| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1 Department of Neurobiology, School of Medicine, University of California, Los Angeles, California 90095-1763; and 2 Department of Zoology, University of British Columbia, Vancouver V6T 1Z4, British Columbia, Canada
 |
ABSTRACT |
|---|
 TOP
 ABSTRACT
 INTRODUCTION
METHODS AND MATERIALS
RESULTS
DISCUSSION
REFERENCES
|
|---|
This study was designed to examine the possibility that respiratory arrest during hypothermia occurs at the level of premotor or motor neurons rather than at the level of the central rhythm generator itself. Specifically, we sought to determine the consequences of hypothermic cooling until respiratory arrest, and subsequent rewarming, on neurons in the pre-Bötzinger Complex, as an indication of the output of the entire rhythmogenic network; and from cervical spinal (phrenic) ventral roots, as an indication of motor neuron output, in an in vitro neonatal rat brain stem-spinal cord preparation. We found that hypothermia led to a slowing of the respiratory rhythm with little or no decrease in the magnitude of phrenic motor output or the field potential of pre-Bötzinger Complex neurons. Ultimate arrest occurred abruptly and simultaneously in recordings from both sites, indicating that the arrest was due to failure of the central rhythm-generating network, primarily due to removal of a conditional excitation. On being rewarmed, the motor output recorded at both sites was usually fractionated, initially suggesting that changes occurred in network synchronization either during cooling or during reactivation following hypothermic arrest.
mammal; control of breathing; breathing pattern; sagittal slice
| |
INTRODUCTION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS AND MATERIALS
RESULTS
DISCUSSION
REFERENCES
|
|---|
IN MAMMALS, PROGRESSIVE HYPOTHERMIA leads to loss of reflex responses, respiratory arrest, and finally, cardiac arrest and death. Failure is not progressive, as both respiration and circulation appear to remain physiologically adequate until immediately before arrest (14). Compared with adults, neonatal mammals endure greater falls in body temperature before respiratory arrest and cardiac failure (6, 7). Furthermore, under acute conditions in neonatal mammals, if progressive rewarming occurs soon enough, both the heart beat and breathing will resume spontaneously, and they will recover fully (1-4, 8). In adult rats, once respiratory arrest occurs, the animals can be resuscitated only so long as the heart keeps beating, and if mechanically ventilated, they can survive for up to 96 h (5, 11). The developmental transition from the newborn tolerance to the adult intolerance is gradual. The more precocial the neonate, the less the developmental difference (4).
Taken together, these data suggest that for both neonates and adults, so long as glucose and oxygen are supplied to the brain, the neural substrate for the generation and transmission of respiratory drive remains viable during hypothermic challenge and can be restarted on warming. This suggests that hypothermia-induced respiratory arrest is due to reversible failure in the network and not to irreversible damage to respiratory neurons themselves.
The mechanistic basis of the initial respiratory arrest in hypothermia as well as the ontogenetic changes in tolerance and in the ability of the system to autoresuscitate on rewarming is poorly understood. Recently, various in vitro preparations have been developed for the study of the neurogenesis and control of ventilatory activity in neonatal rodents. These include the brain stem-spinal cord (or en bloc) and transverse brain stem slice preparations (16, 18, 19). A site in the ventrolateral medulla, the pre-Bötzinger Complex (preBötC), is hypothesized to contain the neuronal circuits that generate the respiratory rhythm, and it is further hypothesized that the rhythmogenesis results from synchronized activity of a network of excitatory neurons with state-dependent, oscillatory bursting or pacemaker properties (13, 15). The rhythmic neural output from the preBötC projects to populations of premotor neurons that impinge on the various motor neuron pools to contract respiratory muscles to produce ventilation. Most of these preparations have been studied at temperatures in the range of 25-30°C, which are well below the normal body temperature range for neonatal rodents (35-37°C) but well above the range where respiratory problems arise. Interestingly, when temperature is lowered from 26 to 24°C in an en bloc preparation from newborn rats (12), respiratory rate is depressed and bursts of activity in Pre-I neurons (one of the candidate preBötC pacemaker neurons) are not always followed by bursts of inspiratory activity in respiratory motor neurons. This suggests that either the number of active Pre-I neurons decreases and is no longer sufficient to activate the motor neuron pools or the threshold for the generation of inspiratory-modulated efferent activity in the motor neuron pools is raised, or both. This, in turn, suggests that respiratory arrest may occur at the level of premotor or motor neurons rather than at the level of the rhythm generator itself.
To examine whether hypothermia-induced respiratory arrest was due to failure of rhythmogenic circuits and/or relay neurons, we sampled both preBötC neuronal activity and motor output during hypothermic challenge. We used a thick saggital slice rather than the conventional en bloc preparation, because it allowed us to determine the consequences of hypothermic cooling until respiratory arrest and subsequent rewarming on the rhythmogenic network (via field potential recordings at the level of the preBötC) and on motor outflow (via suction electrode recordings from cervical ventral roots). Our rationale was that abrupt failure of phrenic activity in the presence of continuing preBötC activity would indicate failure of (or failure of transmission to) the motor neurons, whereas simultaneous failure of activity at both sites (preBötC and phrenic motor neurons) would suggest failure of the central pattern generating (CPG) network.
| |
METHODS AND MATERIALS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS AND MATERIALS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Animal and tissue preparation. All experiments (n = 13) were performed on saggital slice preparations from 0- to 3-day-old rats. Animals were killed, and the brain stem-spinal cord was isolated as reported previously (17). The brain stem was initially transected at the rostral pontine level, the cerebellum was removed, and the spinal cord was transected at roughly the C7/C8 level. The dura was removed, and the preparation was then pinned to an agar block, dorsal surface down, and secured horizontally in a vibratome (Series 1000) with one lateral surface facing up. The tissue block was then sliced serially from lateral to medial (~250 to 350 µm) until the facial nucleus was evident in the cut slice. The preparation was then inverted, and the same procedure was performed on the opposite side. If tissue was removed past the lateral edge of the facial nucleus on either side of the thick slice, respiratory rhythm disappeared. The preparation was then removed to a perspex chamber, transected at the pontomedullary junction, and pinned with one, cut lateral surface facing upward. The preparation was superfused at 27°C with an artificial cerebrospinal fluid (ACSF) composed of (in mM) 113 NaCl, 3.0 KCl, 1.2 NaH2PO4, 1.5 CaCl2, 1.0 MgCl2, 30.0 NaHCO3, and 30.0 Dextrose, and it was gassed with 95% O2-5% CO2.
Population activity recording.
Phrenic motor neuron discharge was recorded extracellularly with a
suction electrode applied to the proximal end of a cut ventral root of
one cervical spinal (C1-C4) nerve. A
second suction electrode was applied to the cut lateral surface of the
medulla just rostral to the most rostral of the hypoglossal rootlets, at a level routinely isolated in the transverse slice for the study of
the rhythmogenic preBötC (Fig. 1,
A and B). Two observations indicated that
rhythmogenic rather than relay neuron populations were sampled:
1) field potential activity increased before activity in the
phrenic motor output (Fig. 1C and Fig.
2) and 2) if mild suction was
applied to the field potential electrode (best done after the end of
the experiment), there was a transient increase in the rate of
respiratory-related rhythmic activity indicative of activation of the
rhythm generator (Fig. 1C).
|
|
Experimental protocol and data analysis. Initially, the preparation was superfused at 27°C for 20-30 min to obtain control recordings. Then the superfusate was cooled at a rate of ~0.5°C/min until respiratory-related discharge ceased (i.e., period >3 min). The preparation was maintained at this temperature for at least 5 min, and then the preparation was rewarmed at the same rate.
Activity from both electrodes was amplified, filtered (band pass = 0.1-10 kHz), fullwave rectified, integrated (time constant ~20 ms), digitized, and stored on computer. From the raw data, we measured cycle period (period between fictive breaths) as well as the peak height and area under the integrated activity in both the phrenic and field potential recordings associated with each fictive breath. For each preparation, using phrenic inspiratory burst onset as the trigger, we averaged the activity of 6 to 10 fictive breaths under control conditions as well as under cold conditions (1-2°C before breathing ceased) and during early recovery (1-2°C after breathing recommenced) and late recovery from severe hypothermia (back at 27°C). Because recording conditions varied between preparations, values for peak and integrated discharge were expressed as percent change from values obtained under initial control conditions. From these measures, we also calculated the temperature at which breathing ceased during cooling and started during rewarming, the mean cycle period for each 0.5°C drop during cooling, and the mean cycle period for all preparations under the four designated conditions of interest: control, cold, early recovery, and late recovery. We examined the ability of two preparations to respond to excitatory stimuli after breathing had ceased during progressive cooling. We used thyrotropin-releasing hormone (TRH) as an excitatory agent, rather than elevated [K+]o, because at 9 mM [K+]o, stable bursting gave way to tonic activity in the thick saggital slice. In these two preparations, after the initial protocol was complete, the preparation was cooled a second time, and, after breathing had ceased with progressive cooling, TRH (1 µM) was added to the perfusate. This reinitiated breathing, and the preparation was then cooled further until breathing ceased again. At this point, the superfusate was switched back to the initial ACSF, and the preparation was rewarmed.Statistical analysis. Data are expressed as means ± SE. Statistical inferences are made using a one-way analysis of variance with a repeated-measures design. Significant differences between means were assessed by Student's t-tests with Bonferroni correction for multiple comparisons, and the fiducial level of significance was set at P < 0.05.
| |
RESULTS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS AND MATERIALS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Figure 3 illustrates the pattern of
discharge seen in the phrenic motor output of a typical preparation
during progressive cooling and rewarming. The pattern of discharge seen
in the field potential was virtually identical (see Figs. 1, 5, and 8),
and all breathing frequency data presented here apply equally to
recordings obtained from both sites. At 27°C, the average rate of
fictive breathing in this preparation was ~6/min. Progressive cooling led to a slowing and, ultimately, cessation of the fictive breaths recorded at both sites. On average, breathing stopped at 17 ± 1.0°C during cooling and reappeared at 19.4 ± 1.2°C during
rewarming (Fig. 4). The period between
breaths increased in an exponential fashion during cooling (Fig. 4),
and despite the slight hysteresis in the temperature at which breathing
returned on rewarming, the period between breaths was not different
during cooling or warming. Control values (9.7 ± 0.7 s at
26.8 ± 0.3°C) were no different from values in late recovery
(12.5 ± 1.0 s at 27.1 ± 0.7°C), whereas values
obtained during late cooling (50.5 ± 5.2 s at 19.1 ± 2.3°C) were no different from values in early recovery (46.9 ± 9.5 s at 21.1 ± 2.4°C) (Fig. 4).
|
|
Figure 5 illustrates the differences in
activity seen in both phrenic motor output and the field potential
under the four active conditions in one preparation. Quantification of
these data for all preparations (Fig. 6)
shows that while breathing slowed with progressive cooling, the field
potential associated with each breath remained unaltered; neither the
peak nor the integrated activity changed. During recovery, both peak
and integrated activity showed a rebound increase. By contrast, phrenic
motor output showed a small decrease in peak amplitude (14 ± 1%)
and a significant fall in mean integrated activity (32 ± 6%)
during cooling, which returned toward control values during recovery, although the mean integrated activity fell further in early recovery, on average, and was still significantly lower (25 ± 3%) even in late recovery. The peak amplitude and integrated activity of both motor
outputs fell to zero, of course, during respiratory arrest.
|
|
We examined the ability of two preparations to respond to excitatory
stimuli after breathing had ceased during progressive cooling. In the
trial depicted in Fig. 7, respiratory
arrest occurred initially with progressive cooling at 18°C.
Superfusion with a 1-µM solution of TRH at this time reactivated
fictive breathing at control frequencies (Fig. 7). Further cooling
again slowed breathing with respiratory arrest occurring once again at
10°C. Interestingly, after TRH, progressive cooling led to
progressive falls in peak and integrated activity in both the phrenic
motor output and the field potential (Fig.
8), with little increase in period until
all activity slowly disappeared. This is extremely different from the
abrupt loss of activity at the higher temperatures before TRH. With a
return to normal ACSF and rewarming, the frequency of fictive breathing
returned to control levels. Although identical results were obtained in
the second preparation, this sample size is small, and the data should
be considered accordingly.
|
|
In all preparations, we noted that while the length of the discharge
bursts did not change during progressive cooling in either the phrenic
motor output or the field potential (Fig. 2), the shape of the burst
was altered dramatically during rewarming. Once fictive breathing had
been reinitiated, the bursts of discharge appeared quite fractionated.
As shown in Fig. 9, in some cases, this
progressed to the point that the breath separated into distinct bursts
of activity (Fig. 9B), and in one case, the bursts became sufficiently separated to give rise to what appeared to be episodic breathing (Fig. 9C). It should be noted that the TRH trial
depicted in Fig. 8 was performed on a preparation following recovery
from a first bout of hypothermia and that such fractionated breathing is evident throughout the trial and is more pronounced after the second
episode of rewarming.
|
| |
DISCUSSION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS AND MATERIALS
RESULTS
DISCUSSION
REFERENCES
|
|---|
With the use of the sagittal slice preparation, we recorded field potentials from an exposed surface cut ~350 µm from the lateral edge of the medulla. Over this exposed lateral surface, rhythmic field potentials could only be obtained from a relatively small area near the ventral surface of the medulla. Several observations suggest that rhythmogenic circuits in preBötC, rather than premotor neurons, were sampled in these recordings: 1) in the rostrocaudal axis, field potentials were recorded just rostral to the first hypoglossal rootlet, at the same level as the transverse slice preparation containing the preBötC (16); 2) in the mediolateral axis, the lateral edge of the facial nucleus, which was used as a landmark here, coincides well with the lateral edge of the preBötC just caudal to it, and it could be easily seen in the saggital slice; if tissue was removed past the lateral margin of the facial nucleus, spontaneous rhythmic motor output disappeared, suggesting that neurons close to the surface of the slice included rhythmogenic preBötC populations; 3) mild suction applied to the field potential electrode increased the rate of fictive breathing, indicative of activation of the rhythm generator (Fig. 1C); and 4) field potential activity increased before activity in the phrenic motor output (Fig. 2).
Effects of cooling. With this preparation, progressive cooling slowed the frequency of fictive breathing with the cycle period increasing exponentially until respiratory-related rhythmic activity ceased. Our hypothesis was that abrupt failure of phrenic activity in the presence of continuing preBötC activity would indicate failure of (or failure of transmission to) the motor neurons, whereas simultaneous failure of activity at both sites (preBötC and phrenic motor neurons) would suggest failure of the CPG network (and hence coincident failure of motor output). There was no decrease in the peak, integrated sum, or duration of the field potential during this process; i.e., although slowing was progressive, arrest was not. The same was not completely true of the phrenic motor output. During progressive cooling, there was a 14% fall in peak amplitude and a 32% fall in the integrated sum of the activity associated with each fictive burst. There also were rare instances at low temperature during both cooling and recovery where bursts of activity in the field potential were not accompanied by any increase in activity in the phrenic motor output (not shown). This is consistent with earlier reports of Onimaru and Homma (12). These data suggest that there must have been some increase in the threshold for generation of activity in the phrenic motor neuron pool relative to the neuron pool from which the field potential was recorded. Respiratory arrest, however, invariably occurred simultaneously at both recording sites and thus appeared to be primarily due to complete and abrupt cessation of activation of the motor neuron pool(s) just as has been observed in vivo (14). Because the field potential was recorded from the area of the preBötC, arrest must have arisen from abrupt cessation of the central rhythm generator.
The temperature at which respiratory arrest occurred in vitro (17 ± 1.0°C) was higher than has been reported for rat pups of this age in vivo (9-15°C) (1, 3), suggesting that something increases cold tolerance in vivo. The Q10 for the slowing of breathing frequency in our study was ~8.5, much greater than would be predicted based on temperature effects on chemical processes alone. In this context, it is interesting to note that in the two preparations in which TRH was administered to the superfusate, in vitro restored fictive breathing following respiratory arrest and that the preparation could be cooled further. Arrest then occurred at a temperature (10°C) that was consistent with what is seen in vivo, yielding a Q10 of 2.7, which is also consistent with predictions based on temperature effects on metabolic processes. One possible explanation for these anecdotal observations is that respiratory arrest in vitro occurred because of removal of a conditional excitatory input, which was necessary to bring the central rhythm generator to threshold. In vivo, other inputs would remain to accomplish this task, and this was mimicked by the application of TRH in the present experiments. This cannot be the whole explanation, however, for in vivo, respiratory arrest is also abrupt and respiration remains physiologically adequate until immediately before arrest (14). In the present study, although TRH was able to reinitiate fictive breathing, with further cooling there was a progressive reduction in the peak and mean integrated activity in both the field potential and the phrenic motor output. Respiratory arrest was now due to both a slowing of breathing and a progressive reduction in motor output. The reasons for these differences between in vitro and in vivo preparations are not clear, but it is not surprising that differences do exist.Effects of rewarming. Although there was some hysteresis in the temperature at which breathing reappeared on warming relative to the temperature at which arrest occurred on cooling, the cycle period, the phrenic motor output, and the field potential were no different at matched temperatures during cooling or rewarming. The field potential (both peak and mean integrated discharge), however, increased above control levels in late recovery and remained there during the period of the experiment (up to 1 h following recovery). Furthermore, the pattern of the discharge was altered. Although in several instances the burst of discharge associated with each fictive breath became fractionated during cooling, this invariably occurred during rewarming. In the most extreme case (Fig. 9C), this pattern of motor output would most likely have given rise to episodic breathing. Although in many instances the fractionation disappeared over time during recovery and rewarming as the activity fused into the prolonged decrementing burst seen under control conditions, in some cases the fractionation was still evident at the termination of the experiment. The mechanistic basis of this fractionation is not obvious, but the data suggest that synchronization of the central rhythm-generating network has been altered. This appears more likely to occur when the system is restarted during rewarming and may reflect the process by which the activity of the oscillatory bursting or pacemaker neurons becomes synchronized.
In summary, hypothermia in the in vitro neonatal rat saggital slice preparation leads to a slowing of the respiratory rhythm with little or no decrease in the magnitude of the motor output. Ultimate arrest appears to occur at the level of the central rhythm-generating network, primarily due to removal of a conditional excitation. The system will recover on rewarming, but the motor output is fractionated, at least initially, suggesting that changes occur in network synchronization either during cooling or during reactivation following arrest in this fashion.| |
ACKNOWLEDGEMENTS |
|---|
This research was funded by the Natural Sciences and Engineering Research Council of Canada (to W. K. Milsom) and National Institutes of Health Grants HL-40959 and HL-37941.
| |
FOOTNOTES |
|---|
Address for reprint requests and other correspondence: N. M. Mellen, Dept. of Neurobiology, Univ. of California Los Angeles Medical Center (CHS), 10833 Le Conte Ave., Box 951763, Los Angeles, CA 90095-1763 (E-mail: nmellen{at}ucla.edu).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
10.1152/ajpregu.00049.2001
Received 30 January 2001; accepted in final form 23 October 2001.
| |
REFERENCES |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS AND MATERIALS
RESULTS
DISCUSSION
REFERENCES
|
|---|
1.
Adolph, EF.
Tolerance to cold and anoxia in infant rats.
Am J Physiol
155:
366-377,
1948.
2.
Adolph, EF.
Lethal limits of cold immersion in adult rats.
Am J Physiol
155:
378-387,
1948.
3.
Adolph, EF.
Responses to hypothermia in several species of infant mammal.
Am J Physiol
166:
75-91,
1951.
4.
Adolph, EF.
How do infant mammals tolerate deep hypothermia?
In: Temperature, Its Measurement and Control in Science and Industry. Part 3. Biology and Medicine, edited by Hardy JD.. New York: Reinhold, 1963, p. 511-515.
5.
Adolph, EF,
and
Goldstein J.
Survival of rats and mice without oxygen in deep hypothermia.
J Appl Physiol
14:
559-604,
1959.
6.
Antoschkina, ED.
Über die Ausbildung der Wärmeregulierung im Laufe der Ontogenese II.
Fiziol Zh
26:
16-29,
1939.
7.
Edwards, WF.
De l'Influence des Agens Physiques Sur la Vie. Paris: Crochard, 1824, p. 654.
8.
Fairfield, J.
Effects of cold on infant rats: body temperatures, oxygen consumption, electrocardiogram.
Am J Physiol
155:
355-365,
1948.
9.
Hill, RW.
Anoxia tolerance to oxygen necessity: paradigm shift in the physiology of survival of apneic deep hypothermia in neonatal rodents.
In: Life in the Cold, edited by Heldmaier G,
and Klingenspor M.. Heidelberg, Germany: Springer-Verlag, 2000, p. 199-205.
10.
Hunter, J.
Methods of induction and effects of "cardiac arrest" in relationship to hypothermic state.
In: Temperature, Its Measurement and Control in Science and Industry. Part 3. Biology and Medicine, edited by Hardy JD.. New York: Reinhold, 1963, p. 485-494.
11.
Mussachia, XJ.
Helium-cold hypothermia, an approach to depressed metabolism and thermoregulation.
In: Regulation of Depressed Metabolism and Thermogenesis, edited by Jansky L,
and Mussachia XJ.. New York: Charles C. Thomas, 1974, p. 137-157.
12.
Onimaru, H,
and
Homma I.
Respiratory rhythm generator neurons in medulla of brainstem-spinal cord preparation from newborn rat.
Brain Res
403:
380-384,
1987[ISI][Medline].
13.
Rekling, JC,
and
Feldman JL.
PreBötzinger complex and pacemaker neurons: hypothesized site and kernel for respiratory rhythm generation.
Annu Rev Physiol
60:
385-405,
1998[ISI][Medline].
14.
Rosenhain, FR,
and
Penrod KE.
Blood gas studies in the hypothermic dog.
Am J Physiol
166:
55-61,
1951.
15.
Smith, JC,
Butera RJ, Jr,
Koshiya N,
Del Negro C,
Wilson CG,
and
Johnson SM.
Respiratory rhythm generation in neonatal and adult mammals: the hybrid pacemaker-network model.
Respir Physiol
122:
131-147,
2000[ISI][Medline].
16.
Smith, JC,
Ellenberger HH,
Ballanyi K,
Richter DW,
and
Feldman JL.
PreBötzinger complex: a brainstem region that may generate respiratory rhythm in mammals.
Science
254:
726-729,
1991
17.
Smith, JC,
and
Feldman JL.
In vitro brain stem-spinal cord preparation for the study of motor systems for mammalian respiration and locomotion.
J Neurosci Methods
21:
321-333,
1987[ISI][Medline].
18.
Smith, JC,
Greer JJ,
Liu G,
and
Feldman JL.
Neural mechanisms generating respiratory pattern in mammalian brain stem-spinal cord in vitro. I. Spatiotemporal patterns of motor and medullary neuron acitivity.
J Neurophysiol
64:
1149-1169,
1990
19.
Suzue, T.
Respiratory rhythm generation in the in vitro brain stem-spinal cord preparation of the neonatal rat.
J Physiol (Lond)
354:
173-183,
1984
This article has been cited by other articles:
|
|
 |
|
  A. K. Tryba and J.-M. Ramirez Hyperthermia Modulates Respiratory Pacemaker Bursting Properties J Neurophysiol, November 1, 2004; 92(5): 2844 - 2852. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. M. MacFarlane and P. B. Frappell Hypothermia and hypoxia inhibit the Hering-Breuer reflex in the marsupial newborn Am J Physiol Regulatory Integrative Comp Physiol, May 1, 2004; 286(5): R857 - R864. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. V. CAREY, M. T. ANDREWS, and S. L. MARTIN Mammalian Hibernation: Cellular and Molecular Responses to Depressed Metabolism and Low Temperature Physiol Rev, October 1, 2003; 83(4): 1153 - 1181. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. K. Tryba and J.-M. Ramirez Response of the Respiratory Network of Mice to Hyperthermia J Neurophysiol, June 1, 2003; 89(6): 2975 - 2983. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
