Neural control of muscle movements in feeding behavior

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Major goal of our research is to know the neural mechanism generating feeding behavior in Aplysia which has simple nervous system. Jaw-closing (JC) muscle in a specific portion is doubly innervated by excitatory (JC) and inhibitory motor neurons (MAl) , which release glutamate (Glu) and acetylcholine (ACh) , respectively. On the other hand, redula-closer (ARC) muscle is innervated by cholinergic excitatory motor neurons. The purpose of this research is to know the characteristics the receptor and channels producing junction potentials, and also the modulatory mechanism of their function by central neurons. The muscle fibers were dissociated by using papain, and whole-cell patch clamp was performed on isolated single muscle cells to study the ionic mechanism associated with ACh or Glu reception. Iontophoretically applied ACh hyperpolarized the JC muscle cells while applied Glu depolarized the same cells, suggesting that ACh and Glu receptors coexist on the membrane of the single cell in the JC muscle. The experiments with different cation and anion compositions in the pipette solution showed that ACh-induced response in the JC muscle cells is caused by Cl^- currents while the response in the ARC muscle cells is cause by Na^+ and partly K^+ currents. These results suggest that the ACh receptors associated with a Cl^- channel in the JC muscle cells, and with a cation channel permeable to both Na+ and K+ in the ARC muscle cells. The effects of peptides (FMRF,Myomodulin A,SCP_A) widely found in Aplysia neurons and muscles on the inhibitory junction potentials (IJPs) were also explored. Application of these peptides reduced the size of IJPs produced in the JC muscle fibers by the MAl firing. In the whole cell clamp experiments, FMRF reduced Cl^- current induced by ACh application, suggesting that FMRF can modulate the function of ACh receptor channels.