GABAB Receptor Antagonist Research Articles

Adenovector GAD65 Gene Delivery into the Rat Trigeminal Ganglion Produces Orofacial Analgesia

BackgroundOur goal is to use gene therapy to alleviate pain by targeting glial cells. In an animal model of facial pain we tested the effect of transfecting the glutamic acid decarboxylase (GAD) gene into satellite glial cells (SGCs) of the trigeminal ganglion by using a serotype 5 adenovector with high tropisms for glial cells. We postulated that GABA produced from the expression of GAD would reduce pain behavior by acting on GABA receptors on neurons within the ganglion.ResultsInjection of adenoviral vectors (AdGAD65) directly into the trigeminal ganglion leads to sustained expression of the GAD65 isoform over the 4 weeks observation period. Immunohistochemical analysis showed that adenovirus-mediated GAD65 expression and GABA synthesis were mainly in SGCs. GABAA and GABAB receptors were both seen in sensory neurons, yet only GABAA receptors decorated the neuronal surface. GABA receptors were not found on SGCs. Six days after injection of AdGAD65 into the trigeminal ganglion, there was a statistically significant decrease of pain behavior in the orofacial formalin test, a model of inflammatory pain. Rats injected with control virus (AdGFP or AdLacZ) had no reduction in their pain behavior. AdGAD65-dependent analgesia was blocked by bicuculline, a selective GABAA receptor antagonist, but not by CGP46381, a selective GABAB receptor antagonist.ConclusionTransfection of glial cells in the trigeminal ganglion with the GAD gene blocks pain behavior by acting on GABAA receptors on neuronal perikarya.

Relating the Neural Representation and Perceptual Quality of Olfactory Stimuli

Event Abstract Back to Event Relating the Neural Representation and Perceptual Quality of Olfactory Stimuli John P. McGann1* 1 Rutgers University, Department of Psychology, United States The mouse olfactory bulb provides a powerful system for exploring the olfactory system because it permit the direct observation of physiological responses to odorants on both the population and single-cell levels while relating those responses to the corresponding perception of the odorant using behavioral olfactory psychophysical experimentation. Fig. 1A shows a fluorescence image of the right olfactory bulb of an anesthetized mouse expressing the exocytosis indicator synaptopHluorin [1] in the axon terminals of its olfactory receptor neurons (ORNs). The image shows the dorsal surface of the bulb visualized in vivo through a cranial window. Note that individual olfactory bulb glomeruli are visible in both the lower (left) and higher (right) magnification views. Fig. 1B (left) illustrates how the presentation of the odorant methyl valerate induces an increase in fluorescence (indicating transmitter release from ORN terminals) in a subset of the glomeruli shown in 1A (right). This pattern of response is odorant-specific, thus serving as the primary sensory representation of the odorant. In this session I will show how changes in this sensory representation may be induced experimentally, though pharmacological manipulation or sensory experience, and how these changes can be linked to olfactory perception. Fig. 1B illustrates how the application of the GABAB receptor antagonist CGP35348 (which blocks the GABA-mediated presynaptic inhibition of neurotransmitter release from ORN terminals) alters the representation of methyl valerate by increasing the magnitude of odor-evoked synaptic input without changing the relative responses across glomeruli [2]. In separate behavioral experiments, mice received bilateral infusions of CGP while performing behavioral tasks designed to quantify their perception of odor intensity and to evaluate their ability to discriminate between chemically similar odorants. The results demonstrate that CGP infusion produces changes in olfactory perceptions that are predictable from its effects on the neurophysiology of odorant responses. These experiments show how this combination of experimental techniques can successfully link the neural representation of odorants with the behaviorally-observed perception of odor intensity and quality. fig1

Tegmental pedunculopontine glutamate and GABA-B synapses mediate morphine reward.

The tegmental pedunculopontine nucleus (TPP) of the midbrain is critical in mediating the acute rewarding effects of opiates. However, the circuitry and neurochemistry underlying this effect has not been determined. Here we identify TPP receptors and cell types involved in systemic morphine reward and suggest an anatomical and neurochemical model for reward in the TPP. Simple hypothetical anatomical models for serial cell arrangements and receptors in the TPP were proposed and predictions of behavioral outcome (reward or no reward) then were made, based on the administration of agonists and antagonists directly into the TPP of rats. We report that TPP-administered NMDA produced rewarding effects, although GABA agonists and antagonists had no motivational effects on their own. However, the NMDA receptor antagonist AP-7 and the GABA-B receptor antagonist saclofen, while having no motivational effects on their own, blocked systemic morphine reward as measured by conditioned place preference. These results provide positive evidence for GABA-B and glutamate synapses in the TPP, which mediates systemic morphine reward and suggest that a serial pathway for morphine reward in the TPP is unlikely.

Source, topography and excitatory effects of GABAergic innervation in cockroach salivary glands

Cockroach salivary glands are innervated by dopaminergic and serotonergic neurons. Both transmitters elicit saliva secretion. We studied the distribution pattern of neurons containing gamma-aminobutyric acid (GABA) and their physiological role. Immunofluorescence revealed a GABA-immunoreactive axon that originates within the subesophageal ganglion at the salivary neuron 2 (SN2) and this extends within the salivary duct nerve towards the salivary gland. GABA-positive fibers form a network on most acinar lobules and a dense plexus in the interior of a minor fraction of acinar lobules. Co-staining with anti-synapsin revealed that some putative GABAergic terminals seem to make pre-synaptic contacts with GABA-negative release sites. Many putative GABAergic release sites are at some distance from other synapses and at distance from the acinar tissue. Intracellular recordings from isolated salivary glands have revealed that GABA does not affect the basolateral membrane potential of the acinar cells directly. When applied during salivary duct nerve stimulation, GABA enhances the electrical response of the acinar cells and increases the rates of fluid and protein secretion. The effect on electrical cell responses is mimicked by the GABA(B) receptor agonists baclofen and SKF97541, and blocked by the GABA(B) receptor antagonists CGP52432 and CGP54626. These findings indicate that GABA has a modulatory role in the control of salivation, acting presynaptically on serotonergic and/or dopaminergic neurotransmission.

Stimulation of α1-adrenoceptors reduces glutamatergic synaptic input from primary afferents through GABAA receptors and T-type Ca2+ channels

Activation of the descending noradrenergic system inhibits nociceptive transmission in the spinal cord. Although both α1- and α2-adrenoceptors in the spinal cord are involved in the modulation of nociceptive transmission, it is not clear how α1-adrenoceptors regulate excitatory and inhibitory synaptic transmission at the spinal level. In this study, inhibitory and excitatory postsynaptic currents (IPSCs and EPSCs, respectively) were recorded from lamina II neurons in rat spinal cord slices. The specific α1-adrenoceptor agonist phenylephrine significantly increased the frequency of GABAergic spontaneous IPSCs in a concentration dependent manner, and this effect was abolished by the α1-adrenoceptor antagonist 2-(2,6-dimethoxyphenoxy)ethylaminomethyl-1,4-benzodioxane (WB4101). Phenylephrine also significantly reduced the amplitude of monosynaptic and polysynaptic EPSCs evoked from primary afferents. The inhibitory effect of phenylephrine on evoked monosynaptic glutamatergic EPSCs was largely blocked by the GABAA receptor antagonist picrotoxin and, to a lesser extent, by the GABAB receptor antagonist CGP55845. Furthermore, blocking T-type Ca2+ channels with amiloride or mibefradil diminished the inhibitory effect produced by phenylephrine or the GABAA receptor agonist muscimol on monosynaptic EPSCs evoked from primary afferents. Collectively, these findings suggest that activation of α1-adrenoceptors in the spinal cord increases synaptic GABA release, which attenuates glutamatergic input from primary afferents mainly through GABAA receptors and T-type Ca2+ channels. This mechanism of presynaptic inhibition in the spinal cord may be involved in the regulation of nociception by the descending noradrenergic system.

Interaction between GABA and norepinephrine in interleukin-1β-induced suppression of the luteinizing hormone surge

Interleukin-1β (IL-1β), a cytokine that is closely associated with inflammation and immune stress, is known to interfere with reproductive functions. Earlier studies have demonstrated that IL-1β inhibits the luteinizing hormone (LH) surge during the afternoon of proestrus in female rats. We have shown that this effect is most probably mediated through a reduction in norepinephrine (NE) levels in the medial preoptic area (MPA) of the hypothalamus. However, the mechanism by which IL-1β decreases NE levels in the MPA is unclear. We hypothesized that the inhibitory neurotransmitter, GABA could play a role in decreasing NE levels in the MPA. To test this, ovariectomized, steroid-primed rats were injected (i.p.) with either PBS–BSA (control) or 5 μg of IL-1β, alone or in combination with i.c.v. administration of GABA-A and GABA-B receptor antagonists, Bicuculline and CGP 35348 (CGP) respectively. Animals were subjected to push–pull perfusion of the MPA and perfusates collected at 30 min intervals were analyzed for both NE and GABA levels using HPLC-EC. Simultaneously, serial plasma samples were obtained through jugular catheters and were analyzed for LH levels using RIA. Compared to control rats, NE levels decreased significantly in the MPA in IL-1β-treated rats ( p < 0.05). Concurrently, there was a significant increase in GABA levels in the MPA ( p < 0.05). The GABA-A receptor antagonist, bicuculline, was able to reverse the effect of IL-1β on NE and LH, while the GABA-B receptor antagonist, CGP 35348 was without any effect. This leads us to conclude that the IL-1β-induced suppression of the LH surge is most probably mediated through an increase in GABA levels in the MPA which causes a reduction in NE levels. This is probably one of the mechanisms by which IL-1β inhibits reproductive functions.

Analgesic α-Conotoxins Vc1.1 and Rg1A Inhibit N-Type Calcium Channels in Rat Sensory Neurons via GABABReceptor Activation

alpha-Conotoxins Vc1.1 and Rg1A are peptides from the venom of marine Conus snails that are currently in development as a treatment for neuropathic pain. Here we report that the alpha9alpha10 nicotinic acetylcholine receptor-selective conotoxins Vc1.1 and Rg1A potently and selectively inhibit high-voltage-activated (HVA) calcium channel currents in dissociated DRG neurons in a concentration-dependent manner. The post-translationally modified peptides vc1a and [P6O]Vc1.1 were inactive, as were all other alpha-conotoxins tested. Vc1.1 inhibited the omega-conotoxin-sensitive HVA currents in DRG neurons but not those recorded from Xenopus oocytes expressing Ca(V)2.2, Ca(V)2.1, Ca(V)2.3, or Ca(V)1.2 channels. Inhibition of HVA currents by Vc1.1 was not reversed by depolarizing prepulses but was abolished by pertussis toxin (PTX), intracellular GDPbetaS, or a selective inhibitor of pp60c-src tyrosine kinase. These data indicate that Vc1.1 does not interact with N-type calcium channels directly but inhibits them via a voltage-independent mechanism involving a PTX-sensitive, G-protein-coupled receptor. Preincubation with a variety of selective receptor antagonists demonstrated that only the GABA(B) receptor antagonists, [S-(R*,R*)][-3-[[1-(3,4-dichlorophenyl)ethyl]amino]-2-hydroxy propyl]([3,4]-cyclohexylmethyl) phosphinic acid hydrochloride (2S)-3[[(1S)-1-(3,4-dichlorophenyl)-ethyl]amino-2-hydroxypropyl](phenylmethyl) phosphinic acid and phaclofen, blocked the effect of Vc1.1 and Rg1A on Ca2+ channel currents. Together, the results identify Ca(V)2.2 as a target of Vc1.1 and Rg1A, potentially mediating their analgesic actions. We propose a novel mechanism by which alpha-conotoxins Vc1.1 and Rg1A modulate native N-type (Ca(V)2.2) Ca2+ channel currents, namely acting as agonists via G-protein-coupled GABA(B) receptors.

Acute anal stretch inhibits NMDA-dependent pelvic-urethra reflex potentiation via spinal GABAergic inhibition in anesthetized rats

The impact of acute anal stretch on the pelvic-urethra reflex potentiation was examined in urethane-anesthetized rats by recording the external urethra sphincter electromyogram activity evoked by the pelvic afferent stimulation. Test stimulation (1 stimulation/30 s) evoked a baseline reflex activity with a single action potential that was abolished by gallamine (5 mg/kg iv). On the other hand, the repetitive stimulation (1 stimulation/1 s) induced spinal reflex potentiation (SRP) that was attenuated by intrathecal 6-cyano-7-nitroquinoxaline-2,4-dione (a glutamatergic alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionat receptor antagonist, 100 microM, 10 microl) and d-2-amino-5-phosphonovalerate [a glutamatergic N-methyl-D-aspartate (NMDA) antagonist, 100 microM, 10 microl]. Acute anal stretch using a mosquito clamp with a distance of 4 mm exhibited no effect, whereas distances of 8 mm attenuated and 12 mm abolished the repetitive stimulation-induced SRP. Intrathecal NMDA (100 microM, 10 microl) reversed the abolition on SRP caused by anal stretch. On the other hand, pretreated bicuculline [gamma-aminobutyric acid (GABA) A receptor antagonist, 100 microM, 10 microl] but not hydroxysaclofen (GABAB receptor antagonist) counteracted the abolition on the repetitive stimulation-induced SRP caused by the anal stretch. All of the results suggested that anal stretch may be used as an adjunct to assist voiding dysfunction in patients with overactive urethra sphincter and that GABAergic neurotransmission is important in the neural mechanisms underlying external urethra sphincter activity inhibited by anal stretch.

Involvement of glutamate neurotransmission and N-methyl- d-aspartate receptor in the activation of midbrain dopamine neurons by 5-HT1A receptor agonists: An electrophysiological study in the rat

Systemic administration of selective 5-HT1A agonists, such as 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OHDPAT), stimulates the electrical activity of ventral tegmental area (VTA) dopamine neurons by a mechanism which remains unknown. We have examined if this activation is dependent on glutamatergic, serotonergic and GABAergic neurotransmission and if 5-HT1A receptors located within the VTA or within the prefrontal cortex (PFC) could contribute. In vivo electrophysiological recordings were obtained from VTA dopamine neurons from anesthetized rats. The i.v. administration of the 5-HT1A agonist 8-OHDPAT induced a strong stimulation of burst and firing activity of dopamine neurons. This activation remained unchanged in rats pre-treated with the 5-HT depleting agent parachlorophenylalanine. However, pre-administration of the GABAB receptor antagonist phaclophen, but not of the GABAA antagonist picrotoxin, significantly reduced the 8-OHDPAT-induced activation. The N-methyl- d-aspartate (NMDA) antagonist MK 801 (dizocilpine), but not the AMPA/kainate antagonist [1,2,3,4-tetrahydro-7-morpholinyl-2,3-dioxo-6-(fluoromethyl)quinoxalin-1-yl] methyl-phosphonate (ZK 200775), partially prevented or reversed the effects of 8-OHDPAT. However, only the combined pre-administration of the two glutamate antagonists did completely prevent the activatory response to 8-OHDPAT and even converted the effect of 8-OHDPAT into an inhibition, in half of the dopamine neurons tested. Inactivation of the local 5-HT1A receptors by the microinfusion within the VTA of the selective 5-HT1A antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide maleate (WAY 100,635), or of pertussis toxin, reduced the ability of 8-OHDPAT to stimulate the firing of dopamine neurons but not their burst activity. On the other hand, burst activation elicited by 8-OHDPAT was strongly reduced following the inactivation of prefrontal 5-HT1A receptors achieved by the microinfusion of WAY 100,635 within the PFC. These results show that activation of midbrain dopamine neurons by the systemic administration of 5-HT1A agonists does involve the inactivation of a tonic GABAergic tone, involving mainly the GABAB receptors, probably leading to the stimulation of a glutamatergic excitatory drive from the PFC to the VTA and an increase in glutamate release. This will excite dopamine neurons, preferentially through NMDA receptors. Furthermore, our results suggest that some 5-HT1A receptors located within the VTA may also participate in this activation.

GabaB receptors activation in the NTS blocks the glycemic responses induced by carotid body receptor stimulation

The carotid body receptors participate in glucose regulation sensing glucose levels in blood entering the cephalic circulation. The carotid body receptors information, is initially processed within the nucleus tractus solitarius (NTS) and elicits changes in circulating glucose and brain glucose uptake. Previous work has shown that γ-aminobutyric acid (GABA) in NTS modulates respiratory reflexes, but the role of GABA within NTS in glucose regulation remains unknown. Here we show that GABAB receptor agonist (baclofen) or antagonists (phaclofen and CGP55845A) locally injected into NTS modified arterial glucose levels and brain glucose retention. Control injections outside NTS did not elicit these responses. In contrast, GABAA agonist and antagonist (muscimol or bicuculline) produced no significant changes in blood glucose levels. When these GABAergic drugs were applied before carotid body receptors stimulation, again, only GABAB agonist or antagonist significantly affected glycemic responses; baclofen microinjection significantly reduced the hyperglycemic response and brain glucose retention observed after carotid body receptors stimulation, while phaclofen produced the opposite effect, increasing significantly hyperglycemia and brain glucose retention. These results indicate that activation of GABAB, but not GABAA, receptors in the NTS modulates the glycemic responses after anoxic stimulation of the carotid body receptors, and suggest the presence of a tonic inhibitory mechanism in the NTS to avoid hyperglycemia.

Dendritic backpropagation and synaptic plasticity in the mormyrid electrosensory lobe

This study is concerned with the origin of backpropagating action potentials in GABAergic, medium ganglionic layer neurones (MG-cells) of the mormyrid electrosensory lobe (ELL). The characteristically broad action potentials of these neurones are required for the expression of spike timing dependent plasticity (STDP) at afferent parallel fibre synapses. It has been suggested that this involves active conductances in MG-cell apical dendrites, which constitute a major component of the ELL molecular layer. Immunohistochemistry showed dense labelling of voltage gated sodium channels (VGSC) throughout the molecular layer, as well as in the ganglionic layer containing MG somata, and in the plexiform and upper granule cell layers of ELL. Potassium channel labelling was sparse, being most abundant in the deep fibre layer and the nucleus of the electrosensory lobe. Intracellular recordings from MG-cells in vitro, made in conjunction with voltage sensitive dye measurements, confirmed that dendritic backpropagation is active over at least the inner half of the molecular layer. Focal TTX applications demonstrated that in most case the origin of the backpropagating action potentials is in the proximal dendrites, whereas the small narrow spikes also seen in these neurones most likely originate in the axon. It had been speculated that the slow time course of membrane repolarisation following the broad action potentials was due to a poor expression of potassium channels in the dendritic compartments, or to their voltage- or calcium-sensitive inactivation. However application of TEA and 4AP confirmed that both A-type and delayed rectifying potassium channels normally contribute to membrane repolarisation following dendritic and axonal spikes. An alternative explanation for the shape of MG action potentials is that they represent the summation of active events occurring more or less synchronously in distal dendrites. Coincidence of backpropagating action potentials with parallel fibre input produces a strong local depolarisation that could be sufficient to cause local secretion of GABA, which might then cause plastic change through an action on presynaptic GABA B receptors. However, STP depression remained robust in the presence of GABAB receptor antagonists.

Attenuation of morphine withdrawal signs by a GABAB receptor agonist in the locus coeruleus of rats

In the present study, the effects of intra-locus coeruleus (LC) injection of GABAB receptor-interacting agents on naloxone-induced withdrawal signs of morphine-dependent rats were examined. The GABAB receptor agonist and antagonists were injected 5min prior to naloxone injection. Baclofen, a GABAB receptor agonist, decreased the TWS in a dose-dependent manner but CGP35348, a GABAB receptor antagonist, alone had no effect. On the other hand, baclofen effects were reversed by CGP35348. It may be concluded that activation of GABAB receptor mechanisms in the LC reduces precipitated withdrawal symptoms from chronic morphine treatment.

Plasticity of pre- and postsynaptic GABAB receptor function in the paraventricular nucleus in spontaneously hypertensive rats

GABA(B) receptor function is upregulated in the paraventricular nucleus (PVN) of the hypothalamus in spontaneously hypertensive rats (SHR), but it is unclear whether this upregulation occurs pre- or postsynaptically. We therefore determined pre- and postsynaptic GABA(B) receptor function in retrogradely labeled spinally projecting PVN neurons using whole cell patch-clamp recording in brain slices in SHR and Wistar-Kyoto (WKY) rats. Bath application of the GABA(B) receptor agonist baclofen significantly decreased the spontaneous firing activity of labeled PVN neurons in both SHR and WKY rats. However, the magnitude of reduction in the firing rate was significantly greater in SHR than in WKY rats. Furthermore, baclofen produced larger membrane hyperpolarization and outward currents in labeled PVN neurons in SHR than in WKY rats. The baclofen-induced current was abolished by either including G protein inhibitor GDPbetaS in the pipette solution or bath application of the GABA(B) receptor antagonist in both SHR and WKY rats. Blocking N-methyl-d-aspartic acid receptors had no significant effect on baclofen-elicited outward currents in SHR. In addition, baclofen caused significantly greater inhibition of glutamatergic excitatory postsynaptic currents (EPSCs) in labeled PVN neurons in brain slices from SHR than WKY rats. By contrast, baclofen produced significantly less inhibition of GABAergic inhibitory postsynaptic currents (IPSCs) in labeled PVN neurons in SHR than in WKY rats. Although microinjection of the GABA(B) antagonist into the PVN increases sympathetic vasomotor tone in SHR, the GABA(B) antagonist did not affect EPSCs and IPSCs of the PVN neurons in vitro. These findings suggest that postsynaptic GABA(B) receptor function is upregulated in PVN presympathetic neurons in SHR. Whereas presynaptic GABA(B) receptor control of glutamatergic synaptic inputs is enhanced, presynaptic GABA(B) receptor control of GABAergic inputs in the PVN is attenuated in SHR. Changes in both pre- and postsynaptic GABA(B) receptors in the PVN may contribute to the control of sympathetic outflow in hypertension.

Paired‐pulse depression of excitatory postsynaptic current sinks in hippocampal CA1 in vivo

Paired-pulse depression (PPD), a short-term neural plasticity, was studied in hippocampal CA1 of urethane-anesthetized rats in vivo, using field potential recordings and current source density analysis. PPD was robust when an ipsilateral CA3 (iCA3) conditioning pulse of moderate stimulus intensity was followed 30-200 ms later by a contralateral CA3 (cCA3) test pulse; the ratio of the conditioned (C) to the nonconditioned (NC) response, as measured by the peak excitatory sink at the apical dendrites, ranged from 0.6 to 0.8. An alveus conditioning pulse evoked a large antidromic population spike in CA1 and a modest depression of the CA3-evoked excitatory sink (C/NC ratio of approximately 0.85). High-intensity paired pulses, both delivered to iCA3, also showed PPD of the proximal excitatory sinks; however, paired-pulse facilitation of the dendritic sinks was found at the mid-apical dendrites, >250 microm from the soma. Local injection of GABA(A) antagonist picrotoxin or bicuculline increased the C/NC ratio at IPIs of <150 ms, as well as the ratio of the amplitude of the population spikes (P2/P1; where P2 and P1 are the population spikes evoked by the second and first pulse, respectively). GABA(B) receptor antagonists, CGP35348 given intracerebroventricularly or CGP56999A administered locally, increased C/NC and P2/P1 at IPIs of 150-400 ms. It is concluded that conditioned depression of the excitatory sinks was caused by mainly feedforward and some feedback inhibition at the apical dendrites. GABA(A)-mediated postsynaptic inhibition dominated at early latencies, while GABA(B)-mediated inhibition prevailed at long latencies, probably at both presynaptic and postsynaptic sites. PPD of the excitatory sinks provides a measure of population dendritic inhibition in vivo.

Antiabsence Effects of Safranal in Acute Experimental Seizure Models: EEG and Autoradiography

We examined the effect of safranal, a constituent of Crocus sativus, in acute experimental animal models of generalized absence seizures. the effect of acute systemic administration of safranal on latency to seizure onset as well as spike and wave discharches (SWD) duration following pharmacologically-induced absence seizures was investigated in wildtype mice. We further characterized its effects on the GABAergic system through the regional modification of [3H] flunitrazepam, a benzodiazepine agonist binding site and [3H] CGP54626A, a GABAB receptor antagonist binding site in mouse brain. The systemic administration of safranal resulted in a significant and dose-dependent attenuation in experimental absence seizures elicited by either gamma-butyrolactone (GBL), baclofen (BAC) or low doses of GABAA receptor antagonists; pentylenetetrazole (PTZ), picrotoxin (PTX) and bicuculline (BMC). After a single intraperitoneal administration of safranal (291 mg/kg), no changes in baseline electrocorticographic (ECoG) recording were observed, however, a significant decrease in [3H] flunitrazepam binding was seen in the cortex (33.16%, p<0.001), hippocampus (27.36%, p<0.01) and thalamus (29.91%, p<0.01) of mouse brain, while the [3H] CGP54626A binding did not show any modification in the same brain regions. These data indicate that there is an antiabsence seizure property in safranal and its effect may be due to modifications on the benzodiazepine binding sites of the GABAA receptor complex.

Role of ventral medial prefrontal cortex in incubation of cocaine craving

Cue-induced drug-seeking in rodents progressively increases after withdrawal from cocaine, suggesting that cue-induced cocaine craving incubates over time. Here, we explored the role of the medial prefrontal cortex (mPFC, a brain area previously implicated in cue-induced cocaine seeking) in this incubation. We trained rats to self-administer cocaine for 10 days (6 h/day, infusions were paired with a tone–light cue), and then assessed after 1 or 30 withdrawal days the effect of exposure to cocaine cues on lever presses in extinction tests. We found that cue-induced cocaine-seeking in the extinction tests was higher after 30 withdrawal days than after 1 day. The time-dependent increases in extinction responding were associated with large (ventral mPFC) or modest (dorsal mPFC) increases in ERK phosphorylation (a measure of ERK activity and an index of neuronal activation). After 30 withdrawal days, ventral but not dorsal injections of muscimol + baclofen (GABAa + GABAb receptor agonists that inhibit neuronal activity) decreased extinction responding. After 1 withdrawal day, ventral but not dorsal mPFC injections of bicuculline + saclofen (GABAa + GABAb receptor antagonists that increase neuronal activity) strongly increased extinction responding. Finally, muscimol + baclofen had minimal effect on extinction responding after 1 day, and in cocaine-experienced rats, ventral mPFC injections of muscimol + baclofen or bicuculline + saclofen had no effect on lever presses for an oral sucrose solution. The present results indicate that ventral mPFC neuronal activity plays an important role in the incubation of cocaine craving.

Involvement of the GABA-B system in the mechanism of action of ultralow-dose antibodies to S-100 protein

The involvement of the GABA-B neurotransmitter system in the realization of anxiolytic and antidepressant activities of ultralow-dose antibodies to S-100 protein is demonstrated. Simultaneous injection of ultralow-dose antibodies to S-100 protein and GABA-B receptor agonist baclofen reduced the anxiolytic and antidepressant effects of the drug, while GABA-B receptor antagonist faclofen stimulated the anxiolytic and reduced the antidepressant effect of ultralow-dose antibodies to S-100 protein. The effect of ultralow-dose antibodies to S-100 protein on the GABA-B-ergic system differs from that of benzodiazepine anxiolytics (diazepam) and tricyclic antidepressants (amitryptiline) not affecting this transmitter system.

What is the role of neurotransmitter systems in cortical seizures?

Epileptic afterdischarges (ADs) elicited by electrical stimulation of sensorimotor cortical area were used as a model to study the role of neurotransmitter systems in cortical seizures in three age groups of developing rats. Drugs augmenting inhibition mediated by GABAA receptors were found to suppress ADs in all age groups, their activity was usually more marked in younger than in 25-day-old rat pups. Drugs potentiating GABAB receptors exhibit lower efficacy and more complicated developmental profile than GABAA-ergic drugs. Effects of an antagonist of GABAB receptor--marked prolongation of ADs in all three age groups--suggest an important role of GABAB receptors in arrest of cortical seizures. Drugs affecting glutamate receptors exhibit variable effects, usually better expressed in older animals than in 12-day-old ones. No specific role for ionotropic as well as metabotropic glutamate receptors could be predicted. Activation of adenosinergic inhibitory modulatory system also exhibited anticonvulsant action in the present model. All three neurotransmitter systems probably participate in mechanisms of generation, maintenance and arrest of cortical seizures.

γ-Aminobutyric AcidB(GABAB)-Receptor Mediation of Different In Vivo Effects of γ-Butyrolactone

The endogenous brain constituent, γ-hydroxybutyric acid (GHB), as well as its prodrug, γ-butyrolactone (GBL), have recently gained interest in the drug addiction field due to their abuse potential and fatalities caused by overdose. It is known that GHB has two sites of actions: the γ-aminobutyric acidB(GABAB) receptor and a specific-GHB binding site. The present study was designed to extend to GBL the investigations on the contribution of the GABABreceptor and the specific-GHB binding site to its in vivo effects. To this aim, DBA mice were pretreated either with GABAB-receptor antagonists, (3-aminopropyl)(diethoxymethyl)phosphinic acid (CGP 35348) and (2S)(+)-5,5-dimethyl-2-morpholineacetic acid (SCH 50911), or a putative antagonist of the specific-GHB binding site, 6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylideneacetic acid (NCS-382), prior to the administration of doses of GBL that induced hypothermia, motor-incoordination (measured as motor-impairment at the Rota-Rod task), and sedation/hypnosis. The capability of SCH 50911 and NCS-382 to protect against GBL-induced lethality was also investigated. Pretreatment with either GABAB-receptor antagonist completely prevented GBL-induced hypothermia, motor-incoordination, and sedation /hypnosis. SCH 50911 also provided complete protection against GBL-associated lethality. Vice versa, NCS-382 failed to exert any antagonistic or protective effect. These results suggest that the in vivo GBL effects tested in the present study are mediated by activation of the GABABreceptor.

Effects of a GABA-B receptor agonist baclofen on cortical epileptic afterdischarges in rats

Inhibition mediated by GABA-B receptors can play a role in epilepsy. We therefore studied its involvement in cortical epileptic afterdischarges in adult rats by means of a GABA-B receptor agonist baclofen. Three different experiments were performed with cortical epileptic afterdischarges and an additional experiment studied possible effect of baclofen on cortical interhemispheric (transcallosal) evoked potentials. Baclofen was administered intraperitoneally in doses of 3 or 6 mg/kg. In contrast to a marked proconvulsant action of a GABA-B receptor antagonist baclofen did not exhibit clear anticonvulsant action against EEG afterdischarges but a moderate effect on motor phenomena was observed. On the contrary, it tended to decrease threshold intensities for individual epileptic phenomena. Augmentation of postictal refractoriness by baclofen was found only with a short poststimulation interval (2 min). Cortical interhemispheric responses induced by single pulses were influenced only moderately by baclofen; paired-pulse potentiation induced by short intervals between stimuli was not changed but there was a depression of the second response induced 200 and 250 ms after the first one with the 6 mg/kg dose of baclofen. Failure of baclofen to exhibit an expected anticonvulsant activity might be due to a complexity of GABA-B inhibitory system (pre- as well as postsynaptic localization of GABA-B receptors).