Evolutionary aspects of "brain-gut peptides": an immunohistochemical study

Insights into midgut cell types and their crucial role in antiviral immunity in the lepidopteran model Bombyx mori

The midgut, a vital component of the digestive system in arthropods, serves as an interface between ingested food and the insect's physiology, playing a pivotal role in nutrient absorption and immune defense mechanisms. Distinct cell types, including columnar, enteroendocrine, goblet and regenerative cells, comprise the midgut in insects and contribute to its robust immune response. Enterocytes/columnar cells, the primary absorptive cells, facilitate the immune response through enzyme secretions, while regenerative cells play a crucial role in maintaining midgut integrity by continuously replenishing damaged cells and maintaining the continuity of the immune defense. The peritrophic membrane is vital to the insect's innate immunity, shielding the midgut from pathogens and abrasive food particles. Midgut juice, a mixture of digestive enzymes and antimicrobial factors, further contributes to the insect's immune defense, helping the insect to combat invading pathogens and regulate the midgut microbial community. The cutting-edge single-cell transcriptomics also unveiled previously unrecognized subpopulations within the insect midgut cells and elucidated the striking similarities between the gastrointestinal tracts of insects and higher mammals. Understanding the intricate interplay between midgut cell types provides valuable insights into insect immunity. This review provides a solid foundation for unraveling the complex roles of the midgut, not only in digestion but also in immunity. Moreover, this review will discuss the novel immune strategies led by the midgut employed by insects to combat invading pathogens, ultimately contributing to the broader understanding of insect physiology and defense mechanisms.

Coordinated transcriptomics and peptidomics of central nervous system identify neuropeptides and their G protein-coupled receptors in the oriental fruit moth Grapholita molesta

The oriental fruit moth Grapholita molesta is a cosmopolitan pest of orchard, which causes serious economic losses to the fruit production. Neuropeptides and their specific receptors (primarily G protein-coupled receptors, GPCRs) regulate multiple biological functions in insects and represent promising next-generation pest management strategy. Here, we generated a transcriptome of the central nervous system (CNS) of G. molesta. Overall, 57 neuropeptide precursor genes were identified and 128 various mature peptides were predicted from these precursors. Using peptidomic analysis of CNS of G. molesta, we identified total of 28 mature peptides and precursor-related peptides from 16 precursors. A total of 41 neuropeptide GPCR genes belonging to three classes were also identified. These GPCRs and their probable ligands were predicted. Additionally, expression patterns of these 98 genes in various larval tissues were evaluated using quantitative real-time PCR. Taken together, these results will benefit further investigations to determine physiological functions and pharmacological characterization of neuropeptides and their GPCRs in G. molesta; and to develop specific neuropeptide-based agents for this tortricid fruit pest control.

Tracing the Origins of the Pituitary Adenylate-Cyclase Activating Polypeptide (PACAP)

Pituitary adenylate cyclase activating polypeptide (PACAP) is a well-conserved neuropeptide characteristic of vertebrates. This pluripotent hypothalamic neuropeptide regulates neurotransmitter release, intestinal motility, metabolism, cell division/differentiation, and immunity. In vertebrates, PACAP has a specific receptor (PAC₁) but it can also activate the Vasoactive Intestinal Peptide receptors (VPAC₁ and VPAC₂). The evolution of the vertebrate PACAP ligand - receptor pair has been well-described. In contrast, the situation in invertebrates is much less clear. The PACAP ligand - receptor pair in invertebrates has mainly been studied using heterologous antibodies raised against mammalian peptides. A few partial PACAP cDNA clones sharing >87% aa identity with vertebrate PACAP have been isolated from a cnidarian, several protostomes and tunicates but no gene has been reported. Moreover, current evolutionary models of the peptide and receptors using molecular data from phylogenetically distinct invertebrate species (mostly nematodes and arthropods) suggests the PACAP ligand and receptors are exclusive to vertebrate genomes. A basal deuterostome, the cephalochordate amphioxus (Branchiostoma floridae), is the only invertebrate in which elements of a PACAP-like system exists but the peptides and receptor share relatively low sequence conservation with the vertebrate homolog system and are a hybrid with the vertebrate glucagon system. In this study, the evolution of the PACAP system is revisited taking advantage of the burgeoning sequence data (genome and transcriptomes) available for invertebrates to uncover clues about when it first appeared. The results suggest that elements of the PACAP system are absent from protozoans, non-bilaterians, and protostomes and they only emerged after the protostome-deuterostome divergence. PACAP and its receptors appeared in vertebrate genomes and they probably shared a common ancestral origin with the cephalochordate PACAP/GCG-like system which after the genome tetraploidization events that preceded the vertebrate radiation generated the PACAP ligand and receptor pair and also the other members of the Secretin family peptides and their receptors.

Chemical identity, function and regulation of enteroendocrine peptides in insects

How animals allocate energy and metabolic decisions are coordinated is a fundamental physiological question. Metabolic research is strongly driven by an increasing obesity rate in humans. For insects-which contain many pest species and disease vectors-the control of feeding is of agroeconomical and medical importance. Regulatory peptides have since long been in focus of metabolic research. In insects, major advances have been made recently, mostly due to research in the genetically tractable Drosophila melanogaster with focus on the central nervous system as a source of neuropeptides. Research on peptides produced by enteroendocrine cells remained peripheral, but this situation is about to change. This review highlights current knowledge and advances on the identity and role of enteroendocrine insect peptides.

Development of the Drosophila entero-endocrine lineage and its specification by the Notch signaling pathway

In this paper we have investigated the developmental-genetic steps that shape the entero-endocrine system of Drosophila melanogaster from the embryo to the adult. The process starts in the endoderm of the early embryo where precursors of endocrine cells and enterocytes of the larval midgut, as well as progenitors of the adult midgut, are specified by a Notch signaling-dependent mechanism. In a second step that occurs during the late larval period, enterocytes and endocrine cells of a transient pupal midgut are selected from within the clusters of adult midgut progenitors. As in the embryo, activation of the Notch pathway triggers enterocyte differentiation and inhibits cells from further proliferation or choosing the endocrine fate. The third step of entero-endocrine cell development takes place at a mid-pupal stage. Before this time point, the epithelial layer destined to become the adult midgut is devoid of endocrine cells. However, precursors of the intestinal midgut stem cells (pISCs) are already present. After an initial phase of symmetric divisions which causes an increase in their own population size, pISCs start to spin off cells that become postmitotic and express the endocrine fate marker, Prospero. Activation of Notch in pISCs forces these cells into an enterocyte fate. Loss of Notch function causes an increase in the proliferatory activity of pISCs, as well as a higher ratio of Prospero-positive cells.

The serendipitous origin of chordate secretin peptide family members

Background

The secretin family is a pleotropic group of brain-gut peptides with affinity for class 2 G-protein coupled receptors (secretin family GPCRs) proposed to have emerged early in the metazoan radiation via gene or genome duplications. In human, 10 members exist and sequence and functional homologues and ligand-receptor pairs have been characterised in representatives of most vertebrate classes. Secretin-like family GPCR homologues have also been isolated in non-vertebrate genomes however their corresponding ligands have not been convincingly identified and their evolution remains enigmatic.

Results

In silico sequence comparisons failed to retrieve a non-vertebrate (porifera, cnidaria, protostome and early deuterostome) secretin family homologue. In contrast, secretin family members were identified in lamprey, several teleosts and tetrapods and comparative studies revealed that sequence and structure is in general maintained. Sequence comparisons and phylogenetic analysis revealed that PACAP, VIP and GCG are the most highly conserved members and two major peptide subfamilies exist; i) PACAP-like which includes PACAP, PRP, VIP, PH, GHRH, SCT and ii) GCG-like which includes GCG, GLP1, GLP2 and GIP. Conserved regions flanking secretin family members were established by comparative analysis of the Takifugu, Xenopus, chicken and human genomes and gene homologues were identified in nematode, Drosophila and Ciona genomes but no gene linkage occurred. However, in Drosophila and nematode genes which flank vertebrate secretin family members were identified in the same chromosome.

Conclusions

Receptors of the secretin-like family GPCRs are present in protostomes but no sequence homologues of the vertebrate cognate ligands have been identified. It has not been possible to determine when the ligands evolved but it seems likely that it was after the protostome-deuterostome divergence from an exon that was part of an existing gene or gene fragment by rounds of gene/genome duplication. The duplicate exon under different evolutionary pressures originated the chordate PACAP-like and GCG-like subfamily groups. This event occurred after the emergence of the metazoan secretin GPCRs and led to the establishment of novel peptide-receptor interactions that contributed to the generation of novel physiological functions in the chordate lineage.

Conserved genetic pathways controlling the development of the diffuse endocrine system in vertebrates and Drosophila

The midgut epithelium is formed by absorptive enterocytes, secretory cells and endocrine cells. Each of these lineages is derived from the pluripotent progenitors that constitute the embryonic endoderm; the mature midgut retains pools of self-renewing stem cells that continue to produce all lineages. Recent findings in vertebrates and Drosophila shed light on the genetic mechanism that specifies the fate of the different lineages. A pivotal role is played by the Notch signaling pathway that, in a manner that appears to be very similar to the way in which Notch signaling selects neural progenitors within the neurectoderm, distinguishes the fate of secretory/endocrine cells and enterocytes. Proneural genes encoding bHLH transcription factors are expressed and required in prospective endocrine cells; activation of the Notch pathways restricts the number of these cells and promotes enterocyte development. In this review we compare the development of the intestinal endocrine cells in vertebrates and insects and summarize recent findings dealing with genetic pathways controlling this cell type.

The comparative anatomy of islets

In the past 20 years, numerous publications on a variety of mammalian and non-mammalian species have appeared in the literature to supplement the excellent comparative work performed in the 70s and 80s by the Falkmer, Epple, and Youson groups. What emerges is that islets are much more complex than once thought and show a lot of similarities in rodents and higher primates. The diversity of lifestyles, metabolic demands, and diets has most likely influenced the great diversity in both structure and cell-type content of islets in lower vertebrate species. In this chapter, I try to provide an overview of the evolution from endocrine cell types in invertebrates to the higher mammals and focus on what has been reported in the literature and some of our own experiences and also include a description of other hormones reported to be found in islets.

Degenerative and regenerative processes involved in midgut pseudotumor formation in the stick insect (Carausius morosus)

Spontaneous and experimentally induced pseudotumor formation in Carausius morosus impairs the midgut tissue homeostasis. Spontaneous pseudotumor formation begins by the break down of a single or a small group of columnar cells (CCs) and is followed by the degeneration of neighboring CCs. There are not only marked similarities but also decisive differences between normal dying CCs in healthy specimens and the degeneration of CCs leading to pseudotumors: in both cases, the apical cell parts with the nucleus are extruded into the midgut lumen, but only during of pseudotumor formation an "amorphous substance" originates from the basal parts of the CCs. Hemocytes are attracted to this substance and form a nodule-like aggregation, which is responsible for the phenotype of pseudotumors. Pseudotumor infestation has also an impact on the midgut nidi, which consist of an intestinal stem cell and several CC progenitor cells. In healthy specimens only one progenitor cell per nidus differentiates at a time, but, several to all progenitor cells differentiate simultaneously in pseudotumor-infested specimens. Extirpation of the ingluvial ganglion in healthy specimens results in an immediate onset of pseudotumor formation and a dramatic acceleration of pseudotumor growth. Importantly, the ultrastructural characteristics of spontaneous and experimentally induced pseudotumors are identical. This supports the idea that the stomatogastric nervous system plays an integral role in the maintenance of midgut tissue homeostasis.

Characterization of mice lacking the gene for cholecystokinin

CCK acts peripherally as a satiating peptide released during meals in response to lipid feeding and centrally functions in the modulation of feeding, exploratory, and memory activities. The present study determined metabolic parameters, food intake, anxiety-like behaviors, and cognitive function in mice lacking the CCK gene. We studied intestinal fat absorption, body composition, and food intake of CCK knockout (CCK-KO) mice by using the noninvasive measurement of intestinal fat absorption along with quantitative magnetic resonance (QMR) imaging and the DietMax system, respectively. Additionally, exploratory and memory capacities were assessed by monitoring running wheel activity and conducting elevated plus-maze and Morris water-maze tests with these mice. Compared with wild-type (WT) littermate controls, CCK-KO mice had normal food intake, fat absorption, body weight, and body mass. CCK-KO mice ate more food than control animals during the light period and less food during the dark period. Energy expenditure was unchanged between the genotypes; however, CCK-KO mice displayed greater fatty acid oxidation. CCK-KO mice were as active as WT animals in the running wheel test. CCK-KO mice spent more time in the closed arms of an elevated plus-maze, indicative of increased anxiety. Additionally, CCK-KO mice exhibited attenuated performance in a passive avoidance task and impaired spatial memory in the Morris water maze test. We conclude that CCK is involved in metabolic rate and is important for memory and exploration. CCK is intimately involved in multiple processes related to cognitive function and food intake regulation.

Comparative Immunohistochemical Study of Carassius RFamide Localization in Teleost Guts in Different Salinity Habitats

Carassius RFamide (C-RFa) is a peptide, isolated originally from the brain of Japanese crucian carp and sharing homologies with mammalian prolactin-releasing peptides. From the physiological aspect, it is known that C-RFa has contraction-promoting action on fish intestines, but its localization in peripheral tissues is unknown. We observed the localization of C-RFa in teleost guts using an immunohistochemical technique. C-RFa-like immunoreactive (irC-RFa) sites were observed in not only the smooth muscle cells in the longitudinal muscle layer, but also in both Auerbach's and Meissner's nerve plexus in the stomach, pyloric ceca and intestine. In epithelial mucous cells, irC-RFa sites were observed in the surface mucous cells in the stomach in freshwater fish (FW), and in the goblet cells of the apical sites in the villi of the pyloric ceca and intestine in all fish. In the stomach, irC-RFa sites were found in the fundic glands of the body regions in seawater (SW) and brackish water (BW) fish, but not in FW fish. This study confirmed that one of the functions of C-RFa is the smooth muscle contraction of the longitudinal muscle layer in digestive organs. We suggest that C-RFa may have functional roles in both central and peripheral neurotransmission. In addition, it appears that the difference in C-RFa localization of SW, BW, and FW fish reflects the adaptation of the stomach function to different salinity habitats.

Fishy tales of prolactin-releasing peptide

Prolactin (PRL) is an important regulator of multiple biological functions, but a specific PRL-releasing factor, PRL-releasing peptide (PrRP), was isolated only recently from mammals and teleosts. Although this peptide seems to be a strong candidate for being a physiologically relevant stimulator of PRL expression and secretion in teleost pituitary and peripheral organs, it may not be a typical or classic hypothalamic releasing factor in rats. We now know that its biological actions are not limited solely to PRL stimulation, because it is also a neuromodulator of several hypothalamus-pituitary axes and is involved in some brain circuits with the regulation of food intake and cardiovascular functions. Moreover, it plays a direct role in hypertension and retinal information processing. It is the purpose of this review to provide a comprehensive survey of our current knowledge of PrRP and to provide a comparative point of view.

The distribution and effects of Dippu-allatostatin-like peptides in the blood-feeding bug, Rhodnius prolixus

Using a polyclonal antiserum to Dippu-allatostatin 7 (Dippu-AST 7; formerly AST 1) of the cockroach Diploptera punctata, we have demonstrated the presence of AST-like immunoreactivity (ALI) in cells and processes throughout the nervous system, gut, and peripheral tissues of unfed fifth instar and adult Rhodnius prolixus. ALI in apparent neurosecretory cells of the brain, suboesophageal ganglion, and mesothoracic ganglionic mass, as well as in midgut endocrine cells, suggests that Rhodnius allatostatins may act as neurohormones/hormones. The presence of ALI in possible interneurons and areas of neuropile throughout the CNS also suggests roles as neuromodulators and/or neurotransmitters. Dippu-AST 7 inhibits spontaneous and leucokinin 1 (LK 1)-induced contractions of the Rhodnius hindgut in a dose-dependent manner. The low concentrations capable of inhibiting both spontaneous (10(-12)M) and LK 1-induced contractions (10(-10) to 10(-9)M) suggest that ASTs may be acting as neurohormones/hormones on the hindgut. We have also shown that Dippu-AST 7 influences the muscle activity of the Rhodnius dorsal vessel at concentrations as low as 10(-11)M.

Immunocytochemical and ultrastructural characterization of endocrine cells in the larval stomach of the frog Rana temporaria tadpoles: a comparison with adult specimens

According to immunostaining and ultrastructural patterns, Rana temporaria tadpole stomach displays a well-differentiated endocrine population comprising, at least, six cellular types: ECL, EC [serotonin], D [somatostatin] - all three of them abundant -, P [bombesin] - less numerous -, CCK-8 [cholecystokinin/gastrin] and A [glucagon/glicentin] - both very scarce. Larval endocrine cells are mainly located in the surface epithelium and show open or closed morphologies. Cellular diversity is similar in tadpoles and frogs, with the exception of immunoreactivity for gastrin-17, found in adults in numerous cells. Larval cells display mature ultrastructural traits, although with smaller secretory granules. The different distribution of endocrine cells, which in adults are preferentially located in the glands, probably refers to different functional requirements. However, the rich vascular plexus present in larval mucosa may be an efficient transport medium of surface hormones to-gastric targets. The enhancement in adults of endocrine population and correlative increase in hormonal secretion indicates a more active functional role, probably related to the shift from herbivorous to carnivorous habits. In summary, the tadpole gastric endocrine population, although not as numerous as that of adult frogs, displays histological traits that indicate a relevant (immunoreactive and ultrastructural properties, cellular diversity) and specific (surface location, relative abundance of open-type cells) role of local regulatory factors in amphibian larval gastric function.

Rainbow trout (Oncorhynchus mykiss) possess two somatostatin mRNAs that are differentially expressed

Previously, we isolated a 624-bp cDNA encoding for a 115-amino acid preprosomatostatin containing [Tyr7,Gly10]-somatostatin (SS)-14 (now designated PPSS-II') obtained from the endocrine pancreas (Brockmann bodies) of rainbow trout. In this study we have characterized a second cDNA obtained from trout pancreas that is 600-bp in length and encodes for a 111-amino acid precursor containing [Tyr7,Gly10]-SS-14 (PPSS-II''). The nucleotide and amino acid identity between the two cDNAs is 82.3 and 80.5%, respectively. Both PPSS-II' and PPSS-II'' mRNA were present in esophagus, pyloric ceca, stomach, upper and lower intestine, and pancreas, whereas only SS-II" mRNA was present in brain. PPSS-II'' mRNA was more abundant than PPSS-II' mRNA in pancreas, whereas PPSS-II' mRNA was more abundant than PPSS-II" mRNA in stomach. Fasting increased pancreatic PPSS-II'' mRNA levels but had no effect on the levels of PPSS-II' mRNA. These results indicate the existence of two nonallelic pancreatic SS-II genes that are differentially expressed, both in terms of distribution among tissues and in terms of relative abundance within the tissues.

Effects of an allatostatin and a myosuppressin on midgut carbohydrate enzyme activity in the cockroach Diploptera punctata

Neuropeptides of the cockroach allatostatin (AST) family are known for their ability to inhibit the production of juvenile hormone by the corpora allata of cockroaches. Since their discovery, they have also been shown to modulate myotropic activity in a range of insect species as well as to act as neurotransmitters in Crustaceans and possibly in insects. The midgut of cockroaches contains numerous endocrine cells, some of which produce AST whereas others produce the FMRFamide-related peptide, leucomyosuppressin (LMS). We have determined if ASTs and LMS are also able to influence carbohydrate-metabolizing enzyme activity in the midgut of the cockroach, Diploptera punctata. Dippu-AST 7 stimulates activity of both invertase and alpha-amylase in a dose-dependent fashion in the lumen contents of ligatured midguts in vitro, but not in midgut tissue, whereas the AST analog AST(b)phi2, a cyclopropyl-ala, hydrocinnamic acid analog of Dippu-AST 6, has no effect. Leucomyosuppressin also stimulates enzyme activity in lumen contents only, although the EC50 is considerably greater than for Dippu-AST. Dippu-AST is also able to inhibit proctolin-induced contractions of midgut muscle, and this action had already been described for LMS [18]. Thus, in this organ, AST and LMS have at least two distinct physiological effects.

Gastrin and cholecystokinin of the bullfrog, Rana catesbeiana, have distinct effects on gallbladder motility and gastric acid secretion in vitro

Many regulatory peptides form families with at least two homologous members. For several such families the divergence of the individual members from a common ancestor can be dated to early in vertebrate history. Cholecystokinin (CCK) and gastrin were originally identified in mammals. Recently, two distinct members of the CCK/gastrin family were identified in the bullfrog (Rana catesbeiana), termed CCK and gastrin. Frog gastrin is very similar to CCK in the region defining biological activity. To evaluate whether the two endogenous peptides have distinct properties, their effects were studied in typical target organs. While porcine gallbladder responded equally to frog gastrin-8 and CCK-8, EC50 values for stimulation of bullfrog gallbladder contractions were 490 nM (gastrin) and 69 nM (CCK). In contrast, gastrin appeared to be a more potent stimulant of acid secretion than CCK; the estimated EC50 values are 3.1 and 17.2 nM, respectively. Furthermore, gastrin had a significantly higher efficacy than CCK-8s. Thus, in spite of their close structural resemblance, there are clear differences between the two endogenous peptides in their action on gallbladder and gastric mucosa. It is concluded that there are distinct gastrin and CCK functions already at the amphibian level of evolution.

The muscular contractions of the midgut of the cockroach, Diploptera punctata: effects of the insect neuropeptides proctolin and leucomyosuppressin

We have previously shown differential expression of leucomyosuppressin (LMS) mRNA in apparent endocrine cells in the anterior region of midguts of the cockroach Diploptera punctata, using in situ hybridization. In contrast, other FMRFamide-related peptides, as revealed by immunohistochemistry, have been found most abundantly in the posterior region in both apparent endocrine cells and nerve tracts. Here, we partially purified extracts of anterior and posterior cockroach midguts, using HPLC coupled with radioimmunoassay, and found, among multiple FMRFamide-like immunoreactive fractions, one fraction co-eluting with LMS in both regions. The presence of a co-eluting fraction in the posterior region, in the absence of LMS mRNA positive endocrine cells suggests that LMS might therefore be present in nerve tracts running along the length of the midgut. Using a circular muscle contraction assay from different portions of midgut, we determined the effects of LMS, proctolin and a variety of other midgut peptides on contractions of the midgut of Diploptera. Proctolin caused a sustained tonic contraction in the anterior midgut, the amplitude of which was dose-dependent. In contrast, LMS, and its relative SchistoFLRFamide, reduced the amplitude of these contractions. LMS and SchistoFLRFamide also inhibited spontaneous phasic contractions, which were elicited by proctolin application in only a few preparations. Other postulated midgut peptides did not induce or inhibit contractions, nor augment the proctolin-induced contractions. The C-terminal truncated sequences of LMS, HVFLRFamide and VFLRFamide, were sufficient to reduce the amplitude of the proctolin-induced contractions. This work illustrates a possible physiological role for LMS in Diploptera midguts, in the passage of food along the alimentary canal.

In situ hybridization analysis of leucomyosuppressin mRNA expression in the cockroach, Diploptera punctata

In the cockroach Diploptera punctata, sequencing of the cDNA for the insect myoinhibitory neuropeptide, leucomyosuppressin (LMS), has demonstrated that LMS is the only Phe-Met-Arg-Phe-amide (NH2) (FMRFamide)-related peptide to be encoded by this gene (Donly et al. [1996] Insect Biochem. Mol. Biol. 26:627-637). However, in the present study, high performance liquid chromatography analysis of brain extracts showed six discrete FMRFamide-like immunoreactive fractions, one of which co-eluted with LMS. This study compared the distribution of FMRFamide-related peptides visualized by immunohistochemistry with LMS mRNA expression demonstrated by in situ hybridization in D. punctata. Immunohistochemistry with a polyclonal antiserum generated against FMRFamide, but which recognizes extended RFamide peptides, demonstrated numerous RFamide-like immunoreactive cells and processes in both nervous and nonnervous tissues. RFamide-like immunoreactivity was found in cells and processes of the brain and optic lobes, the stomatogastric nervous system, including the frontal and ingluvial ganglia, and the suboesophageal ganglion. Immunoreactivity was also present in all ganglia of the ventral nerve cord and in the alimentary canal. Within the alimentary canal, positively stained processes were found in the crop, midgut, and hindgut, and immunoreactive endocrinelike cells were located in the midgut. In situ hybridization with a digoxigenin-labeled RNA probe spanning the entire LMS coding region showed cell bodies containing LMS mRNA in all ganglia studied, other than the ingluvial ganglion. Expression was most abundant in the brain and optic lobes and in the frontal and suboesophageal ganglia. LMS mRNA was also apparent, although less intensely, in all other ganglia of the ventral nerve cord. Within the alimentary canal, LMS mRNA-positive cells were only visible in the anterior portion of the midgut, in the endocrinelike cells. The appearance of LMS mRNA in the central nervous system, stomatogastric nervous system, and midgut suggests that LMS may play a central role in Diploptera and may be associated with feeding and digestion.

Immunocytochemical and ultrastructural characterization of endocrine cells and nerves in the intestine of Rana temporaria

Endocrine cells have been identified in the intestine of the frog Rana temporaria after application of the Grimelius and Masson-Fontana techniques. These endocrine cells were examined using immunocytochemical techniques on paraffin and semithin sections for light microscopy. After testing 19 antisera, 12 immunoreactivities were identified. Numerous serotonin-, somatostatin- and GLP-1-immunoreactive cells; a moderate number of PYY-, glucagon-, VIP-, gastrin/CCK-immunoreactive cells and few human PP-, bombesin-, substance P- and neurotensin-immunoreactive cells were found. VIP- and met-enkephalin were identified in nerve fibers of the muscular layer. Using semithin-thin sections five types of endocrine cells (serotonin-, somatostatin-, gastrin/CCK-, glucagon- and bombesin-immunoreactive cells) have been characterized according to their immunocytochemical reaction and the ultrastructure of the secretory granules.

Multiple peptide immunoreactivities in the nervous system of Aeschna cyanea (Insecta, Odonata). An immunohistochemical study using antisera to cholecystokinin octapeptide, somatoliberin, vasoactive intestinal peptide, motilin and proctolin

By use of the indirect immunoperoxidase method, the brain, the suboesophageal ganglion and the corpora cardiaca of the dragonfly Aeschna cyanea have been shown to be immunoreactive to proctolin antiserum and to several mammalian peptide antisera including unsulfated cholecystokinin octapeptide (CCK-8 NS) (Andriès et al. 1989), vasoactive intestinal peptide (VIP), human somatoliberin (hGRF) (Andriès et al. 1984) and motilin antisera. Immunohistochemical studies have been performed on material fixed in a solution of picricacid paraformaldehyde or in Bouin Hollande's sublimate solution. Antisera were applied on alternate sections or, according to the elution-restaining method of Tramu et al. (1978), one after another on the same section. Multiple peptide immunoreactivities appear expressed in the brain and the suboesophageal ganglion. Cells reactive to both hGRF and VIP antisera show also gastrin/CCK-like immunoreactivity and some of them are also detected by motilin antiserum. Besides, some cells immunopositive to CCK-8 NS and motilin antisera do not show hGRF or VIP immunoreactivity. At least, two pairs of protocerebral cells appear immunoreactive to both CCK-8 NS and proctolin antisera. Therefore, the present observations support our previously developed idea (Andriès et al. 1989) that the population of CCK-like cells is heterogenous.

Immunocytochemical Localization of Glucagon-Related Peptides in the Cerebral Ganglion of the Protochordate Ascidian, Styela plicata

Abstract The central nervous system of the protochordate ascidian Styela plicata has been investigated by means of immunocytochemical techniques in order to localize peptides of the glucagon/secretin family. In particular, glucagon- and peptide histidine isoleucine-containing neurons were localized in the cortex of the cerebral ganglion, and numerous nerve cell bodies containing vasoactive intestinal polypeptide occurred mainly in the medullary zone. Moreover, coexistence of glucagon/peptide histidine isoleucine and glucagon/vasoactive intestinal polypeptide was detected in a few cortical neurons. The localization of peptide histidine isoleucine-like peptides in the central nervous system and alimentary tract supports the occurrence of a 'brain-gut axis' in protochordates as well as in vertebrates and some invertebrates, while glucagon- and vasoactive intestinal polypeptide-like substances can be considered exclusively as neuropeptides.

Recognition, purification, and structural elucidation of mammalian physalaemin-related molecules

Although the PHLIPs are able to enhance gastrointestinal contractility to a very modest extent, the actual physiological significance of the PHLIPs is not completely understood at the present time. Should the high Mr PHLIM be the precursor molecule(s), the PHLIPs may represent partial enzymatic hydrolysis products of the amino-terminal region of the precursor(s). In this regard, it is interesting to note that immunohistochemical staining of rat duodenum indicates the presence of PHY antiserum cross-reacting material in Brunner's glands, which appear to be involved in secretion of mucin. The amphibian peptide, bombesin, has also been detected in amphibian skin mucous glands by immunochemistry; other investigators have indicated that cerulein, an amphibian analog of the carboxy-terminal region of cholecystokinin, is discharged along with mucin from cutaneous glands in Xenopus after the injection of adrenalin.

Immunohistochemical localization of gastrin-cholecystokinin-like material in the central nervous system of the migratory locust

Brain, corpora cardiaca (CC)-corpora allata (CA) complex, suboesophageal ganglion, thoracic and abdominal ganglia of adults, larvae and embryos of Locusta migratoria have been immunohistochemically screened for gastrin cholecystokinin (CCK-8(s]-like material. In adult, numerous immunoreactive neurons and nerve fibres are located, with a marked symmetry, in various parts of the brain and throughout the ventral nerve cord. In the median part of the brain, cell bodies belonging neither to cellular type A1 nor A2 (following Victoria blue-paraldehyde fuchsin staining) are immunopositive; their processes terminate in the upper protocerebral neuropile. In lateral parts of the brain, external cell bodies send axons into CC and some up to CA, other internal have processes which terminate in the neuropile of the brain. Two of these latter cells react also with methionine-enkephalin antiserum. In the ventral nerve cord, in addition to numerous perikarya, immunoreactive arborizations terminate in the neuropile or in close association with the sheath, at the dorsal part of all ganglia. This CCK-8(s) distribution pattern is observed only at the two last larval instars, but is precociously detected in the abdominal nerve cord of embryos, one day before hatching.

Glucosidation of estradiol-17 beta in the cultured ovaries of the silkworm, Bombyx mori

Metabolic pathways of estradiol-17 beta and other vertebrate steroid hormones of cultured silkworm pupal ovaries were examined using 14C-labeled steroids. The isolated ovaries showed significant uptake and metabolic activity of the 14C-labeled estradiol-17 beta added to the medium. Analysis of the metabolized compounds by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) revealed extensive metabolic conversion of [14C]estradiol-17 beta and estrone; i.e., estrone was reduced to estradiol-17 beta and estradiol-17 beta was metabolized to conjugates, including estradiol-3-beta-D-glucoside and estradiol-17-alpha-D-glucoside. [14C]Testosterone was not transformed appreciably by the ovaries. Metabolic activity and physiological significance of the vertebrate steroid hormones in the silkworm ovaries are discussed.

Identification of estradiol in the ovaries of the silkworm, Bombyx mori

Estradiol was extracted and partially purified from the ovaries of the silkworm, Bombyx mori. Identification of estradiol was done by use of radioimmunoassay (RIA) and by gas chromatography-mass spectrometry (GC-MS) after derivatization into the ethyldimethylsilyl derivative. Concentration of estradiol in the ovaries was estimated to be 176 pg/g (RIA) and 63 pg/g (GC-MS).

Immunocytochemical localization of peptidergic neurons and neurosecretory cells in the neuro-endocrine system of the Colorado potato beetle with antisera to vertebrate regulatory peptides

A large number of antisera to regulatory vertebrate peptides was tested immunocytochemically on the nervous system of the Colorado potato beetle to further characterize the peptidergic cells of the neuro-endocrine system and to reveal cells participating in endocrine control mechanisms. Neurons, neurosecretory cells, axons and axon terminals were revealed by antisera to ACTH, gastrin, CCK, alpha-endorphin, beta-endorphin, gamma 1-MSH, insulin, motilin, human calcitonin, growth hormone, somatostatin, CRF, ovine prolactin and rat prolactin. Together with previously described results these findings demonstrate that at least 19 different peptidergic cell types are present in the Colorado potato beetle. Several of these cell types are identical with the known neurosecretory cells, while others have not been identified before. The functions of the immunoreactive neurons are as yet unclear, although in two cases the localization of these cells gives some clues. Thus the lateral neurosecretory cells, which are immunoreactive with antisera to beta-endorphin and ovine prolactin, may regulate corpus allatum activity, whereas a CRF immunoreactive substance seems to be used as neurotransmitter by antennal receptors. These immunocytochemical findings do not imply that the immunoreactive substances are evolutionarily related to the vertebrate peptides to which the antisera were raised. It is postulated that if the part of the substance recognized by a certain antiserum is functionally important for the insect, which should be so if the insect peptide is evolutionarily related to its vertebrate homologue, the antiserum should reveal homologous cells in different insect species. The consequence of this hypothesis is, that if an antiserum does not reveal homologous neurons in different insect species, the immunologically demonstrated substance is probably of little physiological importance, and will not be related evolutionarily to the vertebrate analogue. The positive immunocytochemical results in the Colorado potato beetle are discussed in relation to these considerations.

Neuropeptide immunocytochemistry in protostomian invertebrates, with special reference to insects and molluscs

In some molluscs (Aplysia and Fusitriton) and insects (silkworm and cricket), occurrence and distribution of neuropeptides in the nervous system and gut were studied with following results: in these invertebrates and also in planaria, PP-like immunoreactivity is extensively distributed in neurons and (in insects) in gut endocrine paraneurons. These cells are negative for NPY, the mammalian neuropeptide related to PP in molecular structure. PHI-like immunoreactivity is widely distributed in the neurons of those invertebrates; it occurs also in gut endocrine paraneurons in insects. The PHI-immunopositive cells are immunonegative for VIP and the coexistence of both peptides due to the common precursor in mammals cannot be recognized in these invertebrates. Immunoreactivity for urotensin I, the neuropeptide derived from teleostean urophysial neurons, is widely distributed in the neurons of the invertebrates. In insects (cricket) it occurs in gut endocrine cells.

Localization of pancreatic polypeptide (PP)-like immunoreactivity in the central and visceral nervous systems of the cockroach Periplaneta

The central and visceral nervous systems of the cockroach Periplaneta americana were studied by means of the peroxidase-antiperoxidase immunocytochemical method, with the use of antibody to bovine pancreatic polypeptide (PP). PP-like immunoreactive neuron somata are most numerous in the brain; at least 6 pairs of cell groups occur in clearly defined regions. Three pairs of cells each are also present in the suboesophageal ganglion and the thoracic ganglia, one pair of single cell each in the first abdominal and the frontal ganglia, and 4 to 6 pairs of single cells in the terminal ganglion. No reactive cells were found in the retrocerebral complex and the second to the fifth abdominal ganglia. The axons containing PP-like immunoreactivity issue many branches that are distributed in the entire brain-retrocerebral complex, ventral cord, and visceral nervous system. PP-like immunoreactive material produced in the brain seems to be transported by three routes: protocerebrum to corpora cardiaca (-allata) through the nervi corporis cardiaci, tritocerebrum to visceral nervous system through frontal commissures, and to ventral cord through circumoesophageal connectives. A possible homology between the mammalian brain-GEP (gastro-entero-pancreatic) system and the brain-midgut system of this insect is discussed.