Reelin haploinsufficiency reduces the density of PV+ neurons in circumscribed regions of the striatum and selectively alters striatal-based behaviors

Rationale  Reelin, a large extracellular matrix glycoprotein, is down-regulated in the brain of schizophrenic patients and of heterozygous reeler mice (rl/+). The behavioral phenotype of rl/− mice, however, matches only partially the schizophrenia hallmarks. Objectives  We recently reported (Marrone et al., Eur J Neurosci 24:20062–22070, 2006) that homozygous reeler mutants (rl/rl) exhibit reduced density of parvalbumin-positive (PV+) GABAergic interneurons in anatomically circumscribed regions of the neostriatum. Assuming that in rl/+ mice may also show regional reduction of striatal GABAergic interneurons, behavioral impairments should selectively emerge in tasks depending on specifically altered striatal circuits. Materials and methods  We mapped the density of striatal PV+ interneurons in rl/+ and wild-type (+/+) mice and measured their performance in tasks depending on distinct striatal subregions. Results  Our findings show that, contrary to what would be expected on the basis of gene dosage criteria, the striatal regions in which rl/rl mice exhibited decreased density of PV+ interneurons were either unaltered (rostral striatum) or equally altered (dorsomedial and ventromedial intermediate striatum, caudal striatum) in rl/+ mice. The anatomical findings were paralleled by behavioral deficits in fear extinction and latent inhibition, respectively, requiring the dorsomedial and ventromedial striatal regions. Conversely, active avoidance performance, which requires the dorsolateral region, was unaffected. Conclusions  Reelin haploinsufficiency alters the density of PV+ neurons in circumscribed regions of the striatum and selectively disrupts behaviors sensitive to dysfunction of these targeted regions. This aspect should be considered when designing experiments aimed at evaluating the impact of reelin haploinsufficency in schizophrenia-associated cognitive disturbances in rl/+ mutants.