Re-evaluation of Archival Material for Neuronal Cell Injury Produced by l-2-Chloropropionic Acid in the Rat Brain

Abstract

Previous studies have shown that l-2-chloropropionic acid ( l-CPA) produces necrosis to cerebellar granule cells with some associated Purkinje cell damage in the rat [Neurotoxicology 17 (1996) 471]. We have re-evaluated the neuropathology using the original sections and fresh sections from archived brain material from rats treated with l-CPA at different ages, times after dosing and the following prior treatment with the N-methyl- d-aspartate (NMDA) receptor antagonist, MK-801. In addition we have determined the lobular distribution of cerebellar granule cell necrosis produced by l-CPA. Using Fluoro-Jade staining to detect degenerating neurons, we have identified three new brain regions that show neuronal cell necrosis as a result of exposure to l-CPA, these are the medial habenular nucleus, pontine gray and inferior olivary nucleus. The neuronal cell degeneration was confirmed in conventional haematoxylin and eosin stained sections and in some cases by glial fibrillary acidic protein staining for reactive gliosis. The neuronal cell necrosis at these new sites was both time and dose dependent; young 22-day-old rats, which are refractory to l-CPA-induced cerebellar granule cell necrosis, did however show some neuronal cell degeneration in the medial habenular, pontine gray and inferior olivary nuclei. Treatment of rats with MK-801 30 min prior to l-CPA, afforded complete protection against the neuronal cell injury in the medial habenular, pontine gray and inferior olivary nuclei, similar to that previously reported for the cerebellum, supporting an excitotoxic mechanism of neuronal cell death. In the cerebellum the lobular distribution of the granule cell loss was not uniform, more severe granule cell loss occurring in lobules 1–4 and 9a + b. This localization exactly mirrors that seen previously in the cerebellum of rats given l-CPA and examined by magnetic resonance imaging (MRI). The basis for the neuronal cell loss in the medial habenular nucleus, pontine gray and inferior olivary nucleus, in addition to the major site in the cerebellum, and the sensitivity of particular cerebellar lobes is not currently understood. Anatomical connections between the sites of injury and their likely neurotransmitter use are discussed.