Uninjured C-fiber nociceptors develop spontaneous activity and alpha-adrenergic sensitivity following L6 spinal nerve ligation in monkey.
We investigated whether uninjured cutaneous C-fiber nociceptors in primates develop abnormal responses after partial denervation of the skin. Partial denervation was induced by tightly ligating spinal nerve L6 that innervates the dorsum of the foot. Using an in vitro skin-nerve preparation, we recorded from uninjured single afferent nerve fibers in the superficial peroneal nerve. Recordings were made from 32 C-fiber nociceptors 2-3 wk after ligation and from 29 C-fiber nociceptors in control animals. Phenylephrine, a selective alpha1-adrenergic agonist, and UK14304 (UK), a selective alpha2-adrenergic agonist, were applied to the receptive field for 5 min in increasing concentrations from 0.1 to 100 microM. Nociceptors from in vitro control experiments were not significantly different from nociceptors recorded by us previously in in vivo experiments. In comparison to in vitro control animals, the afferents found in lesioned animals had 1) a significantly higher incidence of spontaneous activity, 2) a significantly higher incidence of response to phenylephrine, and 3) a higher incidence of response to UK. In lesioned animals, the peak response to phenylephrine was significantly greater than to UK, and the mechanical threshold of phenylephrine-sensitive afferents was significantly lower than for phenylephrine-insensitive afferents. Staining with protein gene product 9.5 revealed an approximately 55% reduction in the number of unmyelinated terminals in the epidermis of the lesioned limb compared with the contralateral limb. Thus uninjured cutaneous C-fiber nociceptors that innervate skin partially denervated by ligation of a spinal nerve acquire two abnormal properties: spontaneous activity and alpha-adrenergic sensitivity. These abnormalities in nociceptor function may contribute to neuropathic pain. (+info)
The response of the brachial ventral horn or Xenopus laevis to forelimb amputation during development.
The normal development of the brachial ventral horn of the frog Xenopus laevis and the response of the brachial ventral horn to complete forelimb extirpation at five developmental stages were assessed histologically. Differentiation of brachial ventral horn neurons occurred in pre-metamorphic tadpoles between stages 52/53 and 57. Mean cell number in the brachial ventral horn reached a peak of 2576 (S.E.M. equals +/- 269, N equals 2) per side of the spinal cord at stage 55 and decreased to 1070 (S.E.M. equals +/- 35, n equals 7) by the end of metamorphosis. Cell degeneration was presumed to be the mode of cell loss since it was most prevalent during the period of rapid decrease in cell numbers. The response of the ventral horn to forelimb removal varied with the stage of the animal at amputation. Following amputation at stage 52/53 or 54 the ipsilateral ventral horn neurons appeared less differentiated than those on the control side and a rapid cell loss of about 80% occurred on the operated side. These effects occurred more rapidly after ablation at stage 54 than at stage 52/53. Amputation at stage 58, 61, or 66 caused chromatolysis in the ventral horn, a period of relative cell excess on the operated side, and a delayed neuronal loss of 32-66%. It was concluded that excess cell degeneration accounted for cell loss and that suppression of normal neuronal degeneration caused the relative cell excess on the operated side. The data indicate that the brachial ventral horn was indifferent to the periphery before stage 54, was quickly affected by limb removal between stages 54 and 58, and by stage 58 had entered a phase in which a delay preceded cell death. No forelimb regeneration occurred. (+info)
Receptor subtype mediating the adrenergic sensitivity of pain behavior and ectopic discharges in neuropathic Lewis rats.
Receptor subtype mediating the adrenergic sensitivity of pain behavior and ectopic discharges in neuropathic Lewis rats. We attempted to identify the subtype of alpha-adrenergic receptor (alpha-AR) that is responsible for the sympathetic (adrenergic) dependency of neuropathic pain in the segmental spinal injury (SSI) model in the Lewis strain of rat. This model was chosen because our previous study showed that pain behaviors in this condition are particularly sensitive to systemic injection of phentolamine (PTL), a general alpha-AR blocker. We examined the effects of specific alpha1- and alpha2-AR blockers on 1) behavioral signs of mechanical allodynia, 2) ectopic discharges recorded in the in vivo condition, and 3) ectopic discharges recorded in an in vitro setup. One week after tight ligation of the L5 and L6 spinal nerves, mechanical thresholds of the paw for foot withdrawals were drastically lowered; we interpreted this change as a sign of mechanical allodynia. Signs of mechanical allodynia were significantly relieved by a systemic injection of PTL (a mixed alpha1- and alpha2-AR antagonist) or terazosin (TRZ, an alpha1-AR antagonist) but not by various alpha2-AR antagonists (idazoxan, rauwolscine, or yohimbine), suggesting that the alpha1-AR is in part the mediator of the signs of mechanical allodynia. Ongoing ectopic discharges were recorded from injured afferents in fascicles of the L5 dorsal root of the neuropathic rat with an in vivo recording setup. Ongoing discharge rate was significantly reduced after intraperitoneal injection of PTL or TRZ but not by idazoxan. In addition, by using an in vitro recording setup, spontaneous activity was recorded from teased dorsal root fibers in a segment in which the spinal nerve was previously ligated. Application of epinephrine to the perfusion bath enhanced ongoing discharges. This evoked activity was blocked by pretreatment with TRZ but not with idazoxan. This study demonstrated that both behavioral signs of mechanical allodynia and ectopic discharges of injured afferents in the Lewis neuropathic rat are in part mediated by mechanisms involving alpha1-ARs. These results suggest that the sympathetic dependency of neuropathic pain in the Lewis strain of the rat is mediated by the alpha1 subtype of AR. (+info)
Characterization of antiallodynic actions of ALE-0540, a novel nerve growth factor receptor antagonist, in the rat.
There is growing evidence that nerve growth factor (NGF) may function as a mediator of persistent pain states. We have identified a novel nonpeptidic molecule, ALE-0540, that inhibits the binding of NGF to tyrosine kinase (Trk) A or both p75 and TrkA (IC50 5.88 +/- 1. 87 microM, 3.72 +/- 1.3 microM, respectively), as well as signal transduction and biological responses mediated by TrkA receptors. ALE-0540 was tested in models of neuropathic pain and thermally-induced inflammatory pain, using two routes of administration, a systemic i.p. and a spinal intrathecal (i.th.) route. Morphine was also tested for comparison in the antiallodynia model using mechanical stimuli. We show that either i.p. or i.th. administration of ALE-0540 in rats produced antiallodynia in the L5/L6 ligation model of neuropathic pain. The calculated A50 values (and 95% confidence intervals) for ALE-0540 administered i.p. and i. th. were 38 (17.5-83) mg/kg and 34.6 (17.3-69.4) microgram, respectively. ALE-0540 given i.th., at doses of 30 and 60 microgram, also blocked tactile allodynia in the thermal sensitization model. Although morphine displayed greater potency [A50 value of 7.1 (5.6-8. 8) mg/kg] than ALE-0540 in anti-allodynic effect when given i.p. to L5/L6-ligated rats, it was not active when administered i.th. These data suggest that a blockade of NGF bioactivity using a NGF receptor antagonist is capable of blocking neuropathic and inflammatory pain and further support the hypothesis that NGF is involved in signaling pathways associated with these pain states. ALE-0540 represents a nonpeptidic small molecule which can be used to examine mechanisms leading to the development of agents for the treatment of pain. (+info)
The structural effect of systemic NGF treatment on permanently axotomised dorsal root ganglion cells in adult rats.
The effect of systemic NGF treatment on loss and shrinkage of dorsal root ganglion cells was studied in adult male rats after permanent axotomy. Nineteen 16 to 18-wk-old rats had their right 5th lumbar spinal nerve ligated and cut approximately 7 mm peripheral to the ganglion. Two days before the operation, treatment with subcutaneous injections of human recombinant NGF (1.0-0.5 mg/kg/day) was started in 9 test rats; 10 controls were given saline injections. After 1 mo the levels of substance P (SP) and calcitonin gene related peptide (CGRP) were significantly increased in intact sciatic nerve. The number and mean volume of perikarya were estimated using assumption-free stereological techniques including vertical sections, the Cavalieri principle, optical disectors, the planar rotator and systematic sampling techniques. Systemic NGF administration had no influence on survival of primary sensory neurons after axotomy. The number of perikarya was 14300 (S.D. = 1800) in axotomised ganglia in control rats versus 14700 (S.D. = 2100) in axotomised ganglia of NGF treated rats. The reduction of perikarya volume after axotomy was significantly less after NGF treatment (11600 microm3 in the control group versus 8000 microm3 in the NGF treated group). However, the apparent protection of NGF-treatment on perikaryal volume is explained by a hitherto unrecognised size effect on nonaxotomised dorsal root ganglion cells. The untreated rats had a mean volume of 24700 microm3 (S.D. = 2700 microm3) whereas rats treated with NGF had a volume of 20400 microm3 (S.D. = 1700 microm3) on the nonaxotomised side. In conclusion, systemic NGF treatment in adult rats has no effect on dorsal root ganglion cell loss in permanent axotomy whereas perikaryal size of intact nonaxotomised cells is reduced. (+info)
External oblique abdominal muscle: a new look on its blood supply and innervation.
Numerous reports have discussed the use of the external oblique abdominal muscle as a pedicled or a free flap for defect coverage. A detailed description of the supplying vessels and nerves is a prerequisite for successful tissue transfer but so far is not available in the literature. A study of the arteries and nerves supplying the external oblique abdominal muscle was carried out in 42 cadavers after injection of a mixture of latex and bariumsulfate. In seven fresh cadavers the motor branches were identified with the Karnovsky technique. Three different groups of arteries were identified as the nurturing vessels. The cranial part of the muscle is supplied by two branches of the intercostal arteries. While the lateral branches run on the outer surface of the muscle together with the nerves, the anterior branches enter the muscle from its inner surface. The caudal part of the muscle derives its main blood supply from one or two branches of the deep circumflex iliac artery (94.7%) or the iliolumbar artery (5.3%). The external oblique abdominal muscle is innervated by motor branches of the lateral cutaneous branches of the anterior spinal nerves in a segmental pattern. With the exception of the subcostal nerve the motor branches enter the outer surface of the muscle digitation arising from the rib above. The results show that the cranial half of the external oblique abdominal muscle has a strictly segmental blood and nerve supply while the caudal half of the muscle derives its main blood supply from one artery but still shows a segmental innervation. (+info)
Neuronal nitric oxide synthase mRNA upregulation in rat sensory neurons after spinal nerve ligation: lack of a role in allodynia development.
Pharmacological evidence suggests a functional role for spinal nitric oxide (NO) in the modulation of thermal and/or inflammatory hyperalgesia. To assess the role of NO in nerve injury-induced tactile allodynia, we examined neuronal NO synthase (nNOS) expression in the spinal cord and dorsal root ganglia (DRG) of rats with tactile allodynia because of either tight ligation of the left fifth and sixth lumbar spinal nerves or streptozotocin-induced diabetic neuropathy. RNase protection assays indicated that nNOS mRNA (1) was upregulated in DRG, but not spinal cord, neurons on the injury side beginning 1 d after nerve ligation, (2) peaked (approximately 10-fold increase) at 2 d, and (3) remained elevated for at least 13 weeks. A corresponding increase in DRG nNOS protein was also observed and localized principally to small and occasionally medium-size sensory neurons. In rats with diabetic neuropathy, there was no significant change in DRG nNOS mRNA. However, similar increases in DRG nNOS mRNA were observed in rats that did not develop allodynia after nerve ligation and in rats fully recovered from allodynia 3 months after the nerve ligation. Systemic treatment with a specific pharmacological inhibitor of nNOS failed to prevent or reverse allodynia in nerve-injured rats. Thus, regulation of nNOS may contribute to the development of neuronal plasticity after specific types of peripheral nerve injury. However, upregulation of nNOS is not responsible for the development and/or maintenance of allodynia after nerve injury. (+info)
Sex differences in cholinergic analgesia II: differing mechanisms in two models of allodynia.
BACKGROUND: Cholinergic agents reduce allodynia after nerve injury in animals and may be useful in the treatment of neuropathic pain. Intrathecally administered neostigmine and neuronal nicotinic agonists are more potent in female than in male rats against acute thermal noxious stimuli. The purpose of this study was to determine whether there is also a sex difference in the antiallodynic effects of intrathecal cholinomimetic agents in two models of allodynia and to test their pharmacologic mechanisms. METHODS: Male and female rats with indwelling intrathecal catheters received injections of neostigmine, bethanechol (muscarinic agonist), RJR-2403 (neuronal nicotinic agonist) alone or with atropine (muscarinic antagonist), mecamylamine (nicotinic antagonist), phentolamine (alpha-adrenergic antagonist), or saline control. The effect of these agents was determined on mechanical allodynia produced by either intraplantar injection of capsaicin or ligation of spinal nerves. RESULTS: Neostigmine and RJR-2403 but not bethanechol were more potent in female than in male rats in reducing allodynia after nerve injury, and antagonist studies were also consistent with a nicotinic component to explain this sex difference. Phentolamine did not reverse neostigmine's effect. In contrast, for capsaicin-induced allodynia, neostigmine plus mecamylamine but not neostigmine or RJR-2403 was more potent in female than in male rats. CONCLUSIONS: These data demonstrate a sex difference of intrathecal neostigmine after nerve injury-induced allodynia similar to that observed in normal animals that received acute noxious thermal stimulation. However, this sex difference is not universal to all pain models because it was not present after intradermal capsaicin injection, nor is its interaction with spinal noradrenergic mechanisms consistent in all models. (+info)