Biomedical subjects

C J Gordon

Publications and source records attributed to C J Gordon.

At least 91 records · Page 5Linked to original sources

PubMed1987

Chlordecone-induced effects on thermoregulatory processes in the rat.

To investigate the mechanism(s) involved in chlordecone (CLD)-induced hypothermia, we examined colonic (Tcol) and tail skin (Tsk) temperatures, preferred ambient temperature (Ta), evaporative water loss, and metabolic rate following CLD exposure in the rat. Single ip dosages (0, 50, and 75 mg/kg) in corn oil were administered to Fischer-344 rats. At a Ta of 22.5 degrees C, Tcol was reduced by 50 and 75 mg/kg as early as 0.5 hr, and this effect persisted for 4 hr after dosing. Tcol was increased 24 hr after both CLD dosages. Tsk was elevated 2, 3, 4, and 6 hr after 75 mg/kg and 2 hr after 50 mg/kg. At Ta of 30.5 degrees C, Tcol was decreased at early exposure times after both dosages and was increased 3, 4, and 6 hr after 75 mg/kg. At 10.0 degrees C, an enhanced hypothermia was observed 1-6 hr following 50 and 75 mg/kg CLD. The preferred Ta was significantly decreased by approximately equal to 2.8 degrees C following CLD exposure while activity within the temperature gradient was unchanged. At 25.0 degrees C, evaporative water loss was decreased while metabolic rate was not affected by CLD administration. To study the enhanced hypothermia at 10.0 degrees C, metabolic rate was measured continuously for 2 hr following 75 mg/kg CLD and found to be significantly different from controls. The intensified hypothermia in the cold may be due to the inability of the CLD-treated rat to stimulate metabolic thermogenesis in response to cold in addition to the loss of body heat following cutaneous vasodilation. These data suggest that CLD-induced hypothermia at a neutral Ta is associated with cutaneous vasodilation and not with a decreased metabolic rate or increased evaporative water loss.

Animals↗

PubMed1987

Effects of d-amphetamine on behavioral and autonomic thermoregulation in mice.

d-Amphetamine has well-known behavioral and sympathomimetic effects in rodents, but its effects on thermoregulation are not well characterized. d-Amphetamine was administered IP to mice at doses of 0.1 to 10.0 mg/kg. Locomotor activity and preferred ambient temperature (Ta) were measured for 60 min after injection in a linear temperature gradient, and metabolic rate (MR) and evaporative water loss (EWL) were measured in a metabolic chamber at ambient temperatures of either 20 degrees C or 30 degrees C. Colonic temperatures (Tc) were obtained 60 min after injection in all cases. Doses of d-amphetamine at 0.3 mg/kg and above reduced preferred Ta from the control value of 30 degrees C to about 25 degrees C. Locomotor activity was reduced briefly by 0.3 mg/kg, and increased after 3.0 mg/kg d-amphetamine. Metabolic rate was suppressed by 0.3 mg/kg of the drug at both 20 and 30 degrees C. At 20 degrees C Ta, 10.0 mg/kg d-amphetamine increased MR but not EWL. At 30 degrees C, MR and EWL were both increased by doses of 3.0 and 10.0 mg/kg. Body temperatures varied both as a function of d-amphetamine dose and of apparatus, with pronounced hyperthermia (Tc greater than 38.5 degrees C) evident only after 10 mg/kg in the metabolic chamber. Thus, the behavioral and autonomic heat loss responses induced in mice by d-amphetamine suggest that its thermogenic action is detected by the animal at doses below those producing measurable thermogenesis and that appropriate effectors, from selection of a cool Ta to increasing EWL, are engaged in an orderly progression to maintain normothermia under all but the most challenging conditions.

Animals↗

PubMed1987

Comparative thermoregulatory response to passive heat loading by exposure to radiofrequency radiation.

1. Colonic and tail skin temperature of the unrestrained Fischer rat were measured immediately after a 90 min exposure to 600 MHz radiofrequency radiation in a waveguide-type system. Ambient temperature (Ta) was maintained at either 20, 28 or 35 degrees C. The specific absorption rate (SAR) in dimensions of W/kg was controlled at a constant level through a feedback control circuit. 2. The SAR needed to elevate colonic and tail skin temperature decreased with increasing Ta. For example, a 0.5 degrees C elevation in colonic temperature occurred at SARs of 4.3, 0.9 and 0.5 W/kg when Ta was maintained at 20, 28 and 35 degrees C, respectively. 3. Data from the present study were combined with data from earlier studies to assess the impact of varying Ta on the thermogenic effect of RF radiation in different species. In species ranging in mass from 0.02 to 3.2 kg, a double logarithmic plot of body mass versus SAR needed to elevate colonic temperature by 0.5 degrees C was linear and inverse with a high goodness of fit (r2 = -0.94). 4. The highly correlated allometric relationship shows that, as body mass decreases, the relative impact of Ta on the thermogenic effect of RF radiation increases.

Animals↗

PubMed1987

Effects of chlordimeform on heart rate and body temperature of unanesthetized, unrestrained rats.

Heart rate (HR) and body core temperature (Tco) were monitored in unanesthetized, unrestrained adult Sprague-Dawley rats following intraperitoneal administration of 0, 10, 30, or 60 mg/kg of the pesticide chlordimeform (CDM). Significant non-dose-related decreases were observed in both HR and Tco in all treated groups. Although similar in character, the HR response observed in the present study was of a lesser magnitude than that which was reported in previous studies from this laboratory using anesthetized animals in which Tco was maintained at control levels. It is proposed that the attenuation of the toxic response seen in the present study may be causally related to the concomitant decrease in Tco.

Amidines↗

PubMed1987

Relationship between preferred ambient temperature and autonomic thermoregulatory function in rat.

This study was designed to elucidate the relationships between behavioral and autonomic thermoregulation in three common strains of the laboratory rat. In one experiment eight adult rats of the Sprague-Dawley (SD), Long-Evans (LE), and Fischer (FCH) strains were repeatedly placed in a longitudinal temperature gradient while their preferred ambient temperature (Ta) was recorded. The mean preferred Ta's (+/- SE) for the SD, LE, and FCH strains were 24.9 +/- 0.4, 19.8 +/- 0.3, and 23.4 +/- 0.3 degrees C, respectively. In another experiment, individual adult rats of the same strains were placed in an environmental chamber thermostabilized at 2 degrees C intervals from 14 to 36 degrees C for 90 min while metabolic rate (MR), evaporative water loss (EWL), thermal conductance (C), and colonic temperature (Tcol) were determined. All three strains exhibited a minimal MR at a Ta of 30 degrees C. As Ta decreased below 30 degrees C, MR increased in a nonlinear fashion. EWL and C were minimal at cool Ta's and increased gradually with an elevation in Ta. All three strains maintained a normal Tcol between Ta's of 14 to 30 degrees C. The FCH strain exhibited the best control of Tcol at Ta's above 30 degrees C. Generally, one would predict that the preferred Ta would be associated with minimal thermoregulatory effort. However, the rat is unusual from other rodents (e.g., mouse, hamster, and guinea pig) in that the preferred Ta is well below the lower critical Ta for elevating MR.

Animals↗

PubMed1987

Reduction in metabolic heat production during exposure to radio-frequency radiation in the rat.

The purpose of this study was to assess the ability of the rat to reduce metabolic rate when exposed to deep-penetrating radio-frequency (RF) radiation. Male Sprague-Dawley rats were maintained at an ambient temperature (Ta) of 10 degrees C and exposed to 600-MHz radiation while metabolic rate (MR) was measured by indirect calorimetry. RF radiation exposures were made in a waveguide-type system that permitted the continuous control of specific absorption rate (SAR). SAR's of 2-5 W/kg led to significant reductions in MR when averaged from 30 to 60 min after the initiation of RF radiation exposure. The total decrease in MR during RF radiation exposure accounted for approximately 37% of the total RF heat load. Exposure of another group of rats to the same SAR's at a Ta of 10 degrees C resulted in a significant elevation in colonic temperature. Thus, despite the decrease in MR, heat gain still exceeded heat loss during RF radiation exposure, with a resultant elevation in deep body temperature. In conclusion, in a cold environment the rat exposed to RF radiation decreases its MR. However, the response time and efficiency of the response is not adequate to prevent an increase in body temperature.

Absorption↗

PubMed1986

Effect of a 1.5 T static magnetic field on body temperature of man.

Reports in the literature concerning the effect of static magnetic fields on the body temperature of mammals have been contradictory and confusing. A significant increase in body temperature in human subjects exposed to the static magnetic fields used in magnetic resonance imaging (MRI) would have important safety implications. Therefore, in two separate studies we determined body temperature in 20 subjects exposed to a 1.5 T static magnetic field. One group of subjects (Group I, N = 9) had sublingual pocket temperature measured immediately before and after a 60 min exposure, while another group of subjects (Group II, N = 11) had esophageal temperature determined at 2 min intervals during a 20 min exposure. No statistically significant changes in body temperature were observed in either Group I or II subjects during exposure to the 1.5 T static magnetic field. We conclude that a relatively intense static magnetic field has no effect on body temperature of normal human subjects.

Adult↗

PubMed1986

Relationship between behavioral and autonomic thermoregulation in the guinea pig.

This study was conducted to correlate the preferred thermal environment of the unrestrained guinea pig with the activity of its thermoregulatory effectors when maintained under a wide range of ambient temperatures (Ta). Eight male guinea pigs were used in a series of experiments on behavioral and autonomic thermoregulatory function. In the behavioral experiment, individual guinea pigs were placed in a temperature gradient for 90 min while their position in the gradient was noted at 5 min intervals during the last 30 min of treatment. Their position in the gradient corresponded to a preferred Ta of 30.6 +/- 3.8 (S.D.) degrees C. In the experiments to determine autonomic function, individual guinea pigs were placed in an environmental chamber thermostabilized to Ta's of 16 to 34 degrees C. Metabolic rate (MR) and evaporative water loss (EWL) were continuously monitored for 90 min. After the guinea pigs were in the chamber for 90 min their colonic temperature was measured. MR was relatively stable between Ta's of 20 to 34 degrees C. The lower critical Ta, or the Ta below which MR increased above the resting level, was 20 degrees C for the guinea pig. EWL was minimal between Ta's of 14 and 28 degrees C. Increasing Ta above 28 degrees C led to a gradual increase in EWL. Thermal conductance was minimal and stable between Ta's of 14 and 26 degrees C and increased sharply as Ta increased above 26 degrees C. Colonic temperature was maintained at 38 degrees C between Ta's of 22 to 30 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Effect of sodium pentobarbital on behavioral thermoregulation in rats and mice.

In this study on behavioral thermoregulation, male Sprague-Dawley rats were given intraperitoneal (IP) injections of sodium pentobarbital in doses of 0, 1, 5, 10 or 15 mg/kg and male CBA/J mice were given doses of 0, 5, 10, 15 or 30 mg/kg. The animals were immediately placed in a temperature gradient which allowed them to select their preferred ambient temperature (Ta). The preferred Ta of rats increased following an injection of 10 mg/kg sodium pentobarbital, whereas, the barbiturate had no effect on the preferred Ta of mice. In another study, male rats and mice were given sodium pentobarbital in doses of 0, 5, 10 and 15 mg/kg and then placed into a temperature-controlled environmental chamber set at 30 degrees C for mice and 25 degrees C for rats (i.e., their approximate preferred Ta when dosed with sodium pentobarbital). Colonic temperatures were taken one hour after injection. Sodium pentobarbital induced dose dependent hypothermia in rats at 25 degrees C and hyperthermia in mice at 30 degrees C. These data suggest a direct or indirect block of heat gain/conserving effectors in rats treated with sodium pentobarbital which results in hypothermia and an appropriate compensatory selection of a warmer Ta.

Animals↗

PubMed1986

Sulfolane-induced hypothermia enhances survivability in mice.

Mice injected intraperitoneally with sulfolane (tetrahydrothiophene-1,1-dioxide) underwent a significant decrease in metabolic rate and body temperature at ambient temperatures of 20 and 30 degrees C but not 35 degrees C. If given the opportunity, mice treated with sulfolane preferentially sought a cool ambient temperature. When given an LD50 dose of sulfolane (1270 mg/kg), the percentage mortality varied directly with ambient temperature. For example, at 35 degrees C mortality was 75% whereas at 25 degrees C mortality was only 8%. By undergoing an autonomically and behaviorally mediated decrease in body temperature (i.e., regulated hypothermia), sulfolane-treated mice appear to enhance their chance of survival.

Animals↗

PubMed1986

Temperature regulation in the unrestrained rabbit during exposure to 600 MHz radiofrequency radiation.

Six male New Zealand white rabbits were individually exposed to 600 MHz radiofrequency (RF) radiation for 90 min in a waveguide exposure system at an ambient temperature (Ta) of 20 or 30 degrees C. Immediately after exposure, the rabbit was removed from the exposure chamber and its colonic and ear skin temperatures were quickly measured. The whole-body specific absorption rate (SAR) required to increase colonic and ear skin temperature was determined. At a Ta of 20 degrees C the threshold SAR for elevating colonic and ear skin temperature was 0.64 and 0.26 W/kg, respectively. At a Ta of 30 degrees C the threshold SARs were slightly less than at 20 degrees C, with values of 0.26 W/kg for elevating colonic temperature and 0.19 W/kg for elevating ear skin temperature. The relationship between heat load and elevation in deep body temperature shown in this study at 600 MHz is similar to past studies which employed much higher frequencies of RF radiation (2450-2884 MHz). On the other hand, comparison of these data with studies on exercise-induced heat production and thermoregulation in the rabbit suggest that the relationship between heat gain and elevation in body temperature in exercise and from exposure to RF radiation may differ considerably. When combined with other studies, it was shown that the logarithm of the SAR required for a 1.0 degree C elevation in deep body temperature of the rabbit, rat, hamster, and mouse was inversely related to the logarithm of body mass. The results of this study are consistent with the conclusion that body mass strongly influences thermoregulatory sensitivity of the aforementioned laboratory mammals during exposure to RF radiation.

Animals↗

PubMed1986

Temperature regulation in the mouse and hamster exposed to microwaves in hot environments.

Colonic temperature was measured in naive BALB/c mice and golden hamsters immediately following 90-min exposures to 2450-MHz radiofrequency (RF) radiation at an ambient temperature (Ta) of 32.2 or 35 degrees C (dry air). Exposures were performed in a temperature-controlled waveguide which permitted continuous monitoring of the specific absorption rate (SAR) of RF energy. At a Ta of 32.2 degrees C the threshold SAR for elevating colonic temperature and the SAR resulting in a 0.5 degree C elevation in colonic temperature were, respectively, 4.3 and 6.5 W/kg for the mouse and 0.68 and 1.1 W/kg for the hamster. At a Ta of 35 degrees C these values were 0.12 and 0.63 W/kg for the mouse and 0.46 and 0.8 W/kg for the hamster. The SARs required to elevate body temperature in the mouse and hamster at these relatively warm Ta's are considerably lower than those required at cooler Ta's of 20 to 30 degrees C. Overall, the hamster became hyperthermic at lower SARs than the mouse. Ta's of 35 degrees C and greater are frequently encountered during heat waves in the summer months. Under such stressful environmental conditions where heat loss is impaired, absorption of RF radiation at relatively low SARs may lead to significant hyperthermia which would otherwise be readily dissipated at lower Ta's.

Animals↗

PubMed1986

Integration and central processing in temperature regulation.

Our understanding of the neural control of body temperature has been clarified by research over the past ten years. Overall, ascending thermal inputs are integrated with other thermal and nonthermal inputs, which results in efferent signals with the spatial and temporal characteristics necessary for driving effector organs involved in thermal homeostasis. There is substantial support for the hypothesis that the afferent component of the thermoregulatory system integrates thermal stimuli into several neural patterns, the principal ones being a stepwise, switching response of neuron activity during scrotal thermal stimulation and a proportional response to other thermal inputs. Furthermore, some thermointegrative CNS neurons respond relatively rapidly or slowly during peripheral thermal stimulation, which may be critical in driving behavioral and autonomic motor outputs, respectively. The control of thermoregulatory motor outputs is multifaceted and exhibits proportional, rate-sensitive, and/or on-off regulatory patterns during thermal stimulation. These complex motor patterns indicate the presence of extensive temporal and spatial integration of ascending thermal information. This is supported by the fact that the pattern of efferent nerve activity in various motor systems (e.g. vasomotor) is vastly different from that produced by recordings of primary thermoreceptor activity. Understanding the nature and mechanisms of the CNS transduction of peripheral thermal stimuli to efferent command signals for driving thermoregulatory motor outputs will be a challenging endeavor in the future.

Animals↗

PubMed1986

Improved technique for monitoring electrocardiograms during exposure to radio-frequency radiation.

Studies were conducted utilizing improved methodology that examined the effects of radio-frequency (RF) radiation on heart rate (HR), deep body temperature (Tco), and electrocardiographic (ECG) waveform parameters in anesthetized rats. One group of animals was exposed to two power levels of continuous-wave RF radiation averaging 1.0 and 7.4 W/kg at a frequency of 600 MHz. A second group of animals, treated identically but not exposed to RF radiation, served as a control. The electrodes used for monitoring the ECG during RF exposure were fabricated from carbon-loaded Teflon wire, a semiconductor material that does not perturb the RF field. Analyses of the ECG were conducted by use of a recently developed computer-assisted procedure that quantitates HR and waveform intervals over 25-40 individual ECG complexes. There were no artifacts or arrhythmias in the ECGs of the animals exposed to RF radiation. There was a significant linear correlation between HR and Tco in the RF-exposed group that was not present in the control group.

Animals↗

PubMed1986

Relationship between autonomic and behavioral thermoregulation in the golden hamster.

Preferred ambient temperature (Ta) of male golden hamsters (Mesocricetus auratus) was measured repeatedly by placing the animals in a temperature gradient for 80 min. A total of 180 observations were made during the last 20 min of treatment in the gradient. The mean preferred Ta was 28.2 +/- 0.2 degrees C. In another experiment the same animals were placed in a temperature-controlled chamber for 80 min while metabolic rate, evaporative water loss, thermal conductance, and colonic temperature were measured at Ta's of 14-34 degrees C. The lower critical Ta, the Ta below which metabolic rate increased above the resting level, was 28 degrees C. This Ta corresponds closely to the mean preferred Ta of the hamster when placed in the temperature gradient. Evaporative water loss was minimal at Ta's of 14 and 16 degrees C and increased gradually with increasing Ta. Thermal conductance was minimal between Ta's of 14 and 28 degrees C and then increased sharply with increasing Ta. The data from the hamster are qualitatively similar to the mouse in that the preferred Ta corresponds with the lower critical Ta. It appears that, for these rodents, the control of preferred Ta is critically related to the animal's metabolic requirements.

Animals↗

PubMed1986

Thermoregulatory responses to clinical magnetic resonance imaging of the head at 1.5 tesla. Lack of evidence for direct effects on the hypothalamus.

Warming temperature sensitive neurons in the hypothalamus will induce thermoregulatory heat dissipation. Application of radiofrequency (RF) radiation to the head during magnetic resonance imaging (MRI) could, conceivably, heat the brain, causing a generalized peripheral vasodilation and result in a paradoxical and unnecessary decrease in body temperature. To evaluate the thermoregulatory responses to the RF power deposition used during MRI, we measured body (sublingual pocket) and skin temperatures in 15 patients immediately before and after MRI scans of the head. Ear-skin blood flow was determined by laser-Doppler velocimetry to assess local vasomotor tone. A high-field (1.5 tesla/64 MHz) MRI device (General Electric Company) with a coil designed for head/brain imaging was used in this study. Ambient conditions were room temperature 20-24 degrees C and relative humidity 40-50%. The specific absorption rate averaged over the head ranged from 0.83 to 1.20 W/kg. There was a slight but statistically significant elevation in body temperature (36.5 +/- 0.5 to 36.7 +/- 0.4 degrees C). Skin temperatures of the ear (30.0 +/- 1.2 to 32.0 +/- 0.9 degrees C) and forehead (32.4 +/- 0.5 to 32.8 +/- 0.5 degrees C) increased significantly, while hand (29.9 +/- 1.4 to 29.8 +/- 2.1) skin temperature was unchanged. Ear-skin blood flow also increased a statistically significant amount (average change 36%). The data indicate that there was predominantly surface heating associated with MRI of the head which stimulated a local vasodilating response (i.e. significant increase in ear skin blood flow).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1986

Effect of nickel and cadmium chloride on autonomic and behavioral thermoregulation in mice.

Male BALB/c mice were injected intraperitoneally (i.p.) with nickel chloride (0, 5, 10, and 15 mg/kg) or cadmium chloride (0, 2, 4, and 6 mg/kg) and preferred ambient temperature (Ta) and activity were measured. Both metals caused marked reductions in preferred Ta and activity within 30 min postinjection. Preferred Ta and activity were depressed for up to 90 min. In a second experiment, body temperature was measured 60 min following the injection of nickel or cadmium chloride at a Ta of 20, 30, or 35 degrees C. Nickel and cadmium caused large reductions in body temperature when injected at a Ta of 20 and 30 degrees C but produced either no effect or only a slight elevation in body temperature at a Ta of 35 degrees C. In a third experiment, metabolic rate was measured continuously for 60 min following an i.p. injection of a relatively large dose of nickel (15 mg/kg) or cadmium chloride (6 mg/kg) at a Ta of 20, 30, and 35 degrees C. Both metals caused significant reductions in metabolic rate at TaS of 20 and 30 degrees C. At a Ta of 35 degrees C, cadmium caused a slight inhibition in metabolic rate while nickel had insignificant effects. These data indicate that nickel and cadmium chloride injected i.p. produce hypothermia by reducing metabolic rate and the preferred Ta.

Animals↗

PubMed1985

Effect of ambient temperature on thermoregulation in rats following preoptic/anterior hypothalamic injection of physostigmine.

This experiment was designed to study the effect of ambient temperature (Ta) on the thermoregulatory response after the injection of the acetylcholinesterase blocking agent, physostigmine, into the preoptic/anterior hypothalamic area (POAH) of the rat. Three doses of physostigmine (3.0, 30.0 and 60.0 micrograms) were injected in a volume of 1.0 microliter in the preoptic/anterior hypothalamic area of unrestrained rats at three different ambient temperatures (15, 25 and 35 degrees C). Brain temperature (Tbr) and gross changes in behavior were monitored continuously throughout the duration of each experiment. Physostigmine induced hypothermia at ambient temperatures of 15 and 25 degrees C but not at 35 degrees C. Immediately prior to and during the hypothermic response the animals displayed behavioral reflexes such as fur licking and a sprawled posture which presumably enhanced heat loss. Generally, soon after the peak of the hypothermic response (approximately 30 min), the rats displayed heat-conserving behavior (huddled position, piloerection of the fur). These data indicate that the activity of cholinergic synapses within the preoptic/anterior hypothalamic area increases with decreasing ambient temperature. The behavioral observations suggest some role for the cholinergic system in the activation of heat-dissipating responses in the rat.

Animals↗