In vivo tonic inhibition of spinal substance P (-like material) release by endogenous opioid(s) acting at delta receptors

Localization of the delta opioid receptor and corticotropin-releasing factor in the amygdalar complex: role in anxiety

It is well established that central nervous system norepinephrine (NE) and corticotropin-releasing factor (CRF) systems are important mediators of behavioral responses to stressors. More recent studies have defined a role for delta opioid receptors (DOPR) in maintaining emotional valence including anxiety. The amygdala plays an important role in processing emotional stimuli, and has been implicated in the development of anxiety disorders. Activation of DOPR or inhibition of CRF in the amygdala reduces baseline and stress-induced anxiety-like responses. It is not known whether CRF- and DOPR-containing amygdalar neurons interact or whether they are regulated by NE afferents. Therefore, this study sought to better define interactions between the CRF, DOPR and NE systems in the basolateral (BLA) and central nucleus of the amygdala (CeA) of the male rat using anatomical and functional approaches. Irrespective of the amygdalar subregion, dual immunofluorescence microscopy showed that DOPR was present in CRF-containing neurons. Immunoelectron microscopy confirmed that DOPR was localized to both dendritic processes and axon terminals in the BLA and CeA. Semi-quantitative dual immunoelectron microscopy analysis of gold-silver labeling for DOPR and immunoperoxidase labeling for CRF revealed that 55 % of the CRF neurons analyzed contained DOPR in the BLA while 67 % of the CRF neurons analyzed contained DOPR in the CeA. Furthermore, approximately 41 % of DOPR-labeled axon terminals targeted BLA neurons that expressed CRF while 29 % of DOPR-labeled axon terminals targeted CeA neurons that expressed CRF. Triple label immunofluorescence microscopy revealed that DOPR and CRF were co-localized in common cellular profiles that were in close proximity to NE-containing fibers in both subregions. These anatomical results indicate significant interactions between DOPR and CRF in this critical limbic region and reveal that NE is poised to regulate these peptidergic systems in the amygdala. Functional studies were performed to determine if activation of DOPR could inhibit the anxiety produced by elevation of NE in the amygdala using the pharmacological stressor yohimbine. Administration of the DOPR agonist, SNC80, significantly attenuated elevated anxiogenic behaviors produced by yohimbine as measured in the rat on the elevated zero maze. Taken together, results from this study demonstrate the convergence of three important systems, NE, CRF, and DOPR, in the amygdala and provide insight into their functional role in modulating stress and anxiety responses.

Neuro-reflexotherapy for the management of myofascial temporomandibular joint pain: a double-blind, placebo-controlled, randomized clinical trial

PURPOSE

To assess the efficacy of neuro-reflexotherapy intervention (NRT) for treating temporomandibular joint dysfunction attributed to myofascial pain. Neuro-reflexotherapy intervention consists of the temporary implantation of epidermal devices in trigger points in the back and ear. It has shown efficacy, effectiveness, and cost-effectiveness in treating subacute and chronic common back pain. No study, however, has explored its efficacy in treating myofascial temporomandibular joint pain (MF/TMJP).

PATIENTS AND METHODS

This was a randomized, double-blind, placebo-controlled trial. Patients with MF/TMJP for more than 3 months in spite of conservative treatment, and with no evidence of major structural damage in the joint, were recruited at the Maxillofacial Department of the Hospital Clínico Universitario, a teaching hospital in Madrid, Spain. Patients were randomly assigned to an intervention group and to a control group. Patients in the treated group underwent 2 NRTs, immediately after baseline assessment and 45 days later. Sham interventions in the control group consisted of placement of the same number of epidermal devices within a 5-cm radius of the target zones. In both groups, conservative treatment during follow-up was allowed and recorded. Patients underwent clinical evaluations on 4 occasions: 5 minutes before intervention, 5 minutes after intervention, and 45 and 90 days later. The preintervention assessment was performed by the physician at the hospital service who included the patient in the study. The 3 follow-up assessments were performed independently by 1 of 2 physicians who had no connection with the research team, and who were blinded to patients' assignments. The primary outcome variable was level of pain severity during jaw movements at the last assessment (90 days), and the key comparison of interest was change in pain over time (pain levels at baseline and at 90 days). Level of pain was measured using a visual analog scale (VAS).

RESULTS

Fifty-one patients with MF/TMJP were recruited into the study. Random assignment allocated 27 patients to the intervention group, and 24 to the control group. Differences in pain severity in favor of the intervention group appeared immediately after the intervention, persisted for 45 days, and increased after the second intervention. Differences at last follow-up were highly clinically and statistically significant (4 to 5 points on the VAS, P = .000), allowing for patients in the intervention group to cease drug treatment (P = .005). There were no differences in the evolution of crepitus or clicking in the joint. There were no clinically relevant side effects associated with the intervention.

CONCLUSIONS

For patients in whom conservative treatment has failed, NRT improves the chronic pain associated with MF/TMJP syndrome.

Spinal N-methyl-D-aspartate receptors and nociception-evoked release of primary afferent substance P

Dorsal horn N-methyl-D-aspartate (NMDA) receptors contribute significantly to spinal nociceptive processing through an effect postsynaptic to non-primary glutamatergic axons, and perhaps presynaptic to the primary afferent terminals. The present study sought to examine the regulatory effects of NMDA receptors on primary afferent release of substance P (SP), as measured by neurokinin 1 receptor (NK1r) internalization in the spinal dorsal horn of rats. The effects of intrathecal NMDA alone or in combination with D-serine (a glycine site agonist) were initially examined on basal levels of NK1r internalization. NMDA alone or when co-administered with D-serine failed to induce NK1r internalization, whereas activation of spinal TRPV1 receptors by capsaicin resulted in a notable NK1r internalization. To determine whether NMDA receptor activation could potentiate NK1r internalization or pain behavior induced by a peripheral noxious stimulus, intrathecal NMDA was given prior to an intraplantar injection of formalin. NMDA did not alter the formalin-induced NK1r internalization nor did it enhance the formalin paw flinching behavior. To further characterize the effects of presynaptic NMDA receptors, the NMDA antagonists DL-2-amino-5-phosphonopentanoic acid (AP-5) and MK-801 were intrathecally administered to assess their regulatory effects on formalin-induced NK1r internalization and pain behavior. AP-5 had no effect on formalin-induced NK1r internalization, whereas MK-801 produced only a modest reduction. Both antagonists, however, reduced the formalin paw flinching behavior. In subsequent in vitro experiments, perfusion of NMDA in spinal cord slice preparations did not evoke basal release of SP or calcitonin gene-related peptide (CGRP). Likewise, perfusion of NMDA did not enhance capsaicin-evoked release of the two peptides. These results suggest that presynaptic NMDA receptors in the spinal cord play little if any role on the primary afferent release of SP.

Prognostic factors for neuroreflexotherapy in the treatment of subacute and chronic neck and back pain: a study of predictors of clinical outcome in routine practice of the Spanish National Health Service

STUDY DESIGN

Prospective cohort follow-up study.

OBJECTIVES

To refine the indication criteria for neuroreflexotherapy (NRT) in the treatment of subacute and chronic neck (NP), thoracic (TP) and low back pain (LBP) in the Spanish National Health Service (SNHS), by identifying prognostic factors for clinical outcome.

SUMMARY OF BACKGROUND DATA

NRT consists of the temporary subcutaneous implantation of surgical devices in trigger points. Previous randomized controlled trials have shown its efficacy, effectiveness, and cost-effectiveness for treating subacute and chronic LBP. Clinical audits in routine practice have shown similar results in NP, TP, and LBP patients.

PATIENTS AND METHODS

All 1514 patients from the SNHS in the Balearic Islands in which a NRT intervention was performed and who were discharged between January 1, 2004, and December 31, 2005, were included in this study. Treatment failure was defined as a baseline score equivalent to or lower than the corresponding one at discharge for local pain, referred pain, or LBP-related disability. Multivariate logistic regression models were developed for each of those variables. Maximal models included reason for referral (NP, TP, or LBP), age, sex, baseline values for each variable, number of days in which the surgical devices used in NRT were left implanted, duration of the current episode, time elapsed since the first episode, and previous failed surgery for the current episode. Calibration of the models was assessed through the Hosmer-Lemeshow test, while discrimination was assessed through the area under the ROC curve and the Nagelkerke R test.

RESULTS

When referred to NRT, patients' median (IQR) duration of the episode was 210 (90, 730) days. Failure rates ranged between 9.9% for local pain and 14.5% for disability. Variables associated with a worst prognosis for local pain, referred pain, and disability were surgical devices remaining implanted for a shorter duration and, especially, a longer pain duration. Patients referred for NP were more likely to improve than those referred for TP or LBP. Regarding the evolution of local and referred pain, lesser improvement was observed in the least severe complaint at baseline. Models showed a good calibration. The area under the ROC curve ranged between 0.719 and 0.804, and R ranged between 0.101 and 0.255.

CONCLUSION

A longer duration of the current episode is the worst detected prognostic factor for response to NRT, but prognostic models are inaccurate for predicting the clinical outcome of a given patient. In order to improve the success rate of this technology, these results only support earlier referral for patients complying with current indication criteria.

Implementation of neuroreflexotherapy for subacute and chronic neck and back pain within the Spanish public health system: audit results after one year

Controlled randomized trials have demonstrated the efficacy, safety, effectiveness, and cost-effectiveness of neuroreflexotherapy (NRT) for the management of non-specific back pain. In this audit study, we describe the implementation of NRT into the routine practice of primary care within the Spanish public health service of the Balearic Islands and the results obtained after one year (2004). A referral protocol was made available to all general practitioners (GPs) who could refer eligible patients to specialized units in performing NRT interventions. A total of 1209 patients (median age 52 years, 68% women) were referred to NRT by 412 GPs (80% of all GPs), with a mean (standard deviation (S.D.)) referral rate of 1.57 (0.84) patients per month/10,000 persons affiliated to each practice, and an appropriate referral rate of 95.5%. Pain decreased from a median score (visual analog scale) of 8 at baseline to 1 at discharge, referred pain from 7 to 1, and disability (Roland-Morris Questionnaire) from 12 to 1. NRT was refused by 2.7% of patients. Adverse effects related to the procedure were only a skin reaction in 3.3% of patients. We conclude that it is feasible to implement NRT in the public health service complying with methods and application conditions used in previous randomized controlled trials (RCTs). In such conditions, implementation of this technology obtained positive audit results at one year.

Reversal of ongoing thermal hyperalgesia in mice by a recombinant herpesvirus that encodes human preproenkephalin

Herpesvirus-mediated transfer of the human preproenkephalin gene to primary afferent nociceptors prevents phasic thermal allodynia/hyperalgesia in mice. It is not known, however, whether similar viral treatments would reverse ongoing or chronic pain and allodynia/hyperalgesia. To this end, mice were given intrathecal injections of pertussis toxin (PTX), which produces a weeks-long thermal hyperalgesia apparently by uncoupling certain G proteins from inhibitory neurotransmitter receptors. This treatment produced profound thermal hyperalgesia in both Adelta and C-fiber thermonociceptive tests lasting at least 6 weeks. However, treatment of skin surfaces with an enkephalin-encoding herpesvirus, but not control virus or vehicle, completely reversed this hyperalgesia. This profound anti-hyperalgesia was observed for both Adelta- and C-fiber-mediated responses. Interestingly, however, while the anti-hyperalgesic effect of the enkephalin-encoding virus on C-fiber-mediated responses was reversed by intrathecal application of micro or delta opioid antagonists, only delta antagonists reversed the effect of this virus on Adelta hyperalgesia. Thus, virus-mediated delivery of the proenkephalin cDNA reverses thermal hyperalgesia produced by PTX-induced ribosylation of inhibitory G proteins by an opioid-mediated mechanism. These results suggest that herpesvirus vectors encoding analgesic peptides may be useful in attenuating centrally mediated, ongoing neuropathic pain and/or hyperalgesia.

Intervención neurorreflejoterápica para el tratamiento de las enfermedades mecánicas del raquis. Resultados de una experiencia piloto

BACKGROUND

Previous clinical trials have demonstrated the efficacy, safety, effectiveness and efficiency of neuroreflexotherapy (NRT) in the treatment of subacute and chronic non-specific low back pain. The goal of this study was to describe the implementation of this method into the Spanish National Health System, to assess the viability of the referral protocol, and to obtain the data required for planning the widespread use of this technology.

METHOD

A referral protocol was established and explained in a single clinical session in 18 health centers in Majorca (Spain). During this session, handouts of the referral protocol and a telephone number for questions were also given. After the session, the centers' physicians were authorized to refer their patients to a unit certified for NRT. Demand for this therapy, the applicability of the referral protocol, the appropriateness of referrals, and patient and physician satisfaction were quantified over a four-month period. Data were also collected on patients' clinical outcomes and on adverse effects of the treatment.

RESULTS

Of the 208 physicians, 43 referred 97 patients. The mean rate of referral per 10,000 persons affiliated with each health center was 1.07 patients per month. The rate of appropriate referral was 91.8%, with no physician having to call for assistance. Most of the referred patients had chronic, intense pain, with a poor prognosis and considerable disability. None of the patients refused NRT. There were no complaints, or serious adverse effects. The degree of satisfaction was high, and 98% of patients and 87% of physicians would recommend a relative referral to. In addition, 89% of physicians believed they should be allowed to continue referring their patients. The patients' clinical outcomes were favorable and consistent with those observed in previous clinical trials.

CONCLUSIONS

The method described allows NRT to be included in routine clinical practice within the Spanish National Health System under the conditions in which it was evaluated in previous randomized controlled trials. The referral protocol that was used generates a high rate of appropriate referrals, a high degree of satisfaction among patients and physicians, and clinical results that are consistent with the effectiveness and safety previously demonstrated for this technology.

Relationship between capsaicin-evoked substance P release and neurokinin 1 receptor internalization in the rat spinal cord

The relationship between substance P release and the activation of its receptor in the spinal cord remains unclear. Substance P release is usually measured by radioimmunoassay, whereas the internalization of the neurokinin 1 (NK1) receptor has been used to assess its activation by noxious stimuli. Our objective was to compare substance P release and NK1 receptor internalization produced by capsaicin in rat spinal cord slices. Superfusion of the slices with capsaicin for 3 min produced a gradual increase in substance P release that peaked 3-7 min afterward, and then decreased to baseline levels. The concentration-response curve for capsaicin was biphasic, with concentrations above 10 microM producing significantly less release. The effective concentration for 50% of response (EC(50)) for capsaicin, calculated from its stimulatory phase, was 2.3 microM. However, the potency of capsaicin to elicit NK1 receptor internalization in the same slices was one order of magnitude higher (EC(50)=0.37 microM) in lamina I, probably because NK1 receptors become saturated at relatively low concentrations of substance P. The potency of capsaicin to produce internalization was progressively lower in lamina III (EC(50)=1.9 microM) and lamina IV (EC(50)=14.5 microM), suggesting that neurokinins released in laminae I-II become diluted as they diffuse to the inner dorsal horn. To study the correlation between these two measures, we plotted substance P release against NK1 receptor internalization and fitted a saturation binding function to the points. The correlation was good for laminae I (R(2)=0.82) and III (R(2)=0.78), but it was poor (R(2)=0.35) for lamina IV because NK1 receptor internalization kept on increasing at high concentrations of capsaicin, whereas substance P release decreased. In conclusion, amounts of substance P able to activate NK1 receptors may fall under the threshold of detection of radioimmunoassay. Conversely, radioimmunoassay often detects levels of substance P release well over those required to saturate NK1 receptors in the superficial dorsal horn, but that may be able to activate these receptors in nearby regions of the spinal cord.

Effectiveness and cost-effectiveness analysis of neuroreflexotherapy for subacute and chronic low back pain in routine general practice: a cluster randomized, controlled trial

STUDY DESIGN

A cluster randomized, controlled trial was performed.

OBJECTIVES

To assess the clinical effectiveness and cost-effectiveness of adding patients' referral to neuroreflexotherapy intervention to the usual management of subacute and chronic low back pain in routine general practice.

SUMMARY OF BACKGROUND DATA

Neuroreflexotherapy consists of the temporary implantation of epidermal devices in trigger points in the back and referred tender points in the ear. The efficacy of this procedure for treating subacute and chronic low back pain has been demonstrated in previous randomized, double-blind, controlled clinical trials.

METHODS

Twenty-one primary care physicians working in seven primary care centers of the Spanish National Health Service in Palma de Mallorca, Spain, were randomly assigned to the intervention group (n = 11) or the control group (n = 10). The physicians recruited patients who had low back pain that had lasted for 14 or more days despite drug treatment and who did not meet criteria for surgery. The 45 patients recruited by physicians from the control group were treated according to the standard protocol, whereas the 59 patients recruited by physicians from the intervention group were, in addition, referred to neuroreflexotherapy intervention. The analysis of variables was performed taking into account that physicians, not patients, were randomly assigned.

RESULTS

Patients underwent clinical evaluations at baseline and 15, 60, and 365 days later. At baseline, median intensity of pain was higher in patients undergoing neuroreflexotherapy than in control patients (visual analogue scale, 6.07; range, 4.67-8.80 vs. 5.15, range 4.11-8.00) and median duration of pain was also higher (48.1, range 28.4-211.1 vs. 17.5, range 15.0-91.5 days). At the last follow-up visit, patients treated with neuroreflexotherapy showed greater improvement than did control patients in low back pain (visual analogue scale, 5.5; range, 3.7-8.8 vs. 1.9; range, -1.2-3.0; P < 0.001); referred pain (visual analogue scale, 3.6; range, 2.7-7.3 vs. 0.6; range, -1.5-2.0; P = 0.001); and disability (Roland-Morris scale, 8.7; range, 2.0-13.3 vs. 2.0; range, -1.5-6.7; P = 0.007). Moreover, neuroreflexotherapy intervention was associated with a significantly (P < 0.035) lower number of consultations to private or public specialists, fewer indications of radiographs by primary care physicians, lower cost of drug treatment, and less duration of sick leave throughout the follow-up period. There were also differences in favor of neuroreflexotherapy intervention in the cost-effectiveness ratio for pain, disability, and quality of life that persisted in the most optimistic, the most conservative, and the average (break-even case) assumptions.

CONCLUSIONS

Referral to neuroreflexotherapy intervention improves the effectiveness and cost-effectiveness of the management of nonspecific low back pain.

Selective depression of nociceptive responses of dorsal horn neurones by SNC 80 in a perfused hindquarter preparation of adult mouse

Detailed electrophysiological characterisation of spinal opioid receptors in the mouse has been limited due to various technical difficulties. In this study, extracellular single unit recordings were made from dorsal horn neurones in a perfused spinal cord with attached trunk-hindquarter to investigate the role of delta-opioid receptor in mediating nociceptive and non-nociceptive transmission in mouse. Noxious electrical shock, pinch and heat stimuli evoked a mean response of 20.8+/-2.5 (n=10, P<0.005), 30.1+/-5.4 (n=58, P<0.005) and 40.9+/-6.3 (n=29, P<0.005) spikes per stimulus respectively. In 5 of 22 cells, repetitive noxious electrical stimuli applied to the hindpaw for 20 s produced a progressive increase in spike number, the phenomenon known as 'wind-up' and/or hyperactivity. When the selective delta-opioid receptor agonist (+)-4-[(alpha R)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC 80) was perfused for 8-10 min, these evoked nociceptive responses were reversibly depressed. SNC 80 (2 microM) depressed the nociceptive responses evoked by electrical shock, pinch and heat by 74.0+/-13.7% (n=8, P<0.01), 66.5+/-16.6% (n=10, P<0.01) and 74.1+/-17.0% (n=10, P<0.01) respectively. The maximum depression by 5 microM SNC 80 was 92.6+/-6.8% (n=3). SNC 80 at 5 microM also completely abolished the wind-up and/or hypersensitivity (n=5). The depressant effects of SNC 80 on the nociceptive responses were completely blocked by 10 microM naloxone (n=5) and 3 microM 17-(cyclopropylmethyl)-6,7-dehydro-4,5 alpha-epoxy-14 beta-ethoxy-5 beta-methylindolo [2',3':6',7'] morphinan-3-ol hydrochloride (HS 378, n=8), a novel highly selective delta-opioid receptor antagonist. Interestingly, HS 378 (3 microM) itself potentiated the background activity and evoked responses to pinch and heat by 151.8+/-38.4% (P<0.05, n=8), 34.2+/-6.1% (P<0.01, n=7) and 45.5+/-11.8% (P<0.05, n=5) respectively. In contrast, the responses of non-nociceptive dorsal horn neurones were not inhibited by SNC 80 at a dose of up to 10 microM (n=5). These data demonstrate that delta-opioid receptor modulate nociceptive, but not non-nociceptive, transmission in spinal dorsal horn neurones of the adult mouse. The potentiation of neuronal activity by HS 378 may reflect an autoregulatory role of the endogenous delta-opioid in nociceptive transmission in mouse.

Spinal delta-opioid receptors mediate suppression of systemic SNC80 on excitability of the flexor reflex in normal and inflamed rat

Due to low central nervous system (CNS) bioavailability of delta-opioid peptides, little is known about the effect of systemic administration of delta-opioid receptor ligands. The present study examined the effect of non-peptidergic delta-opioid receptor agonists, (+)-4-[(alphaR)-alpha-((2R,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80) and (-)dibenzoyl-L-tartaric acid salt (SNC86), on the activity of alpha-motoneurons in decerebrate-spinal rats. The flexor reflex was facilitated by C-afferent conditioning inputs, shown by a decrease in mechanical threshold and increase in touch- and pinch-evoked responses. Systemic administration of SNC80 (10 micromol/kg) prevented and reversed the neuronal hyperactivity. We further examined the effect of this agonist on the hypersensitivity of the flexor reflex induced by intraplantar injection of Freund's adjuvant. SNC80 dose-dependently (1, 3, 5 and 10 micromol/kg) increased the mechanical threshold and decreased touch-, pinch- and Abeta-afferent inputs-evoked responses. Similar effects were seen with SNC86 (5 micromol/kg). Pretreatment with either naloxone (20 micromol/kg, i.p.) or (Cyclopropylmethyl)-6,7-dehydro-4,5alpha-epoxy-14beta-ethoxy-5beta-methylindolo [2',3':6',7']morphinan-3-ol hydrochloride (SH378; 5 micromol/kg, intraarterially (i.a.)), a novel selective delta-opioid receptor antagonist, completely abolished the anti-hypersensitivity effect of SNC80. The effect of SNC80 remained following intrathecal administration of mu-opioid receptor antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH(2) (CTOP; 1.5 nmol). These results indicate that systemic injection of SNC80 exerted antihypersensitivity in models of both acute and tonic nociception and these effects are mediated mainly through a spinal delta-opioid mechanism.

delta opioid receptor modulation of several voltage-dependent Ca(2+) currents in rat sensory neurons

Endogenous enkephalins and delta opiates affect sensory function and pain sensation by inhibiting synaptic transmission in sensory circuits via delta opioid receptors (DORs). DORs have long been suspected of mediating these effects by modulating voltage-dependent Ca(2+) entry in primary sensory neurons. However, not only has this hypothesis never been validated in these cells, but in fact several previous studies have only turned up negative results. By using whole-cell current recordings, we show that the delta enkephalin analog [D-Ala(2), D-Leu(5)]-enkephalin (DADLE) inhibits, via DORs, L-, N-, P-, and Q-high voltage-activated Ca(2+) channel currents in cultured rat dorsal root ganglion (DRG) neurons. The percentage of responding cells was remarkably high (75%) within a novel subpopulation of substance P-containing neurons compared with the other cells (18-35%). DADLE (1 microM) inhibited 32% of the total barium current through calcium channels (I(Ba)). A delta (naltrindole, 1 microM), but not a mu (beta-funaltrexamine, 5 microM), antagonist prevented the DADLE response, whereas a DOR-2 subtype (deltorphin-II, 100 nM), but not a DOR-1 (DPDPE, 1 microM), agonist mimicked the response. L-, N-, P-, and Q-type currents contributed, on average, 18, 48, 14, and 16% to the total I(Ba) and 19, 50, 26, and 20% to the DADLE-sensitive current, respectively. The drug-insensitive R-type current component was not affected by the agonist. This work represents the first demonstration that DORs modulate Ca(2+) entry in sensory neurons and suggests that delta opioids could affect diverse Ca(2+)-dependent processes linked to Ca(2+) influx through different high-voltage-activated channel types.

What peptides these deltorphins be

The deltorphins are a class of highly selective delta-opioid heptapeptides from the skin of the Amazonian frogs Phyllomedusa sauvagei and P. bicolor. The first of these fascinating peptides came to light in 1987 by cloning of the cDNA of from frog skins, while the other members of this family were identified either by cDNA or isolation of the peptides. The distinctive feature of deltorphins is the presence of a naturally occurring D-enantiomer at the second position in their common N-terminal sequence, Tyr-D-Xaa-Phe, comparable to dermorphin, which is the prototype of a group of mu-selective opioids from the same source. The D-amino acid and the anionic residues, either Glu or Asp, as well as their unique amino acid compositions are responsible for the remarkable biostability, high delta-receptor affinity, bioactivity and peptide conformation. This review summarizes a decade of research from many laboratories that defined which residues and substituents in the deltorphins interact with the delta-receptor and characterized pharmacological and physiological activities in vitro and in vivo. It begins with a historical description of the topic and presents general schema for the synthesis of peptide analogues of deltorphins A, B and C as a means to document the methods employed in producing a myriad of analogues. Structure activity studies of the peptides and their pharmacological activities in vitro are detailed in abundantly tabulated data. A brief compendium of the current level of knowledge of the delta-receptor assists the reader to appreciate the rationale for the design of these analogues. Discussion of the conformation of these peptides addresses how structure leads to further hypotheses regarding ligand receptor interaction. The review ends with a broad discussion of the potential applications of these peptides in clinical and therapeutic settings.

Spinal mu-, delta- and kappa-opioid receptors mediate intense stimulation-elicited inhibition of a nociceptive reflex in the rat

Intense electrical stimulation of meridian points in the rat inhibits the nociceptive tail withdrawal reflex. The objective of the present study was to determine whether spinal opioid receptors mediate this inhibition. Electrical stimulation was applied with 2 ms square pulses, at 4 Hz for 20 min at 20 times the threshold, to previously defined meridian points in the hindlimb. Threshold was the minimum current required to elicit muscle twitch. In lightly anaesthetized intact rats (n = 8) stimulation inhibited tail withdrawal during and for greater than one hour after the end of stimulation. In unanaesthetized spinal rats (n = 12) this inhibition was less and the post-stimulation effect lasted for 15 min. In control anaesthetized intact (n = 28) and unanaesthetized spinal rats (n = 14) placement of electrodes without stimulation had no effect. In spinal rats, preadministration of naloxone (25 mg/kg, i.p.) blocked the evoked inhibition (n = 11). In intact animals both naloxone (n = 8) and the mu-opioid receptor antagonist, beta-funaltrexamine (10 nmol; n = 9), given via a chronic intrathecal catheter, attenuated inhibitions during and after the end of stimulation by 50-60%. The delta-opioid receptor antagonist H-Tyr-tic psi[CH2NH]Phe-Phe-OH (TIPP[psi]; 10 nmol; n = 7) and the kappa-opioid receptor antagonist nor-binaltorphimine (10 nmol; n = 13) given by lumbar puncture attenuated the inhibition during the stimulation by 30% and 56%, respectively; both antagonists blocked the post-stimulation effect and even facilitated the withdrawal. The data suggest that spinal mu-, delta- and kappa-opioid receptors each contribute to the evoked inhibition.

Dual ultrastructural immunocytochemical labeling of mu and delta opioid receptors in the superficial layers of the rat cervical spinal cord

The delta opioid receptor (DOR) and mu opioid receptor (MOR) are abundantly distributed in the dorsal horn of the spinal cord. Simultaneous activation of each receptor by selective opiate agonists has been shown to result in synergistic analgesic effects. To determine the cellular basis for these functional associations, we examined the electron microscopic immunocytochemical localization of DOR and MOR in single sections through the superficial layers of the dorsal horn in the adult rat spinal cord (C2-C4). From a total of 270 DOR-labeled profiles, 49% were soma and dendrites, 46% were axon terminals and small unmyelinated axons, and 5% were glial processes. 6% of the DOR-labeled soma and dendrites, and < 1% of the glial processes also showed MOR-like immunoreactivity (MOR-LI). Of 339 MOR-labeled profiles, 87% were axon terminals and small unmyelinated axons, 12% were soma and dendrites, and 2% were glial processes. 21% of the MOR-labeled soma and dendrites, but none of the axon terminals also contain DOR-LI. The subcellular distributions of MOR and DOR were distinct in axon terminals. In axon terminals, both DOR-LI and MOR-LI were detected along the plasmalemma, but only DOR-LI was associated with large dense core vesicles. DOR-labeled terminals formed synapses with dendrites containing MOR and conversely, MOR-labeled terminals formed synapses with DOR-labeled dendrites. These results suggest that the synergistic actions of selective MOR- and DOR-agonists may be attributed to dual modulation of the same or synaptically linked neurons in the superficial layers of the spinal cord.

Differential antinociceptive effects of spinal opioids on foot withdrawal responses evoked by C fibre or A delta nociceptor activation

1. Intrathecal application of mu, delta, and kappa opioids attenuate responses on several tests of animal nociception. However, the potency of these opioids differ depending on which tests were used. One factor contributing to these discrepancies is that different types of noxious stimuli activate different sets of nociceptor types, which may be differentially sensitive to opiate inhibition. To examine this hypothesis, we used a recently developed behavioural test which allows for differential assessment of nociception evoked by the activation of myelinated (A delta) and unmyelinated C thermonociceptors. 2. Administration of a kappa-selective agonist was ineffective on either type of response. Delta1 drugs were slightly more potent on C fibre-mediated responses than on A delta-mediated responses. 3. Intrathecal mu and delta2 drugs were antinociceptive on both A delta and C nociceptor-mediated responses. However, unlike the delta1 effects, the dose-response curves for mu and delta2 drugs were significantly more steep for A delta than for C fibre-mediated responses, potentially indicating differences in the mechanisms by which the drugs act on these 2 response types.

Modulation of excitatory synaptic transmission by nociceptin in superficial dorsal horn neurones of the neonatal rat spinal cord

1. The modulatory actions of nociceptin/orphanin FQ on excitatory synaptic transmission were studied in superficial dorsal horn neurones in transverse slices from 7 to 14 day old rats. 2. Glutamatergic excitatory postsynaptic currents (e.p.s.cs) were recorded from the somata of the neurones in the whole-cell patch-clamp configuration. E.p.s.cs were evoked by extracellular electrical stimulation (100 microns, 3-10 V) of the ipsilateral dorsal root entry zone by use of a glass electrode. E.p.s.cs with constant short latency (< 2.3 ms) and with no failures upon stimulation were assumed to be monosynaptic. These e.p.s.cs occurred with an average latency of 1.72 +/- 0.098 ms and exhibited a fast decay with a time constant, tau, of 4.8 +/- 0.53 ms (n = 30). 3. Nociceptin reversibly reduced the amplitudes of e.p.s.cs in a concentration-dependent manner in 25 out of 27 cells tested. Average maximum inhibition was 51.6 +/- 5.7% (mean +/- s.e.mean; n = 9), at concentrations > 3 microM. EC30 was 485 +/- 47 nM and the Hill coefficient was 1.29 +/- 0.09. 4. Inhibition of synaptic transmission by nociceptin (10 microM) was insensitive to the non-specific opioid receptor antagonist naloxone (10 microM) indicating that nociceptin did not act via classical opioid receptors. 5. In order to determine the site of action of nociceptin spontaneous miniature e.p.s.cs (m-e.p.s.cs) were recorded. Nociceptin reduced the frequency of m-e.p.s.cs in 6 out of 7 cells but had no effect on their amplitude distribution or on their time course. These findings suggest a pre- rather than a postsynaptic modulatory site of action. This is in line with the finding that current responses elicited by extracellular application of L-glutamate (10 microM) were not affected by nociceptin (10 microM; n = 7). 6. No positive correlation was found between the degree of inhibition by nociceptin (10 microM) and by the mixed delta- and mu-receptor agonist methionine-enkephalin (10 microM). This suggests that both neuropeptides acted on different but perhaps overlapping populations of synaptic connections. 7. Our results indicate that nociceptin inhibits excitatory synaptic transmission in the superficial layers of the rat dorsal horn by acting on presynaptic, presumably ORL1 receptors. This may be an important mechanism for spinal sensory information processing including nociception.

Local and remote sustained trigger point therapy for exacerbations of chronic low back pain. A randomized, double-blind, controlled, multicenter trial

STUDY DESIGN

A randomized, double-blind, controlled, multicenter trial was conducted.

OBJECTIVES

To assess the efficacy of neuroreflexotherapy in the management of low back pain.

SUMMARY AND BACKGROUND DATA

Neuroreflexotherapy consists of temporary implantation of epidermal devices in trigger points in the back and referred tender points in the ear.

METHODS

The rheumatology and rehabilitation departments of three teaching hospitals in Madrid recruited 78 patients with chronic low back pain. These patients were randomly assigned to the control group (37 patients) or to the treatment group (41 patients). Patients in the treatment group underwent one neuroreflexotherapeutic intervention. The control group received sham treatment consisting of placement of the same number of epidermal devices within a 5-cm radius of the target zones. Patients from both groups were allowed to continue drug treatment as previously prescribed. The use of medications during the trial was recorded.

RESULTS

Patients underwent clinical evaluations on three occasions: within 5 minutes before intervention, within 5 minutes after intervention, and 45 days later. The preintervention assessment was carried out by the physician from each hospital department who included the patient in the study. Each of the two follow-up assessments were carried out independently by two of three physicians who had no connection with the research team. Patients in the treatment group showed immediate lessening of pain compared with the results in patients in the control group. The pain relief was clinically relevant and statistically significant, and it persisted up to the end of the trial.

CONCLUSIONS

Neuroreflexotherapy intervention seems to be a simple and effective treatment for rapid amelioration of pain episodes in patients with chronic low back pain. At this time, the duration of pain relief beyond 45 days has not been evaluated.

Substance P and enkephalin immunoreactivities in axonal boutons presynaptic to physiologically identified dorsal horn neurons. An ultrastructural multiple-labelling study in the cat

A combination of intracellular electrophysiological recording and injection of horseradish peroxidase with ultrastructural immunocytochemistry was used to investigate the synaptic interplay between substance P- and enkephalin-immunoreactive axonal boutons and three types of functionally characterized dorsal horn neurons in the cat spinal cord. The dorsal horn neurons were classified as nociceptive specific, wide dynamic range and non-nociceptive based on their responses to innocuous and noxious stimuli. Most of the nociceptive neurons (either nociceptive specific or wide dynamic range) contained enkephalin immunoreactivity, but none of the non-nociceptive neurons were positive for enkephalin. Three types of immunoreactive boutons were found in contact with the functionally characterized dorsal horn neurons. These boutons were positive for either substance P, enkephalin, or substance P+enkephalin. Quantitative analysis revealed that the percentages of substance P-immunoreactive boutons apposed to the cell bodies, proximal dendrites and distal dendrites of nociceptive neurons were significantly higher than those of non-nociceptive neurons. Furthermore, the percentages of substance P+enkephalin-immunoreactive axonal boutons apposed to the distal dendrites of nociceptive neurons were significantly higher than those of non-nociceptive neurons and the percentages of enkephalin-immunoreactive boutons apposed to the cell bodies and proximal dendrites of nociceptive neurons were significantly higher than in non-nociceptive neurons. Finally, neither enkephalin-immunoreactive nor substance P+enkephalin-immunoreactive boutons were ever seen presynaptic to substance P-immunoreactive boutons. These results provide evidence of an anatomical substrate within the dorsal horn for the interaction of substance P-mediated with enkephalin-mediated mechanisms. The data support the idea that the modulation of nociceptive input in the dorsal horn by enkephalinergic neurons occurs mainly via a postsynaptic mechanism, and thus suggest that dorsal horn enkephalinergic neurons participate in a local inhibitory feedback loop in a distinct pathway from the previously postulated opioid-mediated depression of substance P release from primary afferent terminals.

Delta-Opioid receptor modulation of the release of substance P-like immunoreactivity in the dorsal horn of the rat following mechanical or thermal noxious stimulation

The present study was undertaken to investigate the effects of the opioid peptide Met-enkephalin (met-enk) on the release of substance P-like immunoreactivity (SPLI) in the lumbar dorsal horn during the application of a noxious mechanical or thermal stimulus to the ipsilateral hind paw and lower limb of the rat. A push-pull cannula was introduced to the lumbar dorsal horn in non-anesthetized decerebrate/spinal transected rats. The dorsal horn was perfused with artificial CSF and the collected perfusates were assayed for SPLI using radioimmunoassay. A noxious mechanical or thermal stimulus was applied to different areas of the ipsilateral hind paw and lower limb. Met-enk (500 nM) applied to the dorsal horn through the perfusate reduced the basal release of SPLI by 29 +/- 9% and prevented the increase in the release of SPLI evoked by the noxious mechanical or thermal stimulus. The effect of met-enk was blocked by the selective delta-opioid receptor antagonist naltrindole (500 nM). Naltrindole (NTD) alone elicited a 75 +/- 30% increase in the basal release of SPLI. These data show that met-enk inhibits the thermally or mechanically evoked release of SPLI in the dorsal horn by activating the delta opioid receptors. These receptors are also involved in the tonic spinal regulation of the release of SPLI.

Kappa-opioid receptor modulation of the release of substance P in the dorsal horn

Substance P (SP), a member of the tachykinin peptide family, has been found in high concentrations in the superficial laminae of the dorsal horn and it is thought to play a major role in the transmission of nociceptive information. Dynorphin(1-8), an opioid peptide with high selectivity for the kappa-opioid receptor subtype, is also found in the dorsal horn of the spinal cord. The aim of this study was to determine the effect of dynorphin(1-8) on the release of SP-like-immunoreactivity (SPLI) in the dorsal horn before and during the activation of peripheral nociceptors by a thermal stimulus. A push-pull canula was used to perfuse the dorsal horn of non-anesthetized decerebrate/spinal transected rats and the collected perfusates were assayed for SPLI by using radioimmunoassay. Dynorphin(1-8) applied to the spinal cord at a concentration of 1 microM elicited a 27 +/- 8% decrease in the basal release of SPLI and prevented the increase in the release of SPLI evoked by the application of a noxious thermal stimulus to the ipsilateral hind paw and lower limb. The effect of dynorphin(1-8) was reversed by 2 microM of nor-binaltorphimine (nor-BNI), a selective kappa opioid receptor antagonist. Application of nor-BNI alone to the perfusate resulted in a 62 +/- 23% increase in the basal release of SPLI. In conclusion, dynorphin(1-8) reduces the basal release of SPLI and prevents the increase in the release of SPLI elicited by the application of a noxious cutaneous thermal stimulus. This effect is mediated through the kappa-opioid receptor, which appears to tonically regulate the release of SPLI in the dorsal horn.

Afferent volley patterns and the spinal release of immunoreactive substance P in the dorsal horn of the anaesthetized spinal cat

Microprobes bearing immobilized antibodies to the C-terminus of substance P were used to measure release of this neuropeptide in the spinal cord of the anaesthetized spinal cat in response to peripheral nerve stimulation. Release of substance P was just detectable in laminae I, II with 150 stimuli (0.5 Hz, 5 min) and was near maximal with 300 stimuli. Using two periods of stimulation of 10 min separated by 15 min, greater levels of substance P were detected during the second period. Fifteen to 25 min after two periods of peripheral nerve stimulation levels of substance P detected by microprobes were still elevated above those present prior to stimulation. Stimulation with bursts of three impulses when delivering a fixed number of stimuli resulted in detection of increased levels of substance P at sites adjacent to the areas of maximal release. The results suggest that maximal release of substance P from the central terminals of primary afferent fibres occurs with relatively few impulses and at low frequencies in agreement with what is known of release from the peripheral terminals of these fibres.

Noxious peripheral stimulation produces antinociception mediated via substance P and opioid mechanisms in the rat tail-flick test

Physiological experiments were run to examine the effects of noxious thermal stimulation of one hindpaw on the tail-flick reflex in the lightly anesthetized rat. Male Sprague-Dawley rats were anesthetized with an i.p. injection of a mixture of Na-pentobarbital (20 mg/kg) and chloral hydrate (120 mg/kg). After baseline readings were taken in the tail-flick test, either a non-noxious or a noxious stimulus was applied which consisted of immersion of one hindpaw in water at 40, 45, 50 or 55 degrees C for 1.5 min. After immersion, tail-flick readings were taken at 3-min intervals for at least 16 min. Paw immersion in water at 55 degrees C induced an antinociceptive response, consisting of an increase in the reaction time, at 0.5 min after immersion. Recovery to baseline levels occurred over the next 3-6 min. Immersion at lower temperatures provoked smaller antinociceptive responses, except at 40 degrees C, where readings remained around the baseline values. The increase in reaction time in response to immersion at 55 degrees C was attenuated or blocked by the novel, nonpeptide substance P (NK-1) receptor antagonist, CP-96,345, administered s.c. 30 or 60 min, respectively, prior to paw immersion. Similar injection of CP-96,344, the inactive stereoisomer, had no effect on the response, while another NK-1 receptor antagonist, CP-99,994, also attenuated the antinociceptive effect of the immersion. The increase in reaction time induced by immersion at 55 degrees C was absent in animals treated neonatally with capsaicin.(ABSTRACT TRUNCATED AT 250 WORDS)

The formalin-induced expression of tachykinin peptide and neurokinin receptor messenger RNAs in rat sensory ganglia and spinal cord is modulated by opiate preadministration

Tachykinin peptides such as substance P and neurokinin B have been widely studied as mediators of pain transmission. The expression of neurokinin-1 and neurokinin-3 receptor messenger RNAs in the spinal cord is increased following intense nociception. The opiate ligands morphine and naltrexone alter behavioral responses to formalin-induced pain and alter evoked substance P release. This study investigated whether these opiates similarly alter the expression of substance P-, neurokinin B-, neurokinin-1 receptor- and neurokinin-3 receptor-encoding messenger RNAs in spinal systems following formalin-induced nociception. Expression levels of various messenger RNAs were quantitated using solution hybridization-nuclease protection assays. Six hours after hindpaw treatment, the levels of substance P-encoding preprotachykinin messenger RNA in the lumbar dorsal root ganglia and neurokinin B, neurokinin-1 receptor and neurokinin-3 receptor messenger RNAs in the lumbar dorsal horn were increased by approximately two-fold as compared to sham-treated controls. Pretreatment with naltrexone resulted in a further increase in the nociception-induced substance P messenger RNA expression in the dorsal root ganglia; preprotachykinin messenger RNA expression was not affected by morphine. Nociception-induced neurokinin-1 receptor messenger RNA expression in the dorsal horn was blocked by morphine, but was not affected by naltrexone. Both morphine and naltrexone blocked the formalin-induced increases in neurokinin B and neurokinin-3 receptor messenger RNA levels. Increased neurokinin B messenger RNA expression may reflect increased neurokinin B turnover in spinal interneurons activated by nociception. Neurokinin-3 receptor messenger RNA expression levels varied closely with, and thus may be regulated by, the levels of neurokinin B messenger RNA in the same regions. The results of this study indicate that pretreatment with opiate ligands modulates the expression of tachykinin peptide and neurokinin receptor encoding mRNAs in spinal systems following a peripheral chemogenic inflammatory stimulus. Thus, endogenous opioid systems may be involved in activity-induced changes in the expression of spinal tachykinin peptides and neurokinin receptors.

Opioidergic control of the spinal release of neuropeptides. Possible significance for the analgesic effects of opioids

Several neuropeptides play a key role in the transfer (substance P, calcitonin gene-related peptide, etc) and control (enkephalins, cholecystokinin, etc) of nociceptive messages from primary afferent fibres to spino-thalamic neurones in the dorsal horn of the spinal cord. This first relay in nociceptive pathways has been shown to be a major target for opioids such as analgesic drugs, and the effects of exogenous (mainly morphine) and endogenous opioids on the release of neuropeptides within the dorsal horn are reviewed here for a better understanding of the cellular mechanisms responsible for their antinociceptive action. Complex modulations of the in vitro (from tissue slices) and in vivo (in halothane-anaesthetized rats whose intrathecal space was perfused with an artificial cerebrospinal fluid) release of substance P and calcitonin gene-related peptide by opioids have been reported, depending on the opioid receptor (mu, delta, kappa, and their subtypes) stimulated by these compounds. In particular, the inhibition by delta agonists of substance P release from primary afferent fibres, and that by the concomitant stimulation of mu and kappa receptors of the release of calcitonin gene-related peptide are very probably involved in the analgesic action of specific opioids and morphine at the level of the spinal cord. Furthermore, the negative modulation (through presynaptic opioid autoreceptors) by delta and mu agonists of the spinal release of met-enkephalin, and the complex inhibitory/excitatory influence of delta, mu and kappa receptor ligands on the release of cholecystokinin within the dorsal horn very likely also contribute to the antinociceptive action of these drugs and morphine. The reviewed data strongly support the existence of functional interactions between mu and kappa receptors within the spinal cord, and their key role in the analgesic action of non specific opiates (acting on mu, delta and kappa receptors) such as morphine.

Differential effects of the novel analgesic, S 12813-4, on the spinal release of substance P- and calcitonin gene-related peptide-like materials in the rat

The possible inhibitory control by the novel analgesic S 12813-4 (3-(2-(4-phenylpiperazine-1-yl)-ethyl)-2-oxo-2,3- dihydrooxazolo(b)pyridine) of spinal neurones containing substance P (SP) and/or calcitonin gene-related peptide (CGRP) was assessed in vitro and in vivo in the rat. S 12813-4 (10 nM-0.1 mM) did not affect the spinal release of CGRP-like material (CGRPLM) but inhibited in a concentration dependent manner the K(+)-evoked overflow of SP-like material (SPLM) from slices of the dorsal half of the rat lumbar enlargement. The inhibitory effect of 10 microM S 12813-4 on SPLM release was not additive with that of Na (0.1 mM), and could be prevented by the alpha 2-adrenoceptor antagonist idazoxan (10 microM). Similarly, idazoxan (10 microM) suppressed the inhibition by intrathecally administered S 12813-4 (10 microM) of the spinal outflow of SPLM in halothane anaesthetized rats whose intrathecal space was perfused with an artificial cerebrospinal fluid. These data suggest that the analgesic effect of S 12813-4 might involve some alpha 2-adrenoreceptor-mediated control of SPLM release within the spinal cord. Whether this control concerns SP-containing primary afferent fibres (presynaptic inhibition) or SP-containing interneurones and/or bulbo-spinal SP-ergic pathways (postsynaptic inhibition) deserves further investigations.

Opioid control of the release of calcitonin gene-related peptide-like material from the rat spinal cord in vivo

The possible control by opioids of the spinal release of calcitonin gene-related peptide-like material (CGRPLM) was investigated in halothane-anaesthetized rats whose intrathecal space was perfused with an artificial cerebrospinal fluid. Morphine (20 mg/kg i.v.; or at 10-100 microM added to the perfusing fluid), the mu selective agonist DAGO (10 microM) and the kappa selective agonist U 50488 H (10 microM) did not affect the spontaneous outflow of the CGRPLM. In contrast, the selective delta agonist DTLET (10 microM) significantly increased CGRPLM release. The latter effect could be prevented by the selective delta antagonist naltrindole (10 microM) as expected from the involvement of this class of opioid receptors. However, the addition of naltrindole alone to the perfusing fluid did not modify CGRPLM outflow, indicating that endogenous opioids do not exert a tonic control of CGRP-containing fibers through the stimulation of delta receptors. In contrast, intrathecal perfusion with naloxone (10 microM) or nor-binaltorphimine (10 microM), a selective antagonist of kappa receptors, produced a marked increase in spinal CGRPLM release, suggesting that endogenous opioids acting at mu and kappa receptors, respectively, exert a tonic inhibitory control of CGRP-containing fibers. Indeed, a significant decrease in the spinal release of CGRPLM release could be evoked by the combined addition of U 50488 H (10 microM) plus DAGO (10 microM) to the perfusing medium, indicating that the simultaneous stimulation of both kappa and mu receptors is required for this negative control to occur. This could notably be achieved with morphine (10 microM) in the presence of naltrindole (10 microM) which also produced a significant reduction in the spinal release of CGRPLM. In conclusion, morphine per se did not change CGRPLM release because this drug triggers opposite positive (through the stimulation of delta receptors) and negative (through the concomitant stimulation of both kappa and mu receptors) control mechanisms within the rat spinal cord.

In vitro study of the interaction of salmon calcitonin with mu, delta and kappa opioid agonists

A possible interaction of salmon-calcitonin with opioid systems was studied in isolated tissues. Neurogenic contractions were elicited by electrical stimulation in guinea-pig ileum myenteric plexus-longitudinal muscle strips, rabbit vas deferens and mouse vas deferens. Bremazocine inhibited neurogenic contractions in all three tissues (presumably through kappa-receptors) [D-Pen2, D-Pen5]enkephalin and [Met5]enkephalin inhibited contractions in mouse vas deferens (presumably through delta-receptors), and [D-Ala2, N-Me-Phe4, Gly5-ol]enkephalin (DAMGO) inhibited contractions in guinea-pig ileum and mouse vas deferens (presumably through mu-receptors). All inhibitory effects were concentration-dependent. Salmon-calcitonin 0.1 IU/ml increased the effect of bremazocine in guinea-pig ileum and rabbit vas deferens and also increased the effects of [D-Pen2, D-Pen5]enkephalin and [Met5]enkephalin in mouse vas deferens. In contrast, salmon-calcitonin up to 0.4 IU/ml did not change the effect of bremazocine in mouse vas deferens and the effect of DAMGO in guinea-pig ileum and mouse vas deferens. It is concluded that salmon-calcitonin enhances agonist effects at opioid kappa- and delta- but not at opioid mu-receptors. The level of this interaction remains to be elucidated. The interaction may be the basis of the analgesic effect of salmon-calcitonin in vivo.

Kappa-/mu-receptor interactions in the opioid control of the in vivo release of substance P-like material from the rat spinal cord

The possible involvement of mu and kappa receptors in the opioid control of the spinal release of substance P-like material was assessed in vivo, in halothane-anaesthetized rats whose intrathecal space was continuously perfused with an artificial cerebrospinal fluid supplemented with various opioid receptor agonists and antagonists. Whereas the intrathecal perfusion with the mu agonist DAGO (10 microM) significantly enhanced (approximately + 50%) the spontaneous release of substance P-like material, that with the kappa agonist U 50488 H (10 microM) produced no change in the peptide outflow. The respective antagonists naloxone (10 microM) for the mu receptors and nor-binaltorphimine (10 microM) for the kappa receptors did not affect the spontaneous release of substance P-like material, indicating that endogenous opioids acting at mu and kappa receptors do not exert a tonic control on substance P-containing neurons in the spinal cord of halothane-anaesthetized rats. However, as expected from the involvement of mu receptors, the stimulatory effect of DAGO on the peptide outflow could be prevented by naloxone but not norbinaltorphimine. Furthermore, instead of an increase with DAGO alone, a significant decrease in the spinal release of substance P-like material was observed upon the intrathecal perfusion with DAGO plus U 50488 H. Additional experiments with the respective mu and kappa antagonists naloxone and nor-binaltorphimine demonstrated that this effect actually resulted from the simultaneous stimulation of mu and kappa receptors.(ABSTRACT TRUNCATED AT 250 WORDS)