Gene-environment interaction during early development in the heterozygous reeler mouse: clues for modelling of major neurobehavioral syndromes

Serotonin transporter clustering in blood lymphocytes of reeler mice

Serotonin transporter clustering is an important feature for regulation of this transporter activity. We used immunocytochemistry to analyze alterations in serotonin transporter clustering in blood lymphocytes of reeler mice. Serotonin transporter immunolabelling is observed mostly as a patchy staining in lymphocytes membranes. Comparison of the number and size of serotonin transporter clusters in wild-type mice, heterozygous reeler mice, and homozygous reeler mice showed an increase in the number and size of clusters in heterozygous reeler mice, but only an increase in clusters size in homozygous reeler mice. Reelin is down-regulated in the brain of schizophrenia, autism, and mood disorders, and is also expressed in blood plasma. There is the possibility therefore that alterations in serotonin transporter clustering in blood lymphocytes associated with a decrease in reelin expression may be operative in some cardiovascular or immune system alterations showing comorbidity with these mental disorders.

Staging perspectives in neurodevelopmental aspects of neuropsychiatry: agents, phases and ages at expression

Neurodevelopmental risk factors have assumed a critical role in prevailing notions concerning the etiopathogenesis of neuropsychiatric disorders. Staging, diagnostic elements at which phase of disease is determined, provides a means of conceptualizing the degree and extent of factors affecting brain development trajectories, but is concurrently specified through the particular interactions of genes and environment unique to each individual case. For present purposes, staging perspectives in neurodevelopmental aspects of the disease processes are considered from conditions giving rise to neurodevelopmental staging in affective states, adolescence, dopamine disease states, and autism spectrum disorders. Three major aspects influencing the eventual course of individual developmental trajectories appear to possess an essential determinant influence upon outcome: (i) the type of agent that interferes with brain development, whether chemical, immune system activating or absent (anoxia/hypoxia), (ii) the phase of brain development at which the agent exerts disruption, whether prenatal, postnatal, or adolescent, and (iii) the age of expression of structural and functional abnormalities. Clinical staging may be assumed at any or each developmental phase. The present perspective offers both a challenge to bring further order to diagnosis, intervention, and prognosis and a statement regarding the extreme complexities and interwoven intricacies of epigenetic factors, biomarkers, and neurobehavioral entities that aggravate currents notions of the neuropsychiatric disorders.

Animal models of autism spectrum disorders: information for neurotoxicologists

Recent findings derived from large-scale datasets and biobanks link multiple genes to autism spectrum disorders. Consequently, novel rodent mutants with deletions, truncations and in some cases, overexpression of these candidate genes have been developed and studied both behaviorally and biologically. At the Annual Neurotoxicology Meeting in Rochester, NY in October of 2008, a symposium of clinicians and basic scientists gathered to present the behavioral features of autism, as well as strategies to model those behavioral features in mice and primates. The aim of the symposium was to provide researchers with up-to-date information on both the genetics of autism and how they are used in differing in vivo and in vitro animal models as well as to provide a background on the environmental exposures being tested on several animal models. In addition, researchers utilizing complementary approaches, presented on cell culture, in vitro or more basic models, which target neurobiological mechanisms, including Drosophila. Following the presentation, a panel convened to explore the opportunities and challenges of using model systems to investigate genetic and environment interactions in autism spectrum disorders. The following paper represents a summary of each presentation, as well as the discussion that followed at the end of the symposium.

Combined effect of neonatal immune activation and mutant DISC1 on phenotypic changes in adulthood

Gene-environment interaction may play a role in the etiology of schizophrenia. Transgenic mice expressing dominant-negative DISC1 (DN-DISC1 mice) show some histological and behavioral endophenotypes relevant to schizophrenia. Viral infection during neurodevelopment provides a major environmental risk for schizophrenia. Neonatal injection of polyriboinosinic-polyribocytidylic acid (polyI:C), which mimics innate immune responses elicited by viral infection, leads to schizophrenia-like behavioral alteration in mice after puberty. To study how gene-environmental interaction during neurodevelopment results in phenotypic changes in adulthood, we treated DN-DISC1 mice or wild-type littermates with injection of polyI:C during the neonatal stage, according to the published method, respectively, and the behavioral and histological phenotypes were examined in adulthood. We demonstrated that neonatal polyI:C treatment in DN-DISC1 mice resulted in the deficits of short-term, object recognition, and hippocampus-dependent fear memories after puberty, although polyI:C treatment by itself had smaller influences on wild-type mice. Furthermore, polyI:C-treated DN-DISC1 mice exhibited signs of impairment of social recognition and interaction, and augmented susceptibility to MK-801-induced hyperactivity as compared with vehicle-treated wild-type mice. Of most importance, additive effects of polyI:C and DN-DISC1 were observed by a marked decrease in parvalbumin-positive interneurons in the medial prefrontal cortex. These results suggest that combined effect of neonatal polyI:C treatment and DN-DISC1 affects some behavioral and histological phenotypes in adulthood.

Interactions between neuroactive steroids and reelin haploinsufficiency in Purkinje cell survival

We determined total Purkinje cell (PC) numbers in cerebella of wild-type (+/+) and heterozygous (rl/+) reeler mice of either sex during early postnatal development; in parallel, we quantified levels of neuroactive steroids in the cerebellum with mass spectrometry. We also quantified reelin mRNA and protein expression with RT-PCR and Western blotting. PC numbers are selectively reduced at postnatal day 15 (P15) in rl/+ males in comparison to +/+ males, +/+ females, and rl/+ females. Administration of 17beta-estradiol (17beta-E) into the cisterna magna at P5 increases PC numbers in rl/+ males, but not in the other groups; conversely, estrogen antagonists 4-OH-tamoxifen or ICI 182,780 reduce PC numbers in +/+ and rl/+ females, but have no effect in males. Testosterone (T) levels at P5 are much higher in males than in females, reflecting the perinatal testosterone surge in males. In addition, rl/+ male cerebella at P5 show a peculiar hormonal profile in comparison with the other groups, consisting of increased levels of T and 17beta-E, and decreased levels of dihydrotestosterone. RT-PCR analysis indicated that heterozygosity leads to a 50% reduction of reelin mRNA in the cerebellum in both sexes, as expected, and that 17beta-E upregulates reelin mRNA, particularly in rl/+ males; reelin mRNA upregulation is associated with an increase of all major reelin isoforms. These effects may represent a novel model of how reelin deficiency interacts with variable perinatal levels of neuroactive steroids, leading to gender-dependent differences in genetic vulnerability.