Innervation of the kidney of Aplysia by L10, the LUQ cells, and an identified peripheral motoneuron.

The purpose of this study was to begin to describe the neural circuit within the abdominal ganglion that modulates renal functioning in Aplysia. We found that the previously described cholinergic neuron L10 and peptidergic left upper quadrant (LUQ) neurons have important roles in the control of the kidney. Cell L10 and a subset of the LUQ cells branch extensively within the kidney and send major processes to the renal pore, a sphincter that controls the efflux of urine. The renal pore has circular (closer) and radial (opener) muscle fibers that act as antagonists. Embedded within the wall of the renal pore is a newly identified peripheral neuron, RPO, which is a renal pore opener motoneuron. L10 activity causes opening of the renal pore by directly exciting pore opener muscle, inhibiting closer muscle, and exciting RPO. When RPO is active, it generates synchronous, discrete twitches in the opener muscle fibers. The action potentials recorded in RPO exhibit pronounced broadening at physiological rates of firing. LUQ cells that project to the renal pore cause it to close, and they antagonize the opening generated by an L10 burst. The pore closing caused by the LUQ cells is mediated in part by heterosynaptic inhibition of the L10 to RPO excitatory connection. The previously described central inhibitory connections from L10 to the LUQ cells ensure that these 2 classes of antagonists fire out of phase with each other. Our data, along with those from earlier studies demonstrating that L10 plays an important role in controlling the circulatory system, suggest that L10 and the LUQ cells modulate various aspects of renal function in Aplysia, including filtration and micturition.