In the previous post I looked at GABA receptors in C.Elegans – the Nematode worm. C.Elegans has been extensively studied and there is a very sophisticated understanding of the organism’s biological machinery. What I found fascinating was that the role of the GABA receptors in C.Elegans has been clarified and has been found to play a role in movement as well as a few other functions. There are only 26 neurons in C.Elegans.
The Nematode worm moves by contracting the muscles on one side of its body whilst relaxing the opposing muscles. The GABA receptors are involved in the relaxation of the muscles.
Muscle Relaxation and GABA Receptors
When people are anxious this can cause the muscles to tense. Some drugs acting at the GABA receptors in humans can reduce muscle tone. Some drugs which target these receptors can also alleviate anxiety. Which comes first? This is the chicken and egg scenario. Do you have to be anxious to have tense muscles or do you become anxious because your muscles are tense.
The James-Lange and Cannon-Bard Theories
The question of whether emotions or bodily sensations happen first is dealt with by the James-Lange and Cannon-Bard Theories. Essentially the two theories take differing positions on the question. The James-Lange theory states that emotions happen in response to information coming from the body. When the heart races you feel anxious. The Cannon-Bard theory says that emotions and bodily responses occur independently but can be coordinated by the Thalamus.
Nematode Worms, GABA Receptors and Anxiety in Humans
Nematode worms and our ancestors diverged some 800 million years ago. In that space of time Nematodes and our species have continued to evolve. Nevertheless the conservation of the GABA receptors in both Nematodes and our species is evidence of the importance of these receptors. Some simple connections and a narrative can be constructed to account for the above.
1. Nematodes have developed GABA receptors to facilitate movement
2. GABA receptors enable Nematodes to relax muscles to steer and move in certain directions
3. GABA receptors are part of a movement apparatus
4. As species have evolved and become more complex they have become capable of conscious experience
5. The movement apparatus has been conserved but also become associated with other complex phenomenon such as conscious experience
6. In humans muscle groups oppose each other – reciprocal extensor and flexor muscle groups at the elbow are one example.
7. The underlying relationship with GABA receptors remains
8. Action through the GABA receptors relaxes muscle groups and results in accompanying sensory feedback (small variation in the GABA receptor gene may not be related to anxiety but rather it is the physiological effects that the products of these receptor gene variants have in common).
9. This sensory feedback produces an emotional response – lowering of anxiety
While the above supports the James-Lange theory we could argue that there is a bidirectional relationship. For instance a heightened state of anxiety in response to internal stimuli can increase the tension in the muscle groups.
The above is a testable hypothesis. The hypothesis makes a very specific statement about a receptor in adaptive terms. The GABA receptor facilitates movement of the organism. Whilst it may well be wrong it nevertheless contains implicit assumptions which make it testable against the evidence base. The theory in essence states that the GABA receptor function is conserved and associated with increasingly complex phenomenon. If on moving from Nematode worms to humans there was convincing evidence of loss of motor related GABA receptor function in intermediary species this would contradict the hypothesis.
Jorgensen, E.M. GABA (August 31, 2005), WormBook, ed. The C. elegans Research Community, WormBook, doi/10.1895/wormbook.1.14.1, http://www. wormbook.org.
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