Objectives:A number of physiological responses to the microgravity environment have been previously described. For example, temperature regulation, fluid volume and water intake, calcium metabolism and the neuromuscular control of movement are altered under microgravity. Such adaptations to microgravity may be mediated by corresponding changes in brain neurotransmitter dynamics. This study examined the effect of weightlessness on the neurotransmitter receptors in selected areas of the brain of space-flown rats.
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Approach:
Six flight and six control rats were sacrificed and standard receptor binding assays for receptor number and affinity were performed. Brains were dissected so that the hippocampus and posterior cortex area could be saved for assays, including serotonin, dopamine, noradrenergic, cholinergic and GABA measurements. The Mg-dependent Na+/ K+ ATPase activity was determined by colorimetric assay of Pi formed from trisATP added to cortical membranes. Group sizes varied from three to six depending on the necessity of pooling tissues.
Results:
Data indicate that few receptor changes occurred in the microgravity. When receptor changes did occur, they appeared to be restricted to a particular terminal field, suggesting that microgravity affected terminal mechanisms (e.g., release and uptake) differently, rather than exerting a generalized effect on the projection neuron. The increase in 5HT1 receptor in the hippocampus may reflect altered neuromodulation in this area by serotonergic neurons originating in the raphe nuclei. As it has been suggested that one major function of the hippocampus is to serve as a spatial map of the environment, perhaps the transition to microgravity may necessitate major changes in any spatial map of the environment. The 5HT1 receptor may play a role in such a modification. Similarly, the flight-associated marginal decrease in D2 binding in the stratum might reflect a down-regulation induced by heightened dopaminergic activity in the nigra, associated with novel motor activity under microgravity.
Miller JD, et al. Effects of Weightlessness on Neurotransmitter Receptors in Selected Brain Areas. Abstract S-203. Proceedings of the Seventh Annual Meeting on the IUPS Commission on Gravitational Physiology; 1985 Oct 13-18; Niagara Falls(NY)
Miller JD, McMillen BA, Murakami DM, McConnaughey MM, Williams HL, Fuller CA. Effects of Weightlessness on Neurotransmitter Receptors in Selected Brain Areas. Abstract 83.12. 36th Annual Fall Meeting of the American Physiological Society; 1985 Oct 13-18; Buffalo (NY) Physiologist 1985; 28(4):377.
Miller JD, McMillen BA, Murakami DM, McConnaughey MM, Williams HL, Fuller CA. Effects of Weightlessness on Neurotransmitter Receptors in Selected Brain Areas. Physiologist 1985; 28(6 Suppl):S203-4.
Count, Dopamine receptors, hippocampus, brain, rat, Standard receptor assay
Count, Dopamine receptors, posterior cortex, brain, rat, Standard receptor assay
Count, Gamma-aminobutyric acid (GABA) receptors, hippocampus, brain, rat, Standard receptor assay
Count, Gamma-aminobutyric acid (GABA) receptors, posterior cortex, brain, rat, Standard receptor assay
Count, Noradrenaline receptors, hippocampus, brain, rat, Standard receptor assay
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Count, Noradrenaline receptors, posterior cortex, brain, rat, Standard receptor assay
Count, Serotonin receptors, hippocampus, brain, rat, Standard receptor assay
Count, Serotonin receptors, posterior cortex, brain, rat, Standard receptor assay