[Identification of a gene regulating "behavioral despair" in mice].

We found that CS mice exhibit an extremely low immobility time (almost no immobility) in both the tail suspension test (TST) and forced swimming test (FST). In these tests, animals are subjected to the short-term, inescapable stress of being suspended by their tail or being forced to swim in a water-filled cylinder. In such situations, the animals rapidly adopt a characteristic immobile posture that has been named "behavioral despair" on the assumption that the animals have given up hope of escaping. These tests have been widely used for assessing antidepressant activity and depression-like behavior. Quantitative trait locus (QTL) mapping using CS and C57BL/6J mice revealed significant QTLs on chromosomes (Chrs) 4 (FST) and 5 (TST and FST). To identify the quantitative trait gene on Chr 5, we narrowed the QTL interval to 0.5 Mb using several congenic and subcongenic strains. Ubiquitin-specific peptidase 46 (Usp46) with a lysine codon deletion was located in this region. This deletion affected nest-building, muscimol-induced righting reflex and anti-immobility effects of imipramine. The muscimol-induced current in the hippocampal CA1 pyramidal neurons and hippocampal expression of the 67-kDa isoform of glutamic acid decarboxylase significantly decreased in the Usp46 mutant mice compared to control mice. All these phenotypes were rescued in transgenic mice with bacterial artificial chromosomes containing wild-type Usp46. Thus, Usp46 affects "behavioral despair" and it is implicated in the regulation of GABA action.