Potentiation of Glutamatergic Synaptic Transmission Onto Dorsal Raphe Serotonergic Neurons in the Valproic Acid Model of Autism

Autism spectrum disorder (ASD) is characterized by social and communicative impairments and increased repetitive behaviors. These symptoms are often comorbid with increased anxiety. Prenatal exposure to valproic acid (VPA), an anti-seizure and mood stabilizer medication, is a major environmental risk factor of ASD. Given the important role of the serotonergic (5-HT) system in anxiety, we examined the impact of prenatal VPA exposure on the function of dorsal raphe nucleus (DRn) 5-HT neurons. We found that male rats prenatally exposed to VPA exhibited increased anxiety-like behaviors revealed by a decreased time spent on the open arms of the elevated plus maze. Prenatal VPA exposed rats also exhibited a stereotypic behavior as indicated by excessive self-grooming in a novel environment. These behavioral phenotypes were associated with increased electrical activity of putative DRn 5-HT neurons recorded in vitro. Examination of underlying mechanisms revealed that prenatal VPA exposure increased excitation/inhibition ratio in synapses onto these neurons. The effect was mainly mediated by enhanced glutamate but not GABA release. We found reduced paired-pulse ratio (PPR) of evoked excitatory postsynaptic currents (EPSCs) and increased frequency but not amplitude of miniature EPSCs in VPA exposed rats. On the other hand, presynaptic GABA release did not change in VPA exposed rats, as the PPR of evoked inhibitory postsynaptic currents was unaltered. Furthermore, the spike-timing-dependent long-term potentiation at the glutamatergic synapses was occluded, indicating glutamatergic synaptic transmission is maximized. Lastly, VPA exposure did not alter the intrinsic membrane properties of DRn 5-HT neurons. Taken together, these results indicate that prenatal VPA exposure profoundly enhances glutamatergic synaptic transmission in the DRn and increases spontaneous firing in DRn 5-HT neurons, which could lead to increased serotonergic tone and underlie the increased anxiety and stereotypy after prenatal VPA exposure

Cerebral Developmental Abnormalities in a Mouse with Systemic Pyruvate Dehydrogenase Deficiency.

UNLABELLEDPyruvate dehydrogenase (PDH) complex (PDC) deficiency is an inborn error of pyruvate metabolism causing a variety of neurologic manifestations. Systematic analyses of development of affected brain structures and the cellular processes responsible for their impairment have not been performed due to the lack of an animal model for PDC deficiency.METHODSIn the present study we investigated a murine model of systemic PDC deficiency by interrupting the X-linked Pdha1 gene encoding the α subunit of PDH to study its role on brain development and behavioral studies.RESULTSMale embryos died prenatally but heterozygous females were born. PDC activity was reduced in the brain and other tissues in female progeny compared to age-matched control females. Immunohistochemical analysis of several brain regions showed that approximately 40% of cells were PDH(-). The oxidation of glucose to CO2 and incorporation of glucose-carbon into fatty acids were reduced in brain slices from 15 day-old PDC-deficient females. Histological analyses showed alterations in several structures in white and gray matters in 35 day-old PDC-deficient females. Reduction in total cell number and reduced dendritic arbors in Purkinje neurons were observed in PDC-deficient females. Furthermore, cell proliferation, migration and differentiation into neurons by newly generated cells were reduced in the affected females during pre- and postnatal periods. PDC-deficient mice had normal locomotor activity in a novel environment but displayed decreased startle responses to loud noises and there was evidence of abnormal pre-pulse inhibition of the startle reflex.CONCLUSIONSThe results show that a reduction in glucose metabolism resulting in deficit in energy production and fatty acid biosynthesis impairs cellular differentiation and brain development in PDC-deficient mice

Quantitation of number of the Purkinje cell nuclei in P35 control and PDC-deficient females.

<p>(A) Gaussian histogram of the Purkinje cell nuclei counts. (B) Average counts of the Purkinje cell nuclei. Twenty sections from 2 brains from each group were analyzed. Sections were spaced at 350 mm. Area of the Purkinje cell layer was randomly chosen, its length was 200 µm. Data are means ± S.D., *represents P<0.05.</p

Number of cells with PDH⁺ and PDH⁻ cells in brains of P35 control and PDC-deficient females.

a<p>Data are means ± S.D.</p>b<p>Significant difference (P<0.05) between the two groups of animals for a given type of cells examined.</p>c<p>PDH⁻ as percent of total cells.</p

Each mouse was placed into a novel locomotor chamber and vertical movements (rearing) and horizontal movements (distance) recorded.

<p>PDC-deficient mice and control mice had equivalent activity levels and normal habituation to the novel environment. Data are reported as mean ± SEM (n = 4).</p

Genetic analysis of the <i>Pdha1</i> locus in control and PDC-deficient female progeny.

<p>(A) Depiction of wild-type (<i>Pdha1^wt)</i>, floxed (<i>Pdha1^flox8</i>), and null (<i>Pdha1</i>^Δ<i>ex8</i>) <i>Pdha1</i> alleles and the primers (arrows above the allele representations) used for genotypic analysis. (B) Genotypic analysis of the <i>Pdha1</i> locus in brain (B), liver (L), heart (H) and skeletal muscle (SM) tissues from a female offspring (genotye: <i>Pdha1</i>^Δ<i>ex8</i><i>/Pdha1^wt; Cre^all+</i>) produced from mating a floxed homozygous female with a <i>Cre</i> transgenic male. Upper gel [genotypes: wild-type allele (700 bp), floxed allele (800 bp), and null allele (400 bp)]. Lower gel: [genotype: <i>Cre</i> transgene (240 bp)]. − (minus) Lane: DNA from a wild-type female (700 bp), and+(plus) Lane: floxed allele (800 bp; upper gel) from a floxed female and null allele (240 bp; lower gel) from a PDC-deficient female included as negative and positive controls. M: DNA marker.</p

Plot a shows the acoustic startle response.

<p>Plot b shows pre-pulse inhibition of the acoustic startle response as a function the intensity of the pre-pulse stimulus. Pre-pulse intensity was measured in decibels (dB). PDC-deficient mice had markedly decreased startle responses and evidence of impaired pre-pulse inhibition of the acoustic startle response at the highest pre-pulse stimulus intensity. Error bars indicate standard error of the mean. Data are reported as mean ± SEM (n = 4).</p