Effects of neuromodulator RPCH on short-term dynamics of a key synapse in an oscillatory network of crab Cancer borealis

Central pattern generators (CPGs) generate the rhythmic movements in vertebrates and invertebrates. CPGs must be able to produce stable patterns to produce the rhythmic movement, and be flexible to adapt to the changing environment. CPGs are subject to activity-dependent plasticity and their activity is modified by neuromodulatory substances. Neuromodulators alter the intrinsic properties and synaptic strength. This alteration may then modulate the flexibility of the motor patterns. The pyloric network of the crustacean stomatogastric nervous system is a well-studied CPG that is subject to extensive neuromodulation. Effects of neuromodulators on intrinsic properties of neurons have been studied in great detail, but the effects of neuromodulators on the short-term plasticity of the synapses are overlooked. Therefore, the main goal of this study was to examine the role of neuromodulator RPCH on the short- term dynamics of pyloric LP to PD synapse, a key synapse, by using the crab Cancer borealis as a model system. Our results showed that, RPCH strengthened the LP to PD synapse in a dose-dependent manner, depressed the synapse, but did not affect the peak phase. Results of this study promote the understanding of how modulation of short-term synaptic dynamics of a key synapse affects the generation and the control of the pyloric rhythm. These results will help to better understand the mechanisms underlying pattern generation by CPGs in general. Moreover, such an understanding of modulation of a circuitry used in rhythmic behaviors should lead to treatments of certain illnesses or injuries such as spinal cord injury.