Peptidergic neurons: facts and trends

The neuroendocrine and endocrine systems in insect - Historical perspective and overview

A complex cascade of events leads to the initiation and maintenance of a behavioral act in response to both internally and externally derived stimuli. These events are part of a transition of the animal into a new behavioral state, coordinated by chemicals that bias tissues and organs towards a new functional state of the animal. This form of integration is defined by the neuroendocrine (or neurosecretory) system and the endocrine system that release neurohormones or hormones, respectively. Here we describe the classical neuroendocrine and endocrine systems in insects to provide an historic perspective and overview of how neurohormones and hormones support plasticity in behavioral expression. Additionally, we describe peripheral tissues such as the midgut, epitracheal glands, and ovaries, which, whilst not necessarily being endocrine glands in the pure sense of the term, do produce and release hormones, thereby providing even more flexibility for inter-organ communication and regulation.

Protein-mediated interactions of pancreatic islet cells

The islets of Langerhans collectively form the endocrine pancreas, the organ that is soley responsible for insulin secretion in mammals, and which plays a prominent role in the control of circulating glucose and metabolism. Normal function of these islets implies the coordination of different types of endocrine cells, noticeably of the beta cells which produce insulin. Given that an appropriate secretion of this hormone is vital to the organism, a number of mechanisms have been selected during evolution, which now converge to coordinate beta cell functions. Among these, several mechanisms depend on different families of integral membrane proteins, which ensure direct (cadherins, N-CAM, occludin, and claudins) and paracrine communications (pannexins) between beta cells, and between these cells and the other islet cell types. Also, other proteins (integrins) provide communication of the different islet cell types with the materials that form the islet basal laminae and extracellular matrix. Here, we review what is known about these proteins and their signaling in pancreatic β -cells, with particular emphasis on the signaling provided by Cx36, given that this is the integral membrane protein involved in cell-to-cell communication, which has so far been mostly investigated for effects on beta cell functions.

Connexins: key mediators of endocrine function

The appearance of multicellular organisms imposed the development of several mechanisms for cell-to-cell communication, whereby different types of cells coordinate their function. Some of these mechanisms depend on the intercellular diffusion of signal molecules in the extracellular spaces, whereas others require cell-to-cell contact. Among the latter mechanisms, those provided by the proteins of the connexin family are widespread in most tissues. Connexin signaling is achieved via direct exchanges of cytosolic molecules between adjacent cells at gap junctions, for cell-to-cell coupling, and possibly also involves the formation of membrane "hemi-channels," for the extracellular release of cytosolic signals, direct interactions between connexins and other cell proteins, and coordinated influence on the expression of multiple genes. Connexin signaling appears to be an obligatory attribute of all multicellular exocrine and endocrine glands. Specifically, the experimental evidence we review here points to a direct participation of the Cx36 isoform in the function of the insulin-producing β-cells of the endocrine pancreas, and of the Cx40 isoform in the function of the renin-producing juxtaglomerular epithelioid cells of the kidney cortex.

Diversity of the hypothalamo-neurohypophysial system and its hormonal genes

The hypothalamic neurosecretory cells (NSCs) which produce and release neurohypophysial hormones are involved in controls of diverse physiological phenomena including homeostatic controls of unconscious functions and reproduction. The far and wide distribution of neurosecretory processes in the discrete brain loci and the neurohypophysis is appropriate for coordination of neural and endocrine events that are required for the functions of NSCs. The presence of dye couplings and intimate contacts among NSCs supports harmonious production and release of hormone to maintain the plasma level within a certain range which is adequate for a particular physiological condition. Neurosecretory cells integrate diverse input signals from internal and external sources that define this particular physiological condition, although reactions of NSCs vary among different species, and among different cell types. An input signal to NSC is received by specific receptors and transduced as unique intracellular signals, important for the various functions of neurohypophysial hormones. Orchestration of multiple intracellular signaling systems, activities of which are individually modulated by input signals, determines the rates of synthesis and release of hormone through regulation of gene expression. The first step of gene expression, i.e., transcription, is amenable for diverse reaction of NSCs, because the 5' upstream regions of genes encoding neurohypophysial hormones are highly variable.

Neuropeptides from concept to online database www.neuropeptides.nl

In the early 1970's the term "neuropeptide" was used for the first time by David de Wied for peptides related to peptide hormones but with non-endocrine biological activity in the brain. This early notion appreciated neuropeptides as a specific class of chemical signals produced by neurons, released in a regulated fashion and acting on other neural cells. As we define them today, neuropeptides are encoded by over 70 genes in mammalian genomes. Neuropeptides can be clustered in at least 10 subfamilies according to structural features, for which often shared or related receptors exist. A complete overview is provided through hyperlinks to bioinformatic databases on genome and transcripts, protein structure and brain expression. Other proteineous signaling molecules in the nervous system which originally were discovered in other biological systems, particularly chemokines, growth factors and peptide hormones, share the hallmarks of classical neuropeptides and may be considered as neuropeptides as well.

Evidence for the presence of thyroid stimulating hormone, thyroglobulin and their receptors in Eisenia fetida: a multilevel hormonal interface between the nervous system and the peripheral tissues

The present study describes the localization and distribution of thyroid-stimulating hormone (TSH), thyroglobulin (TGB) and their receptors in Eisenia fetida (Annelida, Oligochaeta) as revealed by immunohistological methods. Immunopositive neuronal and non-neuronal cells are present in both the central nervous system and some peripheral organs (e.g. foregut and coelomocytes). TSH- and TGB-immunopositive neurons in the various ganglia of the central nervous system are differentially distributed. Most of the immunoreactive cells are found in the suboesophageal ganglion. The stained cells also differ in their shapes (round, oval, pear-shaped) and sizes (small, 12-25 microm; medium, 20-35 microm; large, 30-50 microm). In all ganglia of the central nervous system, TSH-positive neurons additionally show gamma aminobutyric acid (GABA) immunopositivity. Non-neuronal cells also take part in hormone secretion and transport. Elongated TSH-positive cells have been detected in the capsule of the central ganglia and bear granules or vacuoles in areas lacking neurons. Many of capillaries show immunoreactivity for all four tested antibodies in the entire central nervous system and foregut. Among the coelomocytes, granulocytes and eleocytes stain for TSH and its receptor and for TGB but not for thyroid hormone receptor. Most of the granulocytes are large (25-50 microm) but a population of small cells (10-25 microm) are also immunoreactive. None of the coelomocytes stain for GABA. We therefore suggest that the members of this hormone system can modify both metabolism and immune functions in Eisenia. Coelomocytes might be able to secrete, transport and eliminate hormones in this system.

Comparative analysis of the chemical neuroanatomy of the mammalian trigeminal ganglion and mesencephalic trigeminal nucleus

A characteristic peculiarity of the trigeminal sensory system is the presence of two distinct populations of primary afferent neurons. Most of their cell bodies are located in the trigeminal ganglion (TG) but part of them lie in the mesencephalic trigeminal nucleus (MTN). This review compares the neurochemical content of central versus peripheral trigeminal primary afferent neurons. In the TG, two subpopulations of primary sensory neurons, containing immunoreactive (IR) material, are identified: a number of glutamate (Glu)-, substance P (SP)-, neurokinin A (NKA)-, calcitonin gene-related peptide (CGRP)-, cholecystokinin (CCK)-, somatostatin (SOM)-, vasoactive intestinal polypeptide (VIP)- and galanin (GAL)-IR ganglion cells with small and medium-sized somata, and relatively less numerous larger-sized neuropeptide Y (NPY)- and peptide 19 (PEP 19)-IR trigeminal neurons. In addition, many nitric oxide synthase (NOS)- and parvalbumin (PV)-IR cells of all sizes as well as fewer, mostly large, calbindin D-28k (CB)-containing neurons are seen. The majority of the large ganglion cells are surrounded by SP-, CGRP-, SOM-, CCK-, VIP-, NOS- and serotonin (SER)-IR perisomatic networks. In the MTN, the main subpopulation of large-sized neurons display Glu-immunoreactivity. Additionally, numerous large MTN neurons exhibit PV- and CB-immunostaining. On the other hand, certain small MTN neurons, most likely interneurons, are found to be GABAergic. Furthermore, NOS-containing neurons can be detected in the caudal and the mesencephalic-pontine junction portions of the nucleus. Conversely, no immunoreactivity to any of the examined neuropeptides is observed in the cell bodies of MTN neurons but these are encircled by peptidergic, catecholaminergic, serotonergic and nitrergic perineuronal arborizations in a basket-like manner. Such a discrepancy in the neurochemical features suggests that the differently fated embryonic migration, synaptogenesis, and peripheral and central target field innervation can possibly affect the individual neurochemical phenotypes of trigeminal primary afferent neurons.

The neuroendocrine system of annelids

In vertebrates the neuroendocrine system is based on chemical signaling between neural and endocrine structures. Final outcomes may be realized via chemical messengers traveling through circulatory conduits to their specific target sites. This process may rely, in part, on neurosecretion of the signaling molecules. The complexity of this system can be readily visualized when one considers the way in which interactions among classical neurotransmitters, cytokines, growth factors, and neuroendocrine hormones, in combination with autocrine and paracrine communication, can regulate cells and tissues. Apart from the neuroendocrine system there is also neuroimmune communication, consisting of reciprocal signaling between neuroendocrine and immune cells, which use the same molecules to coordinate their activity. Thus, our concept of the neuroendocrine system is constantly growing, despite its complexity, but it may be simply summarized as allowing bidirectional communication between neural and endocrine structures over distances greater than that achieved by synaptic communication. In the light of this, I demonstrate in this review that annelids, which are considered "simple" animals, also possess a neuroendocrine system.

Invertebrate opioid precursors: evolutionary conservation and the significance of enzymatic processing

Invertebrate tissues contain mammalian-like proenkephalin, prodynorphin, and proopiomelanocortin. Amino acid sequence determination of these opioid gene products reveals the presence of various opioid peptides exhibiting high sequence identity with their mammalian counterparts. These associated peptides are flanked by dibasic amino acid residues, indicating cleavage sites. Together with the presence of various processing enzymes, i.e., neutral endopeptidase 24.11 and angiotensin-converting enzymes, this suggests that opioid precursor processing is also similar to that described in mammals. It is noted that the levels and/or activity of invertebrate neutral endopeptidase 24.11 can be upregulated by signaling molecules shown to perform the same function in mammals, i.e., morphine. Critical to opioid precursor processing are immunocytes that contain the precursors and transport processing enzymes to sites of inflammation, in part, to cleave these peptide precursors, thus liberating immune-stimulating molecules. Furthermore, in response to lipopolysaccharides, Met-enkephalin levels peak immediately and hours after the exposure, revealing a release and induction process. It appears that the opioid precursors and their processing enzymes first evolved in "simple" animals and the have been maintained and embellished during the course of evolution guided by conformational matching.

Neurotensin-like immunoreactivity in locust supraesophageal ganglion and optic lobes

A substance immunoreactive to antibodies directed against bovine neurotensin (NT) was localized in neurons in the supraesophageal ganglion (SEG) and optic lobes of larval and adult Locusta migratoria L. Two large somata were located in the caudal cortex, ventral to the calyces and symmetrical to the median of the SEG. Four smaller somata also in the caudal cortex were located as two symmetrical pairs at the level of the central body. These somata formed a diffuse network of varicose fibers from the superior lateral to the ventro-lateral protocerebrum between the pedunculi and frontal cortical region. Some fibers crossed the median to the contralateral sides of the SEG. Another pair of immunoreactive somata whose terminating processes remained unclear was found at the level of the antennal lobes. Intrinsic networks of fibers were labeled in the accessory medulla and in layer 4/5 of the medulla. These fibers originated from 8-10 small somata near the dorso-frontal rim of the medulla. All larval stages contained these NT-like immunoreactive structures. Results from isoelectric focusing and press-blot analysis of SEG homogenates, synthetic neurotensin and neurotensin fragments indicate that this substance is similar to bovine neurotensin(1-13).

Glial localization of interleukin-1 alpha in invertebrate ganglia

1. Mytilus pedal ganglion contains a small population of glial cells that are immunopositive for interleukin-1 alpha. Positively stained fibers can also be seen in the neuropil of these sections. 2. The marine worm Nereis diversicolor also exhibits positive neural immunostaining for interleukin-1 alpha. 3. Both organisms contain hemocytes that contain immunoactivity for interleukin-1 alpha. The study suggests interleukin-1 alpha to be an ancient cytokine given its presence in organisms that evolved significantly earlier than mammals.

Invertebrate and vertebrate neuroimmune and autoimmunoregulatory commonalties involving opioid peptides

1. Evidence for bidirectional interrelationships between the nervous system and immune systems of vertebrates and invertebrates involving opioid peptides is briefly discussed. 2. The involvement of opioid peptides in autoimmunoregulatory communication also is discussed. 3. The presence of mammalian interleukin-like (1 & 6) and tumor necrosis factor-like molecules in invertebrates is reviewed as well as an apparent cascading system for these signal molecules. 4. The significance of ACTH and MSH in cellular immunosuppression and autoimmunoregulation is discussed in the context of a potential role in schistosomiasis and human immunodeficiency virus actions. 5. The review concludes with the hypothesis that the mammalian immune system has its origin in the invertebrate immune/defense system given the many similarities noted in the review based on new knowledge about the more "primitive" system.

Localization of myomodulin-like immunoreactivity in the central nervous system and peripheral tissues of Aplysia californica

The distribution of myomodulin-like peptides in the nervous system of Aplysia californica was examined by using immunocytochemical techniques. Neurons and cell clusters containing immunoreactive material were located in each of the major central ganglia. Myomodulin-like immunoreactivity was also present in fibers in each of the connectives between the ganglia and in peripheral nerves. Varicosities containing immunoreactive material were located on specific regions of peripheral tissues associated with the feeding, digestive, cardiovascular, and reproductive systems. Double-labeling experiments were used to demonstrate myomodulin-like immunoreactivity in two identified neurons, the motor neuron B16 in the buccal ganglion and the widely acting interneuron L10 in the abdominal ganglion. Structures in the eye and cerebral ganglion that may correspond to the optic circadian pacemaker system were also stained. The central and peripheral distribution of myomodulin-like immunoreactivity indicates that this family of neuropeptides is present in specific efferent, afferent, and interneuronal elements that participate in a diversity of neural circuits in Aplysia.

Opioid induction of immunoreactive interleukin-1 in Mytilus edulis and human immunocytes: an interleukin-1-like substance in invertebrate neural tissue

The synthetic analog of methionine enkephalin, [D-Ala2-Met5]-enkephalin, when administered in vitro to Mytilus edulis ganglia and hemocytes and human peripheral blood lymphocytes, induces the formation of an immunoreactive interleukin-1-like molecule. Additionally, immunoreactive interleukin-1 (IL-1) activity has been found in Mytilus nervous tissue. The stimulatory actions of the extracted immunoreactive IL-1 on Mytilus hemocytes can be antagonized by an IL-1 antibody demonstrating the specificity of the substance. The evidence suggests that the nervous system, via an opioid-IL-1 relationship, can communicate with the immune/defense system through these similar signal molecules. Furthermore, the results indicate that an interleukin-like molecule must have evolved earlier than previously thought.

Immunohistochemical localization of endothelin-1 in the nervous system of the earthworm Eisenia foetida

The distribution of a substance that resembles endothelin-1 (ET-1) was examined immunohistochemically in the nervous system of the earthworm, Eisenia foetida, using antiserum against ET-1. In the cerebral ganglion, ET-1-like immunoreactivity was demonstrated in two to three pairs of neurons located in the peripheral portion. These immunoreactive neurons projected axons toward the neuropile located in the central portion of the ganglion. Immunoreactive fibers were distributed in the neuropile and proceeded posteriorly to the subesophageal ganglion through the circumpharyngeal connective. In the subesophageal ganglion, no immunoreactive cell bodies were detected, although the immunoreactive fibers were found in the neuropile. In each segmental ganglion, two to eight immunoreactive neurons were observed on each side of the caudo-ventral portion and these neurons sent axons ipsilaterally to the fiber tracts. The pattern of distribution of the immunoreactive neurons in the segmental ganglion was almost identical from one segment to the next. No immunoreactivity was detected in the nerve tracts that emerge peripherally from the cerebral, subesophageal, and segmental ganglia or in other organs, such as the digestive tract and the integument. Specific immunoreactivity to antiserum raised against corticotropin-releasing factor (1-20) was not detected in the nervous system of Eisenia.

A possible immunoregulatory function for [Met]-enkephalin-Arg6-Phe7 involving human and invertebrate granulocytes

Opioid peptides and their analogs have been shown to stimulate adherence, conformational changes and locomotory activity in human as well as invertebrate granulocytes. The present study demonstrates that [Met]-enkephalin-Arg6-Phe7, an opioid substance thus far not included in these immunological tests, exhibits stimulatory effects comparable to those of [Met]-enkephalin in this regard. Furthermore, since neutral endopeptidase 24.11 (enkephalinase; CD10/NEP) exists in invertebrate immunocyte membranes, we demonstrate that its specific inhibitor, phosphoramidon, potentiates the effects of the heptapeptide in inducing conformational change in both human and invertebrate granulocytes. Additionally, the major metabolic products of NEP activity, Phe-Met-Arg-Phe and Tyr-Gly-Gly, appear to be potent antagonists of this enzyme activity, especially the tetrapeptide. The effects of heptapeptide stimulation showed a major difference between vertebrate and invertebrate immunocytes with respect to their time course, namely, the speed of their onset. [Met]-enkephalin-Arg6-Phe7 markedly stimulated the locomotory activity of these cells which becomes most noticeable within 15-45 min for Mytilus cells and in a 5-15 min period for human cells. It also enhanced the mobility and velocity of the responsive human (5 microns/min) and invertebrate cells (2.1 microns/min).

Evidence for an enkephalinergic system in the nervous system of the pond snail, Lymnaea stagnalis

Evidence for the presence of an enkephalinergic system in the ganglia of the pond snail, Lymnaea stagnalis, has been obtained with 3 experimental approaches. Scatchard analysis with [3H]etorphine reveals a monophasic high-affinity opiate binding site (Kd 2.3 nM) which is naloxone-sensitive. Immunocytochemical localization of Met- and Leu-enkephalin-like substances as well as alpha-MSH- and ACTH-like materials was demonstrated within specific populations of neurons. Substances with Met- and Leu-enkephalin and Met-enkephalin sulfoxide RIA reactivities were detected also in HPLC fractions corresponding to the retention times of authentic enkephalin standards. Together, the results provide strong evidence for the presence of enkephalinergic mechanisms in the nervous system of Lymnaea stagnalis. Additionally, the report provides indirect evidence for the existence of a macromolecular opioid precursor. This enkephalinergic system shows striking similarities to opioid mechanisms found in vertebrates and bespeaks a common evolutionary origin.

Immunocytochemical evidence of vertebrate bioactive peptide-like molecules in the immuno cell types of the freshwater snail Planorbarius corneus (L.) (Gastropoda, Pulmonata)

An immunocytochemical investigation was carried out on round and spreading hemocytes of Planorbarius corneus by using 20 antisera to vertebrate bioactive peptides. The immunotests showed the presence of alpha 1-antichymotrypsin-bombesin-, calcitonin-, CCK-8 (INC)-, CCK-39-, gastrin-, glucagon-, Met-enkephalin-, neurotensin-, oxytocin-, somatostatin-, substance P-, VIP-, and vasopressin-immunoreactive molecules in the spreading hemocytes. The round hemocytes were only positive to anti-bombesin, anticalcitonin, anti-CCK-8 (INC), anti-CCK-39, anti-neurotensin, anti-oxytocin, anti-substance P and anti-vasopressin antibodies. No immunostaining was observed with anti-CCK-8 (Peninsula), anti-insulin, anti-prolactin, anti-thyroglobulin and anti-thyroxin (T4) antibodies. As probably in vertebrates, these bioactive peptides may modulate immuno cell function.

Immunocytochemical localization and immunochemical characterization of an insulin-related peptide in the insect Leucophaea maderae

Immunocytochemical tests with eight monoclonal antibodies against either bovine or human insulin and seven polyclonal antibodies against bovine insulin were carried out to determine the presence of insulin-like neuropeptides in the brain and affiliated neuroendocrine structures of the insect Leucophaea maderae. Reaction products identified in the brain, subesophageal ganglion, and corpus cardiacum-corpus allatum complex indicate the presence of materials resembling mammalian insulins in its antigenic properties. The immunostaining observed with monoclonal antibodies appears to indicate the occurrence of an insulin-related peptide that shows sequential similarities with parts of both the A- and B-chains of mammalian insulin molecules. These suppositions are supported by the results of dot-blot and two-site time-resolved immunofluorometric assay (TRI-IFMA) screenings of fractions of Leucophaea tissue extracts obtained by chromatography. The polyclonal antibodies yielded reaction products in some of the same areas and in additional parts of the neuroendocrine system not visualized by the monoclonal antibodies. Immunoreaction was observed in the following areas: the pars intercerebralis of the protocerebrum, the nervi corporis cardiaci I transporting insulin-like material to the corpus cardiacum, the dorsolateral protocerebral area and the optic lobes, the deutocerebrum, the tritocerebrum, and the subesophageal ganglion. In addition, smaller cell bodies with immunoreactive deposits occur at the border between proto- and deuto-cerebrum, and in the central area of the protocerebrum. The distribution of reactive material in the corpus cardiacum-corpus allatum complex after use of both groups of antibodies was the same.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical localization of human growth hormone- and prolactin-like antigenic determinants in the insects, Locusta migratoria and Sarcophaga bullata

1. By use of the peroxidase-antiperoxidase immunocytochemical method, substances immunoreactive to antisera directed against human growth hormone (hGH) and prolactin (hPrl) were localized in the nervous system of larval and adult Locusta migratoria and of adult Sarcophaga bullata belonging to different age groups. 2. No major differences in the distribution of cerebral immunoreactive materials were observed between males and females or between juvenile and adult insects. 3. Differential immuno-labeling of alternating tissue sections demonstrated that materials resembling hGH or hPrl are present in distinct neurons in the locust, whereas neurons immunoreactive to both antisera were detected in the fleshfly (Sarcophaga).

Opioid mechanisms in insects, with special attention to Leucophaea maderae

1. This review article provides information on the evolutionary history of neuroendocrine and related regulatory mechanisms. It focuses on the presence, diverse roles, and modes of operation of one class of neuropeptides, the endogenous opioids, in insects. 2. Opioid peptides, closely resembling those of vertebrates, have been identified in the brain and related neuroendocrine structures by means of immunocytochemistry and high-pressure liquid chromatography. 3. The demonstration of naloxone-sensitive, high-affinity binding sites for Met-enkephalin-like neuropeptides in the brain and digestive tract of Leucophaea deserves special attention because it provides new insights into the functional significance of opiate receptors paralleling those known in vertebrates. 4. Possible roles of receptor-mediated opioid systems in the insects discussed are regulation of the cyclicity of the female reproductive system, maintenance of normal midgut function mediated by the recurrent nerve, and locomotor activity.

Immunocytochemical demonstration of vertebrate peptides in invertebrates: the homology concept

During the last years many positive immunocytochemical reactions have been described in invertebrates using antisera to vertebrate regulatory peptides. However, due to the specificity problems associated with immunocytochemistry, the significance of the majority of these findings remains unclear, as so far only a few of the substances causing the immunoreactions in invertebrates have been isolated. It is proposed that comparing the localizations of "vertebrate" peptides in different and not closely related species of an invertebrate group may give a clue to the physiological relevance of the immunoreactive substances.

Methionine-enkephalin immunoreactivity in the gonads and nervous system of two insect species: Locusta migratoria and Sarcophaga bullata

Methionine(met)-enkephalin immunoreactivity as visualized by the peroxidase-antiperoxidase procedure, is present in spermatogonia, spermatocytes, spermatids, and young ovarian follicles of Locusta (panoistic type) and Sarcophaga (polytrophic type). Follicle cells and mature spermatozoa are always immunonegative as are locust vitellogenic follicles. In oocytes and in trophocytes, the met-enkephalin-like material first appears around the nucleus and is then dispersed throughout the cytoplasm. Later, it is present only in the periphery. In the ovary of both insects, no immunoreactivity is found with antisera against adrenocorticotrophic hormone, melanophore stimulating hormone, beta-endorphin, corticotropin releasing factor, or leucine-enkephalin. All these antisera yield a positive reaction when applied to the central nervous system as does the met-enkephalin antiserum. This study indicates that the met-enkephalin-like peptide may play a role in reproductive physiology.

Immunocytochemical localization of regulatory peptides in six species of trematode parasites

1. Frozen and paraffin sections of six species of trematodes: Schistosoma mansoni, S. mattheei, S. japonicum, Schistosomatium douthitti, Echinostoma paraensei and Fasciola hepatica have been incubated with antisera against leu-enkephalin, FMRF-amide, gastrin-17, luteinizing hormone releasing hormone, neurotensin, oxytocin, prolactin, substance P, thyroid stimulating hormone and cholecystokinin, using indirect immunofluorescence and biotin-avidin horseradish peroxidase detection systems. 2. Of the ten antisera tested, six (leu-enkephalin, FMRF-amide, gastrin-17, luteinizing hormone releasing hormone, substance P and cholecystokinin) showed significant immunoreactivity, primarily in the central and peripheral nervous system, and also perhaps in the osmoregulatory system of the three species of Schistosoma. 3. Immunopositive nerve fibers extended from ganglia to gut wall, uterus and vitelline follicles, and especially from subtegumental nerve plexi to sensory receptors on the surface or in dorsal nippled tubercles.

Influence of neuropeptides on airway smooth muscle

The first bronchoactive (and vasoactive) peptide to be discovered in the lung was isolated and characterized in 1970 from an embryologically related organ, the small intestine. Since then, more than 20 additional peptides have been described in lung tissue and their biologic activities investigated. Many of these are neuropeptides acting as neurotransmitters or neuromodulators to influence airway, pulmonary vascular, and other functions. More neuropeptides are known to exist in the brain and peripheral nervous system; at least some of these are soon likely to be identified in the lung. With the accelerated pace of research, the coming few years should see an increasing definition of the role of neuropeptides in lung physiology and pathophysiology, as well as in improved management of certain respiratory disorders.

Localization of melanotropin-like peptides in the central nervous system of two insect species, the migratory locust, Locusta migratoria, and the fleshfly, Sarcophaga bullata

By use of well characterized antisera in the peroxidase-antiperoxidase method, we were able to demonstrate alpha MSH and beta MSH immunoreactive cells and nerve fibres within the nervous system of adults and larvae of Locusta migratoria and 3-, 5- and 8-day-old adult Sarcophaga bullata. In neither of these insect species, any immunoreaction was obtained with a gamma 3MSH-antiserum. Double immunohistochemical stainings revealed that alpha MSH-like and beta MSH-like substances are located in different cells. These cells show no immunoreactivity to a number of antisera against other POMC-derivatives (anti-beta lipotropin, anti beta endorphin, anti-ACTH1-24); thus they appear to contain alpha MSH- or beta MSH-like material in a specific way. The function of the immunologically detected peptides remains to be demonstrated. The distribution of the immunoreactive material suggests that, like in amphibians and other lower vertebrates, the synthesis or release of melanotropins might be under the influence of external stimuli. The present observations support the recently developed concept that even some of the smallest neuropeptides, the melanotropins, have been highly conserved during a long period of evolution.

Distribution of immunoreactive somatostatin (ISRIF) in the nervous system of the squid, Loligo pealei

Somatostatin (SRIF) is a neuropeptide with a widespread distribution in the mammalian CNS. In the present study we have examined the distribution of immunoreactive-like SRIF (ISRIF)-containing elements in the nervous system of the cephalopod mollusk Loligo pealei, or the Woods Hole squid. ISRIF was localized by light immunocytochemistry in sections of the squid-optic lobe, circumesophageal ganglia-and in stellate ganglion. In the optic lobe, ISRIF neurons were found in the internal granule cell layer and medulla and immunoreactive fibers were seen throughout the lobe and in the optic tract but were absent from the optic nerve, i.e., the projection between the retina and optic lobe. In the supraesophageal complex, ISRIF neurons were found in all lobes, but primarily in the vertical, subvertical, and frontal. In the subesophageal ganglion, ISRIF neurons were seen mainly following unilateral pallial nerve lesions; these neurons were primarily small-to-medium sized. ISRIF fibers were seen in many of the nerves exiting from the brain and in nerves extending between the sub- and supra-esophageal ganglia. In the stellate ganglion, ISRIF was present in many neurons as well as in a plexus of fibers within the ganglion; the peptide was absent from the second-order fibers and the giant axon. The data suggest that a molecule immunologically similar to vertebrate SRIF may be a major transmitter/modulator in this invertebrate. These results provide a foundation for further studies to evaluate the role of this molecule.

Biogenic amines in the snail brain of Helicella virgata (Gastropoda, Pulmonata)

The presence of biogenic amines is demonstrated in the central nervous system of Helicella virgata using a modified glyoxylic acid technique and high-performance liquid chromatography.

Substance P-like immunoreactivity in the central nervous system of the blattarian insect Periplaneta americana L. revealed by a monoclonal antibody

Brains, retrocerebral complexes and frontal and suboesophageal ganglia of adult American cockroaches, Periplaneta americana, were immunohistochemically investigated with a specific monoclonal antibody (McAb) directed against a well characterized antigenic determinant, namely the COOH terminus of the endecapeptide substance P (SP). This resulted in the detection of several neurons and nerve fibres containing a substance antigenically closely related to this typically vertebrate neuropeptide. No difference in staining pattern could be observed between male and female insects. Related to the age of the adult specimens, however, a slight quantitative difference in SP immunoreactivity seems to occur, which probably might have functional implications. The SP-like peptide demonstrated in this study appears to be located in different neuronal structures than the ones that we earlier described as containing ACTH-, CRF-, OT-, AVP-, NP I-, NP II-, BPP-, FMRFamide-, AKH-, met-ENK-, FSH-, LH- and LHRF-like material (Verhaert et al. 1984a, b, 1985; Verhaert and De Loof 1985a, b).

Immunocytochemical localization of a methionine-enkephalin-resembling neuropeptide in the central nervous system of the American cockroach, Periplaneta americana L

Using the peroxidase antiperoxidase immunocytochemical method, we were able to demonstrate within the brain and retrocerebral complex of Periplaneta americana several neuronal structures which were very specifically stained with an anti-methionine-enkephalin antiserum. From the precise localization of this immunoreactive material some speculations about its possible functions could be derived, such as a neurotransmitter- or neuromodulatorlike function and/or a neurohormonal role. These data present new evidence for the recently developed concept that opiate peptides, identical or related to those found in higher species, occur also in invertebrates.

Fine structural organization of the subfornical organ. A concise review

This review of the subfornical organ, with special emphasis on the rat, summarizes the fine structural characteristics of the capillaries, the access route for blood-borne substances, the ependyma through which cerebrospinal fluid-borne substances penetrate the organ, neuronal perikarya, and types of synapses and axons, together with a brief discussion of the principal as yet unresolved problems.

Immunocytochemistry of peptidergic systems in the pond snail Lymnaea stagnalis

Evidence suggests that there exists in the animal kingdom a family of biologically active peptides whose members are related to the molluscan cardio-active tetrapeptide FMRFamide (Phe-Met-Arg-Phe-NH2). Immunocytochemical and ultrastructural studies indicate that several family-members occur in the pond snail Lymnaea stagnalis. Monoclonal antibodies were raised to whole brain homogenates of the pond snail. Selection of antibody producing hybridomas was carried out by staining sections of the central nervous system of the snail with the supernatants of the hybridomas. Certain antibodies stain selectively known (neuro)endocrine centres of the snail, others are directed against particular groups of neurons. It is argued that these antibodies were raised against biologically active peptides and/or their precursors. The antibodies may be used for the isolation of these peptides.

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.

Presence of Met-enkephalin-Arg6-Phe7 in molluscan neural tissues

An extract of pedal ganglia of Mytilus edulis was fractioned by high-pressure liquid chromatography by use of a reverse-phase column. Peak fractions with the same retention time as Met-enkephalin-Arg6-Phe7 were subjected to binding assays in invertebrate neural tissue. The results showed that these fractions have the same binding activities as authentic Met-enkephalin-Arg6-Phe7. The heptapeptide from these fractions was purified by high-pressure liquid chromatography under isocratic conditions. Sequential amino acid analysis showed this peptide to have the same primary structure as Met-enkephalin-Arg6-Phe7. These results indicate that invertebrates such as Mytilus edulis possess enkephalinergic systems similar to those found in in higher organisms.

Immunocytochemical localization of gastrin-releasing peptide/bombesin-like immunoreactive neurons in insects

GRP/bombesin-like immunoreactive material was immunocytochemically detected in neurons of seven insect species belonging to seven orders, while such neurons were not found in three insect species belonging to two other orders. In some insect species certain neurons were found in corresponding places and approximately the same numbers. It seems likely that such neurons have a common evolutionary origin and are homologous. The fact that the GRP-antiserum reveals such homologous neurons in species belonging to different orders, suggests that the part of the GRP/bombesin-like peptide recognized by the antiserum has been relatively stable during evolution. As the GRP-antiserum had to be used in much higher concentrations on insect tissue than for GRP endocrine cells in chicken proventriculus, the chemical resemblance of the insect peptide(s) to GRP and bombesin may be limited.