Immobilization stress in rats: effect on rectal temperature and possible role of brain monoamines in hypothermia

Endotherms trade body temperature regulation for the stress response

Responding to perceived threats is energetically expensive and can require animals to curtail somatic repair, immunity, and even reproduction to balance energy ledgers. In birds and mammals, energetic demands of thermoregulation are often immense, yet whether homeostatic body temperatures are also compromised to aid the stress response is not known. Using data sourced from over 60 years of literature and 24 endotherm species, we show that exposure to non-thermal challenges (e.g. human interaction, social threats) caused body temperatures to decrease in the cold and increase in the warmth, but particularly when species-specific costs of thermoregulation were high and surplus energy low. Biophysical models revealed that allowing body temperature to change in this way liberated up to 24% (mean = 5%) of resting energy expenditure for use towards coping. While useful to avoid energetic overload, these responses nevertheless heighten risks of cold- or heat-induced damage, particularly when coincident with cold- or heatwaves.

Posterior subthalamic nucleus (PSTh) mediates innate fear-associated hypothermia in mice

The neural mechanisms of fear-associated thermoregulation remain unclear. Innate fear odor 2-methyl-2-thiazoline (2MT) elicits rapid hypothermia and elevated tail temperature, indicative of vasodilation-induced heat dissipation, in wild-type mice, but not in mice lacking Trpa1-the chemosensor for 2MT. Here we report that Trpa1-/- mice show diminished 2MT-evoked c-fos expression in the posterior subthalamic nucleus (PSTh), external lateral parabrachial subnucleus (PBel) and nucleus of the solitary tract (NTS). Whereas tetanus toxin light chain-mediated inactivation of NTS-projecting PSTh neurons suppress, optogenetic activation of direct PSTh-rostral NTS pathway induces hypothermia and tail vasodilation. Furthermore, selective opto-stimulation of 2MT-activated, PSTh-projecting PBel neurons by capturing activated neuronal ensembles (CANE) causes hypothermia. Conversely, chemogenetic suppression of vGlut2+ neurons in PBel or PSTh, or PSTh-projecting PBel neurons attenuates 2MT-evoked hypothermia and tail vasodilation. These studies identify PSTh as a major thermoregulatory hub that connects PBel to NTS to mediate 2MT-evoked innate fear-associated hypothermia and tail vasodilation.

CREB deletion increases resilience to stress and downregulates inflammatory gene expression in the hippocampus

The transcription factor CREB (cyclic AMP response element (CRE)-binding protein) is implicated in the pathophysiology and treatment of depression. Structural and functional studies in both animals and humans suggest that abnormalities of the hippocampus may play a role in depression. CREB regulates thousands of genes, yet to date, only a handful that mediate depression or antidepressant response have been identified as relevant CREB targets. In order to comprehensively identify genes regulated by CREB in the hippocampus, we employed translating ribosome affinity purification (TRAP) to detect actively translating mRNAs in wild type and CREB-deficient mice. Using Creb^loxP/loxP; Rosa^LSL-GFP-L10a mice, we conducted whole genome sequencing to identify transcripts only in cells that lack CREB, as introduction of Cre-recombinase simultaneously deleted CREB and expressed GFP-tagged L10a ribosomes that enabled TRAP. We identified over 200 downregulated genes predominantly associated with inflammation and the immune system, including toll-like receptor 1 (TLR1). To determine if baseline disruption in gene expression in the hippocampus of CREB-deficient mice can modulate behavior, we used unpredictable chronic mild stress (UCMS) to produce a set of behavioral alterations with strong validity for depression. We found that CREB-deficient mice demonstrated resilience to the physiological effects of UCMS and also showed changes in affective behaviors specifically in the presence of stress. TLR1 expression was increased following UCMS in control but not in CREB-deficient mice. The results suggest that CREB-mediated regulation of immune system and inflammatory factors may provide additional targets for the treatment of depression.

Stress-induced hyperthermia and hypothermia

Stress affects core body temperature (T_c). Many kinds of stress induce transient, monophasic hyperthermia, which diminishes gradually if the stressor is terminated. Stronger stressors produce a longer-lasting effect. Repeated/chronic stress induces anticipatory hyperthermia, reduces diurnal changes in T_c, or slightly increases T_c throughout the day. Animals that are exposed to chronic stress or a cold environment exhibit an enhanced hyperthermic response to a novel stress. These changes persist for several days after cessation of stress exposure. In contrast, long-lasting inescapable stress sometimes induces hypothermia. In healthy humans, psychologic stress induces slight increases in T_c, which are within the normal range of T_c or just above it. Some individuals, however, develop extremely high T_c (up to 41°C) when they are exposed to emotional events or show persistent low-grade high T_c (37-38°C) during or after chronic stress situations. In addition to the nature of the stressor itself, such stress-induced thermal responses are modulated by sex, age, ambient temperature, cage mates, past stressful experiences and cold exposure, and coping. Stress-induced hyperthermia is driven by mechanisms distinct from infectious fever, which requires inflammatory mediators. However, both stress and infection activate the dorsomedial hypothalamus-rostral medullary raphe region-sympathetic nerve axis to increase T_c.

Effect of fish oil on offensive and defensive factors in gastric ulceration in rats

The effect of fish oil (FO) derived from Scomberoides commersonianus containing omega-3 polyunsaturated fatty acids was studied on gastric ulcers and as well as on offensive and defensive factors in gastric mucosal damage, following experimental gastric ulceration. FO significantly reduced the severity of ulceration in gastric ulcers induced by aspirin, cold-restraint stress (CRS), alcohol, and pylorus ligation. The results also indicated the potentiality of FO in maintaining the integrity of gastric mucosa by virtue of its effect on both offensive and defensive gastric mucosal factors. It decreased the offensive acid-pepsin secretion and augmented the defensive factors like mucin secretion, cellular mucus and life span of mucosal cells following pylorus ligation. FO significantly increased activity of anti-oxidant enzymes (catalase and glutathione peroxidase) and decreased lipid peroxidation in gastric mucosa of CRS rats. The study indicates the beneficial role of FO in gastric ulceration by inhibition of offensive mucosal factors and oxidative stress, and augmentation of defensive mucosal factors.

The welfare impact of gavaging laboratory rats

Gavaging (oral dosing) has previously been shown to have only a short-term effect on behavioural parameters in the laboratory rat. The aim of this study was to determine if the gavaging of laboratory rats influenced their heart rate, blood pressure and body temperature, and if so, whether the duration of this impact correlated with the volume gavaged. The three stress parameters were measured using telemetric transponders placed in the abdomen of eight female Sprague-Dawley (Mol:SPRD) rats. Using a Latin Square cross-over design, the rats were gavaged with three different doses of barium sulphate (4, 10 and 40 ml kg–1); in addition, there was a control of no dose, only insertion of the tube. The heart rate, blood pressure and body temperature of the rats were monitored continuously for 4 h after dosing and again for 1 h, 24 h after dosing. The gavaging of laboratory rats was shown to induce an acute reaction: after 30 min, blood pressure and heart rate were significantly higher than before gavaging, and body temperature was significantly higher 60 min after gavaging — indicators of stress levels comparable to those of other basic experimental procedures. A significant correlation between heart rate and dosage was observed until 10 min after gavaging. This indicates that the dosage gavaged is of only minor importance in causing stress, and only important for the most acute reaction. However, because of the resistance and discomfort observed when administering a 40 ml kg–1 dose, this dose should be administered only with caution.

Synergistic induction of severe hypothermia (poikilothermia) by limbic seizures, acepromazine and physical restraint: role of noradrenergic alpha-1 receptors

The maintained production of extreme reductions in core temperature (20-22 degrees C) or poikilothermia can be reliably produced by the synergistic interaction of limbic seizures (induced by lithium and pilocarpine), postseizure administration of a single injection of acepromazine, and physical restraint. Administration of the specific and nonspecific dopamine antagonists haloperidol, chlorpromazine, SCH23390, or clozapine did not simulate the effect at clinically effective dosages. Single injections of phentolamine and prazosin but not of propranolol instead of acepromazine following the seizures produced the poikilothermia. This effect was also reproduced by reducing the amount of the rats' adipose weight before the induction of the seizures and physical restraint. Rats that had been restrained or not restrained and displayed either euthermia or hypothermia exhibited significantly different patterns in brain damage within limbic and thalamic structures.

The Welfare Impact of Increased Gavaging Doses in Rats

Textbook recommendations for gavaging rats vary between 1-5 ml for an adult rat. Rats weighing either 130 g or 250 g were gavaged with varying dosages of barium sulphate (BaSO4). After dosing, radiographs were taken at 0, 15 and 60 min. Animals showing a section of the small intestine totally filled with BaSO4 were scored as displaying spontaneous release. Other rats of the same sizes were gavaged with similar doses and subsequently tested in an open-field arena for behavioural abnormalities that might indicate stress or pain resulting from the procedure. Body temperature before and after treatment was recorded using microchip transponders. None of the 250 g rats in the 1 ml dosage group showed spontaneous release through the pyloric sphincter. In the 2 ml and 4 ml dosage groups, only one out of five animals showed spontaneous release. In the 6 ml dosage group, half of the animals showed spontaneous release. In the 8 ml and 10 ml dosage groups, five out of six and four out of five, respectively, showed spontaneous release. If doses were higher than 12 ml, no animal was able to keep all of the BaSO4 in its stomach. In the rats weighing 130 g, the 3 ml dosage group showed only one out of four rats with spontaneous release, whereas in the 5 ml and 7 ml dosage groups, all animals showed spontaneous release. After 15 min, all of the rats in both weight groups showed BaSO4 in the duodenum. Ambulation, rearing up onto the hind legs and defecation, as well as body temperature immediately after dosing, correlated very strongly with the dose (ml kg−1); increasing the dose resulted in reduced ambulation, rearing, defecation and body temperature. However, 10 min after performance of the open-field test, neither body temperature, serum corticosterone nor serum glucose showed any correlation with dose. This study indicates that high doses (ie doses up to 10 ml for a 250 g rat) might be safe to use; however, if an adverse impact on the rat is to be avoided, use of much lower doses should be considered—for example, doses that do not enforce opening of the pyloric sphincter in any rat. This would be less than 4 ml kg−1 in a 250 g rat.

Effect of lapachol, a naphthaquinone isolated from Tectona grandis, on experimental peptic ulcer and gastric secretion

Lapachol, a naphthaquinone isolated from the roots of Tectona grandis given at a dose of 5 mg kg-1 p.o. twice daily for 3 days was found to have an anti-ulcerogenic effect on subsequently induced experimental gastric and duodenal ulcers in rats and guinea-pigs. Its action appears to be associated with an effect on the protein content of gastric juice, and it reversed aspirin-induced changes in peptic activity, protein and sialic acid.

Restraint stress in biomedical research: a review

The use of restraint or immobilization for investigations of animal physiology, pathology and pharmacology has an extensive history. The major use of this technique has been as a "stressor" for the induction of stress response syndromes in animals. Many such syndromes have been characterized from the behavioral level to the neurochemical concomitants of stress. As a consequence of this particular use of the restraint procedure, much information concerning drug effects on stress response syndromes has been obtained. Indeed, many researchers in the area of gastrointestinal drugs routinely screen their new compounds in a restraint model of gastric stress ulcer. The purpose of this review is to present for researchers, a summary of the methods for, the parameters of, and known drug effects on, restraint-induced pathology. In our experience, this technique has proven to be a very useful one for the examination of both central and peripheral mechanisms of stress-related disorders, as well as for studying drug effects upon these disorders.

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants: II

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published from 1980 to 1984 but data from many earlier papers are also tabulated.