Neuropathic pain is a chronic debilitating symptom characterized by spontaneous pain and mechanical allodynia. It occurs in distinct forms, including brush-evoked dynamic and filament-evoked punctate mechanical allodynia. Potassium channel 2.1 (Kir2.1), which exhibits strong inward rectification, is and regulates the activity of lamina I projection neurons. However, the relationship between Kir2.1 channels and mechanical allodynia is still unclear. In this study, we first found that pretreatment with ML133, a selective Kir2.1 inhibitor, by intrathecal administration, preferentially inhibited dynamic, but not punctate, allodynia in mice with spared nerve injury (SNI). Intrathecal injection of low doses of strychnine, a glycine receptor inhibitor, selectively induced dynamic, but not punctate allodynia, not only in naïve but also in ML133-pretreated mice. In contrast, bicuculline, a GABA receptor antagonist, induced only punctate, but not dynamic, allodynia. These results indicated the involvement of glycinergic transmission in the development of dynamic allodynia. We further found that SNI significantly suppressed the frequency, but not the amplitude, of the glycinergic spontaneous inhibitory postsynaptic currents (gly-sIPSCs) in neurons on the lamina II-III border of the spinal dorsal horn, and pretreatment with ML133 prevented the SNI-induced gly-sIPSC reduction. Furthermore, 5 days after SNI, ML133, either by intrathecal administration or acute bath perfusion, and strychnine sensitively reversed the SNI-induced dynamic, but not punctate, allodynia and the gly-sIPSC reduction in lamina IIi neurons, respectively. In conclusion, our results suggest that blockade of Kir2.1 channels in the spinal dorsal horn selectively inhibits dynamic, but not punctate, mechanical allodynia by enhancing glycinergic inhibitory transmission.
Animals ; Bicuculline ; pharmacology ; Disease Models, Animal ; Glycine ; metabolism ; Hyperalgesia ; drug therapy ; etiology ; metabolism ; Imidazoles ; pharmacology ; Inhibitory Postsynaptic Potentials ; drug effects ; physiology ; Male ; Mice, Inbred C57BL ; Neurons ; drug effects ; metabolism ; Neurotransmitter Agents ; pharmacology ; Peripheral Nerve Injuries ; drug therapy ; metabolism ; Phenanthrolines ; pharmacology ; Potassium Channels, Inwardly Rectifying ; antagonists & inhibitors ; metabolism ; Receptors, GABA-A ; metabolism ; Receptors, Glycine ; metabolism ; Strychnine ; pharmacology ; Synaptic Transmission ; drug effects ; physiology ; Tissue Culture Techniques ; Touch

BACKGROUND: Pain is a complex mechanism which involves different systems, including the opioidergic and GABAergic systems. Due to the side effects of chemical analgesic agents, attention toward natural agents have been increased. Artemisinin is an herbal compound with widespread modern and traditional therapeutic indications, which its interaction with the GABAergic system and antinoniceptive effects on neuropathic pain have shown. Therefore, this study was designed to evaluate the antinociceptive effects of artemisinin during inflammatory pain and interaction with the GABAergic and opioidergic systems by using a writhing response test. METHODS: On the whole, 198 adult male albino mice were used in 4 experiments, including 9 groups (n = 6) each with three replicates, by intraperitoneal (i.p.) administration of artemisinin (2.5, 5, and 10 mg/kg), naloxone (2 mg/kg), bicuculline (2 mg/kg), saclofen (2 mg/kg), indomethacin (5 mg/kg), and ethanol (10 mL/kg). Writhing test responses were induced by i.p. injection of 10 mL/kg of 0.6% acetic acid, and the percentage of writhing inhibition was recorded. RESULTS: Results showed significant dose dependent anti-nociceptive effects from artemisinin which, at a 10 mg/kg dose, was statistically similar to indomethacin. Neither saclofen nor naloxone had antinociceptive effects and did not antagonize antinociceptive effects of artemisinin, whereas bicuculline significantly inhibited the antinocicptive effect of artemisinin. CONCLUSIONS: It seems that antinocicptive effects of artemisinin are mediated by GABAA receptors.
Acetic Acid ; Adult ; Analgesics ; Analgesics, Opioid ; Animals ; Bicuculline ; Ethanol ; gamma-Aminobutyric Acid ; Humans ; Indomethacin ; Inflammation ; Male ; Mice ; Naloxone ; Neuralgia ; Receptors, GABA

Exploring the transition from inter-ictal to ictal epileptiform discharges (IDs) and how GABA receptor-mediated action affects the onset of IDs will enrich our understanding of epileptogenesis and epilepsy treatment. We used Mg-free artificial cerebrospinal fluid (ACSF) to induce epileptiform discharges in juvenile mouse hippocampal slices and used a micro-electrode array to record the discharges. After the slices were exposed to Mg-free ACSF for 10 min-20 min, synchronous recurrent seizure-like events were recorded across the slices, and each event evolved from inter-ictal epileptiform discharges (IIDs) to pre-ictal epileptiform discharges (PIDs), and then to IDs. During the transition from IIDs to PIDs, the duration of discharges increased and the inter-discharge interval decreased. After adding 3 μmol/L of the GABA receptor agonist muscimol, PIDs and IDs disappeared, and IIDs remained. Further, the application of 10 μmol/L muscimol abolished all the epileptiform discharges. When the GABA receptor antagonist bicuculline was applied at 10 μmol/L, IIDs and PIDs disappeared, and IDs remained at decreased intervals. These results indicated that there are dynamic changes in the hippocampal network preceding the onset of IDs, and GABA receptor activity suppresses the transition from IIDs to IDs in juvenile mouse hippocampus.
Animals ; Animals, Newborn ; Bicuculline ; pharmacology ; Disease Models, Animal ; Epilepsy ; pathology ; GABA-A Receptor Agonists ; pharmacology ; GABA-A Receptor Antagonists ; therapeutic use ; Hippocampus ; drug effects ; metabolism ; physiopathology ; In Vitro Techniques ; Magnesium ; metabolism ; pharmacology ; Male ; Membrane Potentials ; drug effects ; Mice ; Mice, Inbred C57BL ; Muscimol ; pharmacology ; Nerve Net ; drug effects ; Receptors, GABA-A ; metabolism

Here we investigated the central processing mechanisms of mechanical allodynia and found a direct excitatory link with low-threshold input to nociceptive neurons. Experiments were performed on male Sprague-Dawley rats weighing 230-280 g. Subcutaneous injection of interleukin 1 beta (IL-1β) (1 ng/10 µL) was used to produce mechanical allodynia and thermal hyperalgesia. Intracisternal administration of bicuculline, a gamma aminobutyric acid A (GABAA) receptor antagonist, produced mechanical allodynia in the orofacial area under normal conditions. However, intracisternal administration of bicuculline (50 ng) produced a paradoxical anti-allodynic effect under inflammatory pain conditions. Pretreatment with resiniferatoxin (RTX), which depletes capsaicin receptor protein in primary afferent fibers, did not alter the paradoxical anti-allodynic effects produced by the intracisternal injection of bicuculline. Intracisternal injection of bumetanide, an Na-K-Cl cotransporter (NKCC 1) inhibitor, reversed the IL-1β-induced mechanical allodynia. In the control group, application of GABA (100 µM) or muscimol (3 µM) led to membrane hyperpolarization in gramicidin perforated current clamp mode. However, in some neurons, application of GABA or muscimol led to membrane depolarization in the IL-1β-treated rats. These results suggest that some large myelinated Aβ fibers gain access to the nociceptive system and elicit pain sensation via GABA(A) receptors under inflammatory pain conditions.
Animals ; Bicuculline ; Bumetanide ; Capsaicin ; gamma-Aminobutyric Acid ; Gramicidin ; Humans ; Hyperalgesia* ; Injections, Subcutaneous ; Interleukin-1beta ; Male ; Membranes ; Muscimol ; Myelin Sheath ; Neurons ; Nociceptors ; Rats* ; Rats, Sprague-Dawley ; Receptors, GABA-A ; Sensation

The present study investigated the role of central GABA(A) and GABA(B) receptors in orofacial pain in rats. Experiments were conducted on Sprague-Dawley rats weighing between 230 and 280 g. Intracisternal catheterization was performed for intracisternal injection, under ketamine anesthesia. Complete Freund's Adjuvant (CFA)-induced thermal hyperalgesia and inferior alveolar nerve injury-induced mechanical allodynia were employed as orofacial pain models. Intracisternal administration of bicuculline, a GABA(A) receptor antagonist, produced mechanical allodynia in naive rats, but not thermal hyperalgesia. However, CGP35348, a GABA(B) receptor antagonist, did not show any pain behavior in naive rats. Intracisternal administration of muscimol, a GABA(A) receptor agonist, attenuated the thermal hyperalgesia and mechanical allodynia in rats with CFA treatment and inferior alveolar nerve injury, respectively. On the contrary, intracisternal administration of bicuculline also attenuated the mechanical allodynia in rats with inferior alveolar nerve injury. Intracisternal administration of baclofen, a GABA(B) receptor agonist, attenuated the thermal hyperalgesia and mechanical allodynia in rats with CFA treatment and inferior alveolar nerve injury, respectively. In contrast to GABA(A) receptor antagonist, intracisternal administration of CGP35348 did not affect either the thermal hyperalgesia or mechanical allodynia. Our current findings suggest that the GABA(A) receptor, but not the GABA(B) receptor, participates in pain processing under normal conditions. Intracisternal administration of GABA(A) receptor antagonist, but not GABA(B) receptor antagonist, produces paradoxical antinociception under pain conditions. These results suggest that central GABA has differential roles in the processing of orofacial pain, and the blockade of GABA(A) receptor provides new therapeutic targets for the treatment of chronic pain.
Anesthesia ; Animals ; Baclofen ; Bicuculline ; Catheterization ; Catheters ; Chronic Pain ; Facial Pain ; Freund's Adjuvant ; gamma-Aminobutyric Acid* ; Hyperalgesia ; Ketamine ; Mandibular Nerve ; Muscimol ; Nociception* ; Rats* ; Rats, Sprague-Dawley ; Receptors, GABA* ; Receptors, GABA-A

Phasic and tonic gamma-aminobutyric acid(A) (GABA(A)) receptor-mediated inhibition critically regulate neuronal information processing. As these two inhibitory modalities have distinctive features in their receptor composition, subcellular localization of receptors, and the timing of receptor activation, it has been thought that they might exert distinct roles, if not completely separable, in the regulation of neuronal function. Inhibition should be maintained and regulated depending on changes in network activity, since maintenance of excitation-inhibition balance is essential for proper functioning of the nervous system. In the present study, we investigated how phasic and tonic inhibition are maintained and regulated by different signaling cascades. Inhibitory postsynaptic currents were measured as either electrically evoked events or spontaneous events to investigate regulation of phasic inhibition in layer 2/3 pyramidal neurons of the rat visual cortex. Tonic inhibition was assessed as changes in holding currents by the application of the GABA(A) receptor blocker bicuculline. Basal tone of phasic inhibition was maintained by intracellular Ca2+ and Ca2+/calmodulin-dependent protein kinase II (CaMKII). However, maintenance of tonic inhibition relied on protein kinase A activity. Depolarization of membrane potential (5 min of 0 mV holding) potentiated phasic inhibition via Ca2+ and CaMKII but tonic inhibition was not affected. Thus, phasic and tonic inhibition seem to be independently maintained and regulated by different signaling cascades in the same cell. These results suggest that neuromodulatory signals might differentially regulate phasic and tonic inhibition in response to changes in brain states.
Animals ; Automatic Data Processing ; Bicuculline ; Brain ; Calcium-Calmodulin-Dependent Protein Kinase Type 2* ; Cyclic AMP-Dependent Protein Kinases ; Inhibitory Postsynaptic Potentials ; Membrane Potentials ; Nervous System ; Neurons ; Protein Kinases ; Rats* ; Receptors, GABA-A ; Visual Cortex*

.This study is to investigate the analgesic effect produced by intrathecal injection (ith) of oxysophoridine (OSR) and the mechanism of GABAA receptor. Warm water tail-flick test was used to detect the analgesic effect of OSR (12.5, 6.25, and 3.13 mg.kg-1 ith) and to observe the influence of GABA (gamma aminobutyric acid) agonist or antagonist on the analgesic effect of OSR in mice. Immunohistochemistry method were used to detect the influence of OSR (12.5 mg.kg-1, ith) on the GABAARalpha1 protein expression in spinal cord. The results obtained covers that OSR (12.5 and 6.25 mg.kg-, ith) alleviates pain significantly with the warm water tail-flick test (P<0.05, P<0.01), the rate of pain threshold increases by 68.45%; GABA and muscimol (MUS) produces analgesic synergism together with the OSR, picrotoxin (PTX) and bicuculline (BIC) antagonize the analgesic effect of OSR; OSR (12.5 mg.kg-1, ith) significantly increase the positive number of GABAARalpha1 nerve cell in spinal cord (P<0.01) and significantly decrease the average grey levels (P<0.01). In conclusion, OSR intrathecal injection has significant analgesic effect. And GABAA receptor in spinal cord is involved in the analgesic mechanism.
Alkaloids ; administration & dosage ; pharmacology ; Analgesics ; administration & dosage ; pharmacology ; Animals ; Bicuculline ; pharmacology ; Female ; GABA-A Receptor Agonists ; pharmacology ; GABA-A Receptor Antagonists ; pharmacology ; Injections, Spinal ; Male ; Mice ; Muscimol ; pharmacology ; Pain Threshold ; drug effects ; Picrotoxin ; pharmacology ; Random Allocation ; Receptors, GABA-A ; metabolism ; Spinal Cord ; metabolism ; gamma-Aminobutyric Acid ; pharmacology

PURPOSE: The inhibition of phosphodiesterase 5 produces an antinociception through the increase of cyclic guanosine monophosphate (cGMP), and increasing cGMP levels enhance the release of gamma-aminobutyric acid (GABA). Furthermore, this phosphodiesterase 5 plays a pivotal role in the regulation of the vasodilatation associated to cGMP. In this work, we examined the contribution of GABA receptors to the effect of sildenafil, a phosphodiesterase 5 inhibitor, in a neuropathic pain rat, and assessed the hemodynamic effect of sildenafil in normal rats. MATERIALS AND METHODS: Neuropathic pain was induced by ligation of L5/6 spinal nerves in Sprague-Dawley male rats. After observing the effect of intravenous sildenafil on neuropathic pain, GABAA receptor antagonist (bicuculline) and GABAB receptor antagonist (saclofen) were administered prior to delivery of sildenafil to determine the role of GABA receptors in the activity of sildenafil. For hemodynamic measurements, catheters were inserted into the tail artery. Mean arterial pressure (MAP) and heart rate (HR) were measured over 60 min following administration of sildenafil. RESULTS: Intravenous sildenafil dose-dependently increased the withdrawal threshold to the von Frey filament application in the ligated paw. Intravenous bicuculline and saclofen reversed the antinociception of sildenafil. Intravenous sildenafil increased the magnitude of MAP reduction at the maximal dosage, but it did not affect HR response. CONCLUSION: These results suggest that sildenafil is active in causing neuropathic pain. Both GABAA and GABAB receptors are involved in the antinociceptive effect of sildenafil. Additionally, intravenous sildenafil reduces MAP without affecting HR.
Animals ; Baclofen/analogs & derivatives/pharmacology ; Bicuculline/pharmacology ; Blood Pressure/drug effects ; Dose-Response Relationship, Drug ; Heart Rate/drug effects ; Hemodynamics/drug effects ; Male ; Neuralgia/*drug therapy ; Pain Threshold/drug effects ; Phosphodiesterase Inhibitors/*therapeutic use ; Piperazines/*therapeutic use ; Purines/therapeutic use ; Rats ; Rats, Sprague-Dawley ; Receptors, GABA-A/antagonists & inhibitors/physiology ; Receptors, GABA-B/antagonists & inhibitors/physiology ; Sulfones/*therapeutic use

OBJECTIVETo investigate the effect of bicuculline, a selective GABAA receptor antagonist, on airway remodeling in the murine model of chronic allergen-induced asthma.

METHODSForty BALB/C mice were randomized into 4 groups, namely the control group, asthmatic model (induced by ovalbumin sensitization and challenge) group, budesonide inhalation group and bicuculline inhalation group. The mice were sacrificed 24 h after the last ovalbumin inhalation, and the lungs were lavaged with PBS and the total cells, eosinophils and lymphocytes counts were examined. Periodic acid-Schiff (PAS) staining was used for counting mucin-positive goblet cells in the lung tissue, and Masson Trichrome staining was used to evaluate collagen deposition. GABAARbeta2 and VEGF were quantified by immunohistochemistry.

RESULTSThe numbers of the total cells, eosinophils and lymphocytes counts in BALF were significantly greater in the bicuculline group than in the control and budesonide groups (P<0.01), but comparable to those in the asthmatic model group (P>0.05). The airway collagen deposition in the bicuculline group was comparable to that in the control and budesonide group (P>0.05), but was significantly less than that in the asthmatic model group (P<0.05). Significant differences were found in the airway histological mucus index between the bicuculline group and the other 3 groups (P<0.05). The airway GABAARbeta2-positive cell percentage in the bicuculline group was significantly greater that those in the control and budesonide (P<0.01 and 0.05), but similar with that in the asthmatic model group (P>0.05). The percentage of pulmonary perivascular VEGF-positive cells in the bicuculline group was significantly greater in the control and budesonide groups (P<0.01 and P<0.05), but comparable to that in the asthmatic model group (P>0.05).

CONCLUSIONGABAARbeta2 is expressed in both the airway epithelium and smooth muscles. Bicuculline inhalation can effectively suppress collagen deposition with a stronger inhibitory effect on mucus hypersecretion than budesonide.

Airway Remodeling ; drug effects ; Animals ; Asthma ; drug therapy ; pathology ; Bicuculline ; therapeutic use ; Disease Models, Animal ; GABA-A Receptor Antagonists ; therapeutic use ; Male ; Mice ; Mice, Inbred BALB C

BACKGROUND: The intrathecal (IT) administration of glycine or GABAA receptor antagonist result in a touch evoked allodynia through disinhibition in the spinal cord. Glycine is an inhibitory neurotransmitter that appears to be important in sensory processing in the spinal cord. This study was aimed to evaluate the effect of glycine-related amino acids on antagonizing the effects of IT strychnine (STR) or bicuculline (BIC) when each amino acid was administered in combination with STR or BIC. METHODS: A total of 174 male ICR mice were randomized to receive an IT injection of equimolar dose of glycine, betaine, beta-alanine, or taurine in combination with STR or BIC. Agitation in response to innocuous stimulation with a von Frey filament after IT injection was assessed. The pain index in hot-plate test were observed after it injection. The effect of it muscimol in combination with str or bic were also observed. RESULTS: The allodynia induced by STR was relieved by high dose of glycine or betaine. But, allodynia induced by BIC was not relieved by any amino acid. Whereas the STR-induced thermal hyperalgesia was only relieved by high dose of taurine at 120 min after IT injection, the BIC-induced one was relieved by not only high dose of taurine at 120 min but also low dose of glycine or betaine at 60 min after IT injection. The BIC-induced allodynia and thermal hyperalgesia was relieved by IT muscimol. CONCLUSIONS: This study suggests that IT glycine and related amino acids can reduce the allodynic and hyperalgesic action of STR or BIC in mice.
Amino Acids ; Animals ; beta-Alanine ; Betaine ; Bicuculline ; Dihydroergotamine ; Glycine ; Humans ; Hyperalgesia ; Male ; Mice ; Mice, Inbred ICR ; Muscimol ; Neurotransmitter Agents ; Nitrogen Mustard Compounds ; Spinal Cord ; Strychnine ; Taurine