Interactions between analgesics and calcium channel blockers

Nerve terminals in the tumor microenvironment as targets for local infiltration analgesia

Nerve terminals within the tumor microenvironment as potential pain-mitigating targets for local infiltration analgesia is relatively less explored. In this study, we examine the role of key analgesics administered as local infiltration analgesia in a model of cancer-induced bone pain (CIBP). CIBP was induced by administration of allogenic MRMT1 breast cancer cells in the proximal tibia of rats, and tumor mass characterized using radiogram, micro-CT, and histological analysis. In vitro responsiveness to key analgesics δ-opioid receptor agonist (DOPr), Ca2+ channel and TRPV1 antagonists was assessed using ratiometric Ca2+ imaging in sensory neurons innervating the tumor site. Effectiveness of locally infiltrated analgesics administered independently or in combination was assessed by quantifying evoked limb withdrawal thresholds at two distinct sites for up to 14 days. CIBP animals demonstrated DOPr, N-, and L-type and TRPV1 expression in lumbar dorsal root ganglion neurons (DRG), comparable to controls. Evoked Ca2+ transients in DRG neurons from CIBP animals were significantly reduced in response to treatment with compounds targeting DOPr, N-, L-type Ca2+ channels and TRPV1 proteins. Behaviourally, evoked hyperalgesia at the tumor site was strongly mitigated by peritumoral injection of the DOPr agonist and T-type calcium antagonist, via its activity on bone afferents. Results from this study suggest that nerve terminals at tumor site could be utilized as targets for specific analgesics, using local infiltration analgesia.

Resveratrol-induced antinociception is involved in calcium channels and calcium/caffeine-sensitive pools

Resveratrol has been widely investigated for its potential health properties, although little is known about its mechanism in vivo. Previous studies have indicated that resveratrol produces antinociceptive effects in mice. Calcium channels and calcium/caffeine-sensitive pools are reported to be associated with analgesic effect. The present study was to explore the involvement of Ca²⁺ channel and calcium/caffeine-sensitive pools in the antinociceptive response of resveratrol. Tail-flick test was used to assess antinociception in mice treated with resveratrol or the combinations of resveratrol with MK 801, nimodipine, CaCl₂, ryanodine and ethylene glycol tetraacetic acid (EGTA), respectively. The Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and brain-derived neurotrophic factor (BDNF) levels in the spinal cord were also investigated when treated with the above drugs. The results showed that resveratrol increased the tail flick latency in the tail-flick test, in dose-dependent manner. N-methyl-D-aspartate (NMDA) glutamate receptor antagonist MK 801 potentiated the antinociceptive effects of sub-threshold dose of resveratrol at 10 mg/kg. Ca²⁺ channel blocker, however, abolished the antinociceptive effects of resveratrol. In contrast to these results, EGTA or ryanodine treatment (i.c.v.) potentiated resveratrol-induced antinociception. There was a significant decrease in p-CaMKII and an increase in BDNF expression in the spinal cord when combined with MK 801, nimodipine, ryanodine and EGTA. While an increase in p-CaMKII level and a decrease in BDNF expression were observed when high dose of resveratrol combined with CaCl₂. These findings suggest that resveratrol exhibits the antinociceptive effects by inhibition of calcium channels and calcium/caffeine-sensitive pools.

Buspirone-induced antinociception is mediated by L-type calcium channels and calcium/caffeine-sensitive pools in mice

RATIONALE

Previous studies have shown that buspirone, a partial 5-HT(1A) receptor agonist, produces antinociceptive effects in rats and mice; Ca(2+) plays a critical role as a second messenger in mediating nociceptive transmission. 5-HT(1A) receptors have been proven to be coupled functionally with various types of Ca(2+) channels in neurons, including N-, P/Q-, T-, or L-type. It was of interest to investigate the involvement of extracellular/intracellular Ca(2+) in buspirone-induced antinociception.

OBJECTIVES

To determine whether central serotonergic pathways participate in the antinociceptive processes of buspirone, and investigate the involvement of Ca(2+) mechanisms, particularly L-voltage-gated Ca(2+) channels and Ca(2+)/caffeine-sensitive pools, in buspirone-induced antinociception.

METHODS

Antinociception was assessed using the hot-plate test (55 degrees C, hind-paw licking latency) in mice treated with either buspirone (1.25-20 mg/kg i.p.) alone or the combination of buspirone and fluoxetine (2.5-10 mg/kg i.p.), 5-HTP (25 mg/kg i.p.), nimodipine (2.5-10 mg/kg i.p.), nifedipine (2.5-10 mg/kg i.p.), CaCl(2) (25-200 nmol per mouse i.c.v.), EGTA (5-30 nmol per mouse i.c.v.), or ryanodine (0.25-2 nmol per mouse i.c.v.).

RESULTS

Buspirone dose dependently increased the licking latency in the hot-plate test in mice. This effect of buspirone was enhanced by fluoxetine, 5-HTP, nimodipine, and nifedipine. Interestingly, central administration of Ca(2+) reversed the antinociceptive effects of buspirone. In contrast to these, ryanodine or EGTA administered centrally potentiated buspirone-induced antinociception.

CONCLUSIONS

Decreasing neuronal Ca(2+) levels potentiated buspirone-induced antinociception; conversely, increasing intracellular Ca(2+) abolished the antinociceptive effects of buspirone. These results suggest that Ca(2+) influx from extracellular fluid and release of Ca(2+) from Ca(2+)/caffeine-sensitive microsomal pools may be involved in buspirone-induced antinociception.

Role of L-type Ca(2+) channels in pertussis toxin induced antagonism of U50,488H analgesia and hypothermia

Previous studies have shown that the kappa-opioid effects are sensitive to pertussis toxin (PTX) and affected by Ca(2+) fluxes. However, the possible involvement of Ca(2+) channels in PTX-induced inhibition of kappa-opioid effects has not been reported. The effect of intracerebroventricular (i.c.v.) treatment of pertussis toxin (1 microg/rat, PTX) or saline on the kappa-opioid agonist, U-50,488H (U5H) induced tail-flick analgesia and hypothermia in rats was determined. The effect of nimodipine (NIM), a dihydropyridine (DHP)-sensitive Ca(2+) channel blocker (CCB), on PTX-induced modulation of U5H effects was examined. The DHP ligand, [3H]PN200-110 binding was also determined in both PTX and saline treated rats to study the possible involvement of L-type Ca(2+) channels in PTX modulation of kappa-opioid agonist effects. The analgesia and change in colonic temperature were determined using tail-flick analgesiometer and telethermometer, respectively. U5H (40 mg/kg, i.p.) produced significant analgesic and hypothermic responses. PTX treatment significantly (P<0.01) antagonized the analgesic and hypothermic effects of U5H. Acute pretreatment of NIM (1 mg/kg, i.p.) 15 min prior significantly (P<0.01) reversed the PTX-induced antagonism of U5H effects. In the binding study, PTX treatment (72 h before) resulted in a significant (P<0.005) upregulation (+45% vs. saline control) of DHP binding (B(max)) with no change in affinity (K(d)). The results showed significant upregulation of DHP binding in accordance with PTX-induced antagonism of U5H effects and this blockade was reversed by NIM. Thus, present results suggest that U5H-induced analgesia and hypothermia may be mediated through PTX-sensitive transducer G-proteins (G(i/o)) coupled to L-type Ca(2+) channels.

L-type Ca2+ channel modulation by dihydropyridines potentiates kappa-opioid receptor agonist induced acute analgesia and inhibits development of tolerance in rats

The effect of 1,4-dihydropyridine (DHP) calcium channel blockers (CCBs), nimodipine (NIM) and lercanidipine (LDP) on the analgesic response of selective kappa-opioid receptor agonists, U50,488H, PD117,302 and U69,593 was determined in male Sprague-Dawley rats using the tail-flick test. The effect of NIM on development of tolerance to U50,488H-induced analgesia and the status of brain DHP-sensitive Ca(2+) channel (L-type) binding sites in both U50,488H-naive and tolerant rats was determined using the highly selective DHP radioligand, [(3)H]PN200-110. Tolerance was induced by injecting U50,488H (25 mg/kg, i.p.) twice daily for 4 days. Intraperitoneal (i.p.) injection of kappa-opioid receptor agonists produced a dose-dependent acute analgesic response. NIM (1 mg/kg; i.p.) and LDP (0.3 mg/kg; i.p.) used in the study produced no tail-flick analgesia. Administration of NIM and LDP (15 min prior) significantly potentiated the analgesia produced by three kappa-opioid receptor agonists. Tolerance developed completely to the analgesic effect induced by U50,488H (25 mg/kg, i.p.) administered on the 5th day. NIM (1 mg/kg, i.p.) twice daily for 4 days not only completely inhibited the development of tolerance to analgesic response but also significantly potentiated it (supersensitivity). There was a significant up-regulation of DHP binding sites (B(max): +41%) in whole brain membranes of tolerant rats when compared to vehicle treated naive rats, implicating increased influx of Ca(2+) through L-type channels in kappa-opioid tolerance. U50,488H (25 mg/kg, i.p.) and NIM (1 mg/kg, i.p.) twice daily for 4 days also resulted in an equivalent up-regulation of DHP binding sites (+36%) as that of U50,488H alone. These results strongly suggest a functional role of L-type Ca(2+) channels in the regulation of pain sensitivity, mechanism of kappa-opioid analgesia and expression of tolerance.

L-type and T-type calcium channel blockade potentiate the analgesic effects of morphine and selective mu opioid agonist, but not to selective delta and kappa agonist at the level of the spinal cord in mice

We examined the effects of amlodipine, a selective L-type voltage dependent Ca(2+) channel (VDCC) blocker, and mibefradil, a selective T-type VDCC blocker on the antinociceptive effects of morphine, and mu, delta and kappa opioid receptor selective agonist-induced antinociception at the spinal level. Intrathecally administered amlodipine and mibefradil potentiated morphine and [D-Ala(2), N mePhe(4), Gly-ol(5)] enkephalin (DAMGO)-induced antinociception by shifting their dose response curves to the left. However, intrathecally administered amlodipine and mibefradil did not affect [D-Pen(2), D-Pen(5)]enkephalin (DPDPE) and [trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrolidinyl)cyclohexyl] benzene acetamide (U-50, 488H)-induced antinociception. These data indicate that L-type and T-type VDCC blockers synergistically potentiate the analgesic effects of mu opioid receptor agonists, but not delta and kappa opioid receptor agonists, at the spinal level. Additionally, these data suggest that there is an important functional interaction between L-type and/ or T-type VDCC and mu opioid receptors in the process of analgesia.

The influence of divalent cations on the analgesic effect of opioid and non-opioid drugs

It is generally accepted that divalent cations are involved in the nociceptive pathway. The effect of systemic co-administration of magnesium sulfate and calcium channel blockers (nifedipine, verapamil) on the analgesic effect of opioid (mixed mu/kappa: butorphanol) and non-opioid drugs (paracetamol) was investigated. Albino mice and rats were used as experimental animals. Magnesium sulfate and calcium channel blockers were given i.p., 30 min before the administration of butorphanol tartrate and paracetamol. Analgesia was measured using "hot-plate" ( 52.5( composite function)C), "tail-flick" (radiant heat source), "writhing" (acetic acid, 1%, i.p.) and "tail-clip" tests. The pain threshold was evaluated before and after the administration (i.p.) of the different agents. The effect of the combined administration of different agents on behavior, blood pressure and heart rate, was also determined. Nifedipine (5 mg kg(-1), i.p.) and verapamil (10 mg kg(-1), i.p.) potentiated the analgesic effect of butorphanol tartrate (0.25-2 mg kg(-1), i.p.) in all tests (synergism) and enhanced analgesic effect of paracetamol (50-125 mg kg(-1), i.p.), only in acetic acid writhing and tail-clip tests. Magensium sulfate (2.5 mg kg(-1), i.p.) potentiated the analgesic effect of butorphanol, but not that of paracetamol. Co-administration of nifedipine and verapamil with either of butorphanol (0.25-2 mg kg(-1)) or paracetamol (50-125 mg kg(-1), i.p.) produced no significant effects on motor coordination, motor performance, locomotor activity, long-term memory or on the blood pressure and heart rate of experimental animals. Co-administration of magnesium sulfate, however, significantly induced sedation, inhibition of locomotor activity, motor performance and coordination, as well as impairing of long-term memory, as compared with butorphanol and paracetamol, administered alone. We conclude that the systemic co-administration of calcium channel blockers potentiated the analgesic effect of butorphanol against thermal, mechanical and chemical pain but enhanced that of paracetamol only against mechanical and chemical pain. Magensium sulfate enhanced the analgesic effect of butorphanol, but not that of paracetamol. These findings, merit further studies in animals and humans to evaluate the potential therapeutic benefits of such interactions.

Effects of morphine in rats withdrawn from repeated nifedipine administration

The effects of withdrawal from repeated nifedipine treatment on morphine-induced analgesia, hyperthermia and catalepsy as well as on cerebral [3H]nitrendipine binding and on morphine-induced changes in striatal and limbic dopamine and 5-hydroxytryptamine metabolism were studied in rats. Repeated administration of nifedipine (5 mg/kg i.p., twice daily for 14 days) decreased [3H]nitrendipine binding in several brain areas of the rats at 24 h after the last dose but did not change the nociceptive response or rectal temperature of the animals. Further, the antinociceptive potency of acute morphine (2.5 mg/kg s.c.) was significantly reduced in rats withdrawn for 24 h from repeated nifedipine treatment. However, withdrawal from repeated nifedipine treatment failed to affect either the hyperthermia induced by this dose of morphine or the catalepsy and the elevation of dopamine or 5-hydroxytryptamine metabolites induced by 15 mg/kg of morphine. Taken together, these data show that withdrawal from repeated treatment with dihydropyridine calcium channel antagonists selectively reduces the effects of opioids on the nociceptive response.

Effects of intrathecally administered aminoglycoside antibiotics, calcium-channel blockers, nickel and calcium on acetic acid-induced writhing test in mice

1. Antinociceptive effects of intrathecally administered aminoglycoside antibiotics, calcium-channel blockers, nickel and calcium ions on the acetic acid-induced writhing test in mice were examined. 2. Neomycin (0.5-20.0 micrograms/mouse) gentamicin (5-40 micrograms/mouse), nicardipine, diltiazem and verapamil (0.5-80.0 micrograms/mouse) and calcium ions (0.02-1.0 mumol/mouse) exerted a dose-dependent antinociceptive activity on the acetic acid-induced writhing test. Nickel ions (2.5, 5.0 and 10.0 mumol/mouse) were found ineffective in this test. 3. These results suggest that N- and L-type, but not T-type, voltage-dependent calcium channels are implicated in the spinal processing of nociceptive information.

Analgesic effects of amlodipine and its interaction with morphine and ketorolac-induced analgesia

1. The antinociceptive effects of amlodipine, administered subcutaneously (s.c.), intracerebroventricularly (i.c.v.) and intrathecally (i.t.) were examined with the acetic acid writhing and tail-flick tests in mice. Amlodipine was also tested in combination with morphine and ketorolac. Isobolographic analyses were used to define the nature of functional interactions between amlodipine and morphine or ketorolac. 2. The s.c. (0.1, 1.25, 2.5, 5 and 10 mg/kg), i.c.v. (2.5, 5, 10 and 20 micrograms/mice) and i.t. (2.5, 5, 10 and 20 micrograms/mice) administration of amlodipine exhibited a dose-dependent antinociceptive effect in the writhing test but had no effect on the tail-flick latency. Isobolographic analyses revealed an additive interaction between amlodipine and morphine or ketorolac in the writhing test. 3. These results suggest that amlodipine induces antinociception and increases antinociceptive action of morphine and ketorolac, possibly through a decrease in cellular calcium availability.

Antinociceptive effect of nifedipine and verapamil tested on rats chronically exposed to nicotine and after its withdrawal

Antinociceptive effect of nifedipine (15 mg/kg i.p.) and verapamil (10 mg/kg s.c.) was examined in rats chronically exposed to nicotine (6 mg/kg/day via Alzet osmotic pump for 28 days) and after nicotine withdrawal. Sham operated rats served as control for testing DMSO (dimethylsulfoxide, a solvent for nifedipine), nifedipine and verapamil alone. Nociception was measured by the tail-flick technique. Nifedipine, but not verapamil, injected to control rats produced a ceiling tail-flick latency (20 sec) 30 min after the injection, lasting for 10 min. In rats exposed to chronic nicotine for 3 days, nifedipine treatment exhibited ceiling tail-flick latency within 10 min lasting for 80 min. Tested in rats exposed to nicotine for 3 weeks, nifedipine treatment produced this effect 25 min after the injection lasting for 60 min. Nicotine withdrawal abolished this effect. Verapamil did not exhibit any significant changes in tail-flick latencies. These data support our hypothesis that smoking patients treated with nifedipine could be at a potential risk in developing a high pain threshold and missing the first sign of heart attack--a chest pain.

Vasorelaxant effect of the analgesic clonixin on rat aorta

1. A novel vasorelaxant effect of clonixinate of L-lysine (Clx), analgesic and anti-inflammatory, was studied in rat aortic rings. 2. Clx completely relaxed aortic rings contracted by KCl 70 mM and together with its analog flunixin exhibited lesser potency but equal efficacy than verapamil. In comparison, indomethacin, which is a more potent cyclo-oxygenase inhibitor relaxed only about 40% of the maximal contraction of aortic rings. 3. Furthermore, Clx antagonized Ca2+ dependent aortic contraction and BAY K-8644 induced aortic contraction suggesting its calcium antagonist character. 4. From these results it can be concluded that the hypotensive effect seen in rats in vivo after Clx i.v. injection arises because of vasodilatory effect of Clx and gives further support to the proposal that the pharmacological mechanism of action of Clx should be calcium antagonism.

The effect of nifedipine and verapamil on nicotine-induced antinociception in rats

We examined the modulatory effect of nifedipine (NIF, 0.04, 2, 5 and 15 mg/kg i.p.) and verapamil (VER, 2.5 and 10 mg/kg s.c.) on nicotine-induced antinociception in male rats, employing the tail-flick (TF) test. All rats were divided according to their responses to nicotine (1 mg/kg s.c.) alone, and classified as responders and nonresponders; both types were used. Both tested drugs were injected simultaneously with nicotine (NIC). In responders, NIC (1 mg/kg s.c.) alone produced a ceiling TF latency (15 sec) within 2.5 min lasting for 2.5 - 7.5 min. NIF, at the dose of 15 mg/kg i.p., prolonged this effect up to 40-50 min. Lower doses (5, 2 and 0.04 mg/kg) were not effective. VER in either dose did not prolong NIC-induced antinociception. In nonresponders, NIF also potentiated NIC-induced antinociception, and this effect appeared to be dose-related, lasting from 10 up to 40 min. VER was ineffective in either dose. These data support our hypothesis that calcium is involved, at least in part, in nicotine-induced antinociception. The potential risk for smoking patients treated with NIF is discussed.

Calcium channel modulators modify K opioid-induced inhibition of C-fiber-evoked spinal reflexes in rat

The role of L-type Ca2+ channels on the kappa opioid-induced depression of spinal afferent transmission was assessed in spinalized rats, through recording of the C-fiber-evoked spinal flexor reflex. Six successive i.t. doses of the K agonist U-50,488H produced a dose-dependent decrease of the C-reflex duration (ID50: 25.7 nmol), the log dose-response relationship being shifted to left by pretreatment with 5 mg/kg i.v. of the calcium channel blocker verapamil, or to right by pretreatment with .25 mg/kg i.v. of the calcium channel agonist Bay K8644. Verapamil and Bay K8644, administered i.v. after U-50,488H i.t., respectively potentiated or antagonized the depressor effect of the K ligand on the reflex. The results point to a role for Ca2+ availability as a factor involved in depression of afferent nociceptive transmission by K opioids at the spinal cord.

Effects of flunixin and mefenamic acid on cardiac pacemaker cells. Structure-activity relationship and comparison with clonixin

1. The electrophysiological effects of flunixin and mefenamic acid, non-steroidal analgesics, on frog cardiac pacemaker cells, were studied by intracellular action potential recording. 2. Results show that flunixin (Flx) between 2 x 10(-6) and 1 x 10(-4) M, exerts a frequency, OS, APA and Vmax concentration-dependent decrease, similar to the effects of clonixin (Clx) reported elsewhere (Morales et al., Gen. Pharmac. 23, 515-521, 1992). 3. At 2.5 x 10(-4) M, Flx induces a complete cessation of the electrical activity of subsidiary pacemaker cells. 4. Mefenamic acid (Mef), in spite of its structural similarity with Clx and Flx, induces no appreciable electrophysiological changes. 5. Flx effects were partially reversed by increasing external calcium concentration and fully antagonized by BAY K-8644, a calcium L-type channel agonist. 6. By comparing the structures of the three fenamates studied, it is suggested that the nitrogen of the heterocycle and the electron-donor capacity of the bencenic ring are essential features for the calcium-antagonist activity of Clx and Flx.

Modulation of nicotine-induced analgesia by calcium agonist and antagonist in adult rats

The involvement of calcium in nicotine-induced analgesia in male rats was explored using the tail-flick test. A single dose of nicotine (1 mg/kg SC) produced a maximal effect on tail-flick latency (15 s) within 8-10 min, which lasted for 4 min. Pretreatment with the calcium chelator, EDTA (250 microM/kg SC four injections at 15 min intervals), before the single dose of nicotine accelerated the onset and prolonged the duration of the nicotine-induced analgesia. The maximal effect on tail-flick latency occurred within 2 min and lasted for 10-20 min. Conversely, pretreatment with calcium chloride (1.5 mM/kg IP) attenuated nicotine-induced analgesia. It is suggested that nicotine may exert its antinociceptive effects via modulation of calcium fluxes across the neural membrane.

Intake of sweet water attenuates restraint-stress-induced potentiation of morphine analgesia in rats

The analgesia induced in rats by morphine is potentiated by restraint-stress exposure and is reduced in rats that have been consuming a sweet solution. The purpose of the present study was to determine whether the potentiation of morphine-induced analgesia following restraint immobilization would be attenuated in rats consuming a sweet solution. Groups of rats were maintained on unsweetened water or allowed 2 h of daily access to a solution of saccharin and glucose (SG). Half of the rats in each of these groups were subjected to 1 h of restraint stress (groups RS and RS+SG) and the other half in each group were not stressed (groups NS and NS+SG). Rats then underwent 1 h of RS treatment or were nonstressed (NS). The next day all rats were injected subcutaneously with morphine (0.0, 4.0, 8.0, or 16 mg/kg) and analgesia was assessed using the tail flick assay. ED50S (mg/kg) were calculated for each treatment group; NS = 5.8, RS = 1.6, NS+SG = 6.4, and RS+SG = 4.4. Our results demonstrate that RS potentiated morphine-induced analgesia in rats given access to SG as well as non-SG exposed rats that displayed ED50S 1.5 and 3.9 times lower than their respective controls. RS-treated rats that consumed SG solution had significantly lower tail flick latencies than did non-SG exposed rats. Additionally, tail flick latencies of rats in the nonstressed and NS+SG groups did not significantly differ. We conclude that the brain mechanism(s) responsible for RS-induced potentiation of morphine antinociception are attenuated by intake of a sweet solution.(ABSTRACT TRUNCATED AT 250 WORDS)

Antinociceptive effects of Ca2+ channel blockers

The antinociceptive action of four Ca2+ channel blockers, nifedipine, nimodipine, verapamil and diltiazem, was evaluated and compared to that of morphine using three algesiometric tests in mice and rats, namely, formalin, writhing and modified hot-plate test. Dose-response curves for all the drugs tested were similar and a significant dose-dependent antinociceptive action was evident in the formalin and writhing tests. However, in the hot-plate test, only nimodipine exhibited a significant analgesic effect, confirming the misleading results previously reported for this test. The findings suggest a pharmacological role of Ca2+ channel blockers in the modulation of antinociception under acute conditions. The analgesic action of Ca2+ channel blockers could be mediated by an increase in the nociceptive threshold resulting from interference with Ca2+ influx at opioid receptors, because Ca2+ influx is critical for the release of neurotransmitters and other substances implicated in nociception and inflammation. It is suggested that if a substance has a Ca2+ channel blocking effect, it should probably have some antinociceptive properties.

Opioid receptors and their pharmacological profiles

Opioid receptors can be divided into three major classes, which are called mu, delta and kappa-receptors. The molecular basis of the receptors is discussed and a hypothesis of the binding of bivalent ligands to the receptor is presented. Furthermore the mechanism of action, the distribution and the probable function of these classes is overviewed. Increasing evidence is accumulating that the classical binding model cannot explain completely the interaction of opioids with their receptors. In addition to the mu-receptors, high affinity mu 1 binding sites have been demonstrated. Similarly, the delta receptors may be divided in delta 1 and delta 2. The significance of these subclasses is not yet fully understood. The high affinity mu 1-binding sites, however, represent probably an activated receptor complex, e.g. the complex between the receptor and the guanine-nucleotide-binding protein.

Psychopharmacological properties of calcium channel inhibitors

The previous decade has witnessed a major expansion of knowledge of the role played by voltage-sensitive calcium channels in the function of the central nervous system. Significant progress in the field has been made possible with the broadening use of organic calcium channel inhibitors (CCIs, Ca2+ antagonists), until recently considered almost exclusively as peripherally active antianginal and antiarrhythmic drugs. CCIs, however, do penetrate the blood-brain barrier from the periphery. Autoradiographic studies have established a highly heterogeneous distribution of CCI recognition sites within the brain. The existing evidence suggests that CCIs have marked psychotropic properties. The profile of their central activity is unique and spans a wide range of effects. Nevertheless, question regarding potentially confounding potent peripheral effects of these drugs remain. This paper reviews the psychopharmacology of CCIs, concentrating on preclinical data, but including supportive clinical and biochemical evidence as well. It focuses on these drugs' antidepressant, antidopaminergic (neuroleptic-like), anxiolytic and anticonvulsant effects. CCIs may also modify the reinforcing properties of some addictive drugs.

Salmon calcitonin-induced modulation of free intracellular calcium

Salmon calcitonin (sCT), a hormone shown to modulate calcium in the periphery modulated free, intracellular calcium, ([Ca++]i), in mouse brain synaptosomes as measured by changes in fura-2-mediated fluorescence. A 5-min incubation of synaptosomes with sCT produced an increase in the basal levels of [Ca++]i and an increase in KCl-stimulated levels of [Ca++]i. A 5-min pretreatment of mice with intraventricularly administered sCT antagonized morphine-induced antinociception in the tail-flick test, and facilitated naloxone antagonism of morphine. Conversely, pretreatment of synaptosomes for 1 h with salmon CT produced a decrease in depolarization-stimulated levels of [Ca++]i. The sCT-induced decrease in the stimulated rise in [Ca++]i at 1 h correlated temporally to sCT-induced antinociception in vivo. The effects of sCT in the electrically stimulated guinea pig ileum bioassay appeared to correlate to sCT effects in vivo. The data indicate that calcitonin may function as a neuromodulator via modulation of Ca++ within the central nervous system.

Evidence that the action of clonixin is non-dependent of ACh release

1. The present study was designed to verify the ACh-mediated role in the action of ClX using cardiovascular and non-cardiovascular tissues taken from rats. 2. In the vasa deferentia preparations the muscular twitch induced by TNS was not changed by atropine, however in the presence of this drug, ClX induced a significant reduction of the height of the TNS-evoked twitch. 3. In the cardiorespiratory experiments, the administration of ClX produced a dose-dependent decrease in MAP, HR and RF. These effects were not changed by bilateral vagotomy and cervical sympathectomy. 4. The results obtained with atropine and with bilateral vagotomy and sympathectomy, attempt to delineate the possibility of a direct action of ClX. 5. All the evidence taken together does not support the hypothesis that ClX may be acting through an indirect action by releasing ACh.