title: Kindling alters neurosteroid-induced modulation of phasic and tonic GABAA receptor-mediated currents: role of phosphorylation.
abstract: We have previously shown that after kindling (a model of temporal lobe epilepsy), the neuroactive steroid tetrahydrodeoxycorticosterone (THDOC) was unable to augment GABA type A receptor (GABA(A))-mediated synaptic currents occurring on pyramidal cells of the piriform cortex. Phosphorylation of GABA(A) receptors has been shown previously to alter the activity of THDOC, so we tested the hypothesis that kindling induces changes in the phosphorylation of GABA(A) receptors and this accounts for the loss in efficacy. To assay whether GABA(A) receptors are more phosphorylated after kindling, we examined the phosphorylation state of the β3 subunit and found that it was increased. Incubation of brain slices with the protein kinase C activator phorbol 12-myristate 13-acetate (PMA) (100 nM) also increased phosphorylation in the same assay. In patch clamp, recordings from non-kindled rat brain slices PMA also reduced the activity of THDOC in a manner that was identical to what is observed after kindling. We also found that the tonic current was no longer augmented by THODC after kindling and PMA treatment. The protein kinase C (PKC) antagonist bisindolylmaleimide I blocked the effects PMA on the synaptic but not the tonic currents. However, the broad spectrum PKC antagonist staurosporine blocked the effects of PMA on the tonic currents, implying that different PKC isoforms phosphorylate GABA(A) receptors responsible for phasic and tonic currents. The phosphatase activator Li(+) palmitate restored the 'normal' activity of THDOC on synaptic currents in kindled brain slices but not the tonic currents. These data demonstrate that kindling enhances the phosphorylation state of GABA(A) receptors expressed in pyramidal neurons reducing THDOC efficacy.
authors.affiliation: Robarts Research Institute, Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada.
authors.forename: Arash
authors.initials: A
authors.lastname: Kia
authors.forename: Fabiola
authors.initials: F
authors.lastname: Ribeiro
authors.forename: Renee
authors.initials: R
authors.lastname: Nelson
authors.forename: Cezar
authors.initials: C
authors.lastname: Gavrilovici
authors.forename: Stephen S G
authors.initials: SS
authors.lastname: Ferguson
authors.forename: Michael O
authors.initials: MO
authors.lastname: Poulter
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000473:pathology / Q000503:physiopathology; D003900:Desoxycorticosterone / Q000031:analogs & derivatives* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects*; D007696:Kindling, Neurologic / Q000473:pathology*; D008297:Male; D008301:Maleimides / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D018408:Patch-Clamp Techniques / Q000379:methods; D010703:Phorbol Esters / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D017966:Pyramidal Cells / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018079:Receptors, GABA / Q000235:genetics / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D007211:Indoles; D008301:Maleimides; D018377:Neurotransmitter Agents; D010703:Phorbol Esters; D018079:Receptors, GABA; C008874:phorbol-12,13-diacetate; D003900:Desoxycorticosterone; C009413:tetrahydrodeoxycorticosterone; C070515:bisindolylmaleimide I