Chromic gut suture reduces calcitonin-gene-related peptide and substance P levels in the spinal cord following chronic constriction injury in the rat.

The chronic constriction injury (CCI) is an animal model of an experimental peripheral neuropathy. In this model, a mononeuropathy is produced by loosely ligating the left sciatic nerve of the rat with chromic gut suture (Bennett and Xie 1988). Maves et al. (1993) have proposed that chemical constituents of chromic gut suture influence the behavioral changes of rats with the CCI. Considering their results, we became interested in evaluating whether the type of suture material used to produce the CCI also affected spinal levels of calcitonin-gene-related peptide immunoreactivity (CGRP-ir) and substance P immunoreactivity (SP-ir), peptides that are associated with small primary afferent neurons. Using methods of radioimmunoassay (RIA), we measured levels of CGRP-ir and SP-ir in the dorsal quadrants of approximately the lumbar 4-5 (L4-L5) spinal segments of rats with a CCI induced using polyglactin (Vicryl), plain gut, or chromic gut suture. We observed bilateral decreases in CGRP-ir and SP-ir 60 days after a CCI induced with chromic gut suture, but no changes in peptide levels after a CCI induced with either polyglactin or plain gut suture. These results suggest two possibilities: (1) chromic gut suture, when used to produce the CCI, has more than just a constrictive effect on the sciatic nerve, and/or (2) different suture materials produce changes in CGRP-ir and SP-ir with a differential time-course. Our experiments are unable to distinguish between these two possibilities.

Abnormal skin temperature and abnormal sympathetic vasomotor innervation in an experimental painful peripheral neuropathy.

A chronic constriction injury to the sciatic nerve of the rat produces a neuropathic pain syndrome that has many of the symptoms that are seen in humans with painful peripheral neuropathy. In particular, both the clinical and experimental conditions are accompanied by an abnormality of cutaneous temperature regulation in the painful area. A time course study was made of this phenomenon in the experimental model. In normal rats, there is little or no difference between the temperature of the two hind paws (plantar skin). After nerve injury, however, approximately 75% of the rats (N = 30) had abnormally large (greater than +/- 0.9 degrees C) temperature differences (delta T) between the affected and sham-operated sides. The abnormal delta Ts could be either positive or negative, i.e., the affected side could be hotter or colder than normal. For individual cases, the temperature abnormality was highly variable over time periods of hours to days; abnormally hot skin could switch to being abnormally cold, and vice versa, and small delta Ts in the normal range could switch between abnormal extremes. Despite this individual variability, the average delta T of the group as a whole displayed a clear evolution over the course of the 30-day observation period: abnormally hot initially and progressing to abnormally cold. A parallel time course study was made of the status of the sympathetic vasoconstrictor innervation to the affected hind paw (plantar artery and vein). As demonstrated with a histofluorescence method that visualizes catecholamines, there was a gradual loss of norepinephrine (NE)-containing sympathetic efferents on the nerve-injured side. The decrease was first noted on postoperative day 5 (PO5), was very marked by PO10-PO14, and progressed to a complete or nearly complete loss by PO30. There was a concomitant decrease in staining for two other substances found in vasoconstrictor efferents, dopamine-beta-hydroxylase (DBH) and neuropeptide Y (NPY). The NE-containing innervation of the contralateral (sham-operated) plantar vessels appeared to be normal at all times. Lastly, in order to determine whether there was any relation between the temperature abnormality and the status of the sympathetic perivascular plexus, additional rats were sacrificed immediately after skin temperature measurement and the hind paw vessels were stained for NE. The vasculature of some abnormally cold paws had no detectable NE. Some rats that did not appear to have a temperature abnormality also had no detectable NE on the affected hind paw's vasculature. The vasculature of some abnormally hot paws had normal NE.(ABSTRACT TRUNCATED AT 400 WORDS)

Bilateral and differential changes in spinal mu, delta and kappa opioid binding in rats with a painful, unilateral neuropathy.

Quantitative receptor autoradiography was used to assess mu, delta and kappa opioid binding sites in the lumbar spinal cord of rats with neuropathic pain due to a unilateral chronic constriction injury (CCI) of the sciatic nerve. Sections from spinal segment L4 were obtained from animals of treatment groups (left side CCI, right side sham-operated) at 2, 5 and 10 days post surgery and from control animals (left side sham-operated, right side untreated) 10 days post surgery. Autoradiograms were made of the equilibrium binding of the highly selective opioid radioligands, 3H-sufentanil (mu ligand), 3H-[D-Pen2,5]-enkephalin (DPDPE, delta ligand) and 3H-U69593 (Upjohn compound, kappa ligand). Computerized grain counting was performed on discrete regions of the autoradiograms corresponding to areas within laminae I-II, V and X on both sides of the spinal cord; the sciatic nerve's small diameter axons terminate in these areas. With a single exception, there were no changes in binding for any of the ligands in any of the areas at 10 days post surgery in the control animals. The exception was a small increase in kappa binding in laminae I-II on the sham-operated side. After nerve injury, however, there were marked changes (compared to the sham-operated side of the control animals) in the amount of binding for all ligands, and most of these changes were bilateral. Mu binding was significantly increased 2-5 days post injury, bilateral to the injury in laminae V and X but only ipsilateral in laminae I-II. Mu binding in all laminae gradually declined towards control values. By day 10 significant differences remained only in lamina X. Delta binding displayed little change at 2 days post injury but declined gradually thereafter. By day 10 post injury, delta binding was significantly decreased in all three areas; these decreases were bilateral in all areas and approximately equal in laminae V and X but were significantly greater on the nerve-injured side in laminae I-II. Kappa binding displayed a complex pattern of changes at day 2 post injury: a significant increase in ipsilateral laminae I-II and a significant increase in contralateral lamina X but no change on either side in lamina V. There was a rapid decrease in kappa binding in all three areas on both sides of the spinal cord by day 5 post injury, and these decreases were little changed by day 10.(ABSTRACT TRUNCATED AT 400 WORDS)

Transsynaptic degeneration in the superficial dorsal horn after sciatic nerve injury: effects of a chronic constriction injury, transection, and strychnine.

The lumbar and cervical spinal dorsal horns of adult rats with a chronic (8 days) constriction injury of the sciatic nerve on one side (and a sham operation on the other) were examined for signs of transsynaptic degeneration. The incidence of neurons with signs of degeneration (pyknosis and hyperchromatosis; 'dark neurons') was significantly increased in the lumbar dorsal horn on both sides. The ipsilateral lumbar increase was significantly greater than the contralateral increase. There was no increase in the incidence of dark neurons in the cervical dorsal horns of the same rats. The distribution of lumbar dark neurons was similar bilaterally. The majority of the dark neurons were found in the sciatic nerve's territory in laminae I-II. A second group of rats received the same surgery but in addition received a series of 7 daily subconvulsive doses of strychnine. Dark neurons were again found bilaterally (with ipsilateral predominance) in the sciatic nerve's territory in lumbar laminae I-II, but the incidence was significantly greater than that found in the group that did not receive strychnine. The same result was obtained in a third group of strychnine-treated rats when the sham operation was omitted. Thus the appearance of contralateral dark neurons is not dependent on unintentional nerve damage created by the sham procedure. An additional group of rats was sacrificed 8 days after receiving a unilateral sciatic nerve transection, a contralateral sham operation, and the 7 daily strychnine injections. There was no increase in the incidence of dark neurons in any of these rats.(ABSTRACT TRUNCATED AT 250 WORDS)