Developmental regulation of neural cell adhesion molecule in human prefrontal cortex.

Neural cell adhesion molecule (NCAM) is a membrane-bound cell recognition molecule that exerts important functions in normal neurodevelopment including cell migration, neurite outgrowth, axon fasciculation, and synaptic plasticity. Alternative splicing of NCAM mRNA generates three main protein isoforms: NCAM-180, -140, and -120. Ectodomain shedding of NCAM isoforms can produce an extracellular 105-115 kilodalton soluble neural cell adhesion molecule fragment (NCAM-EC) and a smaller intracellular cytoplasmic fragment (NCAM-IC). NCAM also undergoes a unique post-translational modification in brain by the addition of polysialic acid (PSA)-NCAM. Interestingly, both PSA-NCAM and NCAM-EC have been implicated in the pathophysiology of schizophrenia. The developmental expression patterns of the main NCAM isoforms and PSA-NCAM have been described in rodent brain, but no studies have examined NCAM expression across human cortical development. Western blotting was used to quantify NCAM in human postmortem prefrontal cortex in 42 individuals ranging in age from mid-gestation to early adulthood. Each NCAM isoform (NCAM-180, -140, and -120), post-translational modification (PSA-NCAM) and cleavage fragment (NCAM-EC and NCAM-IC) demonstrated developmental regulation in frontal cortex. NCAM-180, -140, and -120, as well as PSA-NCAM, and NCAM-IC all showed strong developmental regulation during fetal and early postnatal ages, consistent with their identified roles in axon growth and plasticity. NCAM-EC demonstrated a more gradual increase from the early postnatal period to reach a plateau by early adolescence, potentially implicating involvement in later developmental processes. In summary, this study implicates the major NCAM isoforms, PSA-NCAM and proteolytically cleaved NCAM in pre- and postnatal development of the human prefrontal cortex. These data provide new insights on human cortical development and also provide a basis for how altered NCAM signaling during specific developmental intervals could affect synaptic connectivity and circuit formation, and thereby contribute to neurodevelopmental disorders.

Synaptophysin and postsynaptic density protein 95 in the human prefrontal cortex from mid-gestation into early adulthood.

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 protein 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 0.1-25 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.

Normal cellular levels of synaptophysin mRNA expression in the prefrontal cortex of subjects with schizophrenia.

BACKGROUND: Previous studies have reported that the 38-kd synaptic vesicle-associated protein, synaptophysin, is decreased in the prefrontal cortex of subjects with schizophrenia. METHODS: To determine whether the decreased protein levels reflect diminished expression of the synaptophysin gene by prefrontal cortex neurons, we used in situ hybridization histochemistry to determine the cellular levels of synaptophysin messenger RNA in prefrontal cortex area 9 from 10 matched pairs of schizophrenic and normal control subjects. RESULTS: Neither the density of neurons with detectable levels of synaptophysin messenger RNA nor the mean level of synaptophysin messenger RNA expression per neuron differed between schizophrenic and control subjects in any cortical layer. CONCLUSIONS: These findings indicate that the expression of synaptophysin messenger RNA is not altered in this brain region in schizophrenia. Consequently, reduced levels of synaptophysin protein in the prefrontal cortex of subjects with schizophrenia are more likely to reflect either posttranscriptional abnormalities of synaptophysin in prefrontal cortex neurons or a diminished number of axonal projections to the prefrontal cortex from other brain regions.

Decreased dendritic spine density on prefrontal cortical pyramidal neurons in schizophrenia.

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. METHODS: To test this hypothesis, we determined the density of dendritic spines, markers of excitatory inputs, on the basilar dendrites of Golgi-impregnated pyramidal neurons in the superficial and deep portions of layer 3 in the dorsolateral prefrontal cortex (area 46) and in layer 3 of the primary visual cortex (area 17) of 15 schizophrenic subjects, 15 normal control subjects, and 15 nonschizophrenic subjects with a psychiatric illness (referred to as psychiatric subjects). RESULTS: There was a significant effect of diagnosis on spine density only for deep layer 3 pyramidal neurons in area 46 (P = .006). In the schizophrenic subjects, spine density on these neurons was decreased by 23% and 16% compared with the normal control (P = .004) and psychiatric (P = .08) subjects, respectively. In contrast, spine density on neurons in superficial layer 3 in area 46 (P = .09) or in area 17 (P = .08) did not significantly differ across the 3 subject groups. Furthermore, spine density on deep layer 3 neurons in area 46 did not significantly (P = .81) differ between psychiatric subjects treated with antipsychotic agents and normal controls. CONCLUSION: This region- and disease-specific decrease in dendritic spine density on dorsolateral prefrontal cortex layer 3 pyramidal cells is consistent with the hypothesis that the number of cortical and/or thalamic excitatory inputs to these neurons is altered in subjects with schizophrenia.

Reduction of synaptophysin immunoreactivity in the prefrontal cortex of subjects with schizophrenia. Regional and diagnostic specificity.

BACKGROUND: Multiple lines of evidence indicate that the prefrontal cortex is a site of dysfunction in schizophrenia. However, the apparent absence of gross structural abnormalities in this area suggests that the pathophysiological characteristics of schizophrenia may involve more subtle disturbances in prefrontal cortical circuitry, such as alterations in synaptic connectivity and transmission. In this study, immunoreactivity for synaptophysin, an integral membrane protein of small synaptic vesicles, was used to assess the integrity of cortical synaptic circuitry in schizophrenia. METHODS: Using immunocytochemical techniques and adjusted optical density measurements, we examined synaptophysin immunoreactivity in prefrontal cortical areas 9 and 46 and in area 17 (the primary visual cortex) from 10 pairs of case subjects with schizophrenia and control subjects matched on a pairwise basis for age, sex, race, and postmortem interval, and in 5 matched pairs of nonschizophrenic psychiatric case subjects and normal control subjects. RESULTS: Compared with levels found in matched control subjects, synaptophysin immunoreactivity in areas 46 and 9 was significantly decreased (P < .001 and P < .008, respectively) across all cortical layers in the case subjects with schizophrenia. In contrast, no differences were observed in area 17. In addition, levels of synaptophysin immunoreactivity in areas 46, 9, and 17 did not differ between 5 nonschizophrenic psychiatric case subjects and their matched controls, suggesting that decreased synaptophysin levels in the prefrontal cortex of patients with schizophrenia may be specific to that disorder. CONCLUSIONS: 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.

Reduction of synaptophysin immunoreactivity in the prefrontal cortex of subjects with schizophrenia. Regional and diagnostic specificity.

BACKGROUND: Multiple lines of evidence indicate that the prefrontal cortex is a site of dysfunction in schizophrenia. However, the apparent absence of gross structural abnormalities in this area suggests that the pathophysiological characteristics of schizophrenia may involve more subtle disturbances in prefrontal cortical circuitry, such as alterations in synaptic connectivity and transmission. In this study, immunoreactivity for synaptophysin, an integral membrane protein of small synaptic vesicles, was used to assess the integrity of cortical synaptic circuitry in schizophrenia. METHODS: Using immunocytochemical techniques and adjusted optical density measurements, we examined synaptophysin immunoreactivity in prefrontal cortical areas 9 and 46 and in area 17 (the primary visual cortex) from 10 pairs of case subjects with schizophrenia and control subjects. matched on a pairwise basis for age, sex, race, and postmortem interval, and in 5 matched pairs of nonschizophrenic psychiatric case subjects and normal control subjects. RESULTS: Compared with levels found in matched control subjects, synaptophysin immunoreactivity in areas 46 and 9 was significantly decreased (P < .001 and P < .008, respectively) across all cortical layers in the case subjects with schizophrenia. In contrast, no differences were observed in area 17. In addition, levels of synaptophysin immunoreactivity in areas 46, 9, and 17 did not differ between 5 nonschizophrenic psychiatric case subjects and their matched controls, suggesting that decreased synaptophysin levels in the prefrontal cortex of patients with schizophrenia may be specific to that disorder. CONCLUSION: 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.