Prepulse inhibition (PPI) disrupting effects of Glycyrrhiza glabra extract in mice: a possible role of monoamines.

Liquorice extract was reported to have nootropic and/or antiamnestic effects. Prepulse inhibition (PPI) of startle response is a multimodal, cross-species phenomenon used as a measure of sensorimotor gating. Previous studies indicated that liquorice/its constituents augmented mouse brain monoamine levels. Increased brain monoamines' transmission was suggested to underlie PPI disruption. However, the effect of antiamnestic dose(s) of the extract on PPI has not been investigated despite the coexistence of impaired memory and PPI deficit in some neurological disorders. The effect of administration of the antiamnestic dose of the extract (150 mg/kg for 7 days) was tested on PPI of acoustic startle response in mice. It resulted in PPI disruption and therefore its effect on monoamines' levels was investigated in a number of mouse brain areas involved in PPI response mediation. Results demonstrated that the extract antiamnestic dose augmented cortical, hippocampal and striatal monoamine levels. It was therefore concluded that liquorice extract (150 mg/kg)-induced PPI deficit was mediated through augmenting monoaminergic transmission in the cortex, hippocampus and striatum. These findings can be further investigated in experimental models for autism, psychosis and Huntington's disease to decide the safety of using liquorice extract in ameliorating memory disturbance in disorders manifesting PPI deficit.