Pathologic axons and synapses in human neuropsychiatric disorders

Ultrastructural studies of cerebral biopsy specimens from patients with various forms of psychomotor retardation and dementia have disclosed pathologic changes in axons and presynaptic or postsynaptic processes. The clinical disorders with lesions in axons and presynaptic terminals are reviewed. Three basic abnormalities have been detected: proliferation of tubulovesicular structures which probably originate from the smooth endoplasmic reticulum, "abnormal" mitochondria, and proliferation of 80 to 100 A filaments. Understanding of the pathogenesis of human disorders associated with axonic or "synaptic" lesions will probably depend on progress in areas of basic biomedical research concerned with the synthesis and turnover of biological membranes and the packaging and secretion of neurotransmitters, elucidation of mechanisms of cytoplasmic streaming and axoplasmic flow, and biophysical and biochemical characteristics and functions of "fibrous" proteins (neurotubules, neurofilaments, pathologic fibrous proteins). In several cases of mental retardation of unknown etiology, abnormal dendritic spines of cortical neurons have been observed with the use of the Golgi method. These dendritic (postsynaptic) disorders have been attributed to defective development ("dysgenesis"). The knowledge provided by ultrastructural analysis of brain tissue from the human disorders of mental retardation or dementia is "still formless, incomplete, lacking the essential threads of connection," and only future developments in lacking neurobiology will make possible the dissection of the primary phenomena from the secretory and probably irrelevant findings.