Induction of the maternal pheromone by cholic acid in the virgin rat

At what age do rat young stop responding to the maternal pheromone?

We tested postweanling rat young to see if they would continue to respond to the maternal pheromone when pheromone-containing feces were made available in the home cage. We found that they do, and that the consumption of pheromone-containing feces is important for such sustained responsiveness. Nonetheless, interest in the pheromone does not continue past 50 days of age. The possible adaptive significance of the continuation and cessation of pheromonal responsiveness was discussed.

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.

The maternal pheromone and brain development in the preweanling rat

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. Previous research suggested that such feces might promote brain development. A series of experiments was carried out in which pups were denied access to maternal feces. These pups were clearly inferior to control pups in brain growth and neurobehavioral maturation, as well as in the quantity of 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.

The maternal pheromone of the rat: testing some assumptions underlying a hypothesis

Herein we report four experiments relating to the maternal pheromone of the rat that show (a) preweanling young consume pheromone-containing feces most conspicuously between 14 and 27 days; (b) they consume those feces preferentially; (c) such feces contain high levels of deoxycholic acid; and (d) preweanling young are deficient in deoxycholic acid. The data of these experiments lend support to the hypothesis that in responding to the pheromone the young ingest deoxycholic acid, a steroid believed to promote gut immunocompetence and brain myelination.

Reduced prolactin binding to liver membranes during pheromonal emission in the rat

Between 14 and 27 days of lactation, female rats excrete a pheromone in their feces that is cholic-acid dependent and that strongly attracts young. Previous research has shown that high circulating levels of prolactin are necessary before the pheromone can be emitted. However, during the time of pheromonal emission prolactin in serum conspicuously declines, while in hepatic cytosol the hormone reaches peak levels. We were interested in the question of how the liver can show peak cytosolic concentrations of prolactin at a time of falling blood levels of prolactin. Accordingly, we examined the prolactin binding capacity of liver membrane fractions during selected periods of lactation. We also studied the livers of virgin and pregnant females for comparison. Three membrane fractions were separated: the cell membrane, the nuclear membrane and a fraction consisting of the cell membrane and large non-nuclear organelles. In all three fractions, there was an increase in available and total prolactin binding in the liver when pregnant females were compared with nulliparous females. However, during the time of pheromonal emission, when prolactin in hepatic cytosol was elevated, there was a significant reduction in the prolactin binding capacity of the liver. How such a reduction increases the cytosolic concentration of the hormone and in turn heightens cholic acid output and pheromonal emission remains unsolved.

Manipulation of testosterone in the neonatal rat and pheromonal emission in the adult

The question we addressed is why the male rat fails to emit the maternal pheromone when caring for young or when injected with prolactin. Our hypothesis was that exposure to androgen neonatally decreases the prolactin sensitivity of the male liver, making that liver incapable of secreting sufficient cholic acid for pheromonal synthesis. Accordingly, we castrated male rats prior to 2 hr of age and injected female rats with testosterone propionate within 8 days of age. Only those animals that had been spared exposure to androgen neonatally showed evidence of the pheromone when injected with prolactin as adults. Moreover, these same animals exhibited a higher output of cholic acid per g liver than their control counterparts (sham-operated males and vehicle-injected females). We conclude that the sex-related capacity for pheromonal emission is differentiated perinatally and involves the sensitivity of the liver to prolactin and its consequent secretion of cholic acid.

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.