Gastrin/cholecystokinin-like immunoreactive peptides in the Dungeness crab, Cancer magister (Dana): immunochemical and biological characterization

Isolation, identification, and synthesis of a disulfated sulfakinin from the central nervous system of an arthropods the white shrimp Litopenaeus vannamei

Two myotropic peptides displaying tyrosyl sulfation have been isolated from an extract of central nervous systems (brain, suboesophageal ganglion, thoracic ganglia, and ventral nerve cord) of the white shrimp Litopenaeus vannamei. Both peptides were identified by mass spectrometry and belong to the sulfakinin family of neuropeptides, which are characterized by the C-terminal hexapeptide Y(SO(3)H)GHMRF-NH(2) preceded by two acidic amino acid residues. Pev-SK 1 (AGGSGGVGGEY(SO(3)H)DDY(SO(3)H)GH(L/I) RF-NH(2)) has two sulfated tyrosyl residues and a unique (L/I) for M substitution in the C-terminal sequence. Pev-SK 2 (pQFDEY(SO(3)H)GHMRF-NH(2)) fully complies with the typical sulfakinin core sequence and is blocked by a pyroglutamyl residue. Synthetic analogs (sulfated and unsulfated) were synthesized and the tyrosyl sulfations were confirmed by myotropic activity studies and co-elution with the native fractions. Pev-SK 1 is the first disulfated neuropeptide elucidated in the phylum of the arthropoda, with the only other reported disulfated neuropeptide, called cionin, found in a protochordate. The similarities in amino acid sequence and posttranslational modifications of the crustacean sulfakinins and protochordate cionin provide further evidence for the hypothesis stating that gastrin/CCK, cionin, and sulfakinins originate from a common ancestral gastrin/CCK-like peptide.

Release of digestive enzymes from the crustacean hepatopancreas: effect of vertebrate gastrointestinal hormones

Vertebrate gastrointestinal hormones were tested on their ability to liberate digestive enzymes from the crustacean midgut gland. CCK-8 (desulfated form), gastrin, bombesin, secretin, and substance P were detected to release enzymes. Maximal concentrations observed were 5 nM CCK for protease release, 1 nM gastrin for protease and 100 nM for amylase release, 100 nM bombesin for protease release, 10 nM secretin for amylase and protease release, and 100 nM substance P for protease release. Unlike in vertebrates, glucagon was unable to stimulate enzyme release in crustaceans, this also applies to the counterpart insulin. These results may support the assumption that Crustacea possess endogenous factors resembling the above mentioned vertebrate hormones, at least in such a way that the appropriate receptors have the capacity to accept these hormones.

Heterogeneity of cholecystokinin/gastrin-like immunoreactivity in the nervous system of the nematode Ascaris suum

A wholemount immunocytochemical method was used for the localization of cholecystokinin (CCK8)-like and gastrin-like immunoreactivity in Ascaris. The patterns of specific neuronal staining given by two antisera and four monoclonal antibodies made against CCK8, and one antiserum made against gastrin were investigated. Preabsorption of these antibodies with CCK8 or gastrin 17 resulted in complete loss of immunoreactivity in almost all of the neurons (two antisera also contained nonspecific antibodies), suggesting that all of the antibodies recognize epitopes, in Ascaris neurons, that include some or all of the C-terminal five amino acids that are identical in CCK8 and gastrin 17. However, the seven different antibodies showed immunoreactivity in different subpopulations of neurons, implying that there are at least seven different species of CCK-like molecules in Ascaris. Fractionation of Ascaris peptide extracts by high performance liquid chromatography (HPLC), monitoring fractions with a CCK8 radioimmunoassay (RIA), also shows heterogeneity of molecules immunologically related to CCK8.

Structure and biological activity of crustacean gastrointestinal peptides identified with antibodies to gastrin/cholecystokinin

Four gastrin/cholecystokinin-like peptides (G/CCK) which cross-react with a specific C-terminal gastrin/CCK antiserum have been isolated from the stomach of the marine crustacean Nephrops norvegicus. The molecular weight of the four peptides was estimated between 1000 and 2000 Da by molecular sieving. By radioimmunoassay, the cross-reactivity of these peptides with human gastrin 17-I was found to be around 0.03%. Pure peptidic fractions were recovered after four successive steps of HPLC. Amino-acid analysis suggested a similarity between the four peptides identified which may belong to a new family. A limited homology between the C-terminus of one Nephrops peptide and vertebrate G/CCK was found after sequencing. Two of the peptides exhibited secretagogue effects on crustacean isolated midgut glands. The Nephrops peptides, although structurally distinct from the vertebrate G/CCKs, appear to serve similar biological functions in crustaceans.

Distribution of cholecystokinin-like immunoreactivity within the stomatogastric nervous systems of four species of decapod crustacea

The distribution of cholecystokinin-like immunoreactivity was studied in the stomatogastric nervous systems, pericardial organs, and haemolymph of four species of decapod crustacea, by using immunocytochemical and radioimmunoassay techniques. Whereas cholecystokinin-like immunoreactivity was found within the stomatogastric nervous systems of all four species, its distribution in each is unique. Two species (Panulirus interruptus and Homarus americanus) have cholecystokinin-like immunoreactivity within fibers and neuropil of the stomatogastric ganglion (STG); two other species (Cancer antenarius and Procambarus clarkii) do not. Further, the cholecystokinin-like immunoreactivity within the STGs of Panulirus and Homarus arise from distinct structures; from a projection of anterior ganglia in Panulirus, and from somata within the posterior motor nerves in Homarus. The staining in the other ganglia of the stomatogastric nervous system also shows some interspecies variability, although it appears to be more highly conserved than staining within the STG. These differences in staining were confirmed by measuring the amount of CCK-like peptide present in tissue extracts of ganglia by radioimmunoassay. In contrast to the variable staining within the STG, all four species have cholecystokinin-like immunoreactivity within the neurosecretory pericardial organs and thoracic segmental nerves. This cholecystokinin-like immunoreactivity is contained within fibers and within varicosities that coat the surface of these structures. The location of this staining and the presence of detectible levels of CCK-like peptide in the haemolymph suggests that CCK-like peptides in decapod crustacea may be utilized as neurohormones.

Localization of immunoreactive gastrin-like cells in the alimentary tract of the ascidian Styela plicata

The occurrence of a gastrin-like immunoreactivity in the alimentary tract of the ascidian Styela plicata has been investigated using immunocytochemical methods. Gastrin-like cells are present only in the gastric epithelium among the cell types responsible for digestion and absorption of food. The physiological role played by the ascidian gastrin-like peptides is discussed together with the evolutionary history of peptides of the gastrin/cholecystokinin family.

Immunochemical and biochemical characterization of gastrin/cholecystokinin-like peptides in Palaemon serratus (Crustacea Decapoda): intermolt variations

Gastrin/cholecystokinin (G/CCK)-like peptides cross-reacting with an antiserum specific for the carboxyamide terminal pentapeptide of gastrin and CCK have been detected in the eyestalks and in the stomach of the prawn Palaemon serratus using immunocytochemical methods. In the eyestalks, immunoreactivity is present in the neuroendocrine cells, the X organ-sinus gland tractus and the neurohemal organ itself. This suggests, for the first time, the existence of a neuroendocrine secretion of G/CCK-like peptides. Hemolymph G/CCK level is about 18 pM. In the stomach, G/CCK-like material has been observed in epithelial cells in the cuticle and in the lumen. Molecular sieving of crude extracts of the medulla terminalis from the eyestalks, the stomach, and the hemolymph samples on a Sephadex G-50 filtration column exhibited a molecular heterogeneity of the G/CCK immunoreactive material. Large components were observed principally in the medulla terminalis and in the hemolymph, and smaller forms in the stomach. A fraction common for the three tissues had an apparent molecular weight of 2500 Da. That fraction was characterized further by HPLC and shown to be more hydrophobic than human G17 I. By radioimmunoassay relatively low levels were detected in all the aforementioned organs. Although the concentration of the G/CCK-like components varies during the intermolt cycle, this was the case mainly in the hemolymph and in the stomach. These observations suggest a possible role of G/CCK-like peptides in molting processes.

Identification and localization of material with gastrin-like immunoreactivity in the neural ganglion of a protochordate, Ciona intestinalis

Little is known of the identity of gastrin/cholecystokinin (CCK)-like peptides in protochordates. These animals are at a level of organization corresponding to that from which the vertebrate line arose; in order to shed light on the origins of gastrin/CCK-like peptides, we have studied by immunochemical methods these peptides in a protochordate, Ciona intestinalis. In radioimmunoassay, boiling water extracts of the neural ganglion reacted with C-terminal specific gastrin/CCK antibodies, but not N-terminal or intact G17 specific antibodies. Of particular importance was the fact that a gastrin antibody which reacts weakly with CCK8 showed full activity with the Ciona material, suggesting that it resembles the C-terminus of gastrin. A single major peak was found by gel filtration and HPLC. In immunohistochemistry, nerve cell bodies were found in the cortical regions of the ganglion, and abundant fibres ramified in the central neuropile. We conclude that peptides of the gastrin/CCK series occur in nervous tissue in protochordates, and that while they are distinguishable from known forms of both gastrin and CCK, they resemble C-terminal fragments of the mammalian gastrins.

Localization and identification of neurons with cholecystokinin and gastrin-like immunoreactivity in wholemounts of Aplysia ganglia

Immunohistochemical procedures were applied to wholemounts of the central nervous system and posterior intestine of the mollusc, Aplysia californica, to facilitate localization of cells that were immunoreactive to several antisera recognizing various epitopes of the peptides cholecystokinin and gastrin. Only antisera that recognized the carboxyl terminal sequence common to cholecystokinin and gastrin reacted with the Aplysia tissues tested. Intracellular electrophysiological studies of identified postsynaptic targets of immunoreactive neurons in the cerebral ganglia indicated that mammalian forms of gastrin 1-17, several cholecystokinin fragments, and the related peptide, amphibian caerulein, did not mimick the synaptic response mediated by the immunoreactive presynaptic neurons. Combinations of electrophysiological, immunohistochemical, and biochemical studies of several neurons in the buccal ganglia indicated that neurons B7 and B13 were immunoreactive to antisera against cholecystokinin and gastrin and that neuron B13 also contained a concentration of the neurotransmitter acetylcholine as high as in the identified cholinergic buccal neurons, B4 and B5. Several differences in the immunoreactivity of the various antisera were observed. Only one of the antisera was effective in staining neurons in the abdominal ganglia and another antiserum stained subsets of neurons that were immunoreactive to most of the other antisera recognizing the carboxyl terminus common to cholecystokinin and gastrin. The giant serotoninergic metacerebral neurons in Aplysia were not immunoreactive to the cholecystokinin/gastrin antisera even though it has been reported that the homologous neurons in a pulmonate mollusc contain cholecystokinin-like immunoreactivity. These studies demonstrated that there are many neurons with cholecystokinin/gastrin-like immunoreactivity in the Aplysia central and peripheral nervous system and suggested that the peptide may differ from vertebrate forms of cholecystokinin and gastrin. The identification of immunoreactive neurons with known postsynaptic target neurons and buccal neurons with acetylcholine co-localized with a cholecystokinin/gastrin-like peptide will facilitate elucidation of the functions of peptides in the nervous system since the Aplysia preparation is well known to be amenable to multidisciplinary studies.

The distribution of cholecystokinin-8 in the central nervous system of turtles: an immunohistochemical and biochemical study

Immunohistochemical techniques, radioimmunoassay (RIA) and high performance liquid chromatography (HPLC) were used to: (1) determine the regional distribution and amounts of cholecystokinin-8 (CCK8)-like immunoreactivity in the turtle central nervous system, and (2) chemically characterize the CCK8-like material present in the turtle central nervous system. High levels of CCK8-like immunoreactivity were found in the turtle central nervous system, with the highest levels being present in the hypothalamus and neurohypophysis. Moderate levels of the CCK8-like material were found in all other regions of the turtle nervous system except the cerebellum, the olfactory bulbs and the dorsal ventricular ridge of the telencephalon, which contained low levels. The bulk (87%) of the CCK8-like material in turtle central nervous system co-eluted with CCK8-sulfate in gradient elution HPLC. The distribution of CCK8-like immunoreactivity (CCK8LI) observed using immunohistochemistry was consistent with the results of the RIA studies. Numerous CCK8LI-containing neurons and fibers were observed in the hypothalamus and neurohypophysis. Neurons and fibers containing CCK8 were, however, more sparsely distributed outside the hypothalamus. The immunohistochemical data provided evidence for the existence of two major CCK8-containing pathways in turtles that have been previously described in mammals: a pathway from the supraoptic and paraventricular magnocellular nuclei to the external zone of the median eminence and neurohypophysis and a pathway from dorsal root ganglia to the dorsal horn of the spinal cord. Overall, the present results, in conjunction with several previous studies, indicate that CCK8 has had a relatively stable evolutionary history as a CNS neuropeptide among land vertebrates. The molecular structure of CCK8 appears to have been largely (if not entirely) conserved, as has its concentration in many brain regions. A noteworthy exception to such conservatism in the localization of CCK8 is that the concentration of CCK8 in the telencephalon, particularly in the telencephalic cortex, is much lower in turtles than in mammals. The present results therefore suggest that CCK8 may not have become a prominent peptide in the telencephalic cortex (or its anatomical equivalents) until the evolution of neocortex in the mammalian lineage.

Rat immunoreactive cholecystokinin (CCK): characterization using two chromatographic techniques

Acid and neutral extracts of rat cerebral cortex and upper small intestine were prepared and the endogenous concentrations of cholecystokinin-like immunoreactivity (CCK-LI) measured by three new CCK-specific radioimmunoassays. The characterization of the immunoreactive CCK molecular forms was undertaken using gel permeation chromatography in the presence of 6 M urea to minimise problems relating to peptide adsorption or aggregation. Reverse-phase high-performance liquid chromatography (HPLC) was also performed on the rat tissue extracts. Rat cortex contained 268 +/- 12 pmol/g CCK-LI, and over 90% resembled the sulphated CCK-8, which was preferentially extracted at neutral pH. In contrast, the rat upper small intestine (97 +/- 8 pmol/g of CCK-LI) contained less than 20% CCK-8, the majority of immunoreactive CCK being of larger molecular size and being preferentially extracted at acid pH. In the small intestine the predominant molecular form(s) was intermediate in size between CCK-33 and CCK-8. Large amounts of CCK-33 and of a molecular form larger than CCK-33 were also detected. It is concluded that post-translational cleavage of CCK differs in rat brain and gut.

Cholecystokinin and its receptors in vertebrates and invertebrates

Recent studies have indicated that cholecystokinin (CCK) peptides have a long evolutionary history. However, whereas all vertebrates examined have been shown to contain CCK-like peptides, this has not been possible to demonstrate for all invertebrate groups. Immunostaining studies indicate that CCK peptides originate only in neurons in groups below the level of the protochordates. It seems likely that CCK gastrointestinal endocrine cells evolved first at the level of the protochordates, possibly from sensory gut neurons similar to those seen in the invertebrates. Immunochemical and biological studies of a few invertebrate CCK-like peptides suggest that those molecules are substantially different in structure from vertebrate CCKs. Gastrin appears to have evolved from CCK at the level of the appearance of amniotes in vertebrate phylogeny. In mammals, central and peripheral CCK receptors differ in specificity for CCK- and gastrin-like peptides. Comparative studies reveal that this is true for birds as well, but reptiles, amphibia, and fish brain and pancreas CCK receptors exhibit nearly identical specificity patterns. This suggests that the lower vertebrate CCK receptor is ancestral to the distinct brain and pancreas CCK receptors seen in birds and mammals.

Immunocytochemical mapping of gastrin/CCK-like peptides in the neuroendocrine system of the blowfly Calliphora vomitoria (Diptera)

The distribution of gastrin/CCK-like immunoreactive material has been studied in the retrocerebral complex of Calliphora. The material reacts with antisera specific for the common COOH terminus of gastrin and CCK but not with N-terminal antisera. The three thoracic ganglia and the fused abdominal ganglia each contain a specific number of symmetrically arranged immunoreactive cells both dorsally and ventrally in pairs on either side of the midline in a sagittal plane. The neuropil of these ganglia also contains a considerable amount of immunoreactive fibres and droplets. Reconstructed axonal pathways suggest that some of the nerve fibres have their origins within the brain and/or the suboesophageal ganglion. Immunoreactive material may also be seen apparently leaving the thoracic ganglion posteriorly via the abdominal nerves, and there is strong evidence of a neurohaemal organ within the dorsal sheath in the region of the metathoracic and abdominal ganglia. There appears to be a direct correlation between the content of peptidergic material of cells and fibres and the age and diet of the flies. The corpus cardiacum contains COOH-terminal specific gastrin/CCK-like material within the intrinsic cells and in the neuropil. It is present also in the cardiac-recurrent nerve entering the corpus cardiacum anteriorly and in the nerves leaving the gland dorsoposteriorly, the aortic or cardiac nerves. It is not observed, however, in the nerves leaving the corpus cardiacum ventroposteriorly, the so-called oesophageal, gastric or crop-duct nerves. The corpus allatum and the hypocerebral ganglion do not contain immunoreactive material of this type. Gastrin/CCK-like and secretin-like immunoreactive materials appear to co-exist in the cells of the corpus cardiacum and co-existence of gastrin/CCK-like and pancreatic polypeptide-like substances occurs within certain cells of the thoracic ganglion.