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Several mechanisms of gabapentin have been proposed after neuropathy including an inhibition of NMDA receptors, inhibition of sodium currents and reducing β4a subunit mediated VGCC trafficking (Hara and Sata 2007; Mich and Horne 2008; Yang et al. 2009). Gabapentin is an anti-epileptic agent but now it is also recommended as first line agent in neuropathic pain, particularly in diabetic neuropathy and post herpetic neuralgia. α2δ-1, an auxillary subunit of voltage gated calcium channels, has been documented as its main target and its specific binding to this subunit is described to produce different actions responsible for pain attenuation 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. Target receptor: Voltage-hated calcium channels, which therefore decreases the release of excitatory neurotransmitters. Mechanism of action: By inhibiting the voltage-gated calcium channels in the CNS, gabapentin reduces the release of excitatory neurotransmitters (mostly noradrenaline, dopamine and serotonin), and therefore decreases Gabapentin has also been shown to induce modulate other targets including transient receptor potential channels, NMDA receptors, protein kinase C and inflammatory cytokines. It may also act on supra-spinal region to stimulate noradrenaline mediated descending inhibition, which contributes to its anti-hypersensitivity action in neuropathic pain. Although the exact mechanism of action with the GABA receptors is unknown, researchers know that gabapentin freely passes the blood-brain barrier and acts on neurotransmitters. Gabapentin has a cyclohexyl group to the structure of the neurotransmitter GABA as a chemical structure. Mechanism of Action. Gabapentin is structurally related to GABA. However, it does not bind to GABA A or GABA B receptors, and it does not appear to influence synthesis or uptake of GABA. High affinity gabapentin binding sites have been located throughout the brain; these sites correspond to the presence of voltage-gated calcium channels Although gabapentin was originally modeled after the structure of GABA, it does not modulate GABA receptor function like conventional GABAergic drugs, and it is inactive at GABA receptors. This review outlines several potential mechanisms of pharmacological action of gabapentin. The mechanisms of the anti-allodynic effects of gabapentin proposed include: CNS effects (potentially at spinal cord or brain level) due to either enhanced inhibitory input of GABA-mediated pathways (and thus reducing excitatory input levels); antagonism of NMDA receptors; and antagonism of calcium channels in the CNS and inhibition of Gamma-aminobutyric acid (GABA) and glutamate (GLU) play crucial roles in the control of neuropathic pain through their actions within the central nervous system (CNS). These neurotransmitters separately activate two distinct classes of receptors: ionotropic and metabotropic. Mechanism of Action Gabapentin is designed as GABA analog (similar to pregabalin ), which means it binds to the α2δ (alpha-2-delta) subunit of presynaptic voltage-sensitive Ca2+ channels (VSCCs), and block the release of excitatory neurotransmitters such as glutamate. Gabapentin is an anti-epileptic drug but its use has expanded to treat multiple other diseases including post-herpetic neuralgia, neuropathic pain, and spasticity. The mechanism of action is not fully understood but may be related to gabapentin’s action on calcium channels leading to diminution of excitatory neurotransmitters. For the benzodiazepines, barbiturates, and loreclezole, actions at the GABA A R are the primary or only known mechanism of antiseizure action. For topiramate, felbamate, retigabine, losigamone and stiripentol, GABA A R modulation is one of several possible antiseizure mechanisms. The mechanisms of the anti-allodynic effects of gabapentin proposed include: CNS effects (potentially at spinal cord or brain level) due to either enhanced inhibitory input of GABA-mediated pathways (and thus reducing excitatory input levels); antagonism of NMDA receptors; and antagonism of calcium channels in the CNS and inhibition of Gabapentin crosses several lipid membrane barriers via system L amino acid transporters. In vitro, gabapentin modulates the action of the GABA synthetic enzyme, glutamic acid decarboxylase (GAD) and the glutamate synthesizing enzyme, branched-chain amino acid transaminase. Mechanism of action. The precise mechanism through which gabapentin exerts its therapeutic effects is unclear. 16,17 The primary mode of action appears to be at the auxillary α2δ-1 subunit of voltage-gated calcium channels (though a low affinity for the α2δ-2 subunit has also been reported). 10,8,14 The major function of these subunits is Alternatively, gabapentin may reduce α2δ-1 interaction with thrombospondin, an astrocyte-secreted protein, and inhibit new synapse formation (but not already formed synapses) (Eroglu et al., 2009). Nevertheless, this action cannot fully account for the relatively rapid onset of gabapentinoid effects on pain hypersensitivity. Mechanism of action of gabapentinoids Site of action The actions of gabapentinoids are mainly at an intracellular site and require active uptake.21 They were originallydesigned as g aminobutyric acid (GABA) analogues but do not have any effects on GABA receptors. Gabapentin binds to a 2d receptors with greater affinity to the a 2d-1 subtype.22 As with many other agents, GBP was licensed for the treatment of epilepsy with little or no understanding of its mechanism of action. Continued research and the parallel development of PGB have contributed to a contemporary pharmacological view of GBP (and PGB) as drugs with multiple modest cellular effects at therapeutic concentrations, but with a single predominant mechanism of action that Mechanisms of action. Gabapentin and pregabalin do not bind to GABA receptors despite their structural similarity but have a high affinity for the α2δ-1 subunit of voltage-gated calcium channels (VGCCs). 19 VGCCs are composed of multiple subunits: α 1, β, γ and α 2 δ.
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