Comparison of Antinociceptive Effect of Octreotide With Morphine in a Rat Model of Acute Inflammatory Pain.

BACKGROUND: Opioids such as morphine are used for treating moderate to severe pain. However, they also produce adverse effects such as nausea, constipation, addiction, and respiratory depression. Thus, other suitable analgesics need to be identified. Somatostatin is an inhibitory neuropeptide that modulates the transmission of pain. However, the half-life of somatostatin is short. In the present study, the antinociceptive effect of octreotide (a stable long-acting analog of somatostatin) was evaluated in rats with acute inflammatory pain. METHODS: Sprague Dawley rats (n = 42) were divided into control (n = 6) and carrageenan injected groups (n = 36). The carrageena group was divided into three equal subgroups and treated with saline, morphine (10 mg/kg), and octreotide (3 µg). Rats belonging to each subgroup (n = 12) were again randomly divided into two equal sets. They were subjected to (a) behavioral evaluation of pain (allodynia) and estimation of paw edema, followed by immunohistochemical analysis of the expression of somatostatin type 2 receptor (sst2r) in the spinal cord and (b) estimation of open-field activity. Allodynia and paw edema were measured by von Frey filaments and plethysmometer, respectively, at 3 and 4 h after carrageenan injection. Expression of sst2r was examined after 24 hours, whereas open-field activity was evaluated after 3 hours. RESULTS: In comparison to the saline-treated group, allodynia was partially attenuated by octreotide, though this was almost completely reversed by morphine. Paw edema was unaffected by octreotide, though it was marginally increased by morphine. This was not related to increased activity of rats, following relief from pain. Immunohistochemistry revealed a significant increase in the expression of sst2r in saline-treated rats, but a decrease in other groups. CONCLUSION: Octreotide has an antinociceptive effect, which was less than morphine. Increased edema following morphine could result from venodilation. Variations in the sst2r expression suggest its involvement in pain modulation at the spinal level. This information may have clinical relevance.

Diverse characters of Brennan's paw incision model regarding certain parameters in the rat.

BACKGROUND: Brennan's rodent paw incision model has been extensively used for understanding mechanisms underlying postoperative pain in humans. However, alterations of physiological parameters like blood pressure and heart rate, or even feeding and drinking patterns after the incision have not been documented as yet. Moreover, though eicosanoids like prostaglandins and leukotrienes contribute to inflammation, tissue levels of these inflammatory mediators have never been studied. This work further investigates the antinociceptive effect of protein C after intra-wound administration. METHODS: Separate groups of Sprague-Dawley rats were used for quantitation of cyclooxygenase (COX) activity and leukotriene B4 level by enzyme-linked immunosorbent assay, as well as estimation of cardiovascular parameters and feeding and drinking behavior after paw incision. In the next part, rats were subjected to incision and 10 µg of protein C was locally administered by a micropipette. Both evoked and non-evoked pain parameters were then estimated. RESULTS: COX, particularly COX-2 activity and leukotriene B4 levels increased after incision. Hemodynamic parameters were normal. Feeding and drinking were affected on days 1 and 3, and on day 1, respectively. Protein C attenuated non-evoked pain behavior alone up to day 2. CONCLUSIONS: Based upon current observations, Brennan's rodent paw incision model appears to exhibit a prolonged period of nociception similar to that after surgery, with minimal interference of physiological parameters. Protein C, which is likely converted to activated protein C in the wound, attenuated the guarding score, which probably represents pain at rest after surgery in humans.

Terminalia chebula supplementation attenuates cisplatin-induced nephrotoxicity in Wistar rats through modulation of apoptotic pathway.

In the present study, we have evaluated the nephroprotective effect of hydroalcoholic extract of Terminalia chebula in cisplatin-induced nephrotoxicity model. Standardised extract was orally administered to Wistar rats for 10 days at different doses. On day 7, 8 mg/kg of cisplatin was administered intra-peritoneally to rats in all groups. T. chebula, in a dose-dependent manner significantly inhibited the elevation of serum creatinine, blood urea nitrogen and oxidant stress markers. The immunohistochemical analysis revealed the increased levels of apoptotic markers and cytokines in cisplatin group were significantly lowered by T. chebula extract. The cisplatin-treated rats kidney showed diffused tubular necrosis and infilteration of inflammatory cells which was reversed in the treatment group. Chemical characterisation of extract by HPLC revealed the presence of corilagin, chebulinic, chebulagic, chebulic, gallic and ellagic acid. The findings of this study discovered that T. chebula ameliorated oxidative and histological damage caused by cisplatin.

Genotype-Phenotype Correlations of Dystrophic Epidermolysis Bullosa in India: Experience from a Tertiary Care Centre.

Recent advances in the field of genomics have seen the successful implementation of whole exome sequencing as a rapid and efficient diagnostic strategy in several genodermatoses. The aim of this study was to explore the potential of molecular studies in dystrophic epidermolysis bullosa (DEB) in India. Whole exome sequencing was performed using genomic DNA from each case of epidermolysis bullosa, followed by massively parallel sequencing. Resulting reads were mapped to the human reference genome hg19. Sanger sequencing subsequently confirmed the potentially pathogenic mutations. Whole exome sequencing of 18 patients with DEB from 17 unrelated Indian families revealed 20 distinct sequence variants in the COL7A1 gene including 2 widely prevalent mutations. Dominant inheritance was seen in 7 patients, while 11 patients showed a highly variable recessive DEB. This preliminary study using exome sequencing is clearly encouraging and will serve as the basis for future large-scale molecular studies to actively identify and understand DEB in the Indian population.

Comparison of the peripheral antinociceptive effect of somatostatin with bupivacaine and morphine in the rodent postoperative pain model.

BACKGROUND AND OBJECTIVES: Infiltration of surgical wound with local anaesthetics attenuate postoperative pain. However, side effects can also occur. Somatostatin (SST) and its analogues like octreotide reportedly reduce peripheral sensitisation. The current study evaluates peripherally mediated antinociceptive effect of SST in a rat model of postoperative pain. This was compared with bupivacaine and morphine under identical experimental conditions. DESIGN: Randomised vehicle-controlled blind study. SETTING: Pain research laboratory, All India Institute of Medical Sciences, New Delhi from February 2014 to July 2017. EXPERIMENTAL SUBJECT: Rodent hind paw incision model. INTERVENTIONS: Sprague-Dawley rats were subjected to incision and one of the following drugs administered into the open wound once by a micropipette: SST (10, 30 or 100 µg), bupivacaine (3, 10, 30, 50 or 100 µg) or morphine (100 µg). Antinociceptive effect of SST was further evaluated for its reversibility, site of action, effect on spinal c-fos expression and blood glucose level. The site of action of morphine was also investigated. MAIN OUTCOME MEASURE: Nociception was estimated by nonevoked (guarding behaviour) and evoked (mechanical allodynia and thermal hyperalgesia) pain behaviours between 2 h and days 4 to 7. RESULTS: Nociception was maximum 2 h after incision. SST (10 to 100 µg) significantly attenuated guarding behaviour between 2 h and day 2. A delayed inhibitory effect was observed on allodynia. Bupivacaine (10 to 100 µg doses) similarly decreased guarding score up to day 2 though evoked pain behaviours were relatively unaffected. In contrast, morphine produced a potent but transient inhibitory effect on guarding score at 2 h, which was mediated by both peripheral and central opioid receptors. The antinociceptive effect of SST was peripherally mediated by type 2 receptors and was associated with decreased c-fos staining. Blood glucose level was unaltered. CONCLUSION: Guarding behaviour, which likely represents pain-at-rest following surgery, was attenuated by both bupivacaine and SST to comparable extents. This novel peripherally mediated antinociceptive effect of SST needs further evaluation.

Involvement of Neuropeptide Y in Post-Incisional Nociception in Rats.

BACKGROUND: Neuropeptide Y (NPY) is abundantly distributed in the mammalian nervous system. Its role in nociception arising from inflammatory and neuropathic pain conditions has been elucidated. However, its involvement in post-incisional nociception, particularly at the spinal cord level, is relatively unknown. PURPOSE: Management of postoperative pain is suboptimal. Evaluation of changes at the spinal level could facilitate better understanding of neural mechanisms underlying this type of pain. METHODS: Rats were subjected to hind paw incision and spatiotemporal pattern of NPY expression in the dorsal horn was investigated by immunohistochemistry. Next, rats were implanted with intrathecal catheters using previously standardized procedure. NPY was injected into the intrathecal space by an indwelling catheter and behavioral assessment of nociception was performed. RESULTS: Higher expression of NPY was observed in the superficial laminae of the dorsal horn. After incision, specific changes were observed like an abrupt decrease at 3 h after incision, which could be correlated with the intense nociception at this time. In contrast to morphine administration, which attenuated all 3 behavioral parameters of nociception, NPY decreased guarding behavior and thermal hyperalgesia during the acute phase. CONCLUSIONS: NPY is extensively expressed in the superficial laminae of the spinal cord and exhibit marked changes after incision. Nociception is also decreased after its administration. Hence, it is likely involved in post-incisional nociception. This information could have clinical relevance.

Diagnosis of Inherited Epidermolysis Bullosa in Resource-Limited Settings: Immunohistochemistry Revisited.

BACKGROUND: Immunofluorescence (IFM) antigen mapping is the most commonly used technique to diagnose and differentiate epidermolysis bullosa (EB). In India, IFM is limited to few research laboratories and is not readily available, making the diagnosis largely clinical and often inaccurate. Ob jective of the Study: To examine the diagnostic usefulness of immunohistochemistry (IHC) as compared to IFM in resource-limited settings. METHODS: Forty-four consecutive EB patients were included in this study. IHC and IFM were performed on 7-µm frozen tissue sections using standard laboratory protocols with a limited panel of antibodies. The kappa coefficient of agreement was calculated with genetic analysis as the gold standard. RESULTS: IFM and IHC accurately identified the subtype of EB in 80.9% (p < 0.001) of the cases, when a clear blister cavity was evident on biopsy. The sensitivities and specificities of IHC and IFM for diagnosing EB simplex, junctional EB, and dystrophic EB were 100, 100, and 60% and 82.4, 100, and 100%, respectively. IHC was equally effective (p < 0.001) in establishing the type of EB as IFM. CONCLUSIONS: IHC staining and its interpretation were simple and comparable to IFM. IHC had an advantage of showing subtle changes in the epidermal architecture that could not be appreciated on IFM and hence can be considered useful in resource-limited settings.

Effect of Nimodipine on Morphine-related Withdrawal Syndrome in Rat Model: An Observational Study.

OBJECTIVE: To observe the effect of L-type calcium channel blocker like nimodipine on morphine's withdrawal when it was administered continuously along with morphine versus a single bolus dose of nimodipine, which was administered at the end of the experiment before the precipitation of withdrawal reaction in morphine-dependent rats. MATERIALS AND METHODS: Four groups of adult male Wistar rats were rendered morphine dependent by subcutaneous injections of morphine at a dose of 10 mg/kg for 10 days. Nimodipine 10 mg/kg intraperitoneally (ip) administered to one group once daily before morphine administration in the entire experimental period, and another group received nimodipine only once at the end of the experiment as a single bolus dose 2 mg/kg before the administration of naloxone. Naloxone 3 mg/kg was administered ip to all the groups to precipitate withdrawal reactions. The withdrawal reactions were evaluated and scored as per the Gellert and Holtzman global withdrawal rating scale. RESULTS: Nimodipine when administered as a single bolus dose before naloxone administration in morphine-dependant rats reduced the features of withdrawal reactions more effectively than continuous administration of nimodipine along with morphine throughout the experimental period. CONCLUSION: We discovered that nimodipine helps in attenuating the severity of morphine withdrawal having potential role encountered during pharmacotherapy with morphine management of opioid dependence, well memory, impairement, cell signaling and phosphorylation of neuron.

Role of fosaprepitant, a neurokinin Type 1 receptor antagonist, in morphine-induced antinociception in rats.

OBJECTIVES: Opioids such as morphine form the cornerstone in the treatment of moderate to severe pain. However, opioids also produce serious side effects such as tolerance. Fosaprepitant is a substance P (SP) receptor antagonist, which is used for treating chemotherapy-induced nausea and vomiting. SP is an important neuropeptide mediating transmission of pain at the spinal level. Thus, it was hypothesized that combining morphine with fosaprepitant would increase the antinociceptive effect of morphine. The objectives were to evaluate the effect of fosaprepitant on morphine-induced antinociception in rats and to investigate its mechanism of action. METHODS: Sprague-Dawley rats were injected with morphine (10 mg/kg twice daily) and/or fosaprepitant (30 mg/kg once daily) for 7 days. Pain threshold was assessed by the hot plate test. Expression of SP and calcitonin gene-related peptide (CGRP) in the spinal cords of these rats was evaluated by immunohistochemistry. RESULTS: Morphine administration resulted in an antinociceptive effect compared to the control group (day 1 and to a lesser extent on day 4). The decreased antinociception despite continued morphine treatment indicated development of tolerance. Co-administration of fosaprepitant attenuated tolerance to morphine (days 1 and 3) and increased the antinociceptive effect compared to control group (days 1-4). Expression of SP was increased in the morphine + fosaprepitant group. CONCLUSIONS: The results show that fosaprepitant attenuates the development of tolerance to morphine and thereby, increases the antinociceptive effect. This is likely linked to decreased release of SP from presynaptic terminals.

Comparative antinociceptive effect of arachidonylcyclopropylamide, a cannabinoid 1 receptor agonist & lignocaine, a local anaesthetic agent, following direct intrawound administration in rats.

BACKGROUND & OBJECTIVES: Treatment of inflammatory pain with opioids is accompanied by unpleasant and, at times, life-threatening side effects.Cannabis produces antinociception as well as psychotropic effects. It was hypothesized that peripheral cannabinoid receptors outside the central nervous system could be selectively activated for relief of pain. This study was undertaken to measure the antinociceptive effect of type 1 cannabinoid receptor (CB1r) agonist arachidonylcyclopropylamide (ACPA) in a rat model of inflammatory pain after intrawound administration and the effects were compared with lignocaine. METHODS: Wounds were produced under controlled conditions by an incision in the right hind paw in rats. ACPA (10, 30 or 100 µg/10 µl) was administered directly into the wound. Antinociception was evaluated by guarding, allodynia and thermal hyperalgesia. This was compared to lignocaine (30 µg/10 µl). Reversal of ACPA (30 µg)-mediated antinociceptive effect was attempted by intrawound AM251 (100 µg), a CB1r antagonist. Antinociception was also evaluated after contralateral administration of ACPA (30 µg). Primary afferent nociceptive input to the spinal cord was investigated by c-Fos expression after ACPA treatment (100 µg). RESULTS: ACPA, but not lignocaine, inhibited guarding behaviour, which was locally mediated. Conversely, lignocaine, but not ACPA, inhibited thermal hyperalgesia and mechanical allodynia. ACPA-mediated inhibitory effect was reversible and dose dependent. It was associated with a decreased c-Fos expression. Locomotor activity was unaffected following ACPA (100 µg) treatment. INTERPRETATION & CONCLUSIONS: Lignocaine attenuated evoked pain behaviour whereas ACPA decreased guarding score. This difference was likely due to blockade of sodium ion channels and the activation of peripheral CB1r, respectively. Central side effects were absent after ACPA treatment. Further studies need to be done to assess the effect of ACPA treatment in clinical conditions.

Antinociceptive effect of 1400 W, an inhibitor of inducible nitric oxide synthase, following hind paw incision in rats.

Acute tissue damage is accompanied by synthesis of nitric oxide (NO) in the inflamed tissue as well as in the spinal cord. NO release at the spinal level is likely involved in the neuroplastic changes contributing to pain. Also, previous studies indicate that this could be due to the inducible isoform of the nitric oxide synthase (iNOS) enzyme. Though, the role of NO has been investigated in several animal models of nociception, the precise contribution of NO to nociception arising from hind paw incision is unknown, which is a rodent model of postoperative pain. In the present work, we have estimated the formation of NO in Sprague-Dawley rats, both at the site of incision and the corresponding spinal cord levels by Griess assay. Subsequently, naive rats were implanted with chronic indwelling intrathecal (i.t.) catheters. Fixed quantity (30 µg) of 1400 W, an iNOS inhibitor, was either administered locally into the wound at the time of incision or into the i.t. space, 15 min before hind paw incision. In a different set, i.t. 1400 W was administered, 20 h after incision. Control group received i.t. saline. Nociception was evaluated by guarding score, mechanical allodynia and thermal hyperalgesia. NO level was significantly increased between 4 h - day 1 locally and at 4 h at the spinal level after incision. Local inhibition of iNOS produced transient decrease of guarding (4-12 h) whereas pronounced decrease of guarding and allodynia was evident after spinal inhibition of iNOS. Also, spinal NO level decreased after i.t. drug administration. Post-incision drug treatment resulted in greater antinociceptive effect at day 1 though not on day 2. These results indicate involvement of NO in postincisional nociception in rats.

Role of somatostatin and somatostatin receptor type 2 in postincisional nociception in rats.

Somatostatin (SST) and the somatostatin receptor type 2 (sstr2) are expressed in the superficial part (Laminae I-III) of the dorsal horn of the spinal cord. Since the neurons in these laminae also receive nociceptive sensation from the periphery, it was hypothesized that both SST and sstr2 could be involved in the modulation of nociceptive transmission. To the best of knowledge, there are no studies on the involvement of SST and sstr2 in hind paw incision model in rats, which mimics postoperative pain in humans. Sprague-Dawley rats were subjected to hind paw incision under isoflurane anaesthesia and the resulting mechanical allodynia and thermal hyperalgesia were evaluated for 5 days. In another set of animals, the spinal cord was isolated at specified time intervals after incision and examined for SST and sstr2 expression using immunohistochemistry and immunoblotting procedures. Finally, nociceptive parameters were again evaluated in incised rats, which had received SST (400 µg/kg i.p. three times per day). Blood glucose level and locomotor activity were determined after SST treatment. Both allodynia and hyperalgesia were highest immediately after incision. Spinal SST expression increased at 2 h. A further increase was noted on day 3. Expression of sstr2 increased initially but decreased at day 1. These changes could be due to exocytosis of SST and internalization of the ligand-receptor complex. SST injection significantly attenuated mechanical allodynia but not thermal hyperalgesia. Significant change in blood glucose level or locomotor activity was absent. SST appears to contribute to postincisional pain. This finding could be of clinical relevance.

Chronic spinal infusion of loperamide alleviates postsurgical pain in rats.

Plantar incision in rat generates spontaneous pain behaviour. The opioid drug, morphine used to treat postsurgical pain produces tolerance after long-term administration. Loperamide, a potent mu-opioid agonist, has documented analgesic action in various pain conditions. However, loperamide analgesia and associated tolerance following continuous spinal administration in postsurgical pain has not been reported. Chronic spinal infusion of drugs was achieved using intrathecal catheters connected to osmotic minipump. Coinciding with the onset of spinal infusion of loperamide or morphine, rats were subjected to plantar incision. Pain-related behaviour was assessed by Hargreaves apparatus (thermal hyperalgesia) and von Frey filaments (mechanical allodynia). Morphine and loperamide (0.5, 1 and 2 microL/h) induced analgesia was observed until 7th day post-plantar incision in Sprague-Dawley rats. Morphine and loperamide produced dose-dependent analgesia. Loperamide, in the highest dose, produced analgesia till 7th day. However, the highest dose of morphine produced inhibition of thermal hyperalgesia till 5th day and mechanical allodynia only till 3rd day post-plantar incision. Morphine and loperamide produced analgesia in postsurgical pain, which may be mediated through different mechanisms. Longer duration of analgesia with loperamide could probably be due sustained blockade of calcium channels.

Locally mediated analgesic effect of bradykinin type 2 receptor antagonist HOE 140 during acute inflammatory pain in rats.

Opioids like morphine form the mainstay of treatment for moderate to severe burn pain. However, lack of dedicated burn care service and potentially serious side effects of opioids often compromise effective treatment. Newer drugs as well as newer routes of administration of analgesic drugs are long-felt needs in the management of burn pain. Bradykinin is a potent inflammatory mediator present at sites of tissue damage. The present study investigated the analgesic effect of bradykinin type 2 receptor antagonist HOE 140 after direct intrawound administration in rats. Also, whether the analgesic effect was locally mediated was further evaluated. Tissue damage was produced by a surgical incision involving skin, fascia, and muscle. It has been reported that there are minor differences in inflammatory mediators underlying incision-related and burn injury-related pain. HOE 140 (1, 3, or 10 µg/10 µl physiological saline) was administered into the wound by a sterile micropipette. After an interval of 30 seconds, the wound was closed. HOE 140-induced analgesic effect was compared to other experimental groups of rats which did not receive any drug or those which were treated with either saline (vehicle) or water. Postincisional pain was determined by monitoring behavior, allodynia, and thermal hyperalgesia. Analgesic effect was also determined after drug administration in contralateral paw. HOE 140 (1, 3, 10 µg) significantly relieved mechanical allodynia and guarding in comparison with vehicle-treated group. The analgesic effect of HOE 140 was locally mediated. Healing of the wound was normal. In conclusion, the results suggest that bradykinin type 2 receptor antagonists such as HOE 140 could be useful in the treatment of acute inflammatory pain.

Antinociceptive effect of intrathecal loperamide: role of mu-opioid receptor and calcium channels.

Morphine is a gold standard analgesic commonly used to alleviate pain. However, its use is associated with unavoidable side effects including the risk for addiction. Peripherally administered loperamide lacks effect on the central nervous system as it is a substrate for the permeability glycoprotein (P-gp) efflux pump which blocks its entry into brain. However, when administered intrathecally, loperamide has been reported to produce analgesia. The present study investigates the mechanism of the central analgesic effect of loperamide. Adult male Sprague-Dawley rats were subjected to surgery for catheter placement. Following baseline testing, different groups of rats were administered fixed intrathecal doses (1 µg, 3 µg, 10 µg and 30 µg) of loperamide and morphine. Analgesia was compared employing Hargreaves paw withdrawal apparatus at 15 min, 30 min, 60 min, 90 min and 120 min. Additionally, CTOP, a specific mu-opioid receptor antagonist was co-administered with loperamide to examine the mu-opioid receptor mediated loperamide analgesia. Furthermore, nefiracetam, a calcium channel opener, was co-administered with loperamide or morphine to evaluate the involvement of Ca(2+) channels in Loperamide showed an analgesic effect which was comparable to morphine. However, loperamide produced longer analgesia and the analgesic effect was significantly better at 42 h and 49 h compared to morphine. CTOP completely reversed loperamide analgesia. Though nefiracetam significantly reversed loperamide analgesia, it did not have any effect on morphine induced analgesia. Our findings suggest that loperamide administered intrathecally produces analgesia which is mediated through mu-opioid receptor and subsequent blockade of downstream calcium channels.

Nimodipine down-regulates CGRP expression in the rat trigeminal nucleus caudalis.

L-type calcium channel blockers like verapamil are used in the prophylaxis of migraine. However, their effect on the expression of CGRP in the trigeminal nucleus caudalis (TNC) is unknown. It is important because an earlier study had shown that olcegepant, a CGRP receptor antagonist, acts at the level of the trigeminal spinal nucleus rather than the trigeminal ganglia. Nimodipine was used in the present study as it crosses the blood-brain barrier. The objective of the study was to determine the pattern of expression of calcitonin gene-related peptide (CGRP) in the TNC after administration of nimodipine and/or morphine. Wistar rats were injected with saline, morphine, nimodipine or morphine + nimodipine for 14 days. Subsequently, the lowest part of the medulla oblongata containing the spinal nucleus was removed and processed for immunohistochemical localization of CGRP. The density of expression was quantified using Image J software. The results were statistically analyzed. CGRP expression was noted over the superficial part of the TNC, which decreased significantly after nimodipine administration. Conversely, morphine produced an up-regulation. The expression was unchanged with reference to saline in the morphine + nimodipine treated group. Decreased expression of CGRP in the trigeminal nucleus caudalis after nimodipine is being reported for the first time. Also, whether CGRP expression can be used as a marker for predicting the therapeutic efficacy of an anti-migraine drug is currently being investigated.

Small-sized neurons of trigeminal ganglia express multiple voltage-sensitive calcium channels: a qualitative immunohistochemical study.

The cell bodies of pseudounipolar neurons of the trigeminal ganglia have been presumed to play a supportive role to neurites, which transmit various sensations like pain from the periphery to the brain stem. However, several studies have recently shown that these neuronal cell bodies could modulate the afferent stimuli by up-regulating various ion channels and also by increasing the synthesis of neuropeptides like calcitonin gene-related peptide (CGRP). Since voltage-sensitive calcium ion channels (VSCCs) determine neuropeptides/neurotransmitters released by neurons, the aim of the present study was to localize the various VSCCs (N-, P/Q-, L-, T- and R-types) in the trigeminal ganglia neurons by immunohistochemistry. The results showed that all the VSCCs are expressed by the cell bodies of neurons though the small-sized neurons showed higher expression of these channels. The small-sized neurons were identified by immunohistochemical localization of CGRP, the most common neuropeptide for pain transmission in the trigeminal ganglia neurons. Some of these channels (N, P/Q and T types) were also expressed on the cell surface though previous electrophysiological studies have shown the expression of all the channels on the cell surface. It is suggested that the cell bodies could play a more active role than hereto ascribed to these, in the modulation of sensory stimuli.

Differential expression of L- and N-type voltage-sensitive calcium channels in the spinal cord of morphine+nimodipine treated rats.

We have earlier reported that nifedipine and nimodipine, both L-type voltage-sensitive calcium channel (L-VSCC) antagonists, attenuate the development of tolerance to chronic administration of morphine in the rat. In the present study, we have investigated the expression of L- and N-type VSCC using immunohisto-chemistry, in the cervical region of the spinal cords from animals treated chronically with morphine alone or in combination with nimodipine. The highest expression of both VSCCs within the spinal cord was detected within the superficial laminae of the dorsal horn, which indicates that these channels play an important role in the spinal processing of pain. After morphine tolerance, the expression of both the channels in the superficial laminae was significantly higher than control animals. However, morphine+nimodipine administration produced a differential effect, that is, the expression of L-VSCC decreased while that of N-VSCC increased. The study shows that the expression of these channels is plastic and subject to change depending upon the drug administered. This in turn can determine overall responsiveness to morphine.