MOTOR SYSTEMS COMPARATIVE STUDY

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The present proposal describes a series of behavioral, anatomical and neurohistochemical experiments designed to evaluate the neural systems underlying the control of movement in the reptile, Caiman crocodilus. Caiman crocodilus was selected as an animal model because the motor system of reptiles is simpler than that of mammals. No direct equivalent of the mammalian motor cortex is present in reptiles, yet precision movement and coordination are nevertheless part of the behavioral repertoire of these species. Pilot work indicates that two neural systems, both derived from the paleostriatum, or basal ganglia, are involved in the control of complex movement in this species. The first of these is derived from the globus pallidus and expresses motor functions largely via the optic tectum. The other is derived from neurons in the ventral pallidum and projects upon portions of the reticular formation afferent to motor neuron pools such as the trigeminal motor nucleus. A new theory of motor behavior in reptiles is advanced which holds that pallidofugal pathways control orientation and tectally mediated behaviors, while the pathways derived from the ventral pallidum control precision movement, particularly of the jaws and mouth region. These systems are anatomically and chemically distinct. Pallidofugal neurons utilize LANT6 and GABA as neurotransmitters while the ventral pallidal region contains many cholinergic neurons. Experiments are proposed to test hypotheses and to further evaluate the chemical, anatomical and behavioral correlates of both systems.