Michael Leon

Thermal control of mother-young contact in rats

Abstract The factors involved in the control of nest bout duration by mother rats were analyzed. Disruption of prolactin or adrenocortical secretions halted the normal progressive decline in daily nesting time, but the behavioral effects of hormone disruption were not mediated by a suppression of milk delivery. Rather, these hormones stimulate a chronic elevation in the body temperature of mother rats which makes mothers vulnerable to the acute thermal consequences of huddling with their litter. The temperature of a mother rat rises further after her ability to dissipate heat decreases when she comes in contact with her young, a rise that eventually limits the duration of nest bouts. Decreasing the efficiency of heat dissipation during nest bouts by elevating room temperature, pup temperature, or by removing the tail (a major pathway for heat dissipation) decreased nest bout duration. Increasing the rate of maternal heat loss by decreasing room temperature, pup temperature, or by partially removing the insulating fur of dams increased nest bout duration. We conclude that nest bouts are normally limited by a rise in maternal temperature, and that the rate of temperature rise determines the duration of each bout.

Dietary control of maternal pheromone in the lactating rat

Abstract The quantity and quality of food eaten by lactating female rats are critical for the emission and the synthesis of the maternal attractant, respectively. Mothers must consume large amounts of food to produce the excess caecotrophe that carries maternal pheromone to the external environment. The kind of food that is eaten determines the nature of the specific odor that is emitted, since different diets induce the synthesis of different odors. The pups appear to learn to associate the caecotrophe odor specific to the maternal diet with an approach response.

Establishment of pheromonal bonds and diet choice in young rats by odor pre-exposure ☆

Abstract Rat pups reared by mothers maintained on a diet inhibiting maternal pheromone production do not exhibit a tendency to approach the pheromone excreted by normally maintained lactating females. The results of the present experiments indicate that following exposure in isolation to the smell of maternal pheromone, rat pups reared by dams not producing maternal pheromone exhibit a strong preference for the odor of maternal pheromone. Furthermore, pups reared by non-pheromone producing dams, and exposed in isolation to an arbitrary odor, exhibit both a preference for that odor and a preference for a diet with which that odor is associated. These results are discussed as demonstrating the importance of stimulus familiarity, rather than association learning, in the development of pheromonal bonds and socially transmitted diet preferences.

Filial Responsiveness to Olfactory Cues in the Laboratory Rat

Publisher Summary Under the care of the mother, the young not only receive her physical protection and nurturance, but the pups and nest are marked with the caecal odor of their mother. This chapter describes the pup responses to olfactory cues, ontogeny of attraction in rat pups, weakening of the pheromonal bond, and the functional aspects of the pheromonal bond. It is proposed that the importance of an animal being surrounded by its own odor lies in its confidence value to the individual by marking the area as safe, and the onset of production of a rats own odor may be particularly effective in increasing the familiarity of its immediate environment, and decreasing its inherent neophobic responses to the stimuli with which they are inundated. The development of the capacity to emit an individual odor may allow the weanling to engage in social responses necessary for the interactions with conspecifics. The maternal pheromone, while important for a specific period in the life of the young rat, is clearly only one of the stimuli that are involved in the growth and maturation of the pups. The first two weeks may find the maternal nest odors and her ventral odors as prepotent cues, only to be replaced in importance by the maternal pheromone, which in turn may be replaced by other cues. The timely changes in the behavior observed in developing rats indicate that they are not becoming more perfect adults, but are uniquely adapting to the problems at each point in maturation.

Development of Olfactory Attraction by Young Norway Rats

Young rats orient toward maternal olfactory cues as early as 2–3 days postpartum (Altman, et al., 1973). The orientation to these cues becomes more and more reliable, until by days 12–14, they not only orient, but they move toward the odor from a distance (Altman et al., 1973; Leon and Moltz, 1972). The pups continue to be attracted to the mother during the period that the young are capable of leaving the nest site but must reunite with the mother for periodic nursing bouts (Rosenblatt and Lehrman, 1963). Termination of the approach response to maternal odor occurs at about 27 days postpartum, which is the time of weaning (Leon and Moltz, 1972).

Dissolution of the pheromonal bond: Waning of approach response by weanling rats

Abstract The approach response of weanling pups to a maternal attractant declines over the last week of the maternal episode. Caecal function in the pups develops, and exposure of pups to their own caecal odor therefore occurs at the same time as the tendency of pups to approach the odor of maternal caecotrophe wanes. Inhibition of the maturation of caecal function in weanlings prolongs the responsiveness of the young to the maternal pheromone. These findings suggest that the odor of an individuals own caecotrophe may act as an ectohormone, suppressing approach responses exhibited toward familiar odors in unfamiliar environments.

Pheromonal Mediation of Maternal Behavior

One critical aspect of the maternal period in rats (Rattus norvegicus) is the fine synchrony which characterizes the interactions between the mother and her young for the duration of the nurtural relationship. It is the close timing of the physiological and behavioral responses of the mother with the continually changing behavioral, physiological, and physical characteristics of her developing pups that insures the survival of the young. While the fine adjustments by the mother are essential for the growth of the litter, the developing young must also make adjustments in response to the changing physiological and behavioral patterns expressed by their mother.