230
WILLIAM C. YOUNG
nest-building behavior might be attributed to a hormonal change induced by stimuli coming from the young, but he excludes this possibility
by recalling the finding of Leblond and Nelson (53, 54) this this behavior was induced in hypophysectomized female and male adults caged
with young mice. Lehrman (7) adds that stimuli from the young and the
effect of progesterone may perhaps be complementary mechanisms for
maintaining nest building during the period when such behavior is
adaptive.
Retrieving of the young is characteristic of many mammals; being
measurable, it is a type of parental behavior which has been studied by
investigators interested in the relationship of the hormones to parental
behavior. Domestic mice, rats, cats, golden hamsters, and the vole
Microtus arvallis have been used. Again the data are confused, chaotic,
and in many cases contradictory. Unanimity exists that the tendency to
retrieve young is most intense just after parturition and continues during
much of the lactation period (368^371), but it has also been reported
that often voles and about 20% of domestic rats retrieve young, regardless
of their reproductive state or sex (50-52, 371-373). Prolactin and pituitary LH given to intact or gonadectomized female and male rats increased
retrieving behavior substantially (49, 50, 373). Prolactin and the luteinizing hormone that was used were more effective in gonadectomized
than in intact animals (50). Cats normally retrieve their litters; Allan
and Wiles (374) reported that nine cats hypophysectomized toward the
end of pregnancy gave birth to normal young, but did not "take care of
them" except in one instance for 2 days. In experiments with rats hypophysectomy did not altogether prevent (50) or interfere (53, 375)
with retrieving behavior. Retrieving behavior does not depend on lactation in the mouse and hamster (52, 376). Retrieving was reported to
have been suppressed by estrone (50, 373, 377), although not in hypophysectomized animals (373). Male mice, on the other hand, displayed retrieving behavior following treatment with estrogen (51). The
retrieval of pups by intact female rats following injections of progesterone (50) was not seen by Lott (378) in female rats and hamsters.
Motivation of females to nurse their young seems to have been assumed during the early studies of prolactin and mating behavior in the
rat (48-50) and to be implied in studies showing that in domestic rats
and rabbits the prolactin content of the pituitary gland is increased by
suckling (379, 380). Again, though, there are difficulties to be resolved.
Collip et al. (375) hypophysectomized lactating rats and found that
although the mammary gland regressed, nursing and other maternal
behavior were not impaired and the young continued to suckle until
they died.
WILLIAM C. YOUNG
nest-building behavior might be attributed to a hormonal change induced by stimuli coming from the young, but he excludes this possibility
by recalling the finding of Leblond and Nelson (53, 54) this this behavior was induced in hypophysectomized female and male adults caged
with young mice. Lehrman (7) adds that stimuli from the young and the
effect of progesterone may perhaps be complementary mechanisms for
maintaining nest building during the period when such behavior is
adaptive.
Retrieving of the young is characteristic of many mammals; being
measurable, it is a type of parental behavior which has been studied by
investigators interested in the relationship of the hormones to parental
behavior. Domestic mice, rats, cats, golden hamsters, and the vole
Microtus arvallis have been used. Again the data are confused, chaotic,
and in many cases contradictory. Unanimity exists that the tendency to
retrieve young is most intense just after parturition and continues during
much of the lactation period (368^371), but it has also been reported
that often voles and about 20% of domestic rats retrieve young, regardless
of their reproductive state or sex (50-52, 371-373). Prolactin and pituitary LH given to intact or gonadectomized female and male rats increased
retrieving behavior substantially (49, 50, 373). Prolactin and the luteinizing hormone that was used were more effective in gonadectomized
than in intact animals (50). Cats normally retrieve their litters; Allan
and Wiles (374) reported that nine cats hypophysectomized toward the
end of pregnancy gave birth to normal young, but did not "take care of
them" except in one instance for 2 days. In experiments with rats hypophysectomy did not altogether prevent (50) or interfere (53, 375)
with retrieving behavior. Retrieving behavior does not depend on lactation in the mouse and hamster (52, 376). Retrieving was reported to
have been suppressed by estrone (50, 373, 377), although not in hypophysectomized animals (373). Male mice, on the other hand, displayed retrieving behavior following treatment with estrogen (51). The
retrieval of pups by intact female rats following injections of progesterone (50) was not seen by Lott (378) in female rats and hamsters.
Motivation of females to nurse their young seems to have been assumed during the early studies of prolactin and mating behavior in the
rat (48-50) and to be implied in studies showing that in domestic rats
and rabbits the prolactin content of the pituitary gland is increased by
suckling (379, 380). Again, though, there are difficulties to be resolved.
Collip et al. (375) hypophysectomized lactating rats and found that
although the mammary gland regressed, nursing and other maternal
behavior were not impaired and the young continued to suckle until
they died.