Modulation of a central pattern generator by two neuropeptides, proctolin and FMRFamide

The neuropeptides, proctolin and FMRFamide, increase the frequency of, and modify the motor pattern produced by, the stomatogastric ganglion (STG) of the crab, Cancer irroratus. Both proctolin-like and FMRFamide-like immunoreactivities are present in fibers in the stomatogastric nerve which terminate in the neuropile of the STG. The neural output of the STG thus appears to be modulated by at least two different groups of peptidergic input fibers.     

Divergent co-transmitter actions underlie motor pattern activation by a modulatory projection neuron

Co-transmission is a common means of neuronal communication, but its consequences for neuronal signaling within a defined neuronal circuit remain unknown in most systems. We are addressing this issue in the crab stomatogastric nervous system by characterizing how the identified modulatory commissural neuron (MCN)1 uses its co-transmitters to activate the gastric mill (chewing) rhythm in the stomatogastric ganglion (STG). MCN1 contains gamma-aminobutyric acid (GABA) plus the peptides proctolin and Cancer borealis tachykinin-related peptide Ia (CabTRP Ia), which it co-releases during the retractor phase of the gastric mill rhythm to influence both retractor and protractor neurons. By focally applying each MCN1 co-transmitter and pharmacologically manipulating each co-transmitter action during MCN1 stimulation, we found that MCN1 has divergent co-transmitter actions on the gastric mill central pattern generator (CPG), which includes the neurons lateral gastric (LG) and interneuron 1 (Int1), plus the STG terminals of MCN1 (MCN1(STG)). MCN1 used only CabTRP Ia to influence LG, while it used only GABA to influence Int1 and the contralateral MCN1(STG). These MCN1 actions caused a slow excitation of LG, a fast excitation of Int1 and a fast inhibition of MCN1(STG). MCN1-released proctolin had no direct influence on the gastric mill CPG, although it likely indirectly regulates this CPG via its influence on the pyloric rhythm. MCN1 appeared to have no ionotropic actions on the gastric mill follower motor neurons, but it did use proctolin and/or CabTRP Ia to excite them. Thus, a modulatory projection neuron can elicit rhythmic motor activity by using distinct co-transmitters, with different time courses of action, to simultaneously influence different CPG neurons.     

Long-term exposure to histamine induces the expression of an embryonic-like motor pattern in an adult nervous system

Neuromodulatory inputs play important roles in shaping the outputs of neural networks. While the actions of neuromodulatory substances over the short term (seconds, minutes) have been examined in detail, far less is known about the possible longer-term (hours) effects of these substances. To investigate this issue, we used the stomatogastric nervous system (STNS) of the lobster to examine the short- and long-term effects of histamine on rhythmic network activity. The application of histamine to the entire STNS had strong inhibitory effects on all three of the STNS networks, observable within minutes. In contrast, longer-term (> 1 h) application of histamine induced the expression of a single, unified rhythm involving neurons from all three networks. Selective application of histamine to different regions of the STNS demonstrated that a unified rhythm arises following the long-term application of histamine to the commissural ganglia (CoGs; modulatory centres), but not the stomatogastric ganglion (site of neural networks). Strikingly, the single rhythm observed following the long-term application of histamine to the CoGs exhibits many similarities with the single rhythm expressed by the embryonic STNS. Together, these results demonstrate that histamine has markedly different short- and long-term effects on network activity; short-term effects arising through direct actions on the networks and long-term effects mediated by actions on modulatory neurons. Furthermore, they indicate that histamine is able to induce the expression of an embryonic-like rhythm in an adult system, suggesting that long-term actions of histamine may play key roles in the development of the STNS networks.     

Distribution of myomodulin-like immunoreactivity in the brain and retrocerebral complex of the locust,schistocerca gregaria

The distribution of myomodulin-like immunoreactivity is described for the brain and retrocerebral complex of an insect, the locust, Schistocerca gregaria. The locust brain contains 70–100 neuronal cell bodies and numerous neuropilar processes exhibiting myomodulin-like immunoreactivity. The most marked feature of the staining is a group of lateral tritocerebral neurones that form a highly immunoreactive tract that gives rise to a complex neuropile of stained processes in the dorsal tritocerebrum. This tract continues dorsally and bifurcates into a major branch that exits the brain via nervi corpora cardiaca 1 (NCC1) to innervate the corpora cardiaca and the corpora allata. A minor branch, consisting of several individual axons, combines with immunoreactive processes from the ventral nerve cord and generates a complex immunoreactive neuropile in the anterior and posterior regions of the protocerebrum. Immunoreactive processes are also found in the structured neuropile of the central body complex. Immunoreactive cell bodies are also found in the antennal lobes, in the lateral margins of the protocerebrum, in the optic lobes, and in a few cells in the pars intercerebralis. The results suggest that myomodulin-like neuropeptides may play roles as central neurotransmitters or neuromodulators in insects as well as being released into the circulation as neurohormones or acting as releasing agents for neurohormones in neurohaemal areas. They also further strengthen the idea that myomodulins, which were first identified in molluscs, may represent another interphyletic family of neuropeptides. © 1995 Wiley-Liss, Inc.     

Peptide neurons in the canine small intestine

The distributions of peptide-containing nerve fibers and cell bodies in the canine small intestine were determined with antibodies raised against seven peptides: enkephalin, gastrin-releasing peptide (GRP), neuropeptide Y, neurotensin, somatostatin, substance P, and vasoactive intestinal peptide (VIP). Immunoreactive nerve cell bodies and fibers were found for each peptide except neurotensin. In the muscle layers there were numerous substance P, VIP, and enkephalin fibers, fewer neuropeptide Y fibers, and very few GRP or somatostatin fibers. The mucosa contained many VIP and substance P fibers, moderate numbers of neuropeptide Y, somatostatin, and GRP fibers and rare enkephalin fibers. Nerve cell bodies reactive for each of the six neural peptides were located in both the myenteric and submucous plexuses. The distributions of nerve cell bodies and processes in the canine small intestine show many similarities with other mammals, for example, in the distributions of VIP, substance P, neuropeptide Y, and somatostatin nerves. There are some major differences, such as the presence in dogs of numerous submucosal nerve cell bodies with enkephalinlike immunoreactivity and of GRP-like immunoreactivity in submucous nerve cell bodies and mucosal fibers.     

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

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

Distribution of myomodulin-like immunoreactivity in the adult and developing ventral nervous system of the locust Schistocerca gregaria

The distribution of myomodulin-like immunoreactivity in the ventral nervous system of an insect, the locust Schistocerca gregaria, both in the adult and during development, is described. The result suggest the presence of a novel modulatory system in insects which uses myomodulin-like neuropeptides. The study also indicates that the myomodulins, which were first identified in mollusks, may represent another interphyletic family of neuropeptides. In the suboesophageal ganglion, immunoreactive cells occur in five groups. The processes from the two anterior ventral midline groups of cells projects to the corpora allata via nervi corpora allata II. Thus myomodulin-like neuropeptides may be involved in the control of the release of juvenile hormone from the corpora allata. The thoracic ganglia contain three groups of immunoreactive cells, including a bilaterally symmetrical group of 12–15 posterior lateral cells, which project to the median nerve and its neurohaemal organs, suggesting a possible neurohaemal role for myomodulin-like peptides. Each thoracic neuromere also contains a single, intensely stained, dorsal unpaired median (DUM) cell that may correspond to the so-called H cell. In the abdominal ganglia, the staining shows sexual dimorphism, both in terms of the number of dorsal and ventral midline cells stained and in terms of the distribution of their immunoreactive processes. Myomodulin-like immunoreactivity is one of the earliest neurotransmitter/neurohormone phenotypes detectable during the development of the locust nervous system. It first appears in the single DUM cells in each of the thoracic neuromeres at 50% development, and the complete adult pattern of staining is present at 85%-90% of development. © 1994 Wiley-Liss, Inc.     

Distribution of NPY and NPY-Y1 receptor-like immunoreactivities in the central nervous system of Triatoma infestans (Insecta: Heteroptera)

The distributions of neuropeptide Y (NPY) -like immunoreactivity (LI) and that of its Y1 receptor (Y1), as well as their coexistence with cholecystokinin (CCK) -LI, were studied in the central nervous system of Triatoma infestans by using immunohistochemistry. NPY-immunoreactive (IR) cell bodies and fibers were observed in the brain, subesophageal ganglion, and thoracic ganglia. NPY-IR somata were seen in the optic lobe and the anteromedial and caudolateral soma rinds of the protocerebrum. Immunostained cell bodies were also found in the lateral edge of the antennal lobe glomeruli as well as in the caudal part of the antennal mechanosensory and motor center. The subesophageal ganglion harbored few NPY-IR perikarya and fibers in the three neuromeres. Positive somata of the prothoracic ganglion were detected near both the cephalic and posterior connectives as well as by the root of prothoracic nerve I, whereas in the posterior ganglion, they were seen by the roots of mesothoracic and abdominal nerves. Coexpression of NPY-LI and CCK-LI was seen in cell bodies of the protocerebrum, the subesophageal and posterior ganglia. Protocerebral Y1-IR cell groups were detected in the anterolateral and posteromedial soma rinds and at the level of the lamina ganglionaris and the external optic chiasma. Numerous positive perikarya surrounded the antennal lobe glomeruli as well as the antennal mechanosensory and motor center. Other immunostained cell bodies were seen in the posterior edge of the esophageal canal and by the roots of the mandibular and the maxillary nerves. Y1-IR cell bodies of the prothoracic ganglion were found near the roots of prothoracic nerves I-II, whereas in the posterior ganglion, they were located mainly in the abdominal neuromeres. Coexpression of Y1-LI and CCK-LI were detected in several brain areas as well as in the metathoracic and abdominal neuromeres of the posterior ganglion. When assessed by immunoblotting, Y1 antibodies detected two protein bands between 34 and 46 kDa. Analysis of the distribution patterns of NPY-LI and Y1-LI suggest that peptide and receptor are mainly involved in the processing of information coming from sensory receptors.     

Differentiation of Transmitter Phenotypes in Rat Cerebral Cortex

Cortical neurons differ in their neurochemical properties. Projection neurons use excitatory amino acids as transmitters, most local interneurons contain the inhibitory transmitter GABA, and specific subtypes of local circuit neurons express distinct neuropeptides. How this cellular diversity is generated during development is not known. We have been studying the transmitter differentiation of cortical neurons in different in vitro systems using immunohistochemical techniques. Transmitter phenotypes of cortical neurons were examined in slice cultures, i.e. in the absence of extrinsic cortical connections, and in dissociated cortical cell cultures, i.e. in the absence of extrinsic and intrinsic cortical connections. The expression of vasoactive intestinal polypeptide in cortical interneurons occurred normally in slice cultures prepared from neonatal rats between birth and 2 days of age, but was strongly impaired in dissociated cell cultures prepared at the same time. These results suggest that the intact cortical environment present in the slice cultures exerts crucial influences for neuropeptide differentiation. In contrast, the transmitters glutamate and GABA were expressed normally in the appropriate cell types and similar in proportions in dissociated cell cultures prepared from cortices at embryonic day 19. Only cells dissociated during S-phase failed to express glutamate and GABA in vitro. When cells were kept for 24 h after mitosis in a cortical slice preparation in vitro , however, they later expressed their appropriate transmitter phenotypes. Thus, signals from the local cortical environment that act early in the cell cycle are required for the specification of transmitter phenotypes of cortical neurons.     

Central somatostatin systems revealed with monoclonal antibodies

The distribution of central neurons displaying somatostatin immunoreactivity was studied using three monoclonal antibodies to cyclic somatostatin. The sensitive ABC immunoperoxidase technique was employed. A large number of positive cell groups including many previously undescribed populations were detected throughout the brain and spinal cord. Telencephalic somatostatin neurons included periglomerular cells in the olfactory bulb, mitral cells in the accessory olfactory bulb, and multipolar cells in the anterior olfactory nuclei, neocortex, amygdala, hippocampus, lateral septum, striatum, and nucleus accumbens. Within the hypothalamus, positive neurons were found in the periventricular, suprachiasmatic, and arcuate nuclei, and throughout the anterior and lateral hypothalamus. The entopeduncular nucleus and zona incerta contained many positive neurons, and the lateral habenula had a dense terminal field suggesting a pallidohabenula somatostatin pathway. Somatostatin neurons were also found in association with many sensory systems. Positive cells were present in the superior and inferior colliculi, the ventral cochlear nuclei, the ventral nucleus of the lateral lemniscus, nucleus cuneatus, nucleus gracilus, and the substantia gelatinosa. Various cerebellar circuits also displayed somatostatin immunoreactivity. Golgi cells throughout the cerebellar cortex were intensely stained, and some Purkinje cells in the paraflocculus also showed a positive reaction. Positive fibers were present in the granular layer and large varicose fibers were present in the inferior cerebellar peduncle. Many nuclei known to project to the cerebellum, including the nucleus reticularis tegmenti pontis, the medial accessory inferior olive, the nucleus prepositus hypoglossi, and many areas of the reticular formation contained positive neurons. These studies demonstrate that these new monoclonal antibodies are of great value for the study of central somatostatin systems. Previously described somatostatin systems are readily detected with these antibodies, and in addition, many otherwise unrecognized somatostatin cell groups have been discovered.     

Occurrence, co-occurrence and topographic distribution of choline acetyl transferase, Met-enkephalin and neurotensin in the stellate ganglion of the cat.

The presence of the classical ganglionic transmitter acetylcholine (ACh), its occurrence and possible co-occurrence with the neuromodulator peptides methionine enkephalin (Met-ENK) and neurotensin (NT), as well as the possible coexistence of these peptides in the preganglionic axon terminals of the cat stellate ganglia were investigated with light and confocal microscopy using immunofluorescence. Choline acetyltransferase (ChAT), Met-ENK, and NT immunoreactivity was detected with light microscopy in axon terminals near tyrosine hydroxylase (TH) immunoreactive (IR) cells. Cell bodies immunopositive for ChAT or Met-ENK were also detected and were TH-negative or TH-positive. Denervation by sectioning preganglionic axons produced two effects: the almost complete elimination of IR fibers and an increase in the number of ChATIR and Met-ENKIR cell bodies, together with the appearance of NTIR cell bodies. Preganglionic ChATIR fibers and boutons form a dense network throughout the entire ganglion, with a homogeneous regional distribution. ChAT, Met-ENK, and NT are essentially stored in different nerve endings, although a low level of co-occurrence was detected. NTIR and Met-ENKIR networks of boutons were observed to have independent and somewhat complementary regional distributions. Further analysis with simultaneous triple labeling for NT, Met-ENK, and TH, and confocal microscopy showed fibers and boutons containing Met-ENK or NT reached distinct neurons separately, or both converge onto the same cells. This finding suggests that modulation (the facilitation-inhibition balance) of ganglionic transmission is achieved mainly by the selective and complementary innervation of boutons containing NT (facilitation) and Met-ENK (inhibition) and only rarely by terminals which coexpress both peptides.     

Guinea pig pancreatic ganglia: projections, transmitter content, and the type-specific localization of monoamine oxidase.

The ganglionated plexus of the guinea pig pancreas was investigated by using histochemical, immunocytochemical, and tract-tracing methods in order to determine whether pancreatic ganglia are analogous to the ganglia of the enteric nervous system (ENS). Three lines of evidence suggest that the ganglia of the pancreas appear to be interconnected with one another, as are enteric ganglia. First, microinjections of the retrograde tracer Fluoro-Gold into individual pancreatic ganglia labeled the perikarya of neurons in distant pancreatic ganglia, whereas no labeling of neurons was observed if injections were placed in the connective tissue adjacent to pancreatic ganglia. Second, when the intercalating dye DiI was microinjected into single pancreatic ganglia in fixed tissues, DiI-labeled terminals were found in additional pancreatic ganglia. Finally, microinjections of the beta subunit of cholera toxin into individual pancreatic ganglia yielded similar results. The ganglionated plexus of the pancreas also expresses a diversity of transmitter content and cell type-specific localization of monoamine oxidase (MAO) that is analogous to the ENS. In common with guinea pig enteric ganglia, pancreatic ganglia contain highly varicose 5-hydroxytryptamine (5-HT)-immunoreactive axons and intrinsic neuropeptide Y (NPY)- and substance P (SP)-immunoreactive neurons. The vast majority, but not all, of SP-immunoreactive fibers in the pancreatic parenchyma also contain calcitonin gene-related peptide (CGRP) immunoreactivity. MAO-B was the primary type of MAO found in the intrinsic elements of the pancreas where it was located in neurons and fibers in the pancreatic parenchyma. In common with serotoninergic enteric neurons, MAO-B immunoreactivity was not found at the LM level in pancreatic serotoninergic neurites. In contrast, NPY- and tyrosine hydroxylase (TH)-immunoreactive perivascular axons were found to contain abundant MAO-A, but no MAO-B immunoreactivity. It is concluded that MAO-B immunoreactivity is characteristic of a portion of the intrinsic innervation of the pancreas, whereas MAO-A immunoreactivity is a marker for the extrinsic sympathetic innervation of the pancreas. Because of its receipt of a direct neural innervation from myenteric ganglia of the bowel (Kirchgessner and Gershon, '90: J. Neurosci 10:1626-1642), similar connections, transmitter content and localization of type-specific MAO, the ganglionated plexus of the pancreas should be regarded as an extension or subset of the ENS.     

Early embryonic expression of a 60-kD glycoprotein in the developing nervous system of the lobster

To investigate the developmental processes that generate the crustacean nervous system, we used a monoclonal antibody that recognises an antigen that is expressed in the developing embryonic nervous system of the lobster, Homarus gammarus. Expression of this antigen commences early in embryogenesis, occurs in all parts of the embryonic central and peripheral nervous systems, and continues into adulthood. Initial expression in the central nervous system correlates with the onset of neuronal process outgrowth. Light microscopic analysis shows that the antigen is found surrounding the cell bodies and processes of all neurons. Biochemical analysis indicates that the antigen, is a glycoprotein with an apparent molecular weight of 60 kD. Due to the early embryonic onset of its expression, this antigen is a useful cellular label for visualisation of- pattern formation in the developing nervous system; this is documented in detail for the developing stomatogastric nervous system. The fact that the 60-kD antigen is expressed early in embryogenesis throughout the nervous system suggests that it might play an important role in the development of the lobster nervous system. © 1994 Wiley-Liss, Inc.     

Evidence for interlaminar inhibitory circuits in the striate cortex of the cat

An interlaminar, ascending, and GABAergic projection is demonstrated in the striate cortex of the cat. We have examined a basket cell, with soma and smooth dendrites in layers V and VI, that was injected intracellularly with HRP in the kitten. Three-dimensional reconstruction of its axon revealed a horizontal plexus in layer V and upper VI, extending about 1.8 mm anteroposteriorly and 0.8 mm mediolaterally; a dense termination in the vicinity of the soma in layers V and VI; and an ascending tuft terminating in layers II and III in register above the soma and about 250 microns in diameter. Many boutons of this cell contacted neuronal somata and apical dendrites of pyramidal cells and subsequent electron microscopy showed that these boutons formed type II synaptic contacts with these structures. A random sample of postsynaptic targets (n = 199) in layers III, V, and VI showed that somata (20.1%), dendritic shafts (38.2%), and dendritic spines (41.2%) were contacted. The fine structural characteristics of postsynaptic elements indicated that the majority originated from pyramidal cells. Direct identification of postsynaptic neurons was achieved by Golgi impregnation of four large pyramidal cells in layer V, which were contacted on their somata and apical dendrites by between three and 34 boutons of the HRP-filled basket cell. Layer IV neurons were not contacted. Golgi-impregnated neurons similar to the HRP-filled basket cell were also found in the deep layers. The axonal boutons of one of them were studied; it also formed type II synapses with somata and apical dendrites of pyramidal cells. Boutons of the HRP-filled neuron were shown to be GABA-immunoreactive by the immunogold method. This is direct evidence in favour of the GABAergic nature of deep layer basket cells with ascending projections. The existence of an ascending GABAergic pathway was also demonstrated by injecting [3H]GABA into layers II and III. The labelled amino acid was transported retrogradely by a subpopulation of GABA-immunoreactive cells in layers V and VI, in addition to cells around the injection site. The axonal pattern and mode of termination of deep basket cells make them a candidate for producing or enhancing directional selectivity, a characteristic of layer V cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Action of tachykinins in the rat hippocampus: modulation of inhibitory synaptic transmission

Substance P and other neuropeptides of the tachykinin family can powerfully excite CA1 hippocampal interneurons present in the CA1 region. In the present work we show that, by exciting hippocampal interneurons, tachykinins can indirectly inhibit pyramidal neurons. We found that tachykinins caused a decrease in the inhibitory synaptic current interval and an increase in the inhibitory synaptic current amplitude in almost all pyramidal neurons tested. This effect was tetrodotoxin sensitive. Tachykinins did not alter the frequency or amplitude of miniature inhibitory synaptic currents and were without effect on evoked inhibitory synaptic currents. Thus, these neuropeptides acted at the somatodendritic membrane of GABAergic interneurons, rather than at their axon terminals. The effect of substance P on spontaneous inhibitory synaptic currents could be mimicked by a selective agonist of NK1 receptors, but not by selective agonists of NK2 and NK3 receptors. It was suppressed by an NK1 receptor antagonist. In CA1 interneurons located in stratum radiatum, substance P generated a sustained tetrodotoxin-insensitive inward current or induced membrane depolarization and action potential firing. This direct excitatory action was mediated by NK1 receptors. Current-voltage relationships indicate that the net tachykinin-evoked current reversed in polarity at or near the K+ equilibrium potential, suggesting that a suppression of a resting K+ conductance was involved. By increasing the excitability of CA1 GABAergic interneurons, tachykinins can powerfully facilitate the inhibitory synaptic input to pyramidal neurons. This indirect inhibition could play a role in regulating short-term and/or long-term synaptic plasticity, promoting neuronal circuit synchronization or, in some physiopathological situations, influencing epileptogenesis.     

Preventive and therapeutic potential of ascorbic acid in neurodegenerative diseases

In this review, we summarize the involvement of ascorbic acid in neurodegenerative diseases by presenting available evidence on the behavioral and biochemical effects of this compound in animal models of neurodegeneration as well as the use of ascorbic acid as a therapeutic approach to alleviate neurodegenerative progression in clinical studies. Ascorbate, a reduced form of vitamin C, has gained interest for its multiple functions and mechanisms of action, contributing to the homeostasis of normal tissues and organs as well as to tissue regeneration. In the brain, ascorbate exerts neuromodulatory functions and scavenges reactive oxygen species generated during synaptic activity and neuronal metabolism. These are important properties as redox imbalance and abnormal protein aggregation constitute central mechanisms implicated in the pathogenesis of neurodegenerative diseases, including Alzheimer's, Parkinson's, and Huntington's diseases, multiple sclerosis, and amyotrophic lateral sclerosis. Indeed, several studies have indicated an association between low serum ascorbate concentrations and neurodegeneration. Moreover, ascorbic acid is a suitable candidate for supplying either antioxidant defense or modulation of neuronal and astrocytic metabolism under neurodegenerative conditions. Ascorbic acid acts mainly by decreasing oxidative stress and reducing the formation of protein aggregates, which may contribute to the reduction of cognitive and/or motor impairments observed in neurodegenerative processes. Although several studies support a possible role of ascorbic acid administration against neurodegeneration, more researches are essential to substantiate the existing results and accelerate the knowledge in this field.     

Differential Regulation of Calcitonin Gene-related Peptide (CGRP) in Regenerating Rat Facial Nucleus and Dorsal Root Ganglion

The content of calcitonin gene-related peptide (CGRP) and CGRP-mRNA were determined in axotomized rat facial motor nucleus and sensory fifth lumbar dorsal root ganglion (L5 DRG) using radioimmunoassay and Northern blot analysis. After facial nerve transection CGRP levels in the facial nucleus showed a biphasic, approximately five-fold increase. A first peak occurred at postoperative day 3 and, after a transient decrease to normal levels at day 9, another increase was observed reaching a peak around the time of reinnervation (postoperative day 21). CGRP-mRNA showed a similar, biphasic increase. The first peak in CGRP mRNA preceded the peptide peak by 2 days, the second peak was approximately day 21. In contrast, a decrease in CGRP levels is seen in L5 DRG after sciatic nerve section, reaching minimal levels of 45% of control during the second postoperative week. CGRP-mRNA in axotomized DRG also decreases preceding the decrease in peptide levels. No recovery to normal levels is seen for either peptide or mRNA levels in regenerating DRG up to 45 days after injury. Thus, axotomy leads to a differential regulation of both CGRP and CGRP-mRNA in regenerating facial motor nucleus and sensory L5 DRG. This difference may be due to different regulating factors present in both the respective target tissues and the CNS regions and could reflect different functions of CGRP in regenerating motor and sensory neurons.     

Dopamine and histamine in the developing stomatogastric system of the lobster Homarus americanus

Dopamine and histamine are neuromodulators found in the adult stomatogastric nervous system (STNS) of several crustacean species. We used antibodies against tyrosine hydroxylase (TH) and histamine to map the distribution and developmental acquisition of the dopamine and histamine neurons in the STNS of the lobster, Homarus americanus. Embryos, larvae, juvenile and adult animals were studied. TH labeling was present in the STNS as early as E80-85 (80-85% of embryonic development). A subset of preparations in embryos, larvae, juveniles, and adults contained 1-5 labeled somata in the stomatogastric ganglion. Histamine staining appeared in the STNS as early as E50. The distribution of both TH and histamine staining remained relatively constant through development. Electrophysiological recordings demonstrated that receptors for both amines are present in the embryo. Bath application of dopamine increased the frequency of the pyloric rhythm in embryos, and evidence for dopaminergic activation of peripherally initiated spiking in motor axons was seen. In embryos and adults, histamine inhibited the motor patterns produced by the stomatogastric ganglion (STG). These data suggest that the dopaminergic and histaminergic systems in H. americanus appear relatively early in development and that the effects of each are largely maintained through development.     

Vasopressin- and proctolin-like immunoreactive efferent neurons in blowfly abdominal ganglia: development and ultrastructure

In the neural sheath of the fused thoracicoabdominal ganglia of the blowfly Calliphora erythrocephala, extensive neurohaemal areas can be seen in the electron microscope. A separate set of neurohaemal areas located in the sheath of the lateral abdominal nerve roots contain neural terminals of at least three morphological types. To determine which bioactive substances are stored and possibly released from the neurons supplying these neurohaemal areas, we applied a large number of antisera raised against different neuropeptides of invertebrate and mammalian type. Antisera to two types of neuropeptides react with neurons innervating the sheath of the abdominal nerve roots: antisera to lysine-vasopressin and proctolin. There are only 14-24 vasopressin-like immunoreactive (VPLI) neurons in the entire nervous system of Calliphora. These are all restricted to a bilateral cluster in the fused abdominal ganglia. From this cluster, the neurohaemal areas in abdominal nerve roots are supplied. Proctolin-like immunoreactivity (PLI) can be seen in a large number of neurons in the nervous system of blowflies. The supply of PLI terminals to the abdominal nerve roots is from 12 to 14 neurons in a bilateral cluster of abdominal PLI neurons. It is clear from light- and electron-microscopic immunocytochemistry that the two antisera label two separate populations of neurons that form overlapping terminals in the neural sheath. The immunoreactive terminals are located just below the permeable acellular basal lamina of the neural sheath. Hence, it is likely that at least two different bioactive peptides can be released neurohormonally into the circulation. An additional set of four efferent PLI neurons send axons into the medial abdominal nerve. These do not form neurohaemal terminals in the nerve root, but may innervate the hindgut. Also in the larval nervous system, VPLI and PLI neurons can be recognized. In the larva, the peptide-containing neurons are segmentally arranged. The 14 larval VPLI neurons supply segmental abdominal nerves with axons that run inside the nerves to their targets. During metamorphosis, the segmental nerves fuse and the VPLI axons invade the neural sheath where they arborize and form varicose terminals. About the same number of PLI neurons could be detected in the abdominal ganglia of larval and adult flies. Only for a set of four caudal PLI neurons could efferent axons be traced in the larva. These axons run inside the medial abdominal nerves. The same four PLI neurons, with the same axonal projections, can be recognized in the adults.     

Distribution of modulatory inputs to the stomatogastric ganglion of the crab, Cancer borealis.

The pyloric and gastric mill neural networks in the crustacean stomatogastric ganglion receive modulatory inputs from more anteriorly located ganglia via the stomatogastric nerve. In this study we employed biocytin backfilling and immunostaining, as well as electron microscopy, to determine the origin of these inputs in the crab, Cancer borealis. Fiber counts from electron micrographs of sections through the stomatogastric nerve showed that this nerve contains 55-60 medium to large diameter fibers (1-13 microns). These fibers were individually wrapped by several layers of membrane, presumably glial in origin. There was also a single cluster of jointly wrapped, small diameter (< 1 micron) fibers that may originate from peripheral sensory somata. Biocytin backfills revealed that approximately two thirds of the individually wrapped fibers in this nerve originate from somata in the other three ganglia of the stomatogastric nervous system, including the paired commissural ganglia and the single oesophageal ganglion. There were approximately 20 biocytin-labeled somata in each commissural ganglion and 3 somata in the oesophageal ganglion. An additional ten somata were localized to the stomatogastric ganglion itself. This accounts for nearly all of the medium to large diameter fibers in the stomatogastric nerve. We used double-labeling with backfills and immunocytochemistry to determine that there are two proctolin-immunoreactive neurons and four FMRFamide-like immunoreactive neurons among the biocytin-labeled neurons in each commissural ganglion. Both peptides modulate neural network activity in the stomatogastric ganglion.(ABSTRACT TRUNCATED AT 250 WORDS)