Development of behavioral responses to thermal challenges

Postnatal rearing environment alters pup cues for caregiver-offspring interactions

Maternal behavior experienced in early life provides essential scaffolding to infant psychobiology with life-long effects on neurobiological and behavioral outcomes. However, infants are not passive recipients of caregiving. Evidence in rodents suggests that pups actively contribute to dam-pup interactions by soliciting maternal care with auditory, tactile, and hormonal cues. The limited bedding and nesting material (LBN) rearing manipulation induces changes in maternal care that have been attributed to maternal stress caused by the low-resource environment. The goal of the current study was to determine whether LBN also alters pup cues for maternal behavior, with implications for the mechanism of LBN-induced effects. Rat dams and pups were randomly assigned to LBN or Control rearing conditions on postnatal day (P) 0-6 and pups were fostered to the same or different condition on P6-13. LBN increased pup-directed maternal behaviors measured through 24 h monitoring using machine learning based automated analysis. LBN altered several pup cues known to affect maternal behavior including reducing pup core body temperature, reducing body weight, and altering pup vocalizations on P6 and P12. P6-13 LBN-exposed pups had elevated serum testosterone, which positively correlated with maternal licking and grooming. LBN reduced pup movement between nest attendance onset and the start of nursing, which was negatively related to dam nursing latency and contributed to longer nursing latency in LBN dams. P0-6 pup exposure to LBN also led to longer nest attendance bouts and shorter licking and grooming bouts on P7 and P9, suggesting lasting effects of LBN on pups. These data demonstrate that LBN changes pup behavioral and hormonal signals consistent with eliciting more maternal care, contributing to augmented pup-directed behaviors. This bidirectional interplay may be a critical mechanism involved in the lasting effects of early life environments.

Hypothalamic Neuromodulation and Control of the Dermal Surface Temperature of Livestock during Hyperthermia

Hyperthermia elicits several physiological and behavioral responses in livestock to restore thermal neutrality. Among these responses, vasodilation and sweating help to reduce core body temperature by increasing heat dissipation by radiation and evaporation. Thermoregulatory behaviors such as increasing standing time, reducing feed intake, shade-seeking, and limiting locomotor activity also increase heat loss. These mechanisms are elicited by the connection between peripheral thermoreceptors and cerebral centers, such as the preoptic area of the hypothalamus. Considering the importance of this thermoregulatory pathway, this review aims to discuss the hypothalamic control of hyperthermia in livestock, including the main physiological and behavioral changes that animals adopt to maintain their thermal stability.

The Role of Brown Adipose Tissue and Energy Metabolism in Mammalian Thermoregulation during the Perinatal Period

Hypothermia is one of the most common causes of mortality in neonates, and it could be developed after birth because the uterus temperature is more elevated than the extrauterine temperature. Neonates use diverse mechanisms to thermoregulate, such as shivering and non-shivering thermogenesis. These strategies can be more efficient in some species, but not in others, i.e., altricials, which have the greatest difficulty with achieving thermoneutrality. In addition, there are anatomical and neurological differences in mammals, which may present different distributions and amounts of brown fat. This article aims to discuss the neuromodulation mechanisms of thermoregulation and the importance of brown fat in the thermogenesis of newborn mammals, emphasizing the analysis of the biochemical, physiological, and genetic factors that determine the distribution, amount, and efficiency of this energy resource in newborns of different species. It has been concluded that is vital to understand and minimize hypothermia causes in newborns, which is one of the main causes of mortality in neonates. This would be beneficial for both animals and producers.

Thermoneutrality effects on developmental programming of obesity

Developmental programming studies using mouse models have housed the animals at human thermoneutral temperatures (22°C) which imposes constant cold stress. As this impacts energy homeostasis, we investigated the effects of two housing temperatures (22°C and 30°C) on obesity development in male and female offspring of Control and FR dams. Pregnant mice were housed at 22°C (cold-exposed, CE) or 30°C (thermoneutrality, TN) room temperature. At gestational age e10, mice were fed either an ad libitum diet (Control) or were 30% food-restricted (FR) to produce low birth weight newborns. Following delivery, all dams were fed an ad libitum diet and maternal mice continued to nurse their own pups. At 3 weeks of age, offspring were weaned to an ad libitum diet and housed at similar temperatures as their mothers. Body weights and food intake were monitored. At 6 months of age, body composition and glucose tolerance test were determined, after which, brain and adipose tissue were collected for analysis. FR/CE and FR/TN offspring exhibited hyperphagia and were significantly heavier with increased adiposity as compared to their respective Controls. There was sex-specific effects of temperature in both groups. Male offspring at TN were heavier with increased body fat, though the food intake was decreased as compared to CE males. This was reflected by hypertrophic adipocytes and increased arcuate nucleus satiety/appetite ratio. In contrast, female offspring were not impacted by housing temperature. Thus, unlike female offspring, there was a significant interaction of diet and temperature evident in the male offspring with accentuated adverse effects evident in FR/TN males.

Comparison of neurotransmitter levels, physiological conditions, and emotional behavior between isolation-housed rats with group-housed rats

Brain monoaminergic neurotransmitters, such as dopamine (DA), serotonin (5-HT), and noradrenaline (NA), play crucial roles in neuronal and physiological functions, including social behaviors. Isolation housing may induce behavioral and neurochemical abnormalities in rats, although its influence on neurotransmitter levels remains obscure. This study investigated the influence of isolation- or group-housing on core body temperature (T_core ), locomotor activity (ACT), emotional behavior, and neurotransmitter levels in male Wistar rats. Behavioral changes were monitored using the open field test (OFT) and social interaction test (SIT). After 4 weeks, brain tissues were collected to quantify 5-HT, DA, and NA concentrations. Body weight and basal T_core during both the light and dark phase were higher in isolation-housed than in group-housed rats, although no significant difference was seen in ACT. No significant differences were observed during the OFT. Isolation-housed rats showed increased line crossing and decreased social behavior during the SIT. Isolation-housed rats exhibited decreased levels of 5-HT in the caudate putamen and amygdala, and elevated and decreased NA levels in the paraventricular hypothalamic nucleus and hippocampus, respectively. However, DA levels were unaffected. Thus, housing environments may affect brain areas that regulate various neuronal and physiological functions, such as memory, stress responses, and emotional behavior.

Homeostatic disturbance of thermoregulatory functions in rats with chronic fatigue

Chronic fatigue syndrome (CFS) is characterized by long-lasting fatigue, and a range of symptoms, and is involved in homeostasis disruption. CFS patients frequently complain of low grade fever or chill even under normal body temperature indicating that thermosensory or thermoregulatory functions might be disturbed in CFS. However, little is known about the detailed mechanisms. To elucidate whether and how thermoregulatory function was altered during the development of chronic fatigue, we investigated temporal changes in body temperature with advance of fatigue accumulation in a chronic fatigue rat model using a wireless transponder. Our findings demonstrated that the body temperature was adaptively increased in response to fatigue loading in the early phase, but unable to retain in the late phase. The tail heat dissipation was often observed and the frequency of tail heat dissipation gradually increased initially, then decreased. In the late phase of fatigue loading, the body temperature for the tail heat dissipation phase decreased to a value lower than that for the non-dissipation phase. These results suggest that adaptive changes in thermoregulatory function occurred with fatigue progression, but this system might be disrupted by long-lasting fatigue, which may underlie the mechanism of fatigue chronification.

Individual differences in early body mass affect thermogenic performance and sibling interactions in litter huddles of the house mouse

We asked whether within-litter differences in early body mass are associated with differences in house mouse pups' thermogenic performance and whether such variation predicts individual differences in competitive interactions for thermally more advantageous positions in the huddle. We explored pups' thermogenic performance in isolation by measuring changes in (maximal) peripheral body temperatures during a 5-min thermal challenge using infrared thermography. Changes in peripheral body temperature were significantly explained by individual differences in body mass within a litter; relatively lighter individuals showed an overall quicker temperature decrease leading to lower body temperatures toward the end of the thermal challenge compared to heavier littermates. Within the litter huddle, relatively lighter pups with a lower thermogenic performance showed consistently more rooting and climbing behavior, apparently to reach the thermally advantageous center of the huddle. This suggests that within-litter variation in starting body mass affects the pups' thermal and behavioral responses to environmental challenges.