The effect of chronic lithium treatment on the calibre of axons and nerve fibres in the rat sural nerve.

Cases of peripheral neuropathy have been reported in humans receiving lithium therapy. However, no previous studies have addressed the question of whether chronic lithium treatment causes morphological changes in the peripheral nervous system in experimental animals. The present study used stereological methods to determine whether long-term administration of lithium affected the calibre of the axons or of the nerve fibres in the rat sural nerve. Twenty-two rats were divided into 2 groups and given either no treatment or lithium, with serum levels averaging from 0.5 to 0.7 mmol/l. After 30 weeks of treatment, the animals were killed and the sural nerve was isolated at the level of the knee and was removed. The cross-sectional area of axons and of nerve fibres was estimated by point counting. Compared with the controls, a strong tendency towards a reduced nerve fibre area in the lithium-treated animals was found, with a between-group difference of 1.79 microns 2 (P = 0.06). For the axon area, the difference was 0.73 micron 2 (P = 0.20).