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GABA Receptors

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psychology
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NYU

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  1. Introduction
  2. GABAA receptors
    1. The affect of pharmacological agents on the activity of GABAA receptors
    2. The metabotropic GABAB receptors
  3. Clinical considerations
    1. Glutamate and aspartate
    2. Ischemia induced neurodegeneration
    3. Chronic neurodegenerative disorders
    4. Schizophrenia
    5. Neuropathic pain
  4. GABA
    1. Epilepsy
    2. Anesthesia pentobarbital
    3. Spasticity Loss of spinal and supraspinal inhibition
  5. Conclusion
  6. References

GABAA Receptor The GABAA receptor is a member of the superfamily of ligand-activated ion channels in the cell membrane. GABA type A (GABAA) receptors are most closely related to strychnine-sensitive glycine receptors, more distantly related to acetylcholine nicotonic receptors and serotonin 5-hydroxytryptamine (5-HT) [5-HT] type receptors, and even more distantly related to glutamate ionotropic receptors (AMPA and kainate receptors and NMDA receptors). GABAA receptors are heteropentameric protein complexes, which when activated undergo a series of conformational changes that form an open channel (pore) selectively permeable to anions, specifically chlorine anion (Cl?) and to a lesser degree (HCO?3). Receptor activation normally results in an influx of Cl? which rapidly and transiently hyperpolarizes the membrane, a process generally referred to as the generation of an inhibitory postsynaptic potential. The increase in Cl? flux also decreases the resistance of the membrane, which acts as a shunt to impede the ability of depolarizing excitatory postsynaptic potentials to elicit action potentials (nerve impulses).

[...] Not only does positive modulation of these allosteric sites result in anticonvulsant activity, increases in GABA availability also seem to be of clinical benefit. Reduction of GABA clearance by inhibition of GABA uptake or reduction of GABA degradation by poisoning GABA transaminase are both effective. A GABA uptake inhibitor has been recently approved for treatment of partial seizures, but it may exacerbate generalized absence seizures. An irreversible inhibitor of GABA transaminase also effective in the treatment of partial seizures is in the late stages of development. [...]


[...] The basis for the persistent hyperexcitable state remains controversial, and the actual involvement of excitatory amino acid receptors in this hyperexcitable state remains unclear. However, there is good evidence that glutamatergic receptors, particularly NMDA types, play a role in the development and enhancement of the kindled or seizure-prone state. NMDA receptor antagonists can prevent the kindling phenomenon despite the expression of seizurelike discharges in in vitro models such as hippocampal slices. A variety of NMDA antagonists, including those that act as channel inhibitors or compete with the glutamate recognition or glycine recognition sites, appear to be highly effective in blocking the development of kindling. [...]


[...] Drugs that bind to them influence the ability of GABA to activate the receptor by either altering the affinity between GABA and its binding sites (GABAA receptors probably possess two GABA binding sites) or by altering the channel open time and rate of receptor desensitization. It now seems unlikely that either of these sites serves a physiological purpose. An unusual characteristic of the benzodiazepine site is that drugs binding to it can exert either a positive modulatory (an agonist) or negative modulatory (an inverse agonist) effect, or no effect at all (an antagonist). [...]

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