Parenchymal and vascular lesions in ageing equine brains: histological and immunohistochemical studies

Many age-related changes are described in the nervous system of different species, but detailed studies of brain lesions in ageing horses are lacking. The aim of the present study was to systematically characterize lesions in the brains of 60 horses aged from 7 to 23 years. No gross changes were present in any brain. Microscopically, spongiform changes, lipofuscin storage, corpora amylacea, gliosis and satellitosis were common, together with axonal and neuronal swellings. The most important findings were the presence of pseudocalcium-calcium (pCa-Ca) deposits and arterial wall degeneration. Scanning electron microscopical examination of two cases with vascular mineralization revealed marked deposition of an amorphous substance in the vessel walls that was probably formed by a polyanionic protein matrix and a mineral component. Immunohistochemically, numerous axonal spheroids were positively labelled for ubiquitin. No PrPsc was detected in sections with neuronal vacuolation. Neuronal swelling, corpora amylacea, hippocampal Tau-positive neurons and methenamine-positive diffuse (preamyloid) plaques were also detected. Congo red staining failed to detect amyloid deposition. The characterization of age-related lesions in the brains of these horses will allow these changes to be discriminated from pathological processes in future studies. Some lesions described here, including some vascular changes, the presence of diffuse plaques and tau accumulation in hippocampal neurons, have not been described previously in the horse.