Structural transformations in sympathetic ganglia and the thoracic part of the vagus nerve in conditions of gravitational overloading.

The aim of the present work was to undertake a complex of studies of structural transformations in the anterior thoracic ganglia of the sympathetic trunk and the thoracic part of the vagus nerve after acute and chronic gravitational overloading (GOL). Studies were performed on 28 white mongrel male rats aged 8-21 weeks. Animals of series I (acute GOL) were rotated in a centrifuge on one day (three rotation sessions with two 20-min breaks, giving a total rotation time of 31 min). Animals of series II (chronic GOL) were rotated in an alternating two-week regime for 13 weeks (total rotation time 20 h 9 min). Rotation was performed in the craniocaudal direction with overloads of 4-6 g. Intact rats served as controls. Histological, electron microscopic, and morphometric analyses were performed. Acute GOL produced mainly reversible reactive changes in the anterior thoracic nodes of the sympathetic trunk and thoracic part of the vagus nerve, probably induced by unusual combinations of afferent spike activity of unusual strength, this probably being one of the causes of impairments seen after rotation. Chronic GOL was followed by the development of mainly destructive and compensatory-adaptive processes, characterized by the destruction of mitochondrial cristae, vacuolization of neuron cytoplasm, and degradation of interneuronal synapses. These changes were probably due to the development of hypoxia, which leads to interneuronal synaptic blockade in sympathetic ganglia. These structural transformations demonstrate the involvement of both the sympathetic and parasympathetic compartments in responses to acute and chronic GOL, providing evidence of the generalization of adaptive processes in the autonomic nervous system.