| Summary: | This study examines aspects of the neural substrate for locomotion in birds. Electrical stimulation of mid- and hindbrain revealed three previously undefined brainstem regions from which locomotion was elicited in the decerebrate animal. The sites lie within the medial longitudinal fasciculus (MLF), intercollicular nucleus (ICo) and medial mesencephalic reticular formation (mMRF). These and previously defined avian locomotor regions were further examined utilizing the microinjection of agonists and antagonists to acetylcholine, GABA, the excitatory amino acids and Substance P to determine the locomotor effects of potential neurotransmitters at these sites. Cholinergic agonists were effective at eliciting locomotion when injected into the MLF, pontobulbar locomotor strip (PLS) and medullary reticular formation. GABAergic antagonists evoked locomotion when infused into the PLS, ICo and pontine and medullary reticular formation. NMDA injection into the PLS, MLF, mMRF and medullary reticular formation elicited locomotion or reduced the electrical stimulation threshold for locomotion, while Substance P injection evoked locomotion when injected into the pontine reticular formation. Phasic peripheral afferent input was found not to be essential for the production of an array of avian locomotor patterns when examined in the spontaneous, electrically stimulated and neurochemically stimulated paralyzed preparations. However, afferent feedback may have a role in setting the activation level required to initiate and set the frequency of locomotor patterns. The preservation of caudal diencephalic neural structures allowed spontaneous locomotion in the high decerebrate bird, implicating the nucleus of the ansa lenticularis, subthalamic nucleus and lateral hypothalamic area as possibly modulating more caudal locomotor regions. Utilizing an integrated approach with the literature data collected from a variety of vertebrates, my results in birds suggest that locomotor-related neural pathways are highly conserved across a broad phylogenetic range. === Medicine, Faculty of === Graduate
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