How rat young govern the release of a maternal pheromone

Effects of early separation of young rats from the mother on their open-field behavior

Changes were studied in the open-field behavior of young rats prematurely separated from their mothers at different ages. Premature separation from the mother on days 15 and 18 of life increased their fear or emotional behavior, as measured by the amount of defecation and locomotor activity. The changes in rats' open-field behavior were due to the absence of the mother rather than to an inadequate food supply after the day of separation.

The maternal pheromone and deoxycholic acid in the survival of preweanling rats

Preweanling rats selectively approach and consume pheromone-containing maternal feces. This selectivity suggests that the consumption of maternal feces might be important for the growing pup. We tested the hypothesis that such feces, because of their high deoxycholic acid content, may protect against acute enteritis. A series of experiments was carried out in which pups were denied access to maternal feces. These pups died more often from acute enteritis than control pups. Additional confirmation of the hypothesis was obtained when feces-denied young fed deoxycholic acid showed a significantly lower mortality than feces-denied young fed laboratory chow alone.

The maternal pheromone and deoxycholic acid in relation to brain myelin in the preweanling rat

We examined the lipid composition of blood and myelin in preweanling rats denied access to maternal feces. Levels of triglycerides and free fatty acids in the blood were reduced and in the brain the amount of myelin and the phospholipid concentration in myelin were also reduced. The addition of deoxycholic acid to ordinary laboratory chow prevented these deficiencies. We conclude that response to the maternal pheromone and the subsequent ingestion of deoxycholic acid through maternal feces promotes the deposition of normal brain myelin.

Dietary influences in the preferences of pre-weanling Long-Evans rats for the anal excreta of adult males

Male rats which ingest feces of lactating females produce anal excreta which is attractive to pups. This excreta is as attractive as that of lactating females and more attractive than the excreta of males eating a diet of lab chow only. Anal excreta of males which consume feces of lactating females is more attractive to pups than excreta of males that consume feces of nonlactating females. These results suggest that group or colony odors may develop from rats eating feces of other colony members and that infant rats may be more attracted to adults that have an odor which is similar to the maternal odor than adults which have different odors.

Preferences of pre- and post-weanling Long-Evans rats for nest odors

Three experiments were conducted on the preferences of infant rats for nest odors. Pre-weanling rats preferred their own nest odor to nests of strange litters and showed low preferences for the nest odors of virgin females. Nest odors of unmated males were investigated less than the pup's own nest odor but more than the odors of virgin females. Male and female rats did not differ in odor preferences. Rats reared with both their dam and sire did not differ in their odor preferences from rats reared with their dam alone when tested at 16-20 days of age, but when tested at 33-38 days of age they showed a greater preference for male odors. Post-weanling rats did not show a preference for the nest odors of lactating females and began to show sex differences in their preferences.

The maternal pheromone of the rat as an innate stimulus for pre-weanling young

We undertook to determine whether previous exposure in the nest is necessary to establish the attractiveness of the maternal pheromone or whether that attractiveness is innately based. In Experiment I we showed that the pheromone is a prepotent stimulus insofar as it is approached in preference to a different but equally familiar odor. Experiment 2 demonstrated that when pups are denied previous exposure to the pheromone they nonetheless approach the pheromone preferentially in a choice test involving a pheromone-emitting and a non-pheromone-emitting female. And finally, in Experiment 3, we again used pups that had been isolated from the pheromone. Here, however, the choice was between a pheromone-emitting female and a female which, while non-pheromone-emitting, carried a thoroughly familiar nest odor. The pups decisively chose the pheromone-emitting female. We conclude that pheromonal attractiveness is innately based and suggest that the pheromone itself may have been selected as a signal during the course of evolution.