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The periaqueductal gray matter (PAG) is an essential structure involved in the elaboration of defensive responses, such as when facing predators and conspecific aggressors. Using a prey vs predator paradigm, we aimed to evaluate the PAG activation pattern evoked by unconditioned and conditioned fear situations. Adult male guinea pigs were confronted either by a Boa constrictor constrictor wild snake or by the aversive experimental context. After the behavioral test, the rodents were euthanized and the brain prepared for immunohistochemistry for Fos protein identification in different PAG columns. Although Fos-protein-labeled neurons were found in different PAG columns after both unconditioned and conditioned fear situations at the caudal level of the PAG, we found greater activation of the lateral column compared to the ventrolateral and dorsomedial columns after predator exposure. Moreover, the lateral column of the PAG showed higher Fos-labeled cells at the caudal level compared to the same area at the rostral level. The present results suggested that there are different activation patterns of PAG columns during unconditioned and conditioned fear in guinea pigs. It is possible to hypothesize that the recruitment of specific PAG columns depended on the nature of the threatening stimulus.
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The periaqueductal gray (PAG) is a complex mesencephalic structure involved in the integration and execution of active and passive self-protective behaviors against imminent threats, such as immobility or flight from a predator. PAG activity is also associated with the integration of responses against physical discomfort (e.g., anxiety, fear, pain, and disgust) which occurs prior an imminent attack, but also during withdrawal from drugs such as morphine and cocaine. The PAG sends and receives projections to and from other well-documented nuclei linked to the phenomenon of drug addiction including: (i) the ventral tegmental area; (ii) extended amygdala; (iii) medial prefrontal cortex; (iv) pontine nucleus; (v) bed nucleus of the stria terminalis; and (vi) hypothalamus. Preclinical models have suggested that the PAG contributes to the modulation of anxiety, fear, and nociception (all of which may produce physical discomfort) linked with chronic exposure to drugs of abuse. Withdrawal produced by the major pharmacological classes of drugs of abuse is mediated through actions that include participation of the PAG. In support of this, there is evidence of functional, pharmacological, molecular. And/or genetic alterations in the PAG during the impulsive/compulsive intake or withdrawal from a drug. Due to its small size, it is difficult to assess the anatomical participation of the PAG when using classical neuroimaging techniques, so its physiopathology in drug addiction has been underestimated and poorly documented. In this theoretical review, we discuss the involvement of the PAG in drug addiction mainly via its role as an integrator of responses to the physical discomfort associated with drug withdrawal.
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The periaqueductal gray (PAG) is a complex mesencephalic structure involved in the integration and execution of active and passive self-protective behaviors against imminent threats, such as immobility or flight from a predator. PAG activity is also associated with the integration of responses against physical discomfort (e.g., anxiety, fear, pain, and disgust) which occurs prior an imminent attack, but also during withdrawal from drugs such as morphine and cocaine. The PAG sends and receives projections to and from other well-documented nuclei linked to the phenomenon of drug addiction including: (i) the ventral tegmental area; (ii) extended amygdala; (iii) medial prefrontal cortex; (iv) pontine nucleus; (v) bed nucleus of the stria terminalis; and (vi) hypothalamus. Preclinical models have suggested that the PAG contributes to the modulation of anxiety, fear, and nociception (all of which may produce physical discomfort) linked with chronic exposure to drugs of abuse. Withdrawal produced by the major pharmacological classes of drugs of abuse is mediated through actions that include participation of the PAG. In support of this, there is evidence of functional, pharmacological, molecular. And/or genetic alterations in the PAG during the impulsive/compulsive intake or withdrawal from a drug. Due to its small size, it is difficult to assess the anatomical participation of the PAG when using classical neuroimaging techniques, so its physiopathology in drug addiction has been underestimated and poorly documented. In this theoretical review, we discuss the involvement of the PAG in drug addiction mainly via its role as an integrator of responses to the physical discomfort associated with drug withdrawal.
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Humans , Amygdala , Morphine , Nociception , Periaqueductal Gray , Substance-Related DisordersABSTRACT
ObjectiveVentrolateral periaqueductal gray (vlPAG) locates in ascending reticular activating system, which plays a key role in the sleep-wake circle. However, the role of vlPAG in general anesthesia has not been identified. To investigate the effect of the dopamine receptor in vlPAG neurons on propofol anesthesia, we used real-time in vivo fiber photometry, microinjection and EEG.MethodsTo observe the alteration of neuronal activity in the vlPAG throughout propofol anesthesia, 10 Sprague-Dawley rats were used for calcium fiber photometry recording. 50 vlPAG bilateral microinjection models were established and assigned into five groups randomly, including D1R agonist group, D1R antagonist group, D2R agonist group, D2R antagonist group, and control group (n=10). Under propofol anesthesia, 1 μL of D1R agonist, D1R antagonist, D2R agonist, D2R antagonist, and isotonic saline were microinjected into the vlPAG of animals in the corresponding groups, respectively. The induction time, recovery time and the changes in electroencephalogram (EEG) before and after microinjection were recorded and analyzed.ResultsThe neuronal activity in the vlPAG was significantly inhibited during the induction period and markedly recovered during the recovery period from propofol anesthesia (P<0.05). Subsequently, the microinjection of D1R agonist into the vlPAG notably prolonged the induction time and reduced the emergence time of propofol anesthesia with a decrease of δ-band ratio. While the microinjection of D1R antagonist accelerated the induction time and prolonged the emergence time of propofol anesthesia with an increase of δ-band ratio and a decrease in β-band ratio in cortical EEG (P<0.05). The induction and recovery time of D2R agonist /antagonist group did not differ with those of control group. As well, EEG before and after microinjection in D2R agonist /antagonist group did not different.ConclusionThese results indicate that vlPAG modulates the process of propofol anesthesia via D1R.
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Objective The main intracellular signal of P2X7 receptor activation is the increasing of Ca2+, which then presents the diversity of its physiological and pathological functions through multiple intracellular signal transduction. To observe the effect of activation of P2X7 receptor on intracellular calcium（Ca2+）level in lateral midbrain periaqueductal gray (lPAG) neurons of primary cultured rat. Methods The primary cultured lPAG neurons were randomly divided into 4 groups: control group(no drug added), only for control; BzATP group(100 μmol/L); A-740003+ BzATP group(incubate with 100 nmol/L A-740003 for 10 min, then add 10 μmol/L ofBzATP); BzATP control group(add in Ca2+-free solution for 20 min, then add BzATP). The incubation solution of control group, BzATP group and A-740003+ BzATP group are DMEM/F12 medium, and the BzATP control group is Ca2+-free. The laser scanning confocal microscopy (LSCM) was used to detect : the changes of cultured neuron Ca2+ levels by different concentrations of BzATP; the effects of A-740003 and Ca2+-free medium preincubation on BzATP-induced Ca2+ level alterations in cultured neurons. Results BzATP dose-dependently increased the Ca2+ levels in cultured lPAG neurons; A-740003 and Ca2+-free medium inhibited the BzATP-induced increasing of Ca2+ level in cultured lPAG neurons. LSCM showed: The intracellular calcium fluorescence insensity(2.48±1.05) in the BzATP group was significantly higher than that in the blank control group, BzATP control group and A-740003+ BzATP group[(1.12±0.03), (1.09±0.03), (1.14±0.08)](P<0.01). Conclusion The activation of P2X7 receptor can increase the level of lPAG neurons Ca2+ , and is associated with the extracellular Ca2+ influx.
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Panic disorder (PD) is an acute paroxysmal anxiety disorder with poorly understood pathophysiology. The dorsal periaqueductal gray (dPAG) is involved in the genesis of PD. However, the downstream neurofunctional changes of the dPAG during panic attacks have yet to be evaluated in vivo. In this study, optogenetic stimulation to the dPAG was performed to induce panic-like behaviors, and in vivo positron emission tomography (PET) imaging with F-flurodeoxyglucose (F-FDG) was conducted to evaluate neurofunctional changes before and after the optogenetic stimulation. Compared with the baseline, post-optogenetic stimulation PET imaging demonstrated that the glucose metabolism significantly increased (P < 0.001) in dPAG, the cuneiform nucleus, the cerebellar lobule, the cingulate cortex, the alveus of the hippocampus, the primary visual cortex, the septohypothalamic nucleus, and the retrosplenial granular cortex but significantly decreased (P < 0.001) in the basal ganglia, the frontal cortex, the forceps minor corpus callosum, the primary somatosensory cortex, the primary motor cortex, the secondary visual cortex, and the dorsal lateral geniculate nucleus. Taken together, these data indicated that in vivo PET imaging can successfully detect downstream neurofunctional changes involved in the panic attacks after optogenetic stimulation to the dPAG.
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Objective To investigate the expression of γ-aminobutyric acid A receptor α1 subunit (GABAAα1) in the ventrolateral periaqueductal gray (vLPAG) in rats with formalin-induced acute pain. Methods The rats were randomly divided into two groups:control group(group C) and formalin-induced pain group(group F),12 rats in each group:0.9% sodium chloride solution or 2% formaldehyde 50 μL was injected into the ventral surface of right hind paw respectively. The pain scores were recorded for every 5 minutes and the mechanical pain threshold were recorded for every 10 minutes until 1 h. The expression levels of GABAAα1in vLPAG were determined by Western blot analysis in each group.Results The rats in formalin group showed significant nociceptive behaviors immedi-ately, such as paw withdrawal and/or paw licking. Results demonstrated that the rats exhibited a biphasic response to pain. The pain behavior scores in group F were significantly higher than that in group C (P<0.05),and the mechanical pain threshold in group F was decreased after injection compared with group C(P<0.05). The expression of GABAAα1 protein in group F was significantly higher than that in group C (P<0.05).Conclusions The up-regulation of GABAAα1 expression in ventrolateral periaqueductal gray is associated with the decrease of pain threshold in rats with acute pain.
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Objective To evaluate the role of P2X7 receptor in the ventrolateral periaqueductal gray (vlPAG) in tramadol-induced reduction of neuropathic pain (NP) in rats.Methods Fifty-four male clean-grade healthy Sprague-Dawley rats,aged 7 days,weighing 190-230 g,were studied.NP was induced by chronic constrictive injury (CCI) to sciatic nerve.Experiment Ⅰ Thirty-six rats were divided into 3 groups (n =12 each) using a random number table method:sham operation group (group S),group NP1 and NP plus tramadol group (group NP1 +T).Tramadol 15 mg/kg was intraperitoneally injected once a day from day 7 to day 14 after CCI in group NP1+T.The mechanical and thermal pain thresholds of the nerve-injured hindlimb were measured before CCI and on 1,5,7,10,12 and 14 days after CCI.Rats were sacrificed after measurement of pain threshold on day 14 after CCI,and the expression of P2X7 receptor in vlPAG was detected by immunohistochemistry and Western blot assay.Experiment Ⅱ Eighteen rats were divided into 3 groups (n =6 each) using a random number table method:group NP2,NP plus tramadol group (group NP2+T) and NP plus tramadol plus a specific P2X7 receptor antagonist A-438079 group (group NP2+T+A).In NP2+T+A group,a catheter was implanted in vlPAG,and the NP model was established on 5th day after successful catheterization.Tramadol 15 mg/kg was intraperitoneally injected once a day from day 7 to day 14 after CCI in group NP2+T.In group NP2+T+A,tramadol 15 mg/kg was intraperitoneally injected once a day from day 7 to day 14 after CCI,followed by a microinjection of A-438079 100 pmol (0.3 μl) via vlPAG before giving tramadol on day 14.The mechanical and thermal pain thresholds were measured at the end of the last tramadol administration and within 1 h after the end of the last tramadol administration.Results Experiment Ⅰ Compared with group S,the mechanical and thermal pain thresholds were significantly decreased at each time point after CCI,the number of P2X7 receptor positive cells was increased,and the expression of P2X7 receptor was up-regulated in the other two groups (P＜0.01).Compared with group NP1,the mechanical and thermal pain thresholds were significantly increased at days 7-14 after CCI,the number of P2X7 receptor positive cells was increased,and the expression of P2X7 receptor was up-regulated in group NP1 +T (P＜0.01).Experiment Ⅱ Compared with group NP2,the mechanical and thermal pain threshold were significantly increased at each time point after CCI in NP2+T and NP2 +T+A groups (P＜0.01).Compared with group NP2 +T,the mechanical and thermal pain thresholds were significantly decreased at each time point after CCI in group NP2+T+A (P＜ 0.01).Conclusion The mechanism by which tramadol mitigates NP is partially related to enhanced function of P2X7 receptors in vlPAG of rats.
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OBJECTIVE: The periaqueductal gray matter (PAG), a small midbrain structure, presents dysfunction in migraine. However, the precise neurological mechanism is still not well understood. Herein, the aim of this study was to investigate the texture characteristics of altered PAG in episodic migraine (EM) patients based on high resolution brain structural magnetic resonance (MR) images. MATERIALS AND METHODS: The brain structural MR images were obtained from 18 normal controls (NC), 18 EM patients and 16 chronic migraine (CM) patients using a 3T MR system. A PAG template was created using the International Consortium Brain Mapping 152 gray matter model, and the individual PAG segment was developed by applying the deformation field from the structural image segment to the PAG template. A grey level co-occurrence matrix was used to calculate the texture parameters including the angular second moment (ASM), contrast, correlation, inverse difference moment (IDM) and entropy. RESULTS: There was a significant difference for ASM, IDM and entropy in the EM group (998.629 ± 0.162 × 10−3, 999.311 ± 0.073 × 10−3, 916.354 ± 0.947 × 10−5) compared to that found in the NC group (998.760 ± 0.110 × 10−3, 999.358 ± 0.037 × 10−3 and 841.198 ± 0.575 × 10−5) (p < 0.05). The entropy was significantly lower among the patients with CM (864.116 ± 0.571 × 10−5) than that found among patients with EM (p < 0.05). The area under the receiver operating characteristic curve was 0.776 and 0.750 for ASM and entropy in the distinction of the EM from NC groups, respectively. ASM was negatively related to disease duration (DD) and the Migraine Disability Assessment Scale (MIDAS) scores in the EM group, and entropy was positively related to DD and MIDAS in the EM group (p < 0.05). CONCLUSION: The present study identified altered MR image texture characteristics of the PAG in EM. The identified texture characteristics could be considered as imaging biomarkers for EM.
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Humans , Biomarkers , Brain , Brain Mapping , Entropy , Gray Matter , Magnetic Resonance Imaging , Mesencephalon , Migraine Disorders , Periaqueductal Gray , ROC CurveABSTRACT
<p><b>OBJECTIVE</b>To observe descending inhibition of cardiac nociception induced by microinjection of endomorphin-1 (EM1) in the ventrolateral periaqueductal gray (VLPAG) in rats effect and explore the role of μ-opioid receptor in mediating this effect.</p><p><b>METHODS</b>Male SD rats were randomized into electromyography (EMG) group and c-Fos group, both of which were further divided into 5 subgroups, namely 0.9% NaCl group, bradykinin (BK) group, BK+EM1 group, BK+CTOP group, and BK+CTOP+EM1 group. Rat models of cardiac nociception were established by intrapericardial injection of BK. The changes of cardiaosomatic motor reflex induced by BK were observed by assessing EMG responses of the dorsal spinotrapezius muscle; c-Fos expression in the spinal dorsal horn at levels T-T was tested.</p><p><b>RESULTS</b>Compared with 0.9% NaCl, intrapericardial BK injection induced obvious EMG activities and significantly increased c-Fos expression in the spinal dorsal horn at T-T ( < 0.05). Compared with BK injection, microinjection of EM1 in the VLPAG dose-dependently inhibited EMG activities and significantly decreased c-Fos expression ( < 0.05); microinjection of CTOP in the VLPAG produced no significant effect on EMG or c-Fos expression ( > 0.05). Microinjection of CTOP obviously reversed EM1-induced inhibition of EMG activities and c-Fos expression ( < 0.05).</p><p><b>CONCLUSIONS</b>Microinjection of EM1 in the VLPAG produces descending inhibition of cardiac nociception in rats by activating μ-opioid receptor.</p>
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Objective@#To observe the analgesic effect and related mechanism of peripheral acupoints electroacupuncture on superficial partial-thickness burn rats.@*Methods@#Eighty SD rats were divided into sham injury group (SI), pure burn group (PB), electroacupuncture group (E), and sham electroacupuncture group (SE) according to the random number table, with 20 rats in each group. Right posterior leg of rats in group SI were sham injured, while superficial partial-thickness scald (hereinafter referred to as burn) model was reproduced on the right posterior leg of rats in the latter three groups. Electroacupuncture of peripheral acupoints of right posterior leg of rats (equivalent to Zusanli point and Sanyinjiao point of human) in group E were performed from post injury hour (PIH) 12 on, while rats in group SE were treated with sham electroacupuncture, with 30 min each time, one time a day for 3 days. Before injury and at PIH 12, 24, 36, 48, 60, and 72, the threshold of mechanical pain of 5 rats in each group was tested, and the threshold of heat pain of another 5 rats in each group was tested. At PIH 48, brain tissue of 5 rats in each group was obtained to observe the morphology and distribution of astrocytes with positive expression of glia fibrillary acidic protein (GFAP) in periaqueductal gray (PAG) area by immunohistochemical staining, and the number of astrocytes was calculated. At the same time, brain tissue of the rest 5 rats in each group was obtained to determine the expression of GFAP of astrocytes in PAG area with Western blotting. Data were possessed with analysis of variance of repeated measurement, one-way analysis of variance, and SNK test.@*Results@#(1) Compared with that in group SI, the threshold of mechanical pain of rats in groups PB and SE had no significant change before injury and at PIH 12 (with P values above 0.05), but was significantly decreased from PIH 24 to 72 (with P values below 0.05); while the threshold of mechanical pain of rats in group E was significantly decreased from PIH 36 to 72 (with P values below 0.05). The threshold of mechanical pain of rats in group E was significantly higher than that in groups PB and SE at PIH 24 (with P values below 0.05). (2) Compared with that in group SI, the threshold of heat pain of rats in groups PB and SE had no significant change before injury (with P values above 0.05), but was significantly decreased from PIH 12 to 72 (with P values below 0.05); while the threshold of heat pain of rats in group E was significantly decreased from PIH 12 to 60 (with P values below 0.05). The threshold of heat pain of rats in group E was significantly higher than that in groups PB and SE from PIH 24 to 48 (with P values below 0.05). (3) The distribution of astrocytes with positive expression of GFAP in PAG area of rats in group SI was diffuse. The cell volume was small with cell body unobvious, and the projections were sparse, fine and short. The distribution of astrocytes with positive expression of GFAP in PAG area of rats in group PB was relatively concentrated. The cell body was hypertrophy and swelling, and the projections were increased and extended. The morphology and distribution of astrocytes with positive expression of GFAP in PAG area of rats in groups SE and E was similar to that in group PB. The numbers of astrocytes with positive expression of GFAP in PAG area of rats in groups SI, PB, E, and SE were 44±4, 39±4, 27±4, and 36±5, respectively. The number of astrocytes with positive expression of GFAP in PAG area of rats in group PB was significantly less than that in group SI (P<0.05), but similar to that in group SE (P>0.05). The number of astrocytes with positive expression of GFAP in PAG area of rats in group E was significantly less than that in groups PB and SE (with P values below 0.05). (4) The expressions of GFAP of astrocytes in PAG area of rats in groups SI, PB, E, and SE were 1.11±0.16, 0.66±0.15, 0.34±0.06, and 0.56±0.09, respectively. The expression of GFAP of astrocytes in PAG area of rats in group PB was significantly lower than that in group SI (P<0.05), but similar to that in group SE (P>0.05). The expression of GFAP of astrocytes in PAG area of rats in group E was significantly lower than that in groups PB and SE (with P values below 0.05).@*Conclusions@#Electroacupuncture of peripheral acupoints can release the pain followed superficial partial-thickness burn in rats at early stage, and the possible mechanism is that it reduces the activation of astrocytes in PAG area.
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OBJECTIVE: To explore the analgesic effect of electroacupuncture(EA)by modulating 5-hydroxytryptamine 7 (5-HT7) receptor in periaqueductal gray (PAG) and plasma calcitonin gene-related peptide (CGRP). METHODS: Forty-two male Sprague Dawley (SD) rats were randomly divided into control，model and EA groups, 14 rat in each one. The neurogenic migraine model was established by repeated electrical stimulation on sagittal sinus duramater. Intracranial electrodes were used in the control group without stimuli. The rats in the EA group received EA (0.5－1 mA, 2 Hz/15 Hz) at "Fengchi" (GB 20) for 10 min after dural electrical stimulation, once a day for 6 days. The expression of 5-HT7 receptor in the PAG was assessed by immunofluorescence and Western blot, respectively; plasma CGRP was measured by radioimmunoassay. RESULTS: Compared with the control group, the positive neuron number and protein expression of 5-HT7 receptor in PAG and plasma CGRP increased after model establishment (all P<0.001). The above mentioned indexes were reversed in the EA group compared with those in the model group (the positive neuron number and protein expression of 5-HT7 receptor, P<0.01; plasma CGRP, P<0.05). CONCLUSIONS: EA at GB 20 can down-regulate the expression of 5-HT7 receptor in the PAG and reduce the content of plasma CGRP in the rats of migraine.
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Objective To investigate the role of GABAAα3and GABAB receptors in the ventrolateral periaqueductal gray in the development of paw acute pain in rats.Methods Twelve male SD rats, weighing 280~320 g, were randomly divided into two groups: normal saline group (group NS), formaldehyde-induced pain group (group F), 6 rats in each group.In group F, rats were subcutaneously injected with 2% formaldehyde 50 μl into the ventral surface of right hind paw to induce periphery inflammatory pain.In group NS, rats were subcutaneously injected with normal saline into the ventral surface of right hind paw.Mechanical threshold was assessed using von Frey hairs for every ten minutes.The rat pain behavior scores were recorded for every five minutes.The thickness of skin and skin temperature were recorded for every fifteen minutes.Results Mechanical hyperalgesia were induced in group F after formalin injection into right hind paw.Compared with group NS, rat pain behavior scores were increased significantly in group F at all time points after injection, mechanical threshold were decreased significantly in group F at 10-60 min after injection, the temperature of the skin and the skin thickness were increased significantly in group F at 15-60 min after injection (P<0.05), the levels of the expression of GABAAα3 and GABAB were significantly increased in group F (P<0.05).Conclusion GABAAα3and GABAB receptors mediates formalin-induced hyperalgesia at ventrolateral portion of the PAG (vlPAG) of rats.
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Objective To evaluate the role of c-Jun N-terminal kinase (JNK) in activation of astrocytes in midbrain periaqueductal gray (PAG) of rats with neuropathic pain.Methods A total of 72 pathogen-free male Sprague-Dawley rats,aged 9 weeks,weighing 160-200 g,were divided into 4 groups using a random number table:control group (group C,n =8),neuropathic pain group (group NP,n =40),dimethyl sulfoxide control group (group DS,n =12) and JNK inhibitor SP600125 group (group SP,n=12).Neuropathic pain was produced by chronic constriction injury (CCI).At 14 days after CCI,10 nmol JNK inhibitor SP600125 0.5 μl was intraperitoneally injected into the PAG in group SP,and 10％ dimethyl sulfoxide 0.5 μl was given instead in group DS.Eight rats were selected in group C,before CCI and at 3,7,14 and 21 days after CCI in group NP,and in DS and SP groups,and the mechanical pain threshold was measured before CCI,before administration on 14 days after CCI and at 30,45,60,75 and 90 min after administration.The rats in group C were sacrificed after the end of measurement of the mechanical pain threshold,and brains were removed for determination of phosphorylated JNK (p-JNK) and glial fibrillary acidic protein expression (by Western blot) in PAG region.The rats in group NP were sacrificed after the end of measurement of the mechanical pain threshold at each time point,and brains were removed for detection of p-JNK expression in PAG region.Four rats in DS and SP groups were sacrificed after the last measurement of the mechanical pain threshold at 45 min after administration,and brains were removed for determination of glial fibrillary acidic protein expression in PAG region.Results Compared with group C,the mechanical pain threshold was significantly decreased at each time point after CCI,and the expression of p-JNK was up-regulated at 7-21 days after CCI in group NP (P＜0.01).Compared with group DS,the mechanical pain threshold was significantly increased at 30 min after administration,and GFAP expression was down-regulated at 45 min after administration in group SP (P＜ 0.01).The mechanical pain threshold was significantly higher at 30-75 min after administration than before administration in group SP (P＜0.01).Conclusion The mechanism underlying activation of astrocytes in PAG is related to activating JNK in the rats with neuropathic pain.
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Background: Exposure to stress-factors caused an array of biochemical, physiological and behavioral changes. According to literature data, specific stressors may elicit specific responses, and different stressors may activate different brain systems by using specific pathways within the central nervous system. Several brain structures, including the periaqueductal gray (PAG), have been implicated in the functional neuroanatomy of stress response. The dorsolateral column of the periaqueductal gray (dlPAG) integrates aversive emotional experiences and represents an important site responding to life threatening situations. It was reported that nitric oxide (NO) affects the neuronal activity of the PAG. The goal of the present study was to investigate the changes of NO activity in the dlPAG of immobilized rats using a histochemical examination of the distribution of NADPH-d reactivity neurons. Our results showed that NO activity in rat’s dlPAG was significantly increased by acute immobilization stress. This suggests a pivotal role of this part of the brain and NO-ergic system in stress response which main role is to attenuate the effect of stress and to restore the homeostasis. Methods: The experiments were carried out on male Wistar rats (180-200g), divided into two groups. The first group represented intact controls. The second group was subjected to acute immobilization stress. Results: The acute stressor – 1 hour immobilization, showed statistically significant increase in the number of the NADPH-d positive neurons compared to the control group (p < 0.01). Conclusion: NO activity in rat’s dlPAG was significantly increased by acute immobilization stress.
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Objective To evaluate the effect of dezocine on the c-fos expression in neurons in the midbrain periaqueductal gray in a rat model of incisional pain.Methods Thirty-six pathogen-free healthy adult male Wistar rats,weighing 250-300 g,were divided into 3 groups (n =12 each) using a random number table:control group (group C),incisional pain group (group I) and dezocine group (group D).A 1 cm longitudinal incision was made through skin,fascia and muscle of the plantar aspect of the right hind paw in sevoflurane-anesthetized rats.In group C,the rats were only anesthetized and underwent no operation.In group I,0.9％ sodium chloride solution 2 ml was injected via the caudal vein at 15 min before the model was established.In group D,dezocine 1 mg/kg (diluted to 2 ml in 0.9％ sodium chloride solution) was injected via the caudal vein at 15 min before the model was established.At 24 h before operation (T0) and 2,6 and 24 h after operation (T1-3),the mechanical paw withdrawal threshold (MWT) and cumulative pain score were measured.After measurement of the pain threshold at T3,the whole brain was removed for determination of the c-fos expression in neurons in the midbrain periaqueductal gray by immunohistochemistry.Results Compared with group C,the MWT was significantly decreased,cumulative pain scores were increased,and the expression of c-fos in neurons in the midbrain periaqueductal gray was upregulated at T1-3 in I and D groups (P＜0.05).Compared with group I,the MWT was significantly increased,the cumulative pain score was decreased,and the expression of c-fos protein in neurons in the midbrain periaqueductal gray was down-regulated at T1.3 in group D (P＜0.05).Conclusion Dezocine mitigates incisional pain through inhibiting the expression of c-fos in neurons in the midbrain periaqueductal gray of rats.
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Objective To evaluate the effect of the opioid switch from morphine to sufentanil on the expression of μ-opioid receptors in the midbrain periaqueductal gray (PAG) of rats.Methods Forty healthy male Wistar rats,aged 8 weeks,weighing 250-290 g,were randomly assigned into 5 groups (n=8 each) using a random number table:control group (group C),7 day sufentanil group (group S),7 day morphine group (group M),14 day morphine group (group MM),and 14 day alternate administration of morphine and sufentanil group (group MS).Normal saline 2 ml/kg,sufentanil 0.01 mg/kg and morphine 10 mg/kg were injected subcutaneously in the cervical region twice a day for 7 consecutive days in C,S and M groups,respectively.In group MM,morphine 10 mg/kg was injected subcutaneously in the cervical region twice a day for 14 consecutive days.In group MS,morphine 10 mg/kg was injected subcutaneously in the cervical region twice a day for 7 consecutive days (1st-7th days),and sufentanil 0.01 mg/kg was then injected subcutaneously in the cervical region twice a day for 7 consecutive days (8th-14th days).The tail flick latency (TFL) to a thermal nociceptive stimulus was measured at 15 and 30 min after the initial administration every day.After the last administration,the rats were sacrificed,and the midbrain PAG was isolated for determination of the expression of the μ-opioid receptor and μ-opioid receptor mRNA using Western blot and real-time reverse transcriptase polymerase chain reaction,respectively.Results Compared with group C,the TFL was significantly prolonged on 1st-6th days after the beginning of administration in M,MM and MS groups,the TFL was significantly prolonged on 1st-7th days after the beginning of administration in group S,and the expression of the μ-opioid receptor and μ-opioid receptor mRNA in the midbrain PAG was significantly down-regulated in M,MM and MS groups (P＜0.05).Compared with group MM,the TFL was significantly prolonged on 8th-14th days after the beginning of administration,and the expression of the μ-opioid receptor and μ-opioid receptor mRNA in the midbrain PAG was significantly up-regulated in group MS (P＜0.05).Conclusion The mechanism by which the opioid switch from morphine to sufentanil reduces morphine tolerance is related to enhanced activity of μ-opioid receptors in the midbrain PAG of rats.
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Objective To observe the distribution and possible mechanism of P2X7R in periaq-ueductal gray matter (PAG)in a rat model with chronic neuropathic pain in vivo.Methods The in-trathecal catheterization and sciatic nerve injury (SNI)were performed.All animals were randomly assigned into 3 groups with 26 rats in each,which was group Sham,control group (group C)and brilliant blue G (BBG)group (group BBG),respectively.Normal saline or BBG 10 μl were intrathe-cally injected after SNI and repeated for seven days.Paw-withdrawal mechanical thresholds (PWT) were measured on day 0,day 7,day 14,and day 21 after SNI.The rats were sacrificed and PAG tis-sues were collected on day 14 and day 21,separately.The distributions of P2X7R were observed by immunofluorescence.The protein contents of P2X7R and GFAP were assessed by Western blot assays.Results The P2X7R was expressed in PAG in rats.The PWTs of the control group showed a significant decrease during the 21-day period compared with the sham group.The P2X7R signals were predominantly expressed in astrocytes in PAG after SNI.Both P2X7R and GFAP expression remark-ably increased.Administration of BBG increased the PWTs,and inhibited the P2X7R and GFAP ex-pressions compared with those atthe same point of time of the control group.Conclusion These results indicated that P2X7R in PAG might participate in nociception modulation in the midbrain in chronic neuropathic pain.
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Objective To assess the influence of Rizatriptan on the cholecystokinin( CCK) expression in periaqueductal gray( PAG) of migraine model rat to investigate the possible mechanism by which Triptans treat mi?graine. Methods A total of 24 rats were randomly divided into four groups:normal control groups(A),migraine model groups(B),Rizatriptan control groups(C) and Rizatriptan treatment groups(D).C and D groups were intra?gastrically perfused with Rizatriptan,1 mg/kg per day. After 7 days,nitroglycerin was subcutaneously injected into the buttocks of the B and D group to induce migraine. Two hours after nitroglycerin injection,the trigeminal ganglia were isolated.CGRP expression in periaqueductal gray were determined using SYBR Green I real?time quantitative PCR and Immunohistochemistry. Results CCK mRNA levels ( target gene mRNA copies per 250 ng total RNA,× 106) in the rat midbrain of A,B,C,D groups were 1.25±0.41,1.71±0.93,0.17±0.12,0.22±0.07 respectively. CCK?8?immunoreactive positive cells in the rat PAG of each group were 37.17±12.62,40.17±11.09,27.33±7.71, 20.67±7.66 respectively. CCK mRNA expression in group C was significantly lower than that of group A(P<0.05) while the CCK mRNA expression in group D was lower than that of group B(P<0.05).The CCK?8?positive cells of the rat PAG in group D were lower than that in group B(P<0.05) . Conclusion Rizatriptan can down regulate the expression of CCK?8 in the PAG of the migraine rats and weaken the CCK?8 induced inhibition of the analgesic effects of opioid peptides.
ABSTRACT
The escape response to electrical or chemical stimulation of the dorsal periaqueductal gray matter (DPAG) has been associated with panic attacks. In order to explore the validity of the DPAG stimulation model for the study of panic disorder, we determined if the aversive consequences of the electrical or chemical stimulation of this midbrain area can be detected subsequently in the elevated T-maze. This animal model, derived from the elevated plus-maze, permits the measurement in the same rat of a generalized anxiety- and a panic-related defensive response, i.e., inhibitory avoidance and escape, respectively. Facilitation of inhibitory avoidance, suggesting an anxiogenic effect, was detected in male Wistar rats (200-220 g) tested in the elevated T-maze 30 min after DPAG electrical stimulation (current generated by a sine-wave stimulator, frequency at 60 Hz) or after local microinjection of the GABA A receptor antagonist bicuculline (5 pmol). Previous electrical (5, 15, 30 min, or 24 h before testing) or chemical stimulation of this midbrain area did not affect escape performance in the elevated T-maze or locomotion in an open-field. No change in the two behavioral tasks measured by the elevated T-maze was observed after repetitive (3 trials) electrical stimulation of the DPAG. The results indicate that activation of the DPAG caused a short-lived, but selective, increase in defensive behaviors associated with generalized anxiety.