Changes of noradrenaline-induced contractility and gene expression in aorta of rats acclimated to heat in two different modes

Salivary Immunoglobulin A Secretion and Polymeric Ig Receptor Expression in the Submandibular Glands Are Enhanced in Heat-Acclimated Rats

Salivary immunoglobulin A (IgA) plays a critical role in mucosal immunity. Chronic exposure to moderate heat induces heat acclimation, which modifies salivary functions. However, the changes in salivary IgA secretion in heat-acclimated rats are unclear. In this study, we investigated salivary IgA secretion and the expression of polymeric Ig receptor (pIgR), a key mediator of mucosal IgA secretion, in the submandibular glands (SMGs) of heat-acclimated rats. Following maintenance at an ambient temperature (T_a) of 24 ± 0.1 °C for 10 days, male Wistar rats were subjected to T_a of 32 ± 0.2 °C for 5 days (HE group) for heat acclimation or maintained at T_a of 24 ± 0.1°C (CN group). The rats were then anesthetized, pilocarpine (0.5 mg/kg) was intraperitoneally injected, and saliva was collected. Afterward, the SMGs and plasma were sampled. The salivary IgA concentration and IgA flow rate were significantly higher in the HE group than in the CN group. Similarly, SMG pIgR expression was significantly higher in HE rats. The levels of plasma cytokines, including interleukin (IL)-5, IL-6, and interferon-γ, were significantly greater in HE rats than in CN rats. Heat acclimation may enhance oral immunity through salivary IgA secretion and pIgR upregulation in the SMGs.

Theobromine Improves Working Memory by Activating the CaMKII/CREB/BDNF Pathway in Rats

Theobromine (TB) is a primary methylxanthine found in cacao beans. cAMP-response element-binding protein (CREB) is a transcription factor, which is involved in different brain processes that bring about cellular changes in response to discrete sets of instructions, including the induction of brain-derived neurotropic factor (BDNF). Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) has been strongly implicated in the memory formation of different species as a key regulator of gene expression. Here we investigated whether TB acts on the CaMKII/CREB/BDNF pathway in a way that might improve the cognitive and learning function in rats. Male Wistar rats (5 weeks old) were divided into two groups. For 73 days, the control rats (CN rats) were fed a normal diet, while the TB-fed rats (TB rats) received the same food, but with a 0.05% TB supplement. To assess the effects of TB on cognitive and learning ability in rats: The radial arm maze task, novel object recognition test, and Y-maze test were used. Then, the brain was removed and the medial prefrontal cortex (mPFC) was isolated for Western Blot, real-time PCR and enzyme-linked immunosorbent assay. Phosphorylated CaMKII (p-CaMKII), phosphorylated CREB (p-CREB), and BDNF level in the mPFC were measured. In all the behavior tests, working memory seemed to be improved by TB ingestion. In addition, p-CaMKII and p-CREB levels were significantly elevated in the mPFC of TB rats in comparison to those of CN rats. We also found that cortical BDNF protein and mRNA levels in TB rats were significantly greater than those in CN rats. These results suggest that orally supplemented TB upregulates the CaMKII/CREB/BDNF pathway in the mPFC, which may then improve working memory in rats.

Neurogenesis in the thermoregulatory system

In response to various internal and external stimuli, neuronal progenitor cells in the hypothalamic area proliferate and differentiate to functionally working neurons even in adult animals. This is the case in the thermoregulatory system, especially in the process of heat acclimation. The heat acclimation process presents two different patterns, namely short-term and long-term heat acclimation. In rats, long-term heat acclimation is attained by exposing subjects to constant heat for more than 4 weeks, while short-term heat acclimation is established within several days of heat exposure. Heat exposure for more than 6 days facilitates cell proliferation in the ependymal layer of the third ventricle. The newborn cells then migrate into the hypothalamic parenchyma. After 33 days of heat exposure, the newborn cells abruptly differentiate to mature neurons. A part of the newborn cells are incorporated in a neuronal circuit in the hypothalamus. However, only 6 days of heat exposure hardly promote neuronal differentiation. An administration of mitosis inhibitor interferes with cell proliferation in the hypothalamic area and attenuates heat acclimation-induced improvement of heat tolerance. Long-term, but not short-term, heat acclimation may be established by generating new functional neurons in the hypothalamic area, which is where an important part of the thermoregulatory circuitry exists in rats.

Spontaneously hypertensive rats are sensitive to thoracic aorta damage induced by a hot and humid environment

The purpose of this study was to investigate the effect of a hot and humid environment on thoracic aorta damage in spontaneously hypertensive rats (SHRs). Wistar-Kyoto (WKY) rats were randomly divided into three groups (n=8 in each group): Control group (WKY-CN), heat exposure for 8 h group (WKY-8) and heat exposure for 24 h group (WKY-24). The CN group was exposed to room temperature (24°C); WKY-8 and WKY-24 group were exposed to heat (32°C) and 65% relative humidity for 8 and 24 h, respectively. Accordingly, SHRs were randomly divided into three groups (n=8 each group): SHR-CN, SHR-8 and SHR-24. After 7 days of heat exposure, the weight, food consumption and blood pressure of rats was measured. Noradrenaline (NA)-induced contraction of aorta rings was measured using an organ bath system, and vascular morphology was observed. Expression levels of apoptotic genes and proteins in the thoracic aorta were also measured. The experimental results indicated that, in the heat exposure environment, rat food intake was reduced. Rat weight was significantly increased in all groups except SHR-24 (all P<0.01 except SHR-8, P<0.05). Heat exposure significantly increased the blood pressure of rats in the WKY-24 (P<0.01 for systolic; P<0.05 for diastolic), SHR-8 and SHR-24 (all P<0.01) groups. This effect was more notable in SHR compared with WKY. NA-induced contraction of aorta rings significantly increased in the SHR-CN group, compared with the WKY-CN group (P<0.01). Heat exposure significantly elevated the NA-induced contraction in both 8 h groups compared with the CN groups (P<0.01). This effect was accompanied by structural damage to the thoracic aorta and increased expression of apoptotic genes and proteins. In conclusion, thoracic aorta damages in SHRs were more sensitive to heat exposure. The enhanced NA-induced contraction may have partly been due to increased apoptosis in the thoracic aorta.

Heat acclimation and thirst in rats

The effects of heat acclimation on water intake and urine output responses to thermal dehydration and other thirst stimuli were studied in male Sprague-Dawley rats. Rats were heat acclimated by continuous exposure to a 34°C environment for at least 6 weeks. Thermal dehydration-induced thirst was brought about by exposing the heat-acclimated rats and control rats housed at 24°C to a 37.5°C environment for 4 h without access to food or water. Heat acclimation reduced evaporative and urinary water losses and the increases in plasma sodium and osmolality during thermal dehydration, which led to a reduction in thermal dehydration-induced thirst. Heat acclimation reduced the rate of rehydration following thermal dehydration but did not alter the final rehydration level, indicating that heat acclimation does not alter the primary control of thermal dehydration-induced thirst. Heat acclimation did not alter water intake or urine output following administration of hypertonic saline, which selectively stimulates intracellular thirst, but led to greater water intake following administration of angiotensin II, which plays an important role in extracellular/volemic thirst, and following water deprivation, which activates both thirst pathways. Cardiovascular responses to angiotensin II were not altered by heat acclimation. Heat acclimation thus reduces water loss during heat exposure in rats, but does not have major effects on thermal dehydration-induced or extracellular thirst but does appear to alter volemic thirst.

Involvement of neurogenesis in the hypothalamic area in establishing long-term heat acclimation in rats

This review summarizes earlier studies of long-term heat acclimation (LHA) in rats. Since thermoregulatory changes of LHA are stable and sustained, persisting functional and morphological changes are expected to occur in the thermoregulatory centers. Heat exposure increases the number of newborn cells in the ependymal layer of the third ventricle. With time, these newborn cells migrate into the hypothalamic parenchyma and differentiate to immature or mature neurons, some of which integrate into hypothalamic neuralne tworks. The generation of new functional neurons in the hypothalamus may be an important mechanism of LHA.

Thoracic aorta vasoreactivity in rats under exhaustive exercise: effects of Lycium barbarum polysaccharides supplementation

Background

Reduced arterial compliance is associated with an increased rate of morbidity and mortality in cardiovascular disease. Exercise is beneficial for compromised arterial compliance. However, the beneficial effects of exercise are lost with exhaustion. Lycium barbarum L. has been used in China for centuries to maintain good health. In this regard, the primary purpose of this study was to characterize the effects of the polysaccharides from Lycium barbarum (LBPs) on arterial compliance during exhaustive exercise.

Methods

A four-week swimming exercise program was designed for rats, and the blood levels of malondialdehyde (MDA), super oxide dismutase (SOD), nitric oxide(NO) and heat shock protein 70(HSP70) were detected. The tension of aorta rings was measured to evaluate the response of rats on noradrenaline (NA)-induced contractions.

Results

The rats administered LBPs showed longer swimming time until exhaustion than the control group of rats. Exercise-induced MDA elevation was repressed by LBPs supplementation. The LBPs-supplemented rats displayed a significant increase of SOD, NO, HSP70 than the non-supplemented rats. Additionally, LBPs significantly up-regulated the expression of eNOS and improved the endothelium-dependent vasodilatation of the aorta ring.

Conclusion

Our study proved that LBPs administration significantly inhibited the oxidative stress, and improved the arterial compliance.