Supersensitivity of spinal opioid receptors to antagonists in intrathecal butorphanol and morphine dependence

The purpose of this investigation was to evaluate changes in the sensitivity of spinal opioid receptors to selective antagonists in rats rendered dependent on intrathecal (i.t.) butorphanol and morphine. Using quantitative autoradiography, competitive binding assays with selective opioid antagonists were performed in the spinal cord sections of i.t. butorphanol- and morphine-dependent rats in which withdrawal was precipitated by i.t. naloxone. In butorphanol-dependent rats, the spinal kappa-opioid receptor developed a greater degree of antagonist supersensitivity than the spinal delta- and mu-opioid receptors did. In contrast, the spinal mu-opioid receptor became more sensitive than the delta-opioid receptor in morphine-dependent rats. These results indicate that differential supersensitivity of spinal opioid receptors was induced after chronic i.t. infusions of butorphanol and morphine.     

Spinal amino acid release and precipitated withdrawal in rats chronically infused with spinal morphine

Glutamate receptors are implicated in the genesis of opioid tolerance and dependence. Factors governing release of amino acids in systems chronically exposed to opiates, however, remain undefined. Using rats, each prepared with a spinal loop dialysis catheter and with a chronic lumbar intrathecal infusion catheter connected to a subcutaneous minipump, the release of amino acids before and during antagonist-precipitated withdrawal in unanesthetized rats was examined. Spinal infusion of morphine (20 nmol/micro l/hr) for 4 d had little effect on resting release of amino acids. In morphine-infused, but not saline-infused, rats naloxone (2 mg/kg, i.p.) evoked an immediate increase in the release of L-glutamate (299 +/- 143%) and taurine (306 +/- 113%) but not other amino acids. The magnitude and time course of the release of these amino acids significantly correlated with behavioral indices of withdrawal intensity. Acute intrathecal pretreatment immediately before naloxone with clonidine (20 microg; alpha2 agonist), MK-801 (3 microg; noncompetitive NMDA antagonist), or aminophosphonopentanoic acid (AP-5; 3 microg; competitive NMDA antagonist) suppressed naloxone-induced increases in spinal L-glutamate and taurine release and behavioral signs of withdrawal in spinal morphine-infused rats. Results point to a correlated increase in spinal L-glutamate release, which contributes to genesis of the opioid withdrawal syndrome. Agents such as clonidine that suppress opioid withdrawal may owe their action to an inhibition of excitatory amino acid release. The effects of MK-801 and AP-5 suggest a glutamate-evoked glutamate release.     

Differential contribution of descending controls to the antinociceptive actions of kappa and mu opioids: an analysis of formalin-evoked C-fos expression

In this study, the effect of intracerebroventricular (icv) administration of (5R)-(5 alpha, 7 alpha, 8 beta)-N-methyl-N-[7-(1-pyrrolindinyl)-1- oxaspiro[4,5]dec-8-yl]-4-benzofurnacetamide monohydrochloride (Cl-977) on pain behaviors and on spinal cord fos-like immunoreactivity (FLI) evoked by unilateral formalin injection into the hindpaw of rats was examined. Intracerebroventricular administration of Cl-977 (0.13-13.00 nmol) produced a dose-dependent inhibition of formalin-evoked pain behaviors, with significant inhibition after 1.30, 4.40 and 13.00 nmol. The estimated ED50 for icv Cl-977 inhibition of formalin-evoked behaviors was 0.95 nmol and the Emax was 53%. The inhibitory effect of 4.40 nmol of icv Cl-977 on formalin-evoked behaviors was prevented by either pretreatment with the kappa selective antagonist nor-binaltorphimine (10 or 100 nmol) or coadministration of the opiate receptor antagonist, naloxone (30 nmol). The lowest dose of icv Cl-977 tested (0.13 nmol) produced a 50% reduction in FLI in the superficial laminae but did not inhibit the expression of FLI in any other regions of the spinal cord. The fos-inhibitory effect of low-dose icv Cl-977 in the superficial cord was reversed by coadministration of naloxone (30 nmol). Higher doses of icv Cl-977 that suppressed formalin-evoked behaviors did not inhibit the expression of FLI in any region of the spinal cord. Finally, neither the inhibitory effect of 4.40 nmol Cl-977 on formalin-evoked behaviors nor the formalin-evoked pattern of FLI expression in the spinal cord of rats treated with this dose of Cl-977 was affected by lesions of the dorsolateral funiculus. These results provide the first evidence that supraspinal kappa receptor-mediated antinociception is not dependent on the integrity of the dorsolateral funiculus and may be mediated exclusively at the supraspinal level, suggesting that there are multiple mechanisms through which opioids can evoke antinociceptive effects.     

Long-term depression of C-fibre-evoked spinal field potentials by stimulation of primary afferent A delta-fibres in the adult rat

Long-term potentiation (LTP) of spinal C-fibre-evoked field potentials can be induced by brief electrical stimulation of afferent C-fibres, by natural noxious stimulation of skin or by acute nerve injury. Here, we report that in urethane anaesthetized, adult rats prolonged high frequency burst stimulation of the sciatic nerve at Adelta-fibre strength produced long-term depression (LTD) of C-fibre-evoked field potentials, and also depressed the increased amplitudes of C-fibre-evoked field potentials recorded after LTP had been established (depotentiation). Electrical stimulation of Abeta-fibres failed to induce LTD or depotentiation. In spinalized rats, prolonged Adelta-fibre conditioning stimulation induced LTP rather than LTD of C-fibre-evoked field potentials. Thus, tonic descending inhibition may determine the direction of plastic changes in C-fibre-mediated synaptic transmission. Spinal application of the N-methyl-D-aspartic acid receptor antagonist D-APV blocked induction of LTD in intact rats and LTP in spinalized rats. The presently described LTD and the depotentiation of established LTP of C-fibre-evoked field potentials in spinal dorsal horn may underlie some forms of prolonged analgesia induced by peripheral nerve stimulation procedures.     

The competence-related abilities of women criminal defendants

Delta9-tetrahydrocannabinol (delta9-THC) elicits antinociception in rodents through the central CB1 cannabinoid receptor subtype. In addition. Delta9-THC stimulates the release of dynorphin-related peptides leading to kappa-opioid spinal antinociception. In this work we describe the effect of a mixture of thiorphan (a neutral endopeptidase EC3.4.24.11 inhibitor) and bestatin (an aminopeptidase inhibitor), administered i.c.v., on the antinociceptive effect of peripherally administered delta9-THC in mice. As in the case of morphine or DAMGO ([D-Ala2.N-Me-Phe4,Gly-ol]enkephalin), a mu-selective opioid receptor agonist, the mixture of enkephalin-degrading enzyme inhibitors also enhanced the antinociceptive effect of delta9-THC. This effect was blocked by the CB1 cannabinoid receptor antagonist, SR-141,716-A, as well as by naloxone. The kappa-opioid receptor antagonist nor-binaltorphimine, administered i.t., also antagonized the effect of this combination. Similar results were obtained with the mu-opioid receptor antagonist beta-funaltrexamine after i.c.v. administration. These results demonstrate the involvement of both mu-opioid supraspinal and kappa-opioid spinal receptors in the interaction of both opioid and cannabinoid systems regulating nociception in mice.     

Isolation from genomic DNA of sequences binding specific regulatory proteins by the acceleration of protein electrophoretic mobility upon DNA binding

To examine a role for the medullary nucleus paragigantocellularis (PGi) in mediation of the symptomatology of opioid withdrawal, bilateral electrical stimulation of the PGi was performed in conscious, unrestrained, opioid naive (nondependent) rats. A characteristic series of behaviors was elicited during each 30-min session of PGi stimulation. The profile of these behaviors resembled qualitatively, but was not quantitatively identical with those seen during precipitated withdrawal from opioid dependence. This behavioral syndrome has been termed, opioid withdrawal-like behavior. The opioid withdrawal-like behaviors were voltage-, but not frequency-, dependent. Tolerance to repeated stimulation of the PGi did not develop following a series of 30-min runs of stimulation over 3.5 h. Intracerebroventricular (i.c.v.) injections of the nonselective opioid antagonist, naloxone, significantly decreased (by 40-50%) the intensity of stimulation-induced behavioral responses, as did injections of either the mu-selective (beta-funaltrexamine, beta-FNA) or the delta-selective (naltrindole, NTI) opioid antagonists. In contrast, similar i.c.v. injections of the kappa-selective antagonist, nor-binaltorphimine (nor-BNI), did not block behavioral responses to PGi stimulation. The results indicate that activation of the PGi by electrical stimulation can elicit behaviors similar to those observed during opioid withdrawal. Endogenous opioids, acting through mu- and delta-, but not kappa-opioid receptors, participate in mediating opioid withdrawal-like behaviors induced by PGi stimulation.     

Nociceptin inhibits non-adrenergic non-cholinergic contraction in guinea-pig airway

1. Electrical field stimulation (EFS) of guinea-pig isolated main bronchi induced a non-adrenergic non-cholinergic (NANC) contractile response. Nociceptin (0.01-1 microm) significantly inhibited the contractile response to EFS (P<0.01), but not to capsaicin (P>0.05). 2. The mu-, delta- and kappa-opioid receptor antagonists, naloxone (0.3 microM), naltrindole (3 microM) and norbinaltorphimine (1 microm), respectively, did not significantly affect the inhibitory effect of nociceptin (0.03 microM; P>0.05). 3. The novel nociceptin antagonist, [Phe1psi(CH2-NH)Gly2]nociceptin(1-13)NH2 (0.03-1 microM); the sigma ligands, carbetapentane (30 microM), 3-phenylpiperidine (30-100 microM) and (+)-cyclazocine (10-100 microM) significantly reversed the inhibitory effect of nociceptin (0.03 microM, P<0.05). In contrast, rimcazole, did not significantly reverse the inhibitory effect of nociceptin (0.03 microM) at any concentration tested (P>0.05). 4. EFS of guinea-pig bronchial preparations significantly increased SP-LI release above basal SP-LI (P<0.05). In the presence of nociceptin (1 microM), EFS induced a significant increase in SP-LI release above basal SP-LI release (P<0.05). Nociceptin caused a 59+11% (n=5) inhibition of EFS-induced release of SP-LI. 5. Nociceptin reduces the release of sensory neuropeptides induced by EFS, but not capsaicin, from guinea-pig airways. These experiments provide further evidence for a role for nociceptin in regulating the release of sensory neuropeptides in response to EFS.     

Naloxone-precipitated changes in biogenic amines and their metabolites in various brain regions of butorphanol-dependent rats

Influence of a naloxone (an opioid receptor antagonist) challenge (5 mg/kg, IP) on levels of biogenic amines and their metabolites in various brain regions of rats infused continuously with butorphanol (a mu/delta/kappa mixed opioid receptor agonist; 26 nmol/microliter/h) or morphine (a mu-opioid receptor agonist; 26 nmol/microliter/h) was investigated using high-performance liquid chromatography with electrochemical detection (HPLC-ED). Naloxone precipitated a withdrawal syndrome and decreased the levels of: dopamine (DA) in the cortex and striatum, 3,4-dihydroxyphenylacetic acid (DOPAC) in the striatum, homovanilic acid (HVA) in the striatum, limbic, midbrain, and pons/medulla regions in butorphanol-dependent rats. However, the levels of norepinephrine (NE), serotonin (5-hydroxytryptamine; 5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) in the regions studied were not affected by naloxone-precipitated withdrawal. In addition, naloxone increased the HVA/DA ratio in the cortex, while this ratio was reduced in the limbic, midbrain, and pons/medulla. The reduction of 5-HIAA/5-HT ratio was also detected in the limbic area. In the animals rendered dependent on morphine, the results obtained were similar to those of butorphanol-dependent rats except for changes of 5-HIAA levels in some brain regions. These results suggest that an alteration of dopaminergic neuron activity following a reduction of DA and its metabolites in specific brain regions (e.g., striatum, limbic, midbrain, and pons/medulla) play an important role in the expression of the opioid withdrawal syndrome.     

Nucleotide sequence of the VP7 gene of human rotavirus isolated in Calcutta, India: possible emergence of a new subtype of serotype I

The present study investigated the possible role of nitric oxide (NO) in the development of the withdrawal contractures of guinea pig isolated ileum after acute activation of mu- and kappa-opioid receptors. After a 4-min in vitro exposure to morphine (mu-opioid receptor preferring, but not selective, agonist), [D-Ala2-N-methyl-Phe4-Gly5-ol-]enkephalin (DAMGO; highly selective mu-opioid receptor agonist), or trans(+/-)-3,4-dichloro-N-methyl-N-2(1-pyrrolidynyl)cyclohexyl-ben zeneacetamide (U50-488H; highly selective kappa-opioid receptor agonist), the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone. L-N(G)-nitro arginine methyl ester (3-300 microM) injected 10 min before the opioid receptor agonists was able dose dependently to reduce the naloxone-induced contraction after exposure to mu- and kappa-opioid receptor agonists whereas D-N(G)-nitro arginine methyl ester at the same concentrations did not affect it. The inhibitory effect of L-N(G)-nitro arginine methyl ester on morphine, DAMGO and U50-488H withdrawal was dose dependently reversed by L-arginine (3-300 microM) but not by D-arginine. Finally, glyceryl trinitrate on its own (3-300 microM) significantly increased the naloxone-induced contraction after exposure to mu- and kappa-opioid receptor agonist and it was also able to reverse the inhibition of opioid withdrawal caused by L-N(G)-nitro arginine methyl ester. These results provide evidence that NO has a role in the development of opioid withdrawal and that mu- or kappa-opioid receptors are involved.     

Biphasic modulation of spinal nociceptive transmission from the medullary raphe nuclei in the rat

The modulatory effects of electrical and chemical (glutamate) stimulation in the rostral ventromedial medulla (RVM) on spinal nociceptive transmission and a spinal nociceptive reflex were studied in rats. Electrical stimulation at a total 86 sites in the RVM in the medial raphe nuclei (n = 54) and adjacent gigantocellular areas (n = 32) produced biphasic (facilitatory and inhibitory, n = 43) or only inhibitory (n = 43) modulation of the tail-flick (TF) reflex. At these 43 biphasic sites in the RVM, facilitation of the TF reflex was produced at low intensities of stimulation (5-25 microA) and inhibition was produced at greater intensities of stimulation (50-200 microA). At 43 sites in the RVM, electrical stimulation only produced intensity-dependent inhibition of the TF reflex. Activation of cell bodies in the RVM by glutamate microinjection reproduced the biphasic modulatory effects of electrical stimulation. At biphasic sites previously characterized by electrical stimulation, glutamate at a low concentration (5 nmol) produced facilitation of the TF reflex; a greater concentration (50 nmol) only inhibited the TF reflex. In electrophysiological experiments, electrical stimulation at 62 sites in the RVM produced biphasic (n = 26), only inhibitory (n = 26), or only facilitatory (n = 10) modulation of responses of lumbar spinal dorsal horn neurons to noxious cutaneous thermal (50 degrees C) or mechanical (75.9 g) stimulation. Facilitatory effects were produced at lesser intensities of stimulation and inhibitory effects were produced at greater intensities of stimulation. The apparent latencies to stimulation-produced facilitation and inhibition, determined with the use of a cumulative sum method and bin-by-bin analysis of spinal neuron responses to noxious thermal stimulation of the skin, were 231 and 90 ms, respectively. The spinal pathways conveying descending facilitatory and inhibitory influences were found to be different. Descending facilitatory influences on the TF reflex were conveyed in ventral/ventrolateral funiculi, whereas inhibitory influences were conveyed in dorsolateral funiculi. The results indicate that descending inhibitory and facilitatory influences can be simultaneously engaged throughout the RVM, including nucleus raphe magnus, and that such influences are conveyed in different spinal funiculi.     

Differential influence of D1 and D2 dopamine receptors on acute opiate withdrawal in guinea-pig isolated ileum

1. The effects exerted by D1 and D2 dopamine agonists and antagonists on the acute opiate withdrawal induced by mu- and kappa-receptor agonists were investigated in vitro. 2. Following a 4 min in vitro exposure to morphine (moderately selective mu-agonist), [D-Ala2, Me-Phe4, Gly-ol5]enkephalin (DAMGO, highly selective mu-agonist) or U-50488H (highly selective kappa-agonist) the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone. 3. The non-selective dopamine receptor antagonist haloperidol when added before or after the opioid agonists, was able dose-dependently to prevent or to reverse the naloxone-induced contracture after exposure to mu- (morphine and DAMGO) and kappa- (U-50488H) opioid agonists. The non-selective dopamine receptor agonist, apomorphine, was able to exert the same effects only at the highest concentration used. 4. The selective D2 dopamine receptor antagonist, sulpiride, was also able to reduce dose-dependently both mu- and kappa-opioid withdrawal, whereas the D1-receptor selective antagonist SCH 23390 did not affect either mu- or kappa-opioid withdrawal. 5. Bromocriptine, a D2 selective dopamine receptor agonist was able to increase significantly, and in a concentration-dependent manner, the naloxone-induced contracture by mu- and kappa-opioid agonists, whereas SKF 38393, a D1 selective dopamine receptor agonist, increased only the withdrawal after morphine or U50-488H. 6. Our data indicate that both D1 and D2 dopamine agonists and antagonists are able to influence opiate withdrawal in vitro, suggesting an important functional interaction between the dopaminergic system and opioid withdrawal at both the mu- and kappa-receptor level. 7. Furthermore, the ability of sulpiride to block strongly opiate withdrawal when compared to SCH 23390, as well as the effect of bromocriptine to increase opiate withdrawal suggest that D2 dopamine receptors may be primarily involved in the control of opiate withdrawal.     

Isoprene from expired air inside a private car

In a rat model of postoperative ileus, induced by abdominal surgery, we investigated the effect of mu- and kappa-opioid receptors. Different degrees of inhibition of the gastrointestinal transit, measured by the migration of Evans blue, were achieved by skin incision, laparotomy or laparotomy plus manipulation of the gut. Morphine (1 mg/kg), a preferential mu-opioid receptor agonist, significantly inhibited the transit after skin incision, while the transit after the laparotomy with or without manipulation was not significantly affected. Fedotozine (5 mg/kg), a peripheral kappa-opioid receptor agonist, enhanced the transit after laparotomy plus manipulation, while naloxone (1 mg/kg), a non-specific opioid receptor antagonist, further inhibited the transit after laparotomy plus manipulation. Naloxone and fedotozine alone had no effect on the transit after skin incision or laparotomy without manipulation. However, naloxone prevented the effect of morphine on the transit after skin incision and of fedotozine on the laparotomy plus manipulation. These results support a role for peripheral kappa-opioid receptors in the pathogenesis of postoperative ileus induced by abdominal surgery.     

Mediation of endothelin-1-induced inhibition of platelet aggregation via the ETB receptor

1. The effects of FR139317 (ETA antagonist) or PD145065 (non-selective ETA/ETB antagonist) on endothelin-1 (ET-1)-induced changes in blood pressure and inhibition of ex vivo platelet aggregation were investigated in the anaesthetized rabbit. 2. ET-1 (1 nmol kg-1, i.a. bolus) caused a sustained increase in mean arterial pressure (MAP) (peak increase 47 +/- 5 mmHg, n = 8). Intravenous infusion of FR139317 at 0.2 (n = 4) or 0.6 mg kg-1 min-1 (n = 4) inhibited the ET-1 pressor response by 83 or 89%, respectively. Infusion of PD145065 at 0.2 (n = 4) or 0.6 mg kg-1 min-1 (n = 4) inhibited the ET-1-induced increase in MAP by 79 or 75%, respectively. 3. The transient depressor response (-16 +/- 3 mmHg) which preceded the rise in blood pressure induced by ET-1 (1 nmol kg-1, i.a., n = 8) was enhanced by an intravenous infusion of FR139317 (0.6 mg kg-1 min-1) to -35 +/- 5 mmHg (P < 0.05, n = 4). This enhancement was abolished by indomethacin (5 mg kg-1, i.v.) pretreatment (-17 +/- 1 mmHg, n = 4). PD145065 (0.2 mg kg-1 min-1, i.v.) attenuated the ET-1-induced fall in blood pressure to -9 +/- 1 mmHg (n = 4), while a higher dose of this antagonist (0.6 mg kg-1 min-1, i.v.) completely abolished the ET-1-mediated depressor response. 4. ET-1 (1 nmol kg-1, n = 8) inhibited ex vivo platelet aggregation by 96% at 5 min after injection of the peptide. FR139317 (0.2 or 0.6 mg kg-1 min-1, i.v.) or PD145065 (0.2mg kg-1 min-1, i.v.) did not affect the inhibition of ex vivo platelet aggregation in response to ET-1. In contrast, intravenous infusion of PD145065 (0.6 mg kg-1 min-1) abolished the anti-aggregatory effects of ET-1.5. Thus, FR139317 inhibits the pressor, but not the depressor actions of ET-1 and has no effect on the ET-l-induced inhibition of ex vivo platelet aggregation. In contrast, PD145065 antagonizes the pressor and depressor responses to ET-1 and abolishes the anti-aggregatory effects of the peptide.6. These results strongly suggest that ET-1-induced vasoconstriction in the anaesthetized rabbit is primarily mediated via the ETA receptor while the depressor and antiaggregatory actions of ET-1 are due to activation of the ETB receptor.     

Effects of morphine and naloxone on Renshaw cells and spinal interneurones in morphine dependent and non-dependent rats

The effects of microelectrophoretically administered morphine, naloxone, levorphanol and dextrorphan have been investigated on Renshaw cells and interneurones in the spinal cord of morphine-dependent and non-dependent anaesthetized rats. Morphine excited cholinoceptive neurones and enhanced the excitatory actins of acetylcholine and L-glutamate. This action of morphine appeared to be stereospecific and was antagonized by naloxone. Naloxone also antagonized acetylcholine-induced excitation but not L-glutamate-induced excitation. In dependent rats morphine was a more effective excitant of cholinoceptive neurones and naloxone was more effective as an antagonist of acetylcholine-induced excitations. These observations were interpreted as indicating that cholinergic mechanisms may be involved in morphine dependence and naloxone-precipitated abstinence.     

Involvement of endothelin in the pressor response following injection of NMDA to the periaqueductal gray area of rats

Microinjection of N-methyl-D-aspartate (NMDA) (0.068 to 6.8 nmol) into the periaqueductal gray area (PAG) of anaesthetized rats caused dose-dependent increases in blood pressure. Preinjection (10 min before) of FR 139317 (an ETA receptor selective antagonist; 5 nmol) or SB 209670 (an ETA/ETB receptor non-selective antagonist; 5 nmol) to the PAG reduced the pressor response to NMDA whereas BQ-788 (an ETB receptor selective antagonist; 5 nmol) did not affect the NMDA-induced hypertension. Pretreatment with DL-2-amino-5-phosphono valeric acid (2-APV) (an NMDA receptor selective antagonist, 5 nmol) also abolished the pressor response induced by NMDA. Dose-dependent increases in blood pressure induced by injection of angiotensin II (0.1-10 nmol) to the PAG were unaffected by FR 139317 or SB 209670. Thus, our data indicate that endogenous ET-1, via an action on ETA receptors, contributes to the pressor effects of NMDA within the brain.     

Preparation and in vitro release studies of ibuprofen-loaded films and microspheres made from graft copolymers of poly(L-lactic acid) on acrylic backbones

Several studies have shown that the anterior pretectal nucleus (APtN) is involved in descending inhibitory pathways that control noxious inputs to the spinal cord and that it may participate in the normal physiological response to noxious stimulation. Among other brain regions known to send inputs to the APtN, the dorsal column nuclei (DCN), pedunculopontine tegmental nucleus (PPTg), deep mesencephalon (DpMe), and dorsal raphe nucleus (DRN) are structures also known to be involved in antinociception. In the present study, the effects of stimulating these structures on the latency of the tail withdrawal reflex from noxious heating of the skin (tail flick test) were examined in rats in which saline or hyperbaric lidocaine (5%) was previously microinjected into the APtN. Brief stimulation of the PPTg, DpMe or DRN, but not the DCN, strongly depressed the tail flick reflex. The antinociceptive effect of stimulating the DRN, but not the PPTg or DpMe was significantly reduced, but not abolished, by the prior administration of the local anaesthetic into the APtN. The antinociception induced by stimulation of the PPTg or DpMe, therefore, is unlikely to depend on connections between these structures and the APtN. Similar inhibition of the effect of stimulating the DRN was obtained from rats previously microinjected with naloxone (2.7 nmol) or methysergide (2 nmol) into the APtN. Strongly labelled cells were identified in the DRN following microinjection of the fluorescent tracer Fast Blue into the APtN. These results indicate that the APtN may participate as a relay station through which the DRN partly modulates spinal nociceptive messages. In addition, they also indicate that endogenous opioid and serotonin can participate as neuromodulators of the DRN-APtN connection.     

Activation of spinal N-methyl-D-aspartate or neurokinin receptors induces long-term potentiation of spinal C-fibre-evoked potentials

The use-dependent increase in synaptic strength between primary afferent C-fibres and second-order neurons in superficial spinal dorsal horn may be an important cellular mechanism underlying central hyperalgesia. This long-term potentiation can be blocked by antagonists of the N-methyl-D-aspartate subtype of glutamate receptor, the neurokinin 1 or the neurokinin 2 receptor. We have tested here whether activation of these receptors by superfusion of the spinal cord with corresponding agonists in the absence of presynaptic activity is sufficient to induce long-term potentiation. In urethane anaesthetized rats C-fibre-evoked field potentials were elicited in superficial laminae of lumbar spinal cord by electrical stimulation of the sciatic nerve. In rats with intact spinal cord, controlled superfusion of the spinal cord at recording segments for 60 min with N-methyl-D-aspartate, substance P or neurokinin A never induced long-term potentiation. Spinal superfusion with a mixture of N-methyl-D-aspartate, substance P and neurokinin A also failed to induce long-term potentiation in four rats tested. In spinalized rats, however, long-term potentiation was induced by either N-methyl-D-aspartate (at 10 microM, to 173 +/- 16% of control) substance P (at 10 microM, to 176 +/- 13% of control) or by neurokinin A (at 1 microM, to 198 +/- .20% of control). The induction of long-term potentiation by N-methyl-D-aspartate, substance P or neurokinin A was blocked by intravenous application of the receptor antagonists dizocilpine maleate (0.5 mg/kg), RP67580 (2 mg/kg) or SR48968 (0.2 mg/kg), respectively. Thus, activation of N-methyl-D-aspartate or neurokinin receptors may induce long-lasting plastic changes in synaptic transmission in afferent C-fibres and this effect may be prevented by tonic descending inhibition.     

Intrathecal CGRP(8-37) results in a bilateral increase in hindpaw withdrawal latency in rats with a unilateral thermal injury

The present study was performed to explore the effects of intrathecal administration of calcitonin gene-related peptide8-37 (CGRP(8-37)) on the hindpaw withdrawal latency (HWL) to pressure in rats with one thermally injured hindpaw. Furthermore, the interaction of CGRP(8-37)and naloxone was studied. Thermal injury was performed by dipping the left paw into 60 degrees C for 20 s. This induced a significant increase in the volume of the left hindpaw (P<0.001) and significant bilateral decreases of the latency of hindpaw withdrawal response to mechanical stimulation (Left: P<0.001; right: P<0.05). Intrathecal administration of 10, 20 and 40 nmol of CGRP(8-37), but not of 1 or 5 nmol, induced a significant bilateral increase in HWLs (P<0.001). The effect of CGRP(8-37) was partly reversed by intrathecal injection of naloxone at a dose of 32 and 64 microg respectively. Using radioimmunoassay, we found a significant bilateral increase in the concentration of CGRP-like immunoreactivity in the perfusate of both hindpaws 24 h after unilateral thermal injury (left: P< 0.001; right: P< 0.05). There was also an increase in the amount of CGRP-like immunoreactivity in the cerebrospinal fluid (P< 0.001), but not in plasma. The results indicate that CGRP plays a role in the transmission of nociceptive information in the spinal cord of thermally injured rats. Furthermore, our findings suggest that opioids can modulate CGRP-related effects in the spinal cord.     

Neurotropin induces antinociceptive effect by enhancing descending pain inhibitory systems involving 5-HT3 and noradrenergic alpha2 receptors in spinal dorsal horn

Neurotropin, a non-protein extract from the inflamed skin of rabbits inoculated with vaccinia virus, has been clinically used as an analgesic drug in Japan. Its analgesic effect has been demonstrated by reduced mechano-nociception in hyperalgesic rats exposed to SART-stress (a repeated cold stress) for 5 days. In order to clarify the mechanism of the analgesic effect of neurotropin at the spinal cord level, we examined the effects of several neurotransmitter receptor antagonists given by intrathecal (i.t.) injection on the antinociceptive effect of intraperitoneally (i.p.) injected neurotropin [100 and 200 Neurotropin Unit (NU)/kg]. The analgesic effect of neurotropin was significantly inhibited not only by methysergide (100 nmol/rat, i.t.), a non-selective antagonist against serotonin (5-HT), but also MDL 72222 (30 nmol/rat, i.t.), a selective 5-HT3 antagonist, but not influenced by ketanserin (100 nmol/rat, i.t.), a 5-HT2A antagonist. The antinociceptive effect of neurotropin (200 NU/kg, i. p.) was significantly inhibited also by yohimbine (30 nmol/rat, i.t.), a noradrenergic alpha2 antagonist. However, the analgesic effect of neurotropin (100 and 200 NU/kg, i.p.) was not influenced by naloxone (30 nmol/rat, i.t.), an opioid antagonist. These results suggest that the mechanism of the antinociceptive effect of neurotropin is via enhancement of endogenous descending pain inhibitory pathways of the serotonergic and noradrenergic systems, especially involving 5-HT3 and noradrenergic alpha2 receptors in spinal dorsal horn in which these neurons terminate. No influence of opioid receptors at the spinal cord level is indicated.     

Immunologic aspects in the pathogenesis and treatment of immune thrombocytopenic purpura in children

1. The nature of the muscarinic receptor involved in mediating cardiovascular changes caused by unilateral microinjection of carbachol (5 nmol) into, and electrical stimulation (200-300 microA) of, the amygdaloid complex was investigated in conscious, unrestrained female Sprague-Dawley rats. 2. Unilateral microinjection of carbachol (5 nmol; n = 6) and electrical stimulation (200-300 microA, 80 Hz, 30 s; n = 4) caused a significant rise in blood pressure of 21 +/- 4 mmHg and 25 +/- 5 mmHg, respectively. These changes were associated with no overall effect on heart rate. The effects of electrical stimulation were found to be repeatable. 3. Pretreatment i.c.v. with pirenzepine (5-20 mmol; n = 6-7 for each dose), dose-dependently inhibited the rise in blood pressure induced by carbachol, whereas AF-DX 116 (100 nmol; n = 6) failed to have any effect on the carbachol-induced pressure response. Neither antagonist alone had any effect on resting baseline variables. 4. Unilateral microinjections of atropine sulphate (1-100 nmol; n = 4-6 for each dose), pirenzepine (0.03-10 nmol; n = 4 for each dose) or AF-DX 116 (10-60 nmol; n = 4-5 for each dose), into the amygdala, dose-dependently inhibited the rise in blood pressure caused by electrical stimulation (200-300 microA). The ID50 values were 1.05, 0.23 and 39.5 nmol, respectively. Although pirenzepine seemed to be more potent than atropine, this difference was not significant. 5. It is concluded that the rise in blood pressure elicited by unilateral microinjection of carbachol into, or electrical stimulation of, the amygdaloid complex is mediated by M1-muscarinic receptors.