218 | Rhythmic Motor Control and Premotor Modulation

Neural Circuits and Systems Neuroscience

Author: Martina Radice | Email: radicemarti@gmail.com

Martina Radice 1°2°, Lidia Szczupak 1°2°

1° Departamento de Fisiología, Biología molecular y celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires
2° Instituto de Fisiología, Biología Molecular y Neurociencias, Universidad de Buenos Aires y CONICET

The execution of rhythmic motor behaviors requires multiple control mechanisms to adjust the behavioral output, narrowing down the degrees of freedom of a system with multiple units.
Leeches crawl on solid surfaces through a succession of elongation and contraction body waves. Each segmental ganglion contains the neurons required to produce this rhythmic motor pattern, and dopamine evokes fictive crawling in isolated midbody ganglia. The pair of premotor NS (nonspiking) neurons are connected to motoneurons through a central network that provides recurrent inhibitory signals onto the motoneurons. We aim at understanding the role of NS in the context of crawling.
During fictive crawling NS neurons receive inhibitory signals, tuned to the contraction phase of crawling, monitored through the DE-3 motoneuron. The results suggest that the inhibitory signals in NS are delivered by the rhythmogenic circuit that controls the motoneuron output. Thus, excitatory signals to DE-3 are correlated to inhibitions in NS that, in turn, can restrict the motoneuron activity.
Extracellular recordings and spike sorting analysis revealed that removing NS from the circuit enhances the firing frequency and duty cycle of DE-3 and motoneurons that fire in-phase with it. Moreover, the firing frequency of motoneurons that are active out of phase from DE-3 is not modified by this.
To this point the data indicates that the premotor NS neuron acts as an homeostatic element, restricting the motor output.