TRPV1 desensitisation and endogenous vanilloid involvement in the enhanced analgesia induced by capsaicin in inflamed tissues

The intra-plantar acute administration of 10 microg of capsaicin to mice which had received complete Freund's adjuvant (CFA) 1 week before inhibits the thermal inflammatory hyperalgesia it induces and even produces a long-lasting analgesia for at least 2 weeks. In this study, we show that the administration of capsaicin (10 microg) also reduces the immediate licking behavior evoked by the intra-plantar administration of a lower dose of capsaicin (0.1 microg), the duration of this inhibitory effect being greater in CFA-inflamed mice (at least 2 weeks) than in non-inflamed animals (less than 4 days). Since this reduction of capsaicin-induced licking behavior may be interpreted as a consequence of the transient receptor potential vanilloid 1 receptor (TRPV1) unresponsiveness, we conclude that the administration of 10 microg of capsaicin into inflamed tissues can render the TRPV1 desensitised. We next explored whether endogenous vanilloids released during inflammation contribute to maintain the analgesia triggered by exogenous capsaicin. The acute administration of capsazepine (10 microg; intra-plantarly (i.pl.)) abolished the analgesic effect induced by the injection of capsaicin 1 week before in inflamed mice. From these results, it may be proposed that the maintenance by endovanilloids of the TRPV1 desensitisation induced by capsaicin could contribute to prolonging the analgesic effect induced by this agonist in inflamed tissues.

Analgesic effects of loperamide in bone cancer pain in mice

The intratibial inoculation of NCTC 2472 cells induces an osteosarcoma in C3H/HeJ mice. These mice show thermal hyperalgesic responses which may be blocked by the local administration of opiates over the tibial tumoral mass (Menéndez L, Lastra A, Hidalgo A, Meana A, Garcia E, Baamonde A. Peripheral opioids act as analgesics in bone cancer pain in mice. NeuroReport 2003b; 14:867-9). The aim of this report was to characterize the analgesic responses obtained by activating peripheral opioid receptors in bone cancer pain. Here, we initially describe that this osteosarcoma induces mechanical as well as thermal hyperalgesia. Loperamide, an opioid agonist unable to cross the blood-brain barrier, inhibits both thermal and mechanical hyperalgesia when s.c. injected, locally over the tibial tumoral mass (7.5-75 microg) or distantly, under the fur of the neck (4 mg/kg). These analgesic effects seem peripherally mediated since they are reverted by the administration of naloxone methiodide (10 mg/kg) and because the withdrawal latencies of the contralateral, non-affected, paws remain unaltered. Furthermore, only cyprodime (1 mg/kg) but not naltrindole (0.1 mg/kg) or nor-binaltorphimine (10 mg/kg) blocked these effects, showing the involvement of gamma-opioid receptors in the peripheral analgesia induced by loperamide on thermal and mechanical hyperalgesia. The advantages of using peripheral acting opiates -- devoid of central colateral effects -- for the treatment of cancer related pain are suggested.

The Neonatal Treatment of Rats with Monosodium Glutamate Induces Morphological Changes in the Subfornical Organ

The parenteral administration of monosodium glutamate (MSG) to neonatal rats induces specific lesions in the central nervous system that lead to a well characterized neuroendocrinological dysfunction. Additionally, it has been shown that MSG-treated rats present a blunted blood pressure response to the injection of nitric oxide synthase inhibitors. Recently, a similar cardiovascular alteration has been reported after the electrolytic lesion of the anteroventral region of the third ventricle affecting the connections of the subfornical organ (SFO). We hypothesized that the treatment of neonatal rats with MSG could affect the nitrergic cells of the SFO. In the present work, we have looked for alterations in the NADPH-diaphorase activity (a commonly used marker for nitrergic neurons) in the SFO of MSG-treated rats of either sex and at two different ages. Our results shown that the treatment of neonatal rats with MSG induced a substantial reduction in the volume of the SFO and in the number of its nitrergic cells with regard to control animals. These findings suggest that the SFO could be implicated in some of the cardiovascular alterations observed in MSG-treated rats.

The analgesic effect induced by capsaicin is enhanced in inflammatory states

Agonists of the vanilloid receptor type 1 (VR1), such as capsaicin, induce an analgesic effect following an initial excitatory response. It has been demonstrated that the vanilloid system plays an important role in inflammatory hyperalgesia. In accordance, we show that the VR1 antagonist capsazepine (30 microg; i.pl.) prevented the thermal hyperalgesia induced by carrageenan or complete Freund's adjuvant (CFA) in mice. Furthermore, we studied whether this inflammation-induced activation of the vanilloid system could enhance the analgesic properties of capsaicin. A single administration of capsaicin (10 microg; i.pl.) induced in control mice an analgesic effect that lasted for 2 days. In contrast, in carrageenan-treated animals, the analgesic effect of this dose of capsaicin lasted for 6 days and in CFA-treated mice for 30 days. This prolongation of capsaicin-induced analgesia during inflammation was mediated through VR1 since it was completely blocked by coadministration of capsazepine (10 microg). Licking behavior induced by capsaicin in carrageenan- and CFA-treated mice was greater than in control animals. However, although capsaicin induced a more prolonged analgesia in CFA-treated mice, the licking behavior was greater in the carrageenan-treated group, suggesting that the prolongation of analgesia is independent of the initial nociceptive input. Overall, these results show that the analgesic effects of capsaicin are importantly enhanced during inflammation, supporting the fact that the stimulation of VR1 could perhaps constitute a suitable strategy to avoid inflammatory hyperalgesia.

Implantation of Tumoral XC Cells Induces Chronic, Endothelin-Dependent, Thermal Hyperalgesia in Mice

1. We describe here the alterations in the nociceptive sensitivity of Swiss CD1 mice receiving an intraplantar (i.pl.) administration of XC Rous sarcoma-virus-transformed rat fibroblasts (XC cells). 2. Histological studies reveal that XC cells remain at the injection site 2-3 weeks after implantation, a time at which an inflammatory reaction is also detected. No tumoral growth was found and 5 weeks after inoculation neither XC cells nor inflammatory reaction were observed. 3. Measures to different types of noxious stimuli were performed. At week 1 after XC cell inoculation, hyperalgesia to thermal, but not mechanical, stimuli as well as to capsaicin injection is present in the implanted paw. At week 5 after XC cell implantation, only thermal hyperalgesia is present, and this enhanced reactivity persisted for even 25 weeks after the disappearance of XC tumoral cells. 4. Pharmacological studies on thermal hyperalgesia were conducted at two different stages, week 1 and week 5 after XC cell inoculation. The systemic administration of morphine (1-10 mg/kg i.p. (intraperitoneal); 30 min before testing) prevents this thermal hyperalgesic reaction both at week 1 and week 5. The endothelin type A (ETA) receptor antagonist BQ-123 (10 nmol; i.pl.; 90 min before testing) abolishes both the early (week 1) and the late (week 5) thermal hyperalgesia. In contrast, the selective endothelin type B (ETB) receptor antagonist, BQ-788 (10 nmol; i.pl.; 90 min before) abolishes thermal hyperalgesia only at week 1, but not at week 5 after XC cell inoculation. 5. It might be concluded that endothelins are probably involved in this type of long-term thermal hyperalgesia produced by the transitory presence of the XC tumoral cell line.

Involvement of endogenous endothelins in thermal and mechanical inflammatory hyperalgesia in mice

Endothelin receptors have been involved in inflammatory, neuropathic and tumoral pain. In the case of inflammatory hyperalgesia, some previous papers have pointed towards the involvement of ETB receptors, although the stimulation of ETA receptors seems to participate in the development of the inflammatory reaction. We have studied the effect of ETA and ETB receptor antagonists in the thermal and mechanical hyperalgesia induced in a model of acute (induced by carrageenan) and chronic (induced by complete Freund's adjuvant, CFA) inflammation in mice. The i.pl. administration of the selective ETA antagonist BQ-123 (1-10 nmol) antagonized the thermal hyperalgesia detected by the unilateral hot plate test, observed in both inflammatory models, whereas the i.pl. administration of the ETB selective antagonist BQ-788 (17.7 nmol) failed to modify this. In contrast, both BQ-123 (3-17.7 nmol) and BQ-788 (3-17.7 nmol) antagonized the mechanical hyperalgesia, as assessed by the Randall-Selitto test in carrageenan- and CFA-treated mice. Both BQ-123 and BQ-788 were able to antagonize the mechanical hyperalgesia induced by ET-1 (200 pmol; i.pl.) in the same dose range. Thus, ETA receptors are involved in both thermal and mechanical hyperalgesia whereas ETB receptors are only involved in mechanical hyperalgesia in these inflammatory models. In conclusion, the role of ETB receptors in inflammatory pain is further supported and new insights into the participation of ETA receptors in inflammatory hyperalgesia are given.

Peripheral opioids act as analgesics in bone cancer pain in mice

Previous reports have shown that systemic administration of morphine can prevent the thermal hyperalgesia induced by the development of an osteosarcoma in C3H/HeJ mice after the implantation of NCTC 2472 cells. We show here that this type of hyperalgesia is also abolished by the local administration of morphine given at low doses (10 nmol), or the peripheral acting opioid receptor agonist loperamide (146 nmol). The analgesic effect of loperamide is prevented by the administration of the opioid receptor antagonist naloxone methiodide (10 mg/kg, i.p.), which is unable to cross the blood-brain barrier. These results provide evidence which supports the fact that peripheral opioids could be useful tools in the management of some types of cancer pain.

Initial thermal heat hypoalgesia and delayed hyperalgesia in a murine model of bone cancer pain

The recent development of rodent models of bone cancer pain has started to provide the basis for demonstrating the particular neurochemical and behavioral entity of cancer pain. Behaviourally, both spontaneous pain and hyperalgesia related to mechanical, but not thermal, noxious stimuli have been described in cancer-bearing animals. We have carried out a histological and behavioural study focused on the reactivity to noxious heat in C3H/HeJ mice receiving an intratibial injection of 10(5) NCTC 2472 cells. These cells, able to induce an osteosarcoma, break through bone into soft tissues 2 weeks after cell inoculation, producing a macroscopical increase of the limb size from the fourth week. Thermal reactivity is diminished during the first 2 weeks after cell implantation, this hypoalgesia being reversed by the administration of naloxone (10 mg/kg). In contrast, during the fourth and fifth weeks after NCTC 2472 cell implantation, an increased nociceptive heat reactivity, instead of hypoalgesia, was obtained. This thermal hyperalgesia was prevented by the systemic administration of morphine (15 mg/kg). Throughout the whole period studied, mice showed signs of spontaneous pain behaviour that reached its maximum 3 weeks after inoculation. In conclusion, we show that the presence of thermal heat hyperalgesia is preceded by an initial opioid-mediated hypoalgesic state, in this murine model of bone cancer pain.

Spinal nociceptin inhibits AMPA-induced nociceptive behavior and Fos expression in rat spinal cord

The effects of intrathecal nociceptin (NOCI) on the nociceptive behavior (biting, scratching and licking; BSL) and the spinal Fos expression induced by intrathecal administration of N-methyl-D-aspartate (NMDA, 4 microg/rat) or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA, 2 microg/rat) were studied. Coadministration of NOCI (3 and 10 nmol/rat) with NMDA did not modify the NMDA-induced BSL or Fos expression. In contrast, NOCI (0.1-3 nmol/rat) dose-dependently inhibited the BSL behavior induced by AMPA. Furthermore, coadministration of NOCI (3 and 10 nmol/rat) significantly reduced the AMPA-induced expression of Fos protein in the superficial layers of the spinal dorsal horn. In order to test whether classical or opioid receptor-like type 1 (ORL1) receptors are involved in the inhibitions by NOCI of AMPA-evoked BSL, the corresponding antagonists were assayed. The administration of the nonselective opioid receptor antagonist, naloxone (10 mg/kg i.p.), did not modify the NOCI-induced inhibition of AMPA-evoked BSL. However, the selective ORL1 receptor antagonist, [N-Phe(1)]nociceptin-(1-13)-NH(2) (90 nmol/rat i.t.), completely prevented the NOCI-mediated inhibition of the nociceptive responses evoked by AMPA. In conclusion, NOCI, acting at ORL1 receptors can, at least in part, induce spinal analgesia by blocking the nociceptive responses produced through the stimulation of AMPA receptors.

Nociceptive reaction and thermal hyperalgesia induced by local ET-1 in mice: a behavioral and Fos study

The peptide endothelin-1 (ET-1) has been involved in nociception independently of its vasoconstrictor effects. We have studied the direct nociceptive behavior produced by this peptide as well as its ability to induce thermal sensitisation (as measured by the unilateral hot plate method, UHP) when intraplantarly (i.pl.) administered in mice. These behavioural measures were complemented by the quantification of Fos-protein immunoreactivity in the superficial laminae of the dorsal horn spinal neurons located ipsilateral to the injected paw.ET-1 induces licking (60-600 pmol, i.pl.) and thermal hyperalgesia (20-200 pmol, i.pl.) in the injected paw, both effects being inhibited by the coadministration of ET-1 with endothelin type A (ET(A)) receptor antagonist, BQ-123 (0.3-10 nmol), but not with endothelin type B (ET(B)) receptor antagonist, BQ-788 (10 nmol). Moreover, the licking behavior induced by ET-1 was dose-dependently inhibited by the prototypical micro -opioid agonist, morphine. The prior i.pl. administration of ET-1 (200 pmol) to mice subjected to thermal heat stimulus (55+/-1 degrees C, 10 s) increases the number of Fos-immunoreactive dorsal horn spinal neurons compared with the application of noxious heat alone. This effect is inhibited by BQ-123 (10 nmol) but not by BQ-788 (10 nmol).Thus, local ET-1 induces nocifensive behavior and thermal hyperalgesia acting through ET(A) receptors. These same receptors seem to be also involved in the amplification of Fos immunoreactivity induced by ET-1 under heat stimulus in the dorsal horn neurons. These results could help to characterize the role of ET-1 in nociceptive processing, a topic of special interest due to the pathophysiological involvement of this peptide in painful states such as cancer.

Spinal nociceptin inhibits septide but not N-methyl-D-aspartate-induced nociceptive behavior in rats

Nociceptin can induce spinal analgesia in rats. Here, we tested the ability of nociceptin to inhibit the nociceptive behavior (biting, scratching, licking) induced by intrathecal administration of N-methyl-D-aspartate (4 microg) or the tachykinin NK(1) receptor agonist, septide (0.5 microg), in rats. Intrathecal nociceptin (3-30 nmol) did not modify the NMDA-induced behavior. However, coadministration of nociceptin (1-10 nmol) inhibited the septide-induced excitatory response. This inhibition was unaffected by systemic (10 mg/kg) or intrathecal (30 nmol) administration of naloxone, but intrathecal coadministration of the ORL1 (opioid receptor-like type 1) receptor antagonist [Nphe(1)]nociceptin-(1-13)-NH(2) (30-90 nmol) prevented it, suggesting the involvement of ORL1 receptors.

Unilateral hot plate test: a simple and sensitive method for detecting central and peripheral hyperalgesia in mice

The application of thermal noxious stimuli forms the basis of some widely used tests to detect either hyperalgesic or analgesic reactions. In the classical hot plate test, mice react by licking their paws and/or jumping. However, tests relying on the unilateral application of thermal radiant heat to the plantar side of the hindpaw, have become popular in recent years since unilateral changes in nociceptive sensitivity can be detected. Based on the aforementioned tests, we developed a testing procedure in mice, the unilateral hot plate (UHP): the plantar side of one hindpaw is placed on a hot plate surface and, thus, the withdrawal latency of each paw can be measured separately. The effectiveness of several analgesic and hyperalgesic drugs measured by the UHP was compared with that measured by a method based on the application of radiant heat (RH) stimuli. In the UHP method, morphine (1-10 mg/kg) increases latencies, while spinal NMDA (0.001-1 ng) or PGE2 (30-300 ng), intraplantar carrageenan (2 - 4%) or PGE2 (30-300 ng) decrease latencies. In all cases, the UHP method detected changes in pain reactivity at lower doses than the RH test. The sensitivity and usefulness of the UHP test for performing pain studies in mice is described.

Effects of the calcium release inhibitor dantrolene and the Ca2+-ATPase inhibitor thapsigargin on spinal nociception in rats

The effects produced by the intrathecal administration of dantrolene and thapsigargin, measured in several analgesic tests in the rat are described. Dantrolene decreases the release of calcium from intracellular stores and thapsigargin is able to inhibit the reticular Ca2+-ATPase, avoiding intracellular calcium storage. Dantrolene (30-300 nmol/rat) and thapsigargin (3-30 nmol/rat) reduced the nociceptive behavior (biting, scratching, licking; BSL) produced by the NK(1) receptor agonist septide (0.5 microg), without affecting the BSL induced by AMPA (2 microg) or NMDA (4 microg). Also, both drugs elicited analgesia in the tail-flick test but not in the formalin test. The antinociceptive effects induced by thapsigargin were more intense and long-lasting than those produced by dantrolene. These results seem to indicate that the intracellular modulation of calcium homeostasis could be an interesting target in order to induce spinal analgesia.

Effects of intraplantar morphine in the mouse formalin test

We studied the effects of intraplantar morphine in the formalin test in mice. Intraplantarly administered morphine (30 - 300 microg) induced analgesic effects at lower doses than intraperitoneally administered morphine. Following the administration of [3H]morphine, the % of radioactivity present in brain was the same by either route. In contrast, higher radioactivity values appeared in the injected paw in those mice intraplantarly injected. Since local morphine induces analgesia at doses lower than the intraperitoneally administered drug, especially in the second phase of the test, and the access to brain is undistinguishable, we propose that local morphine enhances central opiate analgesia in the formalin test in mice.

Intrathecal N-methyl-D-aspartate (NMDA) induces paradoxical analgesia in the tail-flick test in rats

The intrathecal (IT) administration of NMDA in rodents has usually been reported to produce hyperalgesic reactions, although some articles describe that spinal NMDA can lead to analgesia. We show here that the nociceptive behavior (biting, scratching, licking; BSL) observed after NMDA injection (1-8 microg/rat; IT) is followed by a long period of increased tail-flick latencies, not longer detected 24 h after NMDA administration. The NMDA-receptor antagonist CPP (10-100 ng/rat; IT) blocked the BSL behavior induced by NMDA. In the tail-flick test, this antagonist induced analgesia by itself, and was able, at 30 ng/rat, to prevent the NMDA-mediated analgesia. The implication of opiate mechanisms was discarded since naloxone (3 and 10 mg/kg; IP) did not antagonize NMDA-induced analgesia. Finally, the involvement of the intracellular calcium binding protein calmodulin was assessed. The calmodulin inhibitor, calmidazolium (30-300 microg/rat; IT) only blocked the excitatory effect (BSL) without modifying the tail-flick analgesia produced by NMDA (4 microg). These results show that a single intrathecal administration of NMDA sequentially induces both nociceptive and antinociceptive, nonopiate responses in rats.

Effects of DAGO on the rodent hippocampal evoked potentials using different perfusion solutions

Opioid receptor agonists exert excitatory effects in the hippocampus by inhibiting GABA release. We report that the mu-opioid agonist, DAGO, increases the amplitude of the population spikes (PS) measured in the stratum pyramidale of the CA1 cell layer in mouse and rat hippocampal slices perfused with an artificial cerebrospinal fluid (ACSF), but not when perfused in Krebs solution. The GABAA agonist, 3-APS, induces inhibitory responses when perfused in either ACSF or Krebs. Also, the field excitatory postsynaptic potentials (EPSP) measured on stratum radiatum do not differ when the slice is perfused with either ACSF or Krebs. The increase in the amplitude of the PS induced by DAGO is not obtained when perfused in a modified. ACSF whose concentration of MgSO4 was lowered to its concentration in the Krebs solution (from 2.4 mM to 1.2 mM). Thus, changes in the concentration of MgSO4 seem to be responsible for the different responses induced by DAGO.

Effects of diethylstilbestrol on mouse hippocampal evoked potentials in vitro

1. Several steroids and related compounds can bind to central opiate receptors in whole-brain mouse homogenates. Among these drugs, the synthetic estrogen, diethylstilbestrol (DES), exhibits one of the highest affinities in binding experiments labeling opiate receptors with the nonselective opiate antagonist, [3H]diprenorphine. 2. In the search for a functional correlate to this biochemical finding, we have studied the effects of DES on the mouse hippocampal slice in vitro preparation. 3. Previously, binding studies were performed in hippocampal homogenates, labeling opiate receptors with [3H]diprenorphine or with the mu-selective opiate agonist, [3H]DAGO. DES inhibited [3H]diprenorphine and [3H]DAGO binding, the IC50 values obtained being (1.03 +/- 0.16) x 10(-5) and (1 +/- 0.8) x 10(-5) M, respectively. 4. In mice hippocampal slices, we measured the extracellular evoked potentials obtained in the CA1 pyramidal cell layer of the hippocampi and the field excitatory postsynaptic potentials (EPSP) obtained in the stratum radiatum. The presence of DES (10(-5) M) induced an increase in the amplitude of the population spikes measured in the pyramidal layer without modifying the field EPSP. This effect is similar to that obtained in the presence of DAGO in this preparation. The effect produced by DES was not modified by the presence of the opiate competitive antagonist, naloxone (10(-5) M), or by the opiate alkylating agent, beta-chlornaltrexamine (10(-5) M). Conversely, in the presence of the transcription inhibitor, actinomycin D (5 micrograms/ml), the effect produced by DES was inhibited. 5. Our results with DES support the general idea that estrogens increase central excitability. Although diethylstilbestrol can bind to opiate receptors in the hippocampus, the effect induced by this estrogen on hippocampal excitability seems unrelated to a direct action on opiate receptors, and an intracellular effect is suggested.

Study of the density of opioid receptors in the male mouse brain at different stages of sexual maturation

The binding of opiate receptors was evaluated in male Swiss CD1 mice in different stages of maturation, i.e., prepubertal (7 and 20 days old), pubertal (40 days old) and postpubertal (60 days old). The opiate receptors were labeled with [3H]-diprenorphine and the KD and Bmax were measured. A similar KD (0.35-0.42 nM) value was obtained in all age groups tested indicating no changes in opiate affinity with sexual maturation. The maximal opiate binding capacity, Bmax was similar in 20- and 40-day-old mice as compared to 60-day-old mice while lower values were obtained in 7-day-old mice. These data indicate that sexual maturation does not affect the number of opiate receptors. Since different testosterone plasma levels have been described in males of this strain at the different ages included in our study, our results support previous findings showing that testosterone does not influence opiate binding sites in rodents.

Spinal effects of the calmodulin inhibitor calmidazolium on dorsal horn neurons in the rat

Drugs able to inhibit calmodulin activation can prevent some consequences of the rise in intracellular calcium. It has recently been shown that intrathecal injection of calmodulin inhibitors induce analgesia in rats. We study here the effect induced by the calmodulin inhibitor, calmidazolium, on the activity of dorsal horn neurons driven by noxious and non-noxious stimuli. Extracellular recordings of convergent (n = 12), low-threshold mechanoreceptive (n = 5) and proprioceptive (n = 5) units were made in the presence of calmidazolium. Calmidazolium (600 micrograms) reduced the noxious (50 degrees C) heat-evoked responses obtained in convergent neurons. On the contrary, the non-noxious tactile responses obtained in low-threshold mechanoreceptive neurons as well as the joint movement-evoked responses obtained in proprioceptive units remained unmodified. We conclude that calmidazolium can block nociceptive processing in the spinal cord and that this fact can help to explain the analgesic effects that intrathecal W-7 and calmidazolium induce in behavioral tests.

Comparison of the effects of calmidazolium, morphine and bupivacaine on N-methyl-D-aspartate- and septide-induced nociceptive behaviour

We have recently shown that spinal calmodulin inhibitors (W-7 and calmidazolium) dose-dependently inhibit the nociceptive reaction (biting, scratching, licking, BSL) evoked by intrathecal N-methyl-D-aspartate (NMDA) and septide, an agonist of the neurokinin (NK) NK1 receptor. To compare this effect with that induced by standard analgesics, we now report a study of the effects of calmidazolium (14420 nmol), bupivacaine (29-582 nmol) and morphine (26-260 nmol) when coadministered intrathecally with either NMDA (4 microg) or septide (0.5 microg). Calmidazolium had the highest potency for inhibiting septide-induced nociceptive behaviour, acting over a dose range of 34-130 nmol (dose eliciting a half-maximal response, ED50, 67 nmol) lower than that of bupivacaine [ED50 234 (115-475) nmol]. Only the highest dose of morphine (260 nmol) inhibited septide-evoked BSL [ED50=133 (69-255) nmol]. Higher doses of morphine could not be tested due to the appearance of an excitatory aversive reaction. Both calmidazolium [ED50=232 (138-388) nmol] and bupivacaine [ED50=123 (59-256) nmol] dose-dependently reduced NMDA-induced BSL reaching an almost maximal inhibition at the highest doses assayed (420 and 291 nmol, respectively). In contrast, morphine had less effect on NMDA-induced behaviour, inducing only a partial reduction of BSL even with the highest dose assayed (260 nmol). Overall, it can be concluded that the calmodulin inhibitor calmidazolium inhibits septide- and NMDA-evoked nociceptive behaviour with a potency and efficacy at least as high as those of morphine and bupivacaine.

Different types of steroids inhibit [3H]diprenorphine binding in mouse brain membranes

1. The binding of 60 drugs, mainly steroids, to opioid receptors was studied in crude membrane fractions from mouse brains. 2. Competition assays with the different drugs (5 x 10(-7)-10(-4)M) were performed by labeling opiate receptors with [3H]diprenorphine (0.3-0.4 nM). 3. Only 7 drugs (alpha,5beta-tetrahydrodeoxycorticosterone, megestrol acetate, mifepristone, 17alpha-ethynylestradiol, diethylstilbestrol, clomiphene citrate and tamoxifen citrate) inhibited [3H]diprenorphine binding more than 50% at the highest concentration assayed (10(-4) M). The IC50 values ranged between 6x10(-5) M. 4. Thus, the present results show that only a limited number of steroids, from diverse classes, bind to opiate receptors.

Spinal calmodulin inhibitors reduce N-methyl-D-aspartate- and septide-induced nociceptive behavior

The effect of two calmodulin inhibitors, W-7 (N-(6-aminohexyl)-5-chloro-1-naphtalenesulfonamide) and calmidazolium, on the nociceptive behavior induced by the intrathecal injection of NMDA (N-methyl-D-aspartate), AMPA (alpha-amino-3-hydroxy-5-methyl-4-iso xazolepropionic acid) or of septide is described. Lumbar intrathecal injection of NMDA, AMPA or septide induced a caudally directed nociceptive reaction (biting, scratching and licking). The nociceptive behavior induced by NMDA (4 microg) was dose dependently inhibited when W-7 (0.25-1 micromol/rat) or calmidazolium (0.12-0.5 micromol/rat) was coinjected. Biting, scratching and licking produced by AMPA (2 microg) were unaffected by intrathecal calmodulin inhibitors. Finally, septide-evoked nociceptive behavior (2 microg) was antagonized by W-7 (0.12-0.5 micromol/rat) and calmidazolium (0.06-0.25 micromol/rat). Thus, calmodulin inhibitors prevent the nociceptive reaction evoked by drugs that modify intracellular Ca2+, NMDA and septide, without affecting the nociceptive response induced by AMPA, for which Ca2+ is not the main second messenger.

Cyproterone acetate displaces opiate binding in mouse brain

Drugs acting on androgen receptors modify opioid transmission in the central nervous system. To investigate a direct interaction, we studied whether the binding of [3H]diprenorphine to mouse brain membranes was modified by cyproterone acetate (progesterone derivative with antiandrogen activity), flutamide (non-steroidal antiandrogen), 5alpha-dihydrotestosterone and progesterone. Only cyproterone acetate inhibited [3H]diprenorphine binding (IC50 = (1.62 +/- 0.33) x 10(-6) M) without modifying its association rate. These results suggest that cyproterone acetate binds to opiate receptors independently of its classical androgenic intracellular receptor effect.

Role of cyclic nucleotides in contraction induced by oxytocin in the testicular capsule of the rat in vitro

The effects of phosphodiesterase inhibitors, an activator and an inhibitor of guanylyl cyclase, and cAMP and cGMP analogs on oxytocin-induced contractions have been studied in the testicular capsule of rats. The nonspecific phosphodiesterase inhibitors, theophylline and caffeine, attenuated the oxytocin-induced contractions via mechanisms that seem to be related to an increase in cAMP levels, since a similar effect was produced by dibutyryl cAMP. Sodium nitroprusside facilitated oxytocin-induced contractions. This effect was mimicked by dibutyryl cGMP. Methylene blue, an inhibitor of soluble guanylyl cyclase, decreased oxytocin-induced contractions, which suggests an involvement of guanylyl cyclase in the oxytocin effect. These results suggest that cAMP modulates the contraction and that cGMP, contrary to what happens in most smooth muscles, could participate in oxytocin-induced contractions in the testicular capsule of rats.

Spasmolytic and calmodulin inhibitory effect of non-steroidal anti-inflammatory drugs in vitro

The effect of several anti-inflammatory drugs (NSAIDs), the calmodulin inhibitor W-7 and cortisol on vanadate-induced tonic contraction and on calmodulin dependent cAMP-phosphodiesterase activity have been assayed. Indomethacin, diclofenac, phenylbutazone, mefenamic acid, naproxen, tolmetin, piroxicam, aspirin and W-7, but not metimazol, produce dose-dependent relaxation of vanadate-induced tonic contraction on isolated rat uterus. Cortisol relaxes the vanadate contraction up to 45%. None of the drugs assayed inhibit the basal activity of phosphodiesterase with concentrations lower than 1 mM. However, indomethacin, diclofenac, phenylbutazone, mefenamic acid, naproxen, piroxicam, aspirin and W-7 inhibit, in a concentration-dependent way, the calmodulin-stimulated activity of phosphodiesterase. The maximum inhibition achieved with tolmetin (1 mM) and cortisol (1 mM) was 38% and 24%, respectively. Metamizol has no effect on basal or/and stimulated phosphodiesterase. This, as far as we know, is the first description of relationship between NSAIDs and calmodulin-dependent processes and our results suggest that the inhibition of calmodulin with NSAIDs may be directly related to their pKa and liposolubility.