Stereological Investigation of the Rat Ventral Thalamic Nuclei Following Developmental Hyperserotonemia

Elevated blood serotonin in perinatal development is the most consistent neurochemical finding reported in Autism Spectrum Disorder (ASD), and has been implicated in the pathogenesis of the disorder. Accordingly, pre- and postnatal administration of the non-selective serotonin agonist, 5-methoxytryptamine (5-MT), is hypothesized as a model of developmental hyperserotonemia (DHS) to investigate the behavioral and morphological implications in ASD. Our previous study, examining the effects of DHS, found significant neuroanatomical changes in the dendritic architecture and connectivity of neurons in the dentate nucleus of the cerebellum. The present investigation has gone further to describe alterations in the development of the dentate-thalamo-cortical pathway, a neural network involved in motor learning, automaticity of movements, and higher cognitive functions affected in ASD. Using unbiased stereological techniques, serial sections of DHS rats were compared to age-matched controls. Analysis was performed on nuclear volume, estimated cell number, area, distribution, and volume within the principle nuclei of the thalamus. While results did not show a change in the overall volume of the thalamus, when grouped by estimated total brain volume, the mean thalamic volume was significantly reduced in the DHS group relative to controls. Additionally, significant reductions in cell numbers, density and distribution were observed in subdivisions of the principle nuclei including the ventral anterior, ventral lateral, ventral posterolateral, and ventral posteromedial nuclei. Alterations in these areas and their reciprocal connections throughout the brain may effect neuronal organization and be implicated in the neuropathological and behavioral changes observed in ASD.