Catalepsy induced by body pinch: relation to stress-induced analgesia

Microglia ablation alleviates myelin-associated catatonic signs in mice

The underlying cellular mechanisms of catatonia, an executive "psychomotor" syndrome that is observed across neuropsychiatric diseases, have remained obscure. In humans and mice, reduced expression of the structural myelin protein CNP is associated with catatonic signs in an age-dependent manner, pointing to the involvement of myelin-producing oligodendrocytes. Here, we showed that the underlying cause of catatonic signs is the low-grade inflammation of white matter tracts, which marks a final common pathway in Cnp-deficient and other mutant mice with minor myelin abnormalities. The inhibitor of CSF1 receptor kinase signaling PLX5622 depleted microglia and alleviated the catatonic symptoms of Cnp mutants. Thus, microglia and low-grade inflammation of myelinated tracts emerged as the trigger of a previously unexplained mental condition. We observed a very high (25%) prevalence of individuals with catatonic signs in a deeply phenotyped schizophrenia sample (n = 1095). Additionally, we found the loss-of-function allele of a myelin-specific gene (CNP rs2070106-AA) associated with catatonia in 2 independent schizophrenia cohorts and also associated with white matter hyperintensities in a general population sample. Since the catatonic syndrome is likely a surrogate marker for other executive function defects, we suggest that microglia-directed therapies may be considered in psychiatric disorders associated with myelin abnormalities.

A myelin gene causative of a catatonia-depression syndrome upon aging

Severe mental illnesses have been linked to white matter abnormalities, documented by postmortem studies. However, cause and effect have remained difficult to distinguish. CNP (2',3'-cyclic nucleotide 3'-phosphodiesterase) is among the oligodendrocyte/myelin-associated genes most robustly reduced on mRNA and protein level in brains of schizophrenic, bipolar or major depressive patients. This suggests that CNP reduction might be critical for a more general disease process and not restricted to a single diagnostic category. We show here that reduced expression of CNP is the primary cause of a distinct behavioural phenotype, seen only upon aging as an additional 'pro-inflammatory hit'. This phenotype is strikingly similar in Cnp heterozygous mice and patients with mental disease carrying the AA genotype at CNP SNP rs2070106. The characteristic features in both species with their partial CNP 'loss-of-function' genotype are best described as 'catatonia-depression' syndrome. As a consequence of perturbed CNP expression, mice show secondary low-grade inflammation/neurodegeneration. Analogously, in man, diffusion tensor imaging points to axonal loss in the frontal corpus callosum. To conclude, subtle white matter abnormalities inducing neurodegenerative changes can cause/amplify psychiatric diseases.

Immobility response elicited by clamping the neck induces antinociception in a “tonic pain” test in mice

Clamping the neck followed by body inversion to a supine position in mice elicits an immobility response called immobility by clamping the neck (ICN). The noxious pinch to the scruff of the neck produces antinociception in "phasic pain" models (e.g. tail-flick test). Here, a "tonic pain" model was used to test the antinociception associated with the ICN, and naloxone was used to determine the role of opioids in such antinociception. Mice were injected intraperitoneally with 0.3 mL of 0.4% acetic acid to produce writhing responses that were measured for one hour. ICN was induced every five minutes for one hour. Naloxone (5 mg/kg ip) was injected 10 min before acetic acid administration. There was a control group, sham clamping (SCLA). These mice were handled and restricted every five minutes as in the ICN but without real clamping. The repetitive inductions of ICN were able to reduce the writhing behavior; this antinociception was blocked by the naloxone pretreatment. In the SCLA group antinociception was not observed. These findings indicate that as in the "phasic pain" model, ICN also was able to elicit antinociception in this "tonic pain" model, and such antinociception seems to be mediated by opioids.

Differential effect of testosterone and repetitive induction on cataleptic and dorsal immobility in mice

In nature, many species under conditions of stress (e.g., predator attack, pups carried by the mother, mating) show immobility states called "immobility responses" (IRs), which are characterized by the complete absence of movement and a relative unresponsiveness. These IR states can be induced by several kinds of sensorial stimuli. Many brain neurotransmitters from diverse cerebral areas participate in the expression of IRs. Other factors are also involved in IRs, such as learning and hormones, but at present, there is not enough experimental support about these factors. Our purpose was to investigate whether the IRs are subject to sexual hormone modulation and to examine the possible relation to learning processes. We tested the effects of acute testosterone decanoate (30 mg/kg, s.c.) and repetitive induction of two IRs; cataleptic immobility (CAT) and dorsal immobility (DI). These were tested in mice of both sexes which were either gonadectomized or sham-treated. CAT and DI were measured before and then 1 and 5 h after testosterone injection. The results show a differential effect of the repetitive induction on CAT and DI. CAT was augmented with repetition, and DI was decreased. Sex differences of the effects of the acute testosterone treatment were observed. Sham and castrated male mice showed CAT potentiation; in contrast, DI was reduced albeit only in sham male mice. Sham and ovariectomized female mice were not affected by testosterone. These results support the hypothesis that there are multiple immobility systems that can be differentially modulated by brain regions associated with processes of learning.

Cholinergic modulation of tonic immobility and nociception in the NRM of guinea pig

Tonic immobility (TI) is an inborn defensive behavior characterized by a temporary state of profound and reversible motor inhibition elicited by some forms of physical restraint. It is known that endogenous antinociceptive systems are activated during the emission of defensive behaviors including TI. The nucleus raphe magnus (NRM) is related to the modulation of nociceptive and behavioral responses. In the present study, we investigated the role of the cholinergic system of the NRM in the modulation of TI and nociception in guinea pigs. Microinjection of the cholinergic agonist carbachol (0.5 microg/0.2 microl) into the NRM promoted a reduction in the duration of TI episodes and nociception, the latter measured by the vocalization test in guinea pigs. The effect of microinjection of carbachol on TI reduction and antinociception was blocked by the previous microinjection of the cholinergic antagonist atropine (0.5 microg/0.2 microl and 1 microg/0.2 microl, respectively), demonstrating the participation of muscarinic receptors in the modulation of these responses. Microinjection of atropine per se did not interfere with the duration of TI episodes. In summary, the present results demonstrate that cholinergic stimulation of the NRM promoted analgesia and a reduction in the duration of TI in guinea pigs. These data indicate that the NRM possibly contributes to the modulation of defensive and nociceptive behavioral responses, probably by modulating the activity of neurons in the ventral and dorsal horn of the spinal cord, respectively.

The cholinergic stimulation of the central amygdala modifying the tonic immobility response and antinociception in guinea pigs depends on the ventrolateral periaqueductal gray

Tonic immobility (TI), also known as death feigning or animal hypnosis, is a reversible state of motor inhibition that is triggered by postural inversion and/or movement restraining maneuvers but also by repetitive stimulation and pressure on body parts. Our previous studies demonstrated that cholinergic stimulation of the central amygdala (CEA) decreases the duration of TI in guinea pigs. Some reports have demonstrated that electrical or chemical stimulation of the CEA promotes antinociception. Evidence suggests that the CEA performs part of its functions by means of a connection with the ventrolateral periaqueductal gray (vlPAG). In the current study, we investigated the participation of a possible functional and anatomical CEA-vlPAG connection in guinea pigs in the regulation of the TI response and antinociception. Our results showed that the functional CEA-vlPAG connection is essential for the participation of the CEA in the modulation of TI and of antinociception. The reversible exclusion of the vlPAG by means of microinjection of 2% lidocaine blocked the inhibitory effect on TI duration and the antinociceptive effect, as determined by a decrease of the vocalization index (VI) obtained with the administration of carbachol (2.7 nmol/0.2 microl) into the CEA. On the other hand, the exclusion of the CEA by lidocaine did not block the antinociception or the increase in TI induced by microinjection of CCh into the vlPAG. Finally, microinjection of the retrograde neurotracer Fast Blue into the CEA or into the vlPAG demonstrated the existence of a reciprocal anatomical connection between the CEA and vlPAG.

Endogenous opiate analgesia induced by tonic immobility in guinea pigs

A function of the endogenous analgesic system is to prevent recuperative behaviors generated by tissue damage, thus preventing the emission of species-specific defensive behaviors. Activation of intrinsic nociception is fundamental for the maintenance of the behavioral strategy adopted. Tonic immobility (TI) is an inborn defensive behavior characterized by a temporary state of profound and reversible motor inhibition elicited by some forms of physical restraint. We studied the effect of TI behavior on nociception produced by the formalin and hot-plate tests in guinea pigs. The induction of TI produced a significant decrease in the number of flinches (18 +/- 6 and 2 +/- 1 in phases 1 and 2) and lickings (6 +/- 2 and 1 +/- 1 in phases 1 and 2) in the formalin test when compared with control (75 +/- 13 and 22 +/- 6 flinches in phases 1 and 2; 28 +/- 7 and 17 +/- 7 lickings in phases 1 and 2). In the hot-plate test our results also showed antinociceptive effects of TI, with an increase in the index of analgesia 30 and 45 min after the induction of TI (0.67 +/- 0.1 and 0.53 +/- 0.13, respectively) when compared with control (-0.10 +/- 0.08 at 30 min and -0.09 +/- 0.09 at 45 min). These effects were reversed by pretreatment with naloxone (1 mg/kg, ip), suggesting that the hypoalgesia observed after induction of TI behavior, as evaluated by the algesimetric formalin and hot-plate tests, is due to activation of endogenous analgesic mechanisms involving opioid synapses.

Tail-pinch induced analgesia and immobility: altered responses to noxious tail-pinch by prior pinch of the neck

Noxious pinch to the scruff of the neck using a metal clip produces profound immobility and analgesia. Noxious pinch delivered to the tail fails to induce immobility and results in nociceptive behavior directed at the pinched tail. However, when administered shortly after neck-clip removal, noxious tail-pinch reinstated immobility without any nociceptive response. Prior neck-clip also enhanced the antinociception induced by the tail-pinch as measured by nociceptive response to a leg pinch. Immobility, as well as antinociception, decreased as the time interval between neck-clip removal and the tail-pinch application increased. Pharmacological manipulations which reduce nociception produced a similar alteration in the response to tail-pinch. Thus, following local injections antinociceptive doses of lidocaine to the base of the tail and systemic morphine administration tail-pinch produced marked immobility. Transection of the brain at the intercollicular level provides evidence for supraspinal involvement in post-neck pinch effects. Not only was the ability of prior neck-pinch to confer antinociceptive properties on tail-pinch abolished, but increased responsiveness to noxious tail-pinch was seen. We, therefore, propose that prior neck-pinch confers new stimulus properties on noxious pinch of other body regions resulting in an enhanced antinociceptive effect, which affects both remote regions and the site of stimulation, and the ability to induce immobility.

Morphine attenuates antipredator ultrasonic vocalizations in mixed-sex rat colonies

Mixed-sex groups of laboratory rats living in a visible burrow system (VBS) emit 18-27 kHz ultrasound and retreat to the burrow when a cat is placed in the open area of the VBS. The total duration of ultrasonic vocalizations was reliably reduced by pretreatment with 5 mg/kg morphine. In a subsequent study using male-female colony pairs, presentation of a cat to individual rats in the absence of their colony mate indicated significant gender differences in base frequency, degree of emission, and characteristics of pulses elicited. Specifically, females showed a greater number and duration of vocalizations, of higher frequency (kHz), and with shorter individual pulse durations than males. In the same study, morphine (5 mg/kg) produced a general decrease in the level of ultrasonic emissions in both sexes, reduced the mean base frequency (kHz), and increased the mean duration of individual pulses. These data suggest that endogenous opioid mechanisms may be involved in the mediation of ultrasonic vocalization in response to a predator, and are discussed with reference to known involvement of such systems in defensive responding.

Effects of diazepam on behavioural and antinociceptive responses to the elevated plus-maze in male mice depend upon treatment regimen and prior maze experience

Recent studies have shown that brief exposure to an elevated plus-maze (EPM) produces non-opioid antinociception in male mice. The present experiments were designed to assess the effects of diazepam on this phenomenon. When acutely administered, low doses (0.5-1.0 mg/kg) of diazepam failed to produce an anxiolytic profile and exerted rather inconsistent effects on EPM-induced elevations in tail-flick latencies. In EPM-experienced mice, chronic treatment with higher doses of diazepam (2-4 mg/kg, 8 days) produced a weak anxiolytic action and inhibited the early phase of EPM antinociception only. However, in EPM-naive mice, 8-day diazepam pretreatment exerted a marked anxiolytic effect and completely eliminated the antinociceptive response to the maze. Together, these data support the view that anxiety is a key factor in certain forms of adaptive pain inhibition and suggest a possible mediational role for benzodiazepine receptors. Our findings also show that prior exposure to the EPM, rather than chronic handling/injection, greatly reduces the anti-anxiety effect of diazepam. Furthermore, since re-exposure to the maze, per se, decreased time spent on the open arms and central platform, a shift in behavioural baseline ("retest anxiogenesis") may have contributed to the weak behavioural effects of diazepam in test-experienced animals. Importantly, as chronic treatment with diazepam did not influence this anxiogenic-like retest profile, our data suggest that a single prior experience of the EPM may radically alter the nature of the anxiety reaction provoked by this test.

"Paradoxical" effects of morphine on antipredator defense reactions in wild and laboratory rats

In a Fear/Defense Test Battery, measuring defensive reactions to a present, approaching and contacting predator, the highest dose of morphine tested (7.5 mg/kg) reliably reduced vocalization to dorsal contact, to vibrissae stimulation, and to an anesthetized conspecific in laboratory-bred wild R. norvegicus. Except for a dose-dependent reduction in flinch/jump reactions to dorsal contact (taps), other defensive behaviors (flight, freezing, etc.) were not reliably altered by morphine treatment (0, 1.0, 2.5, 7.5 mg/kg). Vocalization responses to vibrissae stimulation in wild-trapped R. rattus were reliably increased following naloxone (1.0 and 10.0 mg/kg) administration, lending support for opiate receptor involvement in the mediation of defensive vocalization. In the Anxiety/Defense Test Battery, measuring defensive reactions to situations associated with a predator (cat) or with cat odor, laboratory rats showed no decrease in defensive behavior with morphine (0, 1.0, 5.0 mg/kg). In direct contrast to the above findings, the effects of morphine treatment in this test battery suggested a generalized increase in defensiveness to noncontacting and nonpainful threat stimuli. These effects included a decrease in time spent near the cat compartment, with a complementary increase in time spent at maximum distance, a decrease in transits between these sections, an increase in crouching, and a decrease in grooming and rearing. This pattern of results suggests that morphine may have two opposing effects on defensive behavior, a generalized enhancement, together with a more specific reduction of responses to tactile or painful stimulation. A very widespread pattern of reliable sex or sex x drug effects in the Anxiety/Defense Test Battery was in good agreement with previous reports of sex differences in these tests, with females generally more defensive than males. Consonant with previous findings, no reliable sex differences were found with the Fear/Defense Test Battery, although several values approached an acceptable level of statistical significance.

Stimulation-produced analgesia in the mouse: evidence for laterality of opioid mediation

The effect of naloxone on periaqueductal gray matter (PAG) stimulation-produced analgesia (SPA) was examined in pentobarbital anesthetized Swiss-Webster mice. Electrodes were placed either in dorsolateral or ventrolateral PAG, and SPA threshold was assessed using the hind paw-flick test (paw withdrawal from radiant heat). SPA threshold did not differ between dorsal and ventral PAG, and naloxone equally attenuated SPA from both areas. SPA threshold for the paw contralateral to the stimulation site was half that for the ipsilateral paw. Elevation of SPA threshold by naloxone was greater for the contralateral than ipsilateral paw. Exposure to analgesic neck pinch prior to SPA almost completely abolished the antinociceptive effect of contralateral PAG stimulation without affecting SPA on the ipsilateral paw. This effect of pinch was itself reversed by prior naloxone administration. We suggest that the substrate of opioid mediated SPA from PAG in the mouse has principally a contralateral organization.

Antinociceptive effects of elevated plus-maze exposure: influence of opiate receptor manipulations

It has been suggested that anxiety may be a critical factor in certain forms of non-opioid environmental analgesia. In the present study, 5-min exposure to the elevated plus-maze test of anxiety (EPM) induced a mild, though enduring, elevation in tail-flick latencies in male mice. Pretreatment with the opiate antagonist naltrexone (0.1-10.0 mg/kg) failed to block EPM-induced antinociception: indeed, the highest dose actually enhanced the response. This effect could not be attributed to intrinsic analgetic activity of naltrexone. Rather, analysis of EPM behaviours suggested that it may have been secondary to an anxiogenic effect of the compound. The involvement of non-opioid substrates in the form of pain inhibition was further supported by the failure of chronic morphine treatment (7 days; 7.5 mg/kg) to alter either the antinociceptive or behavioural response to EPM exposure. Irrespective of treatment history, mice showed a retest EPM profile of enhanced anxiety, with tail-flick data suggesting a major contribution of anticipatory factors. Several important methodological variables are discussed and findings are contrasted with parallel studies on non-opioid defeat analgesia.

Highly potent inhibitory effects of 5-HT3 receptor antagonist, GR38032F, on non-opioid defeat analgesia in male mice

Behavioural and pharmacological evidence indicates that non-opioid analgesia in defeated male mice is initiated by anxiety and that serotongergic (5-HT) substrates are implicated. In the present study, the effects of the novel putative 5-HT3 anxiolytic, GR38032F, on this form of adaptive inhibition of pain have been examined. The results showed that defeat analgesia was totally inhibited by 1 microgram/kg-1 mg/kg of GR38032F, with partial inhibition evident over the dose range of 0.0001-0.1 microgram/kg and loss of efficacy at smaller doses. These highly potent effects of GR38032F are consistent with its anxiolytic profile in animal models and cannot be accounted for by indirect actions on basal nociception. These findings point to a potentially important modulatory role for 5-HT3 receptor mechanisms in defeat analgesia and, more generally, provide further evidence for the involvement of 5-HT in the mediation of non-opioid forms of environmentally-induced antinociception.

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)

Prevention of the analgesic consequences of social defeat in male mice by 5-HT1A anxiolytics, buspirone, gepirone and ipsapirone

Behavioural and pharmacological studies have suggested that anxiety may be an important factor in the initiation of non-opioid analgesia in defeated male mice. In the present study, the effects of three 5-HT1A anxiolytics (buspirone, ipsapirone and gepirone) on basal nociception and defeat analgesia were examined. Results show that the analgesic consequences of social defeat were potently blocked by all three compounds, with a rank-order potency (minimum effective doses) of ipsapirone (0.05 mg/kg) greater than gepirone (0.1 mg/kg) greater than buspirone (0.5 mg/kg). These inhibitory effects on defeat analgesia were observed in the absence of intrinsic activity on basal nociception (tail-flick assay). When administered alone, (-)pindolol produced biphasic effects on defeat analgesia with enhancement at 0.5 mg/kg and inhibition at 5.0 mg/kg. Lower doses of (-)pindolol (0.05 and 0.25 mg/kg) which did not affect defeat analgesia when administered alone, totally blocked the inhibitory effects of ipsapirone (0.5 mg/kg). Data are discussed in relation to the involvement of 5-HT1A receptor mechanisms in this adaptive form of pain inhibition.

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)

Adaptive pain inhibition in murine resident-intruder interactions

In dyadic encounters with aggressive resident conspecifics, male intruder mice display an initial acute nonopioid analgesia followed by a more enduring opioid analgesia. The former reaction occurs in association with active defense (flight or fight) and can be seen in response to the scent of an aggressive conspecific or defeat experience per se. In contrast, the latter (opioid) reaction is associated with passive defense (immobility) and occurs in response to extended conspecific attack. The mechanisms underlying these two ecologically-relevant forms of pain inhibition are contrasted and the phenomena are discussed in relation to the question of adaptive significance.

Clip induced analgesia and immobility in the mouse: activation by different sensory modalities

In the present study we have attempted to characterize, in mice, a situation which appears to simulate real life predation and elicits simultaneous analgesia and immobility. We utilized pinch produced by clip application to various regions of the body and examined its effect on responsiveness to noxious stimuli and motor behavior. Intense noxious clip was applied to the nape of the neck, back and base of the tail. The area most effective for the elicitation of both clip induced analgesia and immobility was the nape of the neck while tail pinch resulted in analgesia but not immobility. Evidence is provided that different systems are responsible for clip induced immobility and analgesia. Temporal dissociation of clip induced analgesia and immobility could be demonstrated with continuous clip application for 30 min showing a different time course for the analgesic and immobilizing effects. Different stimuli were effective in eliciting clip induced analgesia and immobility with noxious stimuli essential for the induction of clip induced analgesia and innocuous stimuli sufficient for clip induced immobility. Thus, low analgesic doses of local anesthetics injected into the nape of the neck prevented noxious clip from inducing analgesia but immobility was still evident. In contrast, nonnoxious pinch to the nape of the neck elicited immobility but not analgesia and clip induced immobility could still be induced after the administration of high doses of morphine which completely blocked responses to noxious stimuli. These results demonstrate that in a situation resembling natural predation both analgesia and immobility are produced concurrently but that these behavioral phenomena can be elicited differentially and may be mediated by different independent systems.