Earthworm gut and mammalian smooth muscle motility can be modulated by neurotransmitters, making the earthworm a useful model to study the pharmacological effects of different neurotransmitters. Research has shown that the earthworm gut is particularly sensitive to the effects of acetylcholine (ACh) (Wu, 1939). This present study investigated the relative influences of ACh, epinephrine, and serotonin (5-HT) on gut motility. The experimental conditions included saline, ACh + epinephrine, and ACh + 5-HT. When exposed to ACh + epinephrine, it was predicted that the gut would show slight excitation, demonstrated through increased contraction frequency and amplitude. It was predicted that 5-HT would be more inhibitory than epinephrine because of the evolutionary importance assigned to its function as a monoamine involved in central nervous system development (Turlejski, 1996).
Our data only included one replication of frequency counts, so no statistical analysis could be run for this measure. However, the frequency value for the ACh + epinephrine condition was larger than those of the other two conditions, suggesting that the excitatory effect of ACh on gut motility was greater than the inhibitory effect of epinephrine. The ACh + 5-HT condition had a decreased contraction force compared to the other two groups as seen in a change in mN (amplitude), suggesting that 5-HT has a strong inhibitory effect on gut motility even when combined with the excitatory neurotransmitter ACh. Our data provided preliminary support for both of our hypotheses. Future research should use a larger sample size and combine epinephrine and ACh at differing concentrations to quantify the magnitude at which ACh is more influential than epinephrine.