Adaptive changes in thermoregulation and their neuropharmacological basis

Reserpine-induced rat model for depression: Behavioral, physiological and PET-based dopamine receptor availability validation

BACKGROUND

Reserpine (RES), a Vesicular Monoamine Transporter 2 (VMAT2) inhibitor agent, has been used in preclinical research for many years to create animal models for depression and to test experimental antidepressant strategies. Nevertheless, evidence of the potential use and validity of RES as a chronic pharmacological model for depression is lacking, and there are no comprehensive studies of the behavioral effects in conjunction with molecular outcomes.

METHODS

Experiment 1. Following baseline behavior testing sensitive to depression-like phenotype and locomotion (Phase 1), 27 Sprague-Dawley (SD) rats received i.p. either vehicle solution (0.0 mg/kg), low (0.2 mg/kg) or high (0.8 mg/kg) RES dose for 20 days using a pre-determined schedule and reassessed for behavioral phenotypes (Phase 2). After 10 days washout period, and a final behavioral assessment (Phase 3), the brains were collected 16 days after the last injection for mRNA-expression assessment. Experiment 2. In a similar timetable as in Experiment 1 but without the behavioral testing, 12 SD rats underwent repetitive dopamine D2/3 receptor PET scanning with [18F]DMFP following each Phase. The binding potential (BPND) of [18F]DMFP was quantified by kinetic analysis as a marker of striatal D2/3R availability. Weight and welfare were monitored throughout the study.

RESULTS

Significant, dose-dependent weight loss and behavioral deficits including both motor (hypo-locomotion) and non-motor behavior (anhedonia, mild anxiety and reduced exploration) were found for both the low and high dose groups with significant decrease in D2R mRNA expression in the accumbal region for the low RES group after Phase 3. Both RES treated groups showed substantial increase in [18F]DMFP BPND (in line with dopamine depletion) during Phase 2 and 3 compared to baseline and Controls.

CONCLUSIONS

The longitudinal design of the study demonstrated that chronic RES administration induced striatal dopamine depletion that persisted even after the wash-out period. However, the behavior phenotype observed were transient. The data suggest that RES administration can induce a rodent model for depression with mild face validity.

Effect of Long-Term Adaptation to Cold and Short-Term Cooling on the Expression of the TRPM2 Ion Channel Gene in the Hypothalamus of Rats

The present study is aimed to elucidate the possible involvement of the thermosensitive TRPM2 ion channel in changing of the temperature sensitivity of the hypothalamus after different cold exposures-long-term adaptation to cold and short-term cooling. Quantitative RT-PCR was used to study the expression of the gene of thermosensitive TRPM2 ion channel in the hypothalamus in the groups of control (kept for 5 weeks at +20 to +22 °C) and cold-adapted (5 weeks at +4 to +6 °C) rats, as well as in the groups of animals which were subjected to acute cooling (rapid or slow) with subsequent restoration of body temperature to the initial level. It has been shown that after long-term adaptation to cold, the decrease in the Trpm2 gene expression was observed in the hypothalamus, while a short-term cooling does not affect the expression of the gene of this ion channel. Thus, long-term adaptation to cold results in the decrease in the activity not only of the TRPV3 ion channel gene, as shown earlier, but also of the Trpm2 gene in the hypothalamus. The overlapping temperature ranges of the functioning of these ion channels and their unidirectional changes during the adaptation of the homoeothermic organism to cold suggest their functional interaction. The decrease in the Trpm2 gene expression may indicate the participation of this ion channel in adaptive changes in hypothalamic thermosensitivity, but only as a result of long-term cold exposure and not of a short-term cooling. These processes occurring at the genomic level are one of the molecular mechanisms of the adaptive changes.

To clot, or not to clot: The dilemma of hormone treatment options for menopause

Untreated menopause may have serious health implications, but treatments can have dangerous side effects. We evaluate menopausal symptoms as well as available treatments -the routes of administration and their effect on blood coagulation. Menopausal females may experience hot flushes, vulva- and vaginal atrophy and osteoporosis. Many treatments are available to relieve these symptoms such as Conjugated Equine Estrogen and bioidentical hormones. The routes of administration include oral and transdermal. Hormones that are administered orally undergo a hepatic first pass metabolism. The by-products have a lower efficacy and possibly enhanced side effects. Furthermore, hormone treatments influence the coagulation cascade through coagulation factors or their regulators. Increased coagulation poses a risk for venous thromboembolism. Currently a definite conclusion on whether the side effects from hormone treatments exceed the risk of untreated menopause cannot be made. However, a more individualised approach to hormone treatments may be the most feasible solution to this dilemma.

Perioperative Hypothermia-A Narrative Review

Unintentional hypothermia (core temperature < 36 °C) is a common side effect in patients undergoing surgery. Several patient-centred and external factors, e.g., drugs, comorbidities, trauma, environmental temperature, type of anaesthesia, as well as extent and duration of surgery, influence core temperature. Perioperative hypothermia has negative effects on coagulation, blood loss and transfusion requirements, metabolization of drugs, surgical site infections, and discharge from the post-anaesthesia care unit. Therefore, active temperature management is required in the pre-, intra-, and postoperative period to diminish the risks of perioperative hypothermia. Temperature measurement should be done with accurate and continuous probes. Perioperative temperature management includes a bundle of warming tools adapted to individual needs and local circumstances. Warming blankets and mattresses as well as the administration of properly warmed infusions via dedicated devices are important for this purpose. Temperature management should follow checklists and be individualized to the patient's requirements and the local possibilities.

Longitudinal course of vasomotor symptoms in perimenopausal migraineurs

OBJECTIVE

To examine the longitudinal course of vasomotor symptoms (VMS) in women with a history of migraine in comparison to women without a history of migraine disease.

METHODS

The study sample consisted of 467 women with a self-reported prior migraine diagnosis and 2,466 women without prior migraine diagnosis who were assessed longitudinally during menopausal transition as part of the Study of Women's Health Across the Nation. Linear mixed regression models with backward elimination were used to evaluate longitudinal associations between VMS and migraine while adjusting for baseline and time-varying demographic, socioeconomic, psychological, and reproductive factors. Additional analyses were performed to further assess the specificity of the association between migraine and VMS that included evaluating the association between migraine and vaginal dryness and between back pain and VMS.

RESULTS

A history of migraine predicted an increased frequency of VMS but not vaginal dryness during menopausal transition. Significant interaction between history of migraine and menopausal status for the prediction of VMS was also identified. Burden of VMS was found to be higher during late-stage perimenopause in women with migraine. In contrast, the history of back pain did not predict the frequency of VMS.

INTERPRETATION

This is the first study to delineate that a history of migraine predicts an increased frequency of VMS in women during menopausal transition. Hypothalamic abnormalities and thermoregulatory dysfunction against a milieu of decreasing estradiol concentrations during menopausal transition may explain the increased frequency of VMS in migraineurs during menopausal transition. ANN NEUROL 2019;85:865-874.

Heat Acclimation Decay and Re-Induction: A Systematic Review and Meta-Analysis

Background

Although the acquisition of heat acclimation (HA) is well-documented, less is known about HA decay (HAD) and heat re-acclimation (HRA). The available literature suggests 1 day of HA is lost following 2 days of HAD. Understanding this relationship has the potential to impact upon the manner in which athletes prepare for major competitions, as a HA regimen may be disruptive during final preparations (i.e., taper).

Objective

The aim of this systematic review and meta-analysis was to determine the rate of HAD and HRA in three of the main physiological adaptations occurring during HA: heart rate (HR), core temperature (T_c), and sweat rate (SR).

Data Sources

Data for this systematic review were retrieved from Scopus and critical review of the cited references.

Study Selection

Studies were included when they met the following criteria: HA, HAD, and HRA (when available) were quantified in terms of exposure and duration. HA had to be for at least 5 days and HAD for at least 7 days for longitudinal studies. HR, T_c, or SR had to be monitored in human participants.

Study Appraisal

The level of bias in each study was assessed using the McMaster critical review form. Multiple linear regression techniques were used to determine the dependency of HAD in HR, T_c, and SR from the number of HA and HAD days, daily HA exposure duration, and intensity.

Results

Twelve studies met the criteria and were systematically reviewed. HAD was quantified as a percentage change relative to HA (0% = HA, 100% = unacclimated state). Adaptations in end-exercise HR decreased by 2.3% (P < 0.001) for every day of HAD. For end-exercise T_c, the daily decrease was 2.6% (P < 0.01). The adaptations in T_c during the HA period were more sustainable when the daily heat exposure duration was increased and heat exposure intensity decreased. The decay in SR was not related to the number of decay days. However, protracted HA-regimens seem to induce longer-lasting adaptations in SR. High heat exposure intensities during HA seem to evoke more sustained adaptations in SR than lower heat stress. Only eight studies investigated HRA. HRA was 8–12 times faster than HAD at inducing adaptations in HR and T_c, but no differences could be established for SR.

Limitations

The available studies lacked standardization in the protocols for HA and HAD.

Conclusions

HAD and HRA differ considerably between physiological systems. Five or more HA days are sufficient to cause adaptations in HR and T_c; however, extending the daily heat exposure duration enhances T_c adaptations. For every decay day, ~ 2.5% of the adaptations in HR and T_c are lost. For SR, longer HA periods are related to better adaptations. High heat exposure intensities seem beneficial for adaptations in SR, but not in T_c. HRA induces adaptations in HR and T_c at a faster rate than HA. HRA may thus provide a practical and less disruptive means of maintaining and optimizing HA prior to competition.

Mechanisms underlying alterations in norepinephrine levels in the locus coeruleus of ovariectomized rats: Modulation by estradiol valerate and black cohosh

Hot flushes are common in menopause. Norepinephrine (NE), primarily synthesized in the locus coeruleus (LC), plays a major role in central thermoregulation. Furthermore, we previously observed decreased dopamine beta hydroxylase (DβH), a key enzyme in NE synthesis, in LC neurons following ovariectomy. In this study, we explore the mechanisms underlying decreased NE levels in the LC (LC-NE) in ovariectomized (OVX) rats, and the modulating effects of estradiol valerate (E2) and black cohosh (ICR). We used high-performance liquid chromatography to detect LC-NE in SHAM, OVX, OVX-E2, and OVX-ICR groups. Western blotting and immunohistochemistry were performed to investigate the expression of NE metabolic enzymes, the NE reuptake transporter (NET), and estrogen receptors (ERs) in the LC. We observed significant LC-NE decreases in the OVX group. E2 and ICR enhanced LC-NE but did not restore them to SHAM levels. Ovariectomy affected NE synthesis, degradation, and reuptake. Levels of NE catabolic enzymes monoamine oxidase A (MAOA) and catechol-O-methyltransferase (COMT) decreased, while NET expression increased. E2 restored MAOA and COMT to SHAM levels but had no effect on NET. ICR restored COMT and NET to SHAM levels but had no effect on MAOA. Moreover, the OVX group also exhibited decreased expression of ERα and ERβ. E2 enhanced the expression of ERα and ERβ, while ICR only enhanced ERβexpression. Taken together, reduced NE in OVX rats resulted from reduced synthesis and increased degradation and reuptake. E2 and ICR may regulate these processes in different ways through various ERs.

The Counterbalance of Skin Metabolism on Orbits and Diseases

Human organ functions are regulated by the nervous system. When human cells receive a message, this message is transmitted to the nervous system through a series of signal transmission processes. Skin conditions that occur after applying skin cream are closely related to signal transmission and nervous regulation. We determined the connection between signal regulation and natural rhythmic operations. The diurnal variations resulting from the earth’s rotation and indicate the relative relationships between the sympathetic nervous system and the parasympathetic nerve system. A spectrum was developed to assess neural transmission conditions by using skin signals which from Fourier transformation of the waves and established the association between the spectrum and diseases. The results could explain the relationships between the neurological illnesses and established spectrum. The objective was to promote the use of this spectrum as a new tool for conducting the nervous system tests in the future.

Effect of the sympathetic nervous system co-transmitters ATP and norepinephrine on thermoregulatory response to cooling

The existence of co-transmitters of the sympathetic nervous system norepinephrine (NE) and ATP implies variations in the neuromodulator mechanisms of physiological processes. The role of ATP, as a transmitter of the peripheral part of sympathetic nervous system in the formation of thermoregulatory response is not clear. Whether ATP modulates any parameters of thermoregulatory response to cold; if yes, whether co-transmitters of sympathetic nervous system ATP and NE differently modulate thermoregulatory response and on which parameters of cold-defense response the influence of ATP is more pronounced. Experiments were carried out on rats. ATP (10(-6)), NE (10(-3)), and their mixture introduced iontophoretically into skin. Their effects on thermoregulatory parameters (temperature parameters, total oxygen consumption, carbon dioxide release, muscle activity, respiratory coefficient) were studied in thermoneutral conditions (without cold load) and under the cooling. In thermoneutral conditions both ATP and NE enhance total metabolism through increase in metabolic rate of lipids, NE effect being more expressed. It was shown that ATP and NE influence predominantly on the different components of the metabolic response to cold. ATP affects to the greatest extent on cold muscular thermogenesis by increasing shivering almost twofold and lowering its initiation temperature thresholds, whereas NE mainly promotes increase in non-shivering thermogenesis. When introducing the mixture of these biological substances the effect of NE is more expressed and the ATP effect is weakened. The obtained results allow to suggest that in vivo the NE effects can be more expressed when the sympathetic nervous system is stimulated by cold. Thus, NE and ATP being co-transmitters and predominantly acting on the different processes of cold thermogenesis (ATP on shivering and NE on non-shivering) may organize the certain sequence of cold defense responses.

A proposed methodology to control body temperature in patients at risk of hypothermia by means of active rewarming systems

Hypothermia is a common complication in patients undergoing surgery under general anesthesia. It has been noted that, during the first hour of surgery, the patient's internal temperature (T_core) decreases by 0.5–1.5°C due to the vasodilatory effect of anesthetic gases, which affect the body's thermoregulatory system by inhibiting vasoconstriction. Thus a continuous check on patient temperature must be carried out. The currently most used methods to avoid hypothermia are based on passive systems (such as blankets reducing body heat loss) and on active ones (thermal blankets, electric or hot-water mattresses, forced hot air, warming lamps, etc.). Within a broader research upon the environmental conditions, pollution, heat stress, and hypothermia risk in operating theatres, the authors set up an experimental investigation by using a warming blanket chosen from several types on sale. Their aim was to identify times and ways the human body reacts to the heat flowing from the blanket and the blanket's effect on the average temperature T_skin and, as a consequence, on T_core temperature of the patient. The here proposed methodology could allow surgeons to fix in advance the thermal power to supply through a warming blanket for reaching, in a prescribed time, the desired body temperature starting from a given state of hypothermia.

Neonates in Ahmedabad, India, during the 2010 heat wave: a climate change adaptation study

Health effects from climate change are an international concern with urban areas at particular risk due to urban heat island effects. The burden of disease on vulnerable populations in non-climate-controlled settings has not been well studied. This study compared neonatal morbidity in a non-air-conditioned hospital during the 2010 heat wave in Ahmedabad to morbidity in the prior and subsequent years. The outcome of interest was neonatal intensive care unit (NICU) admissions for heat. During the months of April, May, and June of 2010, 24 NICU admissions were for heat versus 8 and 4 in 2009 and 2011, respectively. Both the effect of moving the maternity ward and the effect of high temperatures were statistically significant, controlling for each other. Above 42 degrees Celsius, each daily maximum temperature increase of a degree was associated with 43% increase in heat-related admissions (95% CI 9.2–88%). Lower floor location of the maternity ward within hospital which occurred after the 2010 heat wave showed a protective effect. These findings demonstrate the importance of simple surveillance measures in motivating a hospital policy change for climate change adaptation—here relocating one ward—and the potential increasing health burden of heat in non-climate-controlled institutions on vulnerable populations.

Non-hormonal management of vasomotor symptoms

Vasomotor symptoms are the most common indication for the prescription of hormone replacement therapy since it is effective in over 80% of cases. In 1995, 37% of American women took hormone replacement therapy, principally for this purpose. However, following the publication of results from the Women's Health Initiative, as many as half of these women in the US and in the UK and New Zealand discontinued hormone therapy. Discontinuation of estrogen is often accompanied by a return of vasomotor symptoms; however, only a small number (18%) of women report restarting hormone therapy. Alternatives are available, but limited knowledge on etiology and mechanisms of hot flushing represents a major obstacle for the development of new, targeted, non-hormonal treatments, and no current alternatives are as effective as estrogen.

Effects of an isopropanolic-aqueous black cohosh extract on central body temperature of ovariectomized rats

ETHNOPHARMACOLOGICAL RELEVANCE

Black cohosh (Cimicifuga racemosa) is widely used in menopause symptoms strategy.

AIM OF THE STUDY

The aim of this study was to examine the effect of isopropanolic black cohosh extract (iCR) on the central body temperature (CBT) of ovariectomized rats (OVX) and elaborate its possible effects in alleviating menopause related hot flushes.

MATERIALS AND METHODS

64 female Sprague-Dawley rats, weighing 230 ± 10g and aged 6-8 weeks, were divided into four groups: ovariectomy (OVX), sham, ovariectomy plus estradiol valerate (OVX+E), and ovariectomy plus iCR (OVX+ICR). The sham group underwent a sham surgery without ovariectomies, while the other three groups underwent bilateral ovariectomies under sterile conditions and a temperature implant was embedded in the abdominal cavity of all four groups. After 2-week recovery period, the temperature of all animals was monitored for 6 weeks.

RESULTS

CBT of four groups maintained a normal circadian rhythm, with a low day CBT and a high night CBT. CBTs of the sham group were lower than that of the other three groups. The day CBTs of the (OVX+E) group and (OVX+ICR) group were lower than that of the OVX group from day 2 and day 22 respectively. For the difference between day and night CBT, the sham group was smallest, while (OVX+E) and (OVX+ICR) groups were higher than that of OVX group. The amplitude of day and night CBT, CBT fluctuation frequency at 5 min intervals, were higher for the OVX group than the sham group; the amplitude of day and night CBT of (OVX+E) group and the amplitude of night CBT of (OVX+ICR) group were higher than those of OVX group; while the amplitude of day CBT of (OVX+ICR) group was lower than that of OVX group; CBT fluctuation frequency at 5 min intervals was higher for the (OVX+E) and (OVX+ICR) groups than the OVX group.

CONCLUSIONS

Ovariectomized rats had abnormal thermoregulation, demonstrating an increase in day and night CBT, greater difference between day and night CBT, higher amplitude of day and night CBT, and more CBT fluctuation frequency. For the herbal extract iCR, the onset of affecting abnormal thermoregulation took longer than that of estradiol valerate. ICR had a significant effect on day CBT but was only little effective on night CBT of ovariectomized rats.

Feeling too hot or cold after breast cancer: is it just a nuisance or a potentially important prognostic factor?

There is widespread recognition among both patients and caregivers that breast cancer patients often experience debilitating deficiencies in their ability to achieve thermal comfort, feeling excessively hot or cold under circumstances when others are comfortable. However, this symptom receives little clinical or scientific attention beyond identification and testing of drugs that minimise menopausal-like symptoms. Could some of these symptoms represent an important prognostic signal? Could thermal discomfort be among other cytokine-driven sickness behaviour symptoms seen in many breast cancer patients? While the literature reveals a strong link between treatment for breast cancer and some menopausal vasomotor symptoms (e.g. hot flashes also known as "hot flushes"), there is little data on quantitative assessment of severity of different types of symptoms and their possible prognostic potential. However, recent, intriguing studies indicating a correlation between the presence of hot flashes and reduced development of breast cancer recurrence strongly suggests that more study on this topic is needed. In comparison to reports on the phenomenon of breast cancer-associated hot flashes, there is essentially no scientific study on the large number of women who report feeling excessively cold after breast cancer treatment. Since similar acquired thermal discomfort symptoms can occur in patients with cancers other than breast cancer, there may be as yet unidentified cancer- or treatment-driven factor related to temperature dysregulation. In general, there is surprisingly little information on the physiological relationship between body temperature regulation, vasomotor symptoms, and cancer growth and progression. The goal of this article is twofold: (1) to review the scientific literature regarding acquired deficits in thermoregulation among breast cancer survivors and (2) to propose some speculative ideas regarding the possible basis for thermal discomfort among some of these women. Specifically, we suggest a potential association with excessive pro-inflammatory cytokine activity, similar to other cytokine-driven symptoms experienced after breast cancer, including fatigue and depression. We highlight the similarity of some breast cancer-associated thermal discomfort symptoms to those which occur during fever, suggesting the possibility that there may be common underlying changes in pro-inflammatory cytokine activity in both conditions. We anticipate that this contribution will stimulate additional scientific interest among researchers in identifying potential mechanisms and prognostic significance of this under-studied aspect of breast cancer biology and survivorship.

Hot flushes: are there effective alternatives to estrogen?

Hot flushes are the most common indication for the prescription of hormone replacement therapy (HRT) since it is effective in over 80% of cases. In 1995, 37% of American women took HRT, principally for this purpose. However, over the last five years, publications such as those from the Women's Health Initiative (WHI) have caused concern among women since they perceive that the risks outweigh the benefits. Following this publication, half of the women taking HRT in the UK, USA and New Zealand discontinued HRT. With the discontinuation of estrogen many women re-developed hot flushes; however only a small number (18%) of women report restarting hormone therapy. The majority of these (76%) for the recurrence of severe hot flushes or night sweats. Alternatives are available, but limited knowledge on aetiology and mechanisms of hot flushing represents a major obstacle for the development of new, targeted, non-hormonal treatments, and no current alternatives are as effective as estrogen.

Vitex agnus-castus (Chaste-Tree/Berry) in the treatment of menopause-related complaints

BACKGROUND

The origin of the current practice of administering Vitex agnus-castus in menopause-related complaints is uncertain, but appears to be relatively recent. Here we review the evidence for this application of Vitex based on evidence from pharmacological studies and clinical research.

METHODS

The mechanisms of potential relevance in the context of menopause are explored with reference to the current understanding of the endocrinology and neuroendocrinology of menopause and associated symptoms.

CONCLUSIONS

We conclude that, while evidence from rigorous randomized controlled trials is lacking for the individual herb in this context, emerging pharmacological evidence supports a role for V. agnus-castus in the alleviation of menopausal symptoms and suggests that further investigation may be appropriate.

Individual differences in temperature perception: Evidence of common processing of sensation intensity of warmth and cold

The longstanding question of whether temperature is sensed via separate sensory systems for warmth and cold was investigated by measuring individual differences in perception of nonpainful heating and cooling. Sixty-two subjects gave separate ratings of the intensity of thermal sensations (warmth, cold) and nociceptive sensations (burning/stinging/pricking) produced by cooling (29 degrees C) or heating (37 degrees C) local regions of the forearm. Stimuli were delivered via a 4 x 4 array of 8 mm x 8 mm Peltier thermoelectric modules that enabled test temperatures to be presented sequentially to individual modules or simultaneously to the full array. Stimulation of the full array showed that perception of warmth and cold were highly correlated (Pearson r = 0.83, p < 0.05). Ratings of nonpainful nociceptive sensations produced by the two temperatures were also correlated, but to a lesser degree (r = 0.44), and the associations between nociceptive and thermal sensations (r = 0.35 and 0.22 for 37 and 29 degrees C, respectively) were not significant after correction for multiple statistical tests. Intensity ratings for individual modules indicated that the number of responsive sites out of 16 was a poor predictor of temperature sensations but a significant predictor of nociceptive sensations. The very high correlation between ratings of thermal sensations conflicts with the classical view that warmth and cold are mediated by separate thermal modalities and implies that warm-sensitive and cold-sensitive spinothalamic pathways converge and undergo joint modulation in the central nervous system. Integration of thermal stimulation from the skin and body core within the thermoregulatory system is suggested as the possible source of this convergence.

What causes hot flushes? The neuroendocrine origin of vasomotor symptoms in the menopause

Vasomotor symptoms (VMS) such as hot flushes and night sweats are frequently encountered during menopause and can greatly reduce the quality of life. These symptoms are causally related to decreasing estradiol concentrations, mainly in the serum and subsequently also in the hypothalamic temperature regulating centre. The lack of estrogens alters neurotransmitter activity, especially in the serotonergic and noradrenergic pathways. Because sex steroids act as potent neuromodulators, the substitution of ovarian sex steroids by hormone replacement therapy is the most effective treatment option for VMS. When contraindications exist for the use of sex steroids, steroid-free drugs are a possible alternative. A better understanding of the physiology of thermoregulation, thermoregulatory dysfunction and adaptive processes of the brain may facilitate the development of new therapeutic approaches. Such drugs could then be used to treat vasomotor disorders even when the use of steroid hormones is contraindicated. This review article summarises our knowledge on the mechanisms of temperature regulation and describes deviations from this regulation during altered sex steroid conditions. Our current knowledge on neuroendocrinology of thermoregulation may serve as a basis for the use of steroid-free pharmacological intervention.

High ambient temperature increases intravenous methamphetamine self-administration on fixed and progressive ratio schedules in rats

Methamphetamine is a drug that is often consumed at dance parties or nightclubs where the ambient temperature is high. The present study determined whether such high ambient temperatures alter intravenous methamphetamine self-administration in the rat. Male Hooded Wistar rats were trained to self-administer intravenous methamphetamine (0.1 mg/kg/infusion) under a fixed ratio 1 (FR1) or progressive ratio (PR) schedule of reinforcement at an ambient temperature of 23 +/- 1 degrees C. They were then given their daily self-administration session at a raised ambient temperature of 30 +/- 1 degrees C. Methamphetamine self-administration was increased at 30 degrees C under both FR1 and PR reinforcement schedules, with the latter effect indicating that heat enhances the motivation to obtain methamphetamine. High temperatures did not alter self-administration of the D1 receptor agonist SKF 82958 in methamphetamine-experienced rats suggesting some specificity in the methamphetamine effect. When rats were given access to drink isotonic saline solution during methamphetamine self-administration sessions they drank much more solution at 30 degrees C than 23 degrees C. However, availability of isotonic saline to drink did not alter the heat-induced facilitation of methamphetamine self-administration (PR schedule) indicating that the heat effect does not simply reflect increased motivation for intravenous fluids. Hyperthermia was evident in rats self-administering methamphetamine at high ambient temperatures and fluid consumption did not prevent this effect. Heat did not affect blood levels of methamphetamine, or its principal metabolite amphetamine indicating that the facilitatory effect of heat did not reflect altered methamphetamine pharmacokinetics. Overall, these results show that high ambient temperatures increase the reinforcing efficacy of methamphetamine and encourage higher levels of drug intake.

Central and peripheral thermoreceptors. Comparative analysis of the effects of prolonged adaptation to cold and noradrenaline

This report presents results obtained from many years of study of the effects of prolonged adaptation to cold and noradrenaline on the spike activity of central hypothalamic and peripheral skin thermoreceptors. The involvement of the sympathetic nervous system in forming adaptive changes in the regulatory characteristics of temperature homeostasis and the significance of the various components of thermoreceptor activity to the formation of effector responses are discussed. The roles of different groups of thermoreceptors in forming temperature sensations are analyzed.

The association of perimenopausal mood disorders with other reproductive-related disorders

Data regarding the increased incidence of psychiatric illness during midlife in women are still conflicting. However, there is a growing consensus that certain groups of women may in fact be at higher risk for mood symptoms and psychiatric disorders during the perimenopausal transition. Mood symptoms during the perimenopause may be related to mood disorders during other periods of hormonal fluctuation throughout a woman's reproductive lifecycle. Elucidating these associations may advance the understanding of mood disorders during the perimenopausal transition. The epidemiology and treatment of perimenopausal mood symptoms compared with the epidemiology and treatment of mood disorders during the late luteal phase of the menstrual cycle, pregnancy, and postpartum. Common risk factors associated with mood disorders during these periods of hormonal changes or instability include poor lifestyle habits, a history of hormonally related mood disorders, stress and negative life events, ethnicity, and comorbidity. Reproductive-related mood disorders also are subject to an improvement in symptoms in response to treatment with selective serotonin reuptake inhibitors. As the morbidity associated with mood disorders during midlife may be quite significant, and as life expectancy continues to increase, recognition, prevention, and treatment of perimenopausal affective illness is becoming increasingly essential.

Thermoregulation in rats during early postnatal maturation: importance of nitric oxide

Experiments were carried out to determine the role of nitric oxide in mediating autonomic and behavioral thermoregulatory control in rat pups on postnatal days 1-2, 5-6, and 10-11. For an experiment, each pup received a subcutaneous injection of vehicle, NG-nitro-d-arginine methyl ester (d-NAME; 100 mg/kg), or NG-nitro-l-arginine methyl ester (l-NAME; 100 mg/kg) before being placed in a metabolic chamber or in a thermocline with a linear temperature gradient of 23 to 43°C. In the metabolic chamber, oxygen consumption and core temperature were measured as ambient temperature was decreased from 40 to 15°C over a 60-min period. Decreasing ambient temperature elicited an increase in oxygen consumption in all age groups that received vehicle or d-NAME. The lower critical temperature and peak oxygen consumption upon exposure to cold after vehicle were 41 ± 10 ml · kg-1 · min-1 at 30°C, 43 ± 12 ml · kg-1 · min-1 at 28°C, and 55 ± 11 ml · kg-1 · min-1 at 25°C in the 1- to 2-, 5- to 6-, and 10- to 11-day-old pups, respectively. Administration of l-NAME abolished the oxygen consumption response to cold in the 1- to 2- and 5- to 6-day-old pups and significantly attenuated the oxygen consumption response to cold in the 10- to 11-day-old pups. Selected ambient temperature in the thermocline was not significantly affected by prior administration of d-NAME or l-NAME compared with vehicle. Thus our data provide evidence that the nitric oxide system plays a role in mediating autonomic but not behavioral thermoregulatory control in rat pups during early postnatal maturation.

Psychoneuroendocrine immunology: perception of stress can alter body temperature and natural killer cell activity

Psychoimmunology has been credited with using the mind as a way to alter immunity. The problem with this concept is that many of the current psychoimmunology techniques in use are aimed at alleviating stress effects on the immune system rather than at direct augmentation of immunity by the brain. Studies in animals provide a model that permits us to approach the difficulties associated with gaining an understanding of the CNS-immune system connection. A particular advantage of using animals over humans is that psychological and social contributions play a less prominent role for animals than for human subjects, since the animals are all inbred and reared under identical controlled conditions. If the insightful information provided by animal studies is correct, then psychotherapy for the treatment of diseases might be made more effective if some aspect of this knowledge is included in the design of the treatment. We emphasize conditioning as a regimen and an acceptable way to train the brain to remember an output pathway to raise immunity. We propose that a specific drug or perception (mild stress, represented by rotation, total body heating or handling) could substitute and kindle the same output pathway without the need for conditioning. If this view is correct, then instead of using conditioning, it may be possible to use an antigen to activate desired immune cells, and substitute a drug or an external environmental sensory stimulus (perception) to energize the output pathway to these cells. Alternatively, monitoring alterations of body temperature in response to a drug or perception might allow us to follow how effectively the brain is performing in altering immunity. Studies with animals suggest that there are alternative ways to use the mind to raise natural or acquired immunity in man.

Temperature regulation as possible prognostic indicator in patients with acute intracranial lesions

24 patients, 16 after severe head injury and 8 after spontaneous intracranial haematoma, were investigated by external cold load in order to determine their thermoregulatory capabilities. Tympanic temperature, several skin temperatures and oxygen consumption were measured. The patients where examined for SSEP and AEP. The cold induced thermoregulatory threshold temperature was determined by calculating the mean body temperature and by determining mean body temperature at which oxygen consumption increased due to the external cold load. In all patients core temperature and mean body temperature were significantly elevated by 1 degree C compared to controls. There was no difference of the course of the various body temperatures during cold load in the patient groups. In the trauma group 8 patients were able to increase oxygen use (VO2) during cold exposure, the other 8 patients showed no physiological thermoregulatory reaction. The heatproduction threshold temperature was increased by 1 degree C in the patient groups compared to controls. There was no significant correlation of AEP and SSEP findings to a preserved or disturbed thermoregulatory reaction. In the trauma patients, who were able to respond to a cold load, the outcome was significantly better (GOS = 3-5), than in those patients, who did not show a physiological increase of VO2 due to the cold load (GOS = 1-2). In conclusion, measurement of body temperatures alone is not sufficient to determine termoregulatory capacities. An examination using thermophysiological methods however provides more information about the function and structure damaged after severe head injury. An intact thermoregulatory systems seems to be correlated with a better prognosis after head injury.

Comparison of thermoregulatory characteristics of patients with intra- and suprasellar pituitary adenomas

Thermoregulatory capabilities under physiologic cold and heat exposure of 37 patients with suprasellar pituitary adenomas (As) and 10 patients with intrasellar adenomas (Ai) were analyzed and compared to each other and to 13 controls (Ctr.) In Ai no shift of the thermoregulatory threshold temperatures was observed. In As the regulation was shifted to a 0.5 degrees C higher mean body temperature in 82% of the patients, indicating a "set-point" elevation. The accuracy of the regulation against thermal loads was maintained, the velocity was reduced. Postoperative examination of As revealed a normalisation of the "set-point". Modifications of the hypothalamic amine systems by the compressive effect of the suprasellar adenomas are discussed to be the most probable cause for the observed thermoregulatory alterations.

The neuroendocrine system in hibernating mammals: present knowledge and open questions

The present review describes the distribution and the function-dependent reactivity pattern of those peptidergic and aminergic components of the neuroendocrine system of hibernating mammals that have been studied by histological, pharmacological and physiological techniques. Particular attention has been paid to the intrinsic connectivity of the peptidergic apparatus and its input systems. Since the reactivity patterns of the neuroendocrine system show remarkable fluctuations in relation to the various stages of hibernation and euthermia, these fluctuations have been analyzed with respect to (1) their causative role in the regulation of hibernation and (2) their secondary response to physiological changes during hibernation. The author's investigations described in this review have mainly been performed in European hedgehogs (Erinaceus europaeus), European and golden hamsters (Cricetus cricetus, Mesocricetus auratus), dormice (Glis glis), and in Richardson's and Columbian ground squirrels (Spermophilus richardsonii, Spermophilus columbianus), by the use of light- and electron-microscopic immunocytochemistry and histochemistry, in situ hybridization, radioimmunoassays and stereotaxically guided application techniques. These experiments were also performed in hypothermic animals. The (partially published) results obtained by the author and his associates are reviewed with reference to the body of evidence found in the recent literature. With respect to their reactivity patterns, several neuropeptide and transmitter systems can be regarded as candidates for control systems of hibernation. Neuronal complexes immunoreactive for endogenous opiates, in particular enkephalin, and also for vasopressin, somatostatin, substance P, corticotropin-releasing factor and serotonin are probably involved in the neuroendocrine control of hibernation.

Hind leg muscle amino acid balances in cold-exposed rats

The changes in hind leg tissue (muscle and skin) amino acid pool size and arteriovenous balance were measured in rats subjected to 0-90 min of cold exposure (4 degrees C). Tissue free amino acid pools presented a different composition pattern from protein amino acids. Muscle rapidly reacted to cold exposure by releasing small amounts of some amino acids (alanine, aspartate), with only small changes in pool size during the first 30 min. Amino acid oxidation was very limited during the whole period of cold exposure, since at all times tested there was either nil ammonia efflux or net absorption of ammonia and glutamine; i.e. the muscle was in positive nitrogen balance throughout the period studied. Thus most of the amino acid nitrogen taken up from the blood and not found in the free amino acid pools must have been incorporated into protein, since it was not oxidized, as shown by the glutamine and ammonia balance. The data on amino acid incorporation into proteins indicate that hind leg protein turnover is rapidly and widely modulated from a low initial setting upon cold exposure to a higher protein synthesis rate immediately afterwards, suggesting that protein turnover may have an important role in short-term events in cold-exposed muscle, in addition to its influence in long-term adaptation.

Lipid synthesis: a thermogenic mechanism in cold-exposed Zucker fa/fa rats

1. The oxygen consumption and carbon dioxide production of Wistar and Zucker lean (Fa/?) and obese (fa/fa) rats was measured at 4, 10, 20 and 30 degrees C. 2. There was a net synthesis of lipid at the expense of carbohydrate in Wistar rats at 20 degrees C, with active lipid oxidation at 4 degrees C, and increasing heat production at lower temperature. Zucker lean rats also showed this trend. 3. Zucker fa/fa rats synthesized lipid at 4, 10 and 20 degrees C, showing a less marked increase in heat production with lowering temperature. 4. It is postulated that Zucker obese rats synthesize lipids as a way to obtain residual metabolic heat to maintain their body temperature. This is part of a process--fully functional in Wistar and Zucker lean rats, and truncated in Zucker obese rats--in which liver lipogenesis can combine with brown adipose tissue lipolysis to generate enough heat to maintain body functions under a cold environment.

Analysis of ultradian heat production and aortic core temperature rhythms in the rat

The rhythms of aortic core temperature and overall heat production in Wistar rats was analyzed by using long series of recordings of temperature obtained from implanted thermocouple probes and heat release values from a chamber calorimeter. There was a very high degree of repetitiveness in the presentation of actual heat rhythms, with high cross-correlation values ascertained wit paired periodograms. No differences were observed between heat production between male and female adult rats. The cross-correlation for temperature gave similar figures. The cross-correlation study between heat production and aortic core temperature in the same animals was significant and showed a displacement of about 30 minutes between heat release and aortic core temperature. The analysis of heat production showed a strong predominance of rhythms with periods of 24 hours (frequencies < 11.6 microHz) or more; other rhythms detected (of roughly the same relative importance) had periods of 8 or 2.2 hours (35 or 126 microHz, respectively). The analysis of aortic core temperature showed a smaller quantitative contribution of the 8 or 2.2 hours (35 or 126 microHz) rhythms, with other harmonic rhythms interspersed (5.1 and 4.0 hours, i.e. 54 and 69 microHz). The proportion of 'noise' or cycles lower than 30 minutes (< 550 microHz) was higher in internal temperature than in the actual release of heat. The results are in agreement with the existence of a basic period of about 130 minutes (126 microHz) of warming/cooling of the blood, with a number of other harmonic rhythms superimposed upon the basic circadian rhythm.

Serotonin and genetic differences in sensitivity and tolerance to ethanol hypothermia

Mice have been selectively bred for genetic sensitivity (COLD) or insensitivity (HOT) to acute ethanol-induced hypothermia. COLD mice readily develop tolerance to the hypothermic effects of ethanol (EtOH) when it is chronically administered, while HOT mice do not. A number of studies have implicated serotonergic systems in both sensitivity and the development of tolerance to the hypothermic and ataxic effects of EtOH. In the experiments reported here, we administered the serotonin (5HT) neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) to HOT and COLD mice before the acute and chronic administration of equipotent doses of EtOH. 5,7-DHT lesions significantly reduced (by about 65%) whole brain levels of 5HT in both selected lines. This treatment reduced sensitivity to acute EtOH hypothermia in COLD, but not in HOT mice, and blocked the development of tolerance only in COLD mice. Metabolites of 5HT, norepinephrine, and dopamine were generally increased in hypothalamic and brain stem tissue after acute EtOH injection, but HOT and COLD mice were not differentially susceptible to these effects. These results suggest that genes affecting 5HT systems may mediate some of the differences in response to the hypothermic effects of EtOH characterizing HOT and COLD mice.

Fatal hyperthermia in a quadriplegic man. Possible evidence for a peripheral action of haloperidol in neuroleptic malignant syndrome

A patient with a cervical cord transection isolating his hypothalamic thermoregulatory centers from peripheral effectors suffered a fatal hyperthermic episode after receiving haloperidol. This suggests that neuroleptic malignant syndrome is caused by a peripheral, not central, effect of haloperidol.

Effect of food deprivation and refeeding on rat organ temperatures

Small thermocouple sensors were surgically implanted in the liver, kidney, hind leg muscle, interscapular brown adipose tissue, small and large intestines, dorso-lumbar internal side of the skin, periovaric adipose tissue and the lower aorta of Wistar rats. The aortic temperature was taken as core temperature. The sensors allowed continuous long-term monitoring of the temperatures of these organs. A period of 18 hours of food deprivation resulted in an overall decrease of mean core and organ temperature, brown adipose tissue temperature dropping to values lower than those of the aorta in the fed state. Liver, kidney and small intestine maintained higher temperatures than the aorta both in fed and starved states. Refeeding overshot the core temperature with increases in most organs versus both the fed and food-deprived situations. The results are concordant with an active role of brown adipose tissue in dietary induced thermogenesis. Three days of food deprivation did not alter the basic circadian rhythm of core temperatures in the rat kept at 22 degrees C, whereas it did modulate both nightly maximum and diurnal minimum temperatures to much lower settings than either in the fed or refed situations. The rat adapts to starvation by decreasing core and organ temperatures and widening the amplitude of the daily temperature cycle.

A comparative study on the effect of verapamil and prazosin on the thermoregulatory responses induced by cold or exogenous noradrenaline

1. Thermoregulatory responses to verapamil (VER; 5 mg/kg/hr) and prazosin (PRA; 0.75 mg/kg/3 hr) were investigated in rabbits exposed to cold (4 degrees C) and compared with those observed after treatment with noradrenaline (NA; 1.2 mg/kg/2 hr) under thermoneutral conditions (21 degrees C). 2. Both drugs abolished the thermogenic response to cold. 3. In the case of NA hyperthermia, only PRA was effective, i.e. the drug inhibited the thermal, metabolic and vasoconstricting actions of this amine. 4. Possible mechanisms, responsible for the thermoregulatory activity of both drugs are being discussed.

Influence of noradrenergic input into the hypothalamic paraventricular nucleus on fever in the guinea-pig

The febrile response of guinea-pigs to a bacterial pyrogen was tested under different experimental conditions: (1) during electrical stimulation of the hypothalamic paraventricular nucleus (PVN), (2) after destruction of noradrenergic afferents into the PVN by 6-hydroxydopamine (6-OHDA), (3) during a microinfusion of noradrenaline (NA) into the PVN. Electrical stimulation of the PVN neurons by implanted microelectrodes reduced the febrile response to 45% of the control values. This confirmed the proposed antipyretic function of these neurons. Chronic destruction of noradrenergic afferents to the PVN by microinjected 6-OHDA also resulted in a significant reduction of febrile responses to 38% of the control values. A microinfusion of NA into the PVN enhanced the febrile responses to bacterial endotoxin by 39% in comparison to animals microinfused with the solvent (0.9% NaCl). Immunoreactivity to an antiserum against arginine vasopressin (AVP) was compared in PVN neurons of 6-OHDA-treated and of control animals. The number of AVP-immunoreactive perikarya and the intensity of immunoreactivity were increased in the animals treated with 6-OHDA, especially in the medial part of the PVN. Since fever was increased by microinfused NA and decreased by 6-OHDA treatment, we assume an inhibitory influence of noradrenergic brain stem afferents on the proposed antipyretic vasopressinergic system of the PVN.

The efferent connections of the lateral septal nucleus in the guinea pig: intrinsic connectivity of the septum and projections to other telencephalic areas

The distribution of efferent fibers originating in the lateral septal nucleus was investigated in guinea pigs by means of anterograde tracing with Phaseolus vulgaris-leucoagglutinin (PHA-L). Special emphasis was placed on the intraseptal fiber systems. The fibers originating from the different subnuclei of the lateral septal nucleus formed massive horizontal connections in the rostrocaudal axis. Projections to the contralateral, congruent subnuclei were also detected. In the medial septum/diagonal band of Broca complex the largest number of PHA-L-stained fibers was found after application of the tracer into the dorsal subnucleus of the lateral septal nucleus; the density of the efferent fibers decreased progressively after injection into the intermediate or ventral subnuclei. In all cases the diagonal band contained a much higher number of efferent fibers from the lateral septal nucleus than from the medial septal nucleus. In the medial septal nucleus, terminal labeling was generally sparse. Other telencephalic areas (organum vasculosum of the lamina terminalis, nucleus accumbens, bed nucleus of the stria terminalis, amygdala, hippocampal complex, and other cortical areas) contained varying numbers of labeled projections. In double-labeling experiments, a close spatial relationship between PHA-L-stained fibers and vasoactive intestinal polypeptide-immunoreactive perikarya was observed in several of these target areas.