Central innervation of neurones in the inferior mesenteric ganglion and of the large intestine of the cat

A study on preganglionic connections and possible viscerofugal projections from urinary bladder intramural ganglia to the caudal mesenteric ganglion in the pig

The present study was designed to (1) ascertain the distribution and immunohistochemical characteristics of sympathetic preganglionic neurons supplying the caudal mesenteric ganglion (CaMG) and (2) verify the existence of viscerofugal projections from the urinary bladder trigone intramural ganglia (UBT-IG) to the CaMG in female pigs (n = 6). Combined retrograde tracing and immunofluorescence methods were used. Injections of the neuronal tracer Fast Blue (FB) into the right CaMG revealed no retrogradely labelled (FB-positive; FB⁺ ) nerve cells in the intramural ganglia; however, many FB⁺ neurons were found in the spinal cord sympathetic nuclei. Double-labelling immunohistochemistry revealed that nearly all (99.4 ± 0.6%) retrogradely labelled neurons were cholinergic (choline acetyltransferase-positive; ChAT⁺ ) in nature. Many FB⁺ /ChAT⁺ perikarya stained positive for vesicular acetylcholine transporter (63.11 ± 5.34%), neuronal nitric oxide synthase (53.48 ± 9.62%) or cocaine- and amphetamine-regulated transcript peptide (41.13 ± 4.77%). A small number of the retrogradely labelled cells revealed immunoreactivity for calcitonin gene-related peptide (7.60 ± 1.34%) or pituitary adenylate cyclase-activating polypeptide (4.57 ± 1.43%). The present study provides the first detailed information on the arrangement and chemical features of preganglionic neurons projecting to the porcine CaMG and, importantly, strong evidence suggesting the absence of viscerofugal projections from the UBT-IG.

Review article: the pharmacological treatment of acute colonic pseudo-obstruction

Acute colonic pseudo-obstruction (Ogilvie's syndrome) can be defined as a clinical condition with symptoms, signs and radiological appearance of acute large bowel obstruction unrelated to any mechanical cause. Recent reports of the efficacy of cholinesterase inhibitors in relieving acute colonic pseudo-obstruction have fuelled interest in the pharmacological treatment of this condition. The aim of the present review is to outline current perspectives in the pharmacological treatment of patients with acute colonic pseudo-obstruction. The best documented pharmacological treatment of Ogilvie's syndrome is intravenous neostigmine (2-2.5 mg), which leads to quick decompression in a significant proportion of patients after a single infusion. However, the search for new colokinetic agents for the treatment of lower gut motor disorders has made available a number of drugs that may also be therapeutic options for Ogilvie's syndrome. Among these agents, the potential of 5-hydroxytryptamine-4 receptor agonists and motilin receptor agonists is discussed.

Recurrence of acute colonic pseudo-obstruction in selective adrenergic dysautonomia associated with infectious toxoplasmosis

BACKGROUND

Acute colonic pseudo-obstruction is a life-threatening condition associated with several pathologic conditions, whose pathophysiology is still uncertain.

CASE

Autonomic function in a young patient operated on for acute colonic pseudo-obstruction was carefully evaluated; none of the common clinical conditions described in the literature was found to have caused the syndrome. Selective adrenergic failure was suggested by the presence of severe orthostatic hypotension, low basal plasma catecholamine level, and absence of the expected increase on standing and by the findings of provocation tests, cardiovascular tests, and acetylcholine sweat spot test. Biopsy specimens from the colon and small-bowel wall did not show any morphologic or immunohistochemical alteration either in muscle layers or in the autonomic plexus, testifying to the possible occurrence of extrinsic denervation in the presence of an intact plexus. Infectious toxoplasmosis was proved through indirect and direct hemagglutination assays, enzyme-linked immunosorbent assay IgG, IgM, and IgA, immunosorbent agglutination IgM assay, and the protozoa were demonstrated in a biopsy specimen from the rectus abdominis muscle.

CONCLUSIONS

Selective adrenergic denervation of the gut resulted in recurrent episodes of colonic pseudo-obstruction, probably by direct toxicity or a cross-reaction between the immune process and a toxoplasmic antigen, stressing the importance of sympathetic inhibitory modulation on colon motor activity.

The mammalian sympathetic prevertebral ganglia: integrative properties and role in the nervous control of digestive tract motility

The prevertebral ganglia which are a constitutive part of the sympathetic system have long been considered as a simple relay on this efferent pathway. In fact, these ganglia must be considered as true peripheral nervous centres. They possess various integrative properties, such as projections of central and peripheral inputs onto the ganglionic neurones, gating of these projections and pacemaker activity of the ganglionic neurones. These properties explain the ability of these ganglia to participate in the regulation of various visceral functions, including digestive tract motility.

The ratio of pre- to postganglionic neurons and related issues in the autonomic nervous system

The motor outflow of the autonomic nervous system (ANS) is differentiated into two major divisions, parasympathetic (PSNS) and sympathetic (SNS). Both are organized hierarchically into pre- and postganglionic levels, but classically the two divisions have been assumed to differ in their ratios of pre- to postganglionic neurons. The PSNS been characterized as having lower ('one-to-few') ratios, whereas the SNS has been described as possessing higher ('one-to-many') ratios. These patterns have been assumed to measure differing divergences of the outflows. In this review, a ratio of pre- to postganglionic neurons is called a ratio index, and the idea that the PSNS and SNS have characteristically different ratio indexes and divergences is called the ratio rule. The putative differences in the ratio indexes of the two divisions - as well as Fulton's influential proposal that they form one of the bases of contrasting functional capacities of the PSNS and SNS - have been widely accepted for nearly for nearly three quarters of a century. A survey of the original observations yielding the concept of the ratio rule as well as the more recent estimates of pre- and postganglionic numbers, however, challenges both the generality and the adequacy of the ratio rule and indexes. The originally formulated differences between the PSNS and SNS represent an overgeneralization since they were based on observations of only two ganglia, the ciliary ganglion in the PSNS and the superior cervical ganglion in the SNS. Furthermore, these original estimates were based on limited samples and were subject to a number of counting artifacts. A survey of the literature suggests that ratio indexes vary much more within each ANS division than they do between the two divisions. When ganglia other than the ciliary and superior cervical are examined, the two divisions of the ANS have broad, largely overlapping ranges of ratio indexes. Additionally, other PSNS-SNS pairs can be found in which the relative sizes of their respective indexes are completely contrary to the ratio rule. For a given ganglion, there are substantial differences in the ratio index between species, between individuals of the same species, and between stages of development in the same species. Furthermore, both divisions of the ANS have wide and largely overlapping ranges of physiological effects varying from specific to diffuse, from local to widespread. Finally, the ratio index measure ignores the degree of convergence found in different ganglia, and it is insensitive to the fact that many ganglia have multiple functionally distinct motor neuron pools, each with separate inputs varying in their degrees of divergence and/or convergence. Thus ratio indexes do not differentiate the PSNS from the SNS, and conclusions based on such putative distinctions are questionable.

Anal and rectal motility responses to distension of the urinary bladder in the cat

The neural pathways and possible transmission mechanisms of the integrated autonomic nervous control of the urinary bladder and anorectum, were investigated in chloralose anaesthetized cats. Bladder distension and spontaneous detrusor contractions increased internal anal sphincter-tone, a response which was blocked by an alpha-adrenoceptor antagonist. Moreover, a nicotinic transmission step was present. Both the afferent and efferent limbs of the reflex were conveyed in the postganglionic hypogastric nerves and the preganglionic lumbar splanchnic nerves. Intact connection with the central nervous system was therefore essential. Contrasting to the specific reflex response in the internal anal sphincter, bladder distension also elicited a nociceptive vaso-pressor response. Rectal motility appeared to be unaffected by bladder distension.

Changes in enkephalin immunoreactivity of sympathetic ganglia and digestive tract of the cat after splanchnic nerve ligation

The aim of the present study was to analyze changes in the enkephalin immunoreactivity of sympathetic prevertebral ganglia coeliac plexus and inferior mesenteric ganglion) and intestinal tract (myenteric plexus and external muscle layers) in cats 2 days after left thoracic splanchnic nerve ligation, using radioimmunoassay and immunohistochemical techniques. Specific polyclonal antibodies directed against methionine- and leucine-enkephalin were used. The nerve ligation led to a considerable increase in the enkephalin immunoreactivity in the cranial part of the ligated nerves. This finding confirms the presence, in the cat, of an enkephalin output originating from thoracic spinal structures which are probably enkephalin-containing preganglionic neurons. In prevertebral ganglia the nerve ligation induced a marked decrease in the enkephalin immunoreactivity, which was probably due to the interruption of thoracic enkephalin efferents projecting towards both the coeliac plexus and the inferior mesenteric ganglion. In the digestive tract, the nerve ligation depressed the methionine-enkephalin immunoreactivity only in the gastro-duodenal region, and had no effect on the ileo-colonic region. The results of the present study add to the growing evidence that the sympathetic nervous system is involved in regulating the enteric enkephalinergic innervation, which is probably involved in controlling the intestinal motility.

Electrical and integrative properties of rabbit sympathetic neurones re-evaluated by patch clamping non-dissociated cells

1. Voltage recordings were performed on non-dissociated sympathetic neurones from rabbit coeliac ganglia using the whole-cell configuration of the patch clamp technique. 2. Cells were classified depending on their firing pattern as silent cells (63%) producing either phasic (24%) or tonic (76%) spike discharge in response to depolarizing currents, and pacemaker cells (37%). 3. All the cells produced large overshooting spikes and prolonged postspike after-hyperpolarization. The peak-to-peak spike amplitude was 113.8 +/- 1 mV. Spikes were shortened and the after-hyperpolarization was suppressed when calcium channel blockers (Cd2+ and La3+) were added. 4. Silent cells have a resting potential of -58.8 +/- 1.5 mV. At potentials ranging from -50 to -90 mV, the input impedance was 490 +/- 27 M omega at 22-24 degrees C and 426 +/- 47 M omega at 35-36 degrees C. The time constant at voltages corresponding to the high input impedance region was 126 +/- 7 ms at 22-24 degrees C and 86 +/- 7 ms at 35-36 degrees C. 5. The firing frequency of the pacemaker cells was 3.2 +/- 0.5 Hz at 35-36 degrees C in the presence of nicotinic blockers. Evidence is given that the firing did not result from cell injury but was induced by an intrinsic pacemaker mechanism. Input impedance of pacemaker neurones was 580 +/- 47 M omega at 22-24 degrees C and 473 +/- 56 M omega at 35-36 degrees C. 6. Most of the pacemaker cells (63%) were motoneurones, since they were antidromically fired by stimulating post-ganglionic nerves. In addition, they received synaptic inputs from both preganglionic fibres (splanchnic nerves) and the periphery (postganglionic nerves). Long-lasting depolarizations were induced in either silent or pacemaker cells by single shocks applied to pre- and postganglionic nerves. 7. Slowly rising voltage ramps revealed the presence of an N-shaped current-voltage relationship in voltage clamped pacemaker cells. The negative slope was located in a subthreshold voltage range, between -83.4 +/- 1.4 and -59.0 +/- 1.8 mV. It was induced by the activation of a low threshold persistent inward current. Although it was tiny (22 +/- 3 pA at its peak level) this current brought the null-current voltage up to -41.0 +/- 1.4 mV, which resulted in continuous firing. 8. Due to the instability introduced by the N-shaped I-V relationship, pacemaker cells can display bistable behaviour characterized by hyperpolarizing responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute colonic pseudo-obstruction

The syndrome of acute colonic pseudo-obstruction is well delineated but its aetiology remains poorly understood and patients are still treated inappropriately. This article reviews the pathogenesis and surgical management of this condition. Early diagnosis is stressed as a pivotal factor in reducing morbidity and mortality.

Methionine enkephalin presynaptically facilitates and inhibits bullfrog sympathetic ganglionic transmission

The effects of [Met5]enkephalin (ME) on the fast excitatory postsynaptic potential (EPSP) in bullfrog sympathetic ganglion cells were studied with intracellular recording in vitro. The variance and failure methods were used to calculate quantal content and quantal size of the fast EPSP in a low Ca2+/high Mg2+ solution. High concentrations of ME (1 and 10 microM) decreased the amplitude and the mean quantal content of the fast EPSP, whereas low concentrations (10 pM to 10 nM) of the peptide increased EPSP amplitude and quantal content. The mean quantal size of the EPSP was not changed by ME. The inhibitory effect of ME at high concentration (10 microM) was reversibly antagonized by the same concentration of naloxone; the facilitatory effect of ME at low concentration (1 nM) was not affected by 10 times higher concentration of naloxone (10 nM), but inhibited by 10 microM naloxone. A low concentration of naloxone (100 pM) itself increased the amplitude and the mean quantal content of the fast EPSP without changing the mean quantal size. The other concentrations of naloxone used in this study (1 pM to 10 microM) caused no significant change in the fast EPSP. ME (100 fM to 10 microM) and naloxone (1 pM to 10 microM) did not change the resting membrane potential or input resistance, the amplitude and duration of action potentials, and the sensitivity to the acetylcholine applied by iontophoresis. These results indicate that ME may act on preganglionic nerve terminals either to facilitate or to depress transmitter release; the inhibitory action is naloxone sensitive, whereas the facilitatory action is less sensitive to naloxone.

Integration of gut function by sympathetic reflexes

1. The spinal sympathetic outflow that innervates the gastrointestinal tract, including its blood vessels, has an impressive representation quantitatively, yet little is known about the functions of this system and its peripheral or central organization. Electrical stimulation or section of the splanchnic nerves have variable effects on the GI tract and does not, therefore, lead to a deeper understanding of the system. 2. The targets of the sympathetic supply of the GI tract are blood vessels, nonvascular (sphincteric) smooth musculature, myenteric neurones, submucous neurones and gut associated lymphoid tissues. The corresponding functions associated with these targets are regulation of blood flow (particularly through the mucosa) and resistance to flow, of motility, of secretion and absorption and of immune responses. Little is known about the effects of the sympathetic nervous system on the latter function. 3. The sympathetic postganglionic neurones are (at least in the guinea-pig) neurochemically characterized with respect to the targets. Neurones projecting to blood vessels contain neuropeptide Y in addition to noradrenaline, while neurones projecting to the submucous plexus contain somatostatin. No neuropeptide has been detected to date in neurones projecting to the myenteric plexus. 4. Transmission through guinea-pig prevertebral ganglia in vitro have been studied electrophysiologically. The following functions have been demonstrated: (a) transmission and distribution of preganglionic impulse activity to the targets in a relay-like fashion; (b) mediation of peripheral intestinointestinal reflexes between different sections of the GI tract; (c) integration of activity from the spinal cord and from various peripheral sources. The first function may apply particularly to the sympathetic pathway innervating blood vessels. Whether the second function occurs in vivo is questionable. The third function is the most important one for pathways involved in the regulation of motility and probably secretion and absorption. 5. Only limited information is available on preganglionic neurones projecting to prevertebral ganglia. Neurones regulating blood vessels are probably located in the intermediolateral cell column, and non-vascular visceral preganglionic neurones are situated medial to this cell column in the intermediate zone of the spinal cord. Vascular (vasoconstrictor) neurones exhibit a reflex pattern which is largely dependent on the brain stem. Spinal cord transection rostral to the sympathetic outflow causes an immediate abolition of basal and reflex activity in these neurones.(ABSTRACT TRUNCATED AT 400 WORDS)

The distribution within the spinal cord of visceral primary afferent axons carried by the lumbar colonic nerve of the cat

Horseradish peroxidase taken up by the sensory axons in the lumbar colonic nerves in 5 cats was observed in the dorsal root ganglia and in the spinal cord in segments L1 through L5. Reaction product was observed in Lissauer's tract, the dorsal columns and laminae I, V, VII and X in a pattern typical of visceral primary afferents from other nerves. A small number of preganglionic neurons were also labeled.

The effect of a transient outward current (IA) on synaptic potentials in sympathetic ganglion cells of the guinea-pig

The responses to stimulation of preganglionic fibres have been studied in sympathetic neurones in ganglia of the caudal lumbar sympathetic chain (l.s.c.) and in the distal lobes of inferior mesenteric ganglia (i.m.g.) isolated from guinea-pigs. Most l.s.c. neurones were classified as 'phasic' and i.m.g. neurones as 'tonic' (see Cassell, Clark & McLachlan, 1986). The types of preganglionic inputs received by l.s.c. and i.m.g. neurones differed: l.s.c. cells almost invariably received at least one suprathreshold ('strong') input, in addition to several subthreshold ones; i.m.g. neurones more commonly received only subthreshold inputs via the lumbar splanchnic nerves. Prolonged discharges were evoked in some i.m.g. cells by stimulation of lumbar splanchnic nerves at strengths just supramaximal for the conventional fast synaptic responses. These appeared to arise from repetitive discharges evoked in other neurones intrinsic to the i.m.g. The time constants of decay of subthreshold synaptic currents recorded under voltage clamp in l.s.c. neurones (4.9 +/- 0.2 ms) were significantly shorter on average than those recorded in tonic i.m.g. cells (7.1 +/- 0.3 ms), although the values of time constant for the two populations overlapped. In phasic neurones, excitatory synaptic potentials (e.s.p.s) evoked at resting membrane potential by stimulation of preganglionic axons decayed with the same exponential time course as an electrotonic potential. In tonic neurones, the time course of decay of the e.s.p. was briefer, but always followed an exponential with the same time constant as the cell input time constant over the final part of the response. If tonic neurones were hyperpolarized by the passage of current through the recording micro-electrode, the time course of decay of the e.s.p. was prolonged and became the same as that of the electrotonic potential. The shape of e.s.p.s in phasic and tonic neurons could be mimicked in a computer model of the neurones incorporating the different activation/inactivation characteristics of the A current (IA) (Cassell et al. 1986) for each neurone type. It is concluded that, in addition to the contribution of IA to the rhythmic firing properties of tonic sympathetic neurones, this current also markedly inhibits the effects of excitatory synaptic conductance changes in this type of ganglion cell.

Secondary functional properties of lumbar visceral preganglionic neurons

Preganglionic visceral vasoconstrictor (VVC) neurons and motility-regulating (MR) neurons and other visceral preganglionic neurons, which project in the lumbar splanchnic nerves, were analyzed for their segmental distribution, the conduction velocity of their axons, ongoing activity and reflexes elicited by electrical stimulation of visceral afferents in white rami and of somatic afferents in spinal nerves. Identified preganglionic neurons and neurons without ongoing and reflex activity were distributed over segments L1-L5. VVC neurons were distributed over segments L1-L4 and MR neurons over segments L3-L5. VVC axons conducted at 2.8 +/- 2.5 m/s (mean +/- 1 S.D., n = 49), MR axons at 8.1 +/- 4.7 m/s (n = 131). The ongoing activity of VVC neurons was 1.6 +/- 0.7 imp/s (n = 46), that of MR neurons 0.8 +/- 0.7 imp/s (n = 91). There was no correlation between the conduction velocity of preganglionic axons and the rate of ongoing activity for VVC and MR neurons. (4) Electrical stimulation of visceral afferents in white rami and of somatic afferents in spinal nerves elicited short-latency (less than 50 ms) and long-latency (greater than 50 ms) reflexes in practically all VVC neurons, but preferentially short-latency reflexes in only 50 to 60% of the MR neurons. These results show that VVC and MR neurons are not only different in their reflex patterns, elicited by stimulation of visceral receptors and of arterial baro- and chemoreceptors, but also in the 4 properties analyzed in this paper.

Functional characterization of preganglionic neurons projecting in the lumbar splanchnic nerves: vasoconstrictor neurons

Lumbar preganglionic neurons, which project in the lumbar splanchnic nerves and which probably have a vasoconstrictor function (visceral vasoconstrictor, VVC neurons), were analyzed for their discharge patterns. The responses of these neurons to the following natural stimuli were tested: stimulation of arterial baroreceptors, arterial chemoreceptors and visceral afferents from the urinary bladder, the colon and the mucosal skin of the anus. Forty-nine preganglionic neurons were classified as VVC neurons. They showed the following characteristics: the ongoing activity of the VVC neurons exhibited pronounced cardiac rhythmicity and correlated with the cycle of the artificial ventilation. Stimulation of arterial baroreceptors, produced by increase of blood pressure or by increase of pressure in an isolated carotid blind sac, led to inhibition of activity in VVC neurons. Unloading of arterial baroreceptors, produced by decrease of blood pressure, led to an increase in VVC neuron activity. Stimulation of arterial chemoreceptors by bolus injections of CO2-enriched saline solution, close to a carotid glomus, led to a weak excitation of VVC neurons. Stimulation of arterial chemoreceptors by systemic hypoxia led to weak excitation and/or to depression of activity in VVC neurons. Stimulation of visceral afferents from urinary bladder and colon by isovolumetric contractions and distensions of the organs had no effect on most VVC neurons. Anal stimulation also did not induce reflexes in the majority of the VVC neurons. Some 14% of the VVC neurons (7 from 49) were excited by at least one of the visceral stimuli in the same manner as the motility-regulating (MR) neurons. This investigation shows that preganglionic neurons, probably involved in regulation of vascular resistance in colon and pelvic organs, are functionally a distinct population of neurons with some interesting functional overlap with the motility-regulating neurons.

The afferent and sympathetic components of the lumbar spinal outflow to the colon and pelvic organs in the cat. II. The lumbar splanchnic nerves

The cell bodies of the lumbar sensory and sympathetic pre- and postganglionic neurons that project to the inferior mesenteric ganglion in the lumbar splanchnic nerves of the cat have been labeled retrogradely with horseradish peroxidase applied to the central end of their cut axons near the inferior mesenteric ganglion. The numbers, segmental distribution, location, and size of these labeled somata have been determined quantitatively. After all the lumbar splanchnic nerves on one side of an animal were labeled, most labeled cell bodies were situated ipsilaterally in dorsal root ganglia, ganglia of the lumbar sympathetic trunk, and spinal cord segments L2-L5, with the maximum numbers in L3 and L4. A few labeled somata lay contralaterally or rostral to L2. After labeling of only one lumbar splanchnic nerve, the majority of cell bodies were found in the labeled segment, but a few were also present up to three segments rostral or caudal. These variations could always be attributed to extraspinal connections usually via the lumbar sympathetic trunk. Cross-sectional areas of labeled afferent somata were small relative to those of the entire population of dorsal root ganglion cells. Preganglionic cell bodies were labeled in the intermediate gray matter extending from its lateral border ventrolaterally across to the central canal. Two regions of high density were observed: one laterally just medial to the edge of the white matter and the other lateral to the central canal. The dorsolateral group lay somewhat medial and caudal to the usual limits of the intermediolateral column. Labeled preganglionic neurons were on the average larger than the unlabeled cells in the inferior mesenteric ganglion, with the group lying medially being larger than those that were laterally positioned. From the data, it is estimated that about 4,600 afferent axons, about 4,600 preganglionic axons, and about 2,800 postganglionic axons travel in the lumbar splanchnic nerves to the inferior mesenteric ganglion of the cat.

The afferent and sympathetic components of the lumbar spinal outflow to the colon and pelvic organs in the cat. III. The colonic nerves, incorporating an analysis of all components of the lumbar prevertebral outflow

The cell bodies of the lumbar sensory and sympathetic pre- and postganglionic neurons that project to the colon along the inferior mesenteric artery of the cat have been labeled retrogradely with horseradish peroxidase applied to the central end of their cut axons. The numbers, segmental distribution, location, and size of these labeled somata have been determined quantitatively. Afferent cell bodies were symmetrically distributed bilaterally in dorsal root ganglia T13-L5, with the maximum number (about 80%) in L3 and L4 and most of the rest in L2. Labeled afferent somata were small relative to the entire population of DRG cells. Occasionally a few preganglionic somata were labeled in the intermediate zone of L3 and L4 spinal cord segments. Postganglionic cell bodies were labeled bilaterally in the proximal lobes of the inferior mesenteric ganglion (70-95%), in accessory ganglia of the intermesenteric nerve and of the lumbar splanchnic nerves, and in lumbar paravertebral ganglia. The segmental distribution in the lumbar sympathetic trunk was symmetrical on both sides and was the same as that of the afferent cells. Labeled postganglionic cell bodies in both the IMG and the accessory ganglia were larger than labeled and unlabeled ganglion cells in the paravertebral ganglia. From these data, it is estimated that about 2,100 afferent neurons and about 29,000 postganglionic neurons project in the lumbar colonic nerves. In conjunction with equivalent data for the hypogastric and lumbar splanchnic nerves, the results provide a quantitative and spatial description of the afferent and efferent components of the lumbar innervation of the colon and pelvic viscera.

Potentiation of colonic contractility to cholecystokinin and other peptides

Changes in colonic contractility were studied in anesthetized cats following the intravenous injection of several peptides. Increases in contractile activity were observed after the octapeptide of cholecystokinin (CCK-8), pentagastrin, substance P or neurotensin. On the other hand, vasoactive intestinal peptide (VIP) caused an inhibition which, in some cases, was followed by an excitatory response. The responses produced by pentagastrin, substance P or neurotensin, but not by CCK-8, were partially inhibited by atropine. Following bethanechol pretreatment, the stimulation in contractile activity elicited by CCK-8, substance P, neurotensin or pentagastrin was markedly enhanced. Responses were also increased by pretreatment with eserine, hexamethonium or mecamylamine. This potentiation was blocked by atropine. It is concluded that, following treatments which cause an increase in the level of cholinergic input to the colon, an exaggerated motor response to some peptides can develop.

Synaptic and antidromic potentials of visceral neurones in ganglia of the lumbar sympathetic chain of the cat

Intracellular recordings were obtained in vitro from two hundred and twenty post-ganglionic neurones of the fourth and fifth lumbar paravertebral ganglia of cats. Thirty-seven percent of neurones tested evoked antidromic responses during electrical stimulation of post-ganglionic fibres in the inferior lumbar splanchnic nerves. Twenty-seven percent of neurones tested evoked antidromic responses during electrical stimulation of post-ganglionic fibres in the lumbar sympathetic chain. Twenty-four percent of neurones tested evoked convergent antidromic responses during electrical stimulation of post-ganglionic fibres in separate inferior lumbar splanchnic nerves or lumbar sympathetic chain, and by inferior lumbar splanchnic nerves and lumbar sympathetic chain. Eighty-six percent of paravertebral post-ganglionic fibres which project to the inferior lumbar splanchnic nerves or lumbar sympathetic chain were composed of B fibres with maximal conduction velocities ranging from above 2.0 to 16.0 m/s. Fourteen percent of post-ganglionic fibres were composed of C fibres with maximal conduction velocities ranging from 0.2 to 2.0 m/s. Synaptic responses of neurones were recorded intracellularly during electrical stimulation of preganglionic fibres in inferior lumbar splanchnic nerves, lumbar white rami communicantes and lumbar sympathetic chain located one to three segments above the fourth and fifth lumbar ganglia and one to two segments below. Synaptic responses consisting of excitatory post-synaptic potentials and action potentials were mediated via nicotinic receptors. Twenty-seven percent of neurones tested received synaptic input from only one or two segments of the lumbar sympathetic chain. Seventy-three percent of neurones tested received convergent synaptic input from one or two segments of the lumbar sympathetic chain, lumbar white rami communicantes and inferior lumbar splanchnic nerves. It is concluded that central preganglionic fibres which project to inferior lumbar splanchnic nerves also project to the lumbar sympathetic chain to innervate neurones in the L4 and L5 ganglia. Synaptic responses of neurones during electrical stimulation of preganglionic fibres in the lumbar sympathetic chain and in the inferior lumbar splanchnic nerves were reduced in a chronic isolated segment of the sympathetic chain devoid of central preganglionic inputs. It is concluded that synaptic responses elicited in neurones during electrical stimulation of inferior lumbar splanchnic nerves and lumbar sympathetic chain were mediated in part via collaterals of central preganglionic axons and in part via axons whose cell bodies were located in the periphery.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanoreceptor pathways from the distal colon to the autonomic nervous system in the guinea-pig

Electrophysiological and histological techniques were used to trace sensory pathways for stretch mechanoreceptor fibres from the distal colon to dorsal root ganglia. Extracellular and intracellular recording techniques revealed sensory pathways for mechanoreceptors to the prevertebral sympathetic ganglia but no further centrally. Histological studies involving the retrograde transport of horseradish peroxidase revealed sensory pathways from the distal colon to the spinal cord, mainly to the level of the second lumbar vertebra. Few (less than 2000) fibres were involved; their perikarya were small (ca. 25 micron). Sensory perikarya in spinal ganglia in the guinea-pig could be categorized into two populations, F and H cells, after a previously defined nomenclature for murine spinal ganglion cells. F and H cells were distinguished initially by their times to decay by 50% of the action potential. H cells took three times as long to repolarize. F and H cells were distinguished further by their electrical properties including membrane potential, input resistance and amplitude and duration of the after-potential following the action potential. Both F and H cells showed unusual time-dependent rectification following either depolarizing or hyperpolarizing current pulses. Threshold currents to show rectification were different for F and H cells. When taken in conjunction with conduction velocities, the electrophysiological evidence may assist in identifying sensory neurones. For example, H cells appeared to have slow conducting (C fibre) axons. From the lack of electrophysiological evidence and limited histological support for major central sensory pathways, it is concluded that stretch mechanoreceptor information from the colon of the guinea-pig is referred mainly to the prevertebral ganglia with minimal involvement of the spinal cord.

Patterns of innervation of neurones in the inferior mesenteric ganglion of the cat

The patterns of peripheral and central synaptic input to non-spontaneous, irregular discharging and regular discharging neurones in the inferior mesenteric ganglion of the cat were studied in vitro using intracellular recording techniques. All three types of neurones in rostral and caudal lobes received central synaptic input primarily from L3 and L4 spinal cord segments. Since irregular discharging neurones received synaptic input from intraganglionic regular discharging neurones, some of the central input to irregular discharging neurones may have been relayed through the regular discharging neurones. In the rostral lobes of the ganglion, more than 70% of the non-spontaneous and irregular discharging neurones tested received peripheral synaptic input from the lumbar colonic, intermesenteric and left and right hypogastric nerves. Most of the regular discharging neurones tested received synaptic input from the intermesenteric and lumbar colonic nerves; none of the regular discharging neurones received synaptic input from the hypogastric nerves. Some of the peripheral synaptic input from the lumbar colonic and intermesenteric nerves to irregular discharging neurones may have been relayed through the regular discharging neurones. Axons of non-spontaneous and irregular discharging neurones located in the rostral lobes travelled to the periphery exclusively in the lumbar colonic nerves. Antidromic responses were not observed in regular discharging neurones during stimulation of any of the major peripheral nerve trunks. This suggests these neurones were intraganglionic. In the caudal lobes, irregular discharging neurones received a similar pattern of peripheral synaptic input as did irregular discharging neurones located in the rostral lobes. The majority of irregular discharging neurones in the caudal lobes projected their axons to the periphery through the lumbar colonic nerves. Non-spontaneous neurones in the caudal lobes, in contrast to those located in the rostral lobes, received peripheral synaptic input primarily from the hypogastric nerves. Axons of the majority of non-spontaneous neurones located in the caudal lobes travelled to the periphery through hypogastric nerves. The results suggest that non-spontaneous neurones and irregular discharging neurones in the rostral lobes and the majority of irregular discharging neurones in the caudal lobes transact and integrate neural commands destined for abdominal viscera supplied by the lumbar colonic nerves. Non-spontaneous neurones in the caudal lobes transact and integrate neural commands destined for pelvic viscera supplied by the hypogastric nerves.