Projections of pelvic autonomic neurons within the lower bowel of the male rat: an anterograde labelling study

The parasympathetic and sensory innervation of the proximal and distal colon in male mice

Introduction

The distributions of extrinsic neurons innervating the colon show differences in experimental animals from humans, including the vagal and spinal parasympathetic innervation to the distal colon. The neuroanatomical tracing to the mouse proximal colon has not been studied in details. This study aimed to trace the locations of extrinsic neurons projecting to the mouse proximal colon compared to the distal colon using dual retrograde tracing.

Methods

The parasympathetic and sensory neurons projecting to colon were assessed using Cholera Toxin subunit B conjugated to Alexa-Fluor 488 or 555 injected in the proximal and distal colon of the same mice.

Results

Retrograde tracing from the proximal and distal colon labeled neurons in the dorsal motor nucleus of the vagus (DMV) and the nodose ganglia, while the tracing from the distal colon did not label the parasympathetic neurons in the lumbosacral spinal cord at L6-S1. Neurons in the pelvic ganglia which were cholinergic projected to the distal colon. There were more neurons in the DMV and nodose ganglia projecting to the proximal than distal colon. The right nodose ganglion had a higher number of neurons than the left ganglion innervating the proximal colon. In the dorsal root ganglia (DRG), the highest number of neurons traced from the distal colon were at L6, and those from the proximal colon at T12. DRG neurons projected closely to the cholinergic neurons in the intermediolateral column of L6 spinal cord. Small percentages of neurons with dual projections to both the proximal and distal colon existed in the DMV, nodose ganglia and DRG. We also observed long projecting neurons traced from the caudal distal colon to the transverse and proximal colon, some of which were calbindin immunoreactive, while there were no retrogradely labeled neurons traced from the proximal to distal colon.

Discussion

These data demonstrated that the vagal motor and motor and sensory neurons innervate both the proximal and distal colon in mice, and the autonomic neurons in the intermediate zone of the lumbosacral spinal cord do not project directly to the mouse colon, which differs from that in humans.

Interstitial cells of Cajal and human colon motility in health and disease

Our understanding of human colonic motility, and autonomic reflexes that generate motor patterns, has increased markedly through high-resolution manometry. Details of the motor patterns are emerging related to frequency and propagation characteristics that allow linkage to interstitial cells of Cajal (ICC) networks. In studies on colonic motor dysfunction requiring surgery, ICC are almost always abnormal or significantly reduced. However, there are still gaps in our knowledge about the role of ICC in the control of colonic motility and there is little understanding of a mechanistic link between ICC abnormalities and colonic motor dysfunction. This review will outline the various ICC networks in the human colon and their proven and likely associations with the enteric and extrinsic autonomic nervous systems. Based on our extensive knowledge of the role of ICC in the control of gastrointestinal motility of animal models and the human stomach and small intestine, we propose how ICC networks are underlying the motor patterns of the human colon. The role of ICC will be reviewed in the autonomic neural reflexes that evoke essential motor patterns for transit and defecation. Mechanisms underlying ICC injury, maintenance, and repair will be discussed. Hypotheses are formulated as to how ICC dysfunction can lead to motor abnormalities in slow transit constipation, chronic idiopathic pseudo-obstruction, Hirschsprung's disease, fecal incontinence, diverticular disease, and inflammatory conditions. Recent studies on ICC repair after injury hold promise for future therapies.

Characterization of haustral activity in the human colon

Contraction patterns of the human colon are rarely discussed from the perspective of its haustra. Colonic motility was analyzed in 21 healthy subjects using 84-sensor manometry catheters with 1-cm sensor spacing. Capsule endoscopy and manometry showed evidence of narrow rhythmic circular muscle contractions. X-ray images of haustra and sensor locations allowed us to identify manometry motor activity as intrahaustral activity. Two common motor patterns were observed that we infer to be associated with individual haustra: rhythmic pressure activity confined to a single sensor, and activity confined to a section of the colon of 3-6 cm length. Intrahaustral activity was observed by 3-4 sensors. Approximately 50% of the haustra were intermittently active for ∼30% of the time; 2,402 periods of haustral activity were analyzed. Intrahaustral activity showed rhythmic pressure waves, propagating in mixed direction, 5-30 mmHg in amplitude at a frequency of ∼3 cpm (range 2-6) or ∼12 cpm (range 7-15), or exhibiting a checkerboard segmentation pattern. Boundaries of the haustra showed rhythmic pressure activity with or without elevated baseline pressure. Active haustra often showed no boundary activity probably allowing transit to neighboring haustra. Haustral boundaries were seen at the same sensor for the 6- to 8-h study duration, indicating that they did not propagate, thereby likely contributing to continence. The present study elucidates the motility characteristics of haustral boundaries and the nature of intrahaustral motor patterns and paves the way for investigating their possible role in pathophysiology of defecation disorders.NEW & NOTEWORTHY Here, we present the first full characterization and quantification of motor patterns that we infer to be confined to single haustra, both intrahaustral activity and haustral boundary activity, in the human colon using high-resolution manometry. Haustral activity is intermittent but consistently present in about half of the haustra. Intrahaustral activity presents as a cyclic motor pattern of mixed propagation direction dominated by simultaneous pressure waves that can resolve into checkerboard segmentation, allowing for mixing, absorption, and stool formation.

Neuropeptides' Hypothalamic Regulation of Sleep Control in Children Affected by Functional Non-Retentive Fecal Incontinence

Functional non-retentive fecal incontinence (FNRFI) is a common problem in pediatric age. FNRFI is defined as unintended loss of stool in a 4-year-old or older child after organic causes have been excluded. FNRFI tends to affects up to 3% of children older than 4 years, with males being affected more frequently than females. Clinically, children affected by FNRFI have normal intestinal movements and stool consistency. Literature data show that children with fecal incontinence have increased levels of separation anxiety, specific phobias, general anxiety, attention-deficit/hyperactivity disorder (ADHD), and oppositional defiant disorder. In terms of possible relationship between incontinence and sleep, disorders of sleep organization have been observed in the pathogenesis of enuresis so generating the hypothesis that the orexinergic system may have a crucial role not only for the sleep organization per se but also for the sphincterial control in general. This study aimed to focus on specific neurophysiological aspects to investigate on the possible relationship between sleep organizational abnormalities and FNRFI. Specifically, we aimed to measure orexin serum levels in children with FNRFI and assess their polysomnographic sleep macrostructure patterns. Two study groups were considered: FNFRI (n = 45) and typically developed (TD) (n = 45) group. In both groups, sleep patterns and respiratory events were assessed by polysomnographic recordings (PSG) during a period of two nights at least, and plasma levels of Orexin-A were measured in each participant. The findings of this initial investigation seem to support a major role of Orexin-A in sleep organization alterations in children with FNFRI. Also, our data suggest that sleep habits evaluation should be considered as screening and complementary tool for the diagnosis of fecal incontinence in children.

Tonic contraction develops in the colon during anaphylactic hypotension in anesthetized rats

Diarrhea is a gastrointestinal symptom associated with systemic anaphylaxis and could be induced by increased colonic motility. We determined colonic motility and expulsion by measuring the intracolonic pressure (ICP) and expelled fluid weight in anesthetized rats during anaphylactic hypotension. Substantial systemic hypotension occurred in every sensitized rat after antigen injection. One min after antigen injection, ICP began to increase and remained elevated for 5 min, which was revealed to represent tonic contraction by the video-recording procedure, and was accompanied by increased colonic fluid expulsion. Parasympathectomy composed of subdiaphragmatic vagotomy combined with pelvic nerve transection reduced the duration of the tonic contraction, but not expelled colonic fluid. Furthermore, denervation of afferent parasympathetic nerves produced essentially the same effect as parasympathectomy. Sympathectomy did not significantly change any parameters. In conclusion, the colonic motility during anaphylactic hypotension is characterized by 5-min lasting tonic contraction which is associated with increased colonic fluid expulsion and is involved by parasympathetic nerves, especially their afferents, but not sympathetic nerves, in anesthetized rats.

Remodeling of Rectal Innervation After Pullthrough Surgery for Hirschsprung Disease: Relevance to Criteria for the Determination of Retained Transition Zone

BACKGROUND

After pullthrough surgery for Hirschsprung disease (HSCR), Glut1-positive submucosal nerve hypertrophy is used to diagnose retained transition zone in the neorectum. We hypothesized that pelvic nerves, severed during pullthrough surgery, sprout into the neorectum to mimic transition zone.

METHODS

The density (nerves/100x field) and maximum diameter of Glut1-positive submucosal nerves were measured in biopsies and redo resections from 20 patients with post-pullthrough obstructive symptoms. Their original and/or redo resections excluded unequivocal features of transition zone (myenteric hypoganglionosis or partial circumferential aganglionosis) in 17. Postoperative values were compared with control data from 28 cadaveric and 6 surgical non-HSCR specimens, and 14 primary HSCR resections. When possible, nerves were tracked from attached native pelvic soft tissue or aganglionic rectal cuff into the pulled-through colon.

RESULTS

Glut1-positive submucosal nerves were not present in the 11 colons of non-HSCR infants less than 1 year of age, except sparsely in the rectum. In 17 older non-HSCR controls, occasional Glut1-positive nerves were observed in prerectal colon and were larger and more numerous in the rectum. In redo resections, Glut1-positive submucosal innervation in post-pullthrough specimens did not differ significantly from age-appropriate non-HSCR rectal controls and pelvic Glut1-positive nerves were never observed to penetrate the pulled-through colon. However, the density and caliber of Glut1-positive nerves in the neorectums were significantly greater than expected based on the prerectal location from which the pulled-through bowel originated.

CONCLUSIONS

Submucosal innervation in post-pullthrough specimens does not support the hypothesis that native pelvic nerves innervate the neorectum, but suggests remodeling occurs to establish the age-appropriate density and caliber of rectal Glut1-positive innervation. The latter should not be interpreted as transition zone pullthrough in a rectal biopsy from a previously done pullthrough.

Neural interrelationships of autonomic ganglia from the pelvic region of male rats

The aims of the present study were to describe, in male rats, the anatomical organization of the major and accessory pelvic ganglia (MPG, AG; respectively), the interrelationship of the pelvic plexus components, and the morphometry of the pelvic postganglionic neurons. Anatomical, histochemical and histological studies were performed in anesthetized adult Wistar male rats. We found that the pelvic plexus consists of intricate neural circuits composed of two MPG, and three pairs of AG (AGI, AGII, AGIII) anatomically interrelated through ipsilateral and contralateral commissural nerves. Around 30 nerves emerge from each MPG and 17 from AGI and AGII. The MPG efferent nerves spread out preganglionic information to several pelvic organs controlling urinary, bowel, reproductive and sexual functions, while AG innervation is more regional, and it is confined to reproductive organs located in the rostral region of the urogenital tract. Both MPG and AG contain nerve fascicles, blood vessels, small intensely fluorescent cells, satellite cells and oval neuronal somata with one to three nucleoli. The soma area of AG neurons is larger than those of MPG neurons (p < 0.005). The MPG contains about 75% of the total pelvic postganglionic neurons. Our findings corroborated previous reports about MPG inputs, and add new information regarding pelvic ganglia efferent branches, AG neurons (number and morphometry), and neural interrelationship between the pelvic plexus components. This information will be useful in designing future studies about the role of pelvic innervation in the physiology and pathophysiology of pelvic functions.

S1 nerve is the most efficient nerve rootlet innervating the anal canal and rectum in rats

Autonomic and somatic components participate in the defecation process in mammals, combining signals from the brainstem and forebrain. The innervation pattern involved in micturition in rats has been well studied, while defecation has been less studied. The aim of the present study was to identify the most important sensory and motor nerves of the anal canal and rectum involved in defecation. The amplitudes of evoked potential of the anal canal and rectum were higher when L6 and S1 ventral rootlets were stimulated, compared with the other segments (ANOVA and Tukey's post hoc test, all P < 0.05). The S1 segment was more strongly cholera toxin subunit B conjugated to horseradish peroxidase (CB-HRP) positive compared with the other segments (ANOVA and Tukey's post hoc test, P < 0.05). Ventral spinal rootlets of L6 and S1 mainly contributed to the pressure change in the anal canal and rectum when the ventral spinal rootlets from L5 to S3 were stimulated electrically. In conclusion, many afferent and efferent nerves innervate the anal canal and rectum and are involved in defecation, but the S1 nerve rootlet could be the most efficient one. These results could provide a basis for defecation reconstruction, especially for patients with spinal cord injuries.

End-to-side neurorrhaphy for nerve repair and function rehabilitation

BACKGROUND

End-to-side neurorrhaphy is a promising procedure for nerve repair in peripheral nerve injury. However, in previous studies, this technique was limited to somatic nerves. The present study was designed to investigate the feasibility of nerve regeneration after end-to-side neurorrhaphy between autonomic nerve and somatic nerve.

MATERIALS AND METHODS

Thirty adult male Sprague-Dawley rats were randomly divided into the following three groups (n = 10 per group) for different treatments: (1) end-to-side neurorrhaphy group, the left L6 and S1 spinal nerves were transected in the dura, and the distal stump of L6 ventral root (L6VR) was sutured to the lateral face of L4 ventral root (L4VR) through end-to-side coaptation; (2) no repair group, the rats received the same operation as the end-to-side neurorrhaphy group but without coaptation; (3) control group, the rats received the same operation as the end-to-side neurorrhaphy group but the L6VR was preserved. After 4 month, the origin and mechanism of nerve regeneration were evaluated by retrograde nerve tracing. Morphologic and functional properties of the regenerated nerve were investigated by morphologic examination and intravesical pressure measurement.

RESULTS

Retrograde nerve tracing indicated that the new neural reflex pathway was successfully established, and the main regeneration mechanism was axon collateral sprouting. Morphologic examination and intravesical pressure measurement indicated prominent axonal regeneration and good bladder functional rehabilitation in the neurorrhaphy group. Wet weight and morphology of left extensor digitorum longus muscles appeared no detrimental effect on the donor nerve.

CONCLUSIONS

These results indicated that the somatic motor axons growth into autonomic nerve may be achieved through axon collateral sprouting for nerve repair and function rehabilitation after end-to-side neurorrhaphy of autonomic nerve and somatic nerve without apparent impairment of the donor somatic nerve.

Involvement of parasympathetic pelvic efferent pathway in psychological stress-induced defecation

AIM: To investigate the role of the pelvic nerve pathway in stress-induced acceleration of colorectal transit and defecation in rats.

METHODS: Surgical transection of rectal nerves (rectal branches of the pelvic nerve), vagotomy (Vag) or adrenalectomy (Adx) were performed bilaterally in rats. Number of fecal pellet output of these rats was measured during 1-h water avoidance stress (WAS). To evaluate the colonic transit, rats were given phenol red through the catheter indwelled in the proximal colon and subjected to WAS. After WAS session, entire colon and rectum were isolated and distribution of phenol red was measured. Distal colonic and rectal transit was evaluated using glass bead. Rats were inserted the glass bead into the distal colon and evacuation rate of the bead was measured. Neural activation was assessed by immunohistochemical staining of c-Fos and PGP9.5 in colonic whole-mount preparations of longitudinal muscle myenteric plexus (LMMP).

RESULTS: In the sham-operated rats (sham op), WAS significantly increased defecation and accelerated colorectal transit with marked elevation of plasma corticosterone level. Compared with sham-operated rats, increase in the excretion of fecal pellets during WAS was significantly reduced by rectal nerve transection (RNT) (sham op: 6.9 ± 0.8 vs RNT: 4.3 ± 0.6, P < 0.05) or Vag (sham op: 6.4 ± 0.8 vs Vag: 3.7 ± 1.1, P < 0.05), although corticosterone level remained elevated. Adx-rats significantly increased the defecation despite the lower corticosterone level. Distribution pattern of phenol red showed RNT inhibited distal colonic and rectal transit accelerated by WAS, while Vag inhibited proximal colonic transit. Suppression of distal colonic and rectal transit by RNT was further confirmed by the bead evacuation rate (sham op: 80.0% vs RNT: 53.8%). WAS significantly increased the number of c-Fos-immunoreactive neural cells in the LMMP of the proximal and distal colon, whereas c-Fos expression was decreased by RNT in the distal colon (sham op: 9.0 ± 2.0 vs RNT: 4.4 ± 1.0, P < 0.05) and decreased by Vag in the proximal colon.

CONCLUSION: Pelvic nerve conveys WAS stimuli from the brain to the distal colon, and directly activate the myenteric neurons, followed by the increase of its motility.

Sacral neural crest-derived cells enter the aganglionic colon of Ednrb-/- mice along extrinsic nerve fibers

Both vagal and sacral neural crest cells contribute to the enteric nervous system in the hindgut. Because it is difficult to visualize sacral crest cells independently of vagal crest, the nature and extent of the sacral crest contribution to the enteric nervous system are not well established in rodents. To overcome this problem we generated mice in which only the fluorescent protein-labeled sacral crest are present in the terminal colon. We found that sacral crest cells were associated with extrinsic nerve fibers. We investigated the source, time of appearance, and characteristics of the extrinsic nerve fibers found in the aganglionic colon. We observed that the pelvic ganglion neurons contributed a number of extrinsic fibers that travel within the hindgut between circular and longitudinal muscles and within the submucosa and serosa. Sacral crest-derived cells along these fibers diminished in number from fetal to postnatal stages. A small number of sacral crest-derived cells were found between the muscle layers and expressed the neuronal marker Hu. We conclude that sacral crest cells enter the hindgut by advancing on extrinsic fibers and, in aganglionic preparations, they form a small number of neurons at sites normally occupied by myenteric ganglia. We also examined the colons of ganglionated preparations and found sacral crest-derived cells associated with both extrinsic nerve fibers and nascent ganglia. Extrinsic nerve fibers serve as a route of entry for both rodent and avian sacral crest into the hindgut.

Reconstruction of anorectal function through end-to-side neurorrhaphy by autonomic nerves and somatic nerve in rats

BACKGROUND

End-to-side nerve repair is a new tool in managing certain nerve injuries. In previous studies, it was limited to somatic nerves. Herein, we evaluate the feasibility of anorectal reinnervation after end-to-side coaptation of autonomic nerve to somatic nerve.

MATERIALS AND METHODS

Forty adult male Sprague-Dawley rats were randomly divided into three groups: end-to-side coaptation group (n = 16), the left L6 and S1 spinal nerves were transected, and the distal stump of L6 ventral root (L6VR) was sutured to L4VR (L4VR) through end-to-side neurorrhaphy; no coaptation group (n = 12), rats received the same operation as the end-to-side coaptation group but without coaptation; and control group (n = 12), rats received the same operation as the end-to-side coaptation group but the L6VR was preserved. At 16 wk, using double retrograde tracing and histomorphological technique and anorectal manometry, morphological and functional properties of regenerated nerve were investigated.

RESULTS

Retrograde tracing indicated that the new neural pathway was established and the main nerve regeneration mechanism was axon collateral sprouting. Histology showed good axonal regeneration with end-to-side neurorrhaphy. The wet weight and morphology of left tibialis anterior muscles appeared no detrimental effect on donor nerve. Anorectal manometry showed good anorectal functional recovery.

CONCLUSIONS

These results suggest that the somatic motor axon ingrowth into autonomic nerve could be through collateral sprouting after end-to-side coaptation of autonomic nerve to somatic nerve. Our innovative technique of end-to-side coaptation may be of great value in anorectal reinnervation without functional impairment of the donor somatic nerve.

Sympathetic and parasympathetic regulation of rectal motility in rats

INTRODUCTION

The colon and rectum are regulated by the autonomic nervous system (ANS). Abnormalities of the ANS are associated with diseases of the colon and rectum while its modulation is a putative mechanism for sacral nerve stimulation. The purpose of this study is to establish a rat model elucidating the role of the efferent ANS on rectal motility.

MATERIALS AND METHODS

Rectal motility following transection or stimulation of parasympathetic pelvic nerves (PN) or sympathetic hypogastric nerves (HGN) was measured with rectal strain gauge transducers and quantified as a motility index (MI). Colonic transit was measured 24 hours after transection by calculating the geometric center (GC) of distribution of (51)Cr

RESULTS AND DISCUSSION

Transection of PN and HGN decreased MI to 518 +/- 185 g*s (p < 0.05) and increased MI to 5,029 +/- 1,954 g*s (p < 0.05), respectively, compared to sham (975 +/- 243 g*s). Sectioning of PN and HGN decreased transit with GC = 4.9 +/- 0.2 (p < 0.05) and increased transit with GC = 8.1 +/- 0.7 (p < 0.02), respectively, compared to sham (GC = 5.8 +/- 0.3). Stimulation of PN and HGN increased MI to 831 +/- 157% (p < 0.01) and decreased MI to 251 +/- 24% (p < 0.05), respectively.

CONCLUSION

Rectal motility is significantly altered by sectioning or stimulating either HGN or PN. This model may be useful in studying how sacral nerve stimulation exerts its effects and provide insight into the maladies of colonic motility.

Electroacupuncture at acupoint ST-36 promotes contractility of distal colon via a cholinergic pathway in conscious rats

PURPOSE

To investigate the effects and possible mechanism of electroacupuncture (EA) at acupoint ST-36 (Zusanli) on the contractility of the distal colon in conscious rats.

METHODS

Rats were randomized into four groups, including the ST-36 group, the sham group, the saline-plus-ST-36 and the atropine-plus-ST-36 group. Needles were inserted into the acupoints for EA. The distal colonic contractility was measured with a manometric catheter inserted into the distal colon. The colonic contractility was recorded for 1 h before EA, 20 min during EA, and 3 h after EA. Saline or atropine was administrated in the saline-plus-ST-36 or atropine-plus-ST-36 group.

RESULTS

(1) EA at ST-36 significantly increased the contractility of the distal colon. The mean AUC during and after EA were significantly higher than that before EA in the ST-36 group, a 27% increase during EA and 26% after EA. (2) Atropine abolished the accelerating effect of EA at ST-36. The mean AUC remained unchanged during or after EA compared with that before EA in the atropine-plus-ST-36 group.

CONCLUSIONS

EA at ST-36 has a stimulatory effect on the contractility of the distal colon in conscious rats, and the stimulatory effect may be mediated via the cholinergic pathway.

Water avoidance stress activates colonic myenteric neurons in female rats

Stress stimulates colonic motor function and plays a role in functional bowel disorders, prevalently in women. We examined, in conscious female rats, the influence of water avoidance stress for 60 min on colonic myenteric neuron activity using immunohistochemical detection of Fos as a marker of neuronal activity. In control rats, Fos immunoreactive nuclei were rare in proximal and distal colon and no defecation was observed. Water avoidance stimulated fecal pellet output, which was associated with Fos expression in myenteric ganglia of proximal and distal colon including in a population of peripheral choline acetyltransferase-immunoreactive neurons. Atropine blocked fecal pellet output but not Fos expression in myenteric ganglia. These results indicate that psychological stress stimulates the activity of colonic cholinergic myenteric neurons.

Comparison of extrinsic efferent innervation of guinea pig distal colon and rectum

The extrinsic efferent innervation of the distal colon and rectum of the guinea pig was compared, by using retrograde tracing combined with immunohistochemistry. Application of the carbocyanine tracer DiI to the rectum filled significantly greater numbers of extrinsic neurons than similar injections into the distal colon. Approximately three-fourths of all filled neurons from either location were either sympathetic or parasympathetic; the rest were spinal sensory neurons. Nerve cell bodies in sympathetic prevertebral ganglia labelled from the two regions were similar in number. Both regions were innervated by sympathetic neurons in paravertebral ganglia; however, the rectum received much more input from this source than the colon. The rectum received significantly more input from pelvic ganglia than the colon. The rectum also received direct innervation from two groups of neurons in the spinal cord. Neurons located in the spinal parasympathetic nucleus in segment S2 and S3 were labelled by DiI injected into the rectal wall. Similar numbers of neurons, located in intermediolateral cell column and dorsal commissural nucleus of lumbar segments, also projected directly to rectum, but not colon. The great majority (>80%) of retrogradely labelled nerve cell bodies in sympathetic ganglia were immunoreactive for tyrosine hydroxylase. In pelvic ganglia, retrogradely labelled neurons contained choline acetyltransferase and/or nitric oxide synthase or tyrosine hydroxylase. Although the rectum and colon in this species are continuous and macroscopically indistinguishable, they have significantly different patterns of extrinsic efferent innervation, presumably reflecting their different functions.

Electroacupuncture at ST-36 accelerates colonic motility and transit in freely moving conscious rats

Acupuncture is useful for functional bowel diseases, such as constipation and diarrhea. However, the mechanisms of beneficial effects of acupuncture on colonic function have scarcely ever been investigated. We tested the hypothesis that electroacupuncture (EA) at ST-36 stimulates colonic motility and transit via a parasympathetic pathway in conscious rats. Hook-shaped needles were inserted at bilateral ST-36 (lower limb) or BL-21 (back) and electrically stimulated at 10 Hz for 20 min. We also studied c-Fos expression in response to EA at ST-36 in Barrington's nucleus of the pons. EA at ST-36, but not BL-21, significantly increased the amplitude of motility at the distal colon. The calculated motility index of the distal colon increased to 132 +/- 9.9% of basal levels (n = 14, P < 0.05). In contrast, EA at ST-36 had no stimulatory effects in the proximal colon. EA at ST-36 significantly accelerated colonic transit [geometric center (GC) = 6.76 +/- 0.42, n = 9, P < 0.001] compared with EA at BL-21 (GC = 5.23 +/- 0.39, n = 7). The stimulatory effect of EA at ST-36 on colonic motility and transit was abolished by pretreatment with atropine. EA-induced acceleration of colonic transit was also abolished by extrinsic nerve denervation of the distal colon (GC = 4.69 +/- 0.33, n = 6). The number of c-Fos-immunopositive cells at Barrington's nucleus significantly increased in response to EA at ST-36 to 8.1 +/- 1.1 cells/section compared with that of controls (2.4 +/- 0.5 cells/section, n = 3, P < 0.01). It is concluded that EA at ST-36 stimulates distal colonic motility and accelerates colonic transit via a sacral parasympathetic efferent pathway (pelvic nerve). Barrington's nucleus plays an important role in mediating EA-induced distal colonic motility in conscious rats.

Plasticity of pelvic autonomic ganglia and urogenital innervation

Pelvic ganglia contain a mixture of sympathetic and parasympathetic neurons and provide most of the motor innervation of the urogenital organs. They show a remarkable sensitivity to androgens and estrogens, which impacts on their development into sexually dimorphic structures and provide an array of mechanisms by which plasticity of these neurons can occur during puberty and adulthood. The structure of pelvic ganglia varies widely among species, ranging from rodents, which have a pair of large ganglia, to humans, in whom pelvic ganglion neurons are distributed in a large, complex plexus. This plexus is frequently injured during pelvic surgical procedures, yet strategies for its repair have yet to be developed. Advances in this area will come from a better understanding of the effects of injury on the cellular signaling process in pelvic neurons and also the role of neurotrophic factors during development, maintenance, and repair of these axons.

Differential responses of intrinsic and extrinsic innervation of smooth muscle cells in rat colitis

Intestinal smooth muscle cells receive neural input from axons that originate within the intestine, as well as from axons of extrinsic origin. In the inflamed intestine, altered motility may arise from damage to the axon/smooth muscle cell relationship, but the extent of change is unknown. Western blotting, histology and immunocytochemistry were used in the TNBS model of colitis in the rat to evaluate intrinsic and extrinsic axon numbers, which were then correlated with circular smooth muscle cell (CSMC) number during the time course from the acute onset of colitis to apparent recovery, at Day 35 post TNBS. Total axon profiles in the circular smooth muscle layer were reduced by nearly 50% on Day 4 of colitis, to 428 +/- 82 axons/section from 757 +/- 125 in control (n = 8-14 animals). The intrinsic innervation density (axon number per CSMC) dropped sharply by Day 2 to less than 30% of control. Although CSMC number nearly tripled during colitis, innervation density was restored to control levels by Day 6 due to a coordinated three-fold increase in axon number. The subpopulation of extrinsic axons expressing tyrosine hydroxylase showed a unique pattern during colitis, with no initial decrease in axon number, followed by axonal proliferation between Days 6 and 16 post-TNBS. We conclude that loss of intrinsic axons is an early event in colitis, and although reversed by axonal proliferation, transient denervation may promote CSMC hyperplasia as seen in earlier work in vitro. Axonal proliferation of both intrinsic and extrinsic axons is identified as a major homeostatic mechanism, with distinct patterns of damage and repair suggesting a structural basis for the altered motility seen in the inflamed colon.

Phenotypes of neural-crest-derived cells in vagal and sacral pathways

Enteric neurons arise from vagal and sacral level neural crest cells. To examine the phenotype of neural-crest-derived cells in vagal and sacral pathways, we used antisera to Sox10, p75, Phox2b, and Hu, and transgenic mice in which the expression of green fluorescent protein was under the control of the Ret promoter. Sox10 was expressed prior to the emigration of vagal cells, whereas p75 was expressed shortly after their emigration. Most crest-derived cells that emigrated adjacent to somites 1-4 migrated along a pathway that was later followed by the vagus nerve. A sub-population of these vagal cells coalesced to form vagal ganglia, whereas others continued their migration towards the heart and gut. Cells that coalesced into vagal ganglia showed a different phenotype from cells in the migratory streams proximal and distal to the ganglia. Only a sub-population of the vagal cells that first entered the foregut expressed Phox2b or Ret. Sacral neural crest cells gave rise to pelvic ganglia and some neurons in the hindgut. The pathways of sacral neural crest cells were examined by using DbetaH-nlacZ mice. Sacral cells appeared to enter the distal hindgut around embryonic day 14.5. Very few of the previously demonstrated, but rare, neurons that were present in the large intestine of Ret null mutants and that presumably arose from the sacral neural crest expressed nitric oxide synthase, unlike their counterparts in Ret heterozygous mice.

The defecation reflex in rats: fundamental properties and the reflex center

While pharmacological and physiological studies in rats are now increasing, physiological properties of their defecation have been scarcely investigated. This study was performed to define the properties of defecation in decerebrate rats, with special reference to the pontine defecation reflex center, which has been postulated in dogs. Intraluminal pressure was recorded from the colon and rectum with balloon-pressure transducer method using balloons of 15-20 mm in length and 0.1-0.3 ml in volume. Distention of a balloon in the descending colon and rectum with an additional injection of 0.03-0.1 ml air induced propulsive contractions on the descending colon and rectum. The mean of threshold pressures to induce propulsive contraction was 17.0 +/- 5.8 mm Hg (mean+/-S.E.) in the proximal part and 18.3 +/- 3.3 mm Hg in the distal part of the descending colon, and 11.8 +/- 1.3 mm Hg in the rectum. The maximum amplitude of propulsive contractions was 55 mm Hg in the rectum, 47 mm Hg in the distal part of the descending colon and 38 mm Hg in the proximal part. Similar colorectal propulsive contractions were produced by gastric distention (5-10 ml, 20-30 mm Hg) and electrical stimulation of the anal canal. Contrarily, spontaneous contractions of the proximal colon were suppressed by rectal distention and anal-canal stimulation. These results suggest that the descending colon and rectum, but not the proximal colon, were innervated by the pelvic afferent and efferent fibers mediating the defecation reflex. Pontine transection at the cerebellar peduncle level abolished colorectal propulsive contractions induced by distention of the stomach, descending colon and rectum, and stimulation of the anal canal, although much smaller contractions were still induced after the pontine transection. These results suggest that the pontine defecation reflex center exists and works in rats, as in dogs.

Neurochemical characterization of extrinsic innervation of the guinea pig rectum

The presence of markers for parasympathetic, sympathetic, and glutamatergic or peptidergic sensory innervation was investigated by using in vitro tracing with biotinamide, combined with immunohistochemistry, to characterise quantitatively extrinsic axons to myenteric ganglia of the guinea pig rectum. Of biotinamide-filled varicose axons, 3.6 +/- 1.3% were immunoreactive for tyrosine hydroxylase (TH) and 16.0 +/- 4.8% for vesicular acetylcholine transporter (VAChT). TH and vesicular monoamine transporter (VMAT1) showed high coexistence (83-100%), indicating that varicosities lacking TH immunoreactivity also lacked VMAT1. VAChT was detectable in 77% of choline acetyltransferase (ChAT)-immunoreactive varicosities. Calcitonin gene-related peptide (CGRP) was detected in 5.3 +/- 1.6% of biotinamide-labeled varicosities, the vesicular glutamate transporter (VGluT) 1 in 2.8 +/- 0.8%, and VGluT2 in 11.3 +/- 4.2% of varicosities of extrinsic origin. Varicosities from the same axon showed consistent immunoreactivity. A novel type of nerve ending was identified, with branching, flattened lamellar endings, similar to the intraganglionic laminar endings (IGLEs) of the proximal gut. Rectal IGLEs were frequently immunoreactive for VGluT1 and VGluT2. Thus most varicose axons of extrinsic origin, which innervate rectal myenteric ganglia, lack detectable levels of immunoreactivity for TH, VMAT1, VAChT, ChAT, VGluT1/2, or CGRP, under conditions in which these markers are readily detectable in other axons. Although some unlabeled varicosities may belong to afferent axons that lack detectable CGRP or VGluT1/2 in the periphery, this suggests that a large proportion of axons do not release any of the major autonomic or sensory transmitters. We speculate that this may vary under particular circumstances, for example, inflammation or obstruction of the gut.

Nicotinic transmission at functionally distinct synapses in descending reflex pathways of the rat colon

We examined descending reflex pathways in the rat colon using intracellular recording techniques. Inhibitory junction potentials (IJPs) were recorded from circular smooth muscle when descending pathways were excited by combined mucosal compression and distension. IJPs were reduced to 71% of control when synaptic transmission was blocked in the oral stimulation chamber of a divided organ bath suggesting that two reflex pathways exist, the one involving descending sensory neurones and the other involving descending interneurones. Hexamethonium (200 micromol L(-1)) in the recording chamber abolished reflexly evoked IJPs, while in the stimulation chamber, it was as effective as synaptic blockade. When hexamethonium was added to a chamber lying between the stimulation and recording chambers, it again sharply depressed IJPs to 27% of control; an extent similar to synaptic blockade. A P2 receptor antagonist did not reveal any purinergic neurotransmission. Either granisetron (5-HT3 receptor antagonist, 1 micromol L(-1)) or SB204070 (5-HT4 receptor antagonist, 1 micromol L(-1)) in the stimulation chamber significantly decreased IJPs; these decreases were not additive. We conclude that some sensory neurones and interneurones in rat colon have long anally projecting axons and that acetylcholine, acting via nicotinic receptors, is the primary neurotransmitter from sensory neurones, to inhibitory motor neurones and between interneurones.

Nicotinic mechanisms in the autonomic control of organ systems

Most visceral organs are under the control of the autonomic nervous system (ANS). Information on the state and function of these organs is constantly relayed to the central nervous system (CNS) by sensory afferent fibers. The CNS integrates the sensory inputs and sends neural commands back to the organ through the ANS. The autonomic ganglia are the final site for the integration of the message traveling from the CNS. Nicotinic acetylcholine receptors (nAChRs) are the main mediators of fast synaptic transmission in ganglia, and therefore, are key molecules for the processing of neural information in the ANS. This review focuses on the role of nAChRs in the control of organ systems such as heart, gut, and bladder. The autonomic control of these organ systems is discussed in the light of the results obtained from the analysis of mice carrying mutations targeted to nAChR subunits expressed in the ANS.

Enteric nervous system: development and developmental disturbances--part 1

This review, which is presented in two parts, summarizes and synthesizes current views on the genetic, molecular, and cell biological underpinnings of the early embryonic phases of enteric nervous system (ENS) formation and its defects. In the first part, we describe the critical features of two principal abnormalities of ENS development: Hirschsprung's disease (HSCR) and intestinal neuronal dysplasia type B (INDB) in humans, and the similar abnormalities in animals. These represent the extremes of the diagnostic spectrum: HSCR has agreed and unequivocal diagnostic criteria, whereas the diagnosis and even existence of INDB as a clinical entity is highly controversial. The difficulties in diagnosis and treatment of both these conditions are discussed. We then review the genes now known which, when mutated or deleted, may cause defects of ENS development. Many of these genetic abnormalities in animal models give a phenotype similar or identical to HSCR, and were discovered by studies of humans and of mouse mutants with similar defects. The most important of these genes are those coding for molecules in the GDNF intercellular signaling system, and those coding for molecules in the ET-3 signaling system. However, a range of other genes for different signaling systems and for transcription factors also disturb ENS formation when they are deleted or mutated. In addition, a large proportion of HSCR cases have not been ascribed to the currently known genes, suggesting that additional genes for ENS development await discovery.

Unusual autonomic ganglia: connections, chemistry, and plasticity of pelvic ganglia

The pelvic ganglia provide the majority of the autonomic nerve supply to reproductive organs, urinary bladder, and lower bowel. Of all autonomic ganglia, they are probably the least understood because in many species their anatomy is particularly complex. Furthermore, they are unusual autonomic ganglia in many ways, including their connections, structure, chemistry, and hormone sensitivity. This review will compare and contrast the normal structure and function of pelvic ganglia with other types of autonomic ganglia (sympathetic, parasympathetic, and enteric). Two aspects of plasticity in the pelvic pathways will also be discussed. First, the influence of gonadal steroids on the maturation and maintenance of pelvic reflex circuits will be considered. Second, the consequences of nerve injury will be discussed, particularly in the context of the pelvic ganglia receiving distributed spinal inputs. The review demonstrates that in many ways the pelvic ganglia differ substantially from other autonomic ganglia. Pelvic ganglia may also provide a useful system in which to study many fundamental neurobiological questions of broader relevance.

Activation of alpha- and beta-adrenoceptors by sympathetic nerve stimulation in the large intestine of the rat

1. The effects of sympathetic nerve stimulation on the motility of the circular and longitudinal muscle of the large intestine were investigated in vitro, and the involvement of various adrenoceptor subtypes determined. A comparison between the sympathetic supply arising from the prevertebral and pelvic ganglia was also made. 2. In the longitudinal muscle of the distal colon, sympathetic nerve stimulation caused responses which were contractile (0.1-2 Hz), biphasic (5-10 Hz) or purely inhibitory (20-30 Hz). All contractile responses were removed with phentolamine (3 microM), whereas the inhibitory responses were significantly diminished by propranolol (0.1 microM) and completely abolished by alprenolol (3 microM) or nadolol (300 microM). 3. In the longitudinal muscle of the proximal colon, the effects of sympathetic nerve stimulation were predominantly inhibitory. Some of this inhibition was removed by propranolol (0.1 microM), but was largely unaffected by alprenolol (3 microM). The remainder of the inhibitory response was probably non-noradrenergic as it was not removed by a combination of phentolamine (3 microM) and alprenolol (3 microM). 4. In the circular muscle of both the proximal and distal colon, sympathetic stimulation caused a strong contractile response which was completely removed by phentolamine (3 microM) to reveal an inhibitory response. This inhibitory response was unchanged by propranolol (0.1 microM) but was removed by alprenolol (3 microM), following which a weak non-noradrenergic contractile response was unmasked. 5. Stimulation of the hypogastric nerve to activate pelvic sympathetic pathways had no effect on the motility of the longitudinal muscle, but caused a contractile response in the circular muscle which was completely removed by phentolamine (3 microM). 6. We conclude that sympathetic nerves innervate adrenoceptors of different types in the various muscle layers and regions of the colon. They innervate a mixture of alpha-, and beta(3)-adrenoceptors in the longitudinal muscle of the proximal colon, alpha-, classical beta- and beta(3)-adrenoceptors in the distal colon, and primarily alpha-adrenoceptors with a few beta(3)-adrenoceptors in the circular muscle. In addition, the pelvic sympathetic innervation of the rectum differs from the prevertebral supply by innervating only excitatory alpha-adrenoceptors.

Characterisation of the adventitial rectal ganglia in the male rat by their immunohistochemical features and projections

In recent years, considerable progress has been made in characterising the neural circuitry of the pelvic plexus, particularly in the male rat. However, the small ganglia on the adventitial surface of the rectum remain largely unstudied. We have used immunohistochemistry and retrograde tracing techniques to determine the content and projections of these neurons. The adventitial ganglia contain 600-1,000 neurons. All of these are immunoreactive for choline acetyltransferase, 44% are immunoreactive for calbindin, and 35% are immunoreactive for vasoactive intestinal peptide. Very few (1-5%) adventitial neurons contain tyrosine hydroxylase or neuropeptide Y. In contrast, most adventitial neurons are surrounded by varicose axons that do contain tyrosine hydroxylase or neuropeptide Y. Retrograde tracing studies showed that the primary targets of adventitial neurons within the bowel are the internal anal sphincter and the circular muscle directly adjacent to the sphincter. However, more adventitial neurons project out of the gut wall than to targets within the bowel. These are most likely to be viscerofugal and rectospinal neurons. Combining the immunohistochemical and tracing observations, these studies suggest that the rat adventitial ganglia do not represent an additional source of pelvic (autonomic postganglionic) neurons but, instead, that they are comprised primarily of viscerofugal and rectospinal neurons. This is very different from the adventitial rectal ganglia of the cat, which represent merely an extension of the pelvic plexus.