Functional Development

Like morphology, all physiological functions in organisms, as well as their behavior, experience modifications during development. One of the most impressive examples are flies and bees that change their body shape from a worm-like to a beautiful looking animal with legs, wings, and a highly developed nervous system.

The study of physiological development is an important tool to understand the mechanisms in adults. Unfortunately, it is also a very time-consuming approach. The most reliable way to describe physiological development is to apply all those techniques that are used to understand the physiology of adults at each developmental stage. This is because each development stage has its own physiological mechanisms, which might be completely different from those found in adults. It is, therefore, not surprising that the number of detailed physiological characteristics describing the relationship between age and physiology with a high developmental resolution are rarely found in the literature. But since the discovery of the so-called sensitive or critical periods (Wiesel 1982), this knowledge became extremely important. Indeed, it is fundamental to find out not only the extent to which environmental and genetic factors determine the central processes and behavior, but also those periods of life during which these factors have a determining influence.

Most research in the physiology of development related to microgravity was performed in the field of neurobiology, i.e., the study of the nervous system. For this reason, this section exclusively considers space neurobiological experiments. Short descriptions of these developmental characteristics, as well as the effects of microgravity on neuronal activity and behavior in the immature animal models, are presented. To some extent, the results of biochemical investigations that are related to the metabolism and the energy demand during adaptive processes to microgravity are also included.

Figure 5-11. Postembryonic development of a neurophysiological response in microgravity in the cricket Acheta domesticus. The activity of the posture sensitive interneuron (PSI) was recorded extracellularly during a 360-deg lateral rotation of the animal The PSI revealed desensitization immediately after microgravity exposure (Post/light Days 1-8), as shown by the marked depression of the activity modulation during body roll. This desensitization disappeared two weeks after return (Postflight Days 14-16). Adapted from Horn et al (2003).

Figure 5-11. Postembryonic development of a neurophysiological response in microgravity in the cricket Acheta domesticus. The activity of the posture sensitive interneuron (PSI) was recorded extracellularly during a 360-deg lateral rotation of the animal The PSI revealed desensitization immediately after microgravity exposure (Post/light Days 1-8), as shown by the marked depression of the activity modulation during body roll. This desensitization disappeared two weeks after return (Postflight Days 14-16). Adapted from Horn et al (2003).

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