Prepulse inhibition (PPI) is the reduction of the startle reflex when the startling stimulus is shortly preceded by a non-startling stimulus.Previous studies have shown that PPI in rats can be enhanced by auditory fear conditioning (AFC) but weakened by isolation rearing.This study investigated whether isolation rearing affects the effect of AFC on PPI.The results show that PPI was lower in isolation-reared rats than that in socially-reared rats,and it was significantly enhanced by AFC in both isolation-and socially-reared rats.However,the AFC-induced PPI enhancement in isolationreared rats was much lower than that in socially-reared rats.Moreover,regardless of the rearing type,the AFC-induced PPI enhancement was blocked by intraperitoneal injection (1 mg/kg) of the selective antagonist of metabotropic glutamate receptor subtype 5 (mGluR5),2-methyl-6-(phenylethynyl)-pyridine (MPEP),30 rain before AFC.The baseline startle was also enhanced by isolation rearing.Thus isolation rearing impairs not only PPI but also the AFC-induced PPI enhancement,which depends on mGluR5 activity.This study advanced the animal model for investigating both neural bases and cognitive features of schizophrenia.