Distribution and projections of neurons with immunoreactivity for both gastrin-releasing peptide and bombesin in the guinea-pig small intestine

GFAP-directed Inactivation of Men1 Exploits Glial Cell Plasticity in Favor of Neuroendocrine Reprogramming

BACKGROUND & AIMS

Efforts to characterize the signaling mechanisms that underlie gastroenteropancreatic neoplasms (GEP-NENs) are precluded by a lack of comprehensive models that recapitulate pathogenesis. Investigation into a potential cell-of-origin for gastrin-secreting NENs revealed a non-cell autonomous role for loss of menin in neuroendocrine cell specification, resulting in an induction of gastrin in enteric glia. Here, we investigated the hypothesis that cell autonomous Men1 inactivation in glial fibrillary acidic protein (GFAP)-expressing cells induced neuroendocrine differentiation and tumorigenesis.

METHODS

Transgenic GFAP^ΔMen1 mice were generated by conditional GFAP-directed Men1 deletion in GFAP-expressing cells. Cre specificity was confirmed using a tdTomato reporter. GFAP^ΔMen1 mice were evaluated for GEP-NEN development and neuroendocrine cell hyperplasia. Small interfering RNA-mediated Men1 silencing in a rat enteric glial cell line was performed in parallel.

RESULTS

GFAP^ΔMen1 mice developed pancreatic NENs, in addition to pituitary prolactinomas that phenocopied the human MEN1 syndrome. GFAP^ΔMen1 mice exhibited gastric neuroendocrine hyperplasia that coincided with a significant loss of GFAP expression. Men1 deletion induced loss of glial-restricted progenitor lineage markers and an increase in neuroendocrine genes, suggesting a reprogramming of GFAP⁺ cells. Deleting Kif3a, a mediator of Hedgehog signaling, in GFAP-expressing cells attenuated neuroendocrine hyperplasia by restricting the neuroendocrine cell fate. Similar results in the pancreas were observed when Sox10 was used to delete Men1.

CONCLUSIONS

GFAP-directed Men1 inactivation exploits glial cell plasticity in favor of neuroendocrine differentiation.

Roux-en-Y gastric bypass augments the feeding responses evoked by gastrin-releasing peptides

BACKGROUND

Roux-en-Y gastric bypass (RYGB) is the most effective method for the treatment of obesity, and metabolic disease RYGB may reduce body weight by altering the feeding responses evoked by the short-term satiety peptides.

MATERIALS AND METHODS

Here, we measured meal size (MS, chow), intermeal interval (IMI) length, and satiety ratio (SR, IMI/MS; food consumed per a unit of time) by the small and the large forms of gastrin-releasing peptide (GRP) in rats, GRP-10 and GRP-29 (0, 0.1, 0.5 nmol/kg) infused in the celiac artery (CA, supplies stomach and upper duodenum) and the cranial mesenteric artery (CMA, supplies small and large intestine) in an RYGB rat model.

RESULTS

GRP-10 reduced MS, prolonged the IMI, and increased the SR only in the RYGB group, whereas GRP-29 evoked these responses by both routes and in both groups.

CONCLUSIONS

The RYGB procedure augments the feeding responses evoked by exogenous GRP, possibly by decreasing total food intake, increasing latency to the first meal, decreasing number of meals or altering the sites of action regulating MS and IMI length by the two peptides.

Gastrin releasing peptide-29 requires vagal and splanchnic neurons to evoke satiation and satiety

We have shown that gastrin-releasing peptide-29 (GRP-29), the large molecular form of GRP in rats, reduces meal size (MS, intake of 10% sucrose solution) and prolongs the intermeal interval (IMI). In these studies, we first investigated possible pathways for these responses in rats undergoing total subdiaphragmatic vagotomy (VGX, removal of vagal afferent and efferent innervation of the gut), celiaco-mesenteric ganglionectomy (CMGX, removal of splanchnic afferent and efferent innervation of the gut) and combined VGX and CMGX. Second, we examined if the duodenum communicates the feeding signals (MS and IMI) of GRP-29 (0, 0.3, 1.0, 2.1, 4.1, 10.3 and 17.2 nmol/kg) with the feeding control areas of the hindbrain by performing duodenal myotomy (MYO), a procedure that severs some layers of the duodenal wall including the vagal, splanchnic and enteric neurons. We found that GRP-29 (2.1, 4.1, 10.3, 17.2 nmol/kg) reduced the size of the first meal (10% sucrose) and (1, 4.1, 10.3 nmol/kg) prolongs the first IMI but did not affect the subsequent meals or IMIs. In addition, CMGX and combined VGX/CMGX attenuated reduction of MS by GRP-29 and all surgeries attenuated the prolongation of the IMI. Therefore, reduction of MS and prolongation of IMI by GRP-29 require vagal and splanchnic nerves, and the duodenum is the major conduit that communicates prolongation of IMI by GRP-29 with the brain.

Gastrin-releasing peptide messenger ribonucleic acid expression in the hypothalamic paraventricular nucleus is altered by melanocortin receptor stimulation and food deprivation

Gastrin-releasing peptide (GRP) is a bombesin-like peptide widely distributed in the gastrointestinal tract and central nervous system. In the brain, GRP mRNA is located in the hypothalamic paraventricular nucleus (PVN), a region that receives neural input from the arcuate nucleus and plays a critical role in food intake and energy balance. Because GRP neurons are localized in the vicinity of projection sites in the PVN for peptides that participate in energy homeostasis, we investigated whether GRP mRNA expression in the PVN may be sensitive to challenges imposed by either 38 h food deprivation or stimulation of the melanocortin system by the melanocortin 3/4 receptor agonist, melanotan II (MTII). We found that food deprivation significantly decreased GRP mRNA expression, whereas lateral ventricular MTII administration increased GRP mRNA expression in ad libitum-fed rats 4 h after administration. Furthermore, administration of MTII at a dose that reduces 24 h food intake and body weight prevented the decrease in GRP mRNA expression observed in animals that were pair fed to the amount of food consumed by those injected with MTII. These results demonstrate that food deprivation and stimulation of the melanocortin system produce opposing changes in GRP gene expression in the PVN, suggesting that GRP-containing neurons in the PVN may be part of the hypothalamic signaling pathway controlling food intake and energy balance.

Immunohistochemical characterization of the innervation of human colonic mesenteric and submucosal blood vessels

The aim was to characterize quantitatively the classes of nerves innervating human mesenteric and submucosal vessels. Specimens of uninvolved normal human mesentery and colon were obtained with prior informed consent from patients undergoing elective surgery for bowel carcinoma. Mesenteric and submucosal vessels were processed for double-labelling immunohistochemical localization of tyrosine hydroxylase (TH), neuropeptide Y (NPY), calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal polypeptide (VIP), nitric oxide synthase (NOS), somatostatin (SOM), vesicular acetylcholine transporter (VAChT) and enkephelin (ENK), each compared to the pan-neuronal marker protein gene product 9.5. Branching patterns of individual nerve fibres were investigated using in vitro anterograde tracing. Sympathetic neurons containing TH and NPY were the largest population, accounting for more than 85% on all vessels. Extrinsic sensory axons, containing SP but not CGRP comprised a second major population on mesenteric vessels: these axons generally lacked TH, NPY and VAChT. On submucosal, but not mesenteric vessels, an additional population of SOM-immunoreactive fibres was present: these axons did not co-localize with TH. Major similarities and differences with enteric vessel innervation in laboratory animals were identified. Sympathetic neurons comprise the largest input. Extrinsic sensory neurons in humans largely lack CGRP but contain SP. Submucosal vessels receive an additional source of innervation not present in mesenteric vessels, which contain SOM, but are rarely cholinergic. These results have significant implications for understanding the control of blood flow to the human gut.

Observations favouring the occurrence of local production and marked effects of bombesin/gastrin-releasing peptide in the synovial tissue of the human knee joint--comparisons with substance P and the NK-1 receptor

We have previously shown that levels of the neuropeptides substance P (SP) and bombesin/gastrin-releasing peptide (BN/GRP) in blood and synovial fluid correlate with levels of pro-inflammatory cytokines in patients with rheumatoid arthritis (RA). It is well-established that SP is present in nerve endings in the synovium whilst the source of BN/GRP in human joints is completely unknown. Nor is it known whether GRP-receptors (GRP-R) are present in human synovial tissue. This study aimed to investigate the expression pattern of SP, BN/GRP and their receptors (NK-1R and GRP-R) in synovial tissue. Synovial tissue specimens from patients with RA or osteoarthritis (OA) were processed for immunohistochemistry, in situ hybridisation and ELISA. The results show the presence of BN/GRP, but not SP, in cells in the synovial tissue at both the protein and mRNA level. We did not find immunoreactive BN/GRP in nerve structures. NK-1R and GRP-R were also expressed at both protein and mRNA levels in cells associated with blood vessels and cells in the interstitial tissue. ELISA analyses revealed both SP and BN/GRP to be present in synovial tissue extracts and that synovial levels of SP were higher in RA patients than those with OA. Our results indicate that BN/GRP is produced by non-neuronal cells in the synovial tissue. Furthermore, both BN/GRP and SP may exert their effects on the synovial tissue through the respective receptors. These results suggest that BN/GRP and SP may modulate inflammation and vascular events, and possibly healing processes in the synovium. Finally, nerves should not be considered as the source of BN/GRP in synovial tissue although this peptide is presumably intimately involved functionally in synovial tissue, a previously unrecognised fact.

Effectiveness of bombesin and Saccharomyces boulardii against the translocation of Candida albicans in the digestive tract in immunosuppressed rats

PURPOSE

We investigated the effects of bombesin on disseminated candidiasis, and compared the effectiveness of bombesin with Saccharomyces boulardii against Candida albicans translocation from the gastrointestinal tract in immunosuppressed rats.

METHODS

Sixty rats were divided into five groups of 12. Group 1 was given only a laboratory pellet diet and water during the experiments; the other four groups were orally inoculated with C. albicans; and groups 3, 4, and 5 were also given prednisolone intraperitoneally. The treatment groups consisted of group 4, given S. boulardii orally, and group 5, given bombesin subcutaneously. The rats were killed after 10 days, and the large bowel, liver, spleen, and kidneys were removed for microbiological and histopathological examination. Blood samples were taken to measure tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1beta) levels, and the results were compared.

RESULTS

The number of translocated C. albicans colonies from the gastrointestinal tract and the serum TNF-alpha and IL-beta levels were significantly lower in groups 4 and 5 than in group 3 (P < 0.05). Histological analysis revealed that the bombesin-treated group (group 5) had significantly less mucosal ulceration and submucosal inflammation in the large bowel, less inflammation and necrosis in the liver, and less inflammation of the Bowman capsules in the kidney than the S. boulardii-treated group (group 4) (P < 0.05).

CONCLUSIONS

These findings show that both S. boulardii and bombesin inhibit the translocation of C. albicans from the gastrointestinal tract, although mucosal ulceration, submucosal inflammation in the large bowel, and dissemination in the liver and kidneys were significantly less severe in the bombesin-treated immunosuppressed rats.

Gastrin-releasing peptide and cancer

Over the past 20 years, abundant evidence has been collected to suggest that gastrin-releasing peptide (GRP) and its receptors play an important role in the development of a variety of cancers. In fact, the detection of GRP and the GRP receptor in small cell lung carcinoma (SCLC), and the demonstration that anti-GRP antibodies inhibited proliferation in SCLC cell lines, established GRP as the prototypical autocrine growth factor. All forms of GRP are generated by processing of a 125-amino acid prohormone; recent studies indicate that C-terminal amidation of GRP18-27 is not essential for bioactivity, and that peptides derived from residues 31 to 125 of the prohormone are present in normal tissue and in tumors. GRP receptors can be divided into four classes, all of which belong to the 7 transmembrane domain family and bind GRP and/or GRP analogues with affinities in the nM range. Over-expression of GRP and its receptors has been demonstrated at both the mRNA and protein level in many types of tumors including lung, prostate, breast, stomach, pancreas and colon. GRP has also been shown to act as a potent mitogen for cancer cells of diverse origin both in vitro and in animal models of carcinogenesis. Other actions of GRP relevant to carcinogenesis include effects on morphogenesis, angiogenesis, cell migration and cell adhesion. Future prospects for the use of radiolabelled and cytotoxic GRP analogues and antagonists for cancer diagnosis and therapy appear promising.

Retrograde tracing of enteric neuronal pathways

Neuroanatomical tracing techniques, and retrograde labelling in particular, are widely used tools for the analysis of neuronal pathways in the central and peripheral nervous system. Over the last 10 years, these techniques have been used extensively to identify enteric neuronal pathways. In combination with multiple-labelling immunohistochemistry, quantitative data about the projections and neurochemical profile of many functional classes of cells have been acquired. These data have revealed a high degree of organization of the neuronal plexuses, even though the different classes of nerve cell bodies appear to be randomly assorted in ganglia. Each class of neurone has a predictable target, length and polarity of axonal projection, a particular combination of neurochemicals in its cell body and distinctive morphological characteristics. The combination of retrograde labelling with targeted intracellular recording has made it possible to target small populations of cells that would rarely be sampled during random impalements. These neuroanatomical techniques have also been applied successfully to human tissue and are gradually unravelling the complexity of the human enteric nervous system.

Neurochemical coding and projection patterns of gastrin-releasing peptide-immunoreactive myenteric neurone subpopulations in the guinea-pig gastric fundus

The aim of this study was to characterise the projection and neurochemical coding patterns of gastrin-releasing peptide (GRP)-containing subpopulations of myenteric neurones in the guinea-pig gastric fundus. For this purpose, we used retrograde tracing with the dye DiI and immunohistochemistry against GRP, choline acetyltransferase (ChAT), enkephalin (ENK), substance P (SP) and neuropeptide Y (NPY). Cell counts revealed that 44% of the myenteric neurones were GRP-positive. Of the GRP-positive neurones, 92% were ChAT-positive and, hence, 8% were presumptively nitric oxide synthase positive (NOS). The GRP-positive subpopulations were ChAT/GRP (40% of all GRP neurones), ChAT/NPY/GRP (25%), ChAT/SP/GRP/+/-ENK (20%), ChAT/ENK/GRP (8%), NOS/NPY/GRP/+/-ENK (5%) and NOS/GRP (3%). The tracing experiments revealed the relative contributions of the various GRP-positive subpopulations to the innervation of the circular muscle and the mucosa. GRP immunoreactivity was detected in 46 and 38% of the DiI-labelled muscle and mucosa neurones, respectively. GRP was almost exclusively found in ascending ChAT-positive mucosa and muscle neurones. The populations encoded ChAT/SP/GRP/+/-ENK and ChAT/ENK/GRP projected predominantly to the circular muscle, whereas the ChAT/NPY/GRP and ChAT/GRP populations had primarily projections to the mucosa. GRP was colocalised with ChAT, ENK and/or SP in varicose nerve fibres innervating the circular muscle and the muscularis mucosae, whereas in the mucosal epithelium GRP was mainly present in nerve fibres containing ChAT and NPY. The data suggest that in the guinea-pig gastric fundus, the ChAT/SP/GRP/+/-ENK and ChAT/ENK/GRP neurones are ascending excitatory muscle motor neurones, whereas the ChAT/NPY/GRP and ChAT/GRP neurones are very likely involved in the regulation of mucosal functions.

Origins of cholinergic inputs to the cell bodies of intestinofugal neurons in the guinea pig distal colon

Integration of function between gut regions is mediated by means of hormones and long neuronal reflex pathways. Intestinofugal neurons, which participate in one of these pathways, have cell bodies within the myenteric plexus and project their axons from the gut with the mesenteric nerves. They form excitatory synapses on neurons in prevertebral ganglia that in turn innervate other gut regions. The aim of the present study was to characterise immunohistochemically the synaptic input to intestinofugal neurons. The cell bodies of intestinofugal neurons that project from the distal colon were labelled with Fast Blue that was injected into the inferior mesenteric ganglia. Varicosities surrounding Fast Blue-labelled neurons were analysed for immunoreactivity for the vesicular acetylcholine transporter, vasoactive intestinal peptide, and bombesin. Most intestinofugal neurons were surrounded by nerve terminals immunoreactive for the vesicular acetylcholine transporter; many of these terminals also contained vasoactive intestinal peptide and bombesin immunoreactivity. This combination of markers occurs in axons of descending interneurons. Extrinsic denervation had no effect on the distribution of cholinergic terminals around intestinofugal neurons. A decrease in the number of vesicular acetylcholine transporter and vasoactive intestinal peptide immunoreactive terminals occurred around nerve cells immediately anal, but not oral, to myotomy operations. Consistent with previous physiological studies, it is concluded that intestinofugal neurons receive cholinergic synaptic input from other myenteric neurons, including cholinergic descending interneurons. Thus, intestinofugal neurons are second, or higher, order neurons in reflex pathways, although physiological data indicate that they also respond directly to distension of the gut wall.

Intracellular pH regulation in bombesin-stimulated secretion in isolated bile duct units from rat liver

Bombesin, a neuropeptide, stimulates fluid and HCO-3 secretion from cholangiocytes, but the underlying mechanisms are poorly understood. In this study, we aimed to examine the effects of bombesin on ion transport processes involved in the regulation of intracellular pH (pHi) and HCO-3 secretion in polarized cholangiocytes. Isolated bile duct units from normal rat liver were used to measure pHi by 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein 495 nm-to-440 nm dual ratio methods. Bombesin increased Cl--HCO-3 exchange activity but did not affect basal pHi or the activities of Na+/H+ exchange or Na+-HCO-3 symport. Depolarization of cholangiocytes increased basal pHi and the activity of Cl-/HCO-3 exchange, suggesting that an electrogenic Na+-HCO-3 symport might function as a counterregulatory pHi mechanism. Na+-independent acid-extruding mechanisms were not observed. We conclude that bombesin stimulates biliary secretion from cholangiocytes by activating luminal Cl-/HCO-3 exchange, which may be coupled to basolateral electrogenic Na+-HCO-3 symport.

Appositions made by axons of descending interneurons in the guinea-pig small intestine, investigated by confocal microscopy

There are four major classes of descending interneurons in the myenteric plexus of the guinea-pig small intestine. In this study, the connections made by two of these classes of descending interneurons with other interneurons and with inhibitory motor neurons have been investigated using confocal, conventional fluorescence and electron microscopy. The terminals of descending interneurons known to contain both bombesin (BN) and nitric oxide synthase (NOS) were identified by BN immunoreactivity (IR). Cholinergic interneurons known to contain somatostatin (SOM) were identified by SOM-IR. The connections of these two groups of interneurons with the following three classes of nerve cell bodies were examined: those with NOS-IR that also contain gamma-aminobutyric acid (GABA) (inhibitory motor neurons), those with only NOS-IR (descending interneurons and inhibitory motor neurons) and those with only GABA-IR (motor neurons). The BN-IR and SOM-IR interneurons were found to form connections with each other, and both types of interneurons provided inputs to motor neurons. Most previous analyses of interconnections in the enteric plexuses have been by conventional fluorescence microscopy and electron microscopy. In the present work these are compared with confocal microscopy. BN-IR varicosities formed pericellular baskets around each class of nerve cell that were easily identifiable with all techniques. Using confocal microscopy, BN-IR varicosities that were in contact with NOS-IR and GABA-IR nerve cells were quantified. Confocal microscopy demonstrated over twice as many contacts as were shown by a previous electron microscopic study. In contrast, conventional fluorescence microscopy showed little indication that SOM-IR varicosities formed inputs to NOS-IR or GABA-IR nerve cells, despite the fact that confocal microscopy revealed direct appositions and electron microscopy revealed synapses. This study has shown that confocal analysis is a valuable adjunct to conventional fluorescence microscopy for determining neuronal circuitry. Moreover, it allows a more rapid collection of data than does electron microscopy. It is concluded that chains of BN-IR and SOM-IR interneurons from descending pathways in the small intestine and that both types of interneuron connect with muscle motor neurons.

Characterization of bombesin binding sites in the rat stomach

We characterized the bombesin receptor population in the rat stomach and determined the receptor subtype mediating the contractile effect of bombesin in the gastric fundus. Using in vitro receptor autoradiography, we evaluated the ability of the specific gastrin-releasing peptide-preferring receptor antagonist [D-F5,Phe6,D-Ala11]bombesin-(6-13) methyl ester to inhibit binding of 125I-[Tyr4]bombesin to the gastric fundus, corpus and antrum. Binding to these regions was completely inhibited by [D-F5,Phe6,D-Ala11]bombesin-(6-13) methyl ester suggesting that these receptors are the gastrin-releasing peptide-preferring subtype. We found that the rank order of potency for the contractile effect of bombesin, and the related mammalian peptides neuromedin C and neuromedin B, was bombesin > neuromedin C > neuromedin B. [D-F5,Phe6,D-Ala11]bombesin-(6-13) methyl ester was equipotent in antagonizing contractions produced by all three peptides. Furthermore, receptor tachyphylaxis to either neuromedin C or neuromedin B abolished the subsequent contractile response elicited by neuromedin C and neuromedin B, suggesting that one bombesin receptor subtype mediates rat gastric fundal contractions. Together, these results demonstrate that the bombesin receptor subtype in the rat stomach is gastrin-releasing peptide-preferring subtype and that this subtype is responsible for the effects of bombesin-like peptides on fundal smooth muscle contraction.

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.

Immunohistochemical characterisation of viscerofugal neurons projecting to the inferior mesenteric and major pelvic ganglia in the male rat

Viscerofugal neurons in the myenteric plexus project out of the gut to the sympathetic neurons of the prevertebral ganglia and form the afferent arm of the intestino-intestinal inhibitory reflexes. In this study, we retrogradely labelled viscerofugal neurons in the middle and distal colon, and rectum which project to or through the inferior mesenteric ganglion and major pelvic ganglia. We found that 57-81% of these neurons contained immunoreactivity to calbindin, 37-70% contained immunoreactivity to bombesin, and 22-37% contained immunoreactivity to nitric oxide synthase, irrespective of the ganglion to which they projected. However, only 0-12% of viscerofugal neurons labelled in the rectum from the inferior mesenteric ganglion or intermesenteric nerves contained immunoreactivity to vasoactive intestinal peptide (VIP). In contrast, about 45% of viscerofugal neurons labelled from the pelvic ganglia contained VIP. We also have utilised immunoreactivity to bombesin to demonstrate, for the first time, the presence of viscerofugal terminals surrounding some sympathetic neurons in the major pelvic ganglia. The enteric origin of these terminals was confirmed by their degeneration following severance of the connections between the pelvic ganglia and the lower bowel. Our observation that some pelvic neurons receive viscerofugal input suggests that they can integrate peripheral and central messages. However, the majority of pelvic neurons do not receive viscerofugal input and would be predicted simply to relay central messages.

Bombesin-mediated calcium fluxes in myenteric plexus neurons

Dual excitation microfluorimetry (Fura-2) was used to measure changes in intracellular calcium ([Ca2+]i) in individual cultured guinea pig myenteric neurons. Bombesin (5-500 nM) induced concentration-dependent increases in [Ca2+]i responses, with a maximal effect at 500 nM (56% of neurons responding, mean peak Ca2+ response 244 +/- 25 nM vs. basal 65 +/- 7 nM). Removal of Ca2+ from the median did not affect the initial [Ca2+]i peak but eliminated the subsequent plateau phase. The [Ca2+]i responses to bombesin was abolished by preincubation with thapsigargin (1 microM), a Ca(2+)-ATPase inhibitor (91 +/- 7% inhibition). [Ca2+]i responses to bombesin were inhibited by U73122 (1 microM), an inhibitor of phospholipase C (84 +/- 6% inhibition).

Progressive reorganization of the myenteric plexus during one year following reanastomosis of the ileum of the guinea pig

The enteric nervous system appears to play a pivotal role in the functional recovery of the gastrointestinal tract after partial resection and reanastomosis, but the structural changes following surgery are not fully understood. The present study was designed to clarify the processes of myenteric plexus regeneration up to one year after transection and reanastomosis of the ileum of the guinea pig. The following techniques were used: nicotinamide adenine dinucleotide (NADH) diaphorase histochemistry, immunostaining of neuron-specific enolase (NSE) in whole-mount preparations, and transmission electron microscopy. Two months after transection and reanastomosis, myenteric ganglion cells with NADH diaphorase reactions were scarce in the center of the lesion, and were less numerous in adjacent areas (3 mm in width) than in the control ileum. In the areas adjacent to the lesion, a few large extraganglionic neurons that did not completely compensate for the loss of ganglion neurons were observed. The remaining ileum showed no changes in NADH diaphorase staining pattern at this stage. Two to 12 months after transection and reanastomosis, ectopic large neurons gradually increased in number not only in the areas adjacent to the lesion but also in part of the remaining ileum, up to 10 cm from the lesion. Concomitantly, large ganglion neurons decreased in number in these areas. In other ileal regions (more than 10 cm distant from the site of transection), no obvious changes in NADH diaphorase staining were noted throughout the observation period. The outgrowth of NSE-containing nerve fibers from the severed stumps was seen two weeks after transection. Six weeks later, numerous bundles of fine nerve fibers with NSE were shown to interconnect the oral and anal cut ends of the myenteric plexus, but they exhibited no subsequent alterations. Transmission electron microscopy revealed that regenerating nerve fiber bundles appeared initially among irregularly arranged smooth muscle cells eight weeks after the operation, as expected from light-microscopic observations. These findings suggest that myenteric ganglion cell bodies, unlike myenteric nerve fibers, require a longer term of reconstruction than previously believed after transection and reanastomosis of the ileum of the guinea pig.

Release of bombesin-like immunoreactivity from synaptosomal membranes isolated from the rat ileum

In the enteric nervous system, direct effects on peptidergic neurotransmitter release are difficult to assess since the neuronal network predisposes to numerous interactions between the various transmitter systems. The aim of the present study was to examine the release of bombesin-like immunoreactivity from isolated nerve synapses of the enteric nervous system. Enriched synaptosomal fractions were obtained by using homogenized tissue from rat ileum, which was subjected to various steps of differential and sucrose density centrifugation. Specific binding of [3H]saxitoxin served as a marker for neuronal membranes. For comparison, the content of bombesin-like immunoreactivity was determined. Both the enriched synaptosomal fraction (mitochondrial fraction II or P2) and the purified synaptosomal fraction (F2), obtained after discontinuous sucrose density centrifugation, showed substantial enrichment of the neuronal marker [3H]saxitoxin and bombesin-like immunoreactivity. The basal release of bombesin-like immunoreactivity was 52 +/- 17 pg/mg (100%). KCl-evoked depolarization (65 mM) significantly stimulated the release of bombesin-like immunoreactivity to 142.2% (P < 0.05, n = 17). The release was abolished in Ca(2+)-free medium. Stimulation of the release of bombesin-like immunoreactivity was also observed in the presence of the Ca2+ ionophore A-23187 (10(-6) M: 129%, P < 0.05, n = 17), supporting the role of Ca2+ in the release process. Cholinergic stimulation with carbachol elicited a significant dose-dependent release of bombesin-like immunoreactivity (10(-8) M: 106%, 10(-7) M: 175%, P < 0.05, 10(-6) M: 156%, P < 0.05, 10(-5) M: 115%, n = 14), which was reduced by atropine (10(-6) M: 99%, P < 0.01, n = 14). The basal value was 67 +/- 9 pg/mg (100%). The different effects of the muscarinic M1 receptor antagonist pirenzepine, which stimulated release of bombesin-like immunoreactivity in combination with carbachol 10(-6) M (10(-6) M: 123%, n = 10), and of the muscarinic M2 receptor antagonist AFDX 116, which attenuated release of bombesin-like immunoreactivity evoked by carbachol (10(-5) M: 66%, P < 0.01, 10(-6) M: 88%, n = 10), strongly suggest modulation of the release of bombesin-like immunoreactivity at the presynaptic receptor site through an excitatory muscarinic M2 receptor. The basal value was 46 +/- 9 pg/mg (100%). In summary, bombesin-like immunoreactivity can be released from these synaptosomes by both depolarization with KCl in a Ca(2+)-dependent manner and by cholinergic stimulation. The synaptosomes of intrinsic nerves of the gut offer an approach to study the release of neuropeptides and neurotransmitters at the subcellular level independent of the ganglionic network.

Chemoattractant capacity of bombesin, gastrin-releasing peptide and neuromedin C is mediated through PKC activation in murine peritoneal leukocytes

Bombesin-like peptides have been recently shown to regulate immune functions. In the present work, we have studied their action as chemoattractants for murine peritoneal macrophages and lymphocytes. The results showed a significant increase in the number of cells that migrate when they are exposed to a gradient of bombesin, gastrin-releasing peptide (GRP) or neuromedin C (from 10(-8) to 10(-12) M). The most effective of the three neuropeptides studied was GRP, even more than formyl-Met-Leu-Phe peptide (FMLP), an established leukocyte chemoattractant. GRP action was mediated through specific cell receptors as it was significantly reduced in presence of a competitive and specific bombesin receptor antagonist. In the presence of retinal, a protein kinase C (PKC) inhibitor, the chemoattractant capacity of GRP was considerably reduced. In order to investigate further the mechanism of action involved in the GRP effect, we measured PKC activity. Peritoneal cells incubated with GRP experimented an increase in PKC activity to the same extent of that produced by the PKC activator phorbol myristate acetate (PMA). These data prove that bombesin-like peptides are potent chemoattractants for murine peritoneal macrophages and lymphocytes, and that their action is at least in part mediated through PKC activation.

Distribution of NADPH-diaphorase activity in rat paravertebral, prevertebral and pelvic sympathetic ganglia

Paravertebral (superior cervical and stellate), prevertebral (coeliac-superior mesenteric, inferior mesenteric) and pelvic (hypogastric) sympathetic ganglia of the rat were investigated by enzyme histochemistry to ascertain the distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase) activity. In the paravertebral ganglia the majority of the sympathetic neuronal perikarya contained lightly and homogeneously distributed formazan reaction product but there was a range of staining intensities amongst the neuron population. In contrast, in the prevertebral ganglia, intense NADPH-diaphorase staining was present in certain neurons. Firstly, a population of neurons of the coeliac-superior mesenteric ganglion complex were surrounded by densely NADPH-diaphorase-positive 'baskets' of fibres and other stained fibres were seen in interstitial nerve bundles and in nerve trunks connected to the ganglion complex. Secondly, in both the inferior mesenteric ganglion and hypogastric ganglion there were many very intensely NADPH-diaphorase positive neurons. Stained dendritic and axonal processes emerged from these cell bodies. In both ganglia this population of neurons was smaller in size than the lightly stained ganglionic neurons and commonly had only one long (presumably axonal) process. The similarity of these highly NADPH-diaphorase-positive neurons with previously described postganglionic parasympathetic neurons in the hypogastric ganglion is discussed.

A single meal elicits regional changes in bombesin-like peptide levels in the gut and brain

Several studies have demonstrated that exogenous bombesin (BN) elicits a potent satiety effect when administered centrally or systemically. It has been suggested that BN-like peptides may play a physiological role in the control of food intake. The objective of the present study was to determine whether the levels of endogenous BN-like peptides change in response to a meal. All rats were food deprived overnight for a 12 h period. Half the animals were then allowed to feed for 35 min (postprandial group) and the remainder formed the preprandial group. Regions of the brain (hypothalamus, cerebellum, medulla, pons, neocortex, hippocampus, olfactory bulbs, striatum, midbrain and pituitary), gut (oesophagus, fundus, antrum, duodenum, jejunum, ileum, colon) and adrenal glands were analyzed for BN-like peptide levels using radioimmunoassay. Our results indicate significant increases in the levels of BN-like peptides in the hypothalamus and hippocampus, as well as in the antrum of the stomach, after food ingestion. These results are the first to demonstrate the activation of endogenous BN-like peptide mechanisms in response to ingestion. These rapid alterations in peptide levels may support the contention that BN-like peptides play a physiological role in the regulation of ingestive behavior.

Light- and electron-microscopic immunochemical analysis of nerve fibre types innervating the taenia of the guinea-pig caecum

The present work was undertaken to determine by immunocytochemical methods which of the putative enteric neurotransmitters are contained in axons supplying the guinea-pig taenia coli and what proportion of axons is accounted for by the presence of these substances. Numerous fibres displayed immunoreactivity for dynorphin (DYN), enkephalin (ENK), gamma-aminobutyric acid (GABA), nitric oxide synthase (NOS), substance P (SP) and vasoactive intestinal peptide (VIP), but, in contrast to other gut regions, fibres showing immunoreactivity for gastrin-releasing peptide, galanin and neuropeptide Y were rare in the taenia. Fibres reactive for calbindin, calcitonin gene-related peptide, cholecystokinin, 5-hydroxytryptamine and somatostatin were also rare. Tyrosine hydroxylase-like immunoreactivity (TH-LI) was present in numerous fibres that disappeared after extrinsic denervation, a procedure that did not detectably affect any of the other major groups of fibres. Simultaneous staining of extrinsically denervated preparations revealed that SP-LI and VIP-LI were located in separate fibres, and ultrastructural studies showed these to be 58% and 33% of intrinsic fibres supplying the muscle. Immunoreactivity for the general marker, neuron-specific enolase, was located in 95-98% of axons. ENK-LI and DYN-LI were in the same axons, and similar proportions of the fibres with either SP-LI or VIP-LI, about 85%, contained immunoreactivity for ENK and DYN. All VIP-LI fibres, but no SP-LI fibres, were reactive for NOS. The results imply that the taenia of the guinea-pig caecum is innervated by two major groups of enteric neurons: (i) excitatory neurons that contain ACh, SP, other tachykinins, and, in most cases, DYN-LI and ENK-LI; and (ii) inhibitory neurons that contain NOS-LI, VIP-LI, in most cases, the two opioids and, quite probably, ATP as a transmitter. GABA-LI is contained in a smaller population of intrinsic axons. Even though the taenia represents one of the simplest tissues for examining transmission from enteric neurons to intestinal muscle, it shares some of the complexity of other regions, in that four major axon types supply the muscle and both the enteric excitatory and enteric inhibitory neurons contain multiple transmitters.

Enhancement by bombesin of colon carcinogenesis and metastasis induced by azoxymethane in Wistar rats

The effects of bombesin on the incidence, number and histology of colon tumors induced by azoxymethane (AOM), and on their metastases to the peritoneum and/or lymph nodes, were investigated in Wistar rats. Rats received weekly s.c. injections of AOM for 10 weeks, and s.c. injections of bombesin in depot form every other day until the end of the experiment in week 30. Administration of bombesin significantly increased the incidence of colon tumors in week 30. It had no influence on the histological features or depths of involvement of colon adenocarcinomas, but significantly increased the incidence of cancer metastasis to the peritoneum and/or lymph nodes. It also caused a significant increase in the labeling index of the colon epithelial cells. Our findings indicate that bombesin enhances the development and metastasis of colon tumors, and that this effect may be related to its effect in increasing proliferation of epithelial cells of the colon.

The direct contractile effect of gastrin releasing peptide on isolated gastric smooth muscle cells of the guinea pig

Smooth muscle cells isolated from the gastric muscle layers of the guinea pig were used to determine whether gastrin releasing peptide (GRP) can cause contraction by exerting a direct action on muscle cells. In addition, the inhibitory effect of 8-( N,N-diethylamino )-octyl-3,4,5-trimethoxybenzoate hydrochloride ( TMB-8 ), an inhibitor of intracellular Ca2+ release, and verapamil, a Ca2+ channel blocker, on the GRP-induced contraction of gastric smooth muscle cells were examined. GRP elicited a contractile response of gastric muscle cells in a dose-dependent manner. The ED50 was 13 pM. TMB-8 significantly inhibited the contractile effect of GRP in gastric muscle cells. These results demonstrate the direct action of GRP on the gastric smooth muscle cells of the guinea pig, and the importance of Ca(2+)-release from intracellular calcium, stores in the contractile response to GRP.

The mechanism of action of bombesin on cat lower esophageal sphincter

The effect of bombesin on the tone and the responses of strips from the lower esophageal sphincter (LES) to field electrical stimulation (FES) (2 Hz, 0.2 ms, supramaximal current intensity, 20 s duration) was studied. Bombesin dose-dependently increased the LES tone. The threshold for this effect was 10(-14) M and was particularly pronounced with a concentration of 10(-8) M. The response reached maximum between the 3rd and the 5th min after application, persisted for 15-20 min, and was followed by a slight time-dependent decrease. Bombesin increased FES-produced relaxation of LES by 39% as compared to the control. The potentiating effect of bombesin on the LES relaxation was also observed after cholinergic and adrenergic receptor blockade. It is concluded that bombesin may modulate the release of cholinergic, adrenergic and noncholinergic, nonadrenergic inhibitory neurotransmitters.

Blockade of bombesin receptors with [Leu14-psi(CH2NH)-Leu13]bombesin fails to suppress nutrient-induced CCK release from rat duodenojejunum

The present study was undertaken in order to delineate the contribution of enteric bombesin (BBS)-containing nerves in the food-induced release of intestinal cholecystokinin (CCK). For this purpose, the isolated vascularly perfused rat duodenojejunum model was used and the new compound [Leu14-psi(CH2NH)-Leu13]BBS was infused intraarterially at a concentration of 10(-6) M to block the BBS receptors. Vascular infusion of BBS alone (10(-8) M or 10(-9) M) provoked a dose-dependent release of CCK-like immunoreactivity (CCK-LI). The secretion pattern of CCK was biphasic and consisted of a transient peak (300-400% above basal) followed by a sustained response (200-300% above basal). Vascular coinfusion of the BBS analogue with BBS 10(-9) M completely abolished both phases of CCK release while only the second phase of CCK secretion was profoundly reduced upon coadministration of BBS 10(-8) M with the BBS receptor antagonist. Luminal administration of mixed nutrients induced a prompt and well-sustained release of CCK-LI which was unaffected upon arterial infusion of the BBS analogue. These data suggest that the intestinal supply in BBS-producing nerves is not involved in the food-induced release of intestinal CCK in the rat.

Isolation, sequence and biosynthetic significance of a novel fragment of gastrin-releasing peptide from chicken proventriculus

The isolation of bombesin-related peptides in chicken proventriculus was monitored by radioimmunoassay using a C-terminal specific bombesin antibody. Two peptides were identified, one corresponded to the 27-residue, chicken gastrin-releasing peptide (GRP-27) previously identified; the other corresponded to its C-terminal hexapeptide. Chicken GRP-27 stimulated pancreatic and gastric acid secretion in anaesthetized turkeys, but the hexapeptide was inactive. No evidence could be found to suggest that the hexapeptide was an artifact of degradation generated during extraction or isolation. It is proposed that the hexapeptide is produced either by chymotryptic-like cleavage of GRP-27 or by trypsin-like cleavage followed by two cycles of dipeptidylaminopeptidase cleavage. This type of biosynthetic processing may be more common than formerly supposed.

Differential regulation of smooth muscle contraction in rabbit internal anal sphincter by substance P and bombesin

Substance P and bombesin induce contraction of isolated IAS smooth muscle cells by different intracellular mechanisms. The cells contracted in a dose dependent manner to both peptides. The kinetics of contraction were different. Substance P induced contraction peaked at 30 seconds and declined in a time dependent manner while bombesin induced contraction peaked at 30 seconds and was maintained for up to 8 minutes. The absence of extracellular calcium in the medium (0 calcium and 2 mM EGTA) had no affect on substance P induced contraction while it blocked bombesin induced contraction. Substance P induced contraction was blocked by the calmodulin antagonist W7 (10(-9)M) and was not affected by the PKC antagonist H7 (10(-6)M). Bombesin induced contraction was blocked by the PKC antagonist H7 and was not affected by the calmodulin antagonist W7. Our data indicate that substance P induces a transient contraction utilizing intracellular calcium and a calmodulin dependent pathway, while bombesin induces a sustained contraction utilizing calcium from extracellular sources and a calmodulin independent pathway.

Immunocytochemical study of peptidergic structures in Brunner's glands

Nervous and endocrine peptidergic structures in human Brunner's glands were studied by immunofluorescence. Endocrine cells storing immunoreactive components respectively similar to somatostatin 14, the amino-terminal portion (1-14) of somatostatin 28, gastrin-cholecystokinin, and peptide YY were distributed throughout the acini. Peptidergic nerve structures contained materials immunologically related to vasoactive intestinal peptide, peptide histidine methionine, substance P, neuropeptide Y, and gastrin-releasing peptide. The latter peptide was detected in discrete fibers running into the acini but within no cell body in the submucosa. All other neuropeptides were stored in fibers, isolated or grouped in bundles, and in perikarya of submucosal ganglia close to the acini. No immunoreactive structures were detected using antisera directed against pancreatic polypeptide, secretin, motilin, neurotensin, or calcitonin gene-related peptide. The results suggest that several regulatory peptides may be involved in the control of Brunner's glands in humans.

Migration of the myoelectric complex after interruption of the myenteric plexus: intestinal transection and regeneration of enteric nerves in the guinea pig

The effects of surgical interruption of the myenteric plexus (myectomy), extrinsic denervation of a length of small intestine, or transection and reanastomosis of the intestinal wall on migration of phase III of the migrating myoelectric complex was studied in guinea pigs. In addition, the recovery of phase III migration and the regrowth of intestinal nerves and muscle across the reanastomosis was studied at various times up to 60 days after surgery. At 6-9 days after surgery, phase III did not migrate past the myectomy during 50%-60% of recorded migrating myoelectric complexes and transection and reanastomosis of the intestinal wall blocked aboral progression of phase III in 90% of cases. Extrinsic denervation did not alter phase III migration through the denervated segment. Phase III migration past the reanastomosis recovered with time after surgery; 80% recovery occurred by 60 days after surgery. Immunoreactivities for vasoactive intestinal peptide, gastrin-releasing peptide, and somatostatin were used as markers for intestinal nerves that were cut by transaction. Immunoreactivities for vasoactive intestinal peptide and gastrin-releasing peptide are contained in myenteric neurons that project in an oral to anal direction to other myenteric ganglia and to the circular muscle. Immunoreactivity for somatostatin is contained in nerve fibers projecting aborally to other myenteric ganglia. At 7-15 days after surgery, there were accumulations of immunoreactivities for vasoactive intestinal peptide, gastrin-releasing peptide, and somatostatin in nerve fibers on the oral side of the reanastomosis, but nerve fibers containing these peptides were not observed in myenteric ganglia or circular muscle close to the anal edge. At 23-28 days, immunoreactivities for vasoactive intestinal peptide, gastrin-releasing peptide, and somatostatin nerve fibers were traced across the reanastomosis and nerve terminals were detected in ganglia and muscle close to the lesion on the anal side. Nerve fibers traversed the lesion in all cases at 57-60 days and vasoactive intestinal peptide-, gastrin-releasing peptide-, and somatostatin-immunoreactive nerve terminals were detected in the first two to three rows of myenteric ganglia on the anal side. Regrowth of intestinal muscle followed a similar time-course to that observed for nerves. These data suggest that interruption of the myenteric plexus alone does not completely block phase III migration. In addition, recovery of phase III migration past a reanastomosis is associated with a restoration of both nervous and mechanical connections.

Gastrin releasing peptide (GRP) is present in a GRP(1-27) form in anterior pituitary cells of the guinea pig

Immunohistochemical and chromatographic studies were performed on the guinea pig anterior pituitary gland with an antiserum recognizing an epitope within the gastrin releasing peptide (GRP) carboxyterminal amino acid sequence Val-Gly-His-Leu-Met-NH2. Within the anterior pituitary gland GRP-like immunoreactive cells were identified. The GRP-like immunoreactive cells were distributed heterogenously in the gland, predominantly located in ventral aspects of the anterior pituitary. Intracellularly, the immunoreactivity elements were identified as granula-like structures in the cytoplasma. To further characterize the peptide displaying GRP-like immunoreactivity within the pituitary cells, the GRP-like substances were analyzed by radioimmunoassay and gel filtration chromatography. Using this analytical approach it was determined that the guinea pig pituitary extract contained a peptide with characteristics similar to that of authentic porcine GRP(1-27). Only trace amounts of smaller C-terminal fragments were identified. These results indicate, in contrast to findings in other tissues, the GRP(1-27) is not further degraded into smaller peptide fragments.

The neuroendocrine system of the gut

The digestive tract is the richest source of regulatory peptides outside the brain. Such peptides occur all along the gut in the neuroendocrine system which is composed of endocrine/paracrine cells disseminated in the epithelium and of intrinsic neurons that form continuous ganglionic chains in the submucosa and in the muscle layer. Some endocrine/paracrine cells, particularly in the stomach, still have not been associated with an identified regulatory peptide implying that our present knowledge is far from complete. The intracellular processing of regulatory peptide precursors involves multi-step proteolytic cleavage generating several fragments. In many instances more than one biologically active peptide is generated from one and the same precursor. In addition, certain endocrine/paracrine cells and neurons have been found to produce more than one peptide precursor and some are known to harbour 'classical' neurotransmitters, such as 5-hydroxytryptamine, histamine and GABA as well as regulatory peptides. Key questions for the future are the functional significance of the coexistence of multiple messengers within the same cells and the details of how the endocrine/paracrine cells and the neurons in the gut interact.

Human alpha-calcitonin gene-related peptide influences colonic secretion by acting on myenteric neurons

The effect of human alpha-calcitonin gene-related peptide (CGRP) on epithelial ion transport was investigated in guinea pig distal colon set up in Ussing flux chambers. Addition of CGRP to the serosal bathing solution evoked a dose-dependent increase in short-circuit current in whole-thickness tissues with intact myenteric and submucosal ganglia, but not in whole-thickness preparations when neural connections between myenteric and submucosal ganglia were severed, nor in sheets of submucosa/mucosa with intact submucosal ganglia. The effects of CGRP were nearly abolished in chloride-free solutions or after treatment with furosemide. Tetrodotoxin and hexamethonium abolished the effects of CGRP on basal short-circuit current whereas atropine did not. CGRP enhanced neurally evoked chloride secretion both in whole thickness and submucosa/mucosa preparations, but the effect in the latter was considerably smaller. These observations suggest that CGRP stimulates chloride secretion primarily by activating myenteric neurons that project either to submucosal ganglia or to the mucosa of the guinea pig distal colon. Furthermore, CGRP appears to have a greater effect on excitability of myenteric neurons than submucosal neurons.

Projections of peptide-containing neurons in rat colon

The distribution, origin and projections of nerve fibers containing vasoactive intestinal peptide, substance P, neuropeptide Y, galanin, gastrin-releasing peptide, calcitonin gene-related peptide, somatostatin or enkephalin were studied in the midcolon of the rat by immunocytochemistry and immunochemistry. Most of these nerve fibers had an intramural origin as was established by extrinsic denervation (serving of mesenterial nerves). Extrinsic denervation eliminated neuropeptide Y-containing fibers of presumably sympathetic origin together with sensory nerve fibers containing both substance P and calcitonin gene-related peptide. Co-existence of two peptides in the same neuron was studied by double immunostaining. This revealed co-existence of neuropeptide Y and vasoactive intestinal peptide in one population of intramural neurons; an additional population of intramural neurons was found to contain vasoactive intestinal peptide but not neuropeptide Y. All somatostatin-containing neurons in the submucous ganglia were found to harbor calcitonin gene-related peptide. A much larger population of submucous neurons containing calcitonin gene-related but not somatostatin was also detected. Some perivascular calcitonin gene-related peptide-containing nerve fibers (of intrinsic origin) harbored vasoactive intestinal peptide while others (of extrinsic origin) harbored substance P. The polarities and projections of the various peptide-containing intramural neurons in the transverse colon were studied by analysing the loss of nerve fibers upon local disruption of enteric nervous pathways (myectomy or intestinal clamping). Myenteric neurons containing vasoactive intestinal peptide, galanin, gastrin-releasing peptide, calcitonin gene-related peptide, somatostatin or vasoactive intestinal peptide/neuropeptide Y gave off 5-10-mm-long descending projections while those containing substance P or enkephalin issued approx. 5-mm-long ascending projections. Submucous neurons containing calcitonin gene-related peptide, somatostatin/calcitonin gene-related peptide or gastrin-releasing peptide issued both ascending (2-6 mm) and descending (2-6 mm) projections, those containing vasoactive intestinal peptide issued ascending (approx. 2 mm) projections, while those containing galanin or vasoactive intestinal peptide/neuropeptide Y lacked demonstrable oro-anal projections. Enkephalin-containing fibers could not be detected in the mucosa and the mucosal substance P-containing nerve fibers were too few to enable us to delineate their projections.

Quantitative ultrastructural analysis of enkephalin-, substance P-, and VIP-immunoreactive nerve fibers in the circular muscle of the guinea pig small intestine

The present work was undertaken to determine what proportion of all nerve fibers in the circular muscle of the guinea pig small intestine contain the neuropeptides enkephalin, substance P, and vasoactive intestinal peptide and in which combinations these peptides occur in the fibers. It was envisaged that such an analysis would provide insights into the chemical identity of excitatory and inhibitory nerve fibers that innervate the muscle. Whole-mount preparations from normal and extrinsically denervated gut were labelled with antiserum to the individual peptides or with combinations of antipeptide antisera and processed for electron microscopy. Reactive and nonreactive vesicle-containing nerve fiber profiles were examined and counted in ultrathin sections. Vesicle-containing nerve fiber profiles immunoreactive for enkephalin, substance P, or vasoactive intestinal peptide had similar morphologies in that they all contained variable proportions of small clear and large granular vesicles. In all samples stained for single peptides or combinations of peptides, a small proportion of immunoreactive profiles approached smooth muscle cells to within 15-20 nm with no intervening basal lamina. A total of 14,694 vesiculated nerve fiber profiles from three control and three extrinsically denervated animals were scored for the presence of immunoreactivity to enkephalin, substance P, vasoactive intestinal peptide, or combinations of these peptides. Analysis of variance showed that the number of profiles labelled for substance P was not different from the number of profiles labelled for vasoactive intestinal peptide and that the number labelled with the substance P and vasoactive intestinal peptide antisera simultaneously were not different from the sum of the numbers obtained with each alone. The number of profiles labelled for substance P plus enkephalin was greater than the number labelled for substance P alone and the number labelled with vasoactive intestinal peptide plus enkephalin was greater than that with vasoactive intestinal peptide alone. Simultaneous labelling for substance P and vasoactive intestinal peptide resulted in immunoreactivity in the same number of profiles as did reaction for all three peptides at the same time. In both cases, about 95% of the profiles were labelled. The results from extrinsically denervated muscle were not different from control circular muscle. These results indicate that nearly all the intrinsic nerve fibers supplying the circular muscle of the guinea pig small intestine contain either substance P or vasoactive intestinal peptide but not both.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of bombesin receptors on isolated muscle cells from human intestine

Smooth muscle cells were isolated separately from the longitudinal and circular muscle layers of human jejunum obtained at surgery and used to determine whether amphibian bombesin-14 and 3 mammalian homologues, GRP-(1-27), GRP-(18-27) and neuromedin B, can cause contraction by acting directly on muscle cells. Circular and longitudinal muscle cells contracted identically in response to bombesin-14 (C50 2 x 10(-12) M). The contractile response was not affected by selective muscarinic, opioid, CCK or serotonin antagonists but was inhibited by the substance P (SP) derivative, [D-Arg1, D-Pro2, D-Trp7,9, Leu11]SP. All 3 mammalian bombesins were less potent than bombesin-14. GRP-(1-27) and GRP-(18-27) were equipotent (C50 4 x 10(-11) M) but 20 times less potent than bombesin-14. Neuromedin B (C50 6 x 10(-12) M) was 3 times less potent than bombesin-14. All bombesins, however, were more potent than other enteric neuropeptides (e.g., tachykinins, opioid peptides). The study demonstrates conclusively the ability of bombesins to cause direct contraction of intestinal smooth muscle cells.