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3‐Nitropropionic acid induces a spectrum of Huntington’s disease‐like neuropathology in rat striatum

Systemic administration of the mitochondrial toxin 3‐nitropropionic acid (3‐NP) to rats results in selective striatal lesions and serves as an experimental model of Huntington’s disease (HD). However, the effects of the 3‐NP treatment are unpredictable and result in lesions of variable severity. The present study was aimed at further characterizing the variability of the striatal lesions induced by systemic administration of 3‐NP using osmotic pumps. Hematoxylin–eosin (HE) and Nissl stains as well as immunohistochemical labelling of astrocytes and striatal neurones were performed to analyse the neurotoxic effects of 3‐NP. In general, chronic systemic administration of 3‐NP resulted in obvious bilateral striatal lesions, which ranged from mild to severe, together with a subtle, but detectable behavioural lesion. Severe type lesions showed marked neuronal loss and an increased expression of glial fibrillary acidic protein (GFAP) in astrocytes surrounding the lesion area, whereas in the core of the lesion GFAP‐immunoreactivity was absent. The mild type lesion was characterized by a substantial loss of striatal neurones and an increased expression of GFAP‐positive astrocytes throughout the lesion. In a number of 3‐NP‐treated animals, neither type of lesion was observed, although these animals demonstrated behavioural changes in the paw test compared to controls. In the striatum of these tested 3‐NP‐treated animals, compromised rk’ neurones were detected, suggestive of subtle and early 3‐NP‐induced neuronal injury. Similar dark neurones were also detected in mild and severe lesions and were immunocytochemically characterized as γ‐aminobutyric acid (GABA) and substance P containing spiny neurones, which belong to the neuronal population that is affected in early HD. These results indicate that systemic administration of 3‐NP to rats may result in a spectrum of striatal pathology of which the morphology of the mild type lesion resembles the characteristic HD neuropathology most closely.