Abstract
During spaceflight and immediately after it, adaptive neuroplastic changes occur in the sensorimotor structures of the central nervous system, which are associated with changes of mainly vestibular and visual signals. It is known that the movement of the eyeball in the vertical direction is carried out by muscles that are innervated by the trochlear nerve (CN IV) and the oculomotor nerve (CN III). To elucidate the cellular processes underlying the atypical vertical nystagmus that occurs under microgravity conditions, it seems necessary to study the state of these nuclei in animals in more detail after prolonged space flights. We carried out a qualitative and quantitative light-optical and ultrastructural analysis of the nuclei of the trochlear nerve in mice after a 30-day flight on the Bion-M1 biosatellite. As a result, it was shown that the dendrites of motoneurons in the nucleus of the trochlear nerve significantly reorganized their geometry and orientation under microgravity conditions. The number of dendritic branches was increased, possibly in order to amplify the reduced signal flow. To ensure such plastic changes, the number and size of mitochondria in the soma of motoneurons and in axons coming from the vestibular structures increased. Thus, the main role in the adaptation of the trochlear nucleus to microgravity conditions, apparently, belongs to the dendrites of motoneurons, which rearrange their structure and function to enhance the flow of sensory information. These results complement our knowledge of the causes of atypical nystagmus in microgravity.
Highlights
During a long-term spaceflight, a significant change in vestibular function occurs, which can lead to the development of space adaptation syndrome and space motion sickness [1,2,3]
We studied the morphology of motoneurons and neuropil of the trochlear nerve nucleus (CN IV) of mice after a 30-day flight on the Bion-M1 biosatellite, followed by a stay of 13-14 hours under the influence of the Earth's gravity after landing
One of the reasons for visual-vestibular disorders identified after spaceflight in humans and animals is functional disorders of the oculomotor nucleus and nucleus of the trochlear nerve caused by vestibular deprivation
Summary
During a long-term spaceflight, a significant change in vestibular function occurs, which can lead to the development of space adaptation syndrome and space motion sickness [1,2,3] These changes occur in space travelers both during spaceflights and during their return to Earth, but the cellular brain organization of such adaptation is still poorly understood. To elucidate the cellular processes underlying the atypical vertical nystagmus that occurs under microgravity, it seems necessary to study in more detail the state of these motoneurons in animals after prolonged spaceflights. These results will be useful for the development of new, more effective means to facilitate the stay and work of space travelers in a long-term spaceflight. A morphometric study of the nucleus of the trochlear nerve was carried out at the light-optical and ultrastructural levels after a 30-day orbital flight of mice on a biosatellite in the framework of the Bion-M1 program
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