Dopamine Improves Resistance of Dendrites of Mauthner Neurons to Destruction Induced by Sensory Stimulation and Application of Β-Amyloid.

Mauthner neurons in goldfish fry were studied by the methods of light and electron microscopy. The structure and volume of individual dendrites as well as the structure of axodendritic synapses were examined using virtual images of neurons formed from serial 3-µ sections. In short-time (5 h) experiments with application of dopamine, ß-amyloid fragment (25-35), and long-term sensory stimulation affecting afferent inputs to Mauthner neurons, the dendrites were larger than the same dendrites under the same conditions without dopamine application. Application of dopamine induced no pathological changes in the structure of axodendritic chemical and electric synapses containing desmosome-like contacts.

Structure of Interneuronal Contacts in the Neuropil of the Oculomotor Nuclei in Mouse Brain under Conditions of Long-Term Microgravity.

Ultrastructure of the neuropil of the brain oculomotor nuclei was studied in mice after 30-day exposure to microgravity on Bion-M1 biosatellite and after 13-h exposure to Earth gravity. The number of axo-dendritic synapses in the neuropil of the oculomotor nucleus significantly decreased after the flight. Degenerated axon terminals containing conglomerates of presynaptic vesicles appeared. The number of synapses with high functional activity increased and the length of active zones of the axo-dendritic synapses significantly increased. The observed ultrastructural changes of the neuropil of the oculomotor nuclei of mice exposed to microgravity reflect the development of long-term deafferentation of the analyzed brain structures. These changes in the neuropil ultrastructure can determine the disturbances in the oculomotor system, e.g. development of atypical nystagmus under conditions of microgravity.

[ULTRASTRUCTURE OF MOTOR NEURONS AND SYNAPSES IN THE OCULOMOTOR NERVE NUCLEI IN MICE].

Motor neuron and synapse ultrastructure in the somatic area of oculomotor nerve nuclei (cranial nerve III nuclei) was studied in C57 Black/6 mice. It was shown that that axodendritic and axosomatic synapses were characterized by rounded subjunctional bodies, located at the postsynaptic side of the synaptic contact at some distance from postsynaptic density. At the site of the subjunctional densities, the synaptic gap was expanded to 30 µm. In the same synapse, the synaptic gap could be reduced twice or more. Axosomatic and axodendritic synapses occured on spines. On the soma and dendrites of motoneurons, en passant type of synapses were found. No gap junctions were observed.