Differential effects of facial nerve transection on heat shock protein 70 expression in the developing and adult hamster facial nucleus.

In this study, the effects of axotomy on heat shock protein 70 (hsp70) protein levels were analyzed by immunoblotting with a hsp70 antibody that recognized constitutive and inducible forms of the protein. The right facial nerve of postnatal day 4 (neonate) or 100 (adult) hamsters was transected at its exit from the stylomastoid foramen, with the left nerve serving as internal control. Postoperative survival times were 2, 6, 12, and 24 h, with 3 animals per time point. Tissue punches containing individual facial nuclear groups were collected and homogenized. Approximately 10 microg of total protein was loaded onto paired gels and electrophoretically separated. Immunoblots of one gel from each pair were prepared, with the other gel stained in 0.2% Coomassie blue and used for verification of equality of lane loading. The results indicate that hsp70 protein levels increase in the adult, but decrease in the neonate, after axotomy. It is concluded that a stress response to cellular damage is an initial component of the classically described "axon reaction" and that hsp70 plays a role in mediating motoneuron survival after peripheral nerve transection.

Tau in aluminum-induced neurofibrillary tangles.

Aluminum is a neurotoxin and in susceptible species induces a neurofibrillary pathology characterized by argentophilic masses in neuronal perikarya and in axonal spheroids. These inclusions are known to contain neurofilament proteins. Using immunocytochemistry and immunoblotting, we demonstrate that tau is a component of these aluminum-induced neurofibrillary tangles (Al-NFTs) in rabbits. Double-label immunocytochemistry experiments reveal co-localization of phosphorylated neurofilaments (using SMI31) and tau (using tau-1, tau-5, AT8, and PHF-1) in the perikaryal Al-NFTs. Non-phosphorylated tau (detected using tau-1) occupies a smaller area of the Al-NFT than the total pool of tau proteins (detected using tau-5). The area of total tau and non-phosphorylated tau immunolabeling in the Al-NFT increases as the size of the Al-NFT (i.e., the proportion of cell area occupied by the Al-NFT) increases. The proportion of cell area (outside of the Al-NFT) occupied by tau (as indicated by tau-5) decreases as the area of tau in the Al-NFT increases and as the size of the Al-NFT in the cell increases. Immunoblotting experiments demonstrate 1) the specificity of the tau antibody labeling and verify a lack of cross-reactivity of the tau-5 antibody to neurofilament proteins in rabbit tissue; and 2) no alterations in the levels of tau resulting from aluminum-treatment. These data suggest that as the size of the Al-NFT in a cell increases there is less tau in the neuronal perikarya. Therefore, there may be less tau in the perikarya available to perform normal functions such as microtubule polymerization and stabilization. Tau and neurofilament proteins are perturbed in a number of neurodegenerative disorders such as Alzheimer's disease, diffuse Lewy body disease, and Parkinson's disease. Aluminum-induced neurofibrillary pathology may provide a model to study perturbation in tau and neurofilaments, their phosphorylation and deposition into pathological inclusions.