Biomedical subjects
Publications and source records attributed to A F Dixson.
Proceptivity in the common marmoset consisted of brief periods when females remained with body and limbs immobile (IM) or crouched, and then stared, lipsmacked and tongue-flicked at males. Treatment of ovariectomized females with oestradiol activated all these proceptive displays but did not influence the combinations in which they occurred during IM periods.
Repeated measurements of plasma testosterone (T) were made in 56 male marmosets from the day of birth until 300 days of age and in 44 adults (greater than 3 years). The resulting profile of plasma T during postnatal development shows higher levels during infancy (1-90 days) followed by a nadir between 100 and 170 days and then a progressive rise in T during puberty. Although T levels of up to 21 ng/ml were measured in infant males, mean levels (+/- SEM) were 5.4 +/- 0.6 ng/ml (days 1-10), declining gradually to 1.7 +/- 0.1 ng/ml (days 100-110). No increase in mean T levels between 15 and 100 days was identified, and the onset of puberty was earlier in some males than measured previously in this species.
The sexual behaviour of eight pairs of marmosets was observed during blocks of 30 minute tests after the ovariectomized female partners were treated with physiological doses of testosterone, oestradiol and progesterone. The effects of an intra-vaginal progesterone treatment were also investigated. Pre-ovulatory levels of oestradiol significantly increased the females' proceptive and receptive tongue-flicking displays and reduced the percentage of mounts refused. Mid-luteal levels of progesterone, by comparison, virtually abolished proceptive and receptive tongue-flicking and significantly increased mount refusals. Testosterone treatment was without effect. Vaginal application of progesterone unlike subcutaneous implantation of the hormone did not significantly alter the females' sexual behaviour. These results indicate that central actions of oestradiol and progesterone upon proceptivity and receptivity may occur in this primate, although further research using intra-cranial implants of these steroids is required to test this hypothesis.
Luteinizing hormone releasing hormone (LHRH) administered to ovariectomized marmosets treated with a low dose of 17 beta-oestradiol significantly enhanced proceptivity within 2 h. Without oestradiol priming LHRH treatment did not produce this effect. The dose of LHRH given did not significantly alter plasma levels of cortisol or progesterone. The behavioural effect of this treatment is therefore likely to have been mediated via a direct central action rather than indirectly through stimulating adrenocortical steroid secretion. These results provide the first demonstration that LHRH can potentiate the proceptive behaviour of a female primate.
Plasma levels of vasoactive intestinal polypeptide (VIP) in the corpora cavernosa penis and dorsal penile veins greatly exceeded those measured in the limb or caudal veins during anaesthesia in various mammals (Bennett's wallaby, Barbary sheep, cheetah, puma, sooty mangabey, pigtail macaque and chimpanzee). Tactile stimulation of the penis immediately before or during collection of blood samples resulted in an increase. In the wallaby, VIP levels (mean +/- S.E.M.) in blood samples collected from the flaccid penis in the absence of tactile stimulation were very low (0.6 +/- 0.5 pmol/l). A 36-fold increase in VIP occurred after manual extension of the flaccid penis (24.8 +/- 3.2 pmol/l) or during manually stimulated erections (25.1 +/- 1.7 pmol/l). Electrical stimulation of erection produced no significant increase in VIP levels (2.3 +/- 0.9 pmol/l) unless accompanied by tactile stimulation (17.5 +/- 1.4 pmol/l). These studies provide the first demonstration that sensory feedback from the penis plays an important role in regulating vasoactive intestinal polypeptidergic activity. Since VIP is a potent vasodilator its release due to tactile stimuli during copulation may play a role in the maintenance of penile erection.
Unlike in other non-human primates, ovariectomy of the female marmoset did not alter heterosexual interactions. Proceptive behaviour bouts retained the same cyclicity, duration and frequency within tests as during the ovarian cycle. Significant rises in plasma levels of cortisol, progesterone, oestrone and testosterone were found during these proceptive behaviour bouts and in cortisol, progesterone and oestrone at their onset. Results suggest a role for adrenocortical steroids in both maintaining female sexuality and regulating its cyclicity during ovarian cycles in this primate.
Hyperprolactinaemia was induced in castrated, testosterone-treated male rats using ectopic pituitary grafts under the kidney capsules. After 6 weeks the absolute refractory period of stria terminalis neurones in these animals did not differ significantly from long-term castrated rats (mean = 1.72 vs 1.69 ms) in spite of the presence of normal testosterone concentrations. Gonadally intact animals, and sham-operated castrated animals treated with testosterone, showed by comparison the characteristic significantly shorter absolute refractory period normally associated with testosterone stimulation (mean = 1.15 and 1.08 ms respectively). These results provide the first demonstration that hyperprolactinaemia can abolish central sensitivity to testosterone.
A vomeronasal organ and patent nasopalatine ducts were found in adult specimens of Aotus trivirgatus, Arctocebus calabarensis, Ateles geoffroyi and Saguinus fuscicollis. The vomeronasal complex appeared to be functional except in Ateles. However, the relative size of the organ in the Platyrrhini is much reduced compared to that in prosimians. The possible role of the organ in mediating neuroendocrine processes in primates is discussed.
The sexual behaviour of 7 pairs of marmosets was observed during 30 minute tests for 44-68 days and blood samples were collected from females for measurement of plasma progesterone, testosterone and oestrone. Copulations occurred throughout the ovarian cycle of 24-30 days. Females used a "tongue-flicking" display both as an invitational behaviour (proceptive tongue-flicks) and during copulation (receptive tongue-flicks) most frequently during the peri-ovulatory period. Frequencies of proceptivity were correlated positively with high mean levels of testosterone and oestrone during the cycle and with a short follicular phase. Males showed significant increases in tongue-flicks, mounts and ejaculations during the peri-ovulatory phase, together with a shortened post-ejaculatory interval and increased duration of penile erection after ejaculation. A retrospective analysis showed that these changes in the males' behaviour occurred only during tests where females were proceptive and not during other tests in the peri-ovulatory period. Females refused significantly more of the males' mounting attempts during the luteal phase and a corresponding reduction in mount frequency occurred at this time. Grooming, scent-marking, olfactory inspections and some other behaviours did not alter significantly in either sex during the ovarian cycle.
Adult owl monkeys behaved aggressively when paired with unfamiliar members of the same sex. Males showed the greatest aggressive responses. When plugs containing bismuth iodoform paste were inserted into the nasal passages of male owl monkeys they fought less readily and showed less contact aggression. Although intermale aggression was not abolished anosmic males spent longer in proximity and showed an increase in olfactory inspections. Control experiments confirmed that the technique used to induce anosmia had blocked responsiveness to conspecific odours and that decreases in aggression were not due to discomfort or non-specific behavioral effects.
The relationship between hormone levels, plasma catecholamines, and mood disturbances has been investigated in 44 patients during days 2 to 5 of the immediate post-partum period. Fifty-two per cent of the mothers showed periods of emotional lability although there was no significant correlation between plasma concentrations of FSH, prolactin, oestrone, oestradiol, cortisol, or progesterone and the incidence of post-partum blues. In contrast there was a significant reduction of circulating catecholamines which correlated with mood disturbances. Women who experienced only a single day of post-partum blues had significantly lower levels of noradrenaline and adrenaline on that day compared with preceding or subsequent days.
We have shown previously that pregnant mare serum gonadotrophin (PMSG) induces ovulation only in rats weighing over 60 g on the day of injection. The under-60 g rats do not ovulate although they secrete a preovulatory surge of a pleiomorphic form of LH. Presumably this pleiomorph is inactive. Comparisons were made of plasma hormone concentrations in rats treated with PMSG that weighed over and under 60 g. The measurements were made on samples taken between 13.00 and 22.00 h on the day of the expected preovulatory LH surge. Prolactin and corticosterone levels were lower in the lighter group compared with the heavier group. A midday pulse of GH detected in the over-60 g animals did not occur in the under-60 g group. Levels of ACTH were slightly higher in the under-60 g rats and together with the low corticosterone concentrations indicate adrenal insensitivity. Oestradiol, progesterone and TSH concentrations were the same in the two groups. Since progesterone secretion is under LH control, the 'inactive' pleiomorphic form of LH must have steroidogenic activity. There was an indication that the under-60 g rats also secreted a pleiomorphic form of FSH. Reports in the literature indicate that prolactin, corticosterone and GH have a positive modulatory influence on natural puberty. They may also influence precocious puberty induced by PMSG, since in the unresponsive under-60 g rat plasma levels of these three hormones were low. Perhaps the release of one or more of these hormones is dependent upon the physical maturity of the animal as represented by body weight.
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The distribution of monoamine neurons in the brains of ten common marmosets (Callithrix jacchus) was examined by means of the Falck-Hillarp formaldehyde histofluorescence technique. Large populations of catecholamine and indoleamine neurons were found throughout the brain stem. Catecholamine cell bodies corresponded essentially to th noradrenaline and dopamine groups defined as A1-A7 and A8-A14, respectively. In contrast to Old World primate species, however, the noradrenaline cell populations (particularly the pontine coeruleal A6 group) were less numerous. Ascending catecholamine fibre pathways were not observed within the medulla or pons, although numerous axons were found near the mesodiencephalic border. These were fine and smooth in appearance in contrast to those of other species and this finding may represent a significant morphological difference. The catecholamine terminal innervation of the diencephalon was modest in the marmoset and was less dense than in other primates. In contrast, limbic areas and the striatum contained very large numbers of terminals. Indoleamine cell bodies, equivalent to the serotonin groups defined as B1-B9, were also observed. The most rostral cell populations (B7-9) were large. In addition, pontine and medullary indoleamine neurons extended laterally through the tegmentum as noted in other primates, such that they often adjacent to catecholamine neurons. A prominent bundle of indoleamine axons was observed in the mesencephalon and corresponded to a fibre pathway seen in rodents and other primates. No terminal varicosities were noted.
Six adult male owl monkeys were kept in conditions of controlled lighting (12 h white light alternating with 12 h of very dim reg light) and blood samples were taken at different times of day, once a week, for 10 weeks. Plasma testosterone levels correlated with phases of the lighting cycle: highest levels (mean +/- s.e.m.) occurred in the light (24.8 +/- 5.3 ng/ml) and lowest levels during periods of darkness (4.7 +/- 1.2 ng/ml). The owl monkey is nocturnal, and these daily changes in circulating testosterone are the reverse of those reported for some diurnal primates, although the time of the high and low levels in relation to activity patterns is similar.
The post mortem in an adult male gorilla (Gorilla gorilla gorilla) aged approximately 33 years revealed very small testes, and the cut surface of the left testis appeared nodular. Microscopic examination showed a marked atrophy of seminiferous tubules and fibrosis together with a diffuse interstitial cell hyperplasia. Two interstitial cell adenomas were identified in the left testis.
Oesterone, oestradiol-17 beta, progesterone and testosterone were measured by radioimmunoassay in daily plasma samples throughout the ovarian cycle in 4 female owl monkeys. Clearly defined peaks of oestradiol-17 beta occurred at intervals of 15.5 +/- 0.56 days and confirmed the length of the cycle reported previously. Progesterone rose on the day on the day of the oestradiol-17 beta to reach a maximum 4--6 days later, thereafter decreasing gradually to low levels before the onset of the next cycle. On the basis of these data the follicular and luteal phases were estimated to be 6 and 10 days respectively. Osterone and testosterone peaks preceded that of progesterone by 24 and remained elevated throughout the luteal phase. Plasma concentrations of all steroids were markedly higher than for other primate species. Vaginal cytology was considered unsuitable as an indicator of the stage of the ovarian cycle.
A single, timed mating indicated a gestation period of 133 days for Aotus trivirgatus griseimembra. This figure is confirmed by approximate correspondence with minimum inter-birth intervals, results from radioimmunoassay of urinary oestrogens during pregnancy, and general agreement with a logarithmic plot of gestation period against body weight for simian primates. Birth data indicate that owl monkey females in present colonies in captivity breed throughout the year and will, on average, produce 3 infants every 2 years. There is no evidence of a characteristic post-partum oestrus.