Generation and Analysis of GluR5(Q636R) Kainate Receptor Mutant Mice

Abstract

The physiological significance of RNA editing of transcripts that code for kainate-preferring glutamate receptor subunits is unknown, despite the fact that the functional consequences of this molecular modification have been well characterized in cloned receptor subunits. RNA editing of the codon that encodes the glutamine/arginine (Q/R) site in the second membrane domain (MD2) of glutamate receptor 5 (GluR5) and GluR6 kainate receptor subunits produces receptors with reduced calcium permeabilities and single-channel conductances. Approximately 50% of the GluR5 subunit transcripts from adult rat brain are edited at the Q/R site in MD2. To address the role of glutamate receptor mRNA editing in the brain, we have made two strains of mice with mutations at amino acid 636, the Q/R-editing site in GluR5, using embryonic stem cell-mediated transgenesis. GluR5(RloxP/RloxP) mice encode an arginine at the Q/R site of the GluR5 subunit, whereas GluR5(wt(loxP)/wt(loxP)) mice encode a glutamine at this site, similar to wild-type mice. Mutant animals do not exhibit developmental abnormalities, nor do they show deficits in the behavioral paradigms tested in this study. Kainate receptor current densities were reduced by a factor of six in acutely isolated sensory neurons of dorsal root ganglia from GluR5(RloxP/RloxP) mice compared with neurons from wild-type mice. However, the editing mutant mice did not exhibit altered responses to thermal and chemical pain stimuli. Our investigations with the GluR5-editing mutant mice have therefore defined a set of physiological processes in which editing of the GluR5 subunit is unlikely to play an important role.

Altered Behavioral Responses to Noxious Stimuli and Fear in Glutamate Receptor 5 (GluR5)- or GluR6-Deficient Mice

“…The results presented here agree with a previous study that used a selective GluR5 antagonist, LY382884, to show that inhibition of GluR5 activity reduces behavioral responses to formalin (Simmons et al, 1998). Another study showed that mice bearing a targeted mutation at a critical RNA editing site of the GluR5 gene had normal responses to formalin (Sailer et al, 1999). The reason for this discrepancy may be attributable to different levels of functional GluR5 receptors between this transgenic mouse and the ones used here, because the RNA editing mutant retains some functional receptors.…”

Deletion of the Glutamate Receptor 5 Subunit of Kainate Receptors Affects the Development of Morphine Tolerance

“…These data are in agreement with other studies conducted in GluR5 KO maintained on a mixed 129 ϫ C57BL/6 background (Ko et al, 2005) or in GluR5(Q636R) editing mutants (Sailer et al, 1999), which found no difference from WT mice with respect to mechanical or thermal thresholds. The lack of involvement of GluR5 in baseline nociceptive sensitivity is further supported by the finding that acute morphine antinociception (ED 50 value, Table 1) is not different between WT and GluR5 KO.…”

“…A value of p Ͻ 0.05 was considered significant. (Sailer et al, 1999). First, we examined the development of antinociceptive tolerance in WT and GluR5 KO mice after repeated subcutaneous injections of morphine.…”

A Genetic Switch for Epilepsy in Adult Mice

“…However, a role of Q/R site editing of AMPA or kainate receptors suggested by murine models (Sailer et al, 1999;Vissel et al, 2001; this study) remains speculative and has been neither confirmed nor refuted by recent investigations into the editing status of GluR transcripts in brain tissue excised from patients with temporal lobe epilepsy (Grigorenko et al, 1998;Kortenbruck et al, 2001). …”