions (Egoscue,