Localization of [3H]gabapentin to a novel site in rat brain: autoradiographic studies

doi:10.1016/0922-4106(93)90156-4

European Journal of Pharmacology: Molecular Pharmacology

Volume 244, Issue 3, 15 February 1993, Pages 303-309

https://doi.org/10.1016/0922-4106(93)90156-4 Get rights and content

Abstract

The autoradiographical distribution of [³H]gabapentin, the tritiated analogue of the novel anticonvulsant gabapentin (1-(aminomethyl)cyclohexaneacetic acid) was measured in rat brain. Binding to sections was uniformly inhibited by non-radioactive gabapentin and 3-isobutyl-γ-aminobutyric acid (3-isobutyl-GABA). Specific gabapentin binding sites were unevenly distributed throughout the brain with the highest level being found in the outer layers of the cerebral cortex (38 ± 7 fmol/mm²; n = 3) and the lowest amounts in the white matter. In the hippocampus, the distribution of the binding site paralleled the excitatory neuronal input with the highest levels of binding being measured in the outer layers of the dentate gyrus and in the dendritic regions of the CA1 pyramidal cell layer. The binding site appeared absent from the cell body region of granule and pyramidal cells. Lesions performed unilaterally in the striatum using quinolinic acid resulted in a marked loss of [³H]gabapentin binding sites as compared with sham-lesioned animals, suggesting the binding site was localized on neuronal cell bodies. These data complement and extend the results of experiments using [³H]gabapentin with homogenates of rat brain and show the discrete localization of this novel binding site in regions associated with excitatory amino acid input. The data do not support previous indications of an association of the gabapentin binding site and NMDA/glycine receptor complex.

References (34)

D.R. Bristow et al.
Light microscopic autoradiography of [³H]glycine and [³H]strychnine binding sites in rat brain
Eur. J. Pharmacol.
(1986)
C.R. Clark et al.
Hormone receptor autoradiography: recent developments
Trends Biochem. Sci.
(1986)
A. Dubois et al.
Imaging of primary and remote ischaemic and excitotoxic brain lesions. An autoradiographic study of peripheral type benzodiazepine binding sites in the rat and cat
Brain Res.
(1988)
E.W. Harris et al.
Long term potentiation in the hippocampus involves activation of N-methyl-D-aspartate receptors
Brain Res.
(1984)
J.W. McDonald et al.
Characterization and regional distribution of strychnine-insensitive [³H]glycine binding sites in rat brain by quantitative receptor autoradiography
Neuroscience
(1990)
D.T. Monaghan et al.
[³H]Glutamate binds to kainate-, NMDA- and AMPA-sensitive binding sites: an autoradiographic analysis
Brain Res.
(1985)
T. Sprosen
Allosteric Modulation of the NMDA-Receptor Complex
C.P. Taylor et al.
In vitro and in vivo effects of the anticonvulsant gabapentin
Soc. Neurosci. Abstr.
(1988)
G.D. Bartoszyk et al.
Preclinical characterization of the anticonvulsant gabapentin
G.D. Bartoszyk et al.
Gabapentin

N.G. Bowery et al.

Quantitative autoradiography of [³H]MK-801 binding sites in mammalian brain

Br. J. Pharmacol.

(1988)

D. Chadwick

Gabapentin

B.V. Clineschmidt et al.

Anticonvulsant activity of (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-immine (MK-801), a substance with potent anticonvulsant, central sympathomimetic and apparent anxiolytic properties

Drug Dev. Res.

(1982)

J.T. Coyle et al.

Lesions of striatal neurones with kainic acid provides a model for Huntington's chorea

Nature

(1976)

D.J. Dooley et al.

Preclinical pharmacology of gabapentin

A.C. Foster et al.

HA-966 antagonizes N-methyl-D-aspartate receptors through a selective action with the glycine modulatory site

J. Neurosci.

(1989)

A.C. Foster et al.

Neuroprotective effects of MK-801 in vivo: selectivity and evidence for delayed degeneration mediated by NMDA receptor activation

J. Neurosci.

(1988)

Cited by (160)

Gabapentin increases expression of δ subunit-containing GABA <inf>A</inf> receptors
2019, EBioMedicine
Gabapentin is a structural analog of the inhibitory neurotransmitter γ-aminobutyric acid (GABA). Its anticonvulsant, analgesic and anxiolytic properties suggest that it increases GABAergic inhibition; however, the molecular basis for these effects is unknown as gabapentin does not directly modify GABA type A (GABA_A) receptor function, nor does it modify synaptic inhibition. Here, we postulated that gabapentin increases expression of δ subunit-containing GABA_A (δGABA_A) receptors that generate a tonic inhibitory conductance in multiple brain regions including the cerebellum and hippocampus.
Cell-surface biotinylation, Western blotting, electrophysiologic recordings, behavioral assays, high-performance liquid chromatography and gas chromatography-mass spectrometry studies were performed using mouse models.
Gabapentin enhanced expression of δGABA_A receptors and increased a tonic inhibitory conductance in neurons. This increased expression likely contributes to GABAergic effects as gabapentin caused ataxia and anxiolysis in wild-type mice but not δ subunit null-mutant mice. In contrast, the antinociceptive properties of gabapentin were observed in both genotypes. Levels of GABA_A receptor agonists and neurosteroids in the brain were not altered by gabapentin.
These results provide compelling evidence to account for the GABAergic properties of gabapentin. Since reduced expression of δGABA_A receptor occurs in several disorders, gabapentin may have much broader therapeutic applications than is currently recognized.
Supported by a Foundation Grant (FDN-154312) from the Canadian Institutes of Health Research (to B.A.O.); a NSERC Discovery Grant (RGPIN-2016-05538), a Canada Research Chair in Sensory Plasticity and Reconsolidation, and funding from the University of Toronto Centre for the Study of Pain (to R.P.B.).
Antiepileptic drugs as analgesics/adjuvants in inflammatory pain: current preclinical evidence
2018, Pharmacology and Therapeutics
Inflammatory pain is the most common type of pain that is treated clinically. The use of currently available treatments (classic analgesics - NSAIDs, paracetamol and opioids) is limited by insufficient efficacy and/or side effects/tolerance development. Antiepileptic drugs (AEDs) are widely used in neuropathic pain treatment, but there is substantial preclinical evidence on their efficacy against inflammatory pain, too. In this review we focus on gabapentinoids (gabapentin and pregabalin) and dibenzazepine AEDs (carbamazepine, oxcarbazepine, and recently introduced eslicarbazepine acetate) and their potential for relieving inflammatory pain. In models of somatic, visceral and trigeminal inflammatory pain, that have a translational value for inflammatory conditions in locomotor system, viscera and head/face, AEDs have demonstrated analgesic activity. This activity was mostly consistent, dependent on the dose and largely independent on the site of inflammation and method of its induction, nociceptive stimuli, species, specific drug used, its route of administration and dosing schedule. AEDs exerted comparable efficacy with classic analgesics. Effective doses of AEDs are lower than toxic doses in animals and, when expressed as equivalent human doses, they are largely overlapping with AEDs doses already used in humans for treating epilepsy/neuropathic pain. The main mechanism of antinociceptive/antihyperalgesic action of gabapentinoids in inflammatory pain models seems to be α₂δ-dependent suppression of voltage-gated calcium channels in primary sensory neurons that leads to reduced release of neurotransmitters in the spinal/medullar dorsal horn. The suppression of NMDA receptors via co-agonist binding site primarily at spinal sites, activation of various types of K⁺ channels at spinal and peripheral sites, and activation of noradrenergic and serotonergic descending pain modulatory pathways may also contribute. Inhibition of voltage-gated sodium channels along the pain pathway is probably the main mechanism of antinociceptive/antihyperalgesic effects of dibenzazepines. The recruitment of peripheral adrenergic and purinergic mechanisms and central GABAergic mechanisms may also contribute. When co-administered with classic/other alternative analgesics, AEDs exerted synergistic/additive interactions. Reviewed data could serve as a basis for clinical studies on the efficacy/safety of AEDs as analgesics/adjuvants in patients with inflammatory pain, and contribute to the improvement of the treatment of various inflammatory pain states.
R-phenibut binds to the α<inf>2</inf>-δ subunit of voltage-dependent calcium channels and exerts gabapentin-like anti-nociceptive effects
2015, Pharmacology Biochemistry and Behavior
Phenibut is clinically used anxiolytic, mood elevator and nootropic drug. R-phenibut is responsible for the pharmacological activity of racemic phenibut, and this activity correlates with its binding affinity for GABA_B receptors. In contrast, S-phenibut does not bind to GABA_B receptors. In this study, we assessed the binding affinities of R-phenibut, S-phenibut, baclofen and gabapentin (GBP) for the α₂–δ subunit of the voltage-dependent calcium channel (VDCC) using a subunit-selective ligand, radiolabelled GBP. Binding experiments using rat brain membrane preparations revealed that the equilibrium dissociation constants (K_is) for R-phenibut, S-phenibut, baclofen and GBP were 23, 39, 156 and 0.05 μM, respectively. In the pentylenetetrazole (PTZ)-induced seizure test, we found that at doses up to 100 mg/kg, R-phenibut did not affect PTZ-induced seizures. The anti-nociceptive effects of R-phenibut were assessed using the formalin-induced paw-licking test and the chronic constriction injury (CCI) of the sciatic nerve model. Pre-treatment with R-phenibut dose-dependently decreased the nociceptive response during both phases of the test. The anti-nociceptive effects of R-phenibut in the formalin-induced paw-licking test were not blocked by the GABA_B receptor-selective antagonist CGP35348. In addition, treatment with R- and S-phenibut alleviated the mechanical and thermal allodynia induced by CCI of the sciatic nerve. Our data suggest that the binding affinity of R-phenibut for the α₂–δ subunit of the VDCC is 4 times higher than its affinity for the GABA_B receptor. The anti-nociceptive effects of R-phenibut observed in the tests of formalin-induced paw licking and CCI of the sciatic nerve were associated with its effect on the α₂–δ subunit of the VDCC rather than with its effects on GABA_B receptors. In conclusion, our results provide experimental evidence for GBP-like, anti-nociceptive properties of R-phenibut, which might be used clinically to treat neuropathic pain disorders.
Pregabalin is a potent and selective ligand for α <inf>2</inf>δ- 1 and α <inf>2</inf>δ-2 calcium channel subunits
2011, European Journal of Pharmacology
Pregabalin, a synthetic branched chain γ-amino acid with anticonvulsant, anxiolytic, and analgesic activities, has been shown to bind with high affinity to the voltage-gated calcium channel α₂δ subunit. Given the broad therapeutic utility of pregabalin, a series of experiments was undertaken to determine the potency, selectivity, and specificity of pregabalin's receptor-binding profile at α₂δ-1 and α₂δ-2 subunits of voltage-gated calcium channels along with 38 widely studied receptors and channels. Receptor autoradiography was used to assess regional-binding density of pregabalin throughout the rat spinal cord and brain. In addition, a series of studies using in vivo electrophysiological recordings of γ-aminobutyric acid (GABA)_A- and GABA_B-evoked currents was undertaken to determine the interaction of pregabalin with GABAergic receptor subtypes. Together, the results of these studies demonstrate potent and selective binding of pregabalin to α₂δ-1 and α₂δ-2 subunits in native and recombinant human and porcine systems. Pregabalin did not interact with any of the 38 receptors and ion channels evaluated, and a variety of central nervous system (CNS)-targeted therapeutic drugs did not show activity at the α₂δ subunits of voltage-gated calcium channels. Receptor autoradiography demonstrated extensive [³H]-pregabalin binding throughout the CNS, with high-level binding in the cortex, hippocampus, cerebellum, dorsal horn of the spinal cord, and amygdala. Finally, receptor-binding and electrophysiological techniques failed to show evidence of an interaction between pregabalin and GABA_A or GABA_B receptors. These studies suggest that the clinical effects of pregabalin are likely due to direct and selective interactions with α₂δ-1 and α₂δ-2 subunits of voltage-gated calcium channels.
Gabapentin and pregabalin inhibit the itch-associated response induced by the repeated application of oxazolone in mice
2011, Journal of Pharmacological Sciences
We investigated the effects of gabapentin and pregabalin on the itch-associated response in a mouse model of chronic dermatitis induced by the repeated application of 4-ethoxymethylene-2-phenyl-2-oxazolin-5-one (oxazolone). Challenging the mice with oxazolone-induced chronic dermatitis with the oxazolone evoked severe and transient scratching behavior until 1 h after the application of oxazolone. Thereafter, a more mild and continuous scratching behavior was also observed for at least 8 h. Both severe and continuous scratching behaviors were suppressed by systemic injection of gabapentin and pregabalin. This effect of these compounds was correlated with its affinity for the α₂δ subunit of voltage-gated Ca²⁺ channels. Intrathecal injection, but not peripheral treatment, with gabapentin inhibited the scratching behavior in this model. Gabapentin failed to suppress the scratching behavior induced by the intradermal injection of compound 48/80 in normal mice. The expression of the α₂δ-1 subunit in dorsal root ganglion (DRG) from mice following repeated application of oxazolone was significantly higher than that from normal mice. These results suggest that gabapentin and pregabalin show an anti-pruritic activity through α₂δ-subunit binding, and the up-regulation of the α₂δ-1 subunit in DRG may therefore play an important role in its anti-pruritic activity.
Antiepileptic drugs
2009, Current Therapy in Pain

View all citing articles on Scopus

View full text

Regular paperLocalization of [3H]gabapentin to a novel site in rat brain: autoradiographic studies

Abstract

Eur. J. Pharmacol.

Trends Biochem. Sci.

Brain Res.

Brain Res.

Neuroscience

Brain Res.

Soc. Neurosci. Abstr.

Preclinical characterization of the anticonvulsant gabapentin

Gabapentin

Quantitative autoradiography of [3H]MK-801 binding sites in mammalian brain

Br. J. Pharmacol.

Gabapentin

Anticonvulsant activity of (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-immine (MK-801), a substance with potent anticonvulsant, central sympathomimetic and apparent anxiolytic properties

Drug Dev. Res.

Lesions of striatal neurones with kainic acid provides a model for Huntington's chorea

Nature

Preclinical pharmacology of gabapentin

HA-966 antagonizes N-methyl-D-aspartate receptors through a selective action with the glycine modulatory site

J. Neurosci.

Neuroprotective effects of MK-801 in vivo: selectivity and evidence for delayed degeneration mediated by NMDA receptor activation

J. Neurosci.

Regular paper
Localization of [³H]gabapentin to a novel site in rat brain: autoradiographic studies

Quantitative autoradiography of [³H]MK-801 binding sites in mammalian brain