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Alzheimer's disease (AD) and other age-related cognitive deficits are associated with autoimmune phenomena. We recently showed that AD sera contain IgG that binds specifically to the heavy molecular weight neurofilament protein (NF-H) of Torpedo cholinergic neurons. We presently examined the behavioral effects of the induction of such antibodies in rats by prolonged immunization with Torpedo cholinergic NF-H. Immunohistochemical studies revealed the accumulation of IgG in the septum and hippocampus and in white matter tracts of these rats. T-maze alternation and discrimination tests revealed that immunization impaired the short-term working memory of the rats but had no effect on their reference memory. This impairment in short-term memory was reversed by treatment with the acetylcholinesterase inhibitor physostigmine. This animal model, termed experimental autoimmune dementia (EAD), may replicate immunologically induced pathogenic processes in AD.

The studies described have sought to determine what, if any, relationship exists between axons and the senile plaque, a hallmark histopathological feature of Alzheimer's disease. A double stain was performed on both early and late Alzheimer frontal cortex tissues in order to examine the interaction between axons stained with antibodies against the 200,000 mol. wt neurofilament subunit (NFP-200) of the axon cytoskeleton and Thioflavin-S, a fluorescent dye that stains plaques. Serial photomicrographs of plaques were taken and axon and plaque profiles were three-dimensionally reconstructed. Analysis of computer-processed images revealed that there were fewer axons within plaques than in regions lying one and two plaque distances away. When axons were observed passing through plaques, swelling and disruption of normal morphology was frequently present. Statistical analyses of axon counts within and around placques showed a gradient of axon density, with increased numbers occurring at progressive distances from the placque. Similar patterns were seen for early and late stages of the disease. The results of this study indicate that disruption of the axonal cytoskeleton may occur within the regions occupied by plaques.

Intermediate filament proteins of the rat insulinoma RIN5F cell line were characterized. Two-dimensional gel analysis followed by immunostaining of proteins demonstrated that these cells express both peripherin and the low-molecular-mass neurofilament protein (NF-L); this was confirmed for peripherin by immunohistochemistry, peptide analysis and Northern blot. No expression of these proteins could be detected with these same methods either in the adult pancreas or in the tumor at the origin of the cell line, although such expression was apparent on sections of rat pancreas at embryonal day 16. These results were compared to those obtained on the rat pheochromocytoma PC12 cell line: expression in the adrenal medulla of the embryo, no expression either in the adult tissue or in the tumor, but solely in the derived cell line. The expression of neuronal intermediate filament proteins in the rat insulinoma RIN5F cell line is discussed in relation to its similarity in the rat pheochromocytoma PC12 cell line, and its meaning as to the developmental cell lineage; an ectodermal origin is suggested for the pancreatic islet cells.

The spinal cords from seven autopsy cases of sporadic motor neuron disease (MND) and two controls were immunohistochemically examined using antibodies directed to calcitonin gene-related peptide (CGRP) and to neurofilament proteins (Nf). CGRP immunoreactivity was observed in the posterior horns, especially in the laminae I and II, of all the spinal cords examined. In MND cases, in addition, a considerable number of spheroids in the anterior horns were labelled with the antibody. In some spheroids, their entire area was homogeneously immunostained, whereas in others the immunoreactivity was confined to a focal area(s) within the profile of the spheroids and between these two forms of staining several variations of the staining patterns were seen. The anti-Nf intensely and homogeneously labelled all spheroids and there was no appreciable difference in the Nf-immunoreactive pattern between CGRP-positive and -negative spheroids. It is possible that the accumulation of CGRP in spheroids may result from entrapment of CGRP during the anterograde axonal transport, causing loss of CGRP at the neuromuscular junction and producing weakness and atrophy of the muscles.

Mammalian neurofilament triplet proteins (68 K, 160 K and 200 K) have been correlated by a biochemical, immunological and protein chemical study. The 160 K and 200 K triplet proteins are intermediate filament proteins in their own right, since they reveal the alpha-helical coiled-coil rod domain analyzed in detail for the 68 K protein. Triplet proteins display two distinct arrays. Their amino-terminal region built analogously to non-neuronal intermediate filament proteins should allow a co-polymerization process via the interaction of coiled-coil domains. The extra mass of all triplet proteins is allocated to carboxy-terminally located extensions of increasing size and unique amino acid sequences. These may provide highly charged scaffolds suitable for interactions with other neuronal components. Such a domain of 68 K reveals, in sequence analysis, 47 glutamic acids within 106 residues. The epitope recognized by a monoclonal antibody reacting probably with all intermediate filament proteins has been mapped. It is located within the last 20 residues of the rods, where six distinct intermediate filament proteins point to a consensus sequence.