A neuron processes information by integrating many synaptic inputs onto its dendritic tree, leading to its spike output. This project will investigate this neural processing by stimulating individual sensory afferents to a neuron in the vertebrate brainstem, using a sensory pathway which has the unique advantage of lacking topography. As a consequence, its afferent cell bodies are widely distributed in the sensory periphery. Specifically, intracellular recordings in the accessory optic system will be performed in a unique in vitro turtle brain preparation in which the eyes remain attached and the brain remains visually responsive. Neurons in the accessory optic system presumably receive their synaptic inputs from a distinct class of retinal cell, the direction sensitive ganglion cell. The interaction between the presynaptic terminals and a postsynaptic cell performs an essential conversion from local retinal directional information into a measure of global image motion, called retinal slip, that has a well defined role in vestibular and oculomotor reflexes. The turtle's accessory optic system is called the basal optic nucleus, a surface brainstem structure whose neurons are easy to locate in vitro. Postsynaptic events of cells in the basal optic nucleus are readily recorded with high fidelity in the whole cell configuration using patch pipettes. Visual and electrical stimulation of individual retinal afferents will be used to study the size and shape of unitary postsynaptic events as well as their direction tuning. Stimulating two afferents will determine how two synaptic potentials interact on the postsynaptic membrane. This interaction is complicated by the finding that synaptic responses to individual afferents are quite variable in amplitude and that the postsynaptic membrane has voltage sensitive channels that can be modulated by synaptic potentials. To further understand this interaction, we will also study the passive membrane properties of each cell, the voltage sensitive channels in its membrane, the ionic and pharmacological nature of the synaptic currents and the cell's morphology. This full analysis will ultimately clarify the neural transformations from the retinal synaptic input to the accessory optic system output. The results of these studies will provide insights into the functioning of neurons that encode the direction of visual field motion in order to maintain our balance and stabilize our gaze. Such visual processing will also provide an excellent model to understand general mechanisms of synaptic integration and the sensory processing of the brainstem.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS033190-03
Application #
2460579
Study Section
Visual Sciences B Study Section (VISB)
Program Officer
Michel, Mary E
Project Start
1995-08-01
Project End
2000-07-31
Budget Start
1997-08-01
Budget End
2000-07-31
Support Year
3
Fiscal Year
1997
Total Cost
Indirect Cost
Name
Saint Louis University
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
City
Saint Louis
State
MO
Country
United States
Zip Code
63103
Ariel, Michael; Kogo, Naoki (2005) Shunting inhibition in accessory optic system neurons. J Neurophysiol 93:1959-69
Martin, John; Kogo, Naoki; Fan, Tian Xing et al. (2003) Morphology of the turtle accessory optic system. Vis Neurosci 20:639-49
Kogo, Naoki; Fan, Tian Xing; Ariel, Michael (2002) Synaptic pharmacology in the turtle accessory optic system. Exp Brain Res 147:464-72
Ariel, M; Kogo, N (2001) Direction tuning of inhibitory inputs to the turtle accessory optic system. J Neurophysiol 86:2919-30
Kogo, N; Ariel, M (1999) Response attenuation during coincident afferent excitatory inputs. J Neurophysiol 81:2945-55
Martin, J; Kogo, N; Ariel, M (1998) Morphology of basal optic tract terminals in the turtle, Pseudemys scripta elegans. J Comp Neurol 393:267-83
Kogo, N; Rubio, D M; Ariel, M (1998) Direction tuning of individual retinal inputs to the turtle accessory optic system. J Neurosci 18:2673-84
Kogo, N; Ariel, M (1997) Membrane properties and monosynaptic retinal excitation of neurons in the turtle accessory optic system. J Neurophysiol 78:614-27