Afferent Impulses in the Pudendal Nerves of the Cat

Abstract

Ingoing impulses from sense organs in the anal and urethral regions of the cat were recorded in single fibres of the sacral dorsal roots.In the anal region rapidly adapting discharges came from sense organs in the peri-anal skin, in the lining membrane of the anal canal and in the peri-anal tissues. There were slowly adapting stretch receptors in the external anal sphincter.Rapid distension of the urethra gave rise to rapidly adapting discharges in the ingoing fibres. A steady flow of fluid along the urethra caused a sustained but irregular discharge of low voltage from receptors lying in the substance of the urethra.There are typical muscle spindles in the substance of the external anal sphincter and lamellated end organs in the peri-anal tissue. Lamellated end organs of varying sizes are in and around the wall of the urethra: the smallest lamellated end organ lies immediately under the epithelium of the lumen of the urethra.THE pudendal nerves contain afferent fibres from the penis or clitoris, from the mucous membrane of the distal urethra, from the peri-anal skin and from the lining membrane of the anal canal distal to the pectinate line. The sensitivity of the lining membrane of the anal canal in man was tested clinically by Duthie and Gairns [1960] who found that all the modalities in normal skin were present here; indeed the sensitivity seemed to be more acute than in the majority of cutaneous surfaces. In keeping with this acute sensitivity, Duthie and Gairns found a profuse innervation with highly specialized receptors in the lining membrane of the anal canal of man: but they foumd no receptors in the mucosa of the rectum. Walker [1959] found muscle spindles in the external anal sphincter of the cat, while Chennels, Floyd and Gould [1960] confirmed this observation and succeeded in recording the discharge from the spindles.Sensations from stimulation of the urethra in man have been described by Nathan [1956]. The only experimental study of the sensory innervation of the urethra is that of Talaat [1937], who recorded a multifibre discharge of impulses in the pedendal nerve when fluid was made to flow along the urethra of the cat. Garry and Garven [1957] described a variety of organized endings in and around the urethral wall in cats.The aim of the present enquiry was to record and study the nature of the discharge from single sensory units whose fibres pass inwards by the pudendal nerves and to find the nature of the adequate stimulus for these. The histology of the sense organs in the areas supplied by the pudendal nerve was also studied.258

Bladder activation by selective stimulation of pudendal nerve afferents in the cat

“…In the spinal intact cat, there were two distinct afferent pudendal nerve pathways that evoked isovolumetric sustained bladder contractions in response to selective nerve stimulation: high frequency (20 Hz ≤ f ≤ 50 Hz) stimulation of the dorsal genital branch (DNP) and low frequency (2 Hz ≤ f ≤ 5 Hz) stimulation of the cranial sensory (CSN) branch. The distinct excitatory frequency range of these neural pathways was consistent with the flat frequency tuning curve obtained from SN branch stimulation ( Figure 3A), and with the full frequency range of afferent neural discharge recorded during urethral fluid flow (Todd, 1964). The bladder responses evoked by selective electrical stimulation of pudendal afferents following acute spinal transection (SCT) further differentiated these two micturition pathways: high frequency activated DNP (direct spinal) pathway that still evoked robust sustained bladder contractions and the low frequency CSN (spino-bulbo-spinal) pathway that evoked transient bladder contractions analogous to those observed in humans with chronic SCI pressure (Gustafson, et al, 2004.…”

“…The absence of any excitatory bladder activity in response to DNP activation at these stimulus frequencies further supports the notion of the CSN as an independent component of the SN branch. Based on earlier studies, the afferent fibers of the CSN branch are thought to extent cranially along the anterior urethra (Bradley, et al, 1973) and innervate urethral mechanoreceptors (e.g., pacinian corpuscles) located in the membranous and prostatic urethra (Todd, 1964).…”

Improved bladder emptying in urinary retention by electrical stimulation of pudendal afferents

“…Fluid flow in the urethra evokes firing in pudendal afferents innervating the urethra in cats (Talaat 1937, Todd 1964 and rats (Le Feber et al 1998), and this sensory signal augments the amplitude of ongoing bladder contractions in cats (Barrington 1931, 1941, Garry et al 1959 and increases the frequency of isometric bladder contractions in rats (Jung et al 1999). Similarly, electrical stimulation of the urethral sensory branch of the pudendal nerve in cats leads to excitation of the bladder (Mazieres et al 1997, Jiang andLindström 1999), inhibition of the external urethral sphincter, and voiding (Shefchyk and Buss 1998).…”

Elevation of sensory thresholds in the prostatic urethra after microwave thermotherapy

“…The urethral wall in the cat contains nerve endings varying from large lamellated Pacinian corpuscles in the periurethral connective tissue to very small endings just under the epithelium [13], and this is presumably also the case in man. Possible functional denervation might be caused by damage restricted to such nerve endings, a heat-induced membrane injury or a segmental demyelinization of the axons, resulting in decreased conduction velocity and conduction block.…”

“…The afferent nerve ®bres mediate sensations of ow, temperature and pain. In the urethral wall of the male cat [13] the sensory nerve endings are mainly in the proximal part of the urethra. There is evidence that the sensitivity of the posterior urethra is correlated with the micturition re¯ex [14±16] and a well-established method of measuring such sensitivity is to use electrical stimulation.…”