Adult rodents picked up by the tail and slowly descending towards a horizontal surface extend all four limbs in anticipation of contact. Mouse mutants with pathologies in various brain regions and the spinal cord display instead a flexion response, often characterized by paw-clasping and a bat-like posture. These phenotypes are observed in mice with lesions in cerebellum, basal ganglia, and neocortex, as well as transgenic models of Alzheimer's disease. The underlying mechanism appears to include cerebello-cortico-reticular and cortico-striato-pallido-reticular pathways, possibly triggered by changes in noradrenaline and serotonin transmission.
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