Diversity of neuropeptidergic modulation in decapod crustacean cardiac and feeding systems

Decoding Neuropeptide Complexity: Advancing Neurobiological Insights from Invertebrates to Vertebrates through Evolutionary Perspectives

Neuropeptides are vital signaling molecules involved in neural communication, hormonal regulation, and stress response across diverse taxa. Despite their critical roles, neuropeptide research remains challenging due to their low abundance, complex post-translational modifications (PTMs), and dynamic expression patterns. Mass spectrometry (MS)-based neuropeptidomics has revolutionized peptide identification and quantification, enabling the high-throughput characterization of neuropeptides and their PTMs. However, the complexity of vertebrate neural networks poses significant challenges for functional studies. Invertebrate models, such as Cancer borealis, Drosophila melanogaster, and Caenorhabditis elegans, offer simplified neural circuits, well-characterized systems, and experimental tools for elucidating the functional roles of neuropeptides. These models have revealed conserved neuropeptide families, including allatostatins, RFamides, and tachykinin-related peptides, whose vertebrate homologues regulate analogous physiological functions. Recent advancements in MS techniques, including ion mobility spectrometry and MALDI MS imaging, have further enhanced the spatial and temporal resolution of neuropeptide analysis, allowing for insights into peptide signaling systems. Invertebrate neuropeptide research not only expands our understanding of conserved neuropeptide functions but also informs translational applications including the development of peptide-based therapeutics. This review highlights the utility of invertebrate models in neuropeptide discovery, emphasizing their contributions to uncovering fundamental biological principles and their relevance to vertebrate systems.

Peptidergic Modulation of the Lobster Cardiac System Has Opposing Action on Neurons and Muscles

Modulation of neuronal networks, primarily through neuropeptides, generates variations in motor patterns that allow organisms to adapt to environmental changes or sensory inputs. Modulation is complex, with receptors for neuromodulators expressed at various locations within a nervous system; neuromodulators can thus alter muscle dynamics peripherally via the neuromuscular junction (NMJ) and the muscle itself. The neurogenic cardiac neuromuscular system of the American lobster (Homarus americanus) is a well-characterized model for investigating peptidergic modulation. Myosuppressin (pQDLDHVFLRFamide) is an endogenous peptide that interestingly decreases contraction frequency while also increasing contraction force by acting at both the lobster heart central pattern generator (CPG; the cardiac ganglion) and the periphery (cardiac muscles). Myosuppressin decreases heartbeat frequency by decreasing the burst frequency of the cardiac ganglion. Here, we investigated the remaining question, does myosuppressin exert its peripheral effects directly on the cardiac muscle, the NMJ, or both? To elucidate myosuppressin's effects on the cardiac muscle, the muscle was isolated from the CPG, and contractions were evoked using focal application of the endogenous neurotransmitter, l-glutamate, while superfusing myosuppressin over the heart. Myosuppressin increased glutamate-evoked contraction amplitude in the isolated muscle, suggesting that myosuppressin exerts its peripheral effects directly on the cardiac muscle. To examine effects on the NMJ, excitatory junction potentials were evoked by stimulating the motor nerve and recording the intracellular membrane voltage from a single muscle fiber both in control saline and in the presence of myosuppressin. Myosuppressin did not modulate the amplitude of excitatory junction potentials suggesting that myosuppressin acts directly on the muscle and not via the NMJ, to cause an increase in contraction force.

Cardiovascular physiology of decapod crustaceans: from scientific inquiry to practical applications

Until recently, the decapod crustacean heart was regarded as a simple, single ventricle, contraction of which forces haemolymph out into seven arteries. Differential tissue perfusion is achieved by contraction and relaxation of valves at the base of each artery. In this Review, we discuss recent work that has shown that the heart is bifurcated by muscular sheets that may effectively divide the single ventricle into 'chambers'. Preliminary research shows that these chambers may contract differentially; whether this enables selective tissue perfusion remains to be seen. Crustaceans are unusual in that they can stop their heart for extended periods. These periods of cardiac arrest can become remarkably rhythmic, accounting for a significant portion of the cardiac repertoire. As we discuss in this Review, in crustaceans, changes in heart rate have been used extensively as a measurement of stress and metabolism. We suggest that the periods of cardiac pausing should also be quantified in this context. In the past three decades, an exponential increase in crustacean aquaculture has occurred and heart rate (and changes thereof) is being used to understand the stress responses of farmed crustaceans, as well as providing an indicator of disease progression. Furthermore, as summarized in this Review, heart rate is now being used as an effective indicator of humane methods to anaesthetize, stun or euthanize crustaceans destined for the table or for use in scientific research. We believe that incorporation of new biomedical technology and new animal welfare policies will guide future research directions in this field.

Convergent Comodulation Reduces Interindividual Variability of Circuit Output

Ionic current levels of identified neurons vary substantially across individual animals. Yet, under similar conditions, neural circuit output can be remarkably similar, as evidenced in many motor systems. All neural circuits are influenced by multiple neuromodulators, which provide flexibility to their output. These neuromodulators often overlap in their actions by modulating the same channel type or synapse, yet have neuron-specific actions resulting from distinct receptor expression. Because of this different receptor expression pattern, in the presence of multiple convergent neuromodulators, a common downstream target would be activated more uniformly in circuit neurons across individuals. We therefore propose that a baseline tonic (non-saturating) level of comodulation by convergent neuromodulators can reduce interindividual variability of circuit output. We tested this hypothesis in the pyloric circuit of the crab, Cancer borealis Multiple excitatory neuropeptides converge to activate the same voltage-gated current in this circuit, but different subsets of pyloric neurons have receptors for each peptide. We quantified the interindividual variability of the unmodulated pyloric circuit output by measuring the activity phases, cycle frequency, and intraburst spike number and frequency. We then examined the variability in the presence of different combinations and concentrations of three neuropeptides. We found that at mid-level concentration (30 nM) but not at near-threshold (1 nM) or saturating (1 µM) concentrations, comodulation by multiple neuropeptides reduced the circuit output variability. Notably, the interindividual variability of response properties of an isolated neuron was not reduced by comodulation, suggesting that the reduction of output variability may emerge as a network effect.

Unveiling the Impact of Rapeseed Meal on Feeding Behavior and Anorexigenic Endocrine in Litopenaeus vannamei

Litopenaeus vannamei, with high plant protein acceptance and high global aquaculture production, is a potential species for rapeseed meal application. However, rapeseed meal has been associated with anorexia in fish, and whether the same occurs in L. vannamei remains unknown. This study demonstrated the effects of rapeseed meal on the feeding and anorexigenic endocrine of L. vannamei based on feeding behavior and transcriptomics. Soybean meal was replaced with fermented rapeseed meal (50%), and a significant increase in remaining diet and dietary discard was observed with a significant reduction in dietary visits. Transcriptome analysis revealed that the pathways involved in rapeseed meal-induced anorexia mainly included signal transduction, the digestive system, the sensory system, the endocrine system, phototransduction-fly, the thyroid hormone signaling pathway and pancreatic secretion. Moreover, this study further analyzed and identified seven neuropeptides involved in rapeseed meal-induced anorexia, and it explored the complex expression regulation strategies of these neuropeptides. In summary, this study confirmed through feeding behavior that rapeseed meal causes anorexia in L. vannamei, and it identified seven neuropeptides that were closely related to the anorexia process.