Cerebellar Purkinje cells (PCs) exhibit two types of discharge activities: simple spike (SS) and complex spike (CS). Previous studies found that noradrenaline (NA) can inhibit CS and bidirectionally regulate SS, but the enhancement of NA on SS is overwhelmed by the strong inhibition of excitatory molecular layer interneurons. However, the mechanism underlying the effect of NA on SS discharge frequency is not clear. Therefore, in the present study, we examined the mechanism underlying the increasing effect of NA on SS firing of PC in mouse cerebellar cortex in vivo and in cerebellar slice by cell-attached and whole-cell recording technique and pharmacological methods. GABA_A receptor was blocked by 100 µmol/L picrotoxin in the whole process. In vivo results showed that NA significantly reduced the number of spikelets of spontaneous CS and enhanced the discharge frequency of SS, but did not affect the discharge frequency of CS. In vitro experiments showed that NA reduced the number of CS spikelets and after hyperpolarization potential (AHP) induced by electrical stimulation, and increased the discharge frequency of SS. NA also reduced the amplitude of excitatory postsynaptic current (EPSC) of parallel fiber (PF)-PC and significantly increased the paired-pulse ratio (PPR). Application of yohimbine, an antagonist of α2-adrenergic receptor (AR), completely eliminated the enhancing effect of NA on SS. The α2-AR agonist, UK14304, also increased the frequency of SS. The β-AR blocker, propranolol, did not affect the effects of NA on PC. These results suggest that in the absence of GABA_A receptors, NA could attenuate the synaptic transmission of climbing fiber (CF)-PC via activating α2-AR, inhibit CS activity and reduce AHP, thus enhancing the SS discharge frequency of PC. This result suggests that NA neurons of locus coeruleus can finely regulate PC signal output by regulating CF-PC synaptic transmission.
Action Potentials/physiology* ; Animals ; Cerebellar Cortex/metabolism* ; Cerebellum/metabolism* ; Mice ; Norepinephrine/pharmacology* ; Purkinje Cells/metabolism* ; Receptors, Adrenergic, alpha-2/metabolism* ; Receptors, GABA-A/metabolism*

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

The effect of high-frequency repetitive transcranial magnetic stimulation (rTMS) on spasticity following spinal cord injury (SCI) and the action mechanism were investigated. SCI models were established in Sprague-Dawley rats. Five groups were set up: normal control group, SCI-7 day (7D) model group, SCI-14D model group, SCI-7D rTMS group and SCI-14D rTMS group (n=10 each). The rats in SCI rTMS groups were treated with 10 Hz rTMS at 8th day and 15th day after SCI respectively. Motor recovery and spasticity alleviation were evaluated by BBB scale once a week till the end of treatment. Finally, different parts of tissues were dissected out for detection of GABA receptors using Western blotting and polymerase chain reaction (PCR) technique. The results showed that the BBB scores after treatment were significantly higher in SCI-7D rTMS group than in SCI-14D rTMS group (P<0.05). The GABA receptors were down-regulated more significantly in SCI-14D model group than in SCI-7D model group (P<0.05). At different time points, rTMS treatment could affect the up-regulation of GABA receptors: The up-regulation of GABA receptors was more obvious in SCI-7D rTMS group than in SCI-14D rTMS treatment group (P<0.05). It was concluded that 10-Hz rTMS could alleviate spasticity following SCI and promote the motor recovery in rats, which might be attributed to the up-regulation of GABA receptors. It was also suggested that early high-frequency rTMS treatment after SCI may achieve more satisfactory curative effectiveness.
Animals ; Blotting, Western ; Male ; Muscle Spasticity ; physiopathology ; Polymerase Chain Reaction ; Rats ; Rats, Sprague-Dawley ; Receptors, GABA ; physiology ; Spinal Cord Injuries ; physiopathology ; Transcranial Magnetic Stimulation

The mechanism underlying the modulatory effect of substance P (SP) on GABA-activated response in rat dorsal root ganglion (DRG) neurons was investigated. In freshly dissociated rat DRG neurons, whole-cell patch-clamp technique was used to record GABA-activated current and sharp electrode intracellular recording technique was used to record GABA-induced membrane depolarization. Application of GABA (1-1000 μmol/L) induced an inward current in a concentration-dependent manner in 114 out of 127 DRG neurons (89.8 %) examined with whole-cell patch-clamp recordings. Bath application of GABA (1-1000 μmol/L) evoked a depolarizing response in 236 out of 257 (91.8%) DRG neurons examined with intracellular recordings. Application of SP (0.001-1 μmol/L) suppressed the GABA-activated inward current and membrane depolarization. The inhibitory effects were concentration-dependent and could be blocked by the selective neurokinin 1 (NK1) receptors antagonist spantide but not by L659187 and SR142801 (1 μmol/L, n=7), selective antagonists of NK2 and NK3. The inhibitory effect of SP was significantly reduced by the calcium chelator BAPTA-AM, phospholipase C (PLC) inhibitor U73122, and PKC inhibitor chelerythrine, respectively. The PKA inhibitor H-89 did not affect the SP effect. Remarkably, the inhibitory effect of SP on GABA-activated current was nearly completely removed by a selective PKCε inhibitor epilon-V1-2 but not by safingol and LY333531, selective inhibitors of PKCα and PKCβ. Our results suggest that NK1 receptor mediates SP-induced inhibition of GABA-activated current and membrane depolarization by activating intracellular PLC-Ca²⁺-PKCε cascade. SP might regulate the excitability of peripheral nociceptors through inhibition of the "pre-synaptic inhibition" evoked by GABA, which may explain its role in pain and neurogenic inflammation.
Animals ; Female ; Ganglia, Spinal ; physiology ; Male ; Patch-Clamp Techniques ; Protein Kinase C-epsilon ; metabolism ; Rats ; Rats, Sprague-Dawley ; Receptors, GABA-A ; physiology ; Signal Transduction ; Substance P ; physiology

BACKGROUNDOur previous study has confirmed that one bout of exhaustion (Ex) can cause hippocampus neurocyte damage, excessive apoptosis, and dysfunction. Its initial reason is intracellular calcium overload in hippocampus triggered by N-methyl-D-aspartic acid receptor (NMDAR) over-activation. NMDAR activation can be suppressed by γ-aminobutyric acid (A) receptor (GABAAR). Whether GABAAR can prevent intense exercise-induced hippocampus apoptosis, damage, or dysfunction will be studied in this study.

METHODSAccording to dose test, rats were randomly divided into control (Con), Ex, muscimol (MUS, 0.1 mg/kg) and bicuculline (BIC, 0.5 mg/kg) groups, then all rats underwent once swimming Ex except ones in Con group only underwent training. Intracellular free calcium concentration ([Ca2+]i) was measured by Fura-2-acetoxymethyl ester; glial librillary acidic protein (GFAP) and synaptophysin (SYP) immunofluorescence were also performed; apoptosis were displayed by dUTP nick end labeling (TUNEL) stain; endoplasmic reticulum stress-induced apoptosis pathway was detected by Western blotting analysis; Morris water maze was used to detect learning ability and spatial memory.

RESULTSThe appropriate dose was 0.1 mg/kg for MUS and 0.5 mg/kg for BIC. Ex group showed significantly increased [Ca2+]i and astrogliosis; TUNEL positive cells and levels of GFAP, B cell lymphoma-2 (Bcl-2) associated X protein (Bax), caspase-3, caspase-12 cleavage, CCAAT/enhancer binding protein homologous protein (CHOP), and p-Jun amino-terminal kinase (p-JNK) in Ex group also raised significantly compared to Con group, while SYP, synapse plasticity, and Bcl-2 levels in Ex group were significantly lower than those in Con group. These indexes were back to normal in MUS group. BIC group had the highest levels of [Ca2+]i, astrogliosis, TUNEL positive cell, GFAP, Bax, caspase-3, caspase-12 cleavage, CHOP, and p-JNK, it also gained the lowest SYP, synapse plasticity, and Bcl-2 levels among all groups. Water maze test showed that Ex group had longer escape latency (EL) and less quadrant dwell time than Con group; all indexes between MUS and Con groups had no significant differences; BIC had the longest EL and least quadrant dwell time among all groups.

CONCLUSIONSActivation of GABAA R could prevent intense exercise-induced synapses damage, excessive apoptosis, and dysfunction of hippocampus.

Animals ; Apoptosis ; physiology ; Body Weight ; physiology ; Endoplasmic Reticulum Stress ; physiology ; Hippocampus ; metabolism ; Male ; Physical Exertion ; physiology ; Rats ; Rats, Sprague-Dawley ; Receptors, GABA ; genetics ; metabolism ; Synapses ; pathology

OBJECTIVE: We used electrophysiological methods to study that whether GABA could elicit OHCs outward currents provide evidence for exsitence of GABA-A receptor and investige the relationship between the effect of GABA and the development of OHCs. METHOD: We used whole-cell recording OHCs at current-clamp or voltage-clamp to verify the function of GABA receptor on OHCs. Then we counteds the responsive cells vs. total number cells, and according to results to study the relationships between the GABA receptor and development of OHCs. RESULT: OHC was elicited outward current or hyperpolarized by GABA and the responsive cells were decreased with development. CONCLUSION The result of GABA receptor decreasing with development suggested that the receptor may draw efferents to OHCs or facilitate the MOC-OHC synapse formation.
Animals ; Electrophysiological Phenomena ; Hair Cells, Auditory, Outer ; physiology ; Patch-Clamp Techniques ; Rats ; Receptors, GABA-A ; physiology ; gamma-Aminobutyric Acid ; physiology

OBJECTIVETo investigate the effects of ropivacaine on Gamma-aminobutyric acid(GABA)-activated currents in dorsal root ganglion (DRG) neurons in rats and discuss the analgesia mechanism of ropivacaine.

METHODSBy means of using whole-cell patch-clamp technique, to investigate the modulatory effects of ropivacaine on GABA-activated currents (I(GABA)) in acutely isolated dorsal root ganglion neurons.

RESULTS(1) In 48 out of 73DRG cells (65.7%, 48/73), to perfusion ropivacaine bromide (0.1 - 1 000 micromol/L) were sensitive. Which produce in 0 to 380 pA current. (2) The majority of the neurons examined (74.5%, 73/98) were sensitive to GABA. Concentration of 1 - 1 000 micromol/L GABA could activate a concentration-dependent inward current, which manifested obvious desensitization, and the inward currents could be blocked byGABA-receptor selective antagonist of bicuculline (100 micromol/L). (3) After the neurons were treated with ropivacaine (0.1 - 1000 micromol/L) prior to the application of GABA (100 micromol/L) 30 s, GABA currents were obviously increased. Ropivacaine could make dose-response curve of the GABA up, EC50 is 23.46 micromol/L. Ropivacaine shifted the GABA dose-response curve upward and increased the maximum response to the contrast about 153%.

CONCLUSIONThe enhancement of ropivacaine to DRG neurons activation of GABA current, can lead to enhancement of pre-synaptic inhibition at the spinal cord level. This may be one of the reasons for the anesthetic effect and analgesia for ropivacaine in epidural anesthesia.

Amides ; pharmacology ; Animals ; Ganglia, Spinal ; cytology ; physiology ; Membrane Potentials ; drug effects ; Neurons ; cytology ; drug effects ; physiology ; Patch-Clamp Techniques ; Rats ; Rats, Sprague-Dawley ; Receptors, GABA-A ; physiology

BACKGROUNDNeuropathic pain results from a lesion or disease affecting the somatosensory system at either the peripheral or central level. The transmission of nociception within the central nervous system is subject to modulation by release and reuptake of neurotransmitters, which maintain a dynamic balance through the assembly and disassembly of the SNARE complex as well as a series of neurotransmitter transporters (inhibitory GABA transporters GAT and excitatory glutamate transporters GT). Neuronal hyper-excitability or defected inhibition involved in neuropathic pain is one of the outcomes caused by imbalanced neurotransmission. SNAP-25, which is one of the SNARE complexes, can modulate the release of neurotransmitters. Glia glutamate transporter (GLT) is one of the two glutamate transporters which account for most synaptic glutamate uptake in the CNS. The role of SNAP-25 and GLT as well as GAT is not clearly understood.

METHODSWe used the rat chronic constriction injury (CCI) model for research, and degraded SNAP-25 by a single intrathecal administration of BoNT/A. The mechanical (MWT) and thermal withdrawal latency (TWL) were tested. The level of SNAP-25, GLT, and GAT-1 were assayed using RT-PCR and Western blotting.

RESULTSSNAP-25 was suppressed by a single intrathecal administration of 0.01U BoNT/A and the reduction of SNAP- 25 was correlated with the relief of nociceptive responses in CCI rats. MWT and TWL returned to normal from the 5th to 14th day (P < 0.05) after the administration. On the 14th day after surgery, compared to the sham group, the upregulation of SNAP-25 in CCI rats was reversed after BoNT/A treatment (P < 0.05). The decreased GLT was reversed after BoNT/A treatment but increased GAT-1 was not influenced by BoNT/A treatment.

CONCLUSIONSSNAP-25 and GLT play important roles in the development of neuropathic pain, and the mechanism may involve the imbalance of neurotransmission after peripheral nerve injury. Intrathecal administration of BoNT/A reversed the upregulation of SNAP-25 and downregulation of GLT after CCI, but had no significant effect on the expression of GAT-1.

Amino Acid Transport System X-AG ; genetics ; metabolism ; Animals ; Disease Models, Animal ; GABA Plasma Membrane Transport Proteins ; Male ; Neuralgia ; genetics ; metabolism ; Neuroglia ; metabolism ; Rats ; Rats, Sprague-Dawley ; Real-Time Polymerase Chain Reaction ; Synaptic Transmission ; genetics ; physiology ; Synaptosomal-Associated Protein 25 ; genetics ; metabolism

OBJECTIVETo investigate the changes of GABA-activated currents in isolated dorsal root ganglion neurons in rats with neuropathic pain.

METHODSThe neuropathic pain model was established by chronic constriction injury (CCI) 7 days before electrophysiological-recording. The rat DRG neurons were enzymatically dissociated. Whole-cell patch clamp technique was used to record GABA-activated currents. The changes of currents of injured side and opposite side were expected to compare with control group.

RESULTS(1) The currents of injured side of CCI group were notablely decreased compared with control group (GABA concentration, 0.1-1000 micromol/L). (2) By the contrast, opposite side currents of CCI group increased significantly compared with those in injured side and control group (GABA concentration, 0.01-1000 micromol/L).

CONCLUSIONThe data indicates that the chronic constriction injury change both the function of GABAA receptors of injury side and opposite side. The decrease of pre-synaptic inhibition of GABA may be the possible reason of neuropathic pain.

Animals ; Cell Separation ; Constriction ; Ganglia, Spinal ; pathology ; physiopathology ; Male ; Neuralgia ; etiology ; physiopathology ; Neurons ; metabolism ; physiology ; Patch-Clamp Techniques ; Rats ; Rats, Sprague-Dawley ; Receptors, GABA-A ; metabolism ; physiology ; Sciatic Nerve ; injuries

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