|Proposed Statement of Research
University of Texas Medical Branch at Galveston
The objective of this research is to identify the anatomical connections of the vestibular nuclei and other functionally related brainstem nuclei, such as the prepositus, to the visual cortex. This will pave the way for further electrophysiological experiments. Already our lab has found a correlation between prepositus nucleus cell firing rates and vestibular stimulation. The next step will involve defining the nature of the prepositus' connection to the visual cortex. The accurate integration of visual and vestibular information is important for any activities that involve motion and/or orientation. These studies are thus important for addressing the problem of space sickness in which visual and vestibular information conflict and are improperly integrated. Also, understanding this system will provide a base of knowledge from which to examine problems of visual and vestibular integration that might occur due to long term microgravity exposure. These studies are therefore relevant to many questions addressed in space life science.
The hypothesis is that the visual cortex receives polysynaptic input from the prepositus as well as to the vestibular nuclei. This is based on evidence that vestibulo ocular responses are altered by visual input.
The methods involve the injection of the Bartha strain of alpha-Herpes virus (pseudo-rabies virus) into the visual cortex. Stereotaxically positioned pressure injections of 100-300 nl are made in the striate cortex. Incubation times of 28-60 hrs allowed for infection to ensue and for the virus to be transsynaptically transported, with a time of 30hrs, resulting in transport across one synapse, and 48hrs for two synapses. After the incubation time the animal is sacrificed. The tissue is then prepared for histologic examination by an avidin-biotin reaction to amplify and visualize the virus in situ.
Thus far, 20 gerbils were injected at various stereotaxic coordinates and the tissue histologically processed. Preliminary results of visual cortex injections with this transsynaptic retrograde label have shown there are connections originating in the prepositus and projecting transneuronally to the visual cortex. This was the case in 6 animals with longer incubation times of about 50-60 furs. These animals also showed labeling in the superior colliculus, ventral lateral geniculate nucleus, medial vestibular nucleus, and the prepositus. The remaining animals had injections that were either too large or too medial. This usually involved injections that labelled limbic cortex adjacent to the visual cortices resulting in retrograde labeling of the anterior nucleus of the thalamus, the hippocampus, and other limbic areas with the absence of labeling in visual associated structures.
These connections between the brainstem and the visual cortex, could play an important role in integrating vestibular input with visual input. These connections may serve as the substrate for visual influences on vestibular responses during head motion.
Wednesday, 26-Mar-2003 22:10:22 CST
CSR/TSGC Team Web