Cortical Glutamatergic Neurons Mediate the Motor Sedative Action of Diazepam

Abstract

The neuronal circuits mediating the sedative action of diazepam are unknown. Although the motor-depressant action of diazepam is suppressed in ␣1(H101R) homozygous knockin mice expressing diazepam-insensitive ␣1-GABA A receptors, global ␣1-knockout mice show greater motor sedation with diazepam. To clarify this paradox, attributed to compensatory up-regulation of the ␣2 and ␣3 subunits, and to further identify the neuronal circuits supporting diazepam-induced sedation, we generated Emx1-cre-recombinase-mediated conditional mutant mice, selectively lacking the ␣1 subunit (forebrain-specific ␣1 Ϫ/Ϫ ) or expressing either a single wild-type (H) or a single point-mutated (R) ␣1 allele (forebrain-specific ␣1Ϫ/H and ␣1 Ϫ/R mice, respectively) in forebrain glutamatergic neurons. In the rest of the brain, ␣1Ϫ/R mutants are heterozygous ␣1(H101R) mice. Forebrain-specific ␣1 Ϫ/Ϫ mice showed enhanced diazepam-induced motor depression and increased expression of the ␣2 and ␣3 subunits in the neocortex and hippocampus, in comparison with their pseudo-wild-type littermates. Forebrain-specific ␣1 Ϫ/R mice were less sensitive than ␣1Ϫ/H mice to the motor-depressing action of diazepam, but each of these conditional mutants had a similar behavioral response as their corresponding control littermates. Unexpectedly, expression of the ␣1 subunit was reduced in forebrain, notably in ␣1 Ϫ/R mice, and the ␣3 subunit was up-regulated in neocortex, indicating that proper ␣1 subunit expression requires both alleles. In conclusion, conditional manipulation of GABA A receptor ␣1 subunit expression can induce compensatory changes in the affected areas. Specifically, alterations in GABA A receptor expression restricted to forebrain glutamatergic neurons reproduce the behavioral effects seen after a global alteration, thereby implicating these neurons in the motor-sedative effect of diazepam.

The developmental evolution of the seizure phenotype and cortical inhibition in mouse models of juvenile myoclonic epilepsy

“…These results were similar to what was reported previously in P35 Het α1 KO mice (Zeller et al, 2008;Zhou et al, 2013). Interestingly, despite the marked changes in total α1 and α3 subunit expression in the cortices of Het α1 KO and Het α1 AD mice, there was no change in the fraction of total α1 and α3 subunit associated with gephyrin clusters.…”

Altered Cortical GABAA Receptor Composition, Physiology, and Endocytosis in a Mouse Model of a Human Genetic Absence Epilepsy Syndrome

“…Previous Western blots and immunohistochemistry studies in Het ␣1 KO mice reached different conclusions concerning the effects of Het ␣1 KO on total ␣3 subunit expression (14,21). Using both immunofluorescence as well as semiquantitative Western blots with linear protein detection, we demonstrated that Het ␣1 KO did increase total cortical ␣3 subunit expression.…”

Periphilin is strongly expressed in the murine nervous system and is indispensable for murine development

“…Thus, functionally redundant proteins can partly or fully take over the function of the lacking protein without an upregulation of the compensating molecule as shown for members of the cytochrome P450 family (Dalton et al, 2000), homologs of glycogen synthase kinase-3 (Doble et al, 2007), Bcl-2 family members (Hager et al, 2009), and others. Another common mechanism is the transcriptional or translational upregulation of another isoform of the protein in question (Ballou et al, 2000), a functionally and evolutionary related protein (Andrejewski et al, 1999), another member of the same protein family (Memet et al, 1999), another subtype of the same receptor family (Zeller et al, 2008;Todorov et al, 2006) or a functionally related physiological system (Wang et al, 2001), which can partly or fully compensate for a deficiency. In the case of periphilin, the functions of the protein seem to be rather diverse and functionally related proteins or other members belonging to a common family are not known.…”