Using Of Confocal Laser Scanning Microscope In The Examination Of Neural Network Underlying The Gaze And Posture Control

Maintenance of equilibrium depends on various sensory impulses arising from the retina, labyrinthine organs and sensory receptors of skin, muscles and joints. During body displacement the very fine and continuous tuning of gaze fixation and the rapid control of different movements requires a very fast modification of the motor activity to obtain the proper muscle tension and contraction. Despite of its functional importance, the morphological background of the movement control is not yet fully understood. By using different neuronal labeling techniques we have previously contributed to the characterization of neuronal elements of vestibulo-ocular and vestibulo-spinal circuitry, as well as the neuronal circuitry underlying the prey-catching behaviour in the frog. We have found a significant overlap of vestibular and somatosensory terminals in various parts of the central nervous system related to motor coordination suggesting the possibility of the monosynaptic connection between the afferent and efferent neuronal elements. In addition, we have detected that the dendritic arrays of functionally-matched somatomotor neurons involved in the eye movements and prey-catching behavior mix up with each other raising the possibility of synaptic contact between the neighboring dendrites. To examine these possible synaptic connections, double labeling of various cranial nerves of the frog was performed with different fluorescens tracers in vivo. After 4-5 days of survival cross sections of the brainstem were cut with a Vibratome at a thickness of 50 mu m. Images were recorded using an Olympus FV1000 confocal laser scanning microscope. For the latter analysis we used series of 1 mu m thick optical slices. Close appositions were considered if there was no discernable gap between the two profiles, and, if the contact surfaces were found at the same focal plane. We have found that the distance between the neighboring profiles suggested close membrane appositions, presumably synaptic contacts, without intercalating glial or neuronal elements. The functional significance of the monosynaptic components found in different neuronal circuits provides the morphological background of a very fast compensatory movement during the body displacement.