DISTRIBUTION AND MORPHOLOGY OF SACRAL SPINAL-CORD NEURONS INNERVATINGPELVIC STRUCTURES IN XENOPUS-LAEVIS

Relatively little is known about the organization of neural input to p elvic viscera in amphibia. In this study, sacral spinal efferent neuro ns were labeled in Xenopus laevis frogs by application of horseradish peroxidase (HRP) to the tenth spinal nerve, to pelvic musculature, or to the pelvic nerve. DiI was applied to the pelvic nerve with similar results. Labeled spinal neurons were located in the intermediate gray or in the ventral horn. Neurons in the tenth dorsal root ganglion, but not in the spinal cord, were labeled after application of HRP or DiI to the pudendal nerve. The labeled neurons in the spinal cord intermed iate gray were in a position comparable to that of the mammalian sacra l parasympathetic nucleus (SPN). Two apparent subdivisions included 1) a medial cluster of cells with mediolaterally oriented dendrites and 2) a lateral group with dorsoventrally oriented dendrites. An intermed iate group, not clearly classed with the other two, was also identifia ble. In some cases, labeled tenth nerve primary afferents were seen in contact with efferent neurons of the intermediate gray. Labeled neuro ns in the ventral horn medial to the lateral motor column were small, with dendrites oriented mediolaterally, in a position comparable to th at of the mammalian Onuf's nucleus. The peripheral targets of DiI-labe led pelvic nerve axons were the compressor cloaca muscle, cloaca, and bladder. DiI-labeled pudendal nerve axons distributed peripherally to cloacal lip and medial thigh integument. These data suggest that the p udendal nerve in amphibians is purely sensory and that both somatic an d autonomic motor axons traverse the pelvic nerve. (C) 1994 Wiley-Liss , Inc.