The role of basolateral amygdala orexin 1 receptors on the modulation of pain and psychosocial deficits in nitroglycerin-induced migraine model in adult male rats

Background@#Migraine headaches have been associated with sensory hyperactivity and anomalies in social/emotional responses. The main objective of this study was to evaluate the potential involvement of orexin 1 receptors (Orx1R) within the basolateral amygdala (BLA) in the modulation of pain and psychosocial dysfunction in a nitroglycerin (NTG)-induced rat model of migraine. @*Methods@#Adult male Wistar rats were injected with NTG (5 mg/kg, intraperitoneal) every second day over nine days to induce migraine. The experiments were done in the following six groups (6 rats per group): untreated control, NTG, NTG plus vehicle, and NTG groups that were post-treated with intra-BLA microinjection of Orx1R antagonist SB-334867 (10, 20, and 40 nM). Thermal hyperalgesia was assessed using the hot plate and tail-flick tests. Moreover, the elevated plus maze (EPM) and open field (OF) tests were used to assess anxiety-like behaviors. The animals’ sociability was evaluated using the three-chamber social task. The NTG-induced photophobia was assessed using a light-dark box. @*Results@#We observed no change in NTG-induced thermal hyperalgesia following administration of SB-334867 (10, 20, and 40 nM). However, SB-334867 (20 and 40 nM) aggravated the NTG-induced anxiogenic responses in both the EPM and OF tasks. The NTG-induced social impairment was overpowered by SB-334867 at all doses. Time spent in the dark chamber of light-dark box was significantly increased in rats treated with SB-334867 (20 and 40 nM/rat). @*Conclusions@#The findings suggest a role for Orx1R within the BLA in control comorbid affective complaints with migraine in rats.

The ability of orexin-A to modify pain-induced cyclooxygenase-2and brain-derived neurotrophic factor expression is associated with its ability to inhibit capsaicin-induced pulpal nociception in rats

Background@#The rostral ventromedial medulla (RVM) is a critical region for the management of nociception. The RVM is also involved in learning and memory processes due to its relationship with the hippocampus. The purpose of the present study was to investigate the molecular mechanisms behind orexin-A signaling in the RVM and hippocampus’s effects on capsaicin-induced pulpal nociception and cog-nitive impairments in rats. @*Methods@#Capsaicin (100 g) was applied intradentally to male Wistar rats to induce inflammatory pulpal nociception. Orexin-A and an orexin-1 receptor antagonist (SB-334867) were then microinjected into the RVM. Immunoblotting and immunofluorescence staining were used to check the levels of cyclooxygenase-2 (COX-2) and brain-derived neurotrophic factor (BDNF) in the RVM and hippocampus. @*Results@#Interdental capsaicin treatment resulted in nociceptive responses as well as a reduction in spatial learning and memory. Additionally, it resulted in decreased BDNF and increased COX-2 expression levels. Orexin-A administration (50 pmol/1 μL/rat) could reverse such molecular changes. SB-334867 microinjection (80 nM/1 μL/rat) suppressed orexin’s effects. @*Conclusions@#Orexin-A signaling in the RVM and hippocampus modulates capsaicininduced pulpal nociception in male rats by increasing BDNF expression and decreasing COX-2 expression.

Orexin-A inhibits capsaicin-induced changes in cyclooxygenase-2 and brain-derived neurotrophic factor expression in trigeminal nucleus caudalis of rats

BACKGROUND: The trigeminal nucleus caudalis (Vc) is a primary central site for trigeminal transmitting. Noxious stimulation of the trigeminal nociceptors alters the central synaptic releases and neural expression of some inflammatory and trophic agents. Orexin-A and the orexin 1 receptor (OX1R) are expressed in pain pathways including trigeminal pain transmission. However, the the mechanism(s) underling orexin-A effects on trigeminal pain modulation have not been fully clarified. METHODS: Trigeminal pain was induced by subcutaneous injection of capsaicin in the upper lip in rats. The effect of trigeminal pain on cyclooxygenase-2 (COX-2) and brain-derived neurotrophic factor (BDNF) expression in the Vc of animals was determined by immunofluorescence. Subsequently, OX1R agonist (orexin-A) and antagonist (SB-334867-A) was administrated in the Vc to investigate the possible roles of the Vc OX1R on changes in COX-2 and BDNF levels following pain induction. RESULTS: The data indicated an increase in COX-2 and decrease in BDNF immuno-reactivity in the Vc of capsaicin, and capsaicin- pretreated with SB-334867-A (80 nM), groups of rat. However, the effect of capsaicin on COX-2 and BDNF expressions was reversed by a Vc microinjection of orexin-A (100 pM). CONCLUSIONS: Overall, the present data reveals that orexin-A can attenuate capsaicin-induced trigeminal pain through the modulation of pain effects on COX-2 and BDNF expressions in the Vc of rats.

The effects of regular exercise on capsaicin-induced pulpal pain and pain-induced changes in passive avoidance learning and memory in rats

BACKGROUND: Pulpal pain is one of the most common and severe orofacial pain conditions with considerable adverse effects on physiological processes including learning and memory. Regular exercise is known to be effective on cognitive function as well as pain processing in the central nervous system. Here, the possible effects of regular exercise on pulpal pain response as well as pain-induced changes in learning and memory efficiency in rats were investigated. METHODS: Twenty-four male Wistar rats were randomly assigned to the control, capsaicin, exercise, and exercise plus capsaicin groups. Rats in exercise groups were forced to run on a treadmill with a moderate exercise protocol for 4 weeks. Capsaicin was used to induce dental pulp pain. Passive avoidance learning and memory performance was assessed by using a shuttle box apparatus. RESULTS: According to the results, regular exercise could decrease the time course of capsaicin-induced pulpal pain (P < 0.001). Moreover, in capsaicin-treated rats, passive avoidance acquisition was impaired as compared to the control (P < 0.05) and exercise (P < 0.001) groups. Additionally, regular exercise before capsaicin injection could attenuate capsaicin-induced memory impairments (P < 0.05). CONCLUSIONS: Taken together, the present data showed that regular exercise has inhibitory effects on capsaicin-induced pulpal pain as well as pain-induced cognitive dysfunction in rats.

Involvement of Mu opioid receptor signaling in the protective effect of opioid against 6-hydroxydopamine-induced SH-SY5Y human neuroblastoma cells apoptosis

Introduction: The neuroprotective role of opioid morphine against 6-hydroxydopamine-induced cell death has been demonstrated. However, the exact mechanism[s] underlying such neuroprotection, especially the role of subtype receptors, has not yet been fully clarified

Methods: Here, we investigated the effects of different opioid agonists on 6-OHDA-induced neurotoxicity in human neuroblastoma SH-SY5Y cell line as an in vitro model of Parkinson's disease. Cell damage was induced by 150 micro M 6-OHDA and the cells viability was examined by MTT assay. Intracellular calcium, reactive oxygen species and mitochondrial membrane potential were assessed by fluorescence spectrophotometry method. Immunoblot technique was used to evaluate cytochrome-c and activated caspase-3 as biochemical markers of apoptosis induction

Results: The data showed that 6-OHDA caused significant cell damage, loss of mitochondrial membrane potential and increase in intracellular reactive oxygen species and calcium levels as well as activated caspase-3 and cytochrome-c release. Incubation of SH-SY5Y cells with sigma -opioid agonists, morphine and DAMGO, but not with sigma-opioid agonist, DADLE, elicited protective effect and reduced biochemical markers of cell damage and death

Discussion: The results suggest that sigma-opioid receptors signaling participate in the opioid neuroprotective effects against 6-OHDA-induced neurotoxicity

[ effect of intracolonic matricaria recutita L. aqueous extract on acetic acid-induced ulcerative colitis in adult male rats]

Ulcerative colitis [UC] is a chronic inflammation of the colon that results from an abnormal response by the body's immune system. Our previous study has shown that oral Matricaria recutita L. aqueous external because of its anti-inflammatory compounds decreased a number of UC inflammatory indices. In the present study, we evaluate the effect of rectal aqueous extract on a model of acute experimental colitis and compare it with prednisolone. Experiments were performed on six groups [n=7] of male Wistar rats [230-280 g]. Of these, three groups were rectally administered different doses of extract [20, 30 and 60 mg/kg], the fourth group received oral prednisolone, the fifth group received vehicle and the last group was considered as the control group. To induce colitis, the rats fasted for 36 hours after which they received ether as an anesthesia. At the last stage, 2 ml of 4% acetic acid was instilled via the anus. After 24 hours, macroscopic study confirmed the colitis induction. The doses of 30 and 60 mg/kg of extract significantly reduced the colon weight/length ratio. The same effect was observed with prednisolone [1.14 mg/kg]. Extract at all doses [20, 30 and 60 mg/kg] significantly reduced the ulcer index compared to the sham group. Extract [60 mg/kg] effectively decreased the severity and extent of inflammation compared to the prednisolone group. Intracolonic injection of Matricaria recutita L. aqueous extract was effective in treatment against acetic acid-induced colitis in rats

[ Effect of Ducrosiaanethifolia [Dc.] Boissessential Oil on Hot Plate Model of Pain in Adult Male Rats]

Background and Purpose: Ducrosiaanethifolia is an aromatic medicinal plant native to Iran, and has been used in traditional medicine for controlling infection, reducing anxiety and pain. Since analgesic effect of this plant has not been studied experimentally, the aim of the present research is investigating the analgesic effect of Dc. essential oil.

Materials and Methods: In this experimental study, 48 adult Wistar male rats were examined. Rats were divided randomly into 6 groups [n= 8] including: control group, morphine group and Dc. essential oil group [0.06, 0.125, 0.25 and 0.5 ml/kg, IP]. Antinociceptive effects of drugs were assessed using hot plate apparatus. The results were analyzed using SPSS using one-way analysis of variance [ANOVA] followed by post hoc Tukey. Differences were considered significant at p< 0.05.

Results: The Dc. essential oil [0.5 ml/kg] significantly decreased sensitivity to painin comparison with control group. Latency to onset of pain significantly increasedby the Dc. essential oil [0.125 ml/kg] 60 and 120 minutes after injection compared with control group. Also, the Dc. essential oil [0.25ml/kg] reduced pain 120 minutes after injection in comparison with control group.

Conclusion: Based on the findings of present study, the Dc. essential oil has analgesic properties and this plant can lead to decreased sensitivity to pain at some doses in the hot plate model of pain.

effect of oral ascorbic acid pretreatment on feeding changes following injection in nucleus accumbens shell in adult male rats

Ascorbic acid [AA] is not synthesized in the brain but it is actively transported through blood-brain barrier by SVCT2 cotransporter and it is stored in high concentrations with heterogeneous distribution in areas such as nucleus accumbens shell [AcbSh] in the mammalian brain. Previous studies have shown that Ascorbic acid injection into AcbSh decreases feeding; therefore, in the present study we evaluated the effects of oral Ascorbic acid pretreatment on changes in feeding upon its injection in AcbSh in adult male rats. Sixty-three adult male rats [220-280 g] were divided into five treatment and five pretreatment groups. The treatment groups included the control [intact] group, sham-operated Ascorbic acid group that received normal saline as vehicle, and three other groups that received different doses of ascorbic acid [10, 50 and 250 microg/rat] by injection into AcbSh for four days. The pretreatment groups received Ascorbic acid [100 mg/kg] for 15 days via gastric gavage before receiving the aforementioned doses in treatment groups into intra nucleus AcbSh. Feeding measurement was repeated every 12 hours by automatic metabolic cage. The results indicated that all injected doses of Ascorbic acid [10, 50 and 250 microg/rat] into nucleus accumbens shell decrease food intake [P<0.05] in rats and oral Ascorbic acid pretreatment had no effects in this regard. Our findings show that ascorbic acid is an effective factor in feeding regulation. Oral pretreatment seems to have no influence on the central effects of ascorbic acid in the nucleus accumbens shell

Evaluation of Origanum vulgare L. ssp. viridis leaves extract effect on discrimination learning and LTP induction in the CA1 region of the rat hippocampus

The objective of this study was to determine the effect of aqueous extract of Origanum vulgare L. ssp. Viridis [ORG] on discrimination learning and long term potentiation [LTP] in CA1 region of the rat hippocampus. A group of adult male Wistar rats weighing 275 +/- 25 g received aqueous extract of ORG [150, 300, 450 mg/kg/day] by intraperitoenal injection for one week, and the other group received saline [n=6]. A wooden T-maze was used to evaluate the discrimination learning. In electrophysiological experiments, the effects of ORG leaves extract on induction and maintenance long term potentiation [LTP] in CA1 hippocampus area was determined. LTP was evaluated in CA1 region after high-frequency stimulation [200 Hz] of the Schaffer collaterals. Also, serum antioxidant levels were analyzed in the two groups [n=4]. Statistical analysis showed significant decreases in the number of total [significantly at the dose of 300 and 450 mg/kg] and wrong [significantly at the dose of 300 mg/kg] entrance into opposite box of T-maze procedure in ORG-treated animals [P<0.05]. In electrophysiological study, the rats which had received ORG [150, 300, and 450 mg/kg] showed an increase in both population spike amplitude [59.7 +/- 14.1%, 85 +/- 14.7% and 49.3 +/- 8.7% respectively, compared to 39 +/- 9.2% increase in saline group] and maintenance of LTP in hippocampus CA1 after high frequency stimulation in Schaffer collateral pathway. In serum antioxidant assay, level of antioxidants in ORG groups [300 and 450 mg/kg] remarkably increased in comparison to saline group [P< 0.05 and P<0.001, in turn]. Our result suggest that Origanum aqueous extract can improve the learning criteria in rats