Hippocampal α5, subunit-containing GABA_A receptors modulate the expression of prepulse inhibition

Prepulse inhibition (PPI) refers to the phenomenon in which a low-intensity prepulse stimulus attenuates the reflexive response to a succeeding startle-eliciting pulse stimulus. The hippocampus, among other structures, is believed to play an important role in the modulation of PPI expression. In α5(H105R) mutant mice, the expression of the α5 subunit-containing GABA_A receptors in the hippocampus is reduced. Here, we report that PPI was attenuated, and spontaneous locomotor activity was increased in α5(H105R) mutant mice. These effects were apparent in both genders. Thus, α5 subunit-containing GABA_A receptors, which are located extrasynaptically and are thought to mediate tonic inhibition, are important regulators of the expression of PPI and locomotor exploration. Post-mortem analyses of schizophrenia brains have consistently revealed structural abnormalities of a developmental origin in the hippocampus. There may be a possibility that such abnormalities include disturbance of α5 GABA _A receptor function or distribution, given that schizophrenia patients are known to exhibit a PPI deficit. Our data further highlight that the potential use of α5-selective inverse agonists to treat hippocampal-related mnemonic dysfunction needs to be considered against the possibility that such compounds may be adversely associated with deficient sensorimotor gating.