Efferent Response Research Articles

Cardiac vagal afferent neurotransmission in health and disease: review and knowledge gaps.

The meticulous control of cardiac sympathetic and parasympathetic tone regulates all facets of cardiac function. This precise calibration of cardiac efferent innervation is dependent on sensory information that is relayed from the heart to the central nervous system. The vagus nerve, which contains vagal cardiac afferent fibers, carries sensory information to the brainstem. Vagal afferent signaling has been predominantly shown to increase parasympathetic efferent response and vagal tone. However, cardiac vagal afferent signaling appears to change after cardiac injury, though much remains unknown. Even though subsequent cardiac autonomic imbalance is characterized by sympathoexcitation and parasympathetic dysfunction, it remains unclear if, and to what extent, vagal afferent dysfunction is involved in the development of vagal withdrawal. This review aims to summarize the current understanding of cardiac vagal afferent signaling under in health and in the setting of cardiovascular disease, especially after myocardial infarction, and to highlight the knowledge gaps that remain to be addressed.

Efferent Control in Musicians: A Review

It is widely established that musicians possess a higher level in certain auditory perceptual abilities when compared to non-musicians. This improvement may be mediated, at least in part, by changes in the cochlear response induced by reflex activation of the olivocochlear efferent system. In this review, we describe and analyze the scientific evidence regarding possible differences in the efferent response in musicians and non-musicians. The main evidence observed is that musicians present a greater robustness of the efferent olivocochlear reflex when measured by suppression of otoacoustic emissions and compared to non-musicians. Analyzing the articles presented in this review, it is possible to point out that the differential role of the efferent effect in musicians is not yet established. There is not enough evidence to support the idea that the olivocochlear system favors comparative changes in the properties of musicians' auditory filters. New studies with psychoacoustic techniques, among others, are needed to measure the effect of the olivocochlear reflex on tuning, gain, compression, or temporal resolution in musicians and non-musicians.

Effects of focused ultrasound pulse duration on stimulating cortical and subcortical motor circuits in awake sheep.

Low-intensity transcranial focused ultrasound (tFUS) offers new functional neuromodulation opportunities, enabling stimulation of cortical as well as deep brain areas with high spatial resolution. Brain stimulation of awake sheep, in the absence of the confounding effects of anesthesia on brain function, provides translational insight into potential human applications with safety information supplemented by histological analyses. We examined the effects of tFUS pulsing parameters, particularly regarding pulse durations (PDs), on stimulating the cortical motor area (M1) and its thalamic projection in unanesthetized, awake sheep (n = 8). A wearable tFUS headgear, custom-made for individual sheep, enabled experiments to be conducted without using anesthesia. FUS stimuli, each 200 ms long, were delivered to the M1 and the thalamus using three different PDs (0.5, 1, and 2 ms) with the pulse repetition frequency (PRF) adjusted to maintain a 70% duty cycle at a derated in situ spatial-peak temporal-average intensity (Ispta) of 3.6 W/cm2. Efferent electromyography (EMG) responses to stimulation were quantified from both hind limbs. Group-averaged EMG responses from each of the hind limbs across the experimental conditions revealed selective responses from the hind limb contralateral to sonication. The use of 0.5 and 1 ms PDs generated higher EMG signal amplitudes compared to those obtained using a 2 ms PD. Faster efferent response was also observed from thalamic stimulation than that from stimulating the M1. Post-sonication behavioral observation and histological assessment performed 24 h and 1 month after sonication were not indicative of any abnormalities. The results suggest the presence of pulsing scheme-dependent effects of tFUS on brain stimulation and attest its safety in awake large animals.

Failure To Rescue, What Can Be Done To Prevent It?

Introduction: Failure to Rescue (FTR) is the failure to prevent a patient’s death after a complication. It measures the ability of a hospital to prevent the death of patients who develop one or more complication that was not present at the time of admission. Therefore, the aim of this study is to review the factors that contribute to FTR, and the measures and strategies that can be applied to prevent the FTR events, in order to discuss the best way to improve patient outcomes in the hospital setting. Methods: A search was conducted on PUBMED retrieving a total of 464 articles. A review of the selected articles’ bibliography was conducted to find other relevant articles. Sixty studies were reviewed in this paper. Results: Patient factors as increasing age, comorbidities and frailty increase the risk of FTR, as well as an increasing number of complications. Several hospital factors, nursing care, and microsystem also influence FTR. Some track and Trigger Systems (TTS) and Early Warning Scores (EWS) have been shown to predict clinical deterioration. On the other hand, machine learning systems have outperformed EWS. Rapid response teams have become the standard approach to delivery and escalation of care, and cognitive aids and crisis checklists also have potential to help reduce FTR. Conclusion: Patient and hospital factors are often non-modifiable; thus, microsystem factors could be a target for improvement. Creating clinical pathways can improve surveillance, and communication tools like SBAR can help relay information. EWS, machine learning models and continuous monitoring are strategies that can help detect clinical deterioration. In the efferent limb rapid response teams have shown to reduce FTR.

Effect of Use of Aluminum Foil Blanket Against Increased Body Temperature in Patients Hypothermia after Spinal Anesthesia in the Operation Room of the Sele Be Solu Hospital, Sorong West Papua

Local, general, and regional anesthesia is complex actions or events that cannot be separated from electiveor emergency surgery. Anesthesia affects the three thermoregulatory elements consisting of afferent inputelements, signal regulation in the central region, and also the efferent response which can lead to hypothermia.This study aims to determine the effect of the use of aluminum foil blankets on increasing body temperaturein hypothermia patients after spinal anesthesia. This study uses a Pre-Experimental study design with a PrePost Test Only Design approach. Sampling in this study used a purposive sampling technique. 12 sampleswere given the intervention to use aluminum foil blankets. Analysis of data using the Shapiro-Wilk test,Homogeneity of Lavene Test, and Paired sample T-Test. The results of statistical tests using the PairedSample T-Test obtained a p-value of less than 0.05 (<0.05), namely p = 0.000. There is an influence of theuse of aluminum foil blankets to increase body temperature in hypothermia patients after spinal anesthesia.

Anodal block permits directional vagus nerve stimulation

Vagus nerve stimulation (VNS) is a bioelectronic therapy for disorders of the brain and peripheral organs, and a tool to study the physiology of autonomic circuits. Selective activation of afferent or efferent vagal fibers can maximize efficacy and minimize off-target effects of VNS. Anodal block (ABL) has been used to achieve directional fiber activation in nerve stimulation. However, evidence for directional VNS with ABL has been scarce and inconsistent, and it is unknown whether ABL permits directional fiber activation with respect to functional effects of VNS. Through a series of vagotomies, we established physiological markers for afferent and efferent fiber activation by VNS: stimulus-elicited change in breathing rate (ΔBR) and heart rate (ΔHR), respectively. Bipolar VNS trains of both polarities elicited mixed ΔHR and ΔBR responses. Cathode cephalad polarity caused an afferent pattern of responses (relatively stronger ΔBR) whereas cathode caudad caused an efferent pattern (stronger ΔHR). Additionally, left VNS elicited a greater afferent and right VNS a greater efferent response. By analyzing stimulus-evoked compound nerve potentials, we confirmed that such polarity differences in functional responses to VNS can be explained by ABL of A- and B-fiber activation. We conclude that ABL is a mechanism that can be leveraged for directional VNS.

Neural Encoding of Amplitude Modulations in the Human Efferent System.

Most natural sounds, including speech, exhibit temporal amplitude fluctuations. This information is encoded as amplitude modulations (AM)-essential for auditory and speech perception. The neural representation of AM has been studied at various stages of the ascending auditory system from the auditory nerve to the cortex. In contrast, research on neural coding of AM in the efferent pathway has been extremely limited. The objective of this study was to investigate the encoding of AM signals in the medial olivocochlear system by measuring the modulation transfer functions of the efferent response in humans. A secondary goal was to replicate the controversial findings from the literature that efferent stimulation produces larger effects for the AM elicitor with 100Hz modulation frequency in comparison with the unmodulated elicitor. The efferent response was quantified by measuring changes in stimulus-frequency otoacoustic emission magnitude due to various modulated and unmodulated elicitors. Unmodulated, broadband noise elicitors yielded either slightly larger or similar efferent responses relative to modulated elicitors depending on the modulation frequency. Efferent responses to the unmodulated and modulated elicitors with 100Hz modulation frequency were not significantly different. The efferent system encoding of AM sounds-modulation transfer functions-can be modeled with a first-order Butterworth low-pass filter with different cutoff frequencies for ipsilateral and contralateral elicitors. The ipsilateral efferent pathway showed a greater sensitivity to AM information comparted to the contralateral pathway. Efferent modulation transfer functions suggest that the ability of the system to follow AM decreases with increasing modulation frequency and that efferents may not be fully operating on the envelope of the speech.

Activation of µ-opioid receptors in the rostral ventrolateral medulla blocks the sympathetic counterregulatory response to glucoprivation.

Activation of neurons in the rostral ventrolateral medulla (RVLM) following glucoprivation initiates sympathoadrenal activation, adrenaline release, and increased glucose production. Here, we aimed to determine the role of RVLM µ-opioid receptors in the counterregulatory response to systemic glucoprivation. Experiments were performed in pentobarbital sodium anesthetized male Sprague-Dawley rats ( n = 30). Bilateral activation of RVLM µ-opioid receptors with [d-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO) (8 mM, 50 nl) depressed adrenal sympathetic nerve activity for ~60 min ( n = 6; Δ49.9 ± 5.8%, P < 0.05). The counterregulatory response to glucoprivation (measured by adrenal sympathetic efferent nerve activity) induced by 2-deoxyglucose (2-DG) ( n = 6; Δ63.6 ± 16.5%, P < 0.05) was completely blocked 60 min after DAMGO microinjections ( n = 6; Δ10.2 ± 3.5%, P < 0.05). Furthermore, DAMGO pretreatment attenuated the increase in blood glucose levels after 2-DG infusion ( n = 6; 6.1 ± 0.7mmol/l vs. baseline 5.2 ± 0.3mmol/l, P > 0.05) compared with 2-DG alone ( n = 6; 7.6 ± 0.4mmol/l vs. baseline 6.0 ± 0.4mmol/l, P < 0.05). Thus, activation of RVLM µ-opioid receptors attenuated the neural efferent response to glucoprivation and reduced glucose production.

Activation of μ‐opioid receptors in the rostral ventrolateral medulla blocks the sympathetic counter‐regulatory response to glucoprivation

Intensive insulin therapy is the gold standard for managing serum glucose levels in patients with insulin‐deficient diabetes mellitus. Hypoglycaemia‐associated autonomic failure (HAAF) is a clinical syndrome characterised by the absence of a glucose counter‐regulatory response to hypoglycaemia or glucoprivation. The precise physiologic mechanisms underlying HAAF remain unknown. Recent data from human studies suggests activation of the endogenous opioid system during antecedent hypoglycaemia may contribute to unawareness of hypoglycaemia.Here, we aimed to determine whether or not activation of rostral ventrolateral medullary (RVLM) μ‐opioid receptors results in downstream sympathoinhibition, resulting in attenuated glucose production, and an impaired counter‐regulatory response following glucoprivation. Experiments were performed in sodium pentobarbital anaesthetised (65 mg/kg) male Sprague‐Dawley rats (250–350g).Bilateral activation of RVLM μ‐opioid receptors with DAMGO (8 mM, 50 nl) caused depression of adrenal sympathetic nerve activity (ASNA), that lasted at least 60 minutes (Δ−56.9 ± 9.8% vs saline: Δ1.7 ± 4.4%, P&lt;0.05). In parallel, blood glucose levels were also reduced (Δ−0.8 ± 0.2 mM vs saline: Δ0.2 ± 0.3 mM, P&lt;0.05). The counter‐regulatory response to glucoprivation (measured by ASNA efferent activity) induced by 2‐deoxyglucose was completely attenuated 60 minutes following DAMGO microinjections (Δ−4.4 ± 0.7% vs saline+2‐DG: Δ59.6 ± 8.0%, P&lt;0.05). Bilateral μ‐opioid receptor activation also caused a significant decrease in mean arterial pressure (Δ−28.7 ± 6.1 mmHg vs saline: Δ−9.9 ± 7.3 mmHg, P&lt;0.05) and heart rate (Δ−40.4 ± 14.9 bpm vs saline: Δ−11.1 ± 9.7 bpm, P&lt;0.05).In conclusion, activation of RVLM μ‐opioid receptors reproduces features of HAAF (attenuated neural efferent response to glucoprivation). The mechanism underlying HAAF may include activation of RVLM μ‐opioid receptors to facilitate sympathoinhibition. Coupled with this sympathoinhibition, the reduced blood glucose levels may contribute to HAAF by increasing the threshold to elicit counter‐regulatory response.Support or Funding InformationNational Health and Medical Research Council of Australia, The University of Sydney, The Heart Research InstituteThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Baroreflex control of renal sympathetic nerve activity in early heart failure assessed by the sequence method.

The integrity of the baroreflex control of sympathetic activity in heart failure (HF) remains under debate. We proposed the use of the sequence method to assess the baroreflex control of renal sympathetic nerve activity (RSNA). The sequence method assesses the spontaneous arterial pressure (AP) fluctuations and their related changes in heart rate (or other efferent responses), providing the sensitivity and the effectiveness of the baroreflex. Effectiveness refers to the fraction of spontaneous AP changes that elicits baroreflex-mediated variations in the efferent response. Using three different approaches, we showed that the baroreflex sensitivity between AP and RSNA is not altered in early HF rats. However, the sequence method provided evidence that the effectiveness of baroreflex in changing RSNA in response to AP changes is markedly decreased in HF. The results help us better understand the baroreflex control of the sympathetic nerve activity. In heart failure (HF), the reflex control of the heart rate is known to be markedly impaired; however, the baroreceptor control of the sympathetic drive remains under debate. Applying the sequence method to a series of arterial pressure (AP) and renal sympathetic nerve activity (RSNA), we demonstrated a clear dysfunction in the baroreflex control of sympathetic activity in rats with early HF. We analysed the baroreflex control of the sympathetic drive using three different approaches: AP vs. RSNA curve, cross-spectral analysis and sequence method between AP and RSNA. The sequence method also provides the baroreflex effectiveness index (BEI), which represents the percentage of AP ramps that actually produce a reflex response. The methods were applied to control rats and rats with HF induced by myocardial infarction. None of the methods employed to assess the sympathetic baroreflex gain were able to detect any differences between the control and the HF group. However, rats with HF exhibited a lower BEI compared to the controls. Moreover, an optimum delay of 1 beat was observed, i.e. 1 beat is required for the RSNA to respond after AP changing, which corroborates with the findings related to the timing between these two variables. For delay 1, the BEI of the controls was 0.45±0.03, whereas the BEI of rats with HF was 0.29±0.09 (P<0.05). These data demonstrate that while the gain of the baroreflex is not affected in early HF, its effectiveness is markedly decreased. The analysis of the spontaneous changes in AP and RSNA using the sequence method provides novel insights into arterial baroreceptor reflex function.

Vagal tone: effects on sensitivity, motility, and inflammation.

The vagus nerve (VN) is a key element of the autonomic nervous system. As a mixed nerve, the VN contributes to the bidirectional interactions between the brain and the gut, i.e., the brain-gut axis. In particular, after integration in the central autonomic network of peripheral sensations such as inflammation and pain via vagal and spinal afferents, an efferent response through modulation of preganglionic parasympathetic neurons of the dorsal motor nucleus of the vagus and/or preganglionic sympathetic neurons of the spinal cord is able to modulate gastrointestinal nociception, motility, and inflammation. A low vagal tone, as assessed by heart rate variability, a marker of the sympatho-vagal balance, is observed in functional digestive disorders and inflammatory bowel diseases. To restore a normal vagal tone appears as a goal in such diseases. Among the therapeutic tools, such as drugs targeting the cholinergic system and/or complementary medicine (hypnosis, meditation…), deep breathing, physical exercise, VN stimulation (VNS), either invasive or non-invasive, appears as innovative. There is new evidence in the current issue of this Journal supporting the role of VNS in the modulation of gastrointestinal functions.

Effects of Cooling During Exercise on Thermoregulatory Responses of Men With Paraplegia.

People with spinal cord injury (SCI) have an altered afferent input to the thermoregulatory center, resulting in a reduced efferent response (vasomotor control and sweating capacity) below the level of the lesion. Consequently, core body temperature rises more rapidly during exercise in individuals with SCI compared with people who are able-bodied. Cooling strategies may reduce the thermophysiological strain in SCI. The aim of this study was to examine the effects of a cooling vest on the core body temperature response of people with a thoracic SCI during submaximal exercise. Ten men (mean age=44 years, SD=11) with a thoracic lesion (T4-T5 or below) participated in this randomized crossover study. Participants performed two 45-minute exercise bouts at 50% maximal workload (ambient temperature 25°C), with participants randomized to a group wearing a cooling vest or a group wearing no vest (separate days). Core body temperature and skin temperature were continuously measured, and thermal sensation was assessed every 3 minutes. Exercise resulted in an increased core body temperature, skin temperature, and thermal sensation, whereas cooling did not affect core body temperature. The cooling vest effectively decreased skin temperature, increased the core-to-trunk skin temperature gradient, and tended to lower thermal sensation compared with the control condition. The lack of differences in core body temperature among conditions may be a result of the relative moderate ambient temperature in which the exercise was performed. Despite effectively lowering skin temperature and increasing the core-to-trunk skin temperature gradient, there was no impact of the cooling vest on the exercise-induced increase in core body temperature in men with low thoracic SCI.

Reinnervation following catheter-based radio-frequency renal denervation.

What is the topic of this review? Does catheter-based renal denervation effectively denervate the afferent and efferent renal nerves and does reinnervation occur? What advances does it highlight? Following catheter-based renal denervation, the afferent and efferent responses to electrical stimulation were abolished, renal sympathetic nerve activity was absent, and levels of renal noradrenaline and immunohistochemistry for tyrosine hydroxylase and calcitonin gene-related peptide were significantly reduced. By 11months after renal denervation, both the functional responses and anatomical markers of afferent and efferent renal nerves had returned to normal, indicating reinnervation. Renal denervation reduces blood pressure in animals with experimental hypertension and, recently, catheter-based renal denervation was shown to cause a prolonged decrease in blood pressure in patients with resistant hypertension. The randomized, sham-controlled Symplicity HTN-3 trial failed to meet its primary efficacy end-point, but there is evidence that renal denervation was incomplete in many patients. Currently, there is little information regarding the effectiveness of catheter-based renal denervation and the extent of reinnervation. We assessed the effectiveness of renal nerve denervation with the Symplicity Flex catheter and the functional and anatomical reinnervation at 5.5 and 11months postdenervation. In anaesthetized, non-denervated sheep, there was a high level of renal sympathetic nerve activity, and electrical stimulation of the renal nerve increased blood pressure and reduced heart rate (afferent response) and caused renal vasoconstriction and reduced renal blood flow (efferent response). Immediately after renal denervation, renal sympathetic nerve activity and the responses to electrical stimulation were absent, indicating effective denervation. By 11months after denervation, renal sympathetic nerve activity was present and the responses to electrical stimulation were normal, indicating reinnervation. Anatomical measures of renal innervation by sympathetic efferent nerves (tissue noradrenaline and tyrosine hydroxylase) and afferent sensory nerves (calcitonin gene-related peptide) demonstrated large decreases at 1week postdenervation, but normal levels at 11months postdenervation. In summary, catheter-based renal denervation is effective, but reinnervation occurs. Studies of central and renal changes postdenervation are required to understand the causes of the prolonged hypotensive response to catheter-based renal denervation in human hypertension.

Hypothermia--mechanism of action and pathophysiological changes in the human body

This review focuses on the physiological responses and pathophysiological changes induced by hypothermia. Normal body function depends on its ability to maintain thermal homeostasis. The human body can be divided arbitrarily into two thermal compartments: a core compartment (trunk and head), with precisely regulated temperature around 37°C, and a peripheral compartment (skin and extremities) with less strictly controlled temperature, and lower than the core temperature. Thermoregulatory processes occur in three phases: afferent thermal sensing, central regulation, mainly by the preoptic area of the anterior hypothalamus, and efferent response. Exposure to cold induces thermoregulatory responses including cutaneous vasoconstriction, shivering and non-shivering thermogenesis, and behavioral changes. Alterations of body temperature associated with impaired thermoregulation, decreased heat production or increased heat loss can lead to hypothermia. Hypothermia is defined as a core body temperature below 35ºC, and may be classified according to the origin as accidental (e.g. caused by exposure to a cold environment, drugs, or illness) or intentional (i.e. therapeutic), or by the degree of hypothermia as mild, moderate or severe. Classification by temperature is not universal. Lowering of body temperature disrupts the physiological processes at the molecular, cellular and system level, but hypothermia induced prior to cardiosurgical or neurosurgical procedures, by the decrease in tissue oxygen demand, can reduce the risk of cerebral or cardiac ischemic damage. Therapeutic hypothermia has been recommended as a clinical procedure in situations characterized by ischemia, such as cardiac arrest, stroke and brain injuries.

Reinnervation of renal afferent and efferent nerves at 5.5 and 11 months after catheter-based radiofrequency renal denervation in sheep.

Previous studies indicate that catheter-based renal denervation reduces blood pressure and renal norepinephrine spillover in human resistant hypertension. The effects of this procedure on afferent sensory and efferent sympathetic renal nerves, and the subsequent degree of reinnervation, have not been investigated. We therefore examined the level of functional and anatomic reinnervation at 5.5 and 11 months after renal denervation using the Symplicity Flex catheter. In normotensive anesthetized sheep (n=6), electric stimulation of intact renal nerves increased arterial pressure from 99±3 to 107±3 mm Hg (afferent response) and reduced renal blood flow from 198±16 to 85±20 mL/min (efferent response). In a further group (n=6), immediately after denervation, renal sympathetic nerve activity was absent and the responses to electric stimulation were abolished. At 11 months after denervation (n=5), renal sympathetic nerve activity and the responses to electric stimulation were at normal levels. Immunohistochemical staining for renal efferent (tyrosine hydroxylase) and renal afferent nerves (calcitonin gene-related peptide), as well as renal norepinephrine levels, was normal 11 months after denervation. Findings at 5.5 months after denervation were similar (n=5). In summary, catheter-based renal denervation effectively ablated the renal afferent and efferent nerves in normotensive sheep. By 11 months after denervation the functional afferent and efferent responses to electric stimulation were normal. Reinnervation at 11 months after denervation was supported by normal anatomic distribution of afferent and efferent renal nerves. In view of this evidence, the mechanisms underlying the prolonged hypotensive effect of catheter-based renal denervation in human resistant hypertension need to be reassessed.

390 High Fat Diet During the Perinatal Period Decreases Vagal Efferent Motoneuron Excitability and Response to Cholecystokinin Even in the Absence of Obesity

390 High Fat Diet During the Perinatal Period Decreases Vagal Efferent Motoneuron Excitability and Response to Cholecystokinin Even in the Absence of Obesity

Mapping and signaling of neural pathways involved in the regulation of hydromineral homeostasis

Several forebrain and brainstem neurochemical circuitries interact with peripheral neural and humoral signals to collaboratively maintain both the volume and osmolality of extracellular fluids. Although much progress has been made over the past decades in the understanding of complex mechanisms underlying neuroendocrine control of hydromineral homeostasis, several issues still remain to be clarified. The use of techniques such as molecular biology, neuronal tracing, electrophysiology, immunohistochemistry, and microinfusions has significantly improved our ability to identify neuronal phenotypes and their signals, including those related to neuron-glia interactions. Accordingly, neurons have been shown to produce and release a large number of chemical mediators (neurotransmitters, neurohormones and neuromodulators) into the interstitial space, which include not only classic neurotransmitters, such as acetylcholine, amines (noradrenaline, serotonin) and amino acids (glutamate, GABA), but also gaseous (nitric oxide, carbon monoxide and hydrogen sulfide) and lipid-derived (endocannabinoids) mediators. This efferent response, initiated within the neuronal environment, recruits several peripheral effectors, such as hormones (glucocorticoids, angiotensin II, estrogen), which in turn modulate central nervous system responsiveness to systemic challenges. Therefore, in this review, we shall evaluate in an integrated manner the physiological control of body fluid homeostasis from the molecular aspects to the systemic and integrated responses.

Manejo de la hipotermia perioperatoria

Hypothermia (body temperature under 36°C) is the thermal disorder most frequently found in surgical patients, but should be avoided as a means of reducing morbidity and costs. Temperature should be considered as a vital sign and all staff involved in the care of surgical patients must be aware that it has to be maintained within normal limits. Maintaining body temperature is the result, as in any other system, of the balance between heat production and heat loss. Temperature regulation takes place through a system of positive and negative feedback in the central nervous system, being developed in three phases: thermal afferent, central regulation and efferent response. Prevention is the best way to ensure a normal temperature. The active warming of the patient during surgery is mandatory. Using warm air is the most effective, simple and cheap way to prevent and treat hypothermia.

Effects of Activation of TRPM8 Ion Channels on Thermoregulatory Reactions in Cooling

Animal experiments were performed to study the effects of activation of cold- and menthol-sensitive TRPM8 receptors by menthol on thermoregulatory parameters in thermoneutral conditions and on cooling. Total oxygen consumption was measured, along with expiration of carbon dioxide, the respiratory coefficient, the skin vessel constriction reaction, and contractile muscle activity. Application of menthol in thermoneutral conditions led to increased oxygen consumption and a decrease in the respiratory coefficient which, in the absence of shivering, provides evidence of increased non-contractile thermogenesis and lipolysis. Cooling on the background of activation of the TRPM8 receptor was characterized by decreases in the thresholds of all thermoregulatory reactions with no change in their initiation sequence, along with increases in the metabolic components of emergency thermogenesis, leading to improved maintenance of deep body temperature when environmental cold acts on the body. These results provide evidence for a contribution of TRPM8 ion channels to increased activation of thermoreceptor structures generating afferent signals involved in maintaining metabolism in thermoneutral conditions and forming the structure of the efferent response of the body to cold.

Differential control of efferent sympathetic activity revisited

This article reviews 40 years of research (1970-2010) into the capability of the efferent sympathetic nervous system to display differential responsiveness. Discovered first were antagonistic changes of activity in sympathetic filaments innervating functionally different sections of the cardiovascular system in response to thermal stimulation. During the subsequent four decades of investigation, a multitude of differential sympathetic efferent response patterns were identified, ranging from opposing activity changes at the level of multi-fiber filaments innervating different organs to the level of single fibers controlling functionally different structures in the same organ. Differential sympathetic responsiveness was shown to be displayed in response to exogenous or artificial stimulation of afferent sensory fibers transmitting particular exogenous stimuli, especially those activating peripheral nociceptors. Moreover, sympathetic differentiation was found to be characteristic of autonomic responses to environmental changes by which homeostasis in the broadest sense would be challenged. Heat or cold loads or their experimental equivalents, altered composition of inspired air or changes in blood gas composition, imbalances of body fluid control, and exposure to agents challenging the immune system were shown to elicit differential efferent sympathetic response patterns which often displayed a high degree of specificity. In summary, autonomic adjustments to changes of biometeorological parameters may be considered as representative of the capability of the sympathetic nervous system to exert highly specific efferent control of organ functions by which bodily homeostasis is maintained.