AOPEP and schizophrenia: While the PPI-decreasing effect of APO and MK-801 is generally interpreted as modelling dopaminergic hyperactivity and glutamatergic hypoactivity, respectively, both purported to underlie positive symptoms of schizophrenia [39,41], the lack of effect of these drugs in our study may also represent a loss of the neurotransmitter regulation of PPI, as we discussed in a previous study using a developmental rat model of the illness [57].