9723527 Casagrand This research will yield new information on the ways that nerve cells of the brain determine the location of sounds from the information provided by sound receptor cells in the ears. This study will use an animal model, the auditory- evoked escape response of the goldfish to study this problem. The studies will evaluate the auditory activation of the large reticulospinal neurons called Mauthner cells, which previously have been important in many neurophysiological studies. Reticulospinal neurons are crucial for producing coordinated locomotor behavior, such as walking and orientation in all vertebrates, including humans. Yet, little is known about the nature of the acoustic inputs which provide one of the most influential excitatory inputs to these neurons. Recent technological advances now make feasible studies of these inputs. The proposed work will analyze how acoustic information is transmitted to, and processed by, the Mauthner neurons. The experiments will: 1) Characterize the types of acoustic (pressure and acceleration) inputs to the Mauthner neuron; 2) Localize the site(s) of connections between the afferents and the Mauthner neuron; 3) Describe critical morphophysiological features important in auditory processing by the Mauthner neuron; 4) Construct a morphologically and neurophysiologically realistic computer model of sound processing by Mauthner neuron to allow evaluation of hypotheses and improved understanding of how the auditory inputs interact. These four experimental approaches will permit a comprehensive analysis of directional sound processing by the Mauthner system. The new information resulting from the proposed work will be used to further understand how neurons in general, and the reticulospinal system in particular, integrates its sensory inputs to produce coordi nated outputs.
