151
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Ginzburg R, Seltzer Z. Subarachnoid spinal cord transplantation of adrenal medulla suppresses chronic neuropathic pain behavior in rats. Brain Res 1990; 523:147-50. [PMID: 2207684 DOI: 10.1016/0006-8993(90)91649-2] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Several weeks after transection of the sciatic and saphenous nerves, rats respond by self-injury of the denervated limb ('autotomy'). This behavior serves as a model of neuropathic pain. In this study we allografted fragments of rat adrenal medulla into the subarachnoid space of other rats, at lumbar spinal cord level, in an attempt to suppress autotomy behavior. The results show that autotomy was reduced by an average of 63% throughout the 8 week observation period. Catecholamine (CA) histofluorescent staining performed up to 120 days postoperatively (P0) revealed viable transplants in 75% of the rats. Transplant viability correlated with suppression of autotomy. This suggests that medullary chromaffin cells function as a local, long-lasting source of anti-nociceptive agents at the spinal segments which process input from the injured nerves.
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Affiliation(s)
- R Ginzburg
- Physiology Branch, Faculty of Dental Medicine, Hebrew University of Jerusalem, Israel
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152
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Kajander KC, Sahara Y, Iadarola MJ, Bennett GJ. Dynorphin increases in the dorsal spinal cord in rats with a painful peripheral neuropathy. Peptides 1990; 11:719-28. [PMID: 1978300 DOI: 10.1016/0196-9781(90)90187-a] [Citation(s) in RCA: 150] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
It is known that painful tissue injury evokes an increase in dynorphin in spinal neurons. It is not known, however, whether dynorphinergic systems respond similarly to the pain that accompanies peripheral neuropathy. Radioimmunoassays and immunocytochemistry were used to evaluate changes in dynorphin A(1-8) in the spinal cord of rats with a painful peripheral neuropathy. The neuropathy is the result of a constriction injury that is created by tying loose ligatures around the common sciatic nerve. Signs of abnormal pain sensations, hyperalgesia, allodynia (pain after normally innocuous stimuli), and spontaneous pain (or dysesthesia), are first detected 2-5 days after injury, reach peak severity in about 10 days, and persist for 2-3 months (Bennett, G. J.; Xie, Y.-K. Pain 33:87-107; 1988). Dynorphin increased by 5 days in cells in laminae I-II and V-VII in the lumbar spinal cord ipsilateral to the injury. This increase, maximal at 10 days (262%), was still present 20 days after the injury but was now seen only in neurons in the deep laminae (V-VII). Thus, the spinal dynorphinergic system appears to respond to neuropathic pain. Furthermore, our results suggest that dynorphinergic cells in the superficial and deep laminae may have different roles in nociception.
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Affiliation(s)
- K C Kajander
- Neurobiology and Anesthesiology Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, MD 20892
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153
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Abstract
Male and female rats underwent transection and ligation of the sciatic and saphenous nerves, and the development of autonomy was monitored. The deafferented animals were then interbred, always selecting males and females that expressed relatively high and, alternatively, relatively low levels of autotomy. Offspring were similarly operated and interbred. By the sixth generation of selective breeding, lines were achieved in which autotomy was consistently high (HA) or consistently low (LA). There was no indication of sex linkage. Thermal and mechanical nocifensive responsiveness co-selected with propensity to express autotomy following nerve injury: response thresholds were lower in HA than in LA rats. F1 hybrids formed by crossing homozygous HA and LA animals showed low levels of autotomy, similar to LA stock. This indicates recessive inheritance of the autotomy trait. Backcrossing F1 hybrids onto the LA line yielded a low autotomy phenotype in almost all cases; backcrossing F1 hybrids onto HA stock yielded about 50% high autotomy and 50% low autotomy. These ratios are consistent with simple mendelian inheritance of a single gene. Taken together, the data suggest that autotomy is inherited as a single-gene autosomal recessive trait.
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Affiliation(s)
- M Devor
- Neurobehavior Unit, Department of Zoology, Life Sciences Institute, Hebrew University of Jerusalem, Jerusalem 91904 Israel
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154
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Attal N, Jazat F, Kayser V, Guilbaud G. Further evidence for 'pain-related' behaviours in a model of unilateral peripheral mononeuropathy. Pain 1990; 41:235-251. [PMID: 2164179 DOI: 10.1016/0304-3959(90)90022-6] [Citation(s) in RCA: 406] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A model of experimental peripheral neuropathy producing pain-related disorders has recently been described in the rat. The present study aimed to investigate, using a different and quantifiable behavioural approach, the abnormal pain-related sensations in the animals. The neuropathy was produced by 4 ligatures tied loosely around the common sciatic nerve. 6-8 days after surgery, most of the rats exhibited pain-related disorders ipsilateral to the sciatic ligation, which became maximal 2 weeks after surgery. Mechanical noxious stimulation (pinching of the hind paw) revealed hyperalgesia in all the animals. Rats also exhibited allodynia when tested with the vocalization threshold test to paw pressure (mean vocalization thresholds were 65.5 +/- 3.6% of the preoperative control, P less than 0.01, n = 95). Tests using heat (40, 42, 44, 46 degrees C) and cold (10 degrees C) stimulation (immersion of the rat's hind paw in a bath until it was observed to struggle) indicated hyperalgesia to noxious heat (decrease of 30% in the immersion duration (ID) at a temperature of 46 degrees C), and allodynia to non-noxious heat (decrease of 30% in the temperature of the struggle threshold) and to cold stimulation (decrease by 40% in the ID). In addition, the animals showed modifications in the spontaneous postures of the affected hind paw in a natural setting, suggesting a 'spontaneous' pain-related behaviour (the mean 'pain' rating, derived from the technique used for the formalin test and numbered 0-5, was 2.8 +/- 0.4, P less than 0.01, n = 12). Lastly, sensitized responses were observed to mechanical stimulation after thermal stimulation in the non-noxious range applied to the lesioned but not the non-lesioned paw. The time course of pain-related disorders was comparable whatever the behavioural test, with recovery 2 months after surgery. These results clearly show that the neuropathy produces abnormal pain-related disorders in the rat, which are reminiscent of those observed in some human neuropathies.
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Affiliation(s)
- N Attal
- INSERM U 161, 75014 Paris France
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155
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Abstract
This paper describes an automutilation syndrome (OAS) in three species of captive octopuses, Octopus dolfleini, O. bimaculoides, and O. maya, characterized by external arm and mantle lesions. Three clinical patterns in nine animals had similar and characteristic gross and histopathologic features. Axial nerve or brachial artery lesions were observed in six of the nine cases and vascular lesions were seen in two of eight cases with mantle ulcerations. A relationship between automutilation in the octopus and dysesthesias due to neural or vascular pathology is proposed.
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Affiliation(s)
- R Reimschuessel
- Department of Pathology, University of Maryland School of Medicine, Baltimore 21201
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156
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Jänig W. Activation of afferent fibers ending in an old neuroma by sympathetic stimulation in the rat. Neurosci Lett 1990; 111:309-14. [PMID: 2336206 DOI: 10.1016/0304-3940(90)90280-m] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The sciatic nerve in 3 albino Sabra strain rats was cut and ligated on the left side. After 8.5 months, the responses of afferent fibers ending in the neuroma to electrical stimulation of sympathetic supply were tested. In all 3 animals afferent fibers could be activated by this stimulation at low frequencies. The maximal responses per stimulus shock occurred at 0.5-2 Hz. The responses exhibited wind-up, but could not be elicited by adrenaline injected i.v.. The responses ceased 1-2 h after several trains of pulses at 0.2-8 Hz had been applied. The fibers recorded from were most likely unmyelinated. This is a further example demonstrating that stimuli simulating physiological conditions of sympathetic activity can excite afferent C-fibers that end in a neuroma of a very chronically lesioned nerve.
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Affiliation(s)
- W Jänig
- Physiologisches Institut, Christian-Albrechts-Universität, Kiel, F.R.G
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157
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Kayser V, Basbaum AI, Guilbaud G. Deafferentation in the rat increases mechanical nociceptive threshold in the innervated limbs. Brain Res 1990; 508:329-32. [PMID: 2306625 DOI: 10.1016/0006-8993(90)90418-b] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
In this study in the rat, we evaluated the effect of unilateral, multiple cervical dorsal rhizotomy (C5-T1) on nociceptive thresholds in the unoperated limbs. This was tested by measuring the vocalization threshold to paw pressure. We report that deafferentation by dorsal rhizotomy results in a delayed, but transient increase in mechanical nociceptive thresholds in the 3 innervated limbs.
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Affiliation(s)
- V Kayser
- Unité de Recherche en Physiopharmacologie du Système nerveux U. 161, INSERM, Paris, France
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158
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Lenz FA, Kwan HC, Dostrovsky JO, Tasker RR. Characteristics of the bursting pattern of action potentials that occurs in the thalamus of patients with central pain. Brain Res 1989; 496:357-60. [PMID: 2804648 DOI: 10.1016/0006-8993(89)91088-3] [Citation(s) in RCA: 211] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Neurons in the somatosensory thalamus of patients with central pain following spinal cord injury fire in bursts of action potentials more frequently than do similar neurons in patients without pain. Furthermore, the characteristic firing pattern within these bursts is similar to that which is shown to be associated with the occurrence of calcium spikes in intracellular studies of thalamic nuclei. This finding may have significant implications for the etiology and treatment of central pain states.
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Affiliation(s)
- F A Lenz
- Department of Neurosurgery, Johns Hopkins University, Baltimore, MD 21205
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159
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Kingery WS, Vallin JA. The development of chronic mechanical hyperalgesia, autotomy and collateral sprouting following sciatic nerve section in rat. Pain 1989; 38:321-332. [PMID: 2812843 DOI: 10.1016/0304-3959(89)90219-4] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The development of mechanical hyperalgesia over the tarsometatarsal joints subsequent to chronic sciatic section was studied in rats. Mechanical thresholds began to drop within 7 days of sciatic section and continued to decline for 2-3 weeks, resulting in significant hyperalgesia over the original saphenous and sciatic border zones lasting up to 310 days. Contralateral hyperalgesia, which is seen in tissue injury mechanical hyperalgesia, failed to develop. Collateral sprouting of high-threshold mechanoreceptors from the saphenous nerve into the denervated deep and cutaneous tissue was observed. The extent of cutaneous sprouting did not significantly correlate with the severity of hyperalgesia. The simultaneous uniform reduction of mechanical thresholds across all tarsometatarsal areas after chronic sciatic section is consistent with a central modulation of nociceptive afferent input. The severity and temporal development of the hyperalgesia strongly correlated with the extent of autotomy behavior. This animal model of chronic mechanical hyperalgesia following peripheral nerve section closely resembles a human neuropathic pain syndrome and may provide an experimental opportunity to advance our understanding of the neuropathology subserving chronic pain.
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Affiliation(s)
- Wade S Kingery
- Rehabilitation Medicine Service, Veterans Administration Medical Center, Palo Alto, CA 94304 U.S.A. Department of Surgery, Stanford Medical School, Stanford, CAU.S.A
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160
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161
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Seltzer Z, Tal M, Sharav Y. Autotomy behavior in rats following peripheral deafferentation is suppressed by daily injections of amitriptyline, diazepam and saline. Pain 1989; 37:245-250. [PMID: 2748196 DOI: 10.1016/0304-3959(89)90136-x] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Amitriptyline, a tricyclic antidepressant (TCA), was effective in suppressing self-mutilation of a peripherally deafferented hind paw in rats ('autotomy'). This effect was not due to the drug's sedative effect, since locomotor activity was not lower in treated than untreated rats. Daily injections of normal saline also suppressed autotomy, but for a shorter period of time than amitriptyline. This effect was not apparent in diazepam-treated rats, suggesting that the saline injection delayed autotomy as a result of stress-induced anti-nociception. Since amitriptyline is effective in humans in alleviating certain chronic pain disorders, these results further corroborate the suggestion that autotomy is a model of chronic pain, sensitive to centrally acting analgesics and to some forms of stress.
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Affiliation(s)
- Zeev Seltzer
- Department of Physiology, Oral Medicine and Radiology, School of Dental Medicine, Hebrew University - Hadassah, Jerusalem 91010 Israel Department of Anatomy, Oral Medicine and Radiology, School of Dental Medicine, Hebrew University - Hadassah, Jerusalem 91010 Israel Department of Oral Diagnosis, Oral Medicine and Radiology, School of Dental Medicine, Hebrew University - Hadassah, Jerusalem 91010 Israel
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162
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Abad F, Feria M, Boada J. Chronic amitriptyline decreases autotomy following dorsal rhizotomy in rats. Neurosci Lett 1989; 99:187-90. [PMID: 2748012 DOI: 10.1016/0304-3940(89)90287-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
In the rat, unilateral dorsal cervicothoracic rhizotomy (C5-T1), a proposed model of chronic pain, resulted in autotomy of the ipsilateral limb. The self-mutilation lesions were evaluated daily by means of an autotomy score from the 1st to the 80th postoperatory day. The onset of lesions was variable and attained the maximum degree 8-9 weeks after the dorsal roots section. Chronic administration of amitriptyline (5 and 10 mg/kg/day, i.p., over 30 days), started on the 10th day after rhizotomy, decreased autotomy behavior, an effect which persisted 20 days after treatment withdrawal, and lengthened almost two-fold the lag time between rhizotomy and appearance of lesions. A more pronounced effect was observed with the lowest dose of amitriptyline suggesting the existence of a therapeutic window. Possible mechanisms for the antinociceptive effect of amitriptyline in this model are discussed.
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Affiliation(s)
- F Abad
- Department of Pharmacology, Faculty of Medicine, University of La Laguna, Tenerife, Spain
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163
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Barberá J, Garcia G, Lopez-Orta A, Gil-Salu JL. The role of the neuroma in autotomy following sciatic nerve section in rats. Pain 1988; 33:373-378. [PMID: 3419843 DOI: 10.1016/0304-3959(88)90299-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
A delay in the formation of the terminal neuroma following sciatic nerve section in rats was obtained by means of free nerve grafts sutured to the proximal stump of the sectioned sciatic nerve branches. The automutilating behaviour in these animals was statistically compared with that which follows single sciatic section and sciatic section plus end-to-end suture. The results showed that in animals with grafted nerve stumps, autotomy begins significantly later than in those with single sciatic section. However, when the self-mutilation started, it followed the same increasing evolution in both groups. These results suggest that autotomy after a nerve section is behaviour related to the aparition and nature of the terminal neuroma.
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Affiliation(s)
- José Barberá
- Department of Neurosurgery, University of Cadiz, CadizSpain
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164
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Bennett GJ, Xie YK. A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man. Pain 1988; 33:87-107. [PMID: 2837713 DOI: 10.1016/0304-3959(88)90209-6] [Citation(s) in RCA: 4005] [Impact Index Per Article: 111.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
A peripheral mononeuropathy was produced in adult rats by placing loosely constrictive ligatures around the common sciatic nerve. The postoperative behavior of these rats indicated that hyperalgesia, allodynia and, possibly, spontaneous pain (or dysesthesia) were produced. Hyperalgesic responses to noxious radiant heat were evident on the second postoperative day and lasted for over 2 months. Hyperalgesic responses to chemogenic pain were also present. The presence of allodynia was inferred from the nocifensive responses evoked by standing on an innocuous, chilled metal floor or by innocuous mechanical stimulation, and by the rats' persistence in holding the hind paw in a guarded position. The presence of spontaneous pain was suggested by a suppression of appetite and by the frequent occurrence of apparently spontaneous nocifensive responses. The affected hind paw was abnormally warm or cool in about one-third of the rats. About one-half of the rats developed grossly overgrown claws on the affected side. Experiments with this animal model may advance our understanding of the neural mechanisms of neuropathic pain disorders in humans.
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Affiliation(s)
- Gary J Bennett
- Neurobiology and Anesthesiology Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, MD 0892 U.S.A
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165
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Lyerly MA, Rossitch E, Ovelmen-Levitt J, Nashold BS. The deafferentation syndrome in the rat: effects of intraventricular apomorphine. Exp Neurol 1988; 100:188-202. [PMID: 3350088 DOI: 10.1016/0014-4886(88)90211-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
A deafferentation syndrome, produced in rats by dorsal root ganglionectomies, is expressed as scratching of partially deafferented limb areas and/or biting of anesthetic limb areas. This self-mutilation may be objective evidence of dysesthesias, thus serving as an experimental model to study chronic dysesthesias and/or pain from deafferentation in man. This study included behavioral observations of the syndrome and the effects of intraventricular apomorphine, a dopamine agonist, on its expression. Thirty-eight female Sprague-Dawley rats underwent unilateral C5-T2 dorsal root ganglionectomies followed immediately by stereotactically guided cannulation of the right lateral ventricle in 20 of the rats. For 2 weeks continuously via an osmotic minipump, 10 rats received apomorphine (5 micrograms/h) and 10 others received L-ascorbate (the vehicle). Rats with ganglionectomies only, as well as those receiving L-ascorbate, demonstrated early onset, more severe and later onset, less severe biting groups (P less than 0.05 Mann-Whitney U). Animals receiving apomorphine exhibited low autotomy scores irrespective of time of bite onset. Among the control groups, but not the experimental animals, the earlier the onset of biting, the more severe was the autotomy. The rats receiving vehicle via the minipump had earlier bite onsets than the rats in the ganglionectomy only group. This may indicate that the presence of the minipump is a stress which can accelerate the onset of biting. Intraventricular apomorphine can affect the deafferentation syndrome in the rat; it seems to decrease the level of autotomy and disrupt the relationship of bite onset with degree of biting.
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Affiliation(s)
- M A Lyerly
- Department of Surgery, Duke University Medical Center, Durham, North Carolina 27710
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166
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Rossitch E, Ovelmen-Levitt J, Lyerly MA, Nashold BS. The deafferentation syndrome in the rat: effects of intraventricular neurotensin and cholecystokinin. Exp Neurol 1987; 98:264-75. [PMID: 3666078 DOI: 10.1016/0014-4886(87)90241-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
A deafferentation syndrome can be produced in rats by dorsal root ganglionectomies. This syndrome consists of scratching and/or biting of the anesthetic limb to the point of amputation. This behavior may serve as an experimental model to study certain aspects of chronic dysesthesias and/or pain caused by deafferentation in man. In this study, we made behavioral observations on the deafferentation syndrome and examined the possibility that intraventricular neurotensin and cholecystokinin alter the course of this syndrome. We found that neurotensin accelerated the scratching component without affecting the biting behavior. Cholecystokinin, however, attenuated the release of both components of the syndrome.
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Affiliation(s)
- E Rossitch
- Department of Surgery, Duke University Medical Center Durham, North Carolina 27710
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167
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Wiesenfeld-Hallin Z, Nennesmo I, Kristensson K. Autotomy in rats after nerve section compared with nerve degeneration following intraneural injection of Ricinus communis agglutinin I. Pain 1987; 30:93-102. [PMID: 3614983 DOI: 10.1016/0304-3959(87)90087-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Partial unilateral deafferentation of the hind limb of rats was carried out by section of the sciatic nerve or the intraneural injection of Ricinus communis agglutinin 1 (RCA I). The development of autotomy was observed over a 6 week period. The axotomized animals autotomized more than those injected with RCA I. A neuroma developed on the proximal stump of the axotomized nerves. Within 7 days the axons of the RCA I-injected nerve degenerated and the cell bodies in dorsal root ganglia L4 and L5 were destroyed. Since the RCA I-injected animals autotomized, it is concluded that purely central factors have a role in the generation of this abnormal behavior. As the axotomized animals autotomized more than the RCA I-treated ones it is further concluded that abnormal impulse activity arising from a neuroma may be an additional factor in causing autotomy.
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Affiliation(s)
- Z Wiesenfeld-Hallin
- Department of Clinical Neurophysiology, Huddinge University Hospital, S-141 86 HuddingeSweden Department of Pathology, Karolinska Institute, Huddinge University Hospital, S-141 86 HuddingeSweden
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168
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Coderre TJ, Melzack R. Cutaneous hyperalgesia: contributions of the peripheral and central nervous systems to the increase in pain sensitivity after injury. Brain Res 1987; 404:95-106. [PMID: 3567586 DOI: 10.1016/0006-8993(87)91359-x] [Citation(s) in RCA: 142] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
This study assesses the contributions of the peripheral and central nervous systems in the development of hyperalgesia (increased pain sensitivity) after an injury. Experiments were carried out to examine the role of C-fiber afferents, the spinal cord and sympathetic efferents on inflammation, primary hyperalgesia and referred hyperalgesia produced in rats by a heat injury. A peripheral mechanism was indicated since both primary hyperalgesia and inflammation after a heat injury were significantly attenuated by blocking C-fiber afferents with local capsaicin. In addition, a central mechanism was indicated since the spread of hyperalgesia to the paw contralateral to a heat injury was prevented by either spinal anesthesia or the blocking of sympathetic efferents by guanethidine. A further role for central mechanisms was indicated since referred hyperalgesia--the enhancement of self-mutilation (autotomy) of a denervated limb which had previously sustained a heat injury--was reduced by spinal anesthesia or a combined blocking of C-fiber afferents and sympathetic efferents with intrathecal capsaicin + guanethidine. The results strongly suggest that referred hyperalgesia after a heat injury is dependent on increased spinal cord activity. However, autotomy in rats that did not undergo a previous injury was unaffected by either spinal anesthesia or intrathecal capsaicin. This suggests that spinal cord hyperactivity, although it plays a role in hyperalgesia following a heat injury, is not a crucial factor in producing pain and hyperalgesia after a nerve injury.
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