Institute of Theoretical and Experimental Biophysics of RAS, Pushchino, Russia
Large motor neurons in oculomotor nuclei of the brain innervate eye muscles and control eye movements in the vertical and horizontal planes. Structurally and functionally, these neurons are linked with other sensorimotor formations in the brain, such as the vestibular nuclei, the nucleus accumbens and nuclei of abducent nerves, etc. Meanwhile, there is little information about ultrastructure of the neurons in oculomotor nuclei of the intact preparations and after stresses in mice, although these structures are investigated in detail in some mammals (cats, rhesus monkeys, rats). A small number of publications devoted to histology of oculomotor neurons. Thereby the goal of the present work was to develop a method of histological and ultrastructural study of neurons in the oculomotor nuclei of the mouse brain. We studied the large motor neurons in the paired nuclei of cranial nerves, trochlear (nucleus nervus trochlearis) and oculomotor (nucleus nervus oculomotoris), located in the ventromedial region of the midbrain central gray. By comparing data from different atlases used in the study of the mouse brain, we have identified the required nuclei on histological sections and photographed many portions of neurons, which are parts of them, under the electron microscope (nucleus, mitochondria, reticulum, cytoplasm and synapses). It should be noted that in the study of ultrastructure of synaptic contacts in neurons of oculomotor nuclei it can be tentatively concluded about the presence of gap junctions of small extent in them that are similar to the gap junctions in mixed synapses of Mauthner neurons. In neurons of the mouse brain nuclei such observation was made for the first time. As a whole, the collected data on the histology and ultrastructure of the neurons in oculomotor nuclei of the brain of intact mice allows us to give a clear picture of the morphology and function of neurons involved in eye movements and, in general, in a sensory-motor relationship. The results, in our opinion, will be useful in studies of oculomotor nuclei in terms of their involvement in the realization of optokinetic nystagmus under impaired sensory (visual or vestibular) afferent inflow, in particular, after long-term stay in microgravity during space flight or a prolonged performing of optokinetic response during appropriate visual stimulation.