Human exposure to putative pheromones and changes in aspects of social behaviour.

Student volunteers (38 of each sex) were exposed unknowingly overnight to the vapour of pheromonally active substances and compared with controls. The substances were either 5 alpha-16-androsten-3 alpha-ol (androstenol, occurring in human underarm sweat, and known to be pheromonally active in pig and man), or a mixture of short-chain fatty acids (occurring in human vaginal fluid, and known to be sexually attractive to the male rhesus monkey). The following morning, the subjects provided information about their social exchanges since rising, by recording on a standardized test diagram the number, depth, duration and direction of initiation, of all verbal exchanges with other individuals. Irrespective of treatment, males returned significantly higher scores than did females for all exchanges and also for some exchanges initiated by other males. Neither exposure to androstenol nor to the fatty acids had any significant effects on any of the scores of males interacting with either sex, nor on any scores of females with other females. However, exposure of females to androstenol, but not to the fatty acids, resulted in significantly higher scores of exchanges with males, in terms of all parameters for all exchanges. Findings are considered in relation to the origin and maintenance across species of pheromonal communication: evolutionary conservation is seen in terms of the utilization of substances that have provided the means of controlling the social milieu.

Effects of stock differences in the acceleration of puberty in female mice.

Newly born TO strain female mice were exposed daily to the urine from male albino mice of the same and CFLP strains, from feral mice carrying Robertsonian translocation chromosomes and to water as a control condition. At 21 days of age, when exposure was discontinued, there were differences in body weight between treatments which were not present when adult. Exposure to urine from mice with Robertsonian translocations did not accelerate puberty and the interval between vaginal opening and first oestrus was longer (4.2 days) than in mice exposed to the urine from the albino strains (1.8 days). Mice exposed to the urine from the Robertsonian stock were in dioestrus more often than those exposed to the urine from laboratory strains. The Robertsonian mice also differed in their behaviour in an open arena in that they passed fewer faecal pellets than those exposed to the urine from the albino mice. The water control mice defecated the least frequently. The mice exposed to the Robertsonian urine were less active than the laboratory strains but the differences did not reach an acceptable level (P less than 0.06) of significance.

Ano-genital distance as a factor in determining puberty acceleration in mice.

The daily exposure of newly born female mice to the urine of lactating mice with a small ano-genital distance accelerated the onset of first oestrus while the urine from donors with a large ano-genital distance was without effect in advancing puberty. The rate of growth of the mice exposed to the urine of lactating mothers was greater than that of a control sample but it was only those mice exposed to the urine of lactating females with a small ano-genital distance which continued to grow, after the cessation of treatment at 21 days of age, at a faster rate. There was no difference in the mass of the uterus when the mice were killed when adult but there were significant age-dependent differences in the mass of the ovaries and adrenal glands. The mice exposed to the urine from lactating mothers (with both large and small ano-genital indices) had smaller ovaries than the control mice while the adrenal glands of mice exposed to the urine of lactating mothers with a large ano-genital index were of greater mass than those of the control mice and mice exposed to mothers with a small ano-genital distance. Exposure to the urine of lactating mothers had no effect on the subsequent activity of the mice when tested in an automated activity recorder. The results confirm that urine from lactating mothers accelerates the onset of puberty and suggests that the effects are restricted to the urine from mothers with a small ano-genital index.

Long term effects on activity in female mice following exposure to urine from lactating mothers.

Infant female mice exposed to the urine of lactating donors prior to weaning subsequently showed, when adult, activity levels in keeping with those of the donors that provided the urine. Mice with low levels of activity provided urine which acted on target mice to restrict their movements and standing behaviour when tested in an open arena. The urine of high active donors enhanced activity as compared with the urine from donors of mid range activity levels. Housing in large groups reduced the activity of the recipients exposed to urine from the low active donors. The males were more active than the females but the exposure of males to the urine of the donors had no effect on their activity levels.

Post-parturition and late lactation urine: long-term effects of exposure on mouse activity and sniffing behaviour.

From the time of separation from their mothers infant mice were exposed for 10 consecutive days to urine from post-parturitional and late-lactational donor mice. They were then tested when adult on activity and sniffing behaviour. The sample of mice exposed to urine from late-lactational donors was associated with reduced activity when compared with mice exposed to post-parturitional urine and a water control sample. The long term effects of the urine on behaviour were also apparent in positional preferences in an open arena as judged by frequency of entry, and to a lesser extent, the time spent in the left and right hand segments. Mice exposed to late-lactational urine sniffed less than the other treatment samples though preferences for sniffing the urine that they had been exposed to in infancy were less marked. The urine did not accelerate puberty, but mice in the control sample had more vaginal dioestrous smears and fewer smears with a predominance of epithelial cells.

Effects of external chemical environment on the developing olfactory bulbs of the mouse (Mus musculus).

Female mice were reared in observation incubators from day 1 of life for three weeks. During that time they were continuously exposed to the odors of either cyclooctanone, adult male mouse urine or distilled water. The growth rate was temporarily accelerated for the cyclooctanone-exposed mice. There was no difference in age at sexual maturation of the three groups. Olfactory preference, when adult, was not affected by early odor exposure, but sniffing behaviour was markedly increased in the urine-exposed mice as compared with the other two groups. The olfactory bulbs of the cyclooctanone-reared mice were larger than those of the other two groups. Mitral cells in the olfactory bulbs were examined histologically for abnormalities. All mice had some shrunken, darkly staining mitral cells, but the cyclooctanone-reared mice had twice as many as the other two groups, mainly in the dorsal half of the bulb. The urine-exposed mice also had more darkly staining cells than the control mice particularly in the dorsolateral region of the bulb, but also in the dorsomedial region.

Effects of neonatal bulbectomy on later discrimination learning in mice.

The olfactory bulbs of mice were lesioned at 24 h of age and their performance in learning a black-white discrimination task was compared with undernourished mice that grew from birth at the same rate as the bulbectomised animals. The mice were tested at 90 days of age and their behaviour in a Y-maze was compared with that of control operated and unoperated samples. The performance of the bulbectomised mice spent more time at the choicepoint and frequently failed to run the maze. The error rate reduction shown by the bulbectomised mice was similar to that of the controls and is accounted for in terms of a reduced frequency of entry and reversals into the maze arms. The results are discussed in relation to the size of the lesions and factors affecting the neurogenesis of the olfactory brain early in life.

The effect of litter size on the growth, survival and behaviour of neonatal bulbectomised mice.

Bilateral lesions of the olfactory bulbs in 1-day-old mice led to a slow rate of growth both before and after weaning and the growth changes were positively associated with the size of the lesion. Mothers continued to care for the bulbectomised mice which showed no evidence of retarded motor development though their eyes opened later and they were less active when exposed to an artificial perfume. Bulbectomised mice failed to survive in litters of two where both infants were bulbectomised and in litters with a large number of unoperated littermates. Keeping litters small and having both bulbectomised and control mice present enhanced the chances of survival and the presence of infant control mice is a necessary condition for the maintenance of lactation and the survival of the bulbectomised babies. Failure to respond to the odours( pheromones) of the mothers may be responsible for the infrequent suckling and the slow growth and development.