Somatostatin is present in a subpopulation of noradrenergic nerve fibres supplying the intestine

sst1 mRNA is the prominent somatostatin receptor mRNA in the rat gastrointestinal tract: reverse transcription polymerase chain reaction and in situ-hybridization study

The inhibitory peptide hormone somatostatin and its receptors (sst1-sst5) regulate many physiological functions in the gastrointestinal tract. In an attempt to correlate the various effects of somatostatin in gastrointestinal physiology to individual sst subtypes sst1-sst5, mRNAs have been localized by semiquantitative reverse transcription polymerase chain reaction amplification and in situ hybridization of sst1 and sst3 in the rat alimentary tract. sst1-sst4 mRNAs were found throughout the gastrointestinal tract, sst1 mRNA being more abundant than sst2 and much more abundant than sst3 and sst4 mRNAs. sst5 transcripts were at the detection threshold. sst1 and sst3 mRNAs are present in enterocytes and enteric neurons suggesting a role of these subtypes in the somatostatin-mediated inhibition of acetylcholine release from myenteric neurons and of secretomotor neuron activity in the submucous plexus. The presence of sst3 mRNA in smooth muscle cells points to an additional role of this receptor in regulating gut motility.

Pathway-specific expression of PKC and PKA in sympathetic neurons

We used multiple-labelling immunofluorescence, intracellular dye injection, electrophysiological recording and confocal microscopy to examine the expression of immunoreactivity to protein kinase C (PKC) and protein kinase A (PKA) in sympathetic ganglia of guinea-pigs. PKCalpha and PKCgamma were widespread in vasoconstrictor and pilomotor neurons. High levels of PKA RIIalpha and RIIbeta were restricted to neurons that lacked significant expression of PKC, including somatostatin-containing neurons projecting to the gut, and non-noradrenergic vasodilator neurons. In coeliac ganglia, most neurons with PKC contained neuropeptide Y and displayed phasic patterns of action potential firing, often with a long after-hyperpolarization. Tonically firing neurons lacked both neuropeptide Y and PKC. These results show remarkably pathway-specific expression of protein kinases in functionally identified populations of sympathetic neurons.

Effects of sympathetic nerve stimulation on membrane potential in the circular muscle layer of mouse distal colon

Little is known about the effects of sympathetic nerve stimulation on the membrane potential of colonic smooth muscle. In the distal colon of the mouse, intracellular microelectrodes were used to record the effects of lumbar colonic (LCN) and intermesenteric nerve (IMN) stimulation on circular muscle membrane potential in vitro. A two-compartment organ bath was used to selectively perfuse the colon and inferior mesenteric ganglion (IMG). In the presence of nifedipine (1-2 microM) (to the colonic compartment only), spontaneous depolarizations (myoelectric complexes, MCs) were recorded about every 4 min. MCs consisted of a prolonged burst of rapid oscillations in membrane potential (approximately 2 Hz) that were superimposed on a slow depolarization (mean amplitude 12 mV). Single electrical stimuli (600 microseconds duration) delivered to the LCN or IMN did not elicit a detectable change in the membrane potential. However, trains of stimuli (e.g., 60 pulses at 10-20 Hz) to the LCN or IMN during the intervals between MCs evoked a depolarization (with superimposed action potentials in the absence of nifedipine). Trains of stimuli delivered during the plateau phase of the MC reduced or abolished the rapid oscillations, without a further membrane depolarization. The MC period was unaffected by stimulation of the IMN or LCN. Responses were abolished by the selective perfusion of guanethidine (1 microM) to the colon, or by severing the LCN. Hexamethonium (500 microM) (to the colon) abolished MCs, induced sustained depolarization and attenuated the amplitude of the sympathetic depolarizations by 74%. In hexamethonium, sympathetic responses remained attenuated when the membrane of the circular muscle was repolarised by sodium nitroprusside (1 microM). Immunohistochemical studies of the colon revealed intense immunoreactivity for tyrosine hydroxylase in the myenteric plexus but not in the circular muscle layer. It is suggested that responses to sympathetic nerve stimulation in the circular muscle layer of the mouse colon are secondary to actions on the enteric nervous system.

Extrinsic denervation increases myenteric nitric oxide synthase-containing neurons and inhibitory neuromuscular transmission in guinea pig

Enteric nerves can function normally without connections with the central nervous system. A contributing component of the functional autonomy exhibited by enteric nerves is their plasticity. In the present study, the number of nitric oxide synthase-immunoreactive (NOS-ir) myenteric neurons and inhibitory neuromuscular transmission were studied in extrinsically denervated ileal segments. Segments of ileum were extrinsically denervated by crushing the mesenteric blood vessels supplying a loop of ileum in anesthetized guinea pigs. Some unoperated animals were treated with capsaicin or 6-hydroxydopamine (6-OHDA) to disrupt primary afferent and sympathetic nerves, respectively. NOS-ir was localized using indirect immunofluorescence. Nerve-mediated relaxations of longitudinal muscle were studied in vitro using standard methods. At 7 weeks after extrinsic denervation there was a 93% increase in the number of NOS-ir myenteric neurons. The number of neurons containing detectable vasoactive intestinal peptide-ir neurons was not changed after extrinsic denervation. Neurogenic relaxations caused by 10, 20 and 50 Hz transmural stimulation were larger in extrinsically-denervated tissues compared to control tissues. The NOS antagonist, nitro-L-arginine (300 microM) inhibited neurogenic relaxations in control and extrinsically-denervated tissues. Capsaicin- but not 6-OHDA-treatment mimicked the effects of extrinsic denervation on NOS-ir and neurogenic relaxations of the longitudinal muscle. Active or passive properties of the longitudinal muscle were unaffected by extrinsic denervation. These data indicate that extrinsic denervation is associated with an increase in the number of myenteric neurons expressing detectable NOS-ir and potentiation of inhibitory transmission to longitudinal muscle. This effect is due to loss of extrinsic sensory nerves.

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

The tissues of the large intestine which receive an innervation by neurons of the major pelvic ganglia were identified following in vivo and in vitro anterograde labelling with the lipophilic tracer 1,1'didodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate in the male rat. The primary target in the gut of major pelvic ganglion neurons is the myenteric plexus of the distal colon and the rectum. The serosal ganglia, on the surface of the most distal region of the rectum and the circular muscle of the distal colon and rectum were less densely innervated. The pelvic ganglia do not innervate the longitudinal muscle, submucosal blood vessels, submucosal plexus, or mucosa. The pelvic supply reaches the bowel via two groups of rectal nerves and branches of the penile nerves. All of these connections also carry the axons of viscerofugal neurons from the bowel, some of which have terminal axons in the major pelvic ganglia. Finally, the different nerves supplied different targets. In particular, while the rectal nerves carried pelvic axons supplying the myenteric plexus, circular muscle, and serosal ganglia, the penile nerves only innervated the serosal ganglia. In addition, the two groups of rectal nerves innervated slightly different regions of the bowel and provided different projection patterns. However, successful in vivo labelling was achieved in only 6/12 animals and while all in vitro experiments resulted in successful labelling, it was clear that only a proportion of pelvic projections in any given nerve were labelled. These studies have shown that the major pelvic ganglia are primarily involved in the control of motility, but not of vascular and secretomotor functions. Thus pelvic neurons do not innervate the same range of target tissues within the bowel as the prevertebral ganglia. This study has also shown that the different pathways to the gut from the major pelvic ganglia innervate different tissues, suggesting that the autonomic innervation of the gut is not homogeneous along its length.

Differential distribution of substance P binding sites in guinea-pig sympathetic ganglia

We have used a combination of autoradiographic and immunohistochemical techniques to investigate the distribution of binding sites for substance P in relation to the distribution of substance P-immunoreactive nerve fibres and specific functional populations of neurons in the sympathetic ganglia of guinea-pigs. There was considerable heterogeneity in the density of binding sites for Bolton Hunter labelled 125I - substance P (BHSP). Binding sites were more dense in the prevertebral ganglia, such as the coeliac and inferior mesenteric ganglia, than in the paravertebral ganglia, such as the superior cervical or lumbar chain ganglia. The binding sites tended to be clumped within the ganglia. Within the prevertebral ganglia, they were associated predominantly with neurons projecting to the enteric plexuses. Many of these neurons contained somatostatin immunoreactivity. In the lumbar sympathetic chain ganglia, there was a weak association of binding sites with neurons containing immunoreactivity to vasoactive intestinal peptide. Overall, the density of binding sites matched the density of nerve fibres containing immunoreactivity to substance P in different ganglia. However, within particular ganglia, there was little, if any, correlation between the distribution of binding sites and nerve fibres containing substance P. Most of the binding sites in the ganglia had the pharmacological characteristics of NK1 receptors. Our results show that there is considerable heterogeneity in the expression of NK1 receptors in the sympathetic ganglia of guinea-pigs. However, given the relatively poor spatial correlation between the distribution of binding sites and potential sites of substance P release from intraganglionic nerve fibres, we suggest that substance P may diffuse for relatively large distances through the ganglia, with actions only on those neurons selectively expressing NK1 receptors.

Nitric oxide synthase- and neuropeptide Y-containing subpopulations of sympathetic neurons in the coeliac ganglion of the Atlantic cod, Gadus morhua, revealed by immunohistochemistry and retrograde tracing from the stomach

In this study retrograde tracing was used to locate sympathetic ganglion cells innervating the stomach of a teleost fish, Gadus morhua. A subpopulation of small neurons in the coeliac ganglion was retrogradely labelled after Fast Blue injection in the stomach wall. Neurons projecting to the myenteric plexus and muscle layers contained tyrosine hydroxylase immunoreactivity, and neurons projecting to submucosal layers and blood vessels contained neuropeptide Y immunoreactivity in addition to being tyrosine hydroxylase immunoreactive. A population of nitric oxide synthase containing tyrosine hydroxylase immunoreactive neurons was also found in the coeliac ganglion. These neurons were not frequently labelled after injection in any layer of the stomach. The presence of entero-enteric pathways was also surveyed, but too few enteric neurons were labelled with Fast Blue after injection in the coeliac ganglion to indicate a presence of an entero-enteric reflex. We conclude that in teleost fish, as previously reported in a variety of mammals, a pattern of target specific chemical coding of sympathetic neurons exists, but that all reflex systems of mammalian vertebrates are perhaps not present in fish.

GABA- and peptide-immunoreactivities co-localize in the rat central extended amygdala

The central amygdaloid nucleus and the lateral bed nucleus of the stria terminalis are two similar telencephalic structures belonging to the central extended amygdala. These regions contain numerous peptidergic and GABAergic neurones which maintain the neurones projecting to the brain stem under tight intrinsic control. Using immunocytochemistry in colchicine-treated rats, we showed that, in the lateral subdivision of the central amygdaloid nucleus and in the dorsal part of the lateral bed nucleus of the stria terminalis, a population of GABAergic neurones is able to co-synthesize either corticotropin-releasing factor or methionine-enkephalin, but never both peptides. These results suggest that, in the GABAergic intrinsic circuits of the central extended amygdala, co-liberated peptides can have a modulatory role on GABAergic actions.

Neurochemical classification of myenteric neurons in the guinea-pig ileum

A strategy has been developed to identify and quantify the different neurochemical populations of myenteric neurons in the guinea-pig ileum using double-labelling fluorescence immunohistochemistry of whole-mount preparations. First, six histochemical markers were used to identify exclusive, non-overlapping populations of nerve cell bodies. They included immunoreactivity for the calcium binding proteins calbindin and calretinin, the neuropeptides vasoactive intestinal polypeptide, substance P and somatostatin, and the amine, 5-hydroxytryptamine. The sizes of these populations of neurons were established directly or indirectly in double-labelling experiments using a marker for all nerve cell bodies. Each of these exclusive populations was further subdivided into classes by other markers, including immunoreactivity for enkephalins and neurofilament protein triplet. The size of each class was then established directly or by calculation. These distinct, neurochemically-identified classes were related to other published work on the histochemistry, electrophysiology and retrograde labelling of enteric neurons and to the simple Dogiel morphological classification. A classification scheme, consistent with previous studies, is proposed. It includes 14 distinct classes of myenteric neurons and accounts for nearly all neurons in the myenteric plexus of the guinea-pig ileum.

Immunohistochemically-defined subtypes of neurons in the inferior mesenteric ganglion of the guinea-pig

The distribution of somatostatin (SOM), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), substance P (SP), tyrosine hydroxylase (a marker of noradrenergic neurons, NA) and nitric oxide synthase-immunoreactivity (NOS-IR) was examined in the inferior mesenteric ganglion of guinea pigs with double- and triple-labelling immunohistochemistry. About 75% of neurons identified were NA/SOM, almost 20% were NA/NPY and the remainder consisted of small groups of NA/- (1-5%), NA/NPY/SOM (2-5%) and VIP (1-2%) neurons. VIP neurons contained NPY-IR, usually contained SOM-IR and were surrounded by dense pericellular baskets of SP fibres. NOS-IR was found in a small proportion of neurons colocalized with VIP but both NOS- and VIP-IR were also found alone in some neurons. Some NOS reactive varicose fibres throughout the ganglia also contained VIP-IR but much of the NOS- and VIP-IR appeared to be localized in discrete varicosities. SOM-IR was also detectable in TH fibres within myenteric ganglia of the distal colon. We conclude that the subtypes of neurons in the inferior mesenteric ganglion share some properties with other sympathetic and abdominal ganglia but they exist in distinct proportions and may make dissimilar projections along the length of the gut.

Innervation of the liver: morphology and function

Although it has been known for many years that the liver receives a nerve supply, it is only with the advent of immunohistochemistry that this innervation has been analysed in depth. It is now appreciated not only that many different nerve types are present, but also that there are significant differences between species, especially in the degree of parenchymal innervation. This has stimulated more detailed investigation of the innervation of the human liver in both health and disease. At the same time, functional studies have been underlining the important roles that these nerves play in processes as diverse as osmoreception and liver regeneration. This article briefly reviews current understanding of the morphology and functions of the hepatic nerve supply.

Chemical coding of neurons that project from different regions of intestine to the coeliac ganglion of the guinea pig

The chemical codings of neurons that project from the small intestine, caecum, proximal colon, distal colon and rectum to the coeliac ganglion of the guinea pig were investigated. The coeliac ganglion was injected with the retrogradely transported dye Fast Blue, and each of the regions was examined 6 days later in wholemounts that had been prepared for immunohistochemical localisation of pairs of antigens. In both the small and large intestines, all intestinofugal neurons were immunoreactive (IR) for choline acetyltransferase (ChAT). In each region of the large intestine, the largest population, representing 50-60% of retrogradely labelled neurons in each region, was immunoreactive for ChAT, bombesin (BN), calbindin (Calb) and nitric oxide synthase (NOS). Most intestinofugal neurons in the small intestine contain bombesin and VIP-IR along with ChAT-IR but none contain either Calb or NOS. Thus, nerve endings of enteric origin in the coeliac ganglion that contain NOS-IR or Calb-IR come from the large intestine and those with bombesin-IR but not NOS-IR are from the small intestine. The gastric wall was injected with Fast Blue in order to label noradrenergic (NA) neurons in the coeliac ganglion and to determine, by localisation of NOS and bombesin-IR, whether they receive inputs from the small and large intestine. Some NA neurons received inputs from the large intestine (and perhaps also from the small intestine) and some received inputs exclusively from the small intestine. Most NA neurons that received intestinofugal inputs had the chemical code NA/-; some were immunoreactive for somatostatin (NA/SOM neurons), but those with IR for neuropeptide Y (NA/NPY) rarely received intestinofugal inputs.

Neuropeptide Y in submucosal ganglia: regional differences in the innervation of guinea-pig large intestine

Since information about possible regional differences in the innervation of the guinea-pig large intestine is incomplete, a comparative study was made of the occurrence of neurones and nerve fibres of the submucosa showing immunoreactivity (IR) to neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP). In addition, a quantitative analysis was made of submucosal neurones in regions of guinea-pig large intestine selected for probable differences in their function. There were two principal findings: First, the density of NPY-IR neurone somata was high in the ascending colon (mean +/- SEM 3148 +/- 464 neurones/cm2; n = 5 animals) and progressively declined in an anal direction, the descending colon having 348 +/- 125 neurones/cm2 (in the same 5 animals); immunoreactive cell bodies were rare in the rectum. The reduced density was also reflected in a fall in the number of NPY-IR neurones/ganglion from 3.0 +/- 0.3 in the ascending colon to 0.5 +/- 0.2 in the descending colon. Second, varicose NPY-IR intraganglionic fibres were a conspicuous feature of the duodenum, caecum, transverse colon, descending colon and rectum, but not of the ileum, ascending colon or distal spiral. Moreover, in the descending colon and rectum the fibres were arranged in a loose 'cobweb' structure around non-NPY-IR neurone somata; in the caecum, there was an apparent paucity of NPY-IR somata but the exceptionally dense intraganglionic varicose fibre network may have obscured NPY-IR somata. In all regions, fibre baskets were rare. In the ascending colon, only 25 +/- 5% of ganglia (compared to 92 +/- 2% of ganglia in the descending colon) showed any intraganglionic nerve fibres; furthermore, when they occurred, these were not of the 'cobweb' type but, rather, they gave the ganglia a speckled appearance. In very immature fetuses at a stage of development when no neuropeptide somata could be found in either the myenteric or submucosal plexuses, many NPY-IR nerve fibres were present in the submucosa with a distribution similar to that of adult guinea pigs. With respect to the density of VIP-IR neurones in the large intestine, there was only a 40% reduction in the number of neurones/cm2 from proximal to distal colon, in contrast to the corresponding 90% reduction in the density of NPY-IR neurones. The number of VIP-IR neurones/ganglion (6.4) and the proportion of ganglia with VIP-IR fibres (> 90%) were constant. It is concluded that the striking regional dissimilarities in (i) the occurrence of NPY-IR neurone somata and (ii) in the disposition of intraganglionic NPY-IR nerve fibres indicate potentially important regional differences in the functions of neuropeptide Y as an antisecretory peptide in the local regulation of chloride transport in the mucosa and as a modulator of ganglionic transmission, respectively.

Release of somatostatin-like immunoreactivity from enriched enteric nerve varicosities of rat ileum

Synaptosomes were isolated from rat ileum by various steps of differential centrifugation. The peptide content for somatostatin-like immunoreactivity was used as marker for neuronal membranes. The enriched synaptosomal fraction (P2) showed a good enrichment of somatostatin content (4-fold) in comparison to the post-nuclear supernatant. The basal release of somatostatin-like immunoreactivity was 26 +/- 3 pg/mg tissue protein. KCl-evoked depolarization (65 mM) caused a significant increase of somatostatin-like immunoreactivity release (72 +/- 11 pg/mg, n = 12, P < 0.001) compared to basal release. In Ca(2+)-free medium the evoked release of somatostatin-like immunoreactivity was abolished. A substantial increase of somatostatin-like immunoreactivity release (52 +/- 7 pg/mg, n = 12, P < 0.05) was also observed in the presence of the Ca2+ ionophore A-23187. The cholinergic agonist carbachol elicited a dose-dependent release of somatostatin-like immunoreactivity (10(-7) M: 54 +/- 8 pg/mg, 10(-6) M: 63 +/- 6 pg/mg, 10(-5) M: 53 +/- 5 pg/mg, n = 12, P < 0.001), which was blocked by atropine (10(-6) M: 35 +/- 6 pg/mg, n = 12, P < 0.001), but not by hexamethonium. Other presynaptic modulating substances such as serotonin, the selective neurokinin-B agonist [beta Asp4,MePhe7]neurokinin B-(4-10), neurotensin, cholecystokinin-8, caerulein and pentagastrin had no stimulatory effect on release of somatostatin-like immunoreactivity. In summary, somatostatin-like immunoreactivity can be released from enteric synaptosomes by both depolarization with KCl and cholinergic stimulation via a muscarinic mechanism. The synaptosomes of intrinsic nerves offer an approach to study release of neuronal somatostatin on the subcellular level.

Neuropeptide immunoreactivity and co-existence in cardiovascular nerves and autonomic ganglia of the estuarine crocodile, Crocodylus porosus, and cardiovascular effects of neuropeptides

The two aortas of the crocodile are in open connection at two sites, the foramen of Panizzae immediately outside the ventricles, and the arterial anastomosis at the level of the gut. The present study was performed to elucidate the innervation of the cardiovascular structures of the crocodile, in part to provide a further basis for the assumption that the apertures of the foramen and the anastomosis may be altered, possibly leading to changes in the flow profiles of the central vessels. The presence of smooth muscle arranged at the circumference of the foramen and in the walls of the anastomosis was demonstrated. The cardiovascular structures were innervated by nerves containing co-existing tyrosine hydroxylase, NPY and somatostatin immunoreactivities, which also occurred in neurons of the sympathetic ganglia. CGRP and substance P immunoreactive material co-existed in cardiovascular nerves, and in the nodose ganglion. In addition, bombesin, VIP and galanin immunoreactive nerves were found. Effects of neuropeptides on blood flows and blood pressures were studied in vivo. Substance P increased all blood flows measured, NPY increased the flow through the arterial anastomosis while neurotensin caused an initial decrease in the flow through the arterial anastomosis. In conclusion, there is a rich innervation of the heart and major vessels of the estuarine crocodile, including the foramen of Panizza and the arterial anastomosis. These nerves possibly regulate the distribution of blood in the cardiovascular system, which is further suggested by the results of the injection of neuropeptides.

Neuropeptide Y is expressed in islet somatostatin cells of the hamster pancreas: a combined immunocytochemical and in situ hybridization study

Neuropeptide Y (NPY) is known to occur in the autonomic nervous system, including the pancreatic islet innervation. We now present evidence that NPY is also expressed in endocrine islet cells in hamster pancreas. Thus, NPY-immunoreactivity and gene expression were detected in peripheral islet cells, using immunocytochemistry (ICC), in situ hybridization (ISH), and a combination of these techniques. Double immunostaining for NPY and somatostatin enabled localisation of NPY ot the vast majority of the somatostatin cells. However, a few somatostatin cells were devoid of NPY immunoreactivity and an occasional NPY-immunoreactive cell was devoid of somatostatin. ISH with an NPY mRNA specific probe, showed labelling of cells in the islet periphery. Furthermore, combined ISH for NPY mRNA and ICC for somatostatin showed autoradiographic labelling of somatostatin cells to a varying degree. Both somatostatin and NPY are inhibitors of insulin and/or glucagon secretion. Thus, in the islets these two peptides may be coreleased and cooperate in the regulation of islet hormone secretion. The role for NPY emanating from islet cells is probably paracrine rather than endocrine.

Plurichemical transmission and chemical coding of neurons in the digestive tract

The enteric nervous system contains neurons with well-defined functions. However, when neurons of the same function are examined in different regions or species, they are found to show subtle differences in their pharmacologies of transmission and different chemical coding. Individual enteric neurons use more than one transmitter, i.e., transmission is plurichemical. For example, enteric inhibitory neurons have three or more primary transmitters, including nitric oxide, vasoactive intestinal peptide, and possibly adenosine triphosphate and pituitary adenylyl cyclase activating peptide. Primary transmitters are highly conserved, although their relative roles vary considerably between gut regions. Multiple substances, including transmitters and their synthesizing enzymes and nontransmitters (such as neurofilament proteins), provide neurons with a chemical coding through which their functions and projections can be identified. Although equivalent neurons in different regions have the same primary transmitters, other chemical markers differ substantially. Caution must be taken in extrapolating pharmacological and neurochemical observations between species or even between regions in the one species. On the other hand, careful interregion and interspecies comparisons lead to an understanding of the features of enteric neurons that are highly conserved and can be used in valid extrapolation.

Properties of putative cardiac and non-cardiac neurones in the rat stellate ganglion

Intracellular recordings were made from isolated left or right stellate ganglia of Wistar rats and the morphology of neurones studied after intracellular injection of hexammine cobaltic chloride or back-filling from the post-ganglionic nerve with cobalt lysine complex. The experiments attempted to identify the location, electrophysiological properties, morphology and chemosensitivity of putative cardiac neurones in the ganglion. These were identified by antidromic activation of the axon in a cardiac nerve and compared with neurones projecting towards the brachial plexus (non-cardiac neurones). Putative cardiac neurones were localized in the ganglion around the postganglionic nerve entry zone and showed considerable morphological diversity. They had complex dendritic trees with, on average, seven dendrites. They included both phasic and tonic neurones and were depolarized by muscarinic agonists, angiotensin and substance P; they invariably had a synaptic input from the sympathetic trunk and from a T1 or T2 ramus and, in 16% of cells, from a cardiac nerve. Non-cardiac neurones were more widely scattered through the stellate ganglion but were not clearly different in morphology, resting membrane potential or the proportion of phasic and tonic cells from putative cardiac neurones. They also showed depolarizing responses to muscarinic agonists, angiotensin and substance P. Angiotensin responses of stellate ganglion cells were blocked by the peptide antagonist, saralasin (1 microM).

Electrophysiological analysis of the convergence of peripheral inputs onto neurons of the coeliac ganglion in the guinea pig

The convergence of intestinofugal axons from different intestinal regions onto individual neurons in the coeliac ganglion of the guinea pig was investigated using intracellular recording methods in vitro. Peripheral nerve trunks from the distal ileum, the most proximal colon and the colon near the colonic flexure were electrically stimulated along with preganglionic fibres running in the splanchnic nerve. Fast cholinergic excitatory synaptic potentials (EPSPs) were seen in ganglion cells in response to stimulation of each nerve trunk. Roughly half of 78 neurons impaled received inputs from stimulation of peripheral nerves, and almost all of these received input from the proximal colon. Most cells responded to stimulation of more than one peripheral nerve indicating that coeliac neurons receive converging inputs from intestinofugal neurons located in more than one intestinal region. In a second series of experiments, segments of intestine were left attached to the ganglion and distended with saline to stimulate peripheral mechanosensory input to the coeliac ganglion. In each experiment, two segments were stimulated. A subgroup of ganglion cells exhibited spontaneous fast EPSPs and the frequency of these potentials was increased by distension of one or other of the attached intestinal segments. However, few neurons responded to distension of both of the attached intestinal segments suggesting that some of the intestinofugal inputs to the coeliac ganglion identified by electrical stimulation may be sensitive to sensory modalities other than distension. Hexamethonium (0.5 mM) applied to the intestine, and not to the coeliac ganglion, reduced the frequency of the spontaneous synaptic potentials seen in coeliac ganglion cells, but did not abolish the response to distension of the colon (n = 8). When the Ca2+ concentration of the solution bathing the proximal colon was reduced to block all synaptic transmission in the enteric plexuses the background synaptic input was further depressed, but again the response to distension was little changed (n = 4). This suggests that at least some of the neurons projecting from the colon to the coeliac ganglion are first order mechanosensory neurons.

Somatostatin-mediated inhibitory postsynaptic potential in sympathetically denervated guinea-pig submucosal neurones

1. Intracellular recordings were made from submucosal neurones in guinea-pig ileum. In some animals, the extrinsic (sympathetic) nerves to the submucosal plexus were severed 5-7 days previously. The actions of somatostatin and somatostatin analogues on membrane potential, membrane current and inhibitory postsynaptic potentials (IPSPs) were examined. 2. Somatostatin, somatostatin(1-28), [D-Trp8]somatostatin and the somatostatin analogue CGP 23996 all produced equivalent maximum hyperpolarizations or outward currents; half-maximal concentrations (EC50 values) were 9-11 nM. The somatostatin analogue MK 678 had an EC50 of 0.9 nM. Extrinsic sympathectomy did not alter concentration-response relations for somatostatin or its analogues. 3. Somatostatin (> 100 nM) produced hyperpolarization or outward current that declined almost completely during superfusion for 2-4 min; decline of the somatostatin current was exponential with a time constant of 30 s in the presence of 2 microM somatostatin. Desensitization was not altered by extrinsic denervation. 4. Recovery from desensitization was rapid and followed the time course of agonist wash-out. Forskolin, phorbol esters, dithiothreitol, hydrogen peroxide, concanavalin A, or reducing temperature from 35 to 29 degrees C did not alter the time course, degree of, or recovery from desensitization. 5. The somatostatin-induced desensitization was of the homologous type; no cross-desensitization to opiate or alpha 2-adrenoceptor agonists (which activate the same potassium conductance) occurred. 6. Somatostatin desensitization did not alter the adrenergic IPSP seen in sympathetically innervated preparations but abolished the non-adrenergic IPSP recorded from normal preparations and from preparations in which the extrinsic sympathetic nerve supply had been surgically removed. 7. The selective blockade of the non-adrenergic IPSP by the homologous-type somatostatin desensitization characterized in the present study provides strong support for the hypothesis that somatostatin is the neurotransmitter underlying the non-adrenergic IPSP in both normal and extrinsically denervated submucosal neurones.

Characterization of NADPH diaphorase activity in rat sympathetic autonomic ganglia--effect of diabetes and aging

NADPH-diaphorase histochemistry, which identifies neural sites of nitric oxide production, demonstrated intensely stained nerve terminals surrounding the cell bodies of a subpopulation of neurons in rat prevertebral celiac and superior mesenteric sympathetic ganglia but failed to comparably label terminals in paravertebral superior cervical ganglia or perikarya in any sympathetic ganglion. The superior mesenteric ganglia of aged and diabetic rats, in which synaptic dysplasia (neuroaxonal dystrophy) is prominent, failed to show involvement of diaphorase containing nerve terminals.

Neuropeptides in the human celiac/superior mesenteric ganglionic complex: an immunohistochemical study

The occurrence of vasoactive intestinal polypeptide (VIP), peptide histidine-isoleucine (PHI), calcitonin gene-related peptide (CGRP), substance P (SP), somatostatin (SOM), galanin (GAL) and enkephalins (ENK) is studied in the human celiac/superior mesenteric ganglionic complex of pre- and full-term newborns, and adult subjects by means of immunohistochemistry. The antisera used labelled nerve fibres and terminal-like networks for each examined peptide, as well as VIP- and SOM-positive postganglionic neurons. Differences in the relative amount and density of the structures immunoreactive to the various peptides were observed. Moreover, variations in the amount and type of labelled elements were appreciable for each peptide when specimens from subjects at perinatal and adult ages were compared. Double-labelling immunofluorescence for SP and each other peptide showed that co-localization with SP is very frequent for CGRP, moderate to scarce for GAL and SOM, and rare to absent for PHI, VIP and ENK. VIP-, ENK- and CGRP-immunolabeled perikarya bearing the morphological features of the small intensely fluorescent (SIF) cells occurred in the organ. The presence of a paraganglion in one of the specimens examined allowed the detection of VIP- and ENK-positive cell bodies and VIP-, ENK-, SP- and GAL-like immunoreactive varicose nerve fibres in it. The results obtained provide substantial morphological data in support of the involvement of the examined peptides in the chemical interneuronal signalling in the human celiac/superior mesenteric ganglia.

Distributions of neuropeptide Y, vasoactive intestinal peptide and somatostatin in populations of postganglionic neurons innervating the rat kidney, spleen and intestine

Some peripheral peptidergic nerves selectively innervate different types of tissue in abdominal organs. Neuropeptide Y- and vasoactive intestinal peptide-immunoreactive nerve terminals have been identified in the kidney, spleen and intestine and these peptides may have important physiological actions. Somatostatin has been found in sympathetic ganglia, and nerve terminals containing this peptide have been identified in the intestine. We have used fluorescent retrograde tracers to identify renal, splenic and mesenteric postganglionic neurons in rat sympathetic ganglia and then used immunocytochemistry to determine the proportions of these three identified groups of neurons displaying immunoreactivity for neuropeptide Y, vasoactive intestinal peptide and somatostatin. Most renal, splenic and mesenteric neurons were immunoreactive for neuropeptide Y and less than 1% of cells innervating these organs were immunoreactive for vasoactive intestinal peptide. Somatostatin immunoreactivity was present only in a small percentage of mesenteric neurons and not in renal or splenic neurons. The present study demonstrates that (i) the rat kidney, spleen and intestine do not differ in the proportion of innervation by neuropeptide Y-immunoreactive neurons, (ii) the solar plexus, splanchnic ganglion and chain ganglia (T12 and T13) provide very little vasoactive intestinal peptide-immunoreactive inputs to these organs, and (iii) somatostatin-immunoreactive neurons innervate the intestine but not the kidney or spleen.

Distribution of somatostatin-immunoreactive nerve fibres in Peyer's patches

The distribution of somatostatin-immunoreactive nerve fibres in Peyer's patches of the cat was demonstrated by immunocytochemical techniques. A large number of immunoreactive nerve fibres was observed in the tela submucosa very close to the Peyer's patches. Some immunoreactive nerve cell bodies were also found in this layer. The immunoreactive nerve terminals ran around the margin of the follicles and only a few nerve fibres were observed in the centre of follicles. Electron-microscopic investigation showed that these immunoreactive nerve terminals were in very close contact with lymphocytes and plasma cells, where no Schwann cell sheath was interposed. The gap between the nerve processes and the lymphocytes and plasma cells was about 20-200 nm, and occasionally less. These results provide morphological evidence consistent with the view that somatostatin has a neuroimmunomodulatory action.

Immunohistochemical characterization of NPY and substance P containing nerve terminals in aged and diabetic human sympathetic ganglia

To compare the neuropeptide specificity of dystrophic axon formation in aging versus diabetic human sympathetic ganglia we have immunohistochemically characterized neuropeptide Y (NPY) and substance P containing intraganglionic nerve terminals. Prevertebral superior mesenteric but not paravertebral superior cervical ganglia developed markedly swollen NPY containing axonal termini with both aging and diabetes. Substance P containing nerve terminals failed to develop dystrophic changes. Selective loss of classes of nerve terminals may result in discrete functional sequellae.

Transmitter diversity in ganglion cells of the guinea pig gallbladder: an immunohistochemical study

Several neurotransmitters have been reported to exist in the ganglionated plexus of the guinea pig gallbladder. These include substance P, neuropeptide Y (NPY), calcitonin gene-related peptide, vasoactive intestinal peptide (VIP), acetylcholine, norepinephrine, serotonin, and dopamine. To determine which neuropeptides are intrinsic to gallbladder ganglia, we performed immunohistochemistry on colchicine-treated preparations. In separate, single-labeled preparations, a majority of neurons contained substance P-, NPY-, or somatostatin-like immunoreactivity. In double-labeled preparations, a large majority of the neurons that contained substance P-like immunoreactivity also contained NPY-like immunoreactivity and somatostatin-like immunoreactivity. Immunoreactivity for VIP was present in a small percentage of the gallbladder neurons which did not contain substance P-like immunoreactivity. Additional experiments were done to test for the presence of other compounds, known to exist in the neurons of the gut. Although immunoreactivity was found in control preparations of small intestine, the ganglionated plexus of the gallbladder lacked immunoreactivity for galanin, dynorphin, enkephalin, gastrin-releasing peptide, or gamma-aminobutyric acid. We conclude that ganglia of the guinea pig gallbladder contain at least two populations of neurons, based on transmitter phenotype. One of these populations appears to contain substance P, NPY, and somatostatin. Another population, which represents a small contingent of the total population of neurons, contains VIP.

Review article: adrenergic control of motor and secretory function in the gastrointestinal tract

The role that the sympathetic nervous system plays in modulating physiological processes in the gastrointestinal tract is becoming clearer. It is now known that motor, secretomotor and vasomotor activity are all modulated independently by the system. Adrenoreceptor stimulation appears to reduce intestinal contraction (except at sphincters), both via alpha-receptors which inhibit neurotransmitter release and also by a direct beta-receptor mediated action on smooth muscle. There is also evidence for tonic activity in the beta-adrenergic pathway, since beta-antagonists tend to increase contraction pressures. In animals alpha-receptor-mediated pathways modulate fluid and electrolyte absorption, and alpha-adrenergic agonists enhance net absorption and reduce net secretion. In man there is also evidence for a beta-adrenergic pathway which controls secretomotor function. Carbohydrate absorption appears to be dependent on activity in a beta-adrenergic pathway, although this may be an indirect effect of changes in motor function. The time course of changes of both secretomotor and motor activity, induced by modulating sympathetic or adrenergic input, differ from the vascular changes indicating that the effects occur independently of each other. The gastrointestinal response to stressors is mediated, in part at least, by the sympathetic nervous system. Differences between individuals are likely to prove important. Since the sympathetic nervous system regulates gastrointestinal function both in the basal state and under stressful conditions, it will have effects on pathophysiological responses. Modification of such responses is likely to ameliorate symptoms, as has already been found for alpha-2-adrenergic agonists which have an antidiarrhoeal action.

Calbindin-immunoreactive nerve terminals in the guinea pig coeliac ganglion originate from colonic nerve cells

Previous work has shown that calbindin-immunoreactive (calbindin-IR) nerve terminals are numerous in guinea pig prevertebral ganglia. A high proportion of those colonic nerve cells that project to the inferior mesenteric ganglia are calbindin-IR, but none of the neurons that project from the small intestine to the coeliac ganglion are immunoreactive for calbindin. The present work was designed to determine the source of the calbindin-IR fibres and the pathways by which they reach the coeliac ganglion. Sections through the major nerve trunks that connect with the coeliac ganglion revealed numerous calbindin-IR fibres in the inferior coeliac nerves and in the intermesenteric nerves, while there were very few fibres in the splanchnic or superior coeliac nerves. When all peripheral nerve connections to a lobe of the coeliac ganglion were cut, all calbindin-IR terminals degenerated. Cutting the ileo-caeco-colic nerves caused a substantial reduction in the density of nerve fibres in the coeliac ganglion, whereas no significant reduction could be detected when the intermesenteric nerves were cut. However, lesion of both the ileo-caeco-colic and intermesenteric nerves caused all the calbindin-IR nerve fibres in the coeliac ganglion to degenerate. It is concluded that most or all of the calbindin-reactive nerve terminals in the coeliac ganglion originate from the large intestine and that most reach the ganglion via the ileo-caeco-colic nerves. Thus many colonic intestinofugal neurons, supplying both the coeliac and inferior mesenteric ganglia, are immunoreactive for calbindin, whereas small intestinal intestinofugal neurons are not immunoreactive for this protein.

Neuropeptide Y immunoreactivity in the mammalian liver: pattern of innervation and coexistence with tyrosine hydroxylase immunoreactivity

The distribution of nerve fibers displaying neuropeptide Y immunoreactivity in relationship to the catecholaminergic innervation of rat, guinea pig, and rabbit liver was investigated by single- and double-label immunofluorescence methods. In all three species, neuropeptide Y-immunoreactive fibers are prominent in association with the vasculature, biliary pathway, and stromal compartment. The neuropeptide Y innervation of the parenchyma, on the other hand, differs among the three species in term of density. It is quite sparse in the rat and rabbit, particularly in the former species. In the guinea pig liver, numerous single, varicose neuropeptide Y-containing nerve fibers innervate the hepatic parenchyma; often, thin processes surround single hepatocytes and lie close to sinusoids. The immunoreactive pattern of tyrosine hydroxylase, a marker for catecholaminergic neurons and fibers, is comparable to that of neuropeptide Y. Most neuropeptide Y-containing nerve fibers also contain tyrosine hydroxylase immunoreactivity, in all three species, with the exception of the rabbit parenchyma, where a substantial proportion of catecholaminergic fibers lack immunoreactivity for neuropeptide Y. Finally, systemic administration of the sympathetic neurotoxin, 6-hydroxydopamine, in rats and guinea pigs resulted in virtually complete elimination of both neuropeptide Y- and tyrosine hydroxylase-immunoreactive fibers. These findings are consistent with the hypothesis that neuropeptide Y-containing nerve fibers form a subpopulation of the sympathetic innervation of the mammalian liver, which is likely to originate from prevertebral sympathetic ganglia.

Vasomotor, pilomotor and secretomotor neurons distinguished by size and neuropeptide content in superior cervical ganglia of mice

Populations of postganglionic sympathetic neurons projecting to cranial targets from the superior cervical ganglia of mice were identified by retrograde axonal tracing with Fast blue combined with double-labelling immunofluorescence to detect immunoreactivity to tyrosine hydroxylase and neuropeptide Y. Nearly all neurons in the ganglion contained tyrosine hydroxylase immunoreactivity, but only about 50% of them also contained immunoreactivity to neuropeptide Y. The maximum diameter of cells with immunoreactivity to neuropeptide Y was significantly smaller than that of cells without it. Terminal axons containing immunoreactivity to both neuropeptide Y and tyrosine hydroxylase occurred around blood vessels supplying most cranial tissues, including the skin. Axons with immunoreactivity to tyrosine hydroxylase but not to neuropeptide Y innervated the piloerector muscles and the acini of the salivary glands. After injection of Fast blue into the skin or the submandibular salivary gland, populations of vasomotor, pilomotor and secretomotor neurons could be distinguished by soma size and by neuropeptide Y immunoreactivity. Neurons projecting to the salivary glands were the largest (mean diameter: 32 microns) and lacked immunoreactivity to neuropeptide Y; neurons projecting to cutaneous blood vessels were the smallest (mean diameter: 19 microns) and contained immunoreactivity to neuropeptide Y; neurons projecting to piloerector muscles were intermediate in size (mean diameter: 23 microns) and lacked neuropeptide Y immunoreactivity. A cluster analysis procedure confirmed that soma size and peptide content together identify major functional populations of neurons in the superior cervical ganglia of mice.

Ultrastructure and distribution of somatostatin-like immunoreactive neurons and nerve fibres in the coeliac ganglion of cats

Somatostatin-like immunoreactivity was localized in nerve cell bodies and nerve terminals in the cat coeliac ganglion. Two types of somatostatin-immunoreactive cell bodies were revealed, the first being large (diameter 35 microns), numerous and weakly labelled, whereas the second was considerably smaller (diameter 10.4 microns), sparsely distributed and heavily stained. The immunoreactive nerve terminals were in synaptic contact with many immunonegative large neurons and dendrites. However, in a few cases, somatostatin-immunoreactive nerve terminals could also be observed on the surface of lightly stained neurons. Transection of vagal or mesenteric nerves failed to affect the distribution or density of somatostatin-like immunoreactive nerve terminals. These results demonstrate the existence of a synaptic input to the principal neurons of the coeliac ganglion of the cat by somatostatin-containing nerve terminals and suggest that this peptide may act as a neuromodulator or neurotransmitter. It is proposed that somatostatin-positive neurons provide intrinsic projections to other somatostatin-positive and to somatostatin-negative neurons throughout the coeliac ganglion, thereby creating a complex interneuronal system.

Effects of somatostatin on human intestinal lamina propria lymphocytes. Modulation of lymphocyte activation

We have investigated the effect of somatostatin (SOM) on the mitogen-induced activation of lamina propria mononuclear cells isolated from the human intestinal mucosa (LPMNC) and of the autologous peripheral blood lymphocytes (PBMNC). The occurrence of specific SOM receptors and their biological characteristics were also investigated. The counts of interleukin-2 receptor (IL-2R)-positive cells after mitogen stimulation were significantly lower in the presence of SOM. This effect of SOM appeared to be dose dependent, with SOM concentrations ranging between 1 pM and 1 microM. The amount of SOM required for the 50% inhibition of this expression was 1000 times lower in the LPMNC population than in the PBMNC. Binding studies showed that human LPMNC bear specific receptors for SOM and demonstrated that the affinity of these receptors was 1000 times higher than that of the SOM receptors present on the PBMNC (Kd 2.1 +/- 0.34 nM vs. 910 +/- 46 nM, respectively). The inhibitory effect of SOM on the proliferative response appeared to be restricted to PBMNC, with a maximal inhibition at 1 nM SOM, while LPMNC proliferative response was poorly affected. SOM inhibited the in vitro immunoglobulin production of both PBMNC and LPMNC over a wide range of concentrations, with a maximal inhibition at 1 nM. At this concentration the effect of SOM on IgA was more pronounced in the PBMNC than in the LPMNC. Our results lend support to the concept that in humans SOM plays a role in the modulation of the immune response at the level of the intestinal mucosa where cell-to-cell interactions between SOM releasing nerve fibers and cells and the immune system occur.

Somatostatin cells in rat antral mucosa: qualitative and quantitative ultrastructural analyses in different states of gastric acid secretion

In the gastrointestinal tract somatostatin is localized in endocrine cells and in neurons. The antral somatostatin (D-) cell shares features of both cell types. The activity of the antral D-cell is regulated by intragastric pH. Therefore different states of gastric acidity were induced experimentally in order to study D-cell morphology at the electron microscopical level. The morphological findings were related to measurements of plasma and tissue concentrations of the peptide. The D-cell is characterized by extensive membrane interdigitations with neighbouring cells. Changes in the activity of antral D-cells are reflected by an increase in cytoplasmic secretory granule density and a shift of secretory granules towards basal cell processes. Direct endocrine cell contacts at the level of the perikarya were rarely observed. The intracellular distribution of secretory granules suggests that cell communication is more likely to take place at the level of the strongly immunoreactive cytoplasmic processes. No evidence for endocrine or exocrine (luminar) secretion was observed morphologically. This is in agreement with the concept of paracrine secretion of the antral D-cell.

Selective control of sympathetic pathways to the kidney, spleen and intestine by the ventrolateral medulla in rats

1. Electrical activity of multifibre renal, splenic, mesenteric and greater splanchnic nerves and 13th thoracic white rami was recorded in artificially respired, urethane-anaesthetized rats. Discharge of neurones in the rostral ventrolateral medulla was blocked by unilateral microinjections of the inhibitory amino acid glycine and effects on the electrical activity of these sympathetic nerves were compared. 2. Blockade of the rostral ventrolateral medulla caused greater decreases in discharge of renal than splenic nerves and had no consistent effect on mesenteric nerves. This blockade also decreased the discharge of the preganglionic white rami more than that of the preganglionic splanchnic nerves. 3. Postganglionic responses to rostral ventrolateral medulla blockade were always greater than preganglionic responses. 4. The arterial pressure and renal nerve responses to rostral ventrolateral medulla blockade in urethane-anaesthetized rats were not different from those in rats anaesthetized with alpha-chloralose. 5. These findings demonstrate that pre- and postganglionic sympathetic pathways to the kidney are more dependent upon excitatory drive from the rostral ventrolateral medulla than pathways directed to the spleen and intestine.

Calbindin immunoreactivity in sensory and autonomic ganglia in the guinea pig

Immunoreactivity (IR) for the calcium binding protein, calbindin, was localized in sensory ganglia (nodose, trigeminal and dorsal root), in parasympathetic ganglia (otic and sphenopalatine) in sympathetic chain ganglia and in sympathetic pre-vertebral ganglia of guinea pig. In sensory ganglia, fine nerve fibres with calbindin-IR surrounded the majority of cell bodies, a low proportion of which were themselves reactive. In cranial parasympathetic and in sympathetic chain ganglia, a small proportion of nerve cells was surrounded with baskets of calbindin-IR nerve fibres, but very few cell bodies were reactive. In prevertebral sympathetic ganglia, dense networks of terminals surrounded many cell bodies, but few somata were themselves reactive. In the coeliac and inferior mesenteric ganglia, the calbindin-IR nerve fibres surrounded somatostatin-IR cell bodies, but not those with neuropeptide Y-IR. It is concluded that specific subgroups of peripheral autonomic and sensory neurones have calbindin-IR.

Neural blockade in basal and postreceptor-stimulated intestinal transport

Postreceptor protein stimulation significantly alters the transport state of the ex vivo small intestine. This study investigated the effects of neural blockade on basal and stimulated ionic transport. Rabbit ileal segments (n = 46) were arterially perfused with an oxygenated sanguinous buffered electrolyte solution. The lumen was perfused with an isotonic solution containing [14C]polyethylene glycol as a nonabsorbable marker. Net fluxes of H2O, Na+, and Cl- were calculated. Tetrodotoxin (TTX) was used to block enteric neural transmission. Forskolin (FOR) was used to activate adenylate cyclase, and phorbol 12,13-dibutyrate (PDB) served to activate protein kinase C. Two groups were studied. Group A preparations had no TTX pretreatment, while group B preparations were pretreated with TTX. In the Group A preparations, TTX at 10(-6) M and PDB at 10(-5) M caused significant proabsorptive effects with a delta FH2O of +20 +/- 7 and +15 +/- 2 microliters/min, respectively (P less than 0.05), while FOR stimulated significant secretion with a delta FH2O of -14 +/- 3 microliter/min (P less than 0.05). In the Group B TTX-pretreated preparations, FOR did not cause secretion and PDB maintained an absorptive state. These results indicate that neural blockade with TTX reverses basal secretion in the ex vivo intestine, suggesting that an intact enteric nervous system maintains the secretory status of the intestine. FOR-induced adenylate cyclase-activated secretion does not occur in the presence of TTX, implying that intact neural transmission is required for the FOR effect. PDB-induced protein kinase C-activated absorption occurs despite neural blockade, suggesting that the PDB-induced proabsorptive effect is mediated without neural intermediaries.

Central neural control of esophageal motility: a review

We review recent studies on the central neural control of esophageal motility, emphasizing the anatomy and chemical coding of esophageal pathways in the spinal cord and medulla. Sympathetic innervation of the proximal esophagus is derived primarily from cervical and upper thoracic paravertebral ganglia, whereas that of the lower esophageal sphincter and proximal stomach is derived from the celiac ganglion. In addition to noradrenaline, many sympathetic fibers in the esophagus contain neuropeptide Y (NPY), and both noradrenaline and NPY appear to decrease blood flow and motility. Preganglionic neurons innervating the cervical and upper thoracic ganglia are located at lower cervical and upper thoracic spinal levels. The preganglionic innervation of the celiac ganglion arises from lower thoracic spinal levels. Both acetylcholine (ACh) and enkephalin (ENK) have been localized in sympathetic preganglionic neurons, and it has been suggested that ENK acts to pre-synaptically inhibit ganglionic transmission. Spinal afferents from the esophagus are few, but have been described in lower cervical and thoracic dorsal root ganglia. A significant percentage contain calcitonin gene-related peptide (CGRP) and substance P (SP). The central distribution of spinal afferents, as well as their subsequent processing within the spinal cord, have not been addressed. Medullary afferents arise from the nodose ganglion and terminate peripherally both in myenteric ganglia, where they have been postulated to act as tension receptors, and, to a lesser extent, in more superficial layers. Centrally, these afferents appear to end in a discrete part of the nucleus of the solitary tract (NTS) termed the central subnucleus. The transmitter specificity of the majority of these afferents remains unknown. The central subnucleus, in turn, sends a dense and topographically discrete projection to esophageal motor neurons in the rostral portion of the nucleus ambiguous (NA). Both somatostatin-(SS) and ENK-related peptides have been localized in this pathway. Finally, motor neurons from the rostral NA innervate striated portions of the esophagus. In addition to ACh, these esophageal motor neurons contain CGRP, galanin (GAL), N-acetylaspartylglutamate (NAAG), and brain natriuretic peptide (BNP). The physiological effect of these peptides on esophageal motility remains unclear. Medullary control of smooth muscle portions of the esophagus have not been thoroughly investigated.

Opioid-like immunoreactive neurons in secretomotor pathways of the guinea-pig ileum

In this study we sought to establish the distribution, projections and neurochemical coding of opioid immunoreactive neurons in secretomotor pathways of the guinea-pig ileum. Non-cholinergic secretomotor neurons in the submucous ganglia have been shown to be immunoreactive for dynorphin A 1-8, dynorphin A 1-17, dynorphin B and alpha neo-endorphin while cholinergic neurons have been shown to be immunoreactive for dynorphin A 1-8 only. Thus all submucous neurons in the guinea-pig ileum are immunoreactive for prodynorphin-derived peptides. Two major populations of opioid immunoreactive fibres projecting to the submucous ganglia have been established. Firstly, neurons immunoreactive for prodynorphin-derived peptides and vasoactive intestinal peptide project anally from the myenteric plexus to the submucous ganglia. Secondly, a substantial proportion of sympathetic postganglionic fibres immunoreactive for tyrosine hydroxylase, and projecting from the coeliac ganglion to submucous ganglia, have been shown to be immunoreactive for prodynorphin-derived peptides. Other smaller populations of opioid-immunoreactive neurons include fibres immunoreactive for substance P, enkephalin and dynorphin A 1-8 which project from the myenteric plexus to the non-ganglionated plexus of the submucosa. These fibres are probably excitatory motor neurons to the muscularis mucosae. The present paper has described several distinct populations of opioid immunoreactive neurons in secretomotor pathways of the guinea-pig ileum. Furthermore we have shown that these enteric or postganglionic sympathetic neurons contain opioid peptides in combination with other neurotransmitter substances. These results should provide a firmer basis on which to plan functional experiments to elucidate the physiological role of opioid peptides in the enteric nervous system.

Substance P mediates neurogenic vasodilatation in extrinsically denervated guinea-pig submucosal arterioles

1. Arteriolar diameter was measured using an optical method in preparations of guinea-pig submucosal plexus in vitro. Electrical stimulation of one or more neurones in ganglia of the submucosal plexus causes a cholinergic vasodilatation in normal animals. The vasomotor innervation to the arterioles was studied in guinea-pigs in which the extrinsic nerves to the intestine had been removed. Tissues were processed for immunohistochemistry after the in vitro experiments. 2. Extrinsic denervation resulted in complete loss of catecholamine fluorescence, NPY (neuropeptide Y) and CGRP (calcitonin gene-related peptide) immunofluorescence around the blood vessels and no neurogenic vasoconstriction was observed up to 60 days post-denervation. Vasodilatation in response to ganglionic stimulation was increased; smaller arterioles (outside diameter less than 40 microns) showed a greater enhancement of neurogenic vasodilatation than larger arterioles. 3. Nerve-evoked vasodilatations were only partially inhibited by muscarinic antagonists at 30-60 days after extrinsic denervations. 4. The non-cholinergic neurogenic vasodilatation was abolished by the substance P antagonists, spantide, [D-Arg1, D-Pro2, D-Trp7.9, Leu11]substance P and [D-Arg1, D-Phe5, D-Trp7.9, Leu11]substance P. These antagonists did not alter the cholinergic vasodilatation in normal or extrinsically denervated arterioles. 5. Exogenous substance P dilated all submucosal arterioles; the concentration which produced half-maximal vasodilatations was 2.5 mM in both normal and extrinsically denervated arterioles. Substance P antagonists inhibited the vasodilatation caused by substance P at concentrations similar to those needed to block nerve-mediated vasodilatation. 6. There was a strong correlation between the finding of non-cholinergic vasodilatation in response to ganglionic stimulation, and the presence of substance P-immunoreactive fibres running from ganglion to arteriole. This correlation did not exist for VIP (vasoactive intestinal peptide). 7. These results suggest that intrinsic intestinal substance P-containing nerve fibres supply submucosal arterioles after sympathetic efferents and sensory afferents are removed. Stimulation of these nerves releases substance P to produce arteriolar dilatation.

Target-related patterns of co-existence of neuropeptide Y, vasoactive intestinal peptide, enkephalin and substance P in cranial parasympathetic neurons innervating the facial skin and exocrine glands of guinea-pigs

The patterns of co-existence of neuropeptides in cranial autonomic neurons of guinea-pigs have been examined with quantitative double-labelling immunofluorescence and retrograde axonal tracing using Fast Blue. Within the sphenopalatine, otic, sublingual and submandibular ganglia, and a prominent intracranial ganglion associated with the glossopharyngeal nerve, most neurons contained immunoreactivity of vasoactive intestinal peptide, neuropeptide Y, enkephalin and substance P in combinations that were correlated with their projections. Hair follicles in the facial skin formed a major target of sphenopalatine ganglion cells. The combinations of peptides co-existing in these neurons depended upon the region of the skin where the follicles were located. The parotid gland was innervated by neurons with cell bodies in the otic ganglion or the intracranial ganglion. Most of these neurons contained immunoreactivity to all four peptides. The sublingual gland was innervated by local ganglion cells usually containing immunoreactivity to neuropeptide Y, vasoactive intestinal peptide and substance P. The submandibular gland was innervated by local ganglion cells containing enkephalin immunoreactivity and low levels of immunoreactivity to neuropeptide Y. Presumptive vasodilator neurons, containing immunoreactivity to vasoactive intestinal peptide but no other peptide examined here, comprised less than 10% of cranial autonomic ganglion cells. These results demonstrate that the patterns of co-existence of neuropeptides in cranial autonomic neurons show a high degree of target specificity. The discovery that hair follicles form a major parasympathetic target implies a broader range of actions of cranial autonomic neurons than has been suspected until now.

Peptides and vasomotor mechanisms

The multiple and diverse roles played by neuropeptide Y, vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide and other biologically active peptides in the cardiovascular system are considered. A model of the vascular neuroeffector junction is described, which illustrates the interactions of peptidergic and nonpeptidergic transmitters that are possible at pre- and postjunctional sites. The effects of peptides on specific endothelial receptors are also described, which highlights the ability of these agents to act as dual regulators of vascular tone at both adventitial and intimal surfaces, following local release from nerves, or from endothelial cells themselves. Changes in expression of vascular neuropeptides that occur during development and aging in some disease situations and following nerve lesion are discussed.

Structural and functional aspects of acetylcholine peptide coexistence in the autonomic nervous system

The present article is an attempt to briefly review acetylcholine and peptide coexistence in the ANS. For more detailed information the reader is referred to the book by Furness and Costa (1987) and books edited by Elfvin (1983) and Björklund et al. (1988). Acetylcholine is the "classical" transmitter substance between preganglionic and post-ganglionic neurons in both the sympathetic and parasympathetic nervous system but also between postganglionic parasympathetic neurons and effector cells. ENK and NT were early on shown to be present in preganglionic sympathetic neurons whereas SP and SOM have more recently been associated with these cells. Physiological experiments have shown that ENK may presynaptically inhibit cholinergic transmission in sympathetic ganglia. The cholinergic postganglionic parasympathetic neurons contain VIP/PHI. These peptides may be responsible for the atropine-resistant vasodilation seen after stimulation of parasympathetic nerves. In salivary glands VIP has been shown to potentiate the salivatory volume response to ACh. A number of postganglionic sympathetic neurons innervating exocrine sweat glands in the skin are also cholinergic. In addition to VIP/PHI, these neurons contain CGRP and probably also SP. The functional significance of acetylcholine coexisting with four vasodilatory peptides in this cell population is at present unclear. In the enteric ganglia the coexistence situation is very complex. Thus, in the myenteric plexus cholinergic SP-containing excitatory motor neurons seem to be present. In the myenteric plexus other cholinergic neurons may contain at least six different neuronal peptides. These latter neurons seem to be part of the peripheral intestino-intestinal reflex arc which is involved in regulation of gastrointestinal motility and mucosal functions. In the submucous plexus three populations of cholinergic neurons are present, one of which has secretomotor properties and contains CGRP, CCK, GAL, NPY and SOM. In vivo and in vitro studies have shown that developing sympathetic neurons can "change" the "classical" transmitter they-use and alter their neuropeptide expression. If dissociated sympathetic neurons are grown in cultures without any non-neuronal elements they differentiate into a noradrenergic phenotype. However, if the cultures also contain non-neuronal cells, both noradrenergic and cholinergic properties will develop. These changes may also by induced by a conditioned medium, containing a diffusible factor secreted from the non-neuronal cells. In conclusion, the present article underlines the complexity of the chemical neuroanatomy of the ANS and emphasizes the abundance of the peptides in both noradrenergic and cholinergic neurons. Although these peptides can be shown to exert a number of interesting effects in various experimental paradigms, much work is needed to define their exact role in nervous system function.

Neurofilament protein-triplet immunoreactivity in distinct subpopulations of peptide-containing neurons in the guinea-pig coeliac ganglion

A battery of polyclonal and monoclonal antibodies raised against the triplet of identified neurofilament protein subunits was used to investigate neurofilament protein immunoreactivity in neurons of the guinea-pig coeliac ganglion. Using optimal conditions of fixation and tissue processing for each antibody we found that only 20% of the postganglionic sympathetic neurons in the guinea-pig coeliac ganglion contain neurofilament protein-triplet immunoreactivity. Double labelling with neurofilament protein-triplet antibodies raised in different species demonstrated that all of these antibodies labelled the same population of neurons. Double labelling using mouse monoclonal antibodies against neurofilament proteins in combination with rabbit polyclonals to neuronal markers showed that neurofilament protein-triplet immunoreactivity is restricted to specific chemically coded subpopulations of noradrenergic neurons. Approximately 52% of neurons in the ganglion contain neuropeptide Y and are presumed vasomotor neurons projecting to blood vessels in the submucosa of the small intestine. Virtually none of the neuropeptide Y-containing neurons were labelled with neurofilament protein-triplet antibodies. Neurons that contain somatostatin (21%) project to the submucous ganglia of the small intestine. Approximately two-thirds of neurons containing somatostatin are immunoreactive for the neurofilament protein-triplet. The other postganglionic neurons in the ganglion (27%) project to the myenteric plexus of the small intestine and do not contain either neuropeptide Y or somatostatin. Approximately a quarter of these neurons were labelled with neurofilament protein-triplet antibodies. These results suggest that the neurofilament protein-triplet may not be an intrinsic component of the cytoskeleton of all neurons. Furthermore the idea of a chemical coding of neurons should be extended to cytoskeletal proteins. The finding that these neurofilament proteins are confined to specific neuronal subpopulations has important implications for the search for a role of the neurofilament protein-triplet in neurons, for the interpretation of classical neurohistological silver impregnation techniques which appear to stain only neurofilament protein-triplet-containing neurons, as well as for neuropathological conditions that may involve these proteins in disease processes.

Some nerve endings in the rat pelvic paracervical autonomic ganglia and varicosities in the uterus contain calcitonin gene-related peptide and originate from dorsal root ganglia

The pelvic paracervical autonomic ganglia of female rats were studied for a subpopulation of nerve endings that could be derived from sensory nerve fibers. Immunohistochemical staining using an antiserum against the synaptic-terminal protein synapsin I was used to identify terminal boutons, while an antiserum against the neuropeptide calcitonin gene-related peptide was used to reveal a subpopulation of sensory nerve fibers. The uterine cervix was also examined for the existence of calcitonin gene-related peptide and synapsin I immunoreactivity in nerve fiber varicosities. In addition, the location of nerve endings in the paracervical ganglion was compared to that in the superior cervical ganglion. Synapsin I immunoreactivity was present in the paracervical ganglion in abundant boutons around neuron somata and in the cervix in varicose nerve fibers of the myometrium, vasculature and epithelium. Double labeling immunocytochemistry revealed calcitonin gene-related peptide-like immunoreactivity in subpopulations of synapsin I-immunoreactive endings in ganglia and nerve varicosities in the cervix. Injection of a retrograde axonal tracer, fluorogold, into the paracervical ganglion produced labeled neurons in dorsal root ganglia and spinal cord; however, fluorogold-labeled neurons containing calcitonin gene-related peptide immunoreactivity were visualized only in dorsal root ganglia. Injections of fluorogold into the uterine cervix produced labeled neurons in the paracervical ganglion and dorsal root ganglia; however, only those in dorsal root ganglia contained immunoreactivity for calcitonin gene-related peptide. These results suggest that immunoreactivity for calcitonin gene-related peptide is present in a subpopulation of nerve endings in the paracervical ganglion and not merely in fibers of passage. The nerve endings in the ganglion and varicosities in the uterine cervix originate from sensory neurons in dorsal root ganglia. The arrangement of endings in the ganglia could play a role in sensory/autonomic interactions for modulation of visceral activity.

Characteristics of synaptic input to three classes of sympathetic neurone in the coeliac ganglion of the guinea-pig

1. Intracellular recordings from sympathetic neurones in the isolated coeliac ganglion of guinea-pigs have been used to define the synaptic input to three subtypes of neurone, classified on the basis of their discharge during maintained depolarizing current as phasic neurones, neurones with prolonged after-hyperpolarizations (LAH), and tonic neurones. 2. The three classes of neurone were distributed characteristically in different parts of the ganglion. 3. Passive membrane properties differed between the three neurone types. Mean input resistance was highest in phasic neurones and was inversely related to the size of the prolonged calcium-activated potassium conductance in LAH neurones. Mean input time constant was highest in tonic neurones, because of significantly higher cell capacitance. 4. Phasic and LAH neurones usually received one suprathreshold ('strong') as well as several subthreshold excitatory synaptic potentials (ESPs) from the ipsilateral splanchnic nerve. In general, the amplitude and number of splanchnic inputs were greater, and the occurrence of two strong inputs more common, in phasic than in LAH neurones. The input to tonic neurones was small and usually subthreshold, even with supramaximal splanchnic stimulation. In a few (mostly tonic) neurones lying close to the midline, small ESPs were evoked by contralateral splanchnic stimulation. 5. Antidromic action potentials were evoked in more than half of all neurones by high voltage coeliac nerve stimulation. In addition, multiple small subthreshold ESPs were recorded in virtually all tonic neurones (99%) on coeliac nerve stimulation. In contrast, coeliac stimulation rarely evoked a few very small ESPs in LAH neurones (9%), but no synaptic response in phasic neurones. 6. In about half of the tonic neurones tested (but no phasic or LAH neurones), small ESPs were evoked by stimulation of the intermesenteric nerve. 7. Slow depolarization elicited by repetitive activation of splanchnic and coeliac nerve trunks, at voltages supramaximal for the fast cholinergic responses, were recorded from about half of both phasic and tonic neurones, but only one of twenty-four LAH neurones. These responses commonly faded during subsequent trials, so that it was difficult to characterize them. 8. The data indicate that the three broad groups of coeliac neurone, classified on the basis of their voltage- and calcium-dependent potassium conductances, receive different patterns of synaptic input. The differences may be related to the three major functions of vasoconstriction, motility and mucosal secretion in the small intestine.

Effect of the somatostatin analogue SMS-201-995 on the adrenergic response to glucose ingestion in patients with postprandial hypotension

PURPOSE

The somatostatin analogue SMS-201-995 has recently been introduced as a new therapy for postprandial hypotension in patients with autonomic neuropathy. The present study was performed to determine the effect of SMS-201-995 on the adrenergic response to glucose ingestion in patients with this disorder.

PATIENTS AND METHODS

Eleven patients with postprandial hypotension were studied: six with central autonomic dysfunction (multiple system atrophy) and five with peripheral sympathetic dysfunction (progressive autonomic failure). Patients received either a subcutaneous injection of SMS-201-995 or a placebo injection, immediately before administration of a 50-g glucose drink. Each treatment was given on separate, consecutive days in a randomized fashion.

RESULTS

Glucose ingestion caused a decrease in blood pressure (from 82 +/- 6 mm Hg to 66 +/- 7 mm Hg, p less than 0.01) and an increase in plasma norepinephrine level (165 +/- 20 pg/mL to 305 +/- 85 pg/mL, p less than 0.01) in five patients with progressive autonomic failure. Administration of SMS-201-995 prevented both the decline in blood pressure and the increase in norepinephrine. By contrast, glucose ingestion elicited no increase in plasma norepinephrine levels despite profound hypotension (average postprandial mean blood pressure, 55 +/- 3 mm Hg) in six patients with multiple system atrophy. Administration of SMS-201-995 prevented postprandial hypotension in these patients, but had no effect on plasma norepinephrine.

CONCLUSION

Our data indicate that the pressor effect of SMS-201-995 is independent of the sympathetic nervous system in patients with multiple system atrophy, but may suppress the adrenergic response to glucose ingestion in patients with progressive autonomic failure.

An electron microscopic study on VIP-, BOM- and CCK-like immunoreactive terminals in the celiac-superior mesenteric ganglion complex of the guinea pig

The distribution and fine structure were studied of the following 3 peptide-containing fibers of enteric origin, vasoactive intestinal polypeptide (VIP), bombesin (BOM) and cholecystokinin (CCK)-like immunoreactive peptide in the celiac-superior mesenteric ganglion complex (CMG) of the guinea pig. These peptides, especially VIP, were distributed more densely on the mesenteric side than on the celiac side of the CMG, and their distribution shared a similar mosaic pattern. Immunoelectron microscopic analysis revealed that the fibers formed synaptic contacts with the proximal dendrites of the principal ganglion cells, however, the profiles of these synaptic junctions differed between fibers. Those containing VIP or CCK formed symmetrical synapses, while those containing BOM formed assymetrical ones. This suggests that there are some functional differences between these enterofugal fibers in the CMG.