The overall goal of this project is to investigate cellular mechanisms in the premotor neuronal structures of the saccade generating circuit, namely, the excitatory burst neurons (EBN) and the omnipause neurons (OPN). Our first goal in this project is a methodological one: we will attempt to identify these premotor cells using the novel retrograde transynaptic virus labeling technique. Our objective is to obtain a """"""""blueprint"""""""" protocol for labeling these higher order neurons in the saccadic circuit. This will be of immense value for neuronal pathway tracing and for answering future electrophysiological questions in conjunction with fluorescent microscopy. A weak strain of the pseudo-rabies virus will be injected into the extraocular muscle for retrograde transmission. A second objective of this project is to investigate specific cellular and synaptic properties of the EBN and OPN cells in the in vitro preparation. Based on published work from our laboratory and elsewhere, we have made several predictions with regard to the cellular properties of these cells. One of them is the presence of post-inhibitory rebound (PIR) in the EBN and OPN that would explain some of the network properties observed in vivo from live behaving animals. These are the """"""""resonance"""""""" observed in the EBN cells (Gnadt. et. al., 2001) and the post-saccade enhancement observed in the OPN cells (Gandhi and Keller, 1999). Brain slices from the mouse will be harvested from the brainstem in the region of the nucleus interpositus of Raphe close to the midline. These slices will be maintained under physiological conditions and subjected to voltage and current test protocols designed to investigate the rebound and other properties of the cell. Pharmacological manipulations will enable us to identify and characterize the specific ionic channels underlying these phenomena. Our investigations into these questions will provide data that will further advance our knowledge of the saccadic circuit used by mammals to make quick and accurate eye movements to the target. ? ?
