The ontogeny of a neurotoxic lesion in rat brain revealed by combined MRI and histology.

We have used magnetic resonance imaging (MRI) of the living rat brain to longitudinally analyze the ontogenesis of an ibotenic acid lesion targeted at the piriform cortex. The MRI data were systematically compared with data obtained from a battery of histopathological techniques, including Nissl stain, hematoxylin stain, and a stain for cytochrome oxidase activity. Two days after the lesioning, widespread and heterogeneous damage was detected in, around and distant from the toxin-targeted area. Some damage apparently diminished within approximately 10 days, whereas other damage remained throughout the length of this study (60 days). We found that the small-animal MRI technology used by us is useful in determining the initial, transient impact of surgery and neurotoxic lesioning, and in delineating the gross effects of the lesion over time. This is particularly useful for early elimination of animals from the protocol of physiological and behavioral experiments in which the lesion exceeds the target area. Our data also indicate that, in order to avoid confounding effects of transient post-lesioning phenomena, behavioral and physiological tests should be carried out in neurotoxically lesioned animals > 2 weeks after infliction of the lesion.