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Biomedical subjects

A F Dixson

Publications and source records attributed to A F Dixson.

64 records · Page 4Linked to original sources
PubMed1979

Cyclic changes in the circulating and urinary levels of ovarian steroids in the adult female owl monkey (Aotus trivirgatus).

Circulating levels of oestrone and progesterone were measured by radioimmunoassays in plasma samles from 5 female owl monkeys on 60 consecutive days. Both steroids exhibited cyclic fluctuations and based on nadir to nadir intervals the ovarian cycle was estimated to be 15.92 +/- 0.26 days. Levels of oestrone and pregnanediol-3 alpha-glucuronide were also measured in daily urine samples. The fluctuations of urinary steroids reflected those observed in plasma. Ketamine sedation had no effect on the length of the cycle. Peak values of plasma progesterone and oestrone were 250.48 +/- 11.37 and 3.59 +/- 0.066 ng/ml respectively. There was no clear hormonal distinction between the follicular and luteal phase of the cycle in these owl monkeys.

Animals↗
PubMed1978

Effects of ovariectomy and estradiol replacement therapy upon the sexual and aggressive behavior of the greater galago (Galago crassicaudatus crassicaudatus).

The effects of ovariectomy and estradiol treatment upon sexual and aggressive behavior were studied in a prosimian primate, the greater galago. Ovariectomized galagos were sexually unreceptive and frequently aggressive, but retained their sexual attractiveness to males. When females were treated with estradiol monobenzoate, however, their aggression and refusals of males' mounting attempts decreased markedly. Although males mounted these females, they usually failed to copulate, possibly because the females did not perform certain postural adjustments which assist males to intromit. Estradiol benzoate alone, even in large does, does not fully restore patterns of mating behavior in ovariectomized female greater galagos. These observations on a prosimian primate are in striking contrast to the results of similar work on Old World monkeys and chimpanzees.

Aggression↗
PubMed1977

Effects of ejaculation on levels of testosterone, cortisol, and luteinizing hormone in peripheral plasma of rhesus monkeys.

Plasma levels of testosterone (T), luteinizing hormone (LH), and cortisol were measured in 10 adult male rhesus monkeys before and shortly after coitus. Mean levels of T and LH did not increase significantly after coitus or in control (no ejaculation) tests, but cortisol levels did in both cases. In 10 different males, no significant change was found in the plasma levels of T after electroejaculation; but in control tests (electric current withheld), the mean level of T was significantly lower at 80 and 140 min, but not at 50 min, after the test. According to present evidence, the effect of ejaculation on T levels differs in primate and nonprimate species. The effects on T levels produced by living with sexually receptive female rhesus monkeys may differ from those produced by intimate but brief contact with them.

Animals↗
PubMed1976

Effects of testosterone on the sternal cutaneous glands and genitalia of the male greater galago (Galago crassicaudatus crassicaudatus).

Adult male and some female Galago crassicaudatus have a sparsely haired sternal gland which is used in scent marking displays. In both sexes, the skin in the sternal area contains many large sebaceous and apocrine glands. The sebaceous glands are largest in males and are dependent upon testicular androgens. Spines on the glans penis are also androgen dependent; their possible behavioural functions are discussed.

Animals↗
PubMed1975

Changes in social organization during the breeding season of wild talapoin monkeys.

Two adjacent troops of talapoin monkeys were studied near Mbalmayo, Cameroon, during a predicted 3-month breeding season. Mating continued for just over 2 months. One troop began to mate at least 2 weeks before the other, suggesting that, though climatic changes were probably important, precise timing was mediated through some intra-troop social facilitation effect. Before the breeding season, adult males and females lived in separate sub-groups. Males began to move into female sub-groups before there was any sign of the perineal swellings characteristic of receptive talapoin females. Copulation occurred only with females with medium or large swellings, except towards the end of the season. It is probable that the majority of females were monoestrous. At the height of the mating period, females joined mainly male sub-groups, leaving their infants with the mainly female groups which also included a few males. Copulations were observed in both these types of sub-groups. Consort behaviour was not observed, males frequently returning to all-male sub-groups immediately after ejaculation. Intersexual grooming was not characteristic of sexual interactions. At the end of the season, adults were seen more frequently in groups of their own sex or with juveniles only, and there was some indication that increased aggressiveness by newly pregnant females might be partly responsible for this separation.

Age Factors↗