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T. D. McKinney

Division of Allied Health and Life Sciences, University of Texas, San Antonio, Texas 78285, U.S.A.

It has been suggested that sensitivity of the hypothalamic-pituitary unit to feedback inhibition by androgens may decline at the onset of puberty in the rat (Negro-Vilar, Ojeda & McCann, 1973), and that effects of gonadotrophins on testis weight may be greater before than after puberty (Swerdloff, Jacobs & Odell, 1972). In rats, the epithelium of the seminal vesicle is most sensitive to androgen stimulation between 40 and 60 days of age (Hooker, 1942), and the sensitivity of the seminal vesicles in neonatally castrated mice to androgens during adulthood is influenced by neonatal androgen treatment (Bronson & Desjardins, 1969; Bronson, Whitsett & Hamilton, 1972). The present studies were therefore undertaken to examine the effects of various androgen treatments between weaning and puberty on the growth of seminal vesicles of castrated mice.

The mice used were from

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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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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,