Learning deficits in forebrain-restricted brain-derived neurotrophic factor mutant mice

Brain-derived neurotrophic factor (BDNF) participates in synaptic plasticity and the adaptive changes in the strength of communication between neurons thought to underlie aspects of behavioral adaptation. By selectively deleting BDNF from the forebrain of mice using the Cre site-specific DNA recombinase, we were able to study the requirements for BDNF in behaviors such as learning and anxiety. Early-onset forebrain-restricted BDNF mutant mice (Emx-BDNF(KO)) that develop in the absence of BDNF in the dorsal cortex, hippocampus, and parts of the ventral cortex and amygdala failed to learn the Morris Water Maze task, a hippocampal-dependent visuo-spatial learning task. Freezing during all phases of cued-contextual fear conditioning, a behavioral task designed to study hippocampal-dependent associative learning, was enhanced. These mice learned a brightness discrimination task well but were impaired in a more difficult pattern discrimination task. Emx-BDNF(KO) mice did not exhibit altered sensory processing and gating, as measured by the acoustic startle response or prepulse inhibition of the startle response. Although they were less active in an open-field arena, they did not show alterations in anxiety, as measured in the elevated-plus maze, black-white chamber or mirrored chamber tasks. Combined, these data indicate that although an absence of forebrain BDNF does not disrupt acoustic sensory processing or alter baseline anxiety, specific forms of learning are severely impaired.