Christopher J. Tyler

Dual orexin actions on dorsal raphe and laterodorsal tegmentum neurons: noisy cation current activation and selective enhancement of Ca2+ transients mediated by L-type calcium channels.

The hypocretin/orexins (Hcrt/Orxs) are hypothalamic neuropeptides that regulate stress, addiction, feeding, and arousal behaviors. They depolarize many types of central neurons and can increase [Ca2+]i in some, including those of the dorsal raphe (DR) and laterodorsal tegmental (LDT) nuclei-two structures likely to contribute to the behavioral actions of Hcrt/Orx. In this study, we used simultaneous whole cell and Ca2+-imaging methods in mouse brain slices to compare the Hcrt/Orx-activated current in DR and LDT neurons and to determine whether it contributes to the Ca2+ influx evoked by Hcrt/Orx. We found Hcrt/Orx activates a similar noisy cation current that reversed near 0 mV in both cell types. Contrary to our expectation, this current did not contribute to the somatic Ca2+ influx evoked by Hcrt/Orx. In contrast, Hcrt/Orx enhanced the Ca2+ transients produced by voltage steps (-60 to -30 mV) by approximately 30% even in neurons lacking an inward current. This effect was abolished by nifedipine, augmented by Bay-K and abolished by bisindolylmaleimide I. Thus Hcrt/Orx has two independent actions: activation of noisy cation channels that generate depolarization and activation of a protein kinase C (PKC)-dependent enhancement of Ca2+ transients mediated by L-type Ca2+ channels. Immunocytochemistry verified that both these actions occurred in serotonergic and cholinergic neurons, indicating that Hcrt/Orx can function as a neuromodulator in these key neurons of the reticular activating system. Because regulation of Ca2+ transients mediated by L-channels is often linked to the control of transcriptional signaling, our findings imply that Hcrt/Orxs may also function in the regulation of long-term homeostatic or trophic processes.

The effect of cooling prior to and during exercise on exercise performance and capacity in the heat: a meta-analysis

Exercise is impaired in hot, compared with moderate, conditions. The development of hyperthermia is strongly linked to the impairment and as a result various strategies have been investigated to combat this condition. This meta-analysis focused on the most popular strategy: cooling. Precooling has received the most attention but recently cooling applied during the bout of exercise has been investigated and both were reviewed. We conducted a literature search and retrieved 28 articles which investigated the effect of cooling administered either prior to (n=23) or during (n=5) an exercise test in hot (wet bulb globe temperature >26°C) conditions. Mean and weighted effect size (Cohens d) were calculated. Overall, precooling has a moderate (d=0.73) effect on subsequent performance but the magnitude of the effect is dependent on the nature of the test. Sprint performance is impaired (d=−0.26) but intermittent performance and prolonged exercise are both improved following cooling (d=0.47 and d=1.91, respectively). Cooling during exercise has a positive effect on performance and capacity (d=0.76). Improvements were observed in studies with and without cooling-induced physiological alterations, and the literature supports the suggestion of a dose–response relationship among cooling, thermal strain and improvements in performance and capacity. In summary, precooling can improve subsequent intermittent and prolonged exercise performance and capacity in a hot environment but sprint performance is impaired. Cooling during exercise also has a positive effect on exercise performance and capacity in a hot environment.

Microbe-Specific Unconventional T Cells Induce Human Neutrophil Differentiation into Antigen Cross-Presenting Cells

The early immune response to microbes is dominated by the recruitment of neutrophils whose primary function is to clear invading pathogens. However, there is emerging evidence that neutrophils play additional effector and regulatory roles. The present study demonstrates that human neutrophils assume Ag cross-presenting functions and suggests a plausible scenario for the local generation of APC-like neutrophils through the mobilization of unconventional T cells in response to microbial metabolites. Vγ9/Vδ2 T cells and mucosal-associated invariant T cells are abundant in blood, inflamed tissues, and mucosal barriers. In this study, both human cell types responded rapidly to neutrophils after phagocytosis of Gram-positive and Gram-negative bacteria producing the corresponding ligands, and in turn mediated the differentiation of neutrophils into APCs for both CD4+ and CD8+ T cells through secretion of GM-CSF, IFN-γ, and TNF-α. In patients with acute sepsis, circulating neutrophils displayed a similar APC-like phenotype and readily processed soluble proteins for cross-presentation of antigenic peptides to CD8+ T cells, at a time when peripheral Vγ9/Vδ2 T cells were highly activated. Our findings indicate that unconventional T cells represent key controllers of neutrophil-driven innate and adaptive responses to a broad range of pathogens.

Cooling the Neck Region During Exercise in the Heat

CONTEXT Cooling the neck region can improve the ability to exercise in a hot environment. It might improve performance by dampening the perceived level of thermal strain, allowing individuals to override inhibitory signals. OBJECTIVE To investigate whether the enhanced ability to exercise in a hot environment observed when cooling the neck region occurs because of dampening the perceived level of thermal strain experienced and the subsequent overriding of inhibitory signals. DESIGN Crossover study. SETTING Walk-in environmental chamber. PATIENTS OR OTHER PARTICIPANTS Eight endurance-trained, nonacclimated men (age  =  26 ± 2 years, height  =  1.79 ± 0.04 m, mass  =  77.0 ± 6.2 kg, maximal oxygen uptake [V˙O(2max)]  =  56.2 ± 9.2 mL·kg(-1)·min(-1)) participated. INTERVENTION(S) Participants completed 4 running tests at approximately 70% V˙O(2max) to volitional exhaustion: 2 familiarization trials followed by 2 experimental trials (cooling collar [CC] and no collar [NC]). Trials were separated by 7 days. Familiarization and NC trials were performed without a collar and used to assess the test variability. MAIN OUTCOME MEASURE(S) Time to volitional exhaustion, heart rate, rectal temperature, neck skin temperature, rating of perceived exertion, thermal sensation, and feeling scale (pleasure/displeasure) were measured. RESULTS Time to volitional exhaustion was increased by 13.5% ± 3.8% (CC  =  43.15 ± 12.82 minutes, NC  =  38.20 ± 11.70 minutes; t(7)  =  9.923, P < .001) with the CC, which reduced mean neck skin temperature throughout the test (P < .001). Participants terminated exercise at identical levels of perceived exertion, thermal sensation, and feeling scale, but the CC enabled participants to tolerate higher rectal temperatures (CC  =  39.61°C ± 0.45°C, NC  =  39.18°C ± 0.7°C; t(7)  =  -3.217, P  =  .02) and heart rates (CC  =  181 ± 6 beats/min, NC  =  178 ± 9 beats/min; t(7)  =  -2.664, P  =  .03) at the point of termination. CONCLUSIONS Cooling the neck increased the time taken to reach volitional exhaustion by dampening the perceived levels of thermal strain.

Human Vγ9/Vδ2 T cells: Innate adaptors of the immune system

Unconventional T cells are gaining center stage as important effector and regulatory cells that orchestrate innate and adaptive immune responses. Human Vγ9/Vδ2 T cells are amongst the best understood unconventional T cells, as they are easily accessible in peripheral blood, can readily be expanded and manipulated in vitro, respond to microbial infections in vivo and can be exploited for novel tumor immunotherapies. We here review findings that suggest that Vγ9/Vδ2 T cells, and possibly other unconventional human T cells, play an important role in bridging innate and adaptive immunity by promoting the activation and differentiation of various types of antigen-presenting cells (APCs) and even turning into APCs themselves, and thereby pave the way for antigen-specific effector responses and long-term immunological memory. Although the direct physiological relevance for most of these mechanisms still needs to be demonstrated in vivo, these findings may have implications for novel therapies, diagnostic tests and vaccines.

Differential actions of orexin receptors in brainstem cholinergic and monoaminergic neurons revealed by receptor knockouts: implications for orexinergic signaling in arousal and narcolepsy

Orexin neuropeptides influence multiple homeostatic functions and play an essential role in the expression of normal sleep-wake behavior. While their two known receptors (OX1 and OX2) are targets for novel pharmacotherapeutics, the actions mediated by each receptor remain largely unexplored. Using brain slices from mice constitutively lacking either receptor, we used whole-cell and Ca2+ imaging methods to delineate the cellular actions of each receptor within cholinergic [laterodorsal tegmental nucleus (LDT)] and monoaminergic [dorsal raphe (DR) and locus coeruleus (LC)] brainstem nuclei—where orexins promote arousal and suppress REM sleep. In slices from OX−/−2 mice, orexin-A (300 nM) elicited wild-type responses in LDT, DR, and LC neurons consisting of a depolarizing current and augmented voltage-dependent Ca2+ transients. In slices from OX−/−1 mice, the depolarizing current was absent in LDT and LC neurons and was attenuated in DR neurons, although Ca2+-transients were still augmented. Since orexin-A produced neither of these actions in slices lacking both receptors, our findings suggest that orexin-mediated depolarization is mediated by both receptors in DR, but is exclusively mediated by OX1 in LDT and LC neurons, even though OX2 is present and OX2 mRNA appears elevated in brainstems from OX−/−1 mice. Considering published behavioral data, these findings support a model in which orexin-mediated excitation of mesopontine cholinergic and monoaminergic neurons contributes little to stabilizing spontaneous waking and sleep bouts, but functions in context-dependent arousal and helps restrict muscle atonia to REM sleep. The augmented Ca2+ transients produced by both receptors appeared mediated by influx via L-type Ca2+ channels, which is often linked to transcriptional signaling. This could provide an adaptive signal to compensate for receptor loss or prolonged antagonism and may contribute to the reduced severity of narcolepsy in single receptor knockout mice.

Neck cooling and running performance in the heat: single versus repeated application

PURPOSE This study aimed to evaluate the effect of sustained neck cooling during time trial running in a hot environment. METHODS Seven nonacclimated, familiarized males completed three experimental 90-min preloaded time trials in the heat (30.4°C ± 0.1°C and 53% ± 2% relative humidity). During one of the trials, the, participants wore a cooling collar from the start (CC); in another, they wore a collar from the start which was replaced at 30-min intervals (CC(replaced)); and in the last trial, they wore no collar (NC). Participants ran for 75 min at 60% VO(2max) and then performed a 15-min time trial blinded from the distance ran. Distance ran, rectal temperature, neck skin temperature, HR, fluid loss and consumption, peripheral lactate, glucose, dopamine, serotonin and cortisol, RPE, thermal sensation, and feeling scales were recorded. Significance was set a priori at the P < 0.05 level. RESULTS Participants ran further in CC (2779 ± 299 m) compared with NC (2597 ± 291 m, P = 0.007; d = 0.67) and in CC(replaced) (2776 ± 331 m) compared with NC (P = 0.008; d = 0.62). There was no difference in the distance covered in CC compared with that in CC(replaced) (P = 0.998). The collar lowered neck temperature (P < 0.001) and the thermal sensation of the neck region (P < 0.001) but had no effect on any of the other physiological, endocrinological, or perceptual variables. CONCLUSIONS Cooling the surface of the neck improves time trial performance in a hot environment without altering physiological or neuroendocrinological responses. Maintenance of a lower neck temperature via the replacement of a CC has no additional benefit to an acute cooling intervention.

The effect of skin thermistor fixation method on weighted mean skin temperature

The purpose of this study was to investigate the effect of three different skin thermistor attachment methods on weighted mean skin temperature (WMT(sk)) at three different ambient temperatures (approximately 24 °C (TEMP); approximately 30 °C (WARM); approximately 35 °C (HOT)) compared to uncovered thermistors. Eleven, non-acclimated, volunteers completed three 5 min bouts of submaximal cycling (approximately 70 W mechanical work)-one at each environmental condition in sequential order (TEMP, WARM, HOT). One thermistor was fixed to the sternal notch whilst four skin thermistors were spaced at 3 cm intervals on each of the sites on the limbs as per the formula of Ramanathan (1964 J. Appl. Physiol. 19 531-3). Each thermistor was either held against the skin uncovered (UC) or attached with surgical acrylic film dressing (T); surgical acrylic film dressing and hypoallergenic surgical tape (TT) or surgical acrylic film dressing, hypoallergenic surgical tape and surgical bandage (TTC). The WMT(sk) calculated was significantly lower in UC compared to T, TT and TTC (p < 0.001, d = 0.46), in T compared to TT and TTC (p < 0.001, d = 0.33) and in TT compared to TTC (p < 0.001; d = 0.25). The mean differences (across the three temperatures) were + 0.27 ± 0.34 °C, + 0.52 ± 0.35 °C and + 0.82 ± 0.34 °C for T, TT and TTC, respectively. The results demonstrate that the method of skin thermistor attachment can result in the significant over-estimation of weighted mean skin temperature.

Urotensin II acts as a modulator of mesopontine cholinergic neurons

Urotensin II (UII) is a vasomodulatory peptide that was not predicted to elicit CNS activity. However, because we have recently shown that the urotensin II receptor (UII-R) is selectively expressed in rat mesopontine cholinergic (MPCh) neurons, we hypothesize that UII may have a central function. The present study demonstrates that the UII system is able to modulate MPCh neuron activity. Brain slice experiments demonstrate that UII excites MPCh neurons of the mouse laterodorsal tegmentum (LDTg) by activating a slow inward current. Furthermore, microinfusion of UII into the ventral tegmental area produces a sustained increase in dopamine efflux in the nucleus accumbens, as measured by in vivo chronoamperometry. In agreement with UII activation of MPCh neurons, intracerebroventricular injections of UII significantly modulate ambulatory movements in both rats and mice but do not significantly affect startle habituation or prepulse inhibition. The present study establishes that UII is a neuromodulator that may be exploited to target disorders involving MPCh dysfunction.

Effects of a cooling collar on affect, ratings of perceived exertion, and running performance in the heat

Abstract During prolonged exercise, ratings of perceived exertion (RPE) and affect (pleasure; activation) play an important role in performance, especially in hot conditions. Although various mechanisms have been tried to manage the effects of heat (e.g. cooling jackets), the purpose of the current research was to assess the effect of a cooling collar on RPE, affect, thermal sensation, and running performance in the heat. Participants (n =8) wore a cold collar, uncooled collar or no collar as they completed three 90-min preloaded treadmill time-trials in the heat (30.5±0.1°C), which included 75 min at ∼60% [Vdot]O2max followed by a 15-min time-trial. Affect, RPE, and thermal sensation were measured throughout. Performance during the time-trial was significantly improved in the cold collar compared with the uncooled collar and no-collar trials; however, pleasure and activation ratings were highest for the no-collar trial. Findings suggest that a cooling collar may improve performance, but not necessarily “feel good”. Practically, it seems necessary to ensure sufficient education about the benefits, on balance, of the cold collar, while the performance improvements outweighed the reported discomfort of athletes in this study. In addition, the cold collar may prove quite beneficial for individuals who work in hot climates and or conditions, as it may be effective in minimizing discomfort associated with heat for other groups as well.