Effects of centrifugal rotation on analgesia and conditioned flavor aversions

Classical conditioning and pain: conditioned analgesia and hyperalgesia

This article reviews situations in which stimuli produce an increase or a decrease in nociceptive responses through basic associative processes and provides an associative account of such changes. Specifically, the literature suggests that cues associated with stress can produce conditioned analgesia or conditioned hyperalgesia, depending on the properties of the conditioned stimulus (e.g., contextual cues and audiovisual cues vs. gustatory and olfactory cues, respectively) and the proprieties of the unconditioned stimulus (e.g., appetitive, aversive, or analgesic, respectively). When such cues are associated with reducers of exogenous pain (e.g., opiates), they typically increase sensitivity to pain. Overall, the evidence concerning conditioned stress-induced analgesia, conditioned hyperalagesia, conditioned tolerance to morphine, and conditioned reduction of morphine analgesia suggests that selective associations between stimuli underlie changes in pain sensitivity.

Pharmacological studies of centrifugation-induced analgesia

Subjecting rats to a brief period of centrifugal rotation produces a brief analgesia (1-2 min) that is similar to that produced by pretreatment with morphine. The effect of the morphine is blocked by naloxone, while that of the centrifugal rotation is only partially blocked by the same dose of naloxone. Cholinergic blocking agents such as scopolamine are also capable of partially blocking the rotational-induced analgesia. The combination of pretreatment with scopolamine plus naloxone is capable of completely blocking the rotational-induced analgesia, suggesting the involvement of both central cholinergic and endogenous opioid components.

Sodium arsanilate-induced vestibular dysfunction in meadow voles (Microtus pennsylvanicus): effects on posture, spontaneous locomotor activity and swimming behavior

Vestibular dysfunction was chemically induced in male meadow voles (Microtus pennsylvanicus) by intratympanic injections (30 mg per side) of sodium arsanilate (atoxyl). The control group received intratympanic injections of isotonic saline. After a one-week recovery period the voles were behaviorally assayed for integrity of their labyrinthine systems. All subjects were tested for the presence of the air-righting reflex and body rotation-induced nystagmus. Three weeks later a multivariate assessment of spontaneous motor activity of the voles was carried out in the automated Digiscan Activity Monitor. In addition, the swimming behavior of the voles was examined. Voles with vestibular dysfunction exhibited pronounced postural abnormalities (head dorsiflexion), were not able to swim with their nose above the water for a 1 min test period, and displayed disorientation and thrashing movements. In the Digiscan activity test the atoxyl-treated voles displayed significantly more activity in the horizontal measures (Ps less than 0.01), including greater distance travelled per movement and greater speed of movements, relative to the control animals. The labyrinthectomized group also spent significantly (P less than 0.05) less time in vertical movements and exhibited significantly more time in stereotypic behavior (P less than 0.01), relative to controls. Atoxyl-treated voles also showed significantly less thigmotaxis (wall-hugging) than the control animals (P less than 0.01). In general, changes in spontaneous behavior observed in the sodium arsanilate-treated voles were consistent with the presence of postural and balance abnormalities and a redirecting of exploratory vertical movements toward horizontal locomotion to the extent that these animals were clearly hyperactive in this dimension. The multivariate behavioral assessment available in the Digiscan Activity Monitoring system, thus seems to be especially useful in the examination of behavioral components affected by vestibular dysfunction.

Motion sickness in guinea pigs (Cavia porcellus) indexed by body rotation-induced conditioned taste aversions

The presence of motion sickness in albino guinea pigs (Cavia porcellus) was examined by using a conditioned taste aversion (CTA) as an index. Eighteen animals were divided into three groups. One group received four pairings of a novel 0.15% saccharin solution followed by 20 min of body rotation at 70 rpm (on a schedule of 15 sec on and 5 sec off). Another group received four pairings of the saccharin solution followed by exposure to sham rotation. The third group experienced the rotation procedure following access to water. The group receiving the rotation procedure contingent on presentation of the novel saccharin taste exhibited a conditioned aversion to this fluid (relative to the control groups) over days of acquisition (p less than 0.01), which subsequently dissipated when rotation was no longer contingent on the presentation of the saccharin solution (extinction). These data thus demonstrate the presence of motion sickness in guinea pigs when CTA is used as an index.

The effects of naloxone on body rotation-induced analgesia and anorexia in male mice

The effects of body rotation in a horizontal plane and the opiate antagonist, naloxone, on the nociceptive responses and the feeding behavior of male mice were examined. In the first experiment the mice were rotated (70 rpm, schedule of 15 sec on; 5 sec off) for 60 minutes or exposed to sham rotation for the same duration. Midway through the rotation or sham procedure the mice were either injected with naloxone (1 mg/kg) or isotonic saline. At the end of the 60-minute treatment period the animals were placed on a warm surface (47.5 degrees C) and their latency to show a foot-licking response was measured. The rotation procedure produced a significant (p less than 0.01) increase in response latency in the saline-injected mice and the naloxone injections blocked this analgesic effect. This finding provides evidence for opioid involvement in the rotation-induced analgesia. In Experiment 2 mice on a food restriction schedule were rotated (70 rpm, 15 sec on; 5 sec off) or sham exposed for 60 minutes. Midway through this treatment period the mice were either injected with naloxone (1 mg/kg) or isotonic saline. Following the treatment period the mice were given access to food for 2 hours. The rotation procedure produced a significant (p less than 0.01) reduction in feeding (anorexia) in the first 30 minutes of food access for the saline-injected mice. Injections of naloxone significantly (p less than 0.05) enhanced the rotation-induced anorexia. These experiments demonstrate that rotation-induced analgesia in mice is blocked by the opiate antagonist, naloxone, whereas rotation-induced anorexia is not.(ABSTRACT TRUNCATED AT 250 WORDS)

Ginkgo biloba extract facilitates recovery from penetrating brain injury in adult male rats

Adult, male Sprague-Dawley rats received 100 mg/kg Ginkgo biloba extract (GBE) intraperitoneally for 30 days. GBE reduced overall activity and decreased sensitivity to light in the open field maze. The rats were also less responsive to noxious stimuli after 13 days of treatment with GBE. After the last injection, all subjects were trained on a delayed-spatial alternation task. Subsequent to acquisition of the spatial task, the rats received either sham operations and saline or bilateral frontal cortex lesions treated with either saline or GBE. Thirty additional days of treatment began on the day of injury, and open field behavior, analgesia, and metabolic activity measurements were again measured. The rats with lesions treated with saline were more active than their GBE-treated counterparts and sham controls but there were no differences in response to illumination or noxious stimuli. Retention of the delayed-spatial alternation indicated that rats with lesions treated with GBE were less impaired than brain-injured subjects receiving saline treatment. Histological examination showed that GBE reduced the extent of brain swelling in response to the injury.

Differential inhibitory effects of MIF-1, Tyr-MIF-1, naloxone and beta-funaltrexamine on body rotation-induced analgesia in the meadow vole, Microtus pennsylvanicus

The effects of body rotation in a horizontal plane and various opiate antagonists on the nociceptive responses of a day-active microtine rodent, the meadow vole, Microtus pennsylvanicus, were examined. Intermittent rotation (70 rpm, schedule of 30 sec on, 30 sec off) for 30 min induced significant analgesic responses in the voles for 15 min after rotation. These increases in thermal response latency were blocked by intraperitoneal pretreatment with either naloxone or the irreversible mu opiate receptor antagonist beta-funaltrexamine (beta-FNA; 10 mg/kg; 24 hr pretreatment). This antagonistic effect of beta-FNA indicates mu opioid involvement in the mediation of rotation-induced analgesia. The antiopiate peptides MIF-1 (Pro-Leu-Gly-NH2) and Tyr-MIF-1 also significantly reduced, though did not completely block, body rotation-induced opiate analgesia. This suggests that Tyr-MIF-1 and MIF-1 have significant antagonistic effects on mu opioid systems that are involved in the mediation of stress (rotation)-induced analgesia.

Effects of antihistamines on centrifugal rotation-induced analgesia and conditioned flavor aversions

Centrifugal rotation induces short lasting analgesia, as shown in tail flick tests conducted immediately afterwards, and apparently induces visceral upset that can support aversions for flavors ingested immediately beforehand, as indicated in later preference tests. Two experiments were performed with antihistamines to determine whether the analgesic and visceral effects of rotation were attributable to separate neurochemical systems. In each experiment four groups of rats were defined by factorial combination of UCS (rotation at 150 rpm vs. no rotation) and Drug (antihistamine vs. saline). In Experiment 1 the H1 blocker chlorpheniramine (20 mg/kg, IP) was found to be ineffective against analgesia and to block conditioned flavor aversions (CFAs). In Experiment 2 the H2 blocker cimetidine (100 mg/kg, IP) was found to have a nearly significant attenuating effect on analgesia and to have no effect on CFAs. The data support the idea that analgesia and visceral upset are attributable to separate mechanisms, both of which are activated by the same manipulations.

Body-rotation induced analgesia in male mice: effects of duration and type of rotation procedure

The effects of body-rotation in a horizontal plane on the nociceptive responses of male mice were examined. In the first experiment the mice were rotated (70 rpm, schedule of 15 sec on; 5 sec off) for 30 minutes or exposed to sham rotation. The animals were then placed on a warm surface (47.5 degrees C) and their latency to show a foot-licking response was measured. Immediately after the preceding rotation procedure a trend toward a significant increase in response latencies, indicative of analgesia, was observed (p = 0.057). However, if tested 30 minutes after the end of the rotation period, no analgesia could be demonstrated (p greater than 0.50). In Experiment 2 mice were rotated (15 sec on; 5 sec off) or sham rotated for durations of 60 or 90 minutes. Response latencies were significantly elevated (p less than 0.01) after both rotation durations, but not differentially so (p greater than 0.20). In the last experiment the effects of 60 minutes of the intermittent rotation procedure (15 sec on; 5 sec off) were compared to those of 60 minutes of continuous rotation. Both types of rotation resulted in the induction of analgesia and the intermittent procedure produced a significantly greater degree of analgesia than the continuous rotation (p less than 0.05). These experiments demonstrate that 60 to 90 minutes of body-rotation can produce a significant "stress-induced" analgesia in mice and that an intermittent schedule of rotation is more effective than a continuous rotation exposure.(ABSTRACT TRUNCATED AT 250 WORDS)