Microtubule disarray in cortical dendrites and neurobehavioral failure. I. Golgi and electron microscopic studies.

Cortical biopsies obtained from 5 young children with severe neurobehavioral retardation of unknown etiology have been analyzed using Golgi and EM techniques. The normally cylindrical geometry of individual dendritic processes of pyramidal and non-pyramidal neurons is interrupted by the formation of distinct varicosities. While over 90% of observed cells are affected, the extent of varicosity formation varies from cell to cell and is most prominent in medium and small pyramidal cells. Varicosities may occur in the periphery only, or they may extend proximally to primary dendritic trunks. Accompanying changes include thin and irregular proximal processes, loss of dendritic spines, and predominance of long, thin tortuous spines. Ultrastructural analysis reveals characteristic changes in the cytoskeleton of these processes. Microtubules, within the larger proximal processes, twist and turn, relative to one another and relative to the long axis of the process. In varicose regions, microtubules course in roughly parallel array through constricted segments, only to splay away from one another on entering an expansion. Synapses are evident on constricted and expanded segments, as well as on spines. Alterations in dendritic structure of both pyramidal and non-pyramidal neurons may represent a primary target in the pathobiological process underlying neurobehavioral failure.

Microtubular disarray in cortical dendrites and neurobehavioral failure. II. Computer reconstruction of perturbed microtubular arrays.

A previous report details morphological alterations in dendritic structure of cortical neurons in severe neurobehavioral retardation of unknown etiology. Using computer graphic techniques, the present study describes perturbations in the 3-dimensional character of the microtubular array, which correspond to degenerative change in dendritic geometry. In large proximal processes, two types of array have been reconstructed. Segmented microtubules may form a continuous helical swirl which underlies a bulge in the dendritic cylinder. Alternatively, small groups of microtubules, while maintaining orderly internal organization, may be disoriented with respect to the long axis of the process. In varicose regions of the dendrite the microtubular array is discontinuous. Microtubules course side by side through constructed regions, only to splay out and terminate within expanded regions. These pathological alterations in the microtubular array contrast sharply with the cortical dendritic microtubular array reconstructed from the normal adult mouse. Perturbation in those parameters which determine packing of microtubules within the dendritic process is also documented. In the pathological condition, microtubules lose the ability to exclude one another from close approach. The role of cross-linking molecules in maintaining the integrity of the microtubular array, and the role of microtubules in maintaining the geometry of the dendrite, are considered.

Chronic GM1 gangliosidosis presenting as dystonia: I. Clinical and pathological features.

Clinical and pathological studies are reported from investigation of a 27-year-old man with GM1 gangliosidosis who experienced a slowly progressive dystonia that began about age 4, primarily affected the face and limbs, and eventually became almost totally incapacitating. There was only mild intellectual deterioration; myoclonus, seizures, and macular cherry-red spots were never observed. Postmortem examination revealed intraneuronal storage, localized predominantly to the basal ganglia, in which neurons contained round, multilamellated inclusions. Golgi studies revealed meganeurites arising from medium spiny neurons. Other areas of the central nervous system appeared relatively unaffected, although small basilar dilatations were observed in scattered cortical pyramidal neurons and Purkinje cell dendrites showed focal swellings. Vacuolated cells of the reticuloendothelial system were observed, including Kupffer cells and histiocytes in the spleen, marrow, and intestinal tract. Biochemical analysis revealed a generalized beta-galactosidase deficiency with specific accumulation of GM1 ganglioside in the basal ganglia.

Ultrastructure of neurites and meganeurites of cortical pyramidal neurons in feline gangliosidosis as revealed by the combined Golgi-EM technique.

Application of the Golgi-EM technique to the study of altered cortical pyramidal neuron morphology in feline gangliosidosis has revealed the presence of aberrant synapses in relation to multiple neurites and secondary neurites of meganeurites. In addition fine neurites arising from the soma and meganeurite are found to project into and envelope elements of the surrounding neuropil. These observations provide further evidence for a disturbance in neuronal surface membrane regulation in ganglioside storage disease.

Alterations in neuron morphology in feline mannosidosis. A Golgi study.

Studies using the Golgi method were performed on neocortical and cerebellar tissues from a 9-month-old cat with a history of progressive neurological deterioration and a subsequently demonstrated deficiency of the lysosomal enzyme alpha-D-mannosidase in both neural and non-neural tissues. Many cortical pyramidal neurons demonstrated morphological alterations involving formation of abnormal enlargements (meganeurites) at the axon hillock-initial segment area, abnormal sprouting of neurites (secondary neurites) in this same region, and various types of dendritic changes, such as formation of focal enlargements, thinning, and spine loss. Many nonpyramidal neurons also were abnormal but displaced only dendritic changes similar to those seen in pyramidal neurons. Cerebellar Purkinje cells displayed dendritic systems marked by focal swellings and often demonstrated one or more enlargements within axons (axonal spheroids) at some distance from otherwise normal-appearing cell bodies. Feline mannosidosis appears to be another of the lysosomal storage diseases in which highly specialized morphological changes accompany storage of unmetabolized substrate and contribute to the pathogenesis of the disease process.

Autism and mental retardation: neuropathologic studies performed in four retarded persons with autistic behavior.

Four persons who exhibited prominent autistic features throughout life died when 4, 14, 27, and 33 years old. All were mentally retarded. One had documented phenylketonuria, but the cause of mental retardation and autistic behavior was undefined in three. At the time of autopsy, brain weights were within 2 SDs of the norm for age. Complete neuropathologic examination, including analysis of cortical neurons impregnated with the rapid Golgi method, failed to provide clues as to cause or the pathoanatomic substrate of autistic behavior in these cases.

Evidence for autapses in the substantia nigra.

Intracellular recording and intracellular HRP staining were employed to trace the recurrent terminal plexus of cat substantia nigra pars reticulata neurons. Autaptic neurons were labeled. The axon of an autaptic neuron was found to emit a recurrent collateral which distributed 'en passage' and terminal boutons contacting dendrites of the parent cell. Antidromic ventromedial thalamic stimulation elicited a recurrent IPSP in the autaptic neuron.

Pathobiology of cortical neurons in metabolic and unclassified amentias.

Visualization of the neuron in its entirety through the use of the rapid Golgi method has permitted detection of several pathobiological features of neurons that are intimately associated with profound mental retardation in infants and children. In cases of unclassified mental retardation, dendrites and particularly dendritic spines exhibit severe developmental abnormalities. Dendritic spines, the postsynaptic components of axospinodendritic synapses, may be absent or abnormally long and thin in retardates. Evidence is presented that some cases of progressive neurobehavioral deterioration in infancy and early childhood may be due to progressive degeneration of dendritic spine systems (dendritic spine "dysgenesis"). Golgi and electron microscopic studies of neurons in human and feline ganglioside storage diseases indicate that ganglioside accumulation in cortical neurons initiates several complex alterations in neuronal geometry and morphology. Small and medium pyramidal cells form massive structural compartments (meganeurites) that frequently give rise to secondary neurites and other embryonic growth processes. Meganeurites may possess spines and spine-synapses. Other cells such as large pyramidal neurons may exhibit many somatic spines, whereas intrinsic cells of the cortex (and caudate) are unaffected morphologically by ganglioside accumulation. It is suggested that neuronal geometry distortion and aberrant synaptogenesis are important factors in the onset of neuronal dysfunction in ganglioside storage disorders. These studies also point to an important role of gangliosides in neurite formation in immature mammalian cortical neurons. Perisomatic processes and somatic spines are normal morphological components of the cell body of Purkinje cells through the 28th fetal week of human gestation. By 36 weeks the Purkinje cell somas exhibit a smooth surface contour. Prominent polydendritic processes, perisomatic protuberances, and somatic spines are detectable by Golgi methods applied to Purkinje cells in Menkes' disease and Down's syndrome long after these somatic components should normally disappear. Thus Purkinje cell soma membrane differentiation is a particularly sensitive process that can provide information on mechanisms of site-specific membrane regulation.

Fine structure of meganeurites and secondary growth processes in feline GM1-gangliosidosis.

Electron microscope studies were carried out on neurons of the hippocampal formation in a feline mutant with beta-galactosidase deficiency and GMI-gangliosidosis. Fusiform processes with characteristics similar to meganeurites of Golgi studies were identified between cell bodies and axons of pyramidal and granule cells. The presence of dense material subjacent to the plasma membrane at the meganeurite-axon junction provides evidence that meganeurites form at the axon-hillock region and displace the initial axonal segment distally. Meganeurites of hippocampal neurons exhibited pleomorphic secondary processes with fine structural features of growth cones. Spines and spine-synapses were abundant on perikarya and meganeurites. Numerous membranous cytoplasmic bodies (MCBs) were encountered amongst otherwise normally appearing organelles of the cell body. MCBs were densely packed in meganeurites except near their peripheral area. They were less common in dendrites and rare in synapses of the neuropil. The observations provide further support for the view that meganeurites of mature cortical neurons in ganglioside storage diseases have embryonic growth characteristics.