Bilateral analgesic effects of abobotulinumtoxinA (Dysport® ) following unilateral administration in the rat.

BACKGROUND: In addition to inhibition of muscle and glandular hyperactivity, botulinum neurotoxin (BoNT) type A also interferes with pain processing. Previously, in a rat model of paclitaxel-induced polyneuropathy, abobotulinumtoxinA (aboBoNT-A) elicited analgesic effects not only in the injected paw, but also in the contralateral, non-injected paw. METHODS: Here, we assessed bilateral analgesic effects of unilateral aboBoNT-A in several chronic pain models in Sprague-Dawley rats. Effects of aboBoNT-A on the paw withdrawal threshold in response to mechanical pressure was assessed in models of streptozotocin-induced diabetic polyneuropathy, chronic constriction injury (CCI)-associated mononeuropathy, and bilateral carrageenan-induced inflammatory pain. RESULTS: In diabetic polyneuropathy, aboBoNT-A (15, 20 U/kg) reversed hyperalgesia in the toxin-injected and non-injected paws. In unilateral CCI-exposed animals, 20 U/kg aboBoNT-A given ipsilateral to the injury reversed mechanical hyperalgesia, while 30 U/kg aboBoNT-A given contralateral to the injury had no effect. In carrageenan-induced bilateral inflammatory pain, aboBoNT-A (20, 30 U/kg) reversed hyperalgesia in both toxin-injected and non-injected paws. DISCUSSION: These results suggest that unilateral administration of aboBoNT-A results in bilateral reduction in mechanical hyperalgesia across neuropathic and inflammatory pain conditions, bilateral activation of sensory neurons being prerequisite for its expression. Future studies involving effects on other sensory modalities as well as those evaluating diffusion and migration of the toxin away from the injection site can shed light on mechanisms of this phenomenon. SIGNIFICANCE: The results expand evidence on bilateral analgesic effects of aboBoNT-A following unilateral administration across pain modalities, as the phenomenon is seen in more than one model of polyneuropathy as well as in a model of chronic inflammatory pain when the latter is rendered bilateral. The mechanism of bilateral analgesic effects of aboBoNT-A may require activation of the peripheral sensory neurons and involve retrograde axonal transport of the toxin into the spinal cord.

Evaluation of peripheral versus central effects of GABA(B) receptor activation using a novel, positive allosteric modulator of the GABA(B) receptor ADX71943, a pharmacological tool compound with a fully peripheral activity profile.

BACKGROUND AND PURPOSE: The GABA(B) receptor agonist, baclofen, has shown promising effects in patients suffering from pain, post-traumatic stress disorder, alcoholism, overactive bladder and gastroesophageal reflux disease. However, baclofen's short duration of action and side effects limit its wider use. Here we characterized a novel, GABA(B) receptor positive allosteric modulator (PAM) ADX71943. EXPERIMENTAL APPROACH: In vitro, ADX71943 was assessed for pharmacological activity and selectivity using recombinant and native GABA(B) receptors. In vivo ADX71943 was assessed in the acetic acid-induced writhing (AAW) test in mice and formalin tests (FTs) in mice and rats. Marble burying (MB) and elevated plus maze (EPM) tests, rotarod, spontaneous locomotor activity (sLMA) and body temperature (BT) tests in mice and rats were used to investigate centrally-mediated effects. KEY RESULTS: In vitro, in the presence of GABA, ADX71943 increased the potency and efficacy of agonists and showed selectivity at the GABA(B) receptor. ADX71943 reduced pain-associated behaviours in AAW; an effect blocked by GABA(B) receptor antagonist CGP63360. ADX71943 reduced pain in the FT in mice and rats, but was inactive in the MB and EPM despite reaching high concentrations in plasma. ADX71943 had no effect on BT, rotarod and sLMA. CONCLUSIONS AND IMPLICATIONS: ADX71943 showed consistent and target-related efficacy in tests of disorders that have a significant peripheral component (acute and chronic pain), while having no effect in those associated with centrally-mediated anxiety-like reactivity and side effects. Thus, ADX71943 is a useful pharmacological tool for delineation of peripherally- versus centrally-mediated effects of GABA(B) receptor activation.

ADX71441, a novel, potent and selective positive allosteric modulator of the GABA(B) receptor, shows efficacy in rodent models of overactive bladder.

BACKGROUND AND PURPOSE: The GABAB receptor agonist baclofen reduces urethral resistance and detrusor overactivity in patients with spasticity. However, baclofen's side effects limit its use for the treatment of overactive bladder (OAB). Here, we tested a novel GABAB positive allosteric modulator (PAM) ADX71441 in models of OAB in mice and guinea pigs. EXPERIMENTAL APPROACH: Mice were left untreated or given (p.o.) vehicle (1% CMC), ADX71441 (1, 3, 10 mg kg(-1) ) or oxybutynin (100 mg kg(-1) ; Experiment 1) or vehicle (1% CMC), baclofen (1, 3, 6 mg kg(-1) ) or oxybutynin (Experiment 2). Treated mice were then overhydrated with water, challenged with furosemide, before being placed into micturition chambers and monitored for urinary parameters. In anaesthetized guinea pigs, intravesical infusion of acetic acid was used to induce OAB and the effects of ADX71441 (1, 3 mg kg(-1) ) or baclofen (1 mg kg(-1) ), administered i.v., on cystometric parameters were monitored. KEY RESULTS: In mice, 10 mg kg(-1) ADX71441 increased urinary latencies, reduced the number of urinary events and the total and average urinary volumes. In guinea pigs, ADX71441 (1 and 3 mg kg(-1) ) increased the intercontraction interval (ICI) and bladder capacity (BC), and reduced micturition frequency (MF) compared to vehicle. At 3 mg kg(-1) ADX71441 completely inhibited the micturition reflex and induced overflow incontinence in five out of 10 animals. Baclofen slightly increased ICI and BC and reduced MF. CONCLUSION AND IMPLICATIONS: Our findings demonstrate, for the first time, that a GABAB PAM has potential as a novel approach for the treatment of OAB.

Early neonatal experience of Long-Evans rats results in long-lasting changes in morphine tolerance and dependence.

RATIONALE: Daily, 3-h separations from the dam on postnatal days 2-14 produce long-lasting changes in behavioral and neuroendocrine responses to stressors and sensitivity to acute morphine in Long-Evans rats. OBJECTIVE: We tested whether offspring that were separated from their dam for 3 h daily (MS) on postnatal days 2-14 exhibit altered sensitivity to chronic morphine, compared to animals that experienced only brief (15 min) separations (H) from the dam or that were left undisturbed (NH) during the same period. METHODS: Subjects received 1 week SC infusion of either morphine, or saline via osmotic pumps. Twenty-hours after pump removal, the global opioid withdrawal scores were recorded. Four hours later, animals were tested for antinociception (tail-flick and hot-plate tests) during cumulative morphine administration. RESULTS: MS males and MS females undergoing withdrawal from chronic morphine had higher global withdrawal scores compared to NH controls. MS males (but not MS females) were less sensitive to the antinociceptive effects of morphine compared to H and NH controls, primarily in the hot-plate test, regardless of whether they had received a saline or a morphine infusion. MS males consistently exhibited significant morphine tolerance, whereas control males failed to exhibit tolerance either in the hot-plate test (NH group) or in both antinociception assays (H group). In contrast, tolerance was exhibited by all females in both tests for antinociception. CONCLUSIONS: These data indicate that repeated neonatal maternal separation alters sensitivity to chronic morphine administration in a sex-dependent manner.

Repeated neonatal maternal separation alters morphine-induced antinociception in male rats.

Recent studies indicate that Long-Evans rats separated from their dam for 3 h daily over the first 2 weeks of life (maternally separated [MS] rats) exhibit exaggerated behavioral and neuroendocrine responses to stress as adults compared to handled (H) or non-handled (NH) control animals. Our aim was to determine whether repeated neonatal maternal separation results in altered sensitivity to the opioid agonist morphine in male and female adult rats. Sensitivity to morphine was assessed using hot-plate and tail-flick tests. Morphine was less potent inducing antinociception in MS males compared to same-sex controls in the hot-plate, but not in the tail-flick test. Decrease in sensitivity to morphine in MS females compared to same-sex controls was present only as a trend in the hot-plate, but not in the tail-flick test. These results suggest that neonatal maternal separation results in long-lasting changes in opioid responsiveness primarily in male rats.

The medial preoptic area, necessary for adult maternal behavior in rats, is only partially established as a component of the neural circuit that supports maternal behavior in juvenile rats.

To determine whether the neurons of the medial preoptic area (MPOA) are necessary for pup-induced maternal behavior (MB) in juvenile and adult rats, subjects received bilateral injections of the neurotoxin N-Methyl-D-Aspartic acid into the MPOA. Controls were intact or were sham treated by surgical placement of the syringe barrel. The rats were then induced into MB by constant pup exposure. Starting at 27 (juvenile) or 60 (adult) days of age, rats were tested for MB for 12 consecutive days. After histological analysis, rats were categorized as having either large or small lesions of the MPOA. In juveniles, large lesions of the MPOA blocked retrieval and impaired nest-building, but crouching behavior was unaffected; small lesions had no effect on MB. In contrast, in adults, large or small lesions severely impaired all components of MB. The results suggest that in juvenile rats, the role of the MPOA neurons in MB is only partially established, whereas by 60 days of age, the unsubstitutable role of the MPOA in the neural circuit that mediates MB is fully established.

Periodic postpartum separation from the offspring results in long-lasting changes in anxiety-related behaviors and sensitivity to morphine in Long-Evans mother rats.

RATIONALE: According to recent studies daily, 3-h separations from the dam on postnatal days 2-14 produce long-lasting changes in responses to stressors and sensitivity to morphine in Long-Evans offspring. It has not been investigated whether daily dam-litter separations can have long-lasting effects also on the mother beyond weaning of the pups. OBJECTIVE: We tested whether dams that were separated from their litter for 3 h daily (LS) on postpartum days 2-14, like their offspring, exhibit altered anxiety-like behaviors and sensitivity to morphine, compared to dams that experienced only brief (15-min) separations (BS) from the litter or that were left undisturbed (NH) during the same period. METHODS: Four to six weeks after weaning, subjects were tested on the elevated plus-maze, in a novel locomotor activity arena, or were exposed to loud auditory stimuli. Sensitivity to morphine was assessed using hot-plate and tail-flick tests. RESULTS: LS dams spent significantly more time in the open arms of the plus-maze and in the center of the locomotor activity arena, and were more likely to emit ultrasonic vocalizations in response to auditory startle stimuli compared to NH dams. Furthermore, LS dams were less sensitive to morphine, primarily in the tail-flick test. Dams that experienced brief litter separations (BS), like LS dams, exhibited altered performance on the plus-maze and elevated ultrasonic vocalizations. However, BS dams were similar to NH controls in locomotor activity and sensitivity to morphine. CONCLUSIONS: Multiple postpartum separations from the offspring alter the behavior of Long-Evans dams in novel/aversive environments and affect their sensitivity to the antinociceptive effects of morphine.

Induction of c-fos-like and fosB-like immunoreactivity reveals forebrain neuronal populations involved differentially in pup-mediated maternal behavior in juvenile and adult rats.

Juvenile rats can exhibit maternal behavior after being exposed continuously to rat pups, a process called sensitization. Maternal behavior in juveniles is robust and is similar to adult maternal behavior (Mayer and Rosenblatt [1979] Dev. Psychobiol. 12:407-424; Gray and Chesley [684] J. Comp. Psychol. 98:91-99). In this study, immunocytochemical detection of the protein products of two immediate-early genes, c-fos and fosB, was used as a tool to identify forebrain neuronal populations involved in the maternal behavior of 27-day-old juvenile rats compared with 60-day-old adults. To sensitize them, rats were exposed continuously to foster pups. Once they were maternal, they were isolated from pups overnight, reexposed to pups for 2 hours, and then killed. Nonmaternal control animals also were isolated overnight and were either reexposed to pups for 2 hours or kept isolated from pups before killing. The lateral habenula (LH) was the only area in which both maternal juveniles and maternal adults had more c-Fos-immunoreactive (-Ir) neurons compared with controls. In maternal adults, the number of neurons that expressed c-Fos and FosB immunoreactivity increased in the medial preoptic area (MPO) and the ventral bed nucleus of the stria terminalis (BSTv), whereas the dorsal bed nucleus of the stria terminalis (BSTd) and the medial and cortical nuclei of the amygdala (MEA and COA, respectively) had increases only in the number of neurons that expressed c-Fos immunoreactivity. In contrast, juveniles, whether or not they were maternal, had the same number of c-Fos-IR and FosB-Ir neurons in all these areas. The adult-like increase in the number of c-Fos-Ir neurons found in maternal juveniles suggests that the juvenile LH participates in the neural circuit that supports maternal behavior in an adult-like manner. The lack of c-fos or fosB induction in the MPO, BSTv, BSTd, COA, or MEA of maternal juveniles compared with maternal adults may reflect the immaturity of these brain regions in juvenile rats. Exactly what this immaturity consists of and when the responses of these regions become adult-like remain to be determined.