Identifying crustacean neuropeptides and precursor-related peptides by LC/MS: An investigation of strategies for extraction and orthogonal separations

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• Restriction End Date: 2028-06-01

Date: 2023-01-01

Creator: Emily Grace Herndon

Access: Access restricted to the Bowdoin Community

Aortic pressure and heart rate in the lobster Homarus americanus are modulated by mechanical feedback and neuropeptides

Date: 2021-01-01

Creator: Grace Marie Hambelton

Access: Open access

Baroreceptors are stretch receptors located in the aorta of mammals; in response to increased afterload, they elicit a decrease in heart rate, creating a negative feedback loop that lowers blood pressure. Although lobsters (Homarus americanus) do not have baroreceptors like mammals, closely related land crabs have been shown to have baroreceptor-like responses. Heart contraction is also regulated by the Frank-Starling response, where increasing stretch or preload increases the contractile force of the heart. In addition to these types of biomechanical modulations, lobsters use a central pattern generator, the cardiac ganglion, to maintain synchronicity of the heartbeat. The heart is also controlled by the central nervous system via neuromodulators, such as myosuppressin, which has been shown to increase active force and decrease frequency in isolated lobster hearts. We performed experiments on a lobster heart with the main arteries still intact, and varied the preload by stretching anterior arteries, and the afterload by elevating the dorsal abdominal artery. We added myosuppressin to modulate the cardiac ganglion output and muscle contraction. We found that the baroreceptor-like response is most directly modulated by active force, whereas frequency could be a secondary control. Increasing preload does increase active force, but that does not correlate to a higher cardiac output, which shows that how hard the heart pumps is not what determines how effectively it is pumping. Additionally, we found that myosuppressin has a much stronger effect on frequency than active force, and so with myosuppressin, frequency becomes the main determinant of cardiac output.

Context-specific effects of vasotocin on social approach in the male common goldfish, Carassius auratus

Date: 2019-05-01

Creator: Katharine Torrey

Access: Open access

The peptide vasotocin (VT) and its mammalian homologue, vasopressin (VP), produce effects on social behavior that are highly species- and context-specific. We recently sequenced two genes for V1a-like receptors (VTR) in the goldfish brain, one that encodes for a fully-functioning canonical receptor and one that encodes for a non-functional truncated receptor. The current study is an investigation of whether social context may alter expression of these receptor types and thus, potentially, behavioral responses to VT. We used western blotting and immunohistochemistry with custom anti-VTR antibodies to characterize the distribution of VTR throughout the forebrain and the hindbrain. Western blot results showed bands close to the predicted sizes for truncated and canonical VTR constructs, suggesting that both genes are translated into protein in the brain, but the presence of additional bands suggested potential nonspecific binding. Immunohistochemistry data revealed VTR signal throughout the brain in regions associated with social behavior. We additionally examined whether visual and olfactory context alters behavioral responsiveness to VT, potentially by altering the expression of one or both receptors. Behavioral tests suggested that VT inhibits approach to males, but its effect on response to females in reproductive contexts is still undetermined, likely due to interference from a stress response during testing. Further characterization of VTR throughout the brain will clarify how social context might alter VT signaling through context-dependent modulation of its receptors. Additionally, future work should examine the behavioral consequences of such modulation by further studying whether VT’s effect on social approach behavior depends on context.