Determinants of patient satisfaction regarding pain care.

BACKGROUND: The management of pain in hospitalized patients remains a major public hospital priority. It has been the object of three French national programs since 1999. The purpose of this study was to reassess pain prevalence, pain intensity and patient perception of its management ten years after the first national program and to determine the factors related to the patient satisfaction with efforts to decrease pain intensity. METHODS: A 1-day cross-sectional survey in a university hospital. RESULTS: Pain prevalence was 59%. Pain intensity varied according to the medical department with lower intensity in surgery and obstetrics than medicine departments. Eighty-one percent of patients were satisfied with their pain management. Patient satisfaction was higher when doctors and nurses were heavily involved in the process of pain relief (OR=6.6; 95% CI 3.8, 11.4), and when their pain had decreased (OR=2.9; 1.7, 5.0). The magnitude of decrease in pain were higher when the medical team was involved (OR=1.9; 95% IC 1.1, 3.3) and pain intensity was measured (OR=1.6; 1.0, 2.4). Perceptions of doctor and nurse involvement in the patient's care was higher when pain intensity was measured (OR=6.0; 3.4, 10.5), an immediate treatment offered (OR=3.5; 2.0, 6.2), encouragement to ask for an analgesic was provided (OR=2.0; 1.1, 3.5) and for patients with acute pain (OR=2.2; 1.0, 4.7). CONCLUSIONS: This study identifies the factors related to patient satisfaction with pain management and the magnitude of the decrease in pain which should allow further efforts to improve the management of pain and reduce its intensity in hospital inpatients.

Expression and G-protein coupling of mu-opioid receptors in the spinal cord and dorsal root ganglia of polyarthritic rats.

Although chronic inflammatory pain is known to be associated with hypersensitivity to mu opioid receptor agonists, no evidence for changes in the expression and/or characteristics of central mu opioid receptors has yet been reported in relevant models of this type of pain. In the present study, both immunohistochemical and autoradiographic approaches were used to address this question in polyarthritic rats, on the 4th week after intradermal injection of complete Freund's adjuvant, when inflammatory pain was at its maximum. Immunohistochemical labeling with specific anti-mu opioid receptor antibodies and autoradiographic labeling with [3H]DAMGO showed an upregulation of mu opioid receptors in the dorsal root ganglia but no changes in the density of these receptors in the dorsal horn at the level of L4-L6 segments in polyarthritic compared to age-paired control rats. On the other hand, autoradiographic quantification of the concentration-dependent increase in [35S]GTP-gamma-S binding by the mu-opioid receptor agonist DAMGO did not show any significant differences within the lumbar dorsal horn between polyarthritic and control rats. These data indicate that chronic inflammatory pain caused by polyarthritis was associated with an increased expression of mu-opioid receptors in dorsal root ganglion sensory neurones that did not result in an increased spinal density of these receptors, in spite of their well established axonal transport in the central portion of primary afferent fibres to the dorsal horn. In contrast, axonal transport of mu-opioid receptors in the peripheral portion of these fibres probably accounts for the increased receptor density in inflamed tissues already reported in the literature.

The neuropeptide FF analogue, 1DMe, acts as a functional opioid autoreceptor antagonist in the rat spinal cord.

We assessed the possible influence of a neuropeptide FF analogue, 1DMe ([D-Tyr(1),(NMe)Phe(3)]neuropeptide FF), on the inhibitory action of endogenous and exogenous partial differential-opioid receptor agonists on K(+)-evoked [Met(5)]-enkephalin release from superfused rat spinal cord slices. 1DMe (0.1-10 microM) dose-dependently enhanced the increase in superfusate [Met(5)]-enkephalin content due to the peptidase inhibitors thiorphan (1 microM) and bestatin (20 microM), and prevented the reduction in [Met(5)]-enkephalin release due to stimulation of partial differential receptors by 1 microM deltorphin I. Because it had the same effects as partial differential-opioid receptor antagonists, 1DMe might act through the functional blockade of presynaptically located partial differential-opioid autoreceptors.

Therapeutic efficacy in experimental polyarthritis of viral-driven enkephalin overproduction in sensory neurons.

Rheumatoid arthritis is characterized by erosive inflammation of the joints, new bone proliferation, and ankylosis, leading to severely reduced locomotion and intense chronic pain. In a model of this disease, adjuvant-induced polyarthritis in the rat, neurons involved in pain transmission and control undergo plastic changes, especially at the spinal level. These changes affect notably neurons that contain opioids, such as enkephalins deriving from preproenkephalin A (PA) precursor protein. Using recombinant herpes simplex virus containing rat PA cDNA, we enhanced enkephalin synthesis in sensory neurons of polyarthritic rats. This treatment markedly improved locomotion and reduced hyperalgesia. Furthermore, the progression of bone destruction slowed down, which is the most difficult target to reach in the treatment of patients suffering from arthritis. These data demonstrate the therapeutic efficacy of enkephalin overproduction in a model of systemic inflammatory and painful chronic disorder.

Subcutaneous formalin enhances outflow of met-enkephalin- and cholecystokinin-like materials in the rat nucleus accumbens.

Using the microdialysis technique, the present study investigated the effects of a noxious stimulation on the extracellular levels of met-enkephalin and (sulfated octapeptide) cholecystokinin-like materials in the nucleus accumbens of freely moving rats. Injection of 50 microl of 5% formalin into the forepaw produced pain-related behaviours associated with an immediate and sustained (for approximately 2 h) increase (+27%) in the outflow of met-enkephalin-like material within the nucleus accumbens. This treatment also progressively enhanced the local outflow of cholecystokinin-like material that reached 200%-250% of the basal level at the end of the experiment, i.e. 4.5 h after formalin administration. Because naloxone (1.5 mg/kg i.p., 10 min prior to formalin injection) prevented the latter effect, it can be inferred that noxious stimulation-induced activation of cholecystokininergic neurotransmission in the nucleus accumbens probably resulted from the preceding activation of opioidergic systems. These data suggest that the nucleus accumbens may be another structure where interactions between opioids and cholecystokinin play a key role in the control of pain-processing mechanisms.

Met-enkephalin is preferentially transported into the peripheral processes of primary afferent fibres in both control and HSV1-driven proenkephalin A overexpressing rats.

The demonstration of preproenkephalin A gene expression in rat dorsal root ganglia has raised the question of the physiological role of met-enkephalin-containing primary afferent fibres. Recently, we showed that systemic infection with a recombinant Herpes simplex virus encoding preproenkephalin A (HSVLatEnk1) yielded a marked increase in the density of met-enkephalin-like material synthesising neurons in rat dorsal root ganglia. This study further investigated the synthesis, transport and release of met-enkephalin-like material in the central and/or peripheral processes of primary afferent fibres in HSVLatEnk1-infected and control rats. In controls, dorsal root ganglia neurons containing met-enkephalin-like material were scarce and only a few positively labelled processes were seen at the peripheral output of the dorsal root ganglia. Met-enkephalin-like material accumulated at the proximal side of ligatured sciatic nerve, but not in ligatured L4-L5 dorsal roots. In HSVLatEnk1-infected rats with numerous somas and fibres stained for met-enkephalin-like material in dorsal root ganglia, met-enkephalin immunoreactive material largely accumulated at the proximal side of the ligatured sciatic nerve and few positively stained fibres were also observed in ligatured dorsal roots. Electrical stimulation of L4-L5 dorsal roots attached to a dorsal slice of the lumbar enlargement produced an overflow of met-enkephalin-like material which was approximately 70% higher in HSVLatEnk1-infected rats compared to controls. At the periphery, subcutaneous microdialysis showed higher basal levels of met-enkephalin-like material in the interstitial fluid of hindpaw plantar area in HSVLatEnk1-infected rats, and electrical stimulation of the ipsilateral sciatic nerve resulted in an approximately three-fold-higher overflow of this material than in control rats. These data demonstrated that met-enkephalin synthesised in dorsal root ganglion of both control and preproenkephalin A overexpressing rats is preferentially transported into the peripheral processes of primary afferent fibres where the peptide reaches a releasable compartment, thus providing a neuronal source of peripheral met-enkephalin.

The novel analgesic, cizolirtine, inhibits the spinal release of substance P and CGRP in rats.

Although previous studies have established that cizolirtine (5-([(N,N-dimethylaminoethoxy)phenyl]methyl)-1-methyl-1H-pyrazol citrate) is a potent analgesic in rodents, its mechanism(s) of action remain(s) unclear. In vitro and in vivo approaches were used to assess whether cizolirtine could affect the spinal release of two pain-related neuropeptides, substance P (SP) and calcitonin gene-related peptide (CGRP), in rats. Cizolirtine significantly reduced the K(+)-evoked overflow of both the SP-like material (SPLM; -25% at 0.1 microM--0.1 mM) and CGRPLM (-20% at 0.1--1.0 microM) from slices of the dorsal half of the lumbar enlargement of the spinal cord. Intrathecal perfusion in halothane-anaesthetized rats showed that local application of cizolirtine markedly diminished the spinal outflow of SPLM (up to -50% at 0.1 mM) but only marginally that of CGRPLM. Systemic administration of cizolirtine at an analgesic dose (80 mg/kg i.p.) also reduced spinal SPLM outflow (-50%) but not that of CGRPLM. Under both in vitro and in vivo conditions, idazoxan (10 microM) antagonized the effects of cizolirtine on SPLM and CGRPLM release, suggesting their mediation through alpha(2) adrenoceptors.

Enhanced cortical extracellular levels of cholecystokinin-like material in a model of anticipation of social defeat in the rat.

The involvement of cholecystokinin (CCK) in the mechanisms of stress and/or anxiety was assessed by in vivo microdialysis in rats subjected to a social stress paradigm. During the initial 30 min period of each conditioning session, a male Sprague Dawley rat (intruder) was placed in a protective cage inside the cage of a male Tryon Maze Dull rat (resident), allowing unrestricted visual, olfactory, and auditory contacts but precluding close physical contact between them. During the following 15 min period, both the protective cage and the resident were removed (nondefeated intruders) or only the protective cage was removed allowing the resident to attack the intruder (defeated rats). This procedure was repeated once daily for 4 d. On the fifth day, a guide cannula was implanted into the prefrontal cortex of intruders. During a single 30 min test session, performed 4 d later, intruders were subjected to only the 30 min protected confrontation to the resident. Anxiety-like behavior (immobility, ultrasonic vocalizations, and defensive postures), associated with an increase (approximately +100% above baseline) in cortical outflow of CCK-like material (CCKLM), were observed in defeated intruders. Pretreatment with diazepam (5 mg/kg, i.p.), but not buspirone (0.5-2 mg/kg, i.p.), prevented both the anxiety-related behavior and CCKLM overflow. The selective CCK-B receptor antagonist CI-988 (2 mg/kg, i.p.) reduced the anxiety-like behavior without affecting the increase in CCKLM outflow. These data indicate that anticipation of social defeat induces a marked activation of cortical CCKergic neurons associated with anxiety-related behaviors in rats.

Identification of an opioid peptide secreted by rat embryonic mixed brain cells as a promoter of macrophage migration.

Conditioned media from embryonic mixed cells from the rat brain were used in a chemotaxis assay to look for potential chemotactic activity which could account for the infiltration of the developing central nervous system (CNS) by macrophage precursors. The most potent chemotactic activity was found in the conditioned medium from E17 mixed brain cells (E17-CM). Based upon checkerboard analysis, this activity was shown to be chemotactic rather than chemokinetic. This chemoattraction was not restricted to brain macrophages (BM) because it was as pronounced on bone marrow-derived macrophages. The implication of a peptide compound in this activity was suggested by its resistance to heat as well as acid treatments, and by its sensitivity to aminopeptidase M digestion. In agreement with the opioid nature of the peptide, not only naloxone, but also the delta opioid receptor antagonist ICI-174 reduced the migration of BM in response to E17-CM by 60%. This migratory activity was no longer effective when pertussis toxin-treated BM were used. When the chemotactic effects of selective opioid agonists were compared to that of E17-CM, DPDPE, the delta agonist, was the most efficient in attracting BM. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis indicated that delta as well as other known opioid receptors were expressed in both BM and E17 mixed brain cells. Finally, a Met-enkephalin-like reactivity was found by RIA in the E17-CM. Altogether, these observations suggest that a delta-like opioid peptide released from embryonic mixed brain cells could be responsible for the infiltration of the developing CNS by macrophages precursors.

Altered opioid-mediated control of the spinal release of dynorphin and met-enkephalin in polyarthritic rats.

Previous studies showed that spinal opioidergic neurotransmission is markedly altered in the polyarthritic rat, a model of chronic inflammatory pain. Present investigations aimed at assessing possible changes in opioid-mediated control of the spinal outflow of met-enkephalin (ME) and dynorphin (DYN) in these animals. Intrathecal (i.t.) perfusion under halothane anesthesia showed that polyarthritis was associated with both a 40% decrease in the spinal outflow of ME-like material (MELM) and a 90% increase in that of DYNLM. Local treatment with the mu-opioid agonist DAGO (10 microM i.t.) inhibited equally (-30%) the MELM outflow in polyarthritic and control rats, whereas the delta agonist DTLET (10 microM i.t.) also reduced the peptide outflow in controls (-27%) but enhanced it in polyarthritic animals (+56%). On the other hand, both DAGO (10 microM i.t.) and DTLET (10 microM i.t.) decreased (-40 and -49%) DYNLM outflow in polyarthritic rats, but were inactive in controls. Finally, neither MELM outflow nor that of DYNLM were affected by the kappa-agonist U50488H (10 microM i.t.) in both groups of rats. In all cases, the changes due to active agonists could be prevented by specific antagonists which were inactive on their own except the kappa antagonist nor-binaltorphimine (10 microM i.t.) that decreased (-38%) DYNLM outflow in polyarthritic rats. These data indicate that functional changes in spinal opioid receptors may promote enkephalinergic neurotransmission and reduce dynorphinergic neurotransmission in polyarthritic rats, thereby contributing to the analgesic efficacy of opioids in inflammatory pain.

Delta-opioid receptor-mediated increase in cortical extracellular levels of cholecystokinin-like material by subchronic morphine in rats.

Numerous pharmacological data indirectly support the idea that interactions between cholecystokinin (CCK) and opioids participate in the development of tolerance to morphine. Biochemical investigations were performed with the aim of directly assessing the status of such interactions in morphine treated rats. Tolerance to the alkaloid after s.c. implantation of morphine pellets for three days was not associated with any change in the levels of both CCK like-material (CCKLM) and proCCK mRNA in the frontal cortex. However, microdialysis in the freely moving rat showed that this morphine treatment produced a significant increase (+40%) of the cortical spontaneous CCKLM outflow, which could be completely prevented by intracortical infusion of naloxone (10 microM). The opioid receptors responsible for morphine-induced cortical CCKLM overflow appeared to be of the delta type because intracortical infusion of selective delta-opioid receptor antagonists such as naltriben (10 microM) and 7-benzylidenenaltrexone (10 microM) also prevented the effect of morphine, whereas CTOP (10 microM), a selective mu-opioid receptor antagonist, and nor-binaltorphimine (10 microM), a selective K-opioid receptor antagonist, were inactive. These data indicate that morphine tolerance is associated with delta-opioid receptor mediated activation of cortical CCKergic systems in rats.

The neuropeptide FF analogue, 1DME, enhances in vivo met-enkephalin release from the rat spinal cord.

Behavioural studies have suggested that endogenous opioids mediate the antinociceptive action of neuropeptide FF (FLFQPQRF-NH2) at the spinal level in the rat. This hypothesis was directly assessed by investigating the effects of a NPFF analogue, 1DMe ([D-Tyr1,(NMe)Phe3]NPFF), on the spinal outflow of met-enkephalin-like material (MELM) in halothane-anaesthetised rats. Intrathecal infusion (0.1 ml/min) of 1DMe (0.1 microM-0.1 mM, for 45 min) produced a concentration-dependent increase in spinal MELM outflow which persisted for at least 90 min at the highest concentration tested. Intrathecal coadministration of the micro-opioid receptor antagonist CTOP (1 microM) did not significantly affect the spinal MELM overflow due to 0.1 mM 1DMe. In contrast, both naltrindole and nor-binaltorphimine, at concentrations (10 microM) that allow the selective blockade of alpha- and kappa-opioid receptors, respectively, significantly reduced the stimulatory effect of 1DMe on spinal MELM outflow. These data provide the first direct demonstration that met-enkephalin (among other opioid peptides) can mediate the antinociceptive action of NPFF at the spinal level in rats. In addition, they suggest that reciprocal excitatory interactions between opioids and opioid-modulatory factors (such as NPFF) participate in the physiological control of nociception.

Opposite changes in dopamine metabolites and met-enkephalin levels in the ventricular CSF of patients subjected to thalamic electrical stimulation.

High-frequency electrical stimulations of thalamic nuclei are currently used for the suppression of parkinsonian or essential tremor and for the relief of some types of intractable pain in man. However, the mechanisms by which such stimulations exert their therapeutic effects are essentially unknown. Attempts were made to provide some insight into these mechanisms by measuring the levels of the dopamine metabolites homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC), the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) and met-enkephalin-like immunoreactivity in ventricular cerebrospinal fluid (CSF) of patients with Parkinson's disease (PD) or multiple sclerosis (MS) after a 30-minute therapeutic electrical stimulation of the ventralis intermedius nucleus of the thalamus. In nonstimulated control patients, the levels of these compounds did not significantly differ in two CSF samples taken 30 minutes apart. In stimulated patients, a decrease in dopamine metabolite levels associated with a relative increase in met-enkephalin-like immunoreactivity were observed in the CSF sample taken after the 30-minute stimulation as compared to the sample taken immediately before the stimulation. In contrast, the levels of 5-HIAA remained unaffected by the stimulation. These data confirmed the existence of negative interactions between dopaminergic and enkephalinergic systems in man similar to those previously demonstrated in rats. In addition, they suggest that alterations in dopaminergic or enkephalinergic neurotransmission might be involved in the therapeutic action of thalamic electrical stimulation in patients with parkinsonian symptoms and other patients.

Delta(2)-opioid receptor mediation of morphine-induced CCK release in the frontal cortex of the freely moving rat.

Numerous pharmacological data have been accumulated in support of the existence of physiological interactions between cholecystokinin (CCK) and opioids in the central nervous system. With the aim of further characterizing these interactions, an in vivo microdialysis approach was used to directly assess the possible influence of opioids on the extracellular levels of CCK-like material (CCKLM) in the frontal cortex of the awake, freely moving rat. Systemic administration of a high dose of morphine (10 mg/kg i.p.) produced a marked increase (up to +200%) of cortical CCKLM outflow, and this effect could be completely prevented by systemic (1.5 mg/kg i.p.) as well as intracortical (10 microM) administration of the opioid receptor antagonist naloxone. The opioid receptors activated by morphine appeared to be of the delta type because the intracortical infusion of naltrindole (10 microM) also prevented the effect of morphine, whereas CTOP (10 microM), a selective mu-opioid receptor antagonist, and nor-binaltorphimine (10 microM), a selective kappa-opioid receptor antagonist, were inactive. In addition, naltriben (10 microM), which acts selectively at the delta(2) subtype, also abolished the stimulatory effect of morphine on cortical CCKLM outflow, whereas 7-benzylidenenaltrexone (10 microM), a selective delta(1)-opioid receptor antagonist (10 microM), did not alter the morphine effect. Conversely, the direct stimulation of cortical delta(2)-opioid receptors by local infusion of [D-Ala(2)] deltorphin II mimicked the stimulatory effect of systemic morphine on CCKLM outflow. These data indicate that delta(2)-opioid receptors play a key role in opioid-CCK interactions in the rat frontal cortex.

Effects of peripheral axotomy on cholecystokinin neurotransmission in the rat spinal cord.

Because cholecystokinin (CCK) acts as a "functional" endogenous opioid antagonist, it has been proposed that changes in central CCKergic neurotransmission might account for the relative resistance of neuropathic pain to the analgesic action of morphine. This hypothesis was addressed by measuring CCK-related parameters 2 weeks after unilateral sciatic nerve section in rats. As expected, significant decreases (-25-38%) in the tissue concentrations and in vitro release of both substance P and calcitonin gene-related peptide were noted in the dorsal quadrant of the lumbar spinal cord on the lesioned side. In contrast, the tissue levels and in vitro release of CCK were unchanged in the same area in lesioned rats. Measurements in dorsal root ganglia at L4-L6 levels revealed no significant changes in proCCK mRNA after the lesion. However, sciatic nerve section was associated with a marked ipsilateral increase in both CCK-B receptor mRNA levels in these ganglia (+70%) and the autoradiographic labeling of CCK-B receptors by [3H]pBC 264 (+160%) in the superficial layers of the lumbar dorsal horn. Up-regulation of CCK-B receptors rather than CCK synthesis and release probably contributes to increased spinal CCKergic neurotransmission in neuropathic pain.

Polyarthritis-associated changes in the opioid control of spinal CGRP release in the rat.

As a model of chronic inflammatory pain, Freund's adjuvant-induced polyarthritis has been shown to be associated with marked alterations in the activity of opioid- and calcitonin gene-related peptide (CGRP)-containing neurons in the dorsal horn of the spinal cord in rats. Possible changes in the interactions between these two peptidergic systems in chronic inflammatory pain were investigated by comparing the effects of various opioid receptor ligands on the spinal outflow of CGRP-like material (CGRPLM) in polyarthritic and age-paired control rats. Intrathecal perfusion of an artificial cerebrospinal fluid in halothane-anaesthetized animals allowed the collection of CGRPLM released from the spinal cord and the application of opioid receptor ligands. The blockade of kappa-opioid receptors similarly increased CGRPLM release in both groups of rats as expected of a kappa-mediated tonic inhibitory control of CGRP-containing fibres in control, as well as in polyarthritic rats. In contrast, the higher increase in CGRPLM outflow due to the preferential blockade of mu opioid receptors by naloxone in polyarthritic rats as compared to non-suffering animals supports the idea of a reinforced mu opioid receptor-mediated tonic inhibitory control of CGRP-containing fibres in rats suffering from chronic pain. Even more strikingly, the differences observed in the effects of delta-opioid receptor ligands on CGRPLM outflow suggest that delta receptors are functionally shifted from a participation in a phasic excitatory control in non-suffering rats to a tonic inhibitory control in polyarthritic rats. These data indicate that agonists acting at the three types of opioid receptors all exert a tonic inhibitory influence on CGRP-containing nociceptive primary afferent fibres within the spinal cord of polyarthritic rats. Such a convergence probably explains why morphine and other opioids are especially potent to reduce pain in subjects suffering from chronic inflammatory diseases.

[Interactions between central opioidergic and cholecystokininergic systems in rats: possible significance for the development of of opioid tolerance]. / Interactions entre les systèmes opioïdergiques et cholécystokininergiques centraux chez le rat: implications dans le développement de la tolérance aux opioïdes.

Numerous data suggest that cholecystokinin (CCK) acts as an opioid-modulating peptide. Because pharmacological and behavioural studies have shown that CCK reduces the analgesic effects of opioids, an opioid-mediated activation of CCK-containing neurones has been proposed to be responsible for the development of opioid tolerance. In an attempt to directly assess this hypothesis, we have examined, in naive or morphine-tolerant/dependent rats, the possible influence of opioid-receptor ligands on--1 the release of CCK from spinal cord slices and--2 the extracellular levels of CCK in the frontal cortex in awake, freely moving animals. Whereas the stimulation of mu or delta 1 receptors inhibited the release of the peptide, the stimulation of delta 2 receptors increased CCK release. Morphine also increased CCK release, via an action at delta 2 receptors. The blockade of delta 1 receptors resulted in an enhancement of the peptide release, suggesting that endogenous opioids probably exert inhibitory tonic influence on CCK release through the stimulation of delta 1 receptors. In rats rendered tolerant/dependent, the inhibitory effects of opioids on CCK release, due to the stimulation of mu or delta 1 receptors, and the enhancing effect of delta 1 receptor blockade, were no longer present. In contrast, the delta 2-mediated increase in CCK release persisted. Thus, in morphine-tolerant/dependent rats, opioids apparently retain only their excitatory effects on CCK-containing neurones. These data support the idea that morphine exerts an excitatory influence on central CCKergic neurones, which could tend to reduce the analgesic action of the alkaloid, and are in line with the hypothesis that morphine tolerance/dependence is associated with an activation of CCK-containing neurones.

Herpes simplex virus 1-mediated transfer of preproenkephalin A in rat dorsal root ganglia.

Recombinant herpes simplex virus-1 encoding the rat preproenkephalin A (HSVLatEnk1) was generated for driving the expression of preproenkephalin A-derived peptides in dorsal root ganglia of rats in vivo. Three weeks after infection via the hind footpads, quantitative RT-PCR and in situ hybridization experiments showed a strong expression of preproenkephalin A mRNA in lumbar dorsal root ganglia. In addition, a 40-160% increase in radioimmunoassayable Met-enkephalin-like material concentrations was found in the dorsal spinal cord and dorsal root ganglia, respectively, at the lumbar level in HSVLatEnk1-infected rats as compared with animals infected with beta-galactosidase-encoding recombinant herpes simplex virus-1 or control rats. These data demonstrate the efficacy of the preproenkephalin A encoding vector and suggest that it should help in elucidating the role of Met-enkephalin-containing primary afferent fibers in pain transmission and/or control.

Enkephalinergic and dynorphinergic neurons in the spinal cord and dorsal root ganglia of the polyarthritic rat - in vivo release and cDNA hybridization studies.

Complex and contradictory data have been reported regarding the changes in spinal opioidergic systems associated with chronic inflammatory pain in the rat. In an attempt to solve these discrepancies, the in vivo release of met-enkephalin and dynorphin and the expression of the corresponding propeptide genes were investigated at the spinal level in arthritic rats and paired controls. A dramatic increase in the concentration of prodynorphin mRNA (+300-550%) and a less pronounced elevation of that of dynorphin-like material (+40-50%) were found in the dorsal part of cervical and lumbar segments of the spinal cord in rats rendered arthritic by an intradermal injection of Freund's adjuvant four weeks prior to these measurements. In addition, the spinal release of dynorphin-like material (assessed through an intrathecal perfusion procedure in halothane-anaesthetized animals) was approximately twice as high in arthritic rats as in controls. In spite of significant elevations in the levels of both met-enkephalin (+30-70%) and proenkephalin A mRNA (+40-50%) in the dorsal part of cervical and lumbar segments, the spinal release of met-enkephalin-like material was decreased (-50%) in arthritic rats as compared to paired controls. Proenkephalin A mRNA (but not prodynorphin mRNA) could be measured in dorsal root ganglia, and its levels were dramatically reduced in ganglia at the lumbar segments in arthritic rats. Such parallel reductions in the spinal release of met-enkephalin-like material and the levels of proenkephalin A mRNA in dorsal root ganglia of arthritic rats support the idea that the activity of primary afferent enkephalinergic fibres decreases markedly during chronic inflammatory pain.