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Date: 2023-01-01

Creator: Jackie Seddon

Access: Open access

Neuromodulation, the process of altering the electrical outputs of a neuron or neural circuit, allows an organism to control its physiological processes to meet the needs of both its internal and external environments. Previous work shows that the pyloric pattern of the kelp crab (Pugettia producta) stomatogastric nervous system (STNS) neurons responded to fewer neuromodulators than the Jonah crab (Cancer borealis). Since the kelp crab diet primarily eats kelp, it is possible that the movements of the foregut that control digestion may require less flexibility in functional output compared to an opportunistic feeder. To determine whether a reduced flexibility is correlated with diet, this study compared the modulatory responses in Pugettia to two other species of majoid crabs: Chionoecetes opilio and Libinia emarginata, which are both opportunistic feeders. Pooled data for this study found that Libinia and Chionoecetes responded to all twelve modulators tested. When considering the effect of modulators on stomatogastric ganglion (STG) motor outputs, we must consider whether these modulators also alter the excitatory junction potentials (EJPs) at the neuromuscular junction (NMJ), and whether there are differences in responses across species. To test this, the dorsal gastric nerve (dgn) was stimulated while recording intracellularly from the muscle fibers of the associated gm4 muscles. The NMJ of the gm4 in Cancer borealis did not appear to be broadly modulated, as only RPCH and CabTRP showed increases in amplitude, and RPCH decreased facilitation at 5 Hz.

Date: 2020-01-01

Creator: Jacob Salman Kazmi

Access: Open access

Neuromodulation may be a substrate for the evolution of behavioral diversity. The extent to which a central pattern generator is modulated could serve as a mechanism that enables variability in motor output dependent on an organism’s need for behavioral flexibility. The pyloric circuit, a central pattern generator in the crustacean stomatogastric nervous system (STNS), stimulates contractions of foregut muscles in digestion. Since neuromodulation enables variation in the movements of pyloric muscles, more diverse feeding patterns should be correlated with a higher degree of STNS neuromodulation. Previous data have shown that Cancer borealis, an opportunistic feeder, is sensitive to a wider array of neuromodulators than Pugettia producta, a specialist feeder. The observed difference in modulatory capacity may be coincidental since these species are separated by phylogeny. We predict that the difference in modulatory capacity is a product of a differential need for variety in foregut muscle movements. This study examined two members of the same superfamily as P. producta, the opportunistically feeding snow crab (Chionoecetes opilio) and portly spider crab (Libinia emarginata). Using extracellular recording methods, the responses of isolated STNS preparations to various neuromodulators were measured. Initial qualitative results indicate that the STNS of C. opilio is sensitive to all of these neuromodulators. Additionally, previous data on the neuromodulatory capacity of L. emarginata was supported through similar electrophysiological analysis of the isolated STNS. As a first step in determining the mechanism of differential sensitivity between species, tissue-specific transcriptomes were generated and mined for neuromodulators.