Logo by Bonnie Alexander's Class

Neurobiology Team

A question to consider as you read . . .

Vocabulary that will help you understand this section

• central nervous system
• stimuli

Sensory organs provide the only means through which an organism can gather information about its external environment. This environmental information is translated into neural signals, which then travel to and are processed by the organism's nervous system, as determined by its genetic programming and developed during maturation. The development of the sensory structures and their neural pathways to the Central Nervous System (CNS) is probably controlled by both genetic instructions and by environmental cues. It is not known, however, to what extent either genetic instruction or environmental stimuli actually have on the physical developments of the neural pathways. Likewise, the relative importance of environmental stimuli on correct neural connectivity patterns during maturity is still unknown.

Dr. Horn's Experiment

Dr. Horn's experiment is to examine the influence of environment, specifically gravity, on the functional development of sensory organs and their neural pathway connections to the CNS.

Dr. Horn chose crickets (Acheta domesticus) for observation because, compared to humans, they have an increased rate of development. Furthermore, crickets possess a complex gravity sensory system which includes gravity sensors (cerci) on their legs and tail. The cerci are hair-like cells, which if damaged, can regenerate. Located next to the gravity sensors is a sensory system which the cricket uses to detect air currents. Although the sensory receptors of these two systems are located very close together, each has its own specific synapses (connections) with different sets of neural pathways that carry the information to the CNS. By studying crickets that develop or mature in the microgravity environment of space and comparing them to crickets that mature simultaneously in the presence of gravity, Dr. Horn expects to gain information on the relative importance of environmental stimuli versus genetic instructions during neural pathway development, as well as the subsequent efficiency of the neural circuitry in relaying information.

BOTEX System

During the mission, the crickets will be housed in the BOTEX. The BOTEX system was originally designed for botany experiments but can successfully be used for small animals. It has compartments that simulate gravity conditions, so a control group can be compared to the experimental group in microgravity. Groups of crickets in various early developmental stages will experience microgravity conditions for the duration of the mission. By comparing the efficiency of the gravity sensory systems in the experimental group (matured in microgravity) as compared to the control group (matured in the presence of gravity), the investigator will discover the relative importance of environmental factors to neuronal development.

Accuracy and efficiency of neural pathway development in microgravity will be assessed by using three methods.

First, monitoring the cricket's behavior--Although its body may be situated at an angle, the cricket keeps its head as close to vertical as possible. By measuring the compensatory head movement of the cricket during a roll of its body, the accuracy of the synaptic connections can be quantified.

Second, assessing the ability of the cricket to regenerate damaged cerci--A microscope will be used to detect how accurately the cerci regenerated in microgravity are connected, compared to accuracy of cerci regenerated in the presence of gravity, thus analyzing the importance of environmental stimuli (gravity) for accurate nerve regeneration.

Third, analyzing the efficiency of neural pathways or the speed at which they can transmit information--Electrodes will be used to detect and measure the rate at which the cricket's neural pathways transmit a sensory stimulus from both gravity and air current receptors. The speed of information transmission between crickets that developed in microgravity and those that developed in normal gravity environments will be compared.

This study will provide important information on the fundamental issue of the relative importance of external stimuli on developing genetic programs.