Intraperitoneal Injection Of Morphine Research Articles

An experimental model for primary neuropathic corneal pain induced by long ciliary nerve ligation in rats.

Neuropathic corneal pain (NCP) is a new and ill-defined disease characterized by pain, discomfort, aching, burning sensation, irritation, dryness, and grittiness. However, the mechanism underlying NCP remain unclear. Here, we reported a novel rat model of primary NCP induced by long ciliary nerve (LCN) ligation. After sustained LCN ligation, the rats developed increased corneal mechanical and chemical sensitivity, spontaneous blinking, and photophobia, which were ameliorated by intraperitoneal injection of morphine or gabapentin. However, neither tear reduction nor corneal injury was observed in LCN-ligated rats. Furthermore, after LCN ligation, the rats displayed a significant reduction in corneal nerve density, as well as increased tortuosity and beading nerve ending. Long ciliary nerve ligation also notably elevated corneal responsiveness under resting or menthol-stimulated conditions. At a cellular level, we observed that LCN ligation increased calcitonin gene-related peptide (neuropeptide)-positive cells in the trigeminal ganglion (TG). At a molecular level, upregulated mRNA levels of ion channels Piezo2, TRPM8, and TRPV1, as well as inflammatory factors TNF-α, IL-1β, and IL-6, were also detected in the TG after LCN ligation. Meanwhile, consecutive oral gabapentin attenuated LCN ligation-induced corneal hyperalgesia and increased levels of ion channels and inflammation factors in TG. This study provides a reliable primary NCP model induced by LCN ligation in rats using a simple, minimally invasive surgery technique, which may help shed light on the underlying cellular and molecular bases of NCP and aid in developing a new treatment for the disease.

Differential local field potential oscillations in the dorsal striatum and locomotor activity induced by morphine and haloperidol in mice.

Dopamine (DA) depletion in the dorsal striatum underlies symptoms of basal ganglia pathologies, including Parkinson's disease (PD). Various drug compounds are used to enhance DA levels for therapeutic purposes. Understanding neural signaling and movement patterns associated with over‑ and under‑stimulation of the DA system is essential. This study investigated striatal local field potential (LFP) oscillation and locomotor activity following treatments with morphine, a DA release enhancer, and haloperidol (HAL), a DA D2 receptor (D2R) antagonist in mice. After intracranial electrodes were placed into the dorsal striatum of male Swiss albino ICR mice, intraperitoneal injections of morphine or HAL were administered. LFP signals and spontaneous motor activity were recorded simultaneously. The results showed that morphine significantly increased locomotor speed, both low (30.3-44.9 Hz) and high (60.5-95.7 Hz) LFP gamma powers and delta (1-4 Hz)‑gamma (30.3-95.7 Hz) phase‑amplitude coupling. In contrast, HAL treatments were found to significantly decrease these parameters. Moreover, regression analyses also revealed significant positive correlations between locomotor speed and high gamma powers. Taken together, these results demonstrate opposite LFP oscillations in the dorsal striatum with low and high gamma activities, and delta‑gamma couplings in response to a DA release enhancer and D2R antagonist by morphine and HAL, respectively. These parameters reflect fluctuation of neuronal activity in the dorsal striatum that might be useful for pathological research and drug discovery for PD.

Applications of Sumach extract in reduction of male reproductive parameters damages following morphine administration through down-regulated apoptotic genes

Morphine (MO), a psychoactive member of opium family, causes free radicals’ accumulation in cells. Sumach (SU) is a medicinal plant with antioxidative activities. This study was designed to assess the probable ameliorative effects and alteration of apoptotic genes expression after SU extract administration on testopathy caused by chronic MO contamination. Sixty-four male rats were divided into 8 groups: 1, normal; 2, MO; 3, 200 mg/kg SU; 4, 400 mg/kg SU; 5, 800 mg/kg SU; 6, MO + 200 mg/kg SU; 7, MO + 400 mg/kg SU; and 8. MO + 800 mg/kg SU. All intraperitoneal injections of MO (10 mg/kg) were applied on the first day of the experiment, and SU extract was also treated orally (through a nasogastric tube) on the other 2-28 days. Apoptotic genes expression (P53, Bcl2 and caspase-3) and inflammatory cytokines were measured by Real-Time PCR and ELISA techniques, respectively. Also, total antioxidant capacity (TAC) and male reproductive parameters were detected quantitatively. In MO group, significant detrimental changes of testes (including all investigated parameters) were detected in comparison with the normal group (P ˂ 0.01), but genes expression of P53 and caspase-3 and inflammatory cytokine showed a significant incremental trend. In SU (200, 400, and 800 mg/kg) and SU (200, 400, and 800 mg/kg) + MO treated groups, all values were accelerated significantly in comparison with MO group (P ˂ 0.01), but genes expression of P53 and caspase-3, along with inflammatory cytokine indices, were down-regulated. Totally, therapeutic effects of SU extract were approved biochemically and histologically to scavenge MO impacts.

Medial Prefrontal Cortical Cannabinoid CB1 Receptors Mediate Morphine–Dextromethorphan Cross State-Dependent Memory: The Involvement of BDNF/cFOS Signaling Pathways

The present study set out to assess the possible role of the medial prefrontal cortex (mPFC) cannabinoid CB1 receptors and BDNF/cFOS signaling pathways in morphine–dextromethorphan (DXM) cross state-dependent memory (SDM) using male Wistar rats. Changes on the levels of BDNF and cFOS proteins in the PFC were examined by Western blot analysis. Present results revealed that levels of BDNF and cFOS proteins were significantly increased in the animals that were trained in the passive avoidance apparatus. Intraperitoneal injection of morphine (6 mg/kg, i.p.) after training impaired memory which was associated with decreases in the levels of both proteins. Moreover, the injection of a cannabinoid CB1 receptor agonist, ACPA, or a selective CB1 receptor antagonist, AM-251, into the mPFC prior to testing had no effect on memory retrieval by itself and also on morphine-induced memory loss. Pre-test administration of DXM (a NMDA receptors antagonist, 30 mg/kg, i.p.) impaired memory retrieval and attenuated BDNF levels. Moreover, DXM administration (pre-test) prevented morphine-induced memory loss and increased the levels of both proteins, suggesting morphine-DXM cross-SDM. Interestingly, pre-test intra-mPFC injections of ACPA inhibited cross-SDM between the drugs which was associated with an elevation of BDNF expression in the PFC. Additionally, pre-test administration of an ineffective dose of DXM (10 mg/kg, i.p.) could not reverse morphine-induced memory loss, while pre-test intra-mPFC injections of AM-251 potentiated morphine-DXM cross-SDM. Taken together, it can be concluded that mPFC through CB1cannabinoid receptors has a critical role in morphine-DXM cross-SDM which may be associated with the PFC BDNF/cFOS signaling pathway.

Short-Period Influence of Chronic Morphine Exposure on Serum Levels of Sexual Hormones and Spermatogenesis in Rats.

BackgroundIncreased rates of addiction and its broad societal complications are well known. One of the most important systems that may malfunction in drug abusers is the reproductive system, and evaluating patients for this potential risk may lead to increased awareness.Materials and MethodsThirty 60-day-old male rats were divided into control and target groups. The target group underwent 5 mg/kg intraperitoneal injections of morphine twice a day while the control group underwent normal saline injections (at the same dosage). After 60 days, the rats were anesthetized, and after blood sampling, they underwent bilateral orchiepididymectomy. Histological and hormonal evaluations were performed on the samples.ResultsLevels of sex hormonal features and spermatogenesis were significantly reduced in the target group compared to the control group. LH levels showed a meaningful decrease in the target group, but FSH and testosterone levels did not. On histological section analysis, mature sperm were meaningfully decreased in the target group.ConclusionsChronic use of opioids may lead to alterations in sexual features and sexual hormones. Therefore, opioids have the potential to cause infertility. These changes may result from the effect of the drugs on the hypophysis or hypothalamus, the direct effect of the drugs on the seminiferous tubules, or a combination of both. The findings suggest that public awareness about addiction may cause decreased infertility rates.

Inhibition of microglia in the basolateral amygdala enhanced morphine-induced antinociception: Possible role of GABAA receptors

In clinical medicine, morphine is widely used to relieve many types of pain, but it has several side effects such as the development of tolerance and dependence. In order to decrease the side effects of morphine administration for the treatment of pain, the combination of minocycline as a glial inhibitor and morphine has been suggested in previous studies. It is important to understand which synaptic mechanisms are involved in the potentiative effect of minocycline on morphine antinociception. To this aim, male Wistar rats were bilaterally cannulated in the basolateral amygdala by srereotaxic instrument. A tail-flick apparatus was used to measure the pain threshold. The results revealed that intraperitoneal injection of morphine (2.5–7.5mg/kg) induced antinociception. Intra-basolateral amygdala microinjection of minocycline (5–10µg/rat) by itself had no effect on tail-flick latency, while the microinjection of the same doses of minocycline with an ineffective dose of morphine (5mg/kg) induced antinociception. Intra-basolateral amygdala microinjection of different doses of muscimol (0.001–0.005µg/rat) increased the minocycline-induced potentioation on morphine response in the tail-flick test. Intra-basolateral amygdala microinjection of muscimol by itself had no effect on tail-flick latency. On the other hand, intra-basolateral amygdala microinjection of bicuculline (0.01–0.1µg/rat) inhibited minocycline-induced potentiation of morphine antinociception. It should be noted that intra-basolateral amygdala bicucculine by itself had no effect on tail-flick latency. It can thus be concluded that intra-basolateral amygdala minocycline potentiates morphine response in the tail-flick test. Moreover, basolateral amygdala GABAergic system may be involved in the minocycline-induced potentiation of morphine response via GABAA receptors.

Spontaneous Chronic Pain After Experimental Thoracotomy Revealed by Conditioned Place Preference: Morphine Differentiates Tactile Evoked Pain From Spontaneous Pain

Chronic pain after surgery limits social activity, interferes with work, and causes emotional suffering. A major component of such pain is reported as resting or spontaneous pain with no apparent external stimulus. Although experimental animal models can simulate the stimulus-evoked chronic pain that occurs after surgery, there have been no studies of spontaneous chronic pain in such models. Here the conditioned place preference (CPP) paradigm was used to reveal resting pain after experimental thoracotomy. Male Sprague Dawley rats received a thoracotomy with 1-hour rib retraction, resulting in evoked tactile hypersensitivity, previously shown to last for at least 9 weeks. Intraperitoneal injections of morphine (2.5 mg/kg) or gabapentin (40 mg/kg) gave equivalent 2- to 3-hour-long relief of tactile hypersensitivity when tested 12 to 14 days postoperatively. In separate experiments, single trial CPP was conducted 1 week before thoracotomy and then 12 days (gabapentin) or 14 days (morphine) after surgery, followed the next day by 1 conditioning session with morphine or gabapentin, both versus saline. The gabapentin-conditioned but not the morphine-conditioned rats showed a significant preference for the analgesia-paired chamber, despite the equivalent effect of the 2 agents in relieving tactile allodynia. These results show that experimental thoracotomy in rats causes spontaneous pain and that some analgesics, such as morphine, that reduce evoked pain do not also relieve resting pain, suggesting that pathophysiological mechanisms differ between these 2 aspects of long-term postoperative pain. PerspectiveSpontaneous pain, a hallmark of chronic postoperative pain, is demonstrated here in a rat model of experimental postthoracotomy pain, further validating the use of this model for the development of analgesics to treat such symptoms. Although stimulus-evoked pain was sensitive to systemic morphine, spontaneous pain was not, suggesting different mechanistic underpinnings.

The role of histone acetylation in the basolateral amygdala in morphine-associated memory in rats

To examine the regulatory effect of histone acetylation on memory related molecules, 34 healthy male SD rats were randomly divided into control and basolateral amygdala (BLA) intracranial positioning operation groups. In the process of conditioned place preference (CPP) training, Trichostafin A (TSA) was administrated by the route of BLA and morphine was injected into enterocoelia with dimethyl sulfoxide or saline as control. Expression levels of H3K14 acetylation and brain-derived neurotrophic factor (BDNF) in BLA were evaluated by Western blotting.The results showed that CPP could be established by intraperitoneal injection of morphine. Compared with control groups, a stronger place preference was established and expression of H3K14 acetylation and BDNF was significantly increased in the group treated with TSA and morphine. In addition, there was a synergistic effect between morphine and TSA. Our results suggested that the level of histone acetylation in BLA is associated with the formation of morphine memory in rats. Inhibition of the activity of histone deacetylases in BLA can promote the formation of cue-associated memory induced by morphine and the involvement of BDNF in BLA maybe was regulated by histone acetylation.

Divergent Effect of Dezocine, Morphine and Sufentanil on Intestinal Motor Function in Rats

Background: Opioid induced bowel dysfunction is the most common side effect of preoperatively administrated morphine, fentanyl and its derivative. However, the influence of dezocine on intestinal mobility is rarely reported. This study was designed to investigate the effects of dezocine, morphine and sufentanil on both intestinal smooth muscle contraction and propulsion in rats.Methods: Contractile tension and frequency of isolated rat small intestine smooth muscle were measured using tension transducer after incubation with different concentrations of dezocine, morphine and sufentanil. The propulsive rate of methylene blue in rat intestinal tract was measured 30 minutes after intraperitoneal injection of morphine, sufentanil and dezocine. Percent of change in contractile tension and contraction frequency compared to baseline level were calculated to evaluate muscle contraction. Propulsive rate of methylene blue was calculated as the percentage of methylene blue moving distance in intestinal tract compared to the length of the small intestine.Results: Morphine and sufentanil significantly increased the contractile tension of isolated small intestine smooth muscle at high doses. The contraction frequency did not change significantly among the 3 tested doses. Increasing the dose of dezocine from 1.7 mg.L-1 to 10.2 mg.L-1 did not change either the contractile tension or the contraction frequency. The propulsive rate of methylene blue in intestinal tract was significantly decreased after the treatment with morphine, sufentanil and dezocine (45.6%, 43.7%, and 42.1% respectively) compared to control group(57.1%), while the difference among the 3 drug groups were not significant.Conclusion: Morphine and sufentanil may dose dependently increase the contractile tension and contraction ability of isolated rat small intestine smooth muscle, while dezocine has no significant effect on intestine smooth muscle contraction. However, all these opioids might impair small intestinal propulsion.

Interaction between morphine and noradrenergic system of basolateral amygdala on anxiety and memory in the elevated plus-maze test based on a test-retest paradigm.

The amygdala is the key brain structure for anxiety and emotional memory storage. We examined the involvement of β-adrenoreceptors in the basolateral amygdala (BLA) and their interaction with morphine in modulating these behaviors. The elevated plus-maze has been employed for investigating anxiety and memory. Male Wistar rats were used for this test. We injected morphine (4, 5, and 6 mg/kg) intraperitoneally, while salbutamol (albuterol) (1, 2, and 4 μg/rat) and propranolol (1, 2, and 4 μg/rat) were injected into the BLA. Open- arms time percentage (%OAT), open- arms entry percentage (%OAE), and locomotor activity were determined by this behavioral test. Retention was tested 24 hours later. Intraperitoneal injection of morphine (6 mg/kg) had an anxiolytic-like effect and improvement of memory. The highest dose of salbutamol decreased the anxiety parameters in test session and improved the memory in retest session. Coadministration of salbutamol and ineffective dose of morphine presenting anxiolytic response. In this case, the memory was improved. Intra-BLA administration of propranolol (4 μg/rat) decreased %OAT in the test session, while had no effect on memory formation. Coadministration of propranolol and morphine (6 mg/kg) showed an increase in %OAT. There was not any significant change in the above- mentioned parameter in the retest session. Coadministration of morphine and propranolol with the effective dose of salbutamol showed that propranolol could reverse anxiolytic-like effect. We found that opioidergic and β-adrenergic systems have the same effects on anxiety and memory in the BLA; but these effects are independent of each other.

Abstract 2808: Morphine modulates the paracrine interaction between breast tumor cells and macrophages.

Abstract While opioids are highly effective perioperative analgesics, there have been concerns about their effects on the growth and spread of tumor cells when used in cancer surgery patients. Using a mouse syngeneic model of breast cancer, we studied the effect of morphine on breast tumor dissemination to lungs. Intraperitoneal injection of morphine (10mg/kg) to BALB/c mice (n=8) every 12h for 3 consecutive days, caused a reduction in the number of tumor foci in lungs as measured 18 days after intravenous tumor inoculation. Morphine treatment also caused a reduction in circulating extracellular matrix (ECM)-degrading matrix metalloproteinase-9 (MMP-9) measured by gelatin zymography. One of the major contributors to tumor cell invasiveness is the immune cells infiltrating the tumors, particularly macrophages. Therefore, we tested the effect of morphine on the production of gelatinases by murine breast cancer cells 4T1 and macrophages RAW264.7 alone or cultured together. The levels of MMP-9 as well as its endogenous inhibitor tissue inhibitor of metalloproteinase-1 (TIMP-1) were shown to be elevated in the conditioned media of the co-cultures. Interestingly, we found out that although morphine treatment did not have any significant effect on the level of gelatinases produced by individual cells, in the co-cultures it caused a significant decrease in MMP-9 while increasing TIMP-1.We observed the same effect when breast cancer cells were incubated with the conditioned media of morphine-treated macrophages, indicating that cell-cell interaction was not required. Our in vitro data thus suggest that the anti-tumor effect of morphine observed in our animal studies is at least in part mediated through modulating the paracrine communication between tumour cells and tumor associated macrophages in their microenvironment rather than an effect on tumor cells alone. Randomized prospective clinical studies are required to determine how opioids, as a part of the perioperative pain management, could affect breast tumor recurrence and metastasis in patients. Citation Format: Banafsheh Afshar Imani, JoAnne Baran, Peter J. Cabot, Marie-Odile Parat. Morphine modulates the paracrine interaction between breast tumor cells and macrophages. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2808. doi:10.1158/1538-7445.AM2013-2808

Angiotensin II Produces Nociceptive Behavior through Spinal AT1 Receptor-Mediated p38 Mitogen-Activated Protein Kinase Activation in Mice

BackgroundIt has been demonstrated that angiotensin II (Ang II) participates in either the inhibition or the facilitation of nociceptive transmission depending on the brain area. Neuronal Ang II is locally synthesized not only in the brain, but also in the spinal cord. Though the spinal cord is an important area for the modulation of nociception, the role of spinal Ang II in nociceptive transmission remains unclear. Therefore, in order to elucidate the role of Ang II in nociceptive transmission in the spinal cord, we examined the effect of intrathecal (i.t.) administration of Ang II into mice.ResultsI.t. administration of Ang II produced a behavioral response in mice mainly consisting of biting and/or licking of the hindpaw and the tail along with slight hindlimb scratching directed toward the flank. The behavior induced by Ang II (3 pmol) was dose-dependently inhibited by intraperitoneal injection of morphine (0.1-0.3 mg/kg), suggesting that the behavioral response is related to nociception. The nociceptive behavior was also inhibited dose-dependently by i.t. co-administration of losartan (0.3-3 nmol), an Ang II type 1 (AT1) receptor antagonist, and SB203580 (0.1-1 nmol), a p38 MAPK inhibitor. However, the Ang II type 2 (AT2) receptor antagonist PD123319, the upstream inhibitor of ERK1/2 phosphorylation U0126, and the JNK inhibitor SP600125 had no effect on Ang II-induced nociceptive behavior. Western blot analysis showed that the i.t. injection of Ang II induced phosphorylation of p38 MAPK in the lumbar dorsal spinal cord, which was inhibited by losartan, without affecting ERK1/2 and JNK. Furthermore, we found that AT1 receptor expression was relatively high in the lumbar superficial dorsal horn.ConclusionsOur data show that i.t. administration of Ang II induces nociceptive behavior accompanied by the activation of p38 MAPK signaling mediated through AT1 receptors. This observation indicates that Ang II may act as a neurotransmitter and/or neuromodulator in the spinal transmission of nociceptive information.

Anti-inflammatory and antinociceptive effects of 6-(4-chlorophenoxy)-tetrazolo[5,1-a]phthalazine in mice

BackgroundQUAN-0808 (6-(4-chlorophenoxy)-tetrazolo[5,1-a]phthalazine), a new phthalazine tetrazole derivative, was evaluated for the anti-inflammatory and analgesic effects. MethodsXylene-induced ear edema, carrageenan (Carr)-induced paw edema, and acetic acid-induced capillary permeability hyperactivity in mice were used to assess the anti-inflammatory effect; acetic acid-induced writhing and hot plate responses for the analgesic activity. ResultsIn the present study, QUAN-0808 (100, 200, 400mg/kg) and indomethacin (Indo) significantly decreased xylene-induced ear edema by 33.3, 37.5, 46.6, and 45.1%, respectively, decreased Carr-induced paw edema at 1, 2, 4h after Carr injection, and decreased the prostaglandin E2 (PGE2) and nitric oxide (NO) levels on the edema paw at 4h after Carr injection; QUAN-0808 (100, 200, 400mg/kg), and aspirin (Asp, 200mg/kg) significantly decreased Evans blue exudation in acetic acid-induced capillary permeability hyperactivity model by 26.7, 28.7, 32.3 and 29.1%, respectively, and decreased the numbers of acetic acid-induced writhing response in 15min by 40.4, 53.6, 66.4, and 64.5%, respectively. Morphine (10mg/kg) significantly increased the latency of the hot plate response by 136.5,117.4,67.5, and 22.7%, respectively, at 30, 60, 90, 120min after intraperitoneal injection of morphine; however, QUAN-0808 (100, 200 and 400mg/kg) did not produce significantly antinociceptive effects in the hot plate test, suggesting that its antinociceptive action occurs via peripheral rather than a central-acting mechanism. ConclusionsThese results show that QUAN-0808 produced potential anti-inflammatory and peripheral antinociceptive effects, and indicated that the antinociceptive effects of QUAN-0808 were related to its anti-inflammatory activity in a dose-dependent manner. Therefore, as inflammation is a peripheral process, it is suggested that QUAN-0808 exerted peripheral effects. The peripheral effect mechanisms of QUAN-0808 may be related to a decrease in the production of PGE2, NO, bradykinin and other inflammatory mediators.

Effects of a Rhodiola rosea L. extract on the acquisition, expression, extinction, and reinstatement of morphine-induced conditioned place preference in mice

Opioid addiction is a chronic, recurrent brain disease that is characterised by compulsive drug seeking and a high rate of relapse even after long periods of abstinence. Prevention of relapse is the primary goal of addiction treatment and is still the major limitation in drug therapy. The present study investigated the effects of a Rhodiola rosea L. hydroalcoholic extract (RHO), a well-known traditional oriental medicine, on establishment and reinstatement of morphine-induced conditioned place preference (CPP) in mice. CPP was induced by intraperitoneal injection of morphine (10mg/kg) as an 8-day conditioning schedule. The effects of RHO on the rewarding properties of morphine were tested in mice receiving oral administration of RHO (10, 15, and 20mg/kg) 60min prior to each morphine injection (acquisition) or prior to the CPP test on day9 (expression). Once established, CPP was extinguished by repeated testing, during which conditioned mice were injected daily with different doses of RHO. Finally, the efficacy of RHO in blocking reinstatement of CPP provoked by priming injections and physical stress was also evaluated. RHO administration showed dose dependency for prevention of establishment of CPP and was effective in facilitating extinction of morphine-induced CPP. RHO suppressed both priming- and stress-induced reinstatement of CPP in a dose-dependent manner. In conclusion, as RHO was effective for reducing craving and vulnerability to relapse, it might be a very effective natural remedy for the treatment of opioid addiction.

Functional tracing of medial nociceptive pathways using activity-dependent manganese-enhanced MRI

Manganese ion (Mn2+) was used as a paramagnetic contrast agent in T1-weighted magnetic resonance imaging (MRI) images. They enter neural cells though voltage-gated calcium channels and are activity-dependently transported along axons and across synapses. The aim of the present study was to investigate the nociceptive medial thalamus projection in rats by activity-dependent manganese-enhanced magnetic resonance imaging (MEMRI). Rats under urethane and α-chloralose anesthesia were microinjected with manganese chloride (MnCl2, 120mmol/L, iontophoretically with a 5-μA current for 15min) into the right medial thalamus. Innocuous (at a 50-μA intensity for 0.2ms) or noxious (at a 5-mA intensity for 2ms) electrical stimuli were applied through a pair of needles in the left forepaw pads once every 6s for 5h. Enhanced transport of Mn2+ were found in the anterior cingulate cortex, midcingulate cortex, retrosplenial cortex, ventral medial caudate-putamen, nucleus accumbens, and amygdala in the noxious-stimulated group. Enhancements in the anterior cingulate cortex, midcingulate cortex, ventral medial caudate-putamen, nucleus accumbens, and amygdala, but not the retrosplenial cortex, were attenuated by an intraperitoneal injection of morphine (5mg/kg and 1mg/kg/h, intraperitoneal). These results indicate that a combination of MEMRI with activity-induced manganese-dependent contrast is useful for delineating functional connections in the pain pathway.Noxious stimulation induced enhancement of manganese ion transportation from medial thalamus to cingulate cortex and medial striatum, but not motor cortex. A combination of manganese-enhanced magnetic resonance imaging with activity-dependent contrast is useful for delineating functional connections of the medial pain pathway.

Anti-opioid effects of neuropeptide FF receptors in the ventral tegmental area

The present study investigates the modulatory effects of neuropeptide FF (NPFF) receptors on the mesolimbic dopaminergic pathway controlled by opioid receptors. A stable NPFF 2 receptor agonist, dNPA, was injected into the ventral tegmental area (VTA) and the release of dopamine and serotonin within the nucleus accumbens (NAc), induced by intraperitoneal injection of morphine, was monitored using the brain microdialysis, in non-constrained rat. dNPA decreased systemic morphine-induced elevation of dopamine and serotonin metabolites within the NAc. Furthermore, co-injected with morphine into the VTA, NPFF inhibited morphine-induced stereotypy 60–120 min after the injection. This neurochemical and behavioural anti-opioid effect mediated by NPFF 2 receptors at the level of VTA suggests the involvement of NPFF in the rewarding effects of opiates on the mesolimbic dopamine system.

Modulation of basal and morphine‐induced neuronal activity by a NPFF2 selective agonist measured by c‐Fos mapping of the mouse brain

Neuropeptide FF (NPFF) is a neurotransmitter known to modulate opioid-induced analgesia, sensitization, and reward. The expression of the immediate early gene c-Fos was analyzed to map the distribution of neurons whose activity is regulated by central administration of the NPFF(2)-selective agonist dNPA in naive mice and in animals who had received a systemic injection of morphine. The number of c-Fos positive nuclei was quantified in 28 brain regions. Intracerebro-ventricular injection of 1 nmol dNPA alone produced an overall inhibition of basal c-Fos expression in the brain with a statistically significant decrease in the lateral ventral part of the bed nucleus of the stria terminalis, the medial preoptic area, and the medial parvicellular part of the paraventricular nucleus of the hypothalamus. In contrast, intraperitoneal injection of morphine 5 mg.kg(-1) induced a statistically significant increase in c-Fos expression in the prelimbic cortex, the nucleus accumbens core and shell, the ventral pallidum, the lateral hypothalamus, and the nucleus of the tractus solitarius. dNPA counteracted morphine effect only in the nucleus accumbens shell and the ventral pallidum. The inhibitory effects of a low dose of dNPA in the hypothalamus and its afferents suggest that NPFF(2) receptors negatively regulate the hypothalamic-pituitary-adrenal axis in mouse. Moreover, our study identified the nucleus accumbens shell and ventral pallidum as putative sites of interaction between NPFF and opioid systems in relation with the modulation of acute morphine rewarding and locomotor effects.

Intrathecally Administered D-Cycloserine Produces Nociceptive Behavior Through the Activation of N-Methyl-D-aspartate Receptor Ion-Channel Complex Acting on the Glycine Recognition Site

Intrathecal (i.t.) administration of D-cycloserine (100 and 300 fmol), a partial agonist of the glycine recognition site on the N-methyl-D-aspartate (NMDA) receptor ion-channel complex, produced a behavioral response mainly consisting of biting and/or licking of the hindpaw and the tail along with slight hindlimb scratching directed toward the flank in mice, which peaked at 5 – 10 min and almost disappeared at 15 min after the injection. The behavior induced by D-cycloserine (300 fmol) was dose-dependently inhibited by an intraperitoneal injection of morphine (0.5 – 2 mg/kg), suggesting that the behavioral response is related to nociception. The nociceptive behavior was also dose-dependently inhibited by i.t. co-administration of 7-chlorokynurenic acid (0.25 – 4 nmol), a competitive antagonist of the glycine recognition site on the NMDA receptor ion-channel complex; D-(−)-2-amino-5-phosphonovaleric acid (62.5 – 500 pmol), a competitive NMDA receptor antagonist; MK-801 (62.5 – 500 pmol), an NMDA ion-channel blocker; ifenprodil (0.5 – 8 nmol); arcaine (31 – 125 pmol); and agmatine (0.1 – 10 pmol), all being antagonists of the polyamine recognition site on the NMDA receptor ion-channel complex. However, [D-Phe7,D-His9]-substance P(6 – 11), a specific antagonist for substance P (NK1) receptors, and MEN-10,376, a tachykinin NK2-receptor antagonist, had no effect on D-cycloserine-induced nociceptive behavior. These results in the mouse spinal cord suggest that D-cycloserine-induced nociceptive behavior is mediated through the activation of the NMDA receptor ion-channel complex by acting on the glycine recognition site and that it does not involve the tachykinin receptor mechanism.

Endogenous histamine inhibits the development of morphine-induced conditioned place preference

The conditioned place preference (CPP) paradigm was used to investigate the effects of endogenous histamine on the processes leading to morphine-induced reward-seeking behavior in Sprague-Dawley rats. The model of CPP was used to assess the rewarding effect of morphine. The levels of histamine, glutamate, γ-aminobutyric acid (GABA), dopamine (DA) and 3,4-dihydroxyphenyl-acetic acid (DOPAC) in rat brains were measured with high-performance liquid chromatography. Immunohistochemistry technique was used to observe the morphological changes of neurons. Intraperitoneal injection of morphine (2, 5 or 10 mg/kg) induced the development of CPP in a dose-dependent manner. In addition, morphine administrations (10 mg/kg) decreased the histamine content and reduced the number and size of histaminergic neurons in the tuberomammillary nucleus (TM), as well as markedly increasing the DOPAC/DA ratios in the ventral tegmental area (VTA) and nucleus accumbens (NAc). Intraperitoneal injection of histidine (50,100 or 200 mg/kg) dose-dependently inhibited the development of morphine-induced CPP. Bilateral lesions of the TM, which decreased the histamine levels in the VTA and NAc, potentiated the development of CPP induced by morphine (1 mg/kg, a dose that produced no appreciable effect when given alone) and increased the DOPAC/DA ratios in the VTA and NAc, but did not change the glutamate or GABA levels in these nuclei. Histidine reversed the effects of the TM lesions. These results indicate that endogenous histamine plays a role in inhibiting the development of morphine-induced reward-seeking behavior, and the inhibition may involve the modulation of dopaminergic activity.

S-(+)-fenfluramine-induced nociceptive behavior in mice: Involvement of interactions between spinal serotonin and substance P systems

Intrathecal (i.t.) administration into mice of S-(+)-fenfluramine (0.01-0.1nmol), a serotonin (5-hydroxytryptamine, 5-HT) releaser, produced a behavioral response consisting of scratching, biting and licking. Here, we report the behavioral characteristics and the involvement of interactions between 5-HT and substance P (SP) systems in the S-(+)-fenfluramine-induced behavioral response. The S-(+)-fenfluramine-induced behavioral response peaked at 5-15min and almost disappeared at 20min after injection. The behavior induced by S-(+)-fenfluramine (0.1nmol) was dose-dependently inhibited by an intraperitoneal injection of morphine (0.02-0.5mg/kg), suggesting that the behavioral response is related to nociception. The S-(+)-fenfluramine-induced nociceptive behavior was significantly inhibited by pretreatment with 5-HT antiserum and co-administration of ketanserin, a selective 5-HT2 receptor antagonist. However, WAY-100635, a selective 5-HT1A receptor antagonist, and ramosetron, a selective 5-HT3 receptor antagonist, were not active. On the other hand, SP antiserum and RP67580, a selective neurokinin-1 (NK1) receptor antagonist, significantly inhibited S-(+)-fenfluramine-induced nociceptive behavior. These results suggest that i.t.-administered S-(+)-fenfluramine releases SP through the activation of 5-HT2 receptors subsequent to 5-HT release, and, as a result, produces nociceptive behavior.