Nerves and major accessory ganglia of the pelvic plexus are described from 12 rats perfused with methylene blue. Nerves to ventral and dorsal aspects of the urinary bladder, and three groups of nerves to the penis (clitoris) are reported in detail.Myelinated nerve fiber diameters ranged from 1-10 P in the pelvic nerve and 1-6 EL in the hypogastric nerve. When the pelvic nerve was deaerentated, by spinal ganglionectomy 28 days previously, 80% of myelinated fibers degenerated, and the remaining fiber-size spectrum resembled that of the hypogastric nerve. Myelinated fibers ranged from 1-7 EL in nerves to bladder and 1-3 P in the lateral nerve to the penis. Myelinated fibers were afferent in these nerves, since spinal ganglionectomy eliminated all of them. In the main nerve to the penis, myelinated fibers ranged from 1-8 EL in diameter. A few fibers remained after deafferentation by spinal ganglionectomy. Since these were preganglionic efferent fibers, they indicate that terminal ganglia were present in the penis. All myelinated fibers degenerated with transection of pelvic and hypogastric nerves. The mode diameter of myelinated fibers was 2 EL in all pelvic plexus nerves.The role of pelvic ganglia in regulation of pelvic visceral activity is not well understood. One factor complicating the investigation of pelvic ganglia is the complexity of the pelvic plexus in most experimental animals. In most cases, the pelvic plexus is comprised of many widely dispersed ganglia with multiple interconnections. The pelvic plexus of the rat, however, has a single major ganglion with distinct sympathetic (hypogastric nerve) and parasympathetic (pelvic nerve) inputs and postganglionic nerves to the pelvic viscera (Langworthy, '65). This arrangement suggests the pelvic plexus of the rat as an ideal model for the investigation of ganglionic activity regulating pelvic viscera.Gross and microscopic structure should form a base for the interpretation of electrophysiologic data. Histochemical studies of the pelvic plexus have been reported for several species (Sjostrand, '65; Owman and Sjostrand, '65; El Badawi and Schenk, '66, '68, '70, '71a,b). However, fiber spectra of the nerves of the pelvic plexus of the rat has not been reported. The objectives of this paper are (1) to reinvestigate the gross morphology of the pelvic plexus of the rat with particular emphasis on the nerves to the bladder and penis (clitoris); (2) to report the fiber spectrum of the pelvic nerve, hypogastric nerve and nerves to the bladder and penis distal to the pelvic ganglion; and ( 3 ) to determine the presence of afferent fibers and/or preganglionic efferent fibers projecting through the ganglion to the pelvic viscera. METHODSPelvic ganglia and associated nerves were dissected using a Zeiss operating microscope in 12 male and female white rats Received Oct. 9 '72. Accepted Nov. 30, '72.

Innervation to muscles of the feline perineum was examined by gross dissection of the sacral nerve plexus and quantitation of efferent and afferent myelinated fibers in selected nerves derived from the plexus. In addition, distribution of muscle fiber sizes and muscle spindle content were determined for muscles innervated by the nerves studied.Efferent myelinated fiber populations were bimodal in nerves innervating muscles with many spindles and unimodal in nerves innervating muscles in which few or no spindles were observed. Coccygeus and levator ani muscles had similar numbers of muscle spindles, but the spindles were different in the two muscles based on afferent innervation. In both coccygeous and external and sphincter muscles, primary spindle endings must be associated with relatively small afferent nerve fibers. The pelvic urethra received more large myelinated afferent fibers than the penis. The three divisions of the external anal sphincter muscle had three distinct populations of muscle fibers, based on size distribution. The homologous bulbospongiosus and constrictor vulvae muscles had different populations of muscle fibers.

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Urinary bladders and urethrae were collected from six adult and two juvenile female dogs. Five urethral regions and the neck and body of the bladder were sampled. Volume fractions for connective tissue including elastic fibers, smooth and striated muscle, and epithelium were obtained by projecting section images onto an array of points and computing the number of points overlying a tissue constituent per total points overlying the tissue section. Smooth muscle occupied approximately half the volume of the bladder wall, one-third the volume of the vesical neck, and one-fourth the volume of the proximal urethra. Striated muscle was present in the distal half of the urethra, where the total muscle coat occupied about one-third of the urethral wall volume. Smooth muscle was practically absent in the terminal urethra, where the striated urethralis muscle encircles urethra and vagina in common. Epithelial area and lumen perimeter were not significantly different along the length of the urethra except that urethral epithelium was significantly thicker adjacent to the vesical neck. In terms of histological proportions, the vesical neck was intermediate between the body of the bladder and the proximal urethra.

Lumbar and sacral afferent axons in the submucosa of the urinary bladder were recognized by degeneration in seven cats subjected to spinal ganglionectomies. Of 2,935 observed terminating axon profiles, 145 were found degenerating. Lumber afferent axons were 3.7 times more numerous than sacral afferent axons in the submucosa, a reversal of the ratio reported for the muscle coat of the bladder. Sacral afferent axons were evenly distributed to different regions of the bladder, but lumbar afferents were concentrated in the bladder neck. Apparent afferent endings in the submucosa of the urinary bladder were principally free nerve endings. Synaptic vesicles were found in 57% of observed terminating axon profiles. The bladder neck had more terminating axon profiles of all kinds than other regions of the urinary bladder.

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Metabolite concentrations and concentration ratios determined with 3-T (1)H MRS were not identical to those in humans and were determined for clinical and research investigations of canine brain disease.