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HEIDI H. SWANSON

A single dose of an androgen or oestrogen at birth affects the development and functioning of the reproductive system of rats and mice (for review, see Harris, 1964). The present study shows that hamsters react in a similar way.

Complete litters of hamsters were injected s.c. on the 2nd day after birth with either 300 μg. testosterone propionate (TP) or 150 μg. oestradiol benzoate (OB) in 0·05 ml. arachis oil. Litters of controls received the vehicle only.

No abnormalities of the external genitalia were observed in animals of either sex. There were no vaginal manifestations of the oestrous cycle (Orsini, 1961) in any of the hormone-treated animals; vaginal smears showed persistent cornification.

After being subjected to a number of behavioural tests (Swanson, 1966a, b) the animals were killed, their reproductive organs and adrenals weighed (Table 1) and processed by routine methods for histological study.

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No significant sex differences in

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HEIDI H. SWANSON

SUMMARY

Unlike rats, the adult female hamster is heavier and longer than the male. The small size of the males appears to be dependent on the continuous presence of androgens, since castration before or after puberty results in an immediate acceleration of ponderal and linear growth, which is maintained until the female size is reached. The growth of females is not affected by gonadectomy.

Another sexual dimorphism which is reversed in hamsters in comparison with rats is adrenal weight; males have heavier adrenals than females. Castration reduces both absolute and relative adrenal weights of males to the levels of females. It is possible that the sex difference in growth is mediated through a differential secretion of adrenal hormones.

On the other hand, the sexual dimorphism in pituitary weights of hamsters is similar to rats; females have heavier pituitaries than males. This may reflect a sex difference in the pattern of gonadotrophin secretion, which may be similar in both species.

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A. P. PAYNE and H. H. SWANSON

There is considerable evidence that androgens facilitate the display of aggression in male vertebrates, while ovarian steroids do not (e.g. Guhl, 1961; Suchowsky, Pegrassi & Bonsignori, 1969). The golden hamster is unusual in that both sexes are aggressive, the female being dominant over the male (Dieterlen, 1959; Payne & Swanson, 1970). This study was undertaken to discover whether implanting ovarian tissue into castrated male hamsters influences their aggressive behaviour.

Twenty-eight adult male hamsters were castrated under ether anaesthesia. Simultaneously, in half of these a portion of ovarian tissue, freshly removed from an adult female, was implanted under the right kidney capsule. Six to 7 months later, both groups of castrated animals were tested by placing each animal in a neutral cage with a strange, intact male of the same body weight (± 3 g) for a 10-min observation period on 3 successive days. During each test the behaviour of both

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E. L. M. Bolwerk and H. H. Swanson

ABSTRACT

Oxytocin is released during parturition and may also play a role in maternal behaviour. Oxytocin, injected in the cerebral ventricles, has been reported to accelerate the onset of maternal behaviour in oestrogen-pretreated virgin Sprague—Dawley rats within 2 h of injection. This study was an attempt to replicate and extend these findings in Wistar rats. In the first experiment, 16 virgin females were ovariectomized and a cannula was placed into the cerebral ventricle. Forty-eight hours after a single injection of 24 μg oestradiol benzoate (OB), 400 ng oxytocin or saline were injected into the ventricle. In the second experiment three groups were observed: an untreated control group plus two ovariectomized and cannulated groups treated with OB in a regimen designed to mimic pregnancy. After 10 days of OB administration they received an injection of either saline or oxytocin (400 ng) into the ventricle. Immediately after this injection they were exposed to the pups and observations started. In both experiments no rat became maternal in the first 1·5 h after the intracerebroventricular injection. Oxytocin therefore did not induce a rapid onset of maternal responsiveness in oestrogen-pretreated Wistar rats.

J. Endocr. (1984) 101, 353–357

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A. P. PAYNE and H. H. SWANSON

SUMMARY

Male golden hamsters received either 300 μg testosterone propionate or oil on day 1 of life. As adults they were observed (i) when intact (ii) when castrated and (iii) when receiving 1 mg testosterone propionate per day in interactions with intact dioestrous females. Male controls which had received oil neonatally resembled normal untreated males in showing less aggressive behaviour than females. Castration and subsequent androgen administration did not affect aggression in the controls. Conversely, neonatally androgenized males showed comparable levels of aggression to the females with which they interacted. Castration reduced aggressive behaviour in these males, while subsequent androgen administration resulted in them showing significantly more aggression than females. In particular, when intact or receiving androgen replacement, neonatally androgenized males attacked and bit females, a behaviour seldom seen in normal males or in those given oil neonatally. Sexual investigation and following decreased in both groups of males after castration, and increased under androgen replacement. These changes were more pronounced in the neonatally androgenized males, indicating a greater behavioural responsiveness to androgens in this group. It is suggested that the behaviour of the normal male hamster is incompletely 'masculinized' during neonatal development, and the possible adaptive significance of this is discussed.

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E. van Leengoed, E. Kerker and H. H. Swanson

ABSTRACT

Endogenous oxytocin released into the brain at parturition may stimulate the onset of maternal behaviour. In this study an attempt was made to block spontaneous maternal behaviour following natural delivery in Wistar rats by the injection of an antagonist of oxytocin into the cerebral ventricles. The analogue antagonist, d(CH2)5-8-ornithine-vasotocin, was administered by injection into a chronically implanted cannula in the right lateral ventricle at hourly intervals, beginning immediately after the expulsion of the first pup. The antagonist did not interfere with the normal progress of parturition or birth-related behaviours.

After delivery of the last pup, mothers rested for 40 min in the test cage with the pups having been removed. Four pups and standard nesting material were then presented. Latency to pup carrying and duration of pup manipulation, nest building, and time spent on the nest with the pups, as well as duration of autogrooming and general activity were determined. Saline-injected controls started gathering the pups immediately and usually showed all elements of maternal behaviour within 10 min. Antagonist-treated mothers showed a marked delay in the onset of pup grouping and other maternal behaviours. At the end of 1 h, two out of six mothers had not yet picked up a single infant. Pups left overnight with their mothers were gathered into the nest and suckled, and no long-term effects of the antagonist were evident on retesting.

The effectiveness of oxytocin antagonist in suppressing the rapid onset of post-partum maternal behaviour supports the hypothesis that centrally released oxytocin is involved in this process. It is noteworthy that these effects were obtained in Wistar rats, a strain in which oxytocin has failed to accelerate responsiveness to pups in virgin females.

J. Endocr. (1987) 112, 275–282

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H. E. SWANSON and J. J. VAN DER WERFF TEN BOSCH

SUMMARY

A single s.c. injection of 0·5 mg. testosterone propionate to rats aged 2 or 5 days affected development and subsequent activity of the reproductive tract, and somatic growth. As adults, females displayed prolonged vaginal oestrus with lack of ovulation and with uteri smaller than in control-injected animals likewise killed when in oestrus; males had smaller testes, seminal vesicles and ventral prostates.

Body growth increased in treated females and decreased in males. Data on specific gravity and weights of heart, liver and kidneys, indicate that both the normal sex difference and the changes in weight due to early androgen administration are attributable to overall differences in size and not to specific differences in any particular body component. These effects of the steroid appear to be comparable to those noted after castration at an early age.

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M. Rand-Weaver, P. Swanson, H. Kawauchi and W. W. Dickhoff

ABSTRACT

Somatolactin (SL), a newly discovered fish pituitary protein belonging to the GH/prolactin family, was isolated from coho salmon (Oncorhynchus kisutch). Antibodies were raised to purified coho SL, and a homologous radioimmunoassay was developed and validated. The assay was specific for SL as indicated by the absence of cross-reactivity with coho salmon GH, gonadotrophins I and II and less than 0·2% cross-reaction to prolactin. Serial dilutions of plasma and pituitary extracts from Oncorhynchus species including coho salmon, chinook salmon and rainbow trout were parallel to the coho salmon SL standard curve. Displacement curves for dilutions of Atlantic salmon (Salmo salar) plasma, but not pituitary extract were parallel to the standards. Plasma levels of SL were measured in coho salmon throughout the final year of reproductive maturation. During the period of gonadal growth, plasma SL levels increased and were highly correlated to oestradiol levels in females and 11-ketotestosterone levels in males. Peak levels of SL were observed at the time of final maturation and spawning in both sexes. It is hypothesized that SL may regulate some physiological aspect of reproduction.

Journal of Endocrinology (1992) 133, 393–403