Central pattern generators (CPGs) are neural networks that produce rhythmic movements, such as walking, chewing, and breathing, in both the presence and absence of sensory input. Exploring the relationship between sensory-regulated and intrinsically controlled CPG activity is crucial for better understanding disorders of rhythmic movement. The stomatogastric nervous system (STNS) of the Jonah crab, Cancer borealis, includes two feeding-related CPGs, which are ideal models to study CPG function. The gastric mill CPG coordinates chewing in the foregut via the movement of gastric mill muscles; one of these muscles, gm1, is directly below the shell (carapace). We sought to determine how chewing activity (as measured by gm1 activity) differs between food types. We used noninvasive photoplethysmography (PPG) recordings to measure gm1 muscle activity (defined as frequencies between 0.04-0.20 Hz) during feeding and non-feeding conditions. Each feeding involved one of three food types: squid, shrimp, or sardine. We analyzed the PPG signal from the start of feeding to three hours post-feeding to determine its composition in terms of low (0.04-0.093 Hz), medium (0.094-0.147 Hz), and high (0.148-0.20 Hz) gastric mill frequencies and compared the results between food types. We found that the frequency composition of the PPG signal differed between sardine and squid feedings and between sardine and shrimp feedings, but not between squid and shrimp feedings. This difference was mirrored in our sclerometery experiment: sardine required significantly less force to puncture than squid and shrimp, but there was no significant difference between the latter two. Future research will aim to investigate the food-specific reasons for the chewing differences between food types (such as texture and nutritional content), to elucidate the physiological mechanisms that allow crabs to produce different gastric mill patterns in response to food, and to quantify characteristics of the PPG signal apart from frequency (such as amplitude and waveform).
Author(s): Sarah G. Johnson, Evan G. Burke, Abby E. Smith
Advisor(s): Dawn M. Blitz, Biology
Barathan Gnanabharathi, Biology