Neural pathways of somatic and visceral reflexes of the external urethral sphincter in female rats

The external urethral sphincter (EUS) plays a crucial role in maintaining urinary continence. The activity of the EUS is modulated by bladder and urethra sensory neurons. However, a complete understanding of the somatic or visceral sources that modulate the EUS is lacking. The aims of the present study were to characterize the response of the EUS to perineal skin, genital, rectal, and urethral mechanical stimulation, as well as to determine the peripheral neural pathways of the reflex. EUS reflex electromyographic activity (EMG), innervation of pelvic and perineal structures, and the anatomy of afferent and efferent nerves were determined in anesthetized female rats. The EUS responds to cutaneous as well as genital and rectal stimuli. However, the EUS EMG response is significantly larger when induced by genital stimulation. The dorsal nerve of the clitoris and the cavernous nerve both innervate the distal urethra and the distal vagina, as well as the clitoris and perigenital skin and are the main afferent pathways for the genito‐sphincteric reflex. Efferent axons travel through the pudendal nerve and the lumbosacral trunk and converge in the motor branch of the lumbosacral plexus, which innervates the EUS. Because the nerves are located on the vaginal walls, they are susceptible to damage during childbirth. Physiology and anatomy of the different neural pathways that regulate EUS activity are important to consider when inducing nerve damage to create models of urinary incontinence. J. Comp. Neurol., 520:3120–3134, 2012. © 2012 Wiley Periodicals, Inc.     

Discharge patterns of intramural mechanoreceptive afferents during selective distension of the cat's rectum

The afferent input from the rectum to the central nervous system (CNS) has yet to be thoroughly characterized. The characteristics of mechanoreceptive rectal afferents have been studied in unanaesthetized decerebrate cats. Following lumbo-sacral laminectomy, single-unit activity (occasionally multi-unit activity) was recorded from centrally cut filaments of the sacral dorsal roots (predominantly S2), while a balloon was inflated in the rectum. Starting from their background activities (mean 15.1 imp sec⁻¹, SD 7.6 imp sec⁻¹), afferent discharge rate increased with increasing balloon pressure (mean threshold 6.3 mmHg, SD 3.6 mmHg). The dependence of firing rate on intrarectal pressure began to flatten out at 25 mmHg (mean; SD 10 mmHg). For 22 out of 29 units (76%) complete saturation occurred at 35 mmHg (mean; SD 15 mmHg) with a maximum discharge rate of 31 imp sec⁻¹ (mean; SD 12.6 imp sec⁻¹). In a number of recording sessions, cyclical rectal contractions were observed. In these cases, changes in firing of the units were closely related to changes in intrarectal pressure. Pressure-related afferent activity could be enhanced by parasympathomimetic drugs which augmented rectal contractions. We conclude that sacral dorsal roots contain afferents from low-threshold mechanoreceptors located in the rectal wall, and that these afferents monitor the filling state and contraction level of the rectum.     

Neurophysiological evaluation of sexual dysfunction in familial amyloidotic polyneuropathy - Portuguese type

Familial amyloidotic polyneuropathy (FAP) - Portuguese type, is an autosomal dominant polyneuropathy related with an abnormal transthyrretin (TTR Met 30). In males, the first complaint can be sexual dysfunction. Fifteen FAP patients, mean age 37 ± 7.7 years, mean disease duration 5.2 ± 2.2 years, all males, complaining of sexual dysfunction were studied with pudendal evoked potentials (PEP), bulbocavernous reflex (BCR) and sympathetic skin response (SSR). PEP and BCR reflect the central somatosensory pathways and sacral arch functioning; SSR relates with autonomic pathways. The aims of this study were: to correlate clinical and EMG scores with somatic and autonomic fibres involvement; to evaluate the timing of somatic and autonomic nerves lesion in disease evolution. Results showed: that PEP and BCR abnormalities have a statistically significant correlation with clinical and EMG scores; abnormal SSR in the plant precede other clinical or EMG abnormalities in the present study.     

Principles of Sacral Nerve Stimulation (SNS) for the Treatment of Bladder and Urethral Sphincter Dysfunctions

Objectives. Sacral nerve stimulation (SNS) (Medtronic, Inc., Minneapolis, MN) is an exciting new treatment for refractory voiding disorders including urinary incontinence, retention, and voiding dysfunction. It is known that both voiding and continence reflex mechanisms are organized in the sacral spinal cord and that pathologic conditions can alter the balance between these two opposing mechanisms. Methods. The background and surgical technique of SNS will be presented. This will be followed by a discussion of hypotheses on how SNS works. Results. The beneficial effects of SNS are most reasonably attributed to activation of somatic afferent axons in the sacral spinal roots. This evoked afferent activity in turn modulates sensory processing and micturition reflex pathways in the spinal cord. Hyperactive voiding can be suppressed by direct inhibition of bladder preganglionic neurons as well as inhibition of interneuroneal transmission in the afferent limb of the micturition reflex. On the other hand, voiding in patients with urinary retention can be facilitated by inhibition of reflex pathways to the urethral outlet (guarding reflexes). Conclusions. SNS, a nonablative, minimally invasive technique for urologists, holds great promise for a large number of patients who suffer debilitating and refractory urinary symptoms.     

Distribution of somatic and visceral primary afferent fibres within the thoracic spinal cord of the cat

Transport of horseradish peroxidase (HRP) through somatic and visceral nerve fibres was used to study the patterns of termination of somatic and visceral primary afferent fibres within the lower thoracic segments of the cat's spinal cord. A concentrated solution of HRP was applied for at least 5 hours to the central end of the righ greater splanchnic nerve and of the left T9 intercostal nerve of adult cats. Some animals remained under chloralose anaesthesia for the duration of the HRP transport times (up to 53 hours) whereas longer HRP application and transport times (4-5 days) were allowed in animals that recovered from barbiturate anaesthesia. Somatic afferent fibres and varicosities (presumed terminals) were found in laminae I, II, III, IV, and V of the ipsilateral dorsal horn and in the ipsilateral Clarke's column. The density of the somatic projection was particularly high in the superficial dorsal horn. In parasagittal sections of the cord, bundles of somatic fibres were seen joining the dorsal horn from the dorsal roots via the dorsal columns and Lissauer's tract. A medio-lateral somatotopic arrangement of somatic afferent terminations was observed, with afferent fibres from the ventral parts of the dermatome ending in the medial dorsal horn and afferent fibres from the dorsal parts of the dermatome ending in the lateral dorsal horn. The total rostro-caudal extent of the somatic projection through a single spinal nerve was found to be of 2 and 2/3 segments, including the segment of entry, the entire segment rostral to it and two-thirds of the segment caudal to it. A lateral to medial shift in the position of the somatic projection was observed in the rostro-caudal axis of the cord. Visceral afferent fibres and varicosities (presumed terminals) were seen in laminae I and V of the ipsilateral dorsal horn. The density of the visceral projection to the dorsal horn was substantially lower than that of the somatic projection. Visceral afferent fibres reached the dorsal horn via Lissauer's tract and joined a lateral bundle of fine fibres that run along the lateral edge of the dorsal horn. The substantia gelatinosa (lamina II) appeared free of visceral afferent fibres. These results are discussed in relation to the mechanisms of viscero-somatic convergence onto sensory pathways in the thoracic spinal cord.     

Electro-acupuncture stimulation to a hindpaw and a hind leg produces different reflex responses in sympathoadrenal medullary function in anesthetized rats

The effects of electro-acupuncture stimulation (EAS) of two different areas of a hindlimb with different stimulus intensities on sympathoadrenal medullary functions were examined in anesthetized artificially ventilated rats. Two needles of 160 microm diameter and about 5 mm apart were inserted about 5 mm deep into a hindpaw (Chungyang, S42) or a hind leg (Tsusanli, S36) and current of various intensities passed to excite various afferent nerve fiber groups at a repetition rate of 20 Hz and pulse duration of 0.5 ms for 30-60 s. Fiber groups of afferent nerves stimulated in a hindlimb were monitored by recording evoked action potentials from the afferents innervating the areas stimulated. The sympathoadrenal medullary functions were monitored by recording adrenal sympathetic efferent nerve activity and secretion rates of catecholamines from the adrenal medulla. EAS of a hindpaw at a stimulus strength sufficient to excite the group III and IV somatic afferent fibers produced reflex increases in both adrenal sympathetic efferent nerve activity and the secretion rate of catecholamines. EAS of a hind leg at a stimulus strength sufficient to excite the group III and IV afferent fibers produced reflex responses of either increases or decreases in sympathoadrenal medullary functions. All responses of adrenal sympathetic efferent nerve activity were lost after cutting the afferent nerves ipsilateral to the stimulated areas, indicating that the responses are the reflexes whose afferents nerve pathway is composed of hindlimb somatic nerves. It is concluded that electro-acupuncture stimulation of a hindpaw causes an excitatory reflex, while that of a hind leg causes either excitatory or inhibitory reflex of sympathoadrenal medullary functions, even if both group III and IV somatic afferent fibers are stimulated.     

Influences of pelvic floor structures and sacral innervation on the response to distension of the cat rectum

The contributions to the rectal response to distension of the pelvic floor structures surrounding the rectum and of the sacral spinal innervation have never been studied. Using paralysed intercollicularly decerebrate, anaesthesia-free cats, we studied pressure-volume relationships during slow ramp distensions of the rectum. Results obtained from animals with intact pelvic cavities were compared with those following mobilization of the rectum from the pelvic floor musculature. To assess the influences of spinal outflow and afferent input, rectal pressure-volume relationships were measured in the mobilized rectum following bilateral sequential transection of the spinal roots S1 to S3, first dorsal, then ventral. Isolation of the rectum from the pelvic floor structures resulted in a decrease in balloon volume in the lower range of distension pressure but did not affect volumes at higher pressures. The only afferent effect was seen after sectioning of dorsal roots S1, which resulted in a decrease in balloon volume. The only efferent effect was seen after sectioning of ventral roots S3, which decreased balloon volume further. In conclusion, the rectal response to distension depends on the properties of the rectal wall. It may be influenced by somatic inputs, inputs from the myenteric nervous plexus, and from the parasympathetic and sympathetic nervous systems. Afferent inputs and spinal autonomic reflexes may decrease the tone of the rectal musculature during distension.     

Influences of neck afferents on sympathetic and respiratory nerve activity

It is well established that the vestibular system influences the sympathetic nervous system and the respiratory system; presumably, vestibulosympathetic and vestibulorespiratory responses participate in maintaining stable blood pressure and blood oxygenation during movement and changes in posture. Many brainstem neurons that generate vestibulospinal reflexes integrate signals from the labyrinth and neck muscles to distinguish between head movements on a stable body and whole body movements. In the present study, responses were recorded from the splanchnic (sympathetic), hypoglossal (inspiratory) and abdominal (expiratory) nerves during stimulation of the C2 dorsal root ganglion or C2 or C3 nerve branches innervating dorsal neck muscles. Stimulation of neck afferents using low current intensities, in many cases less than twice the threshold for producing an afferent volley recordable from the cord dorsum, elicited changes in sympathetic and respiratory nerve activity. These data suggest that head rotation on a stable body would elicit both cervical and vestibular inputs to respiratory motoneurons and sympathetic preganglionic neurons. The effects of cervical afferent stimulation on abdominal, splanchnic and hypoglossal nerve activity were not abolished by transection of the brainstem caudal to the vestibular nuclei; thus, pathways in addition to those involving the vestibular nuclei are involved in relaying cervical inputs to sympathetic preganglionic neurons and respiratory motoneurons. Transection of the C1-3 dorsal roots enhanced responses of the splanchnic and abdominal nerves to pitch head rotations on a fixed body but diminished responses of the hypoglossal nerve. Thus, neck and vestibular afferent influences on activity of respiratory pump muscles and sympathetic outflow appear to be antagonistic, so that responses will occur during whole body movements but not head movements on a stationary trunk. In contrast, neck and vestibular influences on tongue musculature are complementary, presumably to produce tongue protrusion either during movements of the head alone or of the whole body.     

Change in the background afferent influx to the spinal cord after transsecting the sciatic nerve and early enhancement of monosynaptic reflexes]

Background impulse activity (BIA) of separate fibres of dorsal roots of 5 lumbar segment of rats after one-sided cutting of the sciatic nerve which caused early enhancement of monosynaptic segmental reflexes (5 days after operation) has been recorded. It is revealed that afferent fibres with BIA are found more rarely on side of cutting than on the opposite side and frequency of background activity is lower than in the opposite root. It is concluded that development of spontaneous activity of the spinal ganglion neurons after cutting nerves does not ensure a higher BIA level in afferent fibres. The given phenomenon cannot be a reason of early enhancement of monosynaptic reflexes after the nerve cutting.     

Afferent innervation of the lower oesophageal sphincter of the cat. An HRP study

Labeling of afferent neurons by the retrograde axonal transport of horseradish peroxidase (HRP) was performed on anaesthetized cats in order to examine the afferent innervation of the lower oesophageal sphincter (LOS), involving both the vagal and the sympathetic nerves. The labeled cells, whose fibres follow the sympathetic pathways were found in dorsal root ganglia from T1 to L2. Nerve section experiments indicated that the main pathways involved were the splanchnic nerves, as expected from classical data. Additional pathways passing through the sympathetic cardiac branch emerging from the stellate ganglion and the thoracic sympathetic branches were also evidenced. This work corroborated the electrophysiological data showing the richness of the LOS sensory vagal innervation. Nevertheless, in this case the difficulties related to the HRP technique are particularly enhanced since the abdominal sensory vagal fibres can be affected by HRP injections.     

Innervation of the guinea pig trachea: a quantitative morphological study of intrinsic neurons and extrinsic nerves

The innervation of the guinea pig trachea was studied in wholemount preparations stained for acetylcholinesterase, catecholamines, and substance P immunoreactivity and by electron microscopy. The majority of parasympathetic and afferent nerve fibres arrive from the vagus via branches of the recurrent laryngeal nerves. The recurrent laryngeal nerves are composed of several fascicles comprising 600-700 small myelinated fibres (2-5 microns diameter) and about 1,000-2,000 unmyelinated fibres; both components exit from the nerve and project in fine branches to the trachea. A separate component of 200-250 large myelinated fibres (more than 5 microns diameter) runs the full length of the nerve and innervates the striated muscles of the larynx. The recurrent laryngeal nerves are slightly asymmetric in their origin, length, number, and composition of fibres, with the right nerve being shorter but with more numerous and thinner myelinated fibres. At the distal end of the recurrent nerve, a fine branch called the ramus anastomoticus connects it to the superior laryngeal nerve. In the tracheal plexus, there are on average 222 ganglion cells (range 166-327), distributed mostly in small ganglia of 12 or fewer neurons. The ganglionated plexus is situated entirely outside the tracheal wall, overlying the smooth muscle. Ligation experiments show that sympathetic nerve fibres reach the trachea with the recurrent nerves via anastomoses between the sympathetic chain and vagus nerves, or occasionally with recurrent nerves directly, the largest being at the level of the ansa subclavia. There are also perivascular sympathetic nerve plexuses. Substance P immunoreactive fibres enter the trachea from the vagus nerves and by pathways similar to those of sympathetic nerves. There are also paraganglion cells within the recurrent laryngeal nerve that contain catecholamines and are surrounded by substance P immunoreactive fibres. After cervical vagotomy, all the large myelinated fibres of the ipsilateral recurrent laryngeal nerve degenerate and so do all but 10 or 20 small myelinated fibres and all but a few unmyelinated fibres. Degenerating fibres are found within the entire tracheal plexus, indicating bilateral innervation. The small myelinated fibres that survive cervical vagotomy probably represent sympathetic or afferent nerves with their cell bodies located in sympathetic or dorsal root ganglia.     

The projection of the medial and posterior articular nerves of the cat's knee to the spinal cord

We studied the spinal projections of the medial and posterior articular nerves (MAN and PAN) of the knee joint in the cat with the aid of the transganglionic transport of horseradish peroxidase. The afferent fibers of the MAN entered the spinal cord via the lumbar dorsal roots L5 and L6 and those of the PAN entered via the dorsal roots L6 and L7. Within the dorsal root ganglia, most labeled neurons had small to medium diameters. A relatively higher number of medium-size cell bodies were labeled from the PAN than from the MAN. In the spinal cord labeled MAN afferent fibers and terminations were most dense in the L5 and L6 segments, and those of the PAN were most dense in L6 and L7, that is, in the respective segments of entry. Labeled afferent fibers from both nerves projected rostrally at least as far as L1 and caudally as far as S2. Labeled fibers were found in Lissauer's tract as well as in the dorsal column immediately adjacent to the dorsal horn. In the spinal gray matter, both nerves had two main projection fields, one in the cap of the dorsal horn in lamina I, the other in the deep dorsal horn in laminae V-VI and the dorsal part of lamina VII. Both nerves, but particularly the PAN, projected to the medial portion of Clarke's column. No projection was found to laminae II, III, and IV of the dorsal horn or to the ventral horn. Since these findings parallel observations on hindlimb muscle afferent fibers, the present data support the existence of a common pattern for the central distribution of deep somatic afferent fibers.     

Unitary discharges in dorsal and ventral roots after the administration of 4-aminopyridine in the cat

The administration of 4-aminopyridine (4-AP) in decerebrate paralyzed cats induces centrifugal rhythmic discharges in both ventral and dorsal roots. This study describes the mode of discharge of individual primary afferents as well as some ventral root fibers. Several patterns of antidromic discharge have been observed in primary afferents after the administration of 4-AP. A large proportion of the units (n = 96; 53%) showed rhythmic bursts of discharge related (n = 41) or not (n = 55) to the ongoing rhythmic activity in the peripheral nerves. Other units (n = 86; 47%) discharged either tonically, sporadically or had no antidromic activity at all. The conduction velocity of the non-bursting units was significantly higher (89.7 +/- 18.4 m/s) than that of the bursting units (70.6 +/- 15.4 m/s; P less than 0.01). Ventral roots showed rhythmic activity although less intense than that of the dorsal roots. As in dorsal roots, some fibers showed a rhythmical pattern of discharge related to the mass activity recorded from whole dorsal roots or peripheral nerves, while other units were not related. It is concluded that bursting activity which occurs in peripheral nerves after the administration of 4-AP is mainly the result of the antidromic activation of medium to small size primary afferent fibers.     

Supraspinal regulation of spinal reflex discharge into cardiac sympathetic nerves

(1) In chloralose anaesthetized cats, reflex responses were recorded in inferior cardiac nerves following stimulation of intercostal nerves and hind limb afferent nerves. (2) In 80% of cats, a long latency reflex response alone was recorded, whereas, in the others, a short and long latency response was present to intercostal nerve stimulation. (3) In cats displaying only a long latency somatocardiac reflex response, damage to the ventral quadrant of the ipsilateral cervical spinal cord, through which runs a bulbospinal inhibitory pathway, resulted in the appearance of shorter latency reflexes to intercostal nerve stimulation. Lesions elsewhere in the cervical cord did not do this. (4) The characteristics of the early responses indicated that they were somatosympathetic reflexes and not dorsal root reflexes. (5) The early reflexes remained and the late reflex disappeared on subsequent complete transection of the spinal cord. The early reflexes were therefore spinal reflexes, and suppressed in the animal with cord intact. (6) Lesions at C4, which included a contralateral hemisection and a section of dorsal columns extending into the dorsal part of the lateral funiculus, abolished the inhibition of a sympathetic reflex that followed stimulation of some somatic afferent nerve fibres. These sections did not release the spinal reflex. Therefore, this reflex inhibition was not responsible for the suppression of the spinal somatosympathetic reflex. (7) The descending inhibitory influence on the segmental reflex pathway was not antagonized by strychnine, bicuculline or picrotoxin. (8) The possibility is discussed that the spinal reflex pathway into cardiac sympathetic nerves is tonically inhibited by a bulbospinal pathway originating from the classical depressor region of the ventromedial reticular formation.     

Ventral root potentials of the cat's sacrococcygeal segments evoked by stimulation of intact and transected dorsal roots

The latency and amplitude of reflex-evoked potentials in the sacrococcygeal ventral roots of acute spinalized cats were investigated. The characteristics of the potentials were examined in response to electrical stimulation of intact and acutely transected dorsal roots. We found that: the last sacral and caudal (coccygeal) segments of the cat's spinal cord are endowed with electrophysiologic characteristics that distinguish them from other spinal segments (e.g., L7-S1); afferent stimulation of the corresponding intact dorsal roots evokes in the ventral root of segment S2 a small monosynaptic response, whereas no monosynaptic response is seen in segment Ca6; acute transection of the dorsal roots provokes an increment of the monosynaptic response in all segments studied except for Ca6; rhizotomy provokes in Ca5 the appearance of polysynaptic responses to electrical stimulation of the corresponding dorsal root; and transection of the cutaneous afferent fibers of the coccygeal motoneurons resulted in an increment of monosynaptic and polysynaptic responses, indicating the removal of inhibitory effects.     

Regulation of peripheral inflammation by spinal adenosine: role of somatic afferent fibers

Spinal administration of adenosine inhibits neutrophil accumulation in skin. The neural pathways mediating this action are unknown. We investigated individually the roles of capsaicin sensitive primary afferent fibers, sympathetic efferent fibers, and dorsal roots in this regulation. One week after implantation of intrathecal (IT) catheters into rats, the adenosine receptor agonist cyclohexyladenosine (CHA) or vehicle was injected intrathecally. Inflammatory skin lesions were induced by intradermal carrageenan. Three hours later, skin was harvested and assayed for neutrophils by measuring myeloperoxidase (MPO) activity. Intrathecal CHA (5 microg/kg) decreased neutrophil infiltration into skin lesions. Nociceptive peptides were largely depleted from central terminals of primary afferents by IT capsaicin pretreatment. This depletion had no effect on either basal neutrophil infiltration or CHA-mediated modulation. Sympathetic fibers were largely destroyed by systemic 6-hydoxydopamine (6-OHDA) pretreatment; sympathectomy did not affect basal neutrophil infiltration or block its suppression by IT CHA. Thus, spinal adenosine effects on skin neutrophil trafficking appear to be independent of sympathetic nerves and primary afferent peptides, although incomplete lesions by chemical pretreatments may have confounded our results. Sensory fibers were interrupted by prior unilateral dorsal rhizotomies. This procedure had no effect on neutrophil accumulation in control rats. However, rhizotomy blocked the CHA effect, with MPO levels 45 +/- 18% greater in denervated than control skin in IT CHA-treated animals (P < 0.05). It is clear that the spinal adenosine effect requires intact somatic connectivity. Information on pain and inflammation in the periphery is transmitted to the nervous system, where increased spinal adenosine levels can suppress peripheral inflammation.     

Central distribution of afferent pathways from the uterus of the cat.

Afferent pathways from the uterus of the cat were labeled by injections of horseradish peroxidase (HRP), wheat germ agglutinin-HRP, or fluorescent dyes into the uterine cervix and uterine horns. Afferent input to the uterus arises from small to medium size neurons (average size 31 x 28 microns) in dorsal root ganglia at many levels of the spinal cord (T12-S3). The segmental origin correlates with the location of the afferent terminal field in the uterus. Eighty-seven percent of the dorsal root ganglion cells (average, 822 on one side) innervating the cervix are located in sacral ganglia, whereas 97% of the cells innervating the uterine horn (average 479 on one side) are located in lumbar ganglia. Double dye labeling experiments indicate that a small percentage (average 15%) of lumbar neurons innervating the uterine cervix also innervate the uterine horn. The majority (70-80%) of afferent input to the uterine cervix passes through the pelvic nerve and the remainder through the pudendal nerve, whereas afferent input to the uterine horn must travel in sympathetic nerves. Ovariectomy (10-14 days) did not change significantly the number, sizes, or segmental distribution of uterine afferent neurons. In some cats (25%) injections of WGA-HRP into the uterine cervix labeled neurons (90-125 per animal) in lamina VII in the S2 spinal segment in the region of the sacral parasympathetic nucleus. Central projections of uterine horn afferent neurons were not labeled; however, afferent projections from the cervix were detected in the sacral spinal cord. The most prominent labeling was present in Lissauer's tract and in lamina I and outer lamina II on the lateral edge of the dorsal horn. From this region some labeled axons extended through lamina V into the dorsal gray commissure. Very few afferents were labeled on the medial side of the dorsal horn. These results are discussed in regard to the physiological function of uterine afferents and the possible transmitter role of vasoactive intestinal polypeptide, which is present in a large percentage (70%) of cervical afferent neurons.     

The role of neuropeptides in the sacral autonomic reflex pathways of the cat

Immunohistochemical and pharmacological studies were conducted to examine the origin and function of peptidergic nerves in the sacral autonomic system of the cat. Leucine-enkephalin (L-Enk) immunoreactivity was identified in nerve terminals in peripheral ganglia on the surface of the urinary bladder and in the parasympathetic nucleus in the sacral spinal cord. In colchicine-treated animals L-Enk was also detected in sacral preganglionic neurons (sPGN) identified by retrograde transport of a fluorescent dye. L-Enk terminals in bladder ganglia are believed to arise from sPGN since the terminals were eliminated by transection of the sacral ventral roots. Pharmacological studies indicated that exogenous as well as endogenously released enkephalins have an inhibitory action at both ganglionic and spinal sites in the sacral outflow to the urinary bladder. Peptides were also associated with afferents nerves in the sacral autonomic system. The distribution of substance P, VIP and cholecystokinin in the sacral dorsal horn paralleled the distribution of visceral afferent projections as demonstrated with HRP techniques. Dye labeling combined with immunohistochemistry revealed that some dorsal root ganglion cells projecting to the pelvic viscera contain substance P or VIP.     

Localization of NADPH diaphorase in the lumbosacral spinal cord and dorsal root ganglia of the cat

The distribution of NADPH-d activity in the spinal cord and dorsal root ganglia of the cat was studied to evaluate the role of nitric oxide in lumbosacral afferent and spinal autonomic pathways. At all levels of the spinal cord NADPH-d staining was present in neurons and fibers in the superficial dorsal horn and in neurons around the central canal and in the dorsal commissure. In addition, the sympathetic autonomic nucleus in the rostral lumbar segments exhibited prominent NADPH-d cellular staining whereas the parasympathetic nucleus in the sacral segments was not well stained. The most prominent NADPH-d activity in the sacral segments occurred in fibers extending from Lissauer's tract through laminae I along the lateral edge of the dorsal horn to lamina V and the region of the sacral parasympathetic nucleus. These fibers were very similar to VIP-containing and pelvic nerve afferent projections in the same region. They were prominent in the S₁–S₃ segments but not in adjacent segments (L₆–L₇ and Cx₁) or in thoracolumbar and cervical segments. NADPH-d activity and VIP immunoreactivity in Lissauer's tract and the lateral dorsal horn were eliminated or greatly reduced after dorsal-ventral rhizotomy (S₁–S₃), indicating the fibers represent primary afferent projections. A population of small diameter afferent neurons in the L₇–S₂ dorsal root ganglia were intensely stained for NADPH-d. The functional significance of the NADPH-d histochemical stain remains to be determined; however, if NADPH-d is nitric oxide synthase then this would suggest that nitric oxide may function as a transmitter in thoracolumbar sympathetic preganglionic efferent pathways and in sacral parasympathetic afferent pathways in the cat. © 1994 Wiley-Liss, Inc.