Early maternal separation promotes alterations in the thermoregulatory profile of adult Wistar rats.

Stressful lifelong events may influence psychiatric diseases, like depression and anxiety. Interestingly, depressed patients have dysfunction of thermoregulatory cooling mechanisms. Thus, understanding the mechanisms related to the thermoregulatory changes in stress-related pathologies is important to better understand the symptoms and treatments for those diseases. However, the influence of early-life stress on the thermoregulatory profile of adults is unknown. In this study, we aimed to evaluate the thermoregulatory profile of adult male Wistar rats submitted to early-life stress by maternal separation (MS). On postnatal days 2-14, rats were submitted daily to MS for 3 h per day. At 3-4 months of age, anxiety-like behavior was evaluated using the open field test and elevated plus maze, depression-like behavior was evaluated using the forced swim test and thermoregulatory profile were also evaluated. In the behavioral tests, MS animals exhibited anxiety- and depression-like behaviors, and had higher core body temperatures during dark period of the circadian cycle, when compared to controls. In addition, MS animals presented higher hyperthermic and vasoconstriction responses than control animals when exposed to the warmth environment, and engaged in cold-seeking behavior whenever possible to select their preferred ambient temperature. The results suggest that, besides emotional alterations, MS induces a change in the thermoregulatory profile of rats that persists into adulthood.

Thermoregulatory profile of neurodegeneration-induced dementia of the Alzheimer's type using intracerebroventricular streptozotocin in rats.

AIM: Here, we have extensively investigated the relationship between thermoregulation and neurodegeneration-induced dementia of the Alzheimer's type using intracerebroventricular injections of streptozotocin (icv-STZ). METHODS: Male Wistar rats were treated with bilateral injections of icv-STZ, and their thermoregulatory profiles (core body temperature, tail-skin temperature, cold and heat defence responses and thermal place preference) were evaluated. Spatial memory, locomotor activity, social interaction, brain ventricular volume, and Aß1-42 and tau protein levels in the brain were analysed to characterize the effects of STZ on the brain and behaviour. RESULTS: In addition to deficits in spatial memory, reduced social interaction and an increased brain ventricular volume, icv-STZ rats presented a pattern of hyperthermia, as demonstrated by an increased core body temperature. Hyperthermia was due to the activation of both autonomic heat conservation and behavioural cold avoidance, as STZ-treated rats presented tail-cutaneous vasoconstriction and an altered thermal preference. They also showed a distinct cold defence response when exposed to cold. CONCLUSION: Our data bring evidence that icv-STZ in rats causes hyperthermia, with activation of both autonomic and behavioural thermoregulatory defence responses when challenged at colder temperatures, leading us to hypothesize that they are more efficient in preventing hypothermia. These data are relevant for a better understanding of neurodegenerative disease mechanisms.

TRPV4 activates autonomic and behavioural warmth-defence responses in Wistar rats.

AIM: In this study, we aimed at investigating the involvement of the warmth-sensitive channel - TRPV4 (in vitro sensitive to temperatures in the range of approx. 24-34 °C) - on the thermoregulatory mechanisms in rats. METHODS: We treated rats with a chemical selective agonist (RN-1747) and two antagonists (RN-1734 and HC-067047) of the TRPV4 channel and measured core body temperature, metabolism, heat loss index and preferred ambient temperature. RESULTS: Our data revealed that chemical activation of TRPV4 channels by topical application of RN-1747 on the skin leads to hypothermia and this effect was blocked by the pre-treatment with the selective antagonist of this channel. Intracerebroventricular treatment with RN-1747 did not cause hypothermia, indicating that the observed response was indeed due to activation of TRPV4 channels in the periphery. Intravenous blockade of this channel with HC-067047 caused an increase in core body temperature at ambient temperature of 26 and 30 °C, but not at 22 and 32 °C. At 26 °C, HC-067047-induced hyperthermia was accompanied by increase in oxygen consumption (an index of thermogenesis), while chemical stimulation of TRPV4 increased tail heat loss, indicating that these two autonomic thermoeffectors in the rat are modulated through TRPV4 channels. Furthermore, rats chemically stimulated with TRPV4 agonist choose colder ambient temperatures and cold-seeking behaviour after thermal stimulation (28-31 °C) was inhibited by TRPV4 antagonist. CONCLUSION: Our results suggest, for the first time, that TRPV4 channel is involved in the recruitment of behavioural and autonomic warmth-defence responses to regulate core body temperature.