Alterations in the hippocampal and striatal catecholaminergic fiber densities of heterozygous reeler mice

The heterozygous reeler mouse (HRM), haploinsufficient for reelin, shares several neurochemical and behavioral similarities with patients suffering from schizophrenia. It has been shown that defective reelin signaling influences the mesolimbic dopaminergic pathways in a specific manner. However, there is only little information about the impact of reelin haploinsufficiency on the monoaminergic innervation of different brain areas, known to be involved in the pathophysiology of schizophrenia. In the present study using immunocytochemical procedures, we investigated HRM and wild-type mice (WT) for differences in the densities of tyrosine hydroxylase (TH)-immunoreactive (IR) and serotonin (5-HT)-IR fibers in prefrontal cortex, ventral and dorsal hippocampal formation, amygdala and ventral and dorsal striatum. We found that HRM, compared to WT, shows a significant increase in TH-IR fiber densities in dorsal hippocampal CA1, CA3 and ventral CA1. In contrast, HRM exhibits a significant decrease of TH-IR in the shell of the nucleus accumbens (AcbShell), but no differences in the other brain areas investigated. Overall, no genotype differences were found in the 5-HT-IR fiber densities. In conclusion, these results support the view that reelin haploinsufficiency differentially influences the catecholaminergic (esp. dopaminergic) systems in brain areas associated with schizophrenia. The reelin haploinsufficient mouse may provide a useful model for studying the role of reelin in hippocampal dysfunction and its effect on the dopaminergic system as related to schizophrenia.

CPB-K mice a mouse model of schizophrenia? Differences in dopaminergic, serotonergic and behavioral markers compared to BALB/cJ mice

Schizophrenia is characterized by disturbances in social behavior, sensorimotor gating and cognitive function, that are discussed to be caused by a termination of different transmitter systems. Beside morphological alterations in cortical and subcortical areas reduced AMPA- NMDA-, 5-HT2-receptor densities and increased 5-HT1-receptor densities are found in the hippocampus.The two inbred mouse strains CPB-K and BALB/cJ are known to display considerable differences in cognitive function and prepulse inhibition, a stable marker of sensorimotor gating. Furthermore, CPB-K mice exhibit lower NMDA-, AMPA- and increased 5-HT-receptor densities in the hippocampus as compared to BALB/cJ mice. We investigated both mouse strains in social interaction test for differences in social behavior and with immuncytochemical approaches for alterations of dopaminergic and serotonergic parameters. Our results can be summarized as follows: compared to BALB/cJ, CPB-K mice showed:(1) significantly reduced traveling distance and number of contacts in social interaction test, (2) differences in the number of serotonin transporter-immunoreactive neurons and volume of raphe nuclei and a lower serotonergic fiber density in the ventral and dorsal hippocampal subfields CA1 and CA3, (3) no alterations of dopaminergic markers like neuron number, neuron density and volume in subregions of substantia nigra and ventral tegmental area, but a significantly higher dopaminergic fiber density in the dorsal hippocampus, the ventral hippocampus of CA1 and gyrus dentatus, (4) no significant differences in serotonergic and dopaminergic fiber densities in the amygdala.Based on our results and previous studies, CPB-K mice compared to BALB/cJ may serve as an important model to understand the interaction of the serotonergic and dopaminergic system and their impact on sensorimotor gating and cognitive function as related to neuropsychiatric disorders like schizophrenia.

Region-specific alteration of GABAergic markers in the brain of heterozygous reeler mice

Heterozygous reeler mice (HRM), haploinsufficient for reelin, have been proposed to be a genetic mouse model of schizophrenia. Beside behavioural similarities, HRM also demonstrate several neuroanatomical traits similar to patients suffering from schizophrenia. In the present study using immunocytochemical procedures, we investigated HRM and wild-type mice (WT) for differences in the numbers and densities of glutamic acid decarboxylase (GAD)67 and parvalbumin (PARV)-immunoreactive (IR) neurons in the hippocampus, tyrosine hydroxylase (TH)-IR neurons in the ventral tegmental area (VTA) and substantia nigra (SN), and serotonin transporter (5-HT-T)-IR neurons of the raphe nuclei. We found that HRM, compared with WT, show a significant decrease of GAD67-IR neurons in hippocampal subregion CA1 [stratum pyramidale (SP)], CA2 [stratum oriens (SO), stratum pyramidale (SP) and stratum radiatum (SR)] and dentate gyrus [granule cell layer (GL)], and also a significant decrease of PARV-containing neurons in CA1 (SO, SP) and CA2 (SP). No morphological differences were found in the SN/VTA or raphe nuclei. In conclusion, these results support a hippocampal γ-aminobutyric acid (GABA)ergic dysfunction in HRM as previously described by other authors, and may be based on a downregulation of GAD67 and PARV expressions. In summary, the reelin haploinsufficient mouse may provide a useful model for studying the interaction between reelin and hippocampal GABAergic system, its effect on dendritic spine maturation and plasticity related to schizophrenia.