Physiology& Behavior,Vol. 50, pp. 461--463. ©PergamonPress plc, 1991.Printedin the U.S.A.
0031-9384/91 $3.00 + .00
BRIEF COMMUNICATION
Lipopolysaccharide Increases Ambient Temperature Preference in C57BL/6J Adult Mice C H A N A AKINS, DEL THIESSEN 1 AND ROBERT COCKE
Department of Psychology, University o f Texas, Austin, TX 78712 Received 4 September 1990 AKINS, C., D. THIESSEN AND R. COCKE. Lipopolysaccharide increases ambient temperature preference in C57BL/6J adult mice. PHYSIOL BEHAV 50(2) 461--463, 1991.--Tbc hypothesis was tested that animals exposed to a potentially dangerous endotoxin would attempt to behaviorallyelevate their body temperature, perhaps in an effort to engage those immunologicalmechanisms which would counter the adverse effects of the endotoxin. Lipopolysaccharide (LPS) from Escherichia coil injected subcutaneously (100 p.g) in adult C57BL/6J mice increased gradient temperature preference by 2.4°(2 over saline controls. The increase in body temperature of 1.1°C after LPS injection was due to the preference for higher ambient temperatures and was not the result of a systemic reaction to LPS (animalsnot exposed to the gradient did not differ in body temperature). In summary, our data indicate that adult mice self-induce a febrile response, perhaps as an attempt to compensate for the physiological impact of the endotoxin. Lipopolysaccharide
C57BI/6Jm i c e
Temperaturepreference
Body temperature
(7,8). When gerbils are exposed to odors from stressed conspecifics, body temperature is elevated about 0.38°(2 within 20 minutes. This effect is consistent with recent observations that many forms of stress elevate body temperature (19), The gerbil becomes inactive in the presence of the odor, and if given an opportunity, will avoid the odor. We have noted similar behavioral effects with BALB/cJ (27) and C57BL/6J mice (28), and, in addition, have measured an immunological suppression of T-cell proliferation in mitogen assays of BALB/cJ mice (8,23). These observations led us to hypothesize that mice made ill with the injection of a bacterial endotoxin, lipopolysacchaxide (LPS), or those who are stressed, and who are immunologically compromised, may seek out a higher environmental temperature in order to initiate a febrile response and perhaps facilitate immunological reactivity. This hypothesis is consistent with the behavior of reptiles (25) and infant rabbits (21).
WHEN a pathogen invades a host of complex pattern of events is initiated. Regardless of the nature of the pathogen, the initial response observed among most mammals is an increase in body temperature (2). The febrile response, or associated processes, are adaptive, in that the spread of the infection is retarded and longevity is increased (9, 15-18). Benefits are gained by the reduction of blood levels of iron and zinc which are necessary for the proliferation of pathogens (13,26). Increased body temperature also facilitates T-cell activity and interferon synthesis and thus brings the force of the immune system into play at an early stage of infection (10,11). In addition to these early reactions, infected animals typically become inactive, display shivering and nonshivering thermogenesis, lose interest in eating and drinking, and cease body maintenance behaviors (13). The specific processes underlying the physiological and behavioral events are not entirely clear. Fever, which appears central to many of the effects, results from an "endogenous pyrogen" (EP) from activated macrophages and other phagocytic cells (5,10). EP may involve a number of different cytokines, including intedeukin-I (IL-lr, and [3), the tumor necrosis factor (TNF), interferon-8, interferon-J31 and interferon-132. These cytokines may have similar influences on body temperature, anorexia and heat conserving behaviors. The specific functions of each of these cytokines are unknown, although the critical febrile response common to them all may involve the release of prostaglandins in or near the region of the hypothalamus (4,22). Our interest in these problems stems from observations on the gerbil, Meriones unguiculatus, and the mouse Mus musculus
METHOD
Animals Forty-eight male C57BL/6J mice, approximately 60 days of age at the beginning of the study, were randomly divided into four groups of 12 and assigned to the following conditions: Group 1 (N= 12), temperature gradient animals receiving 100 p,g lipopolysaccharide (LPS) dissolved in 0,05 ml isotonic sterile saline; Group 2 (N= 12), temperature gradient animals receiving 0.05 ml isotonic sterile saline; Group 3 (N= 12), nongradient animals receiving 100 Ixg LPS dissolved in 0.05 ml
1Requests for reprints should be addressed to Dr. Dcl Thiessen, Departmentof Psychology, Universityof Texas, Austin, TX 78712.
461
462
AKINS, THIESSEN AND COCKE
147.3 cm I
mOiStI ' n l R E
I
|
1.4Oill
Water
Ll~
M
M
ti
FIG. 2. Gradient temperature preference and body temperature of C57BL/6J male mice receiving lipopolysaccharide (LPS) (100 p.g) or saline. L
FIG. 1. Diagram of the thermal gradient used to measure ambient temperature preference.
isotonic sterile saline; Group 4 (N = 12), nongradient animals receiving 0.05 ml isotonic sterile saline. The dose level of 100 ~,g of LPS was selected from preliminary experiments showing that this dose induced apparent sickness (huddling and piloerection) but did not prevent general locomotion. Animals were housed four to a cage (one from each condition) in colony cages measuring 18.8 × 21.6× 20.3 cm 14 to 21 days prior to behavioral testing. Animals were provided with Purina Laboratory Chow and water ad lib. Ambient temperature of the colony was approximately 26°C with 40% relative humidity and a 12/12 hour light/dark cycle. Each animal was ear punched for identification.
Apparatus A schematic of the temperature gradient is seen in Fig. 1. The gradient was constructed of metal and measured 147.3 cm in length and 11.4 cm in width. The ambient temperature gradient was maintained from 22°C to 42°C, in increments of 0.14°C per cm with water conduits and heating tapes underneath the runway. The runway was enclosed with a removable Plexiglas hood. The apparatus was housed in a room adjacent to the colony room, and was illuminated by ceiling fluorescent lights. A plastic round isolation cage measuring 20.3 cm in diameter and 22.9 cm in height was near the temperature gradient and was used to hold control animals receiving LPS or saline during the gradient testing of animals from the same conditions. The isolation cage remained at room temperature, approximately 25°(2. An RCA video camera and VCR were used to record the trials, and a Bailey Type T thermocouple probe (Model BAT12) with a needle were used to measure subcutaneous body temperature (TB). T B was measured to the nearest 0.1°C.
Procedure The gradient was preheated. Two LPS animals (gradient and nongradient) and two saline animals (gradient and nongradient) were tested each day. Testing occurred during the light half of the 12/12 light cycle. On the day of testing the test animals were brought to the testing room in a carrying cage. On a random basis, they were injected either with LPS or saline and one was
placed on the gradient and the other placed in the isolation chamber. The video camera was started. Ninety minutes later the trial was terminated. Both animals were measured for T B to the nearest 0. I°C with the Bailey probe placed subcutaneously between the scapulae. The probe was left in place until the reading stabilized (around 5 s). T B was not measured at the beginning of the trial because of possible stress effects of handling. The videotape was later scanned to determine where the animal was on the gradient during the 90 rain period. It's preference was considered to be that gradient temperature where the animal first rested for a minimum of 5 min during the 90 min test. Animals usually did not move from the preferred area after settling. After the trial the animals were returned to the colony and the gradient and isolation chamber were thoroughly cleaned with ethanol and water. No animal was tested twice. RESULTS
Gradient Temperature Preference and Body Temperature Mice injected with LPS selected a mean temperature of 33.0°C-+0.52, whereas saline control mice selected a mean temperature of 30.6°C-+0.66 (t=2.71, p
0031-9384/91 $3.00 + .00
BRIEF COMMUNICATION
Lipopolysaccharide Increases Ambient Temperature Preference in C57BL/6J Adult Mice C H A N A AKINS, DEL THIESSEN 1 AND ROBERT COCKE
Department of Psychology, University o f Texas, Austin, TX 78712 Received 4 September 1990 AKINS, C., D. THIESSEN AND R. COCKE. Lipopolysaccharide increases ambient temperature preference in C57BL/6J adult mice. PHYSIOL BEHAV 50(2) 461--463, 1991.--Tbc hypothesis was tested that animals exposed to a potentially dangerous endotoxin would attempt to behaviorallyelevate their body temperature, perhaps in an effort to engage those immunologicalmechanisms which would counter the adverse effects of the endotoxin. Lipopolysaccharide (LPS) from Escherichia coil injected subcutaneously (100 p.g) in adult C57BL/6J mice increased gradient temperature preference by 2.4°(2 over saline controls. The increase in body temperature of 1.1°C after LPS injection was due to the preference for higher ambient temperatures and was not the result of a systemic reaction to LPS (animalsnot exposed to the gradient did not differ in body temperature). In summary, our data indicate that adult mice self-induce a febrile response, perhaps as an attempt to compensate for the physiological impact of the endotoxin. Lipopolysaccharide
C57BI/6Jm i c e
Temperaturepreference
Body temperature
(7,8). When gerbils are exposed to odors from stressed conspecifics, body temperature is elevated about 0.38°(2 within 20 minutes. This effect is consistent with recent observations that many forms of stress elevate body temperature (19), The gerbil becomes inactive in the presence of the odor, and if given an opportunity, will avoid the odor. We have noted similar behavioral effects with BALB/cJ (27) and C57BL/6J mice (28), and, in addition, have measured an immunological suppression of T-cell proliferation in mitogen assays of BALB/cJ mice (8,23). These observations led us to hypothesize that mice made ill with the injection of a bacterial endotoxin, lipopolysacchaxide (LPS), or those who are stressed, and who are immunologically compromised, may seek out a higher environmental temperature in order to initiate a febrile response and perhaps facilitate immunological reactivity. This hypothesis is consistent with the behavior of reptiles (25) and infant rabbits (21).
WHEN a pathogen invades a host of complex pattern of events is initiated. Regardless of the nature of the pathogen, the initial response observed among most mammals is an increase in body temperature (2). The febrile response, or associated processes, are adaptive, in that the spread of the infection is retarded and longevity is increased (9, 15-18). Benefits are gained by the reduction of blood levels of iron and zinc which are necessary for the proliferation of pathogens (13,26). Increased body temperature also facilitates T-cell activity and interferon synthesis and thus brings the force of the immune system into play at an early stage of infection (10,11). In addition to these early reactions, infected animals typically become inactive, display shivering and nonshivering thermogenesis, lose interest in eating and drinking, and cease body maintenance behaviors (13). The specific processes underlying the physiological and behavioral events are not entirely clear. Fever, which appears central to many of the effects, results from an "endogenous pyrogen" (EP) from activated macrophages and other phagocytic cells (5,10). EP may involve a number of different cytokines, including intedeukin-I (IL-lr, and [3), the tumor necrosis factor (TNF), interferon-8, interferon-J31 and interferon-132. These cytokines may have similar influences on body temperature, anorexia and heat conserving behaviors. The specific functions of each of these cytokines are unknown, although the critical febrile response common to them all may involve the release of prostaglandins in or near the region of the hypothalamus (4,22). Our interest in these problems stems from observations on the gerbil, Meriones unguiculatus, and the mouse Mus musculus
METHOD
Animals Forty-eight male C57BL/6J mice, approximately 60 days of age at the beginning of the study, were randomly divided into four groups of 12 and assigned to the following conditions: Group 1 (N= 12), temperature gradient animals receiving 100 p,g lipopolysaccharide (LPS) dissolved in 0,05 ml isotonic sterile saline; Group 2 (N= 12), temperature gradient animals receiving 0.05 ml isotonic sterile saline; Group 3 (N= 12), nongradient animals receiving 100 Ixg LPS dissolved in 0.05 ml
1Requests for reprints should be addressed to Dr. Dcl Thiessen, Departmentof Psychology, Universityof Texas, Austin, TX 78712.
461
462
AKINS, THIESSEN AND COCKE
147.3 cm I
mOiStI ' n l R E
I
|
1.4Oill
Water
Ll~
M
M
ti
FIG. 2. Gradient temperature preference and body temperature of C57BL/6J male mice receiving lipopolysaccharide (LPS) (100 p.g) or saline. L
FIG. 1. Diagram of the thermal gradient used to measure ambient temperature preference.
isotonic sterile saline; Group 4 (N = 12), nongradient animals receiving 0.05 ml isotonic sterile saline. The dose level of 100 ~,g of LPS was selected from preliminary experiments showing that this dose induced apparent sickness (huddling and piloerection) but did not prevent general locomotion. Animals were housed four to a cage (one from each condition) in colony cages measuring 18.8 × 21.6× 20.3 cm 14 to 21 days prior to behavioral testing. Animals were provided with Purina Laboratory Chow and water ad lib. Ambient temperature of the colony was approximately 26°C with 40% relative humidity and a 12/12 hour light/dark cycle. Each animal was ear punched for identification.
Apparatus A schematic of the temperature gradient is seen in Fig. 1. The gradient was constructed of metal and measured 147.3 cm in length and 11.4 cm in width. The ambient temperature gradient was maintained from 22°C to 42°C, in increments of 0.14°C per cm with water conduits and heating tapes underneath the runway. The runway was enclosed with a removable Plexiglas hood. The apparatus was housed in a room adjacent to the colony room, and was illuminated by ceiling fluorescent lights. A plastic round isolation cage measuring 20.3 cm in diameter and 22.9 cm in height was near the temperature gradient and was used to hold control animals receiving LPS or saline during the gradient testing of animals from the same conditions. The isolation cage remained at room temperature, approximately 25°(2. An RCA video camera and VCR were used to record the trials, and a Bailey Type T thermocouple probe (Model BAT12) with a needle were used to measure subcutaneous body temperature (TB). T B was measured to the nearest 0.1°C.
Procedure The gradient was preheated. Two LPS animals (gradient and nongradient) and two saline animals (gradient and nongradient) were tested each day. Testing occurred during the light half of the 12/12 light cycle. On the day of testing the test animals were brought to the testing room in a carrying cage. On a random basis, they were injected either with LPS or saline and one was
placed on the gradient and the other placed in the isolation chamber. The video camera was started. Ninety minutes later the trial was terminated. Both animals were measured for T B to the nearest 0. I°C with the Bailey probe placed subcutaneously between the scapulae. The probe was left in place until the reading stabilized (around 5 s). T B was not measured at the beginning of the trial because of possible stress effects of handling. The videotape was later scanned to determine where the animal was on the gradient during the 90 rain period. It's preference was considered to be that gradient temperature where the animal first rested for a minimum of 5 min during the 90 min test. Animals usually did not move from the preferred area after settling. After the trial the animals were returned to the colony and the gradient and isolation chamber were thoroughly cleaned with ethanol and water. No animal was tested twice. RESULTS
Gradient Temperature Preference and Body Temperature Mice injected with LPS selected a mean temperature of 33.0°C-+0.52, whereas saline control mice selected a mean temperature of 30.6°C-+0.66 (t=2.71, p
