Body temperature, activity patterns and hunting in free-living cheetah: biologging reveals new insights.

As one of the few felids that is predominantly diurnal, cheetahs (Acinonyx jubatus) can be exposed to high heat loads in their natural habitat. Little is known about long-term patterns of body temperature and activity (including hunting) in cheetahs because long-term concurrent measurements of body temperature and activity have never been reported for cheetahs, or, indeed, for any free-living felid. We report here body temperature and locomotor activity measured with implanted data loggers over 7 months in 5 free-living cheetahs in Namibia. Air temperature ranged from a maximum of 39 °C in summer to -2 °C in winter. Cheetahs had higher (∼0.4 °C) maximum 24-h body temperatures, later acrophase (∼1 h), with larger fluctuations in the range of the 24-h body temperature rhythm (approximately 0.4 °C) during a hot-dry period than during a cool-dry period, but maintained homeothermy irrespective of the climatic conditions. As ambient temperatures increased, the cheetahs shifted from a diurnal to a crepuscular activity pattern, with reduced activity between 900 and 1500 hours and increased nocturnal activity. The timing of hunts followed the general pattern of activity; the cheetahs hunted when they were on the move. Cheetahs hunted if an opportunity presented itself; on occasion they hunted in the midday heat or in total darkness (new moon). Biologging revealed insights into cheetah biology that are not accessible by traditional observer-based techniques.

Cheetah do not abandon hunts because they overheat.

Hunting cheetah reportedly store metabolic heat during the chase and abandon chases because they overheat. Using biologging to remotely measure the body temperature (every minute) and locomotor activity (every 5 min) of four free-living cheetah, hunting spontaneously, we found that cheetah abandoned hunts, but not because they overheated. Body temperature averaged 38.4°C when the chase was terminated. Storage of metabolic heat did not compromise hunts. The increase in body temperature following a successful hunt was double that of an unsuccessful hunt (1.3°C ± 0.2°C versus 0.5°C ± 0.1°C), even though the level of activity during the hunts was similar. We propose that the increase in body temperature following a successful hunt is a stress hyperthermia, rather than an exercise-induced hyperthermia.

Activity re-assignment and microclimate selection of free-living Arabian oryx: responses that could minimise the effects of climate change on homeostasis?

Predicting whether behaviour could buffer the effects of climate change on long-lived mammals requires a better understanding of the long-term behavioural responses of mammals to environmental stress. Using biologging, we measured locomotor activity and microclimate selection, over eight months, in five Arabian oryx (Oryx leucoryx) living free in a Saudi Arabian desert. The oryx displayed seasonal flexibility in activity patterns, shifting from a continuous 24-h activity pattern with crepuscular peaks in cooler months to a predominantly nocturnal activity pattern during the hottest months, without reducing the total 24-h activity level. The proportion of total 24-h activity that occurred during daylight hours was just 29±8% during the hottest months, versus 53±8% (mean±SD, n=5 oryx) in the other months. The attenuation in diurnal activity levels during the hot months was accompanied by the selection of cooler microclimates, presumably via shade seeking, during the heat of the day. Analysis of miniature black globe (miniglobe) temperature from a remote sensor on the collar of two female animals revealed that oryx selected microclimates cooler than the microclimates in direct sun at higher environmental heat loads across all periods, but with enhanced efficiency during the dry periods. We have quantified activity re-assignment and microclimate selection as responses to hot arid conditions in a free-living artiodactyl. Such flexible behavioural processes may act to buffer the adverse effects of the progressively hotter and drier conditions predicted to occur with climate change.

Selective brain cooling in Arabian oryx (Oryx leucoryx): a physiological mechanism for coping with aridity?

Selective brain cooling is a thermoregulatory effector proposed to conserve body water and, as such, may help artiodactyls cope with aridity. We measured brain and carotid blood temperature, using implanted data loggers, in five Arabian oryx (Oryx leucoryx) in the desert of Saudi Arabia. On average, brain temperature was 0.24±0.05°C lower than carotid blood temperature for four oryx in April. Selective brain cooling was enhanced in our Arabian oryx compared with another species from the same genus (gemsbok Oryx gazella gazella) exposed to similar ambient temperatures but less aridity. Arabian oryx displayed a lower threshold (37.8±0.1°C vs 39.8±0.4°C), a higher frequency (87±6% vs 15±15%) and a higher maximum magnitude (1.2±0.2°C vs 0.5±0.3°C) of selective brain cooling than did gemsbok. The dominant male oryx displayed less selective brain cooling than did any of the other oryx, but selective brain cooling was enhanced in this oryx as conditions became hotter and drier. Enhanced selective brain cooling in Arabian oryx supports the hypothesis that selective brain cooling would bestow survival advantages for artiodactyl species inhabiting hot hyper-arid environments.

Does size matter? Comparison of body temperature and activity of free-living Arabian oryx (Oryx leucoryx) and the smaller Arabian sand gazelle (Gazella subgutturosa marica) in the Saudi desert.

Heterothermy, a variability in body temperature beyond the normal limits of homeothermy, is widely viewed as a key adaptation of arid-adapted ungulates. However, desert ungulates with a small body mass, i.e. a relatively large surface area-to-volume ratio and a small thermal inertia, are theoretically less likely to employ adaptive heterothermy than are larger ungulates. We measured body temperature and activity patterns, using implanted data loggers, in free-ranging Arabian oryx (Oryx leucoryx, ±70 kg) and the smaller Arabian sand gazelle (Gazella subgutturosa marica, ±15 kg) inhabiting the same Arabian desert environment, at the same time. Compared to oryx, sand gazelle had higher mean daily body temperatures (F(1,6) = 47.3, P = 0.0005), higher minimum daily body temperatures (F(1,6) = 42.6, P = 0.0006) and higher maximum daily body temperatures (F(1,6) = 11.0, P = 0.02). Despite these differences, both species responded similarly to changes in environmental conditions. As predicted for adaptive heterothermy, maximum daily body temperature increased (F(1,6) = 84.0, P < 0.0001), minimum daily body temperature decreased (F(1,6) = 92.2, P < 0.0001), and daily body temperature amplitude increased (F(1,6) = 97.6, P < 0.0001) as conditions got progressively hotter and drier. There were no species differences in activity levels, however, both gazelle and oryx showed a biphasic or crepuscular rhythm during the warm wet season but shifted to a more nocturnal rhythm during the hot dry season. Activity was attenuated during the heat of the day at times when both species selected cool microclimates. These two species of Arabian ungulates employ heterothermy, cathemerality and shade seeking very similarly to survive the extreme, arid conditions of Arabian deserts, despite their size difference.

Effects of serotonin agonists and doxapram on respiratory depression and hypoxemia in etorphine-immobilized impala (Aepyceros melampus).

Respiratory depression is a common side effect when opioids are used to immobilize wildlife. Serotonergic ligands have the potential to reverse opioid-induced respiratory depression. We examined whether any of three serotonergic ligands could reverse this depression in etorphine-immobilized (0.07 mg/kg) impala (Aepyceros melampus). The study took place in September-December 2007. Impala received intravenous injections of metoclopramide (10 mg/kg, n=6), buspirone (0.05 mg/kg, n=8), pimozide (1 mg/kg, n=8), doxapram (1 mg/kg, n=6), and control solutions on separate occasions. During the immobilization, partial pressures of oxygen (PaO(2), mmHg) and carbon dioxide (PaCO(2), mmHg), respiratory rate (breaths/min), ventilation (l/min), peripheral O(2) saturation (%), tidal volume (l), and respiratory exchange ratio were measured before and after injection of the experimental drugs. Etorphine immobilization caused respiratory depression and hypoxia (mean+/-SD, PaCO(2)=51+/-2 mmHg, PaO(2)=40+/-3 mmHg). Metoclopramide and buspirone, but not pimozide, attenuated the hypoxic effects of etorphine; 3 min after injection, metoclopramide increased the PaO(2) by 7.5+/-6.3 mmHg and buspirone by 6+/-6.6 mmHg (F=3.9, P=0.02). These effects were similar to those of doxapram (8+/-7 mmHg, F=3.9; P>0.05). Neither metoclopramide nor buspirone significantly increased ventilation, but they increased PaO(2) by significantly improving the alveolar-arterial oxygen partial pressure gradient (A-a gradient, F=1.4, P<0.05), indicating improved oxygen diffusion. Metoclopramide and buspirone transiently improved blood oxygenation of opioid-immobilized impala, probably by improving ventilation-perfusion ratios, without reversing catatonic immobilization.

Variation in the daily rhythm of body temperature of free-living Arabian oryx (Oryx leucoryx): does water limitation drive heterothermy?

Heterothermy, a variability in body temperature beyond the limits of homeothermy, has been advanced as a key adaptation of Arabian oryx (Oryx leucoryx) to their arid-zone life. We measured body temperature using implanted data loggers, for a 1-year period, in five oryx free-living in the deserts of Saudi Arabia. As predicted for adaptive heterothermy, during hot months compared to cooler months, not only were maximum daily body temperatures higher (41.1 ± 0.3 vs. 39.7 ± 0.1°C, P = 0.0002) but minimum daily body temperatures also were lower (36.1 ± 0.3 vs. 36.8 ± 0.2°C, P = 0.04), resulting in a larger daily amplitude of the body temperature rhythm (5.0 ± 0.5 vs. 2.9 ± 0.2°C, P = 0.0007), while mean daily body temperature rose by only 0.4°C. The maximum daily amplitude of the body temperature rhythm reached 7.7°C for two of our oryx during the hot-dry period, the largest amplitude ever recorded for a large mammal. Body temperature variability was influenced not only by ambient temperature but also water availability, with oryx displaying larger daily amplitudes of the body temperature rhythm during warm-dry months compared to warm-wet months (3.6 ± 0.6 vs. 2.3 ± 0.3°C, P = 0.005), even though ambient temperatures were the same. Free-living Arabian oryx therefore employ heterothermy greater than that recorded in any other large mammal, but water limitation, rather than high ambient temperature, seems to be the primary driver of this heterothermy.

Winter body temperature patterns in free-ranging Cape ground squirrel, Xerus inauris: no evidence for torpor.

The body temperature (T(b)) of Cape ground squirrels (Xerus inauris, Sciuridae) living in their natural environment during winter has not yet been investigated. In this study we measured abdominal T(b) of eight free-ranging Cape ground squirrels over 27 consecutive days during the austral winter. Mean daily T(b) was relatively stable at 37.0 ± 0.2°C (range 33.4 to 40.2°C) despite a marked variation in globe temperature (T(g)) (range -7 to 37°C). Lactating females (n = 2) consistently had a significantly higher mean T (b) (0.7°C) than non-lactating females (n = 3) and males. There was a pronounced nychthemeral rhythm with a mean active phase T(b) of 38.1 ± 0.1°C and a mean inactive phase T(b) of 36.3 ± 0.3°C for non-lactating individuals. Mean daily amplitude of T(b) rhythm was 3.8 ± 0.2°C. T(b) during the active phase closely followed T(g) and mean active phase T(b) was significantly correlated with mean active phase T(g) (r(2) = 0.3-0.9; P < 0.01). There was no evidence for daily torpor or pronounced hypothermia during the inactive phase, and mean minimum inactive phase T(b) was 35.7 ± 0.3°C for non-lactating individuals. Several alternatives (including nocturnal huddling, an aseasonal breeding pattern and abundant winter food resources) as to why Cape ground squirrels do not employ nocturnal hypothermia are discussed.

Body temperature, thermoregulatory behaviour and pelt characteristics of three colour morphs of springbok (Antidorcas marsupialis).

Using intra-abdominal miniature data loggers, we measured core body temperature in female springbok (Antidorcas marsupialis) of three colour morphs (black, normal and white), free-living in the Karoo, South Africa, for one year. During winter, white springbok displayed lower daily minimum body temperatures (37.4+/-0.5 degrees C), than both black (38.1+/-0.3 degrees C) and normal (38.0+/-0.6 degrees C) springbok. During spring, black springbok displayed higher daily maximum body temperatures (40.7+/-0.1 degrees C) than both white (40.2+/-0.2 degrees C) and normal (40.2+/-0.2 degrees C) springbok. These high maximum body temperatures were associated with larger daily amplitudes of nychthemeral rhythm of body temperature (2.0+/-0.2 degrees C), than that of white (1.6+/-0.1 degrees C) and normal (1.7+/-0.2 degrees C) springbok. Biophysical properties of sample springbok pelts were consistent with these patterns, as the black springbok pelt showed lower reflectance in the visible spectral range, and higher heat load from simulated solar radiation, than did the pelts of the other two springbok. Black springbok had lower diurnal activity in winter, consistent with them having to forage less because their metabolic cost of homeothermy was lower, but were disadvantaged in hot periods. White springbok, by contrast, were more protected from solar heat load, but potentially less able to meet the energy cost of homeothermy in winter. Thus energy considerations may underlie the rarity of the springbok colour morphs.

The relative roles of the parasol-like tail and burrow shuttling in thermoregulation of free-ranging Cape ground squirrels, Xerus inauris.

As small arid-zone mammals, Cape ground squirrels (Xerus inauris) are unusual in being diurnally active. It is postulated that they remain active during the day by using their parasol-like tails to shade their bodies whilst foraging. However, no studies have continuously measured body temperature to determine the effect of using the tail as a parasol, relative to other thermoregulatory behaviours, such as burrow retreat. We caught four free-ranging Cape ground squirrels (673+/-36 g) and surgically implanted miniature temperature-sensitive data loggers into their abdomens, to record body temperature every 5 min to an accuracy of 0.04 degrees C, before they were released back into their home range and observed for two weeks. Mean daily peak black globe temperature was 41 degrees C, and daily peak body temperature reached 40 degrees C. Ground squirrels raised their tails significantly more often at globe temperatures above 30 degrees C, but raising the tail did not decrease body temperature, nor prevent body temperature rising. Ground squirrels retreated to burrows, at 18 degrees C, significantly more often at high body temperatures and body temperature dropped 1-2 degrees C before re-emergence. We believe that the tail was raised to provide thermal comfort during high solar radiation exposure, and that burrow retreat was employed to dissipate a heat load and remain active diurnally.

Hyperthermia in captured impala (Aepyceros melampus): a fright not flight response.

To investigate the patterns and mechanisms of capture-induced hyperthermia, we surgically implanted 26 impala (Aepyceros melampus) with miniature thermometric data loggers, which measured body temperatures continuously throughout capture procedures. Four groups of impala, which were habituated to varying levels of handling and boma-housing, were captured by net restraint or by chemical immobilization. The study took place between July 1999 and December 2005. Irrespective of whether impala were chemically captured, net-captured, or disturbed by exposure to a stressor, they developed a precipitous increase in body temperature. This increase in body temperature was not related to activity levels; animals that had low activity levels before immobilization had larger increases in body temperature compared to those that had high activity levels but were not immobilized (t = 3.6, P = 0.001, n = 5). Similarly this increase in body temperature was not related to environmental heat load at the time of darting and immobilization (r = -0.05, P = 0.85). Body temperature increase also did not depend on whether the animals were captured using drugs or not. However, we found that those animals that were habituated more to handling and boma-housing had smaller increases in body temperatures (F = 37, P<0.001) and smaller stress responses, indicated by lower plasma cortisol concentrations (F = 5.5, P<0.05), and less fractious behavior, compared to those animals that were habituated less or not at all. Therefore we believe that capture-induced hyperthermia in impala is caused predominantly by stress, which induces a rapid rise in body temperature.

Fever and sickness behavior during an opportunistic infection in a free-living antelope, the greater kudu (Tragelaphus strepsiceros).

To study their thermal responses to climatic stress, we implanted seven greater kudu (Tragelaphus strepsiceros) with intra-abdominal, brain, carotid, and subcutaneous temperature data loggers, as well as an activity logger. Each animal was also equipped with a collar holding a miniature black globe thermometer, which we used to assess thermoregulatory behavior. The kudu ranged freely within succulent thicket vegetation of the Eastern Cape Province, South Africa. The kudu spontaneously developed a bacterial pneumonia and consequent fever that lasted between 6 and 10 days. The fever was characterized by a significant increase in mean 24-h abdominal temperature from 38.9 +/- 0.2 degrees C to 40.2 +/- 0.4 degrees C (means +/- SD, t(6) = 11.01, P < 0.0001), although the amplitude of body temperature rhythm remained unchanged (t(6) = 1.18, P = 0.28). Six of the kudu chose warmer microclimates during the fever than when afebrile (P < 0.0001). Despite the selection of a warmer environment, on the first day of fever, the abdominal-subcutaneous temperature difference was significantly higher than on afebrile days (t(5) = 3.06, P = 0.028), indicating vasoconstriction. Some kudu displayed increased frequency of selective brain cooling during the fever, which would have inhibited evaporative heat loss and increased febrile body temperatures, without increasing the metabolic maintenance costs of high body temperatures. Average daily activity during the fever decreased to 60% of afebrile activity (t(6) = 3.46, P = 0.014). We therefore have recorded quantitative evidence for autonomic and behavioral fever, as well as sickness behavior, in the form of decreased activity, in a free-living ungulate species.

The time course of inflammatory cytokine secretion in a rat model of postoperative pain does not coincide with the onset of mechanical hyperalgesia.

We characterized the time course of inflammatory cytokine release at the site of injury and in plasma after surgery on the rat tail. Anesthetized Sprague-Dawley rats had a 20 mm long incision made through the skin and fascia of their tails. Control rats were anesthetized, but no incision was made. Blood and tissue samples were taken 2 h and 1, 2, 4, and 8 days after surgery and analysed by ELISA for interleukin-1beta (IL-1beta), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and cytokine-induced neutrophil chemoattractant-1 (CINC-1). In another group of rats, daily behavioral measurements were made of the rats' responses to a blunt noxious mechanical stimulus (4 Newtons) applied to their tails. Primary hyperalgesia developed within 2 h of surgery and lasted for 6 days. The tissue concentrations of IL-1beta, IL-6, and CINC-1 increased within 24 h of surgery, and TNF-alpha concentration increased within 48 h of surgery. Thereafter, cytokine concentrations remained elevated for 4 (IL-1beta and IL-6) to 8 days (CINC-1, TNF-alpha) after surgery. Control animals did not develop hyperalgesia and no changes in cytokines concentrations were detected. Thus, in our model of postoperative pain, secretion of inflammatory cytokines IL-1beta, IL-6, TNF-alpha, and CINC-1 was not essential for the initiation of postoperative hyperalgesia.

Tramadol is more effective than morphine and amitriptyline against ischaemic pain but not thermal pain in rats.

The aim of this study was to compare the analgesic efficacies of tramadol, which acts on opioid receptors and inhibits monoamine reuptake, to amitriptyline, a monoamine reuptake inhibitor as well as to morphine, an opioid receptor agonist. We compared the motor function impairment and response latencies to noxious thermal and noxious ischaemic challenges after tramadol administration to those after morphine and after amitriptyline administration. We injected Sprague-Dawley rats (i.p.) with either tramadol (1, 5, 15 and 25 mg kg(-1)), morphine (0.01, 0.1, 1 and 5 mg kg(-1)) or amitriptyline (1, 3 and 10 mg kg(-1)) and a control injection of saline (100 microl). We measured the tail flick latency to a noxious thermal challenge after tail immersion in a 49 degrees C water bath and response latency to noxious ischaemia, induced by a tourniquet inflated at the base of the tail, was recorded as ischaemic escape latency. In a separate group of rats, we assessed motor function by placing the rats on a rotarod, rotating at 25 rpm, for a maximum of 30 min after drug administration. We recorded the time to the rat's third fall from the rotarod. Tramadol (15 mg kg(-1)) produced a 107% increase in response latency from pre-injection value as did 25 mg kg(-1) tramadol (79%), 1 mg kg(-1) morphine (85%), 5 mg kg(-1) morphine (138%) and 10 mg kg(-1) amitriptyline (46%) against a noxious thermal challenge. The escape latency against noxious ischaemia after morphine and amitriptyline administration did not change, despite an increase in dose, while increasing doses of tramadol (1-25 mg kg(-1)) provided increasing analgesia against noxious ischaemia. Significant impairment to motor function occurred after morphine (5 mg kg(-1)), tramadol (15 mg kg(-1)) and amitriptyline (10 mg kg(-1)) administration, with only 11, 50 and 38% of animals, respectively, completing the rotarod trial, compared to 100% completion after saline administration. As previously demonstrated, morphine was more potent than tramadol for the relief of thermal pain but tramadol may be a more beneficial drug for relieving severe ischaemic pain.

Long-acting neuroleptics used in wildlife management do not impair thermoregulation or physical activity in goats (Capra hircus).

Long-acting neuroleptics commonly are used in wildlife management to decrease stress-related mortality in wild animals, but with possible effects on thermoregulation, which may contribute to residual morbidity and mortality. We investigated the effects of haloperidol (0.01, 0.1, 1 mg kg(-1), n=4), zuclopenthixol (0.1, 1, 10 mg kg(-1), n=4) and perphenazine (0.1, 1, 10 mg kg(-1), n=8), as well as control injections of sunflower oil, on body temperature and physical activity of laboratory goats under hot, cold and thermoneutral ambient temperatures. Implanted data loggers continuously recorded abdominal temperature, and data loggers attached externally on the foreleg recorded movement of unrestrained goats, in a climatic chamber at 35 degrees C, 10 degrees C and 22 degrees C. Cycling ambient temperature between 35 degrees C in daytime and 10 degrees C at night time caused a significant increase in amplitude of the circadian rhythm of body temperature in goats given sunflower oil (P=0.0012, unpaired t-test, n=8), but the administration of zuclopenthixol or perphenazine did not affect this change in amplitude (P>0.05, two-way ANOVA, n=4). Mean daily body temperature after administration of zuclopenthixol or perphenazine, and mean daily activity after zuclopenthixol administration, were not significantly different to those after control injections, at any ambient temperature, for the expected duration of drug activity (all P>0.05, two-way ANOVA, n=4). Thermal response indices, and mean activity, during heat, cold or thermoneutral exposure, of goats for 7 h after haloperidol injection, were not significantly different, at any dose or any ambient temperature, to those following control injections (all P>0.05, repeated measures ANOVA, n=4). Long-acting neuroleptics did not impair activity or thermoregulation of goats subjected to inescapable thermal challenges.

Interactions between metoclopramide and morphine: enhanced antinociception and motor dysfunction in rats.

1. Opioid analgesics and anti-emetics are often used concomitantly to treat pain and nausea and vomiting in people with malignant disease. We investigated interactions between the opioid analgesic morphine and the anti-emetic metoclopramide, a dopamine D2 receptor antagonist, on nociception and gross motor function. 2. To assess for antinociceptive interactions, 11 Sprague-Dawley rats were injected intraperitoneally with morphine (5.0 mg/kg) or saline in combination with metoclopramide (0.5, 1.5 and 5.0 mg/kg) or saline and, 30 min later, the tail-flick latencies to a noxious thermal stimulus (49 degrees C water) were measured. Immediately thereafter we induced reperfusion hyperalgesia in the rats' tails using a tourniquet cuff and tested nociception again. Because, in addition to its ability to block D2 receptors, metoclopramide is also a weak 5-HT(3) receptor antagonist, we assessed in a further 11 rats whether any antinociceptive interactions occurred between morphine (5.0 mg/kg) and ondansetron (0.2 and 2.0 mg/kg), an anti-emetic that selectively antagonizes 5-HT(3) receptors. To assess for motor interactions, we injected another group of nine rats with morphine (5.0 mg/kg) or saline in combination with metoclopramide (0.5 and 5.0 mg/kg) or saline and tested the ability of the animals to run on an 80 mm diameter rod rotating at 25 r.p.m. for 30 min. 3. Metoclopramide was not inherently analgesic or antihyperalgesic, but the highest dose of metoclopramide (5.0 mg/kg) enhanced the analgesic and antihyperalgesic effects of morphine. Neither dose of ondansetron was analgesic or antihyperalgesic or enhanced the antinociceptive actions of morphine. 4. Only the high dose of metoclopramide compromised running performance when administered with saline. However, coadministering morphine with metoclopramide (both doses) decreased motor performance. 5. Therefore, metoclopramide, possibly through its actions on D2 receptors and not 5-HT(3) receptors, enhances the analgesic and antihyperalgesic effects of morphine, but morphine exacerbates metoclopramide-induced motor dysfunction in rats.

Exposure of the rat tail to ultraviolet A light produces sustained hyperalgesia to noxious thermal and mechanical challenges.

We aimed to establish whether exposing the tails of rats to ultraviolet A (UVA) light generated sustained hyperalgesia to noxious thermal and mechanical challenges. The tails of 21 rats underwent eight 40s exposures of UVA light, with 260s between each exposure. As a control procedure, during UVA-light exposure the tails of 11 of those rats were shielded with aluminium foil. Thermal hyperalgesia was assessed by immersing the rat tail in 49 degrees C water (modified tail flick test). Mechanical hyperalgesia was assessed by applying a bar algometer onto the tail and timing the escape response. Exposure to direct UVA light produced hyperalgesia for 8 days to the noxious thermal challenge (P<0.05, two-way ANOVA, Tukey post hoc tests) and at least 16 days to the noxious mechanical challenge (P<0.05, two-way ANOVA, Tukey post hoc tests). They gained mass throughout the study at the same rate as the control rats. The control rats did not develop thermal nor mechanical hyperalgesia. The tails of a further 20 rats were exposed similarly, and tail tissue examined histologically. Both exposed and control rats developed mild chronic inflammation unrelated to the hyperalgesia.