Showing 1 - 2 of 2 Items

Date: 2021-01-01

Creator: Audrey Elizabeth Jordan

Access: Open access

Networks of neurons known as central pattern generators (CPGs) generate rhythmic patterns of output to drive behaviors like locomotion. CPGs are relatively fixed networks that produce consistent patterns in the absence of other inputs. The heart contractions of the Homarus americanus are neurogenic and controlled by the CPG known as the cardiac ganglion. Neuromodulators can enable flexibility in CPG motor output, and also on muscle contractions by acting on the neuromuscular junction and the muscle itself. A tissue-specific transcriptome gleaned from the cardiac ganglion and cardiac muscle of the American lobster was used to predict the sites and sources of a variety of crustacean neuromodulators. If corresponding receptors were predicted to be expressed in the cardiac muscle, then it was hypothesized that the neuropeptide had peripheral effects. One peptide for which a cardiac muscle receptor was identified is myosuppressin. Myosuppressin has been shown to have modulatory effects at the cardiac neuromuscular system of the American lobster. In previous research, myosuppressin had modulatory effects on the periphery of cardiac neuromuscular system alone. It remains an open question of whether myosuppressin acts on the cardiac muscle directly, if it is exerting its effects at the neuromuscular junction (NMJ), or both. To test this, I performed physiological experiments on the isolated NMJ. Myosuppressin did not modulate the amplitude of the excitatory junction potentials. Since no modulatory effects were seen at the NMJ, the cardiac muscle was isolated from the cardiac ganglion and then glutamate-evoked contractions were stimulated. I showed that myosuppressin increased glutamate-evoked contraction amplitude. These data suggest myosuppressin exerts its peripheral effects at the cardiac muscle and not the NMJ.

Date: 2024-01-01

Creator: Katrina Carrier

Access: Open access

The ability of nervous systems to maintain function when exposed to global perturbations in temperature and salinity is a non-trivial task. The nervous system of the American lobster (H. americanus), a marine osmoconformer and poikilotherm, must be robust to these stressors, as they frequently experience fluctuations in both. I characterized the effects of temperature on the output of the pyloric circuit, a central pattern generator in the stomatogastric nervous system (STNS) that controls food filtration and established the maximum temperature that neurons in this circuit can withstand without “crashing” (ceasing to function but recovering when returned to normal conditions). I established a range of saline concentrations that did not cause the system to crash, and then determined whether combinatorial changes in temperature and salinity concentrations alter the maximum temperature the system tolerated. Even as burst frequency increased as temperature increased, phase constancy was observed. Interestingly, the system crashed at higher temperatures upon exposure to lower saline concentrations and lower temperatures in higher saline concentrations. I also established the range of saline concentrations that the lobster’s whole heart and cardiac ganglion (CG), the nervous system that controls the lobster’s heartbeat, can withstand. Then, I examined whether exposure to altered salinity and elevated temperature alters the crash temperature of the whole heart and CG. The CG crashed at higher temperatures than the whole heart in each saline concentration. Like the STNS, the whole heart and CG both crashed at higher temperatures in lower saline concentrations and higher temperatures in lower saline concentrations.