Biomedical subjects

J E Jans

Publications and source records attributed to J E Jans.

9 recordsLinked to original sources

PubMed1995

Role of the nutritional status of the litter and length and frequency of mother-litter contact bouts in prolonging lactational diestrus in rats.

Food restricting lactating rat dams over the first 2 weeks of lactation results in a prolongation of the period of lactational diestrus. Such food restriction has not only a direct effect on the dam but also the pups are undernourished, and the pattern of dam-litter contact is also changed. In a series of studies, we investigated the effects of nursing undernourished pups and the change in dam-litter interaction on the prolongation of lactational diestrus. While nursing undernourished pups in the last 2 weeks of lactation is sufficient to extend lactational diestrus in ad lib-fed dams nursing well-nourished pups in the last 2 weeks of lactation is not necessary for the prolongation of lactational diestrus seen in food-restricted dams. Further, neither nursing underfed pups nor increased nest time in the first 2 weeks postpartum are necessary factors for the prolongation of lactational diestrus in food-restricted dams.

Animals↗

PubMed1990

Nest temperature: effects on maternal behavior, pup development, and interactions with handling.

These studies compared the patterns of mother-young contact under different thermal environments and assessed the implications of the differing patterns of contact for pup development and the dam's behavior. In the first experiment, the warm surface dramatically reduced the total amount of contact time between dams and litters and the dam's food intake, but the effects on the pups were limited to smaller adrenal glands. A replication of the first experiment in which daily weighing and handling of the pups was eliminated produced no differences in development. In a third experiment, during which dams had access to a warm surface outside of the next area and the daily weighing and handling was resumed, the pups showed smaller adrenal glands, lower body temperatures and less thermoregulatory ability. A comparison of results suggests that handling increased the weight of adrenal glands of pups reared under the unmanipulated condition, but not the warm-rearing condition.

Adipose Tissue, Brown↗

PubMed1988

Neuroendocrine basis of thermally regulated maternal responses to young in the rat.

Over the first two weeks postpartum there is a decline in the amount of time that the rat dam spends with her young, resulting from a decrease in the duration of each nest bout. The duration of each nest bout is limited by the rate of rise of maternal temperature when she huddles with her litter. This pattern of mother-young contact is dependent on the dam's hormonal status, because adrenalectomised dams fail to show the expected decline in mother-young contact over time. Ovariectomy, on the other hand, does not have any effect on this behavior. Replacement therapy with glucocorticoids or placing the dam in a warm (25 degrees C) ambience reinstates the normal pattern of mother-litter contact in adrenalectomised-ovariectomised dams. These data suggest that the elevated level of serum glucocorticoids in lactating dams affects maternal behavior by increasing maternal heat load, thereby making the dam vulnerable to an acute rise in temperature when huddling with her young. Prolactin suppression also results in an increase in contact time between mother and young, but only in the second week postpartum. The effects of prolactin suppression are reversed by progesterone replacement or placing prolactin-suppressed females in a warm ambience. However, progesterone is ineffective in restoring the normal pattern of mother-litter contact in adrenalectomised females. These findings suggest that progesterone raises the thermal set point, thereby permitting the thermogenic effects of glucocorticoids to occur.

Adrenal Cortex Hormones↗

PubMed1987

Effects of litter age, litter size, and ambient temperature on the milk ejection reflex in lactating rats.

Under a number of circumstances the duration of mother-young contact in the rat can be drastically reduced while pup growth is maintained. We investigated the possibility that under some of these conditions the timing of milk delivery is changed. We assessed the time of onset and pattern of milk delivery over a nest bout in litters of two different ages (Day 4 or Day 10) and three different sizes (4, 8, or 12 pups). Ambient temperature fluctuated over the course of the study and was found to correlate significantly with the latency to the first milk ejection (ME). Specifically, the warmer the ambient temperature, the quicker the first ME occurred. Durations between successive MEs correlated with ambient temperature in a similar fashion. Analysis of covariance revealed that the onset of the first ME occurred earlier in Day 10 litters than in Day 4 litters, but litter size had no effect. Durations between successive MEs were not affected by either litter age or litter size. These data indicate one possible mechanism by which adequate milk delivery can be maintained despite some reduction in mother-young contact.

Age Factors↗

PubMed1987

Effects of food restriction during concurrent lactation and pregnancy in the rat.

The ability of rat dams to cope with food restriction as well as a concurrent lactation and pregnancy was examined by varying the duration, time of onset and severity of the food restriction schedule. Groups of females impregnated in the postpartum estrus and nursing 8 pups were either allowed to feed ad lib, given 60% of an ad lib ration from days 1-7, 1-14, 8-14 or 15-21 postpartum or 40% of an ad lib ration from days 1-7. Food restriction regimens that extended through the estimated time of implantation for females nursing 8 pups (days 1-14 and 8-14) resulted in a prolongation of pregnancy. Food restriction in the first week postpartum did not result in a prolongation of pregnancy and did not affect the number of females carrying the pregnancy to term. Dams food restricted in the third week postpartum had pregnancies of the same length as ad lib females but a smaller proportion of this group gave birth to a second litter.

Animals↗

PubMed1985

The effects of rearing environment on pup development.

Norway rats were reared either in a standard laboratory cage or in a nest constructed by the dam from newspaper strips. Growth, thermoregulatory ability, and adrenal, gonad, adipose tissue, and brain weights were measured at weaning on Day 21 postpartum. While there was no difference in growth, nest-reared animals had lower body temperatures, but could thermoregulate as well as cage-reared animals. Nest-reared animals also had relatively smaller adrenals and less brown adipose tissue. Gonad and brain weights were similar. An interesting finding was that males and females were differentially affected by the nest-rearing. Differences between cage- and nest-reared animals were more evident in females, and thermoregulatory ability was more closely associated with the quality of the nest during the first 10 days than body weight in females. For males, body weight was more important. These latter data are discussed in relation to differential interaction between the dam and male and female pups.

Animals↗

PubMed1983

Determinants of mother-young contact in Norway rats.

Rat dams choose to care for their pups in a relatively warm area, apparently because they have an elevated thermal set point for the regulation of their body temperature. Since the duration of their contact bouts with their pups is limited by an acute hyperthermia that they experience while on the pups, their choice limits the time that they can spend with their pups. When dams could choose the temperature at which they cared for their young they spent only about half the time in contact with their offspring as did dams caring for their pups at the ambient temperature of the laboratory. We conclude that rat dams do not attempt to maximize the duration of their contact bouts with their offspring. Dams also do not attempt to minimize the amount of time that they spend away from their offspring. The duration of the intervals between contact bouts was influenced by the ability of the dams to dissipate the heat gained during the contact bout with the pups. Again, dams did not seek out a cool area in which to spend their interbout intervals, preferring to remain in relatively warm areas. Their thermal preference facilitated the retention of their body heat and prolongation of the interbout intervals. Dams may return to the nest periodically for brief bouts during which the state of the pups is monitored. Pups were found to play both passive and active roles in modulating the overall pattern of maternal contact, for dams maintained contact with pups if the pups were cool, but failure to attach to the nipples soon after contact was established frequently led to rapid bout termination, particularly with warm pups. Contact is maintained if the pups are cool or if they attach to the nipples. Finally, it was found that pups could actively curtail interbout intervals by emitting ultrasonic vocalizations.

Animals↗

PubMed1983

The effects of lactation and ambient temperature on the body temperature of female Norway rats.

Norway rat dams were placed in an ambient temperature of 4 degrees C, 22 degrees C, or 28 degrees C. Body temperatures were recorded over a two hour period on three days; each female was observed on Day 4 and Day 10 of lactation and three days after lactation was stopped. Body temperatures were initially higher during lactation than after lactation had stopped. Dams were less able to maintain their body temperatures in the 28 degrees C ambience on Day 4 of lactation than after lactation, and on Day 10 of lactation, were even less able to maintain their body temperatures than on Day 4. During lactation, dams were able to maintain and even increase their body temperatures in the 4 degrees C ambience. The data support the hypothesis that the acute hyperthermia encountered by rat dams during contact with their litters may be due to a physical restriction on maternal heat loss.

Animals↗

PubMed1980

Short-term remembering of discriminative stimuli in pigeons.

Pigeons learned to peck the left or right of two white keys depending on whether a red or a green stimulus was displayed on a third key. The opportunity to peck the white keys was then dealyed for zero to six seconds after the red or green (to-be-remembered) stimulus. On half the trials, the feeder operated during the delay to interrupt behavior that might mediate discriminated responding. No events were scheduled on the remaining trials. In a later condition, the pigeons had the opportunity to peck the white keys during the delay. In general, accuracy decreased as delay increased in all conditions, but performance was least accurate following feeder operations and most accurate when pecking was allowed during the delay. The procedures may be analogous to varying the opportunity for rehearsal in studies of human short-term memory.

Animals↗