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C J Gordon

Publications and source records attributed to C J Gordon.

At least 109 records · Page 6Linked to original sources
PubMed1985

Relationship between autonomic and behavioral thermoregulation in the mouse.

Preferred ambient temperature (Ta) was measured in nine mice of the BALB/c strain using a temperature gradient. When tested over four consecutive days the mean preferred Ta was 30.9 degrees C. In another study using the same animals, metabolic rate, evaporative water loss, whole-body thermal conductance, and colonic temperature were measured at specific Ta's over a range of 18 to 34 degrees C. The preferred Ta of 30.9 degrees C was associated with the lower critical Ta (i.e., Ta below which metabolic rate increased) a 57% elevation in evaporative water loss when expressed in units of mg water evaporated per ml consumed oxygen, a thermal conductance that was 92% above baseline levels, and a normothermic colonic temperature of between 37.0 to 37.5 degrees C. The data indicate that mice will select an environmental temperature associated with a minimal energy expenditure but a higher than minimal rate of evaporation and higher thermal conductance.

Animals↗
PubMed1985

Temporal response of neurons to ambient heating in the preoptic and septal area of the unanesthetized rabbit.

The firing rates of single neurons were recorded in the septal and preoptic areas of unanesthetized rabbits during brief periods of ambient heating. The temporal response for neurons responsive to ambient temperature were calculated as the interval of time between the onset of heating and the point at which the unit's activity reached 63% (i.e. 1-1/e) of its total change in activity. Thirty-one neurons were isolated in 5 rabbits. Fourteen neurons were facilitated, 10 were inhibited and 7 were unaffected by heating. Temporal responses ranged from less than 5 to 122 s. We observed a bimodal relationship in the number of neuronal responses to ambient temperature vs temporal response: a sharp 0- to less than 10-s peak comprising 22% of all responses and a relatively broad peak with a mode of 60 to less than 70 s. These data resemble the temporal response patterns of thermally excitable neurons throughout the central nervous system.

Animals↗
PubMed1985

Thermoregulation in mice following acute chlordimeform administration.

CBA/J mice were injected intraperitoneally (i.p.) with the formamidine insecticide chlordimeform (CDM) while colonic temperature, preferred ambient temperature (Ta), and lethality were monitored. In the first experiment there was a dose-dependent decrease in colonic temperature when measured 60 min after administering CDM doses of 0, 15, 30, 60, and 75 mg/kg. The hypothermic effect of CDM was more pronounced at a Ta of 20 degrees C than at 30 degrees C. In the second experiment, CDM at doses greater than 30 mg/kg caused a dose-dependent reduction in preferred Ta from the normal value of approx. 30 degrees C to approx. 22 degrees C. Thus, the CDM-treated mouse lowered body temperature by selecting a cool Ta which accelerated the hypothermic effect. In the final experiment, a 90 mg/kg i.p. injection of CDM (the approximate LD50 dose) caused 10% and 0% mortality at a Ta of 20 and 30 degrees C, respectively, and 80% mortality at a Ta of 35 degrees C. It is concluded that the physiological and behavioral response to CDM administration, i.e., selecting a cool Ta and lowering body temperature, may be beneficial to survival.

Amidines↗
PubMed1985

Effect of sulfolane on behavioral and autonomic thermoregulation in the rat.

Sulfolane (tetrahydrothiophene 1,1-dioxide), a commonly used extraction solvent, promotes rapid changes in the thermoregulatory system. Colonic temperature, skin temperature, metabolic rate, and preferred ambient temperature (Ta) were measured over an 8-h period in the Sprague-Dawley rat following an intraperitoneal injection of sulfolane at 800 mg/kg or of physiological saline. At Ta values of 15 and 25 degrees C, sulfolane caused a significant inhibition in metabolic rate and reduction in colonic temperature, which lasted over the 8-h measuring period. At both Ta values, metabolic rate tended to recover approximately 4 h after sulfolane injection. Colonic temperature recovered with time but was still significantly reduced at 8 h postinjection. Tail skin temperature was unaffected. Preferred Ta in the sulfolane-treated rat was not significantly different from the controls. In spite of their hypothermic condition, the sulfolane-treated animals did not select a warm Ta. Since sulfolane toxicity appears to be greater with increased tissue temperature, the sulfolane-induced hypothermia may enhance survival of the rat following exposure to toxic levels of sulfolane.

Animals↗
PubMed1984

Effect of ambient temperature on the hypometabolic and hypothermic effects of sulfolane in rats.

Sulfolane toxicity may be partially due to its effects on body temperature. To examine the effects of sulfolane on thermoregulation, we measured metabolic rate (oxygen uptake) and body temperature in rats injected intraperitoneally with sulfolane at dosages of 0, 200, 400, and 800 mg/kg. At ambient temperatures (Ta) of 15 and 25 degrees C sulfolane caused a dose-related inhibition of metabolic rate accompanied by hypothermia 60 min post-injection. At a Ta of 35 degrees C, sulfolane had no effect on body temperature or metabolic rate. The hypometabolic and hypothermic effect of sulfolane at a Ta of 25 degrees C at least 2.5 h. Sulfolane had near identical effects on body temperature at TaS of 15 and 25 degrees C, hence, the sulfolane-treated rat had some control over body temperature at a relatively low Ta.

Animals↗
PubMed1984

Measurement of ventilatory frequency in unrestrained rodents using microwave radiation.

A novel technique for remote determination of breathing frequency in unrestrained rodents using microwave radiation is described. Single mice were placed inside a rectangular waveguide operating at 2450 MHz. Because mice efficiently absorb radio frequency energy at 2450 MHz, any change in their absorption, as occurs rhythmically with breathing, can be detected by monitoring the changes in power transmitted through the waveguide. When the volume of the mouse increases during inspiration, transmitted power through the waveguide momentarily decreases - during expiration the reverse takes place. By differential amplification of the analog output of the power meter used to monitor transmitted power, breathing frequency can be easily recorded on conventional recording equipment. The microwave technique has a definite advantage over other methods in that breathing frequency can be remotely monitored without the need to attach wire leads or surgically implant telemetry probes. This greatly reduces unnecessary stress to the animal. By use of larger waveguides the principle of this technique may be applied to larger species.

Absorption↗
PubMed1984

Ventilatory frequency of mouse and hamster during microwave-induced heat exposure.

Ventilatory frequency was recorded in unrestrained mice and hamsters using microwave radiation. The microwave exposure system was also used to impact varying heat loads to the rodents at ambient temperatures of 10, 20 and 30 degrees C. The absorbed heat load accrued from microwave exposure was measured as the time-averaged rate of energy absorption per unit body weight or specific absorption rate (SAR, W/kg). In both species there was an inverse relationship between ambient temperature (Ta) and threshold SAR to invoke an increase in ventilatory frequency. However, the threshold SAR's for mice were 270 to 450% higher than for hamsters depending on Ta. Above threshold SAR the increase in ventilatory frequency per unit elevation in SAR increased directly with Ta in mice but not with hamsters. On the basis of rate of absorbed energy normalized to body weight (i.e., W/kg), mice can tolerate much more heat from microwave exposure than hamsters. The differences in sensitivity to microwave exposure in the mouse and hamster are probably attributable to species-specific characteristics, and especially differences in body mass and, consequently, passive heat loss.

Absorption↗
PubMed1984

Effect of triethyltin on autonomic and behavioral thermoregulation of mice.

The organotin compound, triethyltin (TET), produces toxic effects in a variety of physiological systems. Thermoregulatory control appears to be especially susceptible to TET toxicity, since TET administration has been shown to cause a pronounced hypothermia in rats. To further elucidate effects of TET on thermoregulation, we measured metabolic rate, evaporative water loss (EWL), body temperature, and preferred ambient temperature (Ta) of mice treated intraperitoneally with TET (bromide salt). At a Ta of 23 to 24 degrees C, TET (6 and 8 mg/kg) inhibited metabolic rate by 23 and 66%, respectively. TET resulted in hypothermia at Ta's of 20 and 30 degrees C but not 35 degrees C. TET had little effect on EWL. Mice given TET at doses of 4, 6, and 8 mg/kg selected a cooler Ta (ca. 25 degrees C) compared to controls (ca. 29 degrees C). Thus, the mice selected a Ta associated with a hypothermic body temperature. At a relatively cool Ta, mice treated with TET had a reduced rate of heat production and, consequently, were hypothermic. At a relatively warm Ta, TET had no effect on heat production and did not increase active heat dissipation (i.e., EWL), thus the mice remained normothermic. The behavioral data indicate that TET evokes a type of regulated hypothermia in mice.

Animals↗
PubMed1984

Role of beta-endorphin in the control of body temperature in the rabbit.

There is evidence of release of the opioid peptide beta-endorphin (beta-E) in the hypothalamus during development of fever and stress-induced hyperthermia. In the unanesthetized rabbit, microinjection of beta-E in the preoptic/anterior hypothalamus (POAH) results in peripheral vasoconstriction, inhibition of evaporative heat loss, and a prolonged elevation of body temperature. These reactions are magnified with increases in ambient temperature. Injections of beta-E nearly abolish vasodilation to back heating and also postural enhancement of heat dissipation ( sprawling , limb extension) in a hot environment. beta-E has also been found to reduce the thermal sensitivity of single POAH neurons to ambient heating. However, POAH beta-E injections do not alter metabolic rate at ambient temperatures from 2 to 27 degrees C, and to this extent beta-E-induced hyperthermia is distinct from fever. It is suggested that beta-E reduces sensitivity of POAH neurons to high ambient temperature and that this reduction leads to increased peripheral vasoconstriction, inhibition of evaporative heat loss, and modification of behavioral thermoregulation resulting in a regulated-type elevation in body temperature. A general neural model is proposed to explain the thermoregulatory effects of beta-E in the rabbit.

Animals↗
PubMed1984

Scaling the physiological effects of exposure to radiofrequency electromagnetic radiation: consequences of body size.

We have demonstrated that a comparative analysis of the physiological effects of exposure of laboratory mammals to radiofrequency electromagnetic radiation (RFR) may be useful in predicting exposure thresholds for humans if the effect is assumed to be due only to heating of tissue. The threshold specific absorption rate (SAR) necessary to affect a thermoregulatory parameter shows an inverse and linear relationship to body mass. The inverse relationship between threshold SAR and body mass is attributed to a surface area: body mass relationship. In comparison to small mammals, relatively large mammals have a reduced capacity to dissipate an internal heat load passively, and are therefore physiologically more sensitive to RFR exposure. The threshold for a thermoregulatory response depends on the type of response measured, species, ambient temperature, etc. By extrapolation, it can be shown that a SAR of only 0.2-0.4 W/kg is required to promote a thermoregulatory response in a mammal with a body mass of 70 kg (e.g. weight of adult human). The specific absorption rate bioeffects data collected from laboratory mammals can be related by means of a simple power formula: threshold SAR (W/kg) = aMb, where M is body mass in kg, a is a constant and b is equal to approximately -0.5. Through this equation we have illustrated that a threshold SAR measured in a species weighing 100 g would be 10 times greater than that of a species weighing 10 000 g. Accordingly, a relatively low SAR that is physiologically ineffective in small mammals may be stressful to larger species.

Animals↗
PubMed1983

A review of terms for regulated vs. forced, neurochemical-induced changes in body temperature.

Deviations of the body temperature of homeothermic animals may be regulated or forced. A regulated change in core temperature is caused by a natural or synthetic compound that displaces the set-point temperature. A forced shift occurs when an excessive environmental or endogenous heat load, or heat sink, exceeds the body's capacity to thermoregulate but does not affect set-point. A fever is the paradigm of a regulated increase in body temperature, but the term fever has acquired a strict pathological definition over the past two decades. Consequently, other forms of nonpathological, regulated elevations in body temperature have generally been classified as hyperthermia; and decreases in core temperature--either forced or regulated--have generally been classified as hypothermia. Since the terms hyperthermia and hypothermia fail to distinguish a regulated vs. a forced temperature change, a confusion of terms has been created in the literature. It would appear that "resisted or unregulated hyperthermia" and "hypothermia," respectively, are appropriate terms for describing a forced increase and decrease in core temperature. A nonpathological but regulated elevation in temperature may be defined as unresisted or regulated hyperthermia, whereas a regulated decrease in temperature may be termed unresisted or regulated hypothermia. This simple scheme appears to be the most practical means for distinguishing between forced and regulated changes in core temperature.

Animals↗
PubMed1983

A device for monitoring position of unrestrained animals in a temperature gradient.

The design and use of an automated system which permits continuous monitoring of the position of an animal in a temperature gradient is demonstrated. Animal position in the gradient is detected with phototransistors. Through simple electronic switching, the information from the phototransistors is converted to an analog DC signal that is directly proportional to the position of the animal in the temperature gradient. The temperature gradient method permits continuous automated monitoring of thermoregulatory behavior in unrestrained animals.

Animals↗
PubMed1983

Reassessment of the neural control of body temperature: importance of oscillating neural and motor components.

1. Components in the sensory, integrative, and motor divisions of the thermoregulatory system exhibit rhythmic activity covering a frequency range over five orders of magnitude. In spite of these rhythmic properties, current models of thermoregulation are nonoscillatory. 2. The connectivity of the current neural models is empirically correct when applied to predicting changes in metabolism during central thermal and/or neurochemical stimulation. 3. However, because these models lack a temporal compensation, the operating principles of a thermoregulatory neural network remains unclear. 4. This paper presents strong evidence that integrative thermoregulatory neurons exert a variety of rhythmic control over all thermoregulatory motor outputs. 5. Furthermore, it is shown that without an oscillating integrative and motor system, especially pathways controlling peripheral heat loss, a thermoregulatory system is unstable. 6. The preponderant rhythmic activity in the thermoregulatory systems indicates that neural modelling of physiological regulation should be designed with oscillatory control.

Action Potentials↗
PubMed1983

Influence of heating rate on control of heat loss from the tail in mice.

Although heating rate is important for stimulating thermoregulatory reflexes, it is not known if the control system differentiates between total heat gain and rate of heat gain. Exposing animals to microwaves inside a waveguide permits continuous monitoring of whole-body heat absorption. Tail skin temperature of restrained mice was recorded during whole-body exposure to 2,450-MHz microwave radiation at specific absorption rates (SAR) of either 11.5, 21.7, or 43.5 W . kg-1 and whole-body heat loads of 0.3-14 J . g-1. The integration of tail skin temperature with time, defined as the skin temperature index (STI), was measured as a function of absorbed heat load. At ambient temperatures of 20 and 25 degrees C the STI, averaged with respect to heat load, increased significantly with SAR. Depending on SAR, the sensitivity of heat loss from the tail to microwave exposure increased 32-71% per 1 degree C elevation in ambient temperature. The data indicate that heat loss from the tail increases with the whole-body heat load accrued from microwave exposure. When heat loss is averaged with respect to heat load, the rate of heat absorption and ambient temperature increase the sensitivity of thermoregulatory centers that control peripheral heat loss from the tail of mice.

Animals↗
PubMed1983

Behavioral and autonomic thermoregulation in mice exposed to microwave radiation.

Preferred ambient temperature (Ta) and breathing rate were measured in free-moving mice exposed to 2,450-MHz microwaves. A waveguide-exposure system was imposed with a longitudinal temperature gradient that permitted mice to select their preferred Ta. Breathing rate was determined by analyzing the rhythmic shifts in microwave energy not absorbed by the animal. Without microwave exposure mice selected an average Ta of 31 degrees C. This preferred Ta did not change until the specific absorption rate (SAR) at 2,450 MHz exceeded approximately 7.0 W X kg-1. Mice maintained their breathing rate near baseline levels by selecting a cooler Ta during microwave exposure. In contrast, mice maintained at 31 degrees C underwent a sharp increase in breathing rate when SAR exceeded approximately 7.0 W X kg-1. Mice exposed to microwaves in a waveguide with a temperature gradient increased breathing rate 0.6 breaths/min per unit increase in SAR, whereas without the temperature gradient breathing rate increased by 9.6 breaths/min per unit increase in SAR. Data from this study support previous studies that have shown behavioral thermoregulation is more effective (or efficient) in minimizing a thermal load than autonomic thermoregulation.

Animals↗