Developmental models of brain dysfunctions induced by targeted cellular ablations with methylazoxymethanol

Abnormal brain development represents one of the major causes of neurological disorders in humans, and determining the factors responsible for generating specific brain malformations represents a formidable task for developmental neurobiology. The knowledge of the precise neurogenetic time table and the use of toxins, like methylazoxymethanol, able to interfere with neuroepithelial cells entering their last mitotic cycle, have allowed for targeted neuronal ablations in specific brain areas of the central nervous system (CNS) when administered at different gestational or postnatal days in various animal species. Of particular relevance are the studies in which ablations of neuronal populations of cortex, hippocampus, and cerebellum have been made. The results obtained show that these early ablations induce a number of neuroanatomic, neurochemical, and electrophysiological changes that give us the possibility to unravel the biochemical strategies utilized by surviving neurons to adapt to the perturbated environment. Most striking are the findings that target deprivation does not affect the survival of afferent neurons in the CNS (except for neurons of the lateral geniculate nucleus), in sharp contrast to the notion of target dependence for peripheral nervous system neurons. Animals showing selective ablations in the Ammon's hom of the hippocampus allow us to understand the complex biochemical pathways leading to changes in activity-dependent synaptic plasticity, and the data underscore the fundamental role of diverse Ca2+-dependent protein kinases, and their substrates, in modulating pre- and postsynaptic events during induction and maintenance of long-term potentiation (LTP). Because LTP represents a useful model to study molecular substrates of learning and memory, this animal model might be of relevance in understanding cognitive brain dysfunctions.