Central immune overactivation in the presence of reduced plasma corticosterone contributes to swim stress-induced hyperalgesia.

Although it is widely known that immunological, hormonal and nociceptive mechanisms are altered by exposure to repeated stress, the interplaying roles of each function in the development of post-stress hyperalgesia are not completely clear. Thus, we wanted to establish how interleukin 1-beta (IL-1ß), corticosterone and microglia interact to contribute in the development of hyperalgesia following repeated forced swim. Rats were subjected to either forced swim, sham swim or non-conditioned. Each group was then treated with minocycline, ketoconazole, or saline. Thermal nociception was measured via the hot plate test, before and after the behavioral conditioning, whereas blood and lumbar spinal cord tissue samples were obtained at the end of the protocol. Serum levels of corticosterone, spinal tissue concentration of IL-1ß and spinal OX-42 labeling (microglial marker) were determined. Rats exposed to forced swim stress developed thermal hyperalgesia along with elevated spinal tissue IL-1ß, increased OX-42 labeling and relatively diminished serum corticosterone. Pre-treatment with minocycline and ketoconazole prevented the development of thermal hyperalgesia and the increase in IL-1ß, without significantly modifying serum corticosterone. These results suggest that the development of forced swim-induced thermal hyperalgesia requires the simultaneous presence of increased spinal IL-1ß, microglial activation, and relatively decreased serum corticosterone.

Lack of correlation between the central anti-nociceptive and peripheral anti-inflammatory effects of selective COX-2 inhibitor parecoxib.

Non-steroidal anti-inflammatory drugs (NSAIDs) are thought to exert their pharmacological actions by a common mechanism: inhibition of cyclooxygenase (COX)-mediated prostanoid synthesis. Yet, differences and dissociation between their analgesic and anti-inflammatory effects have not been related to this enzymatic mechanism but mainly to pharmacokinetic factors. Thus, we have compared the effects of an equieffective anti-inflammatory dose (6 mg/kg i.p.) of two NSAIDs with comparable spinal pharmacokinetics, ketoprofen (moderately preferential for COX-1) and parecoxib (selective COX-2), on the activation of spinal nociceptive neurons (measured as c-Fos expression) induced by carrageenan-induced acute inflammation in the rat paw. Both NSAIDs showed a similar anti-inflammatory effect when administered after carrageenan injection (post-treatment). Post-treatment with ketoprofen produced inhibition of c-Fos but parecoxib did not have any significant effect. In addition, parecoxib anti-inflammatory effect was greater than that of ketoprofen, when administered before carrageenan injection (pre-treatment). Paradoxically, pre-treatment with ketoprofen produced a greater inhibition of c-Fos expression than with parecoxib, in all lamina of ipsilateral dorsal horn of the lumbar spinal cord. This suggests that NSAIDs therapeutic profile is related to their selectivity for COX isoforms and COX-2 is involved in the initiation but not in the maintenance of nociceptive spinal activation, which depends on COX-1.

Antinociceptive activity of Syzygium jambos leaves extract on rats.

Syzygium jambos (L.) Alston (Myrtaceae) (syn Eugenia jambos) is a widespread medicinal plant traditionally used in sub-Saharan Africa to treat several diseases. The analgesic potential of leaf hydro-alcoholic extracts was assessed in rats. Hot plate and formalin tests were used to estimate cutaneous nociception whereas measurements of forelimb grip force were done to assess muscular nociception under normal and inflammatory conditions. In the hot plate test, Syzygium jambos extract produced a significant increase in the withdrawal response latencies in a dose-dependant manner (10-300 mg/kg i.p.) and with a maximal effect (analgesic efficacy) similar to that of morphine. The extract (100-300 mg/kg i.p.) significantly reduced pain scores in all the phases of the formalin test with an analgesic efficacy higher than that shown by diclofenac. Although the extract (300 mg/kg) did not alter grip force in intact rats, it reversed the reduction in grip force induced by bilateral injection carrageenan in the forelimb triceps. This analgesic effect of the extract on muscle hyperalgesia was not antagonized, but enhanced, by naloxone. Thus, the Syzygium jambos extract has remarkable analgesic effects on both cutaneous and deep muscle pain that is not mediated by opioid receptors.

Perfil dopaminérgico del compuesto 2-aminoindano N-aralquil sustituido / Profile dopaminergic of the compound 2-aminoindane substituted N-araquil

El sistema dopaminergico central está implicado en las diversas etiologías que involucran a patologías neuropsiquiátricas, tales como la enfermedad de Parkinson, la depresión y la esquizofrenia. Son numerosas las drogas dopaminérgicas utilizadas en el tratamiento de esas dolencias, sin embargo estas terapias causan serios efectos adversos. En este contexto, la génesis de nuevos y más eficientes agentes dopaminergicos, representa un vasto campo de investigación. En el presente trabajo se sintetizó el compuesto 3, concebido como un ligando dopaminérgico, y se evaluó el perfil de su acción dopaminérgica mediante administración central del compuesto y la determinanción de parámetros conductuales como el comportameinto estereotipado (roer) y la medición de la respuesta renal en ratas. Los resultados de la evaluación farmacológica muestran que el compuesto 3 bloquea significativamente la estereotipia inducida por apomorfina, e inhibe la diuresis y natriuresis inducida por la administración central de dopamina. Estos hallazgos sugieren que el compuesto 3 se comporta como un antagonista dopaminérgico, frente a la respuesta tanto conductuales como renales

Increased perception of post-ischemic paresthesias in depressed subjects.

A psychophysical assessment of sensory activity linked to unmyelinated and myelinated primary afferents was conducted by estimating the intensity of thermal and tactile post-ischemic paresthesias in 11 nontreated depressed subjects (Zung's index > or =50) and 19 controls. Blood flow in the dominant forearm was arrested until ischemic pain tolerance was reached. Ischemic pain and post-ischemic paresthesias were numerically rated. The duration of blood flow occlusion to the time of ischemic pain tolerance was similar in both groups. Thermal (warm/cool) and tactile (tingling) paresthesias were 96% and 57% more intense in depressed than in control subjects, respectively. Zung's depression scores were positively correlated with the tingling and thermal paresthesias. Ischemic pain intensity correlated positively with thermal paresthesias. These findings suggest that depression is associated with enhanced sensory paresthesias that are known to be predominately linked to unmyelinated afferent activity.

Substance P and calcitonin gene-related peptide increase IL-1 beta, IL-6 and TNF alpha secretion from human peripheral blood mononuclear cells.

We found that substance P (SP) and calcitonin gene-related peptide (CGRP) (0.3-1 microM) increased, in a concentration-dependent manner, the basal secretion of interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF alpha) from cultured lymphocyte-enriched mononuclear cells isolated from human peripheral blood. SP and CGRP (0.1 microM) synergistically increased basal TNF alpha secretion. Dynorphin A((1-17)) (0.1-1 microM) did not modify basal cytokine secretion. Lipopolysaccharide (10 ng/ml)-induced cytokine secretion and [(3)H]thymidine uptake were not altered by any neuropeptide (at 0.1 microM). Thus, SP and CGRP stimulate the production of pro-inflammatory cytokines from lymphocytes only at high concentrations, similar to those reached during tissue damage.

Long-lasting delayed hyperalgesia after subchronic swim stress.

Rats subjected to an inescapable subchronic stress, consisting of 10-20 min of forced swimming for 3 days, showed a thermal hyperalgesia and an enhanced nociceptive behavior to the subcutaneous administration of formalin 24 and 48 h, respectively, after the last swim session. Hyperalgesia to thermal and chemical stimulants was still present 8 and 9 days after the last swim session, respectively. Chemical, but not thermal, nociception was negatively correlated with the swim effort or struggle times during the last swim session. The serotonin-selective reuptake inhibitors clomipramine (2.5 mg/kg/day, i.p., started 3 or 7 days before stress) and fluoxetine (0.25 mg/kg/day, i.p., started 7 days before stress), or serotonin precursor tryptophan (3 mg/kg/day, i.p., 24 h before each swim stress) blocked the development of both the thermal and the chemical hyperalgesia and increased swim effort times compared to vehicle-treated rats. These treatments did not affect nociceptive responses in control rats subjected to sham swimming. These findings suggest that repeated stress can produce a long-lasting increase in pain sensitivity to both phasic or tonic noxious stimuli by diminishing central serotonin activity. This model may help elucidate the underlying neural mechanisms that mediate the effects of repeated stress on pain sensitivity and affective states.

Chemical composition and biological activity of extracts from arrabidaea bilabiata.

Consumption of Arrabidaea bilabiata fresh leaves produces a paraplegic syndrome in cattle. For isolation of the active principle, isopropanol and methanol extracts were prepared from the aerial parts of the plant; these were administered to Sprague-Dawley rats at doses of 0.5, 1, and 2 mg/kg, orally, to determine the presence of substances affecting spontaneous motor activity. The isopropanol extract produced significant increases of long-pause and short-pause movements (112 and 54%, respectively). The methanol extract tended to increase motor activity, but the effect did not reach statistical significance. Chemical and spectroscopic analysis of the isopropanol extract showed allantoin was the major constituent. It was administered to rats, at doses of 1.2, 12, and 120 mg/kg. A complex dose-response curve was observed, but at the highest dose, there was a 52% increase in the number of long-pause movements. It was inferred that allantoin and the constituents of the alcholic extracts might not be responsible for the paraplegic synndrome in cattle. The alteration of cattle motor activity could be caused by other non-alcoholic constituents. Additionally, extracts were assayed for in vitro activity against Escherichia coli , Klebsiella pneumonae , Pseudomonas aeruginosa , Staphylococcus aureus , Bacillus sp. and Candida albicans . All microbial strains were found to be resistant to the extracts with the exception of C. albicans , suggesting a possible antifungal activity.

Opposite modulation of capsaicin-evoked substance P release by glutamate receptors.

Substance P and glutamate are present in primary afferent C-fibers and play important roles in persistent inflammatory and neuropathic pain. In the present study, we have examined whether activation of different glutamate receptor subtypes modulates the release of substance P evoked by the C-fiber selective stimulant capsaicin (1 microM) from rat trigeminal nucleus slices. The selective NMDA glutamate receptor agonist L-CCG-IV (1-10 microM) enhanced capsaicin-evoked substance P release about 100%. This facilitatory effect was blocked by 0.3 microM MK-801, a selective NMDA receptor antagonist. The metabotropic glutamate receptor agonists L-AP4 (group III) and DHPG (group I) (30-100 microM) inhibited capsaicin-evoked substance P release by approximately 60%. These inhibitory effects were blocked by the selective metabotropic glutamate receptor antagonist (+/-)-MCPG (5 microM). On the other hand, AMPA and kainate (0.1-10 microM), did not significantly affect capsaicin-evoked substance P release. Thus, substance P release from non-myelinated primary afferents, and possibly nociception, may be under the functional antagonistic control of some metabotropic and ionotropic glutamate receptor subtypes.

Multiphasic morphine modulation of substance P release from capsaicin-sensitive primary afferent fibers.

Morphine produces a multiphasic modulation of K+-evoked substance P release from trigeminal slices and dorsal root ganglion neurons in culture. We now found that the C-fiber stimulant, capsaicin (1 microM), evoked release of substance P that was inhibited, enhanced and inhibited by 0.1 nM, 1 microM, and 10 microM morphine, respectively. This morphine's multiphasic effect was blocked by naloxone (100 nM). Neonatal treatment with capsaicin produced thermal hypoalgesia and abolished the multiphasic effect of morphine on substance P release evoked by 50 mM K+. These findings suggest that the multiphasic modulation of substance P release by morphine is dependent on C-type afferents and may be of relevance to nociception.

Dynorphin A increases substance P release from trigeminal primary afferent C-fibers.

Dynorphin A-(1-17) has been found to produce spinal antianalgesia and allodynia. Thus, we studied whether dynorphin A-(1-17) modulates substance P release evoked by the C-fiber-selective stimulant capsaicin (1 microM) from trigeminal nucleus caudalis slices. Very low concentrations of dynorphin A-(1-17) (0.01-0.1 nM) strongly facilitated capsaicin-evoked substance P release. This dynorphin A-(1-17) effect was not blocked by the opioid receptor antagonists naloxone (100 nM), beta-funaltrexamine (20 nM), naloxonazine (1 nM), nor-binaltorphimine (3 nM) and ICI 174,864 (N,N-dialyl-Tyr-Aib-Phe-Leu; 0.3 microM). Yet, the effect of dynorphin A-(1-17) was blocked by the NMDA receptor antagonist MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5-10-imine maleate; 0.3 microM). Neonatal treatment with capsaicin (50 mg/kg s.c.), which destroys substance P-containing primary afferents, abolished the excitatory effect of dynorphin A-(1-17) on K+-evoked substance P release. In conclusion, dynorphin A-(1-17) increases substance P release from C-fibers by the activation of NMDA receptors which supports the involvement of presynaptic mechanisms in dynorphin-induced antianalgesia and allodynia.

Reduced tolerance and cardiovascular response to ischemic pain in minor depression.

BACKGROUND: A paradoxical association between a higher prevalence of clinical pain and a reduced sensitivity to brief experimental pain seems to exist during depression. METHODS: We assessed the responses to sustained ischemic pain produced by a maximal effort tourniquet procedure in 32 controls and 11 individuals with minor depression (Zung autoscale > or =50). Stethoscopic blood pressures and heart rates were monitored throughout the procedure. RESULTS: Measures of pain threshold, and measures of pain intensity and pain unpleasantness during the ischemic procedure were similar in depressed and control subjects. Yet, the overall numerical ratings of ischemic pain during the procedure was 28% higher and pain tolerance was 44% lower in depressed compared to control subjects. Clinical pain complaints were reported by 91% of depressed but only by 41% of control subjects (P = 0.01). Sustained ischemic pain induced significant elevations of systolic and mean arterial blood pressures in controls but not in depressed subjects. LIMITATIONS: The main limitation of the present study was the preponderance of females in the depressed group. Yet, we did not find significant gender differences in the sensory-affective and autonomic responses to ischemic pain in our sample. CONCLUSIONS: These findings suggest alterations in the sensory and autonomic nervous systems during minor depression.

Motor activity and quantitative autoradiographic analysis of muscarinic receptors in the brain of rats subjected to the forced swimming test.

A cholinergic dysfunction has been involved in the neurobiological mechanisms of stress and depression. In the present study, we determined the autoradiographic distribution of muscarinic cholinergic receptors in the brain of rats subjected to the forced swimming test for 15 days. Motor activity was automatically analyzed daily before swimming. In the forced swimming test group, both total horizontal activity and ambulatory movements exhibited a significant decrease, when the data from 1st and 15th day were compared. Neither the affinity of [3H]-quinuclidinyl benzilate nor the maximal number of receptors were affected by the forced swimming test in the caudate-putamen, cortex, and hippocampus. The distribution of [3H]-quinuclidinyl benzilate binding sites did not show significant differences in the 30 analyzed areas. Further analysis of muscarinic receptor subtypes after forced swimming test would be necessary to discard any cholinergic involvement.

Alterations of excitatory amino acid receptors in the brain of manganese-treated mice.

An excessive activation of excitatory amino acid (EAA) receptors has been associated with oxidative stress, which is considered the primary cause of manganese (Mn) poisoning neurotoxicity. Therefore, the EAA receptor distribution was analyzed by autoradiographic methods in several brain regions during Mn intoxication. We found that chronic treatment of mice with MnCl2 during 8 wk significantly alters the L-[3H]glutamate (L-[3H]Glu) binding to total glutamate (Glu) receptors, as well as to N-methyl-D-aspartate (NMDA) and quisqualate (QA) receptor subtypes. A generalized decrease of 16-24% of the L-[3H]Glu binding to total Glu receptors was found in all cortex, hippocampus, basal ganglia (except globus pallidus), and cerebellum. Saturation studies showed a significant reduction of the maximal number of receptors (Bmax) in Mn-treated mice, whereas the affinity (Kd) was not altered. L-[3H]Glu binding to NMDA sites was mainly decreased (10-21%) in a few cortical regions, basal ganglia (except globus pallidus), and hippocampus, whereas binding to QA receptor subtype was diminished (16-30%) in cortex, hippocampus, and cerebellum. The decrease of Glu receptor binding sites during Mn poisoning could reflect a receptor downregulation more than neuronal loss, since these reductions are moderate and diffuse. Thus, this down-regulation might mean a protection mechanism against an excitotoxic process associated with Mn toxicity.

Manganese poisoning reduces strychnine-insensitive glycine binding sites in the globus pallidus of the mouse brain.

Manganese (Mn) poisoning is characterized by central nervous system manifestations, including psychiatric disturbances and extrapyramidal disorders. This metal is thought to produce neuronal degeneration due to cytotoxic products originated by oxidative stress and through an indirect excitotoxic process. In previous studies, we have found a reduction in the density of N-methyl-D-aspartate (NMDA) recognition sites in some brain areas of Mn-treated mice. Due to the close relationship between NMDA sites and strychnine-insensitive glycine (Gly) modulatory sites in the NMDA receptor complex, the [3H]-glycine ([3H]-Gly) binding was analyzed by autoradiographic methods in the brain of mice treated with manganese chloride for 8 weeks. Among all analyzed areas, only the globus pallidus showed a significant reduction in [3H]-Gly binding (27-28%). The Gly binding decrease, focalized in the globus pallidus, could reflect a degeneration of structures containing strychnine-insensitive Gly receptors, since this area is the most frequently reported damaged brain region in Mn intoxication. However, it might also be due to a Gly receptor down-regulation to control NMDA complex activation during Mn poisoning.

Morphine produces a biphasic modulation of substance P release from cultured dorsal root ganglion neurons.

We have previously reported that morphine produces a concentration-dependent multiphasic modulation (inhibitions and facilitations) of substance P (SP) release from trigeminal nucleus caudalis slices by activation of distinct populations of mu-, delta- and kappa-opioid receptors. In the present study, we have examined a wide range of morphine concentrations on K(+)-evoked SP release from dissociated rat dorsal root ganglion (DRG) neurons in culture. SP immunoreactivity was measured in the release buffer. Morphine produced a biphasic effect on K(+)-evoked SP release without affecting basal release. A concentration of 30 nM morphine facilitated SP release while a concentration of 1 microM suppressed release. Higher concentrations of morphine (10-30 microM) did not alter SP release. The facilitatory effect evoked by 30 nM morphine was abolished by opioid-receptor blockade with naloxone (30 nM) and the inhibitory effect produced by 1 microM morphine tended to be reversed. We conclude that an intact neuronal circuitry is not required for morphine to produce an opioid receptor mediated biphasic modulation of SP released from unmyelinated primary afferents. It is plausible that the dose-dependent biphasic effects of opioid agonists may also produce biphasic effects on nociception.

Autoreceptor presynaptic control of dopamine release from striatum is lost at early stages of manganese poisoning.

Manganese (Mn) poisoning in man produces an early psychotic disorder that is later followed by a Parkinson-like syndrome. Since alterations in the brain DA system are thought to be involved, we assessed the presynaptic autoreceptor regulation of K(+)-evoked 3H-DA release from superfused striatal slices of mice treated i.p. with 5 mg Mn/kg weight/day for 2 and 8 weeks. Mn poisoning did not change basal and evoked DA release. In controls, 1 microM apomorphine (APO), a D2-like DA receptor agonist, produced an inhibition of K(+)-evoked 3H-DA release that was blocked by the D2-like DA receptor antagonist, S(-)-sulpiride (1 microM). Yet, APO lost its capacity to inhibit the K(+)-evoked 3H-DA release after 2 weeks of Mn poisoning. After 8 weeks of Mn poisoning, APO was again able to reduce K(+)-evoked 3H-DA release. MK-801 (0.3 microM), a NMDA-glutamate receptor antagonist, could restore APO inhibitory control on DA release lost at week 2 of Mn poisoning. These findings suggest a NMDA-glutamate-receptor-mediated loss of autoreceptor presynaptic control of striatal DA release at early Mn poisoning.

Activation of kappa opioid receptors by U50488H and morphine enhances the release of substance P from rat trigeminal nucleus slices.

The modulation of the release of substance P (SP) from sensory primary afferents by activation of kappa opioid receptors is not only equivocal, but also contradictory. Thus, in the present study, we have determined the effect of nanomolar concentrations of the highly selective kappa opioid receptor agonist trans-(+)-3,4-dichloro-N-methyl-N-[2-91- (pyrrolidinyl)cyclohexyl]benzacetamide methane sulphonate (U50488H), as well as micromolar concentrations of moderately mu-selective agonist morphine, on K(+)-evoked SP release from rat trigeminal nucleus caudalis slices. U50488H (10-30 nM) and morphine (10-30 microM) increased K(+)-evoked SP release without stimulating basal SP release. Both U50488H and morphine concentration-response curves were biphasic because the highest and the lowest concentrations of U50488H (100 nM) and morphine (3 microM) tested, respectively, inhibited SP release. Enhancement of K(+)-evoked SP release induced by 30 nM U50488H and 30 microM morphine was blocked by the opioid receptor antagonists naloxone (30 nM; nontype selective) and norbinaltorphimine (3 nM; kappa selective), but not by N,N diallyl Tyr-Aib-Aib-Phe-Leu (0.3 microM; delta selective), naloxonazine (1 nM; mu 1 selective) or beta-funaltrexamine (20 nM; mu selective). These findings indicate that activation of at least one population of kappa opioid receptors increases the release of SP from trigeminal nucleus caudalis. Excitatory presynaptic kappa opioid receptors on SP-containing primary afferents may be involved in the hyperalgesia of inflammatory processes, the "anti-analgesic" effect of dynorphin and the paradoxical "analgesia" produced by low doses of naloxone.

Delta-opioid-receptor activation by [D-Pen2,D-Pen5]enkephalin and morphine inhibits substance P release from trigeminal nucleus slices.

The release of substance P (SP) from spinal dorsal horn slices is partially inhibited by micromolar concentrations of selective delta-opioid receptor agonists. In the present study, we have examined the effect of nanomolar concentrations of [D-Pen2,D-Pen5]enkephalin (DPDPE, delta-opioid receptor agonist) and low micromolar of concentrations morphine on K(+)-evoked SP release from rat trigeminal nucleus caudalis (TNC) slices. DPDPE and morphine inhibited SP release with an apparent maximal effect at 3 nM and at 3 microM, respectively. DPDPE and morphine produced U-shaped concentration-response curves that were completely autoinhibited at 100 nM DPDPE and 1 microM morphine. The inhibition of SP release produced by 3 nM DPDPE and 3 microM morphine was blocked by the opioid receptor antagonists naloxone (30 nM; non-selective) and ICI 174,864 (0.3 microM; delta-selective) but not by nor-binaltorphimine (3 nM n-BNI; kappa-selective), naloxonazine (1 nM; micro 1-selective) or beta-funaltrexamine (20 nM beta-FNA; mu-selective). These findings indicate that delta-opioid receptor-mediated inhibition of SP release from TNC can be achieved by nanomolar concentrations of selective delta-opioid receptor agonists. Activation of delta-opioid receptors by morphine might be involved in the residual analgesia observed after mu 1-opioid receptor blockade and in the analgesia produced by high doses of morphine.

Multiphasic effect of morphine on the release of substance P from rat trigeminal nucleus slices.

It is generally accepted that morphine acts presynaptically to inhibit substance P (SP) release from afferent terminals in the trigeminal nucleus. Recent studies, however, provide evidence that opioids produce both inhibitory and excitatory effects on SP release which are concentration- and receptor subtype-dependent. In the present study, we have examined a wide range of morphine concentrations on K(+)-evoked SP release from rat trigeminal nucleus caudalis slices. Immunoreactive SP was measured in perfusates. Morphine produced multiphasic effects on K(+)-evoked SP release without affecting basal release. A very low nanomolar concentration (1 nM) suppressed release, higher nanomolar concentrations (100-300 nM) facilitated release, a low micromolar concentration (3 microM) suppressed release, and a higher micromolar concentration (30 microM) facilitated release. These effects were abolished by opioid receptor blockade with naloxone (30 nM). Thus, morphine produces a complex bi-directional modulation of SP release from TNC which is concentration- and possibly receptor subtype-dependent.