Developmental metformin exposure does not rescue physiological impairments derived from early exposure to altered maternal metabolic state in offspring mice.

OBJECTIVE: The incidence of gestational diabetes mellitus (GDM) and metabolic disorders during pregnancy are increasing globally. This has resulted in increased use of therapeutic interventions such as metformin to aid in glycemic control during pregnancy. Even though metformin can cross the placental barrier, its impact on offspring brain development remains poorly understood. As metformin promotes AMPK signaling, which plays a key role in axonal growth during development, we hypothesized that it may have an impact on hypothalamic signaling and the formation of neuronal projections in the hypothalamus, the key regulator of energy homeostasis. We further hypothesized that this is dependent on the metabolic and nutritional status of the mother at the time of metformin intervention. Using mouse models of maternal overnutrition, we aimed to assess the effects of metformin exposure on offspring physiology and hypothalamic neuronal circuits during key periods of development. METHODS: Female C57BL/6N mice received either a control diet or a high-fat diet (HFD) during pregnancy and lactation periods. A subset of dams was fed a HFD exclusively during the lactation. Anti-diabetic treatments were given during the first postnatal weeks. Body weights of male and female offspring were monitored daily until weaning. Circulating metabolic factors and molecular changes in the hypothalamus were assessed at postnatal day 16 using ELISA and Western Blot, respectively. Hypothalamic innervation was assessed by immunostaining at postnatal days 16 and 21. RESULTS: We identified alterations in weight gain and circulating hormones in male and female offspring induced by anti-diabetic treatment during the early postnatal period, which were critically dependent on the maternal metabolic state. Furthermore, hypothalamic agouti-related peptide (AgRP) and proopiomelanocortin (POMC) neuronal innervation outcomes in response to anti-diabetic treatment were also modulated by maternal metabolic state. We also identified sex-specific changes in hypothalamic AMPK signaling in response to metformin exposure. CONCLUSION: We demonstrate a unique interaction between anti-diabetic treatment and maternal metabolic state, resulting in sex-specific effects on offspring brain development and physiological outcomes. Overall, based on our findings, no positive effect of metformin intervention was observed in the offspring, despite ameliorating effects on maternal metabolic outcomes. In fact, the metabolic state of the mother drives the most dramatic differences in offspring physiology and metformin had no rescuing effect. Our results therefore highlight the need for a deeper understanding of how maternal metabolic state (excessive weight gain versus stable weight during GDM treatment) affects the developing offspring. Further, these results emphasize that the interventions to treat alterations in maternal metabolism during pregnancy need to be reassessed from the perspective of the offspring physiology.

Brain volume in chronic ketamine users - relationship to sub-threshold psychotic symptoms and relevance to schizophrenia.

RATIONALE: Ketamine may model aspects of schizophrenia arising through NMDA receptor activity deficits. Although acute ketamine can induce effects resembling both positive and negative psychotic symptoms, chronic use may be a closer model of idiopathic psychosis. OBJECTIVES: We tested the hypotheses that ketamine users had lower brain volumes, as measured using MRI, and greater sub-threshold psychotic symptoms relative to a poly-drug user control group. METHODS: Ketamine users (n = 17) and poly-drug using controls (n = 19) were included in the study. All underwent volumetric MRI imaging and measurement of sub-threshold psychotic symptoms using the Comprehensive Assessment of At-Risk Mental State (CAARMS). Freesurfer was used to analyse differences in regional brain volume, cortical surface area and thickness between ketamine users and controls. The relationship between CAARMS ratings and brain volume was also investigated in ketamine users. RESULTS: Ketamine users were found to have significantly lower grey matter volumes of the nucleus accumbens, caudate nucleus, cerebellum and total cortex (FDR p < 0.05; Cohen's d = 0.36-0.75). Within the cortex, ketamine users had significantly lower grey matter volumes within the frontal, temporal and parietal cortices (Cohen's d 0.7-1.31; FDR p < 0.05). They also had significantly higher sub-threshold psychotic symptoms (p < 0.05). Frequency of ketamine use showed an inverse correlation with cerebellar volume (p < 0.001), but there was no relationship between regional brain volumes and sub-threshold psychotic symptoms. CONCLUSIONS: Chronic ketamine use may cause lower grey matter volumes as well as inducing sub-threshold psychotic symptoms, although these likely arise through distinct mechanisms.

Functional brain defects in a mouse model of a chromosomal t(1;11) translocation that disrupts DISC1 and confers increased risk of psychiatric illness.

A balanced t(1;11) translocation that directly disrupts DISC1 is linked to schizophrenia and affective disorders. We previously showed that a mutant mouse, named Der1, recapitulates the effect of the translocation upon DISC1 expression. Here, RNAseq analysis of Der1 mouse brain tissue found enrichment for dysregulation of the same genes and molecular pathways as in neuron cultures generated previously from human t(1;11) translocation carriers via the induced pluripotent stem cell route. DISC1 disruption therefore apparently accounts for a substantial proportion of the effects of the t(1;11) translocation. RNAseq and pathway analysis of the mutant mouse predicts multiple Der1-induced alterations converging upon synapse function and plasticity. Synaptosome proteomics confirmed that the Der1 mutation impacts synapse composition, and electrophysiology found reduced AMPA:NMDA ratio in hippocampal neurons, indicating changed excitatory signalling. Moreover, hippocampal parvalbumin-positive interneuron density is increased, suggesting that the Der1 mutation affects inhibitory control of neuronal circuits. These phenotypes predict that neurotransmission is impacted at many levels by DISC1 disruption in human t(1;11) translocation carriers. Notably, genes implicated in schizophrenia, depression and bipolar disorder by large-scale genetic studies are enriched among the Der1-dysregulated genes, just as we previously observed for the t(1;11) translocation carrier-derived neurons. Furthermore, RNAseq analysis predicts that the Der1 mutation primarily targets a subset of cell types, pyramidal neurons and interneurons, previously shown to be vulnerable to the effects of common schizophrenia-associated genetic variants. In conclusion, DISC1 disruption by the t(1;11) translocation may contribute to the psychiatric disorders of translocation carriers through commonly affected pathways and processes in neurotransmission.

Planar Airy beam light-sheet for two-photon microscopy.

We demonstrate the first planar Airy light-sheet microscope. Fluorescence light-sheet microscopy has become the method of choice to study large biological samples with cellular or sub-cellular resolution. The propagation-invariant Airy beam enables a ten-fold increase in field-of-view with single-photon excitation; however, the characteristic asymmetry of the light-sheet limits its potential for multi-photon excitation. Here we show how a planar light-sheet can be formed from the curved propagation-invariant Airy beam. The resulting symmetric light sheet excites two-photon fluorescence uniformly across an extended field-of-view without the need for deconvolution. We demonstrate the method for rapid two-photon imaging of large volumes of neuronal tissue.

A bell-shaped dependence between amyloidosis and GABA accumulation in astrocytes in a mouse model of Alzheimer's disease.

Functioning at the interface between the nervous and immune systems, in the amyloid-depositing brain, astrocytes become hypertrophic and accumulate around senile plaques. Moreover, hippocampal astrocytes upregulate their γ-aminobutyric acid (GABA) content and enhance tonic inhibition, likely causing local circuit imbalance. It remains, however, unclear whether this effect is hippocampus specific and how it is regulated during disease progression. Here, we studied changes in astrocytic morphology and GABA content in the frontal cortex and dentate gyrus of control and amyloid-depositing mice. Healthy aging was accompanied by a transient increase in astrocytic GABA content at middle age and region-specific alterations of soma size. In contrast, amyloid deposition caused a gradual cortex-accentuated increase in soma size. Importantly, our data uncovered a bell-shaped relationship between the mouse age and astrocytic GABA content in both brain regions. Moreover, in mice carrying an Alzheimer's disease-related mutation in presenilin 1, astrocytes accumulated GABA even in the absence of amyloidosis. These data question the proposed inhibition of astrocytic GABA synthesis as a universal strategy for treating network dysfunction in Alzheimer's disease.

Genome-Wide Transcriptional Profiling and Structural Magnetic Resonance Imaging in the Maternal Immune Activation Model of Neurodevelopmental Disorders.

Prenatal exposure to maternal infection increases the risk of neurodevelopmental disorders, including schizophrenia and autism. The molecular processes underlying this pathological association, however, are only partially understood. Here, we combined unbiased genome-wide transcriptional profiling with follow-up epigenetic analyses and structural magnetic resonance imaging to explore convergent molecular and neuromorphological alterations in corticostriatal areas of adult offspring exposed to prenatal immune activation. Genome-wide transcriptional profiling revealed that prenatal immune activation caused a differential expression of 116 and 251 genes in the medial prefrontal cortex and nucleus accumbens, respectively. A large part of genes that were commonly affected in both brain areas were related to myelin functionality and stability. Subsequent epigenetic analyses indicated that altered DNA methylation of promoter regions might contribute to the differential expression of myelin-related genes. Quantitative relaxometry comparing T1, T2, and myelin water fraction revealed sparse increases in T1 relaxation times and consistent reductions in T2 relaxation times. Together, our multi-system approach demonstrates that prenatal viral-like immune activation causes myelin-related transcriptional and epigenetic changes in corticostriatal areas. Even though these abnormalities do not seem to be associated with overt white matter reduction, they may provide a molecular mechanism whereby prenatal infection can impair myelin functionality and stability.

A distinct subtype of dopaminergic interneuron displays inverted structural plasticity at the axon initial segment.

The axon initial segment (AIS) is a specialized structure near the start of the axon that is a site of neuronal plasticity. Changes in activity levels in vitro and in vivo can produce structural AIS changes in excitatory cells that have been linked to alterations in excitability, but these effects have never been described in inhibitory interneurons. In the mammalian olfactory bulb (OB), dopaminergic interneurons are particularly plastic, undergoing constitutive turnover throughout life and regulating tyrosine hydroxylase expression in an activity-dependent manner. Here we used dissociated cultures of rat and mouse OB to show that a subset of bulbar dopaminergic neurons possess an AIS and that these AIS-positive cells are morphologically and functionally distinct from their AIS-negative counterparts. Under baseline conditions, OB dopaminergic AISs were short and located distally along the axon but, in response to chronic 24 h depolarization, lengthened and relocated proximally toward the soma. These activity-dependent changes were in the opposite direction to both those we saw in non-GABAergic OB neurons and those reported previously for excitatory cell types. Inverted AIS plasticity in OB dopaminergic cells was bidirectional, involved all major components of the structure, was dependent on the activity of L-type CaV1 calcium channels but not on the activity of the calcium-activated phosphatase calcineurin, and was opposed by the actions of cyclin-dependent kinase 5. Such distinct forms of AIS plasticity in inhibitory interneurons and excitatory projection neurons may allow considerable flexibility when neuronal networks must adapt to perturbations in their ongoing activity.