Letter: experimental brain tumours

Chronic Low-Dose Exposure of Sodium Nitrite in VM-Strain Mice: Central Nervous System Changes

1 There is suggestive evidence that nitrite may be a causative factor in cerebral glioma.

2 To test this hypothesis we selected the VM mouse strain, known for its susceptibility to spontaneous glioma formation, and exposed 300 animals to 0.2% sodium nitrite in their drinking water. One hundred of this group were exposed both in utero and throughout their adult lives. The remaining 200 animals received nitrite from the time of weaning. A further 200 mice were used as controls and received distilled water.

3 All animals were maintained until their natural death and were then subjected to autopsy and routine histological examination.

4 There was no excess of nervous system tumours in the experimental groups.

Brain tumours in mice, with particular reference to astrocytoma

In a survey of 75,000 brains from 23 inbred mouse strains studied during research work on scrapie, astrocytoma was by far the commonest neuroectodermal tumour. It occurred in VM and BRVR mice at a 1% incidence, but was virtually absent from other strains. In VM mice it occurred nearly twice as often in males as in females, sometimes causing neurological signs of circling, depression or spinal paralysis, but more often showing no clinical effects and being discovered only during routine neuropathology carried out for other purposes. Astrocytomas occurred in mice in the spinal cord or in the brain, with equal frequency in the fore-, mid- and hindbrain. A dual origin has never been confirmed, but astrocytomas occasionally co-existed with other central nervous system tumours. Macroscopically they cause no distortion of the brain; this contrasts with the rare oligodendroglioma, in cases of which the brain is sometimes swollen and misshapen. Astrocytomas characteristically spread through white-matter tracts, but in some grey-matter localities neoplastic astrocytes can co-exist with viable neurons, suggesting that they may subserve some functions of normal astrocytes. The astrocytomas found in this study often co-existed with scrapie lesions. Scrapie-induced vacuolation penetrated some astrocytomas in grey matter, and the specific scrapie-associated argyrophilic (amyloid) plaques occurred in the middle of an astrocytoma in several mice. However, there is no relationship between the occurrence of astrocytoma and scrapie infection, and the neoplasm also occurs independently both of the Sinc gene, which controls the pathogenesis of scrapie, and of the histocompatibility type of the strains concerned. The spontaneous VM astrocytoma is transplantable intracerebrally and, in the early series of in vivo subpassages, it only grew in the brains of mice of the strain of origin and its crosses. The age occurrence of astrocytoma and the incidence of other CNS tumours in mice are discussed in this paper.