Showing 1 - 7 of 7 Items

Date: 2020-01-01

Creator: Grace Bukowski-Thall

Access: Open access

Central pattern generators (CPGs) are neural networks that generate the rhythmic outputs that control behaviors such as locomotion, respiration, and chewing. The stomatogastric nervous system (STNS), which contains the CPGs that control foregut movement, and the cardiac ganglion (CG), which is a CPG that controls heartbeat, are two commonly studied systems in decapod crustaceans. Neuromodulators are locally or hormonally released neuropeptides and amines that change the output patterns of CPGs like the STNS and CG to allow behavioral flexibility. We have hypothesized that neuromodulation provides a substrate for the evolution of behavioral flexibility, and as a result, systems exhibiting more behavioral flexibility are modulated to a greater degree. To examine this hypothesis, we evaluated the extent to which the STNS and the CG are modulated in the majoid crab species Chionoecetes opilio, Libinia emarginata, and Pugettia producta. C. opilio and L. emarginata are opportunistic feeders, whereas P. producta has a highly specialized kelp diet. We predicted that opportunistic feeding crabs that chew and process a wide variety of food types would exhibit greater STNS neuromodulatory capacity than those with a specialized diet. The STNS of L. emarginata and C. opilio responded to the seven endogenous neuromodulators oxotremorine, dopamine, CabTrp Ia, CCAP, myosuppressin, proctolin, and RPCH, whereas the STNS of P. producta only responded to proctolin, oxotremorine, myosuppressin, RPCH (25% of the time), variably to dopamine, and not at all to CabTrp and CCAP. Because P. producta, L. emarginata, and C. opilio all belong to the Majoidea superfamily, their primary distinctions are their feeding habits. For this reason, we further predicted that there would be no relationship between diet and modulatory capacity in the cardiac ganglion (CG) of the neurogenic heart. This would suggest that a lack of STNS modulatory capacity in P. producta relative to L. emarginata and C. opilio is specific to evolved foregut function. Whole-heart recordings from P. producta indicated that, unlike the STNS, the CG responds to CabTrp and CCAP. P. producta hearts also responded to oxotremorine and inconsistently to dopamine and proctolin. The CG of C. opilio was modulated by CabTrp, CCAP, dopamine, proctolin, myosuppressin, and oxotremorine, but not RPCH. The CG of L. emarginata responded to CCAP, and inconsistently to CabTrp, dopamine, and proctolin, but not to myosuppressin, RPCH, and surprisingly oxotremorine. Although cardiac responses were not identical between species, opportunistic and specialist feeders responded more similarly to the modulators tested in the heart than in the STNS. Notably, P. producta responded to each modulator in a similar manner to C. opilio and/or L. emarginata. However, L. emarginata’s surprising lack of cardiac response to oxotremorine suggests that phylogenetic closeness may not control for differences in CG and STNS function between species. Nevertheless, sample sizes of all three species were quite small, and individual differences lead to inconsistencies in the data. As a result, sample size must be enlarged to draw firm conclusions.

Date: 2020-01-01

Creator: Benjamin Harley Wong

Access: Open access

Neuropeptides are important modulators of neural activity, allowing neural networks, such as the central pattern generators (CPGs) that control rhythmic movements, to alter their output and thus generate behavioral flexibility. Isoforms of a neuropeptide family vary in physical structure, allowing potentially distinct functional neuromodulatory effects on CPG systems. While some familial neuropeptide isoforms can differentially affect a system, others in the same family may elicit indistinguishable effects. Here, we examined the effects elicited by members of a novel family of six peptide hormone isoforms (GSEFLamides: I-, M-, AL-, AM-, AV-, and VM-GSEFLamide) on the pyloric filter and gastric mill CPGs in the stomatogastric nervous system (STNS) of the American lobster, Homarus americanus. Recent unpublished work from the Dickinson lab found that five of the six GSEFLamides elicited similar increases in contraction amplitude when perfused through the isolated lobster heart, while one (AVGSEFLamide) had virtually no effect. Using extracellular recordings, we found the pattern of GSEFLamide effects on the STNS gastric mill to be similar to the pattern observed in the lobster cardiac system; the gastric mill circuit was fairly consistently activated by all isoforms except AVGSEFLamide. The intrinsically active pyloric pattern was also significantly enhanced by three out of five peptide isoforms, and nearly significantly enhanced by two more, but was likewise non-responsive to AVGSEFLamide. While the reason AVGSEFLamide had no effect on either pattern is unknown, the similar phenomenon noted in the isolated whole heart potentially indicates that this isoform lacks any function in the lobster.

Date: 2023-01-01

Creator: Elise Martin

Access: Open access

This project sought to answer the following question: what is the relationship between the extent of neuromodulation in a nervous system, and the behavioral demands on that system? A well-characterized CPG neuronal circuit in decapod crustaceans, the stomatogastric nervous system (STNS), was used as a model circuit to answer this question. The stomatogastric ganglion (STG) in the STNS is responsible for muscular contractions in the stomach that aid in digestion. It has been shown that the neural networks in the STG are subject to neuromodulation. One feature of neuromodulation is that it enables circuit flexibility, which confers upon a system the ability to produce variable outputs in response to specific physiological demands. It was hypothesized that opportunistic feeders require more extensively modulated digestive systems compared to exclusive feeders, because opportunistic feeders require a greater variety of digestive outputs to digest their varied diets. In this study, Chionoecetes opilio and Libinia emarginata, the opportunistic feeders, showed greater neuromodulatory capacity of the STNS than Pugettia producta, the exclusive feeder. The hypothesis that neuromodulatory capacity of the STNS correlates with dietary diversity was supported. The results detailed in this study lend credence to the idea that evolutionary basis for neuromodulatory capacity of a system is related to the behavioral demands on that system.

Date: 2022-01-01

Creator: Anthony Yanez

Access: Open access

Central pattern generators are neural circuits that can independently produce rhythmic patterns of electrical activity without central or periphery inputs. They control rhythmic behaviors like breathing in humans and cardiac activity in crustaceans. Rhythmic behaviors must be flexible to respond appropriately to a changing environment; this flexibility is achieved through the action of neuromodulators. The cardiac ganglion of Homarus americanus, the American lobster, is a central pattern generator made up of four premotor neurons and five motor neurons. Membrane currents in each cell type, which can be targeted for modulation by various molecules, generate rhythmic bursts of action potentials. Myosuppressin, a FMRFamide-like peptide, is one such neuromodulator. The currents targeted for neuromodulation by myosuppressin are unknown. I investigated the molecular and physiological underpinnings of the modulatory effect of myosuppressin on motor neurons in the cardiac ganglion. First, using single cell RT-qPCR, I determined that across animals, motor neurons express myosuppressin receptor subtype II at equal levels relative to each other. Using sharp intracellular recordings, I showed that myosuppressin decreased burst frequency and the rate of depolarization during the inter-burst interval. I predicted that this effect resulted from the modulation of either A-type potassium current or calcium-dependent potassium current. Using two-electrode voltage clamp, I found that total outward current did not substantially change after treatment with myosuppressin. This result was surprising and provides grounds for explorations of subtle forms of neuromodulation in simple neural circuits.

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: 2024-01-01

Creator: Karin van Hassel

Access: Open access

The cardiac ganglion (CG) is a central pattern generator, a neural network that, when activated, produces patterned motor outputs such as breathing and walking. The CG induces the heart contractions of the American lobster, Homarus americanus, making the lobster heart neurogenic. In the American lobster, the CG is made up of nine neurons: four premotor pacemaker neurons that send signals to five motor neurons, causing bursts of action potentials from the motor neurons. These bursts cause cardiac muscle contractions that vary in strength based on the burst duration, frequency, and pattern. The activity of the CG is modulated by feedback pathways and neuromodulators, allowing for flexibility in the CG’s motor output and appropriate responses to changes in the animal’s environment. Two feedback pathways modulate the CG motor output, the excitatory cardiac muscle stretch and inhibitory nitric oxide feedback pathways. Despite our knowledge of the modulation of the CG by feedback pathways and neuromodulators separately, little is known about how neuromodulators influence the sensory feedback response to cardiac muscle stretch. I found one neuromodulator to modulate each phase of the stretch response differently, one neuromodulator to generally not affect the stretch response, and three neuromodulators to suppress the stretch response. These results suggest neuromodulators can act to produce flexibility in a CPG’s motor output, allowing the system to respond appropriately to changes in an organism’s environment, and allow for variation in CPG responses to different stimuli.

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.