Background:The pathophysiological characteristics of schizophrenia appear to involve altered synaptic connectivity in the dorsolateral prefrontal cortex. Given the central role that layer 3 pyramidal neurons play in corticocortical and thalamocortical connectivity, we hypothesized that the excitatory inputs to these neurons are altered in subjects with schizophrenia.

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Previous studies of postnatal synaptic development in human frontal cortex have shown that synaptic density rises after birth, reaches a plateau in childhood and then decreases to adult levels by late adolescence. A similar pattern has been seen in nonhuman primate cortex. These earlier studies in human cortex are limited, however, by significant age gaps in study subjects at critical inflection points of the developmental curve. Additionally, it is unclear if synaptic development occurs in different patterns in different cortical layers in prefrontal cortex (PFC). The purpose of this study was to examine synaptic density in human PFC across development by measuring two synaptic marker proteins: synaptophysin (presynaptic), and postsynaptic density-95 (PSD-95; postsynaptic). Western blotting was used to assess the relative levels of synaptophysin and PSD-95 in dorsolateral PFC of 42 subjects, distributed in age from 18 weeks gestation to 25 years. In addition, synaptophysin immunoreactivity was examined in each layer of areas 9 and 46 of PFC in 24 subjects, ranging in age from 0.1 to 25 years. Synaptophysin levels slowly increased from birth until age 5 and then increased more rapidly to peak in late childhood around age 10. Synaptophysin subsequently decreased until the adult level was reached by mid-adolescence, around age 16. PSD-95 levels increased postnatally to reach a stable plateau by early childhood with a slight reduction in late adolescence and early adulthood. The pattern of synaptophysin immunoreactivity seen with immunohistochemistry was similar to the Western experiments but the changes across age were more subtle, with little change by layer within and across age. The developmental patterns exhibited by these synaptic marker proteins expand upon previous studies of developmental synaptic changes in human frontal cortex; synaptic density increases steadily from birth to late childhood, then decreases in early adolescence to reach adult levels by late adolescence. Keywordsadolescence; development; human; synapses; pruning; synaptogenesisThe human brain has the most protracted period of development of any species, with neurodevelopment continuing well into early adulthood. Imaging studies have shown that in the human, the overall volume of the brain increases during childhood and adolescence (Giedd Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptNeuroscience. Author manuscript; available in PMC 2008 November 9. Sowell et al. 2002;Gilmore et al. 2007). Specifically, the cortical gray matter volume, particularly the f...

Additional studies are required to determine if the decrease in levels of synaptophysin immunoreactivity is caused by a decrease in the number or size of presynaptic terminals, a decrease in the number of synaptic vesicles per terminal, or a decrease in the expression of synaptophysin. However, all of these potential explanations are consistent with a disturbance in synaptic transmission in the prefrontal cortex of patients with schizophrenia.

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Additional studies are required to determine if the decrease in levels of synaptophysin immunoreactivity is caused by a decrease in the number or size of presynaptic terminals, a decrease in the number of synaptic vesicle per terminal, or a decrease in the expression of synaptophysin. However, all of these potential explanations are consistent with a disturbance in synaptic transmission in the prefrontal cortex of patients with schizophrenia.

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