PSA-NCAM expression in the rat medial prefrontal cortex.

The rat medial prefrontal cortex, an area considered homologous to the human prefrontal cortex, is a region in which neuronal structural plasticity has been described during adulthood. Some plastic processes such as neurite outgrowth and synaptogenesis are known to be regulated by the polysialylated form of the neural cell adhesion molecule (PSA-NCAM). Since PSA-NCAM is present in regions of the adult CNS which are undergoing structural remodeling, such as the hypothalamus or the hippocampus, we have analyzed the expression of this molecule in the medial prefrontal cortex of adult rats using immunohistochemistry. PSA-NCAM immunoreactivity was found both in cell bodies and in the neuropil of the three divisions of the medial prefrontal cortex. All cell somata expressing PSA-NCAM corresponded to neurons and 5' bromodeoxyuridine labeling after long survival times demonstrated that these neurons were not recently generated. Many of these PSA-NCAM immunoreactive neurons in the medial prefrontal cortex could be classified as interneurons on the basis of their morphology and glutamate decarboxylase, isoform 67 expression. Some of the PSA-NCAM immunoreactive neurons also expressed somatostatin, neuropeptide Y and calbindin-D28K. By contrast, pyramidal neurons in this cortical region did not appear to express PSA-NCAM. However, some of these principal neurons appeared surrounded by PSA-NCAM immunoreactive puncta. Some of these puncta co-expressed synaptophysin, suggesting the presence of synapses. Since the etiology of some psychiatric disorders has been related to alterations in medial prefrontal cortex structural plasticity, the study of PSA-NCAM expression in this region may open a new approach to the pathophysiology of these mental disorders.