Terminal Ganglion Research Articles

GABA- and Glutamate-Activated Channels in Green Fluorescent Protein-Tagged Gonadotropin-Releasing Hormone Neurons in Transgenic Mice

Mice were generated expressing green fluorescent protein (GFP) under the control of the gonadotropin-releasing hormone (GnRH) promoter. Green fluorescence was observed in, and restricted to, GnRH-immunopositive neuronal somata in the olfactory bulb, ganglion terminale, septal nuclei, diagonal band of Broca (DBB), preoptic area (POA), and caudal hypothalamus, as well as GnRH neuronal dendrites and axons, including axon terminals in the median eminence and organum vasculosum of the lamina terminalis (OVLT). Whole-cell recordings from GFP-expressing GnRH neurons in the OVLT-POA-DBB region revealed a firing pattern among GFP-expressing GnRH neurons distinct from that of nonfluorescent neurons. Nucleated patches of GFP-expressing GnRH neurons exhibited pronounced responses to fast application of GABA and smaller responses to L-glutamate and AMPA. One-fifth of the nucleated patches responded to NMDA. The GABA-A, AMPA, and NMDA receptor channels on GnRH neurons mediating these responses may play a role in the modulation of GnRH secretory oscillations.

Frequency-intensity characteristics of cricket cercal interneurons: broadband units

The bilateral pairs of cercal interneurons 10-2a and 10-3a in the cricket terminal ganglion are supposed to constitute a functional system for measuring the direction of air-borne signals, based on their phase-locked responses and selective directional sensitivity. The purpose of this study was to obtain information on the frequency and intensity characteristics and thus the potential working range of this system. By recording intracellularly from the axons of the interneurons we measured responses for stimuli of varying frequency, intensity, and direction. Typically, the stimulus frequency range examined extended from 5 to 600 Hz, at intensities of 0.03–30 mm s−1 (peak-to-peak air-particle velocity). The results show that interneurons 10-2a and 10-3a preserved their level of activity, response type, and direction tuning in the whole frequency range tested. Stimulus-response cross-correlograms revealed that spike trains were synchronized with stimulus waves at even higher frequencies, at least up to 1000 Hz. At a given air-particle velocity in the range of about 2–2.5 logarithmic units, the spike number responses of the interneurons were nearly constant over a wide frequency range. Directional diagrams appeared to be independent of stimulus frequency, both in orientation and in amplitude.

Cytoarchitecture of histamine-, dopamine-, serotonin- and octopamine-containing neurons in the cricket ventral nerve cord.

The present article provides a comparative neuroanatomical description of the cellular localization of the biogenic amines histamine, dopamine, serotonin and octopamine in the ventral nerve cord of an insect, namely the cricket, Gryllus bimaculatus. Generally, different immunocytochemical staining techniques reveal a small number of segmentally distributed immunoreactive (-IR) amine-containing neurons allowing single cell reconstruction of prominent elements. Aminergic neurons share common morphological features in that they innervate large portions of neurophil and often connect different neuromeres by intersegmental 'wide-field' projections of varicose appearance. In many cases aminergic terminals are also found on the surface of peripheral nerves suggesting additional neurohemal release sites. Despite such morphological similarities histological analysis demonstrates for any given amine functionally distinct neuron types with specific innervation patterns establishing discrete pathways. Histamine-IR interneurons are characterized by both ascending and descending projections forming central and peripheral terminals. The descending branches from dopamine-IR cells mainly converge within the terminal ganglion, whereas serotonin-IR interneurons with ascending projections often terminate within the brain. Serotonin is also present in sensory and motor neurons. In contrast to other aminergic neurons, most octopamine-IR cells represent unpaired neurons projecting through motor nerves of the soma-containing neuromere. Octopamine-IR cells with intersegmental branches are only rarely found. Based on these findings, a colocalization of different amines within the same neuron seems to be unlikely to occur in the cricket ventral nerve cord. With respect to the neuroanatomical description of amine-containing neurons known physiological effects of biogenic amines and their possible neuromodulatory functions in insects are discussed.

Quantification of periviscerokinin-1 in the nervous system of the American cockroach, Periplaneta americana. An insect neuropeptide with unusual distribution.

This study was undertaken to reveal the quantitative distribution of the insect neuropeptide periviscerokinin-1 (Pea-PVK-1) in the central nervous system of Periplaneta americana and to demonstrate that neurons stained in a previous immunohistochemical study contain authentic Pea-PVK-1. For this, we combined ELISA, HPLC, and MALDI-TOF mass spectrometry. The high specificity of the used antiserum enabled the quantification of Pea-PVK-1 in unseparated tissue extracts. No cross-reactivities with other insect neuropeptides were detected in ELISA. Only two immunoreactive fractions, coeluting with synthetic Pea-PVK-1 in its oxidized and nonoxidized form, were found in HPLC-separated extracts of the brain, suboesophageal ganglion, metathoracic ganglion, second abdominal ganglion with or without perisympathetic organ, and terminal ganglion. By using MALDI-TOF mass spectrometry, we were able to confirm the existence of authentic Pea-PVK-1 in these fractions. The abdominal perisympathetic organs contained 6.3 pmol Pea-PVK-1 per animal; another 1.3 pmol were found in the abdominal ganglia. More than 90% of the total 8.2 pmol in the central nervous system was found in the abdominal ganglia and their perisympathetic organs. The corpora cardiaca and corpora allata did not contain immunoreactive material, suggesting that Pea-PVK-1 is not released by the cephalic neurohaemal system. The quantitative distribution of Pea-PVK-1 differs considerably from that of other known insect neuropeptides.

Quantification of periviscerokinin‐1 in the nervous system of the American cockroach, Periplaneta americana: An insect neuropeptide with unusual distribution

This study was undertaken to reveal the quantitative distribution of the insect neuropeptide periviscerokinin-1 (Pea-PVK-1) in the central nervous system of Periplaneta americana and to demonstrate that neurons stained in a previous immunohistochemical study contain authentic Pea-PVK-1. For this, we combined ELISA, HPLC, and MALDI-TOF mass spectrometry. The high specificity of the used antiserum enabled the quantification of Pea-PVK-1 in unseparated tissue extracts. No cross-reactivities with other insect neuropeptides were detected in ELISA. Only two immunoreactive fractions, coeluting with synthetic Pea-PVK-1 in its oxidized and nonoxidized form, were found in HPLC-separated extracts of the brain, suboesophageal ganglion, metathoracic ganglion, second abdominal ganglion with or without perisympathetic organ, and terminal ganglion. By using MALDI-TOF mass spectrometry, we were able to confirm the existence of authentic Pea-PVK-1 in these fractions. The abdominal perisympathetic organs contained 6.3 pmol Pea-PVK-1 per animal; another 1.3 pmol were found in the abdominal ganglia. More than 90% of the total 8.2 pmol in the central nervous system was found in the abdominal ganglia and their perisympathetic organs. The corpora cardiaca and corpora allata did not contain immunoreactive material, suggesting that Pea-PVK-1 is not released by the cephalic neurohaemal system. The quantitative distribution of Pea-PVK-1 differs considerably from that of other known insect neuropeptides. Arch. Insect Biochem. Physiol. 40:203–211, 1999. © 1999 Wiley-Liss, Inc.

Distribution of gonadotropin-releasing hormone immunoreactive systems in the brain of the Senegalese sole, Solea senegalensis.

The present paper reports the immunohistochemical distribution of the gonadotropin-releasing hormone (GnRH) structures in the brain of the Senegalese sole, Solea senegalensis. In this study, we have used two antibodies against the salmon GnRH and chicken GnRH-II forms and the streptavidin-biotin-peroxidase complex method. Immunoreactive cell bodies are observed at the junction between the olfactory bulbs and the telencephalon (terminal nerve ganglion cells), in the ventral telencephalon, in the preoptic parvocellular nucleus, and in the synencephalic nucleus of the medial longitudinal fasciculus. GnRH-immunoreactive fibres were found extensively throughout the brain, located in the telencephalon, preoptic area, hypothalamus, hypophysis, optic tectum, midbrain and rhombencephalon. The antisera used in this study against the two GnRH forms exhibited cross-reactivity on the same cell masses and did not allow cell populations expressing different GnRH forms to be discriminated clearly. However, anti-salmon GnRH immunostained the GnRH cells and fibres of the forebrain much more intensely, whereas the anti-chicken GnRH antiserum shows a higher immunoreactivity on synencephalic cells of the medial longitudinal fasciculus.

Voltage-activated currents in identified giant interneurons isolated from adult crickets gryllus bimaculatus

The electrophysiological properties of cultured giant interneurons isolated from the terminal ganglion of adult crickets (Gryllus bimaculatus) were investigated using whole-cell patch-clamp techniques. To allow for unequivocal identification of these interneurons in cell culture, a protocol for fast and selective labeling of their cell bodies was established. Prior to cell dissociation, the giant interneurons were backfilled through their axons in situ with a fluorescent dye (dextran tetramethylrhodamine). In primary cell cultures, the cell bodies of giant interneurons were identified among a population of co-cultured neurons by their red fluorescence. Action potentials were recorded from the cell bodies of the cultured interneurons suggesting that several types of voltage-activated ion channels exist in these cells. Using voltage-clamp recording techniques, four voltage-activated currents were isolated and characterized. The giant interneurons express at least two distinct K+ currents: a transient current that is blocked by 4-aminopyridine (4x10(-3 )mol l-1) and a sustained current that is partially blocked by tetraethylammonium (3x10(-2 )mol l-1) and quinidine (2x10(-4 )mol l-1). In addition, a transient Na+ current sensitive to 10(-7 )mol l-1 tetrodotoxin and a Ca2+ current blocked by 5x10(-4 )mol l-1 CdCl2 have been characterized. This study represents the first step in an attempt to analyze the cellular and ionic mechanisms underlying plasticity in the well-characterized and behaviorally important giant interneuron pathway in insects.

Current injection into interneurones of the terminal ganglion modifies turning behaviour of walking crickets

Ascending interneurones of the terminal ganglion of orthopterous insects are known to carry information on wind stimuli perceived by cercal receptors to thoracic and cephalic ganglia. Neurones of these anterior ganglia control evasive walking behaviour. We demonstrate that current injection into individual wind-sensitive local non-spiking interneurones and ascending giant interneurones of the terminal ganglion can influence the orientation behaviour of walking crickets. To induce a change of turning during “wind puff stimulation” by current injection into the lateral giant interneurone, its spike activity has to be modified by at least 100%. In 5 of 12 different types of non-spiking interneurones a moderate shift of the membrane potential results in a change of the mean speed of rotation and/or the frequency of turns. All preparations tested with different amounts of current injection showed a proportional change of turning frequency. Normally, the turning behaviour is evasive with respect to the wind source. During current injection this dependence is preserved, but the general orientation is readjusted. Taking into account known connections between some of these interneurones and ascending neurones the tested wind-sensitive local non-spiking interneurones of the terminal ganglion are likely to impose an offset on the mean direction of orientation controlled by cephalic and thoracic neuronal networks.

Central regulation of sympathetic ganglia development: heterogeneous response of paravertebral, prevertebral, and terminal ganglia.

These studies expand previous observations regarding the central control of neuronal maturation and indicate that paravertebral, prevertebral, and terminal ganglia are all under central influences, but in varying degrees. These variations are probably related to the relative contributions that central pathways exert on specific peripheral neuronal populations during growth and development as well as the various roles of more peripheral developmental modulators such as target organs and hormones, especially in the case of the HG. It is apparent, therefore, that during development central injury may result in heterogeneous deficits depending on the unique intrinsic and extrinsic environment that each ganglion population shares.

Regeneration of cercal filiform hair sensory neurons in the first‐instar cockroach restores escape behavior

Neural regeneration in the escape circuit of the first-instar cockroach is described using behavioral analysis, electrophysiology, intracellular staining, and electron microscopy. Each of the two filiform hairs on each of the animal's cerci is innervated by a single sensory neuron, which specifically synapses with a set of giant interneurons (GIs) in the terminal ganglion. These trigger a directed escape run. Severing the sensory axons causes them to degenerate and perturbs escape behavior, which is restored to near normal after 4–6 days. Within this time, afferents regenerate and reestablish arborizations in the terminal ganglion. In most cases, regenerating afferents enter the cercal glomerulus and re-form most of the specific monosynaptic connections they acquired during embryogenesis, although their morphology deviates markedly from normal; these animals reestablish near normal escape behavior. In a few cases, regenerating afferents remain within the cercus or bypass the cercal glomerulus, and thereby fail to re-form synapses with GIs; these animals continue to exhibit perturbed escape behavior. We conclude that in most cases, specific synapses are reestablished and appropriate escape behavior is restored. This regeneration system therefore provides a tractable model for the establishment of synaptic specificity in a simple neuronal circuit. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 439–458, 1997

Regeneration of cercal filiform hair sensory neurons in the first-instar cockroach restores escape behavior

Neural regeneration in the escape circuit of the first-instar cockroach is described using behavioral analysis, electrophysiology, intracellular staining, and electron microscopy. Each of the two filiform hairs on each of the animal's cerci is innervated by a single sensory neuron, which specifically synapses with a set of giant interneurons (GIs) in the terminal ganglion. These trigger a directed escape run. Severing the sensory axons causes them to degenerate and perturbs escape behavior, which is restored to near normal after 4-6 days. Within this time, afferents regenerate and reestablish arborizations in the terminal ganglion. In most cases, regenerating afferents enter the cercal glomerulus and re-form most of the specific monosynaptic connections they acquired during embryogenesis, although their morphology deviates markedly from normal; these animals reestablish near normal escape behavior. In a few cases, regenerating afferents remain within the cercus or bypass the cercal glomerulus, and thereby fail to re-form synapses with GIs; these animals continue to exhibit perturbed escape behavior. We conclude that in most cases, specific synapses are reestablished and appropriate escape behavior is restored. This regeneration system therefore provides a tractable model for the establishment of synaptic specificity in a simple neuronal circuit.

Neuroanatomical distribution of chicken-I gonadotropin-releasing hormone (cGnRH-I) in the brain of the male red-sided garter snake.

Immunocytochemistry was used to investigate the neuroanatomical distribution of the chicken-I form of gonadotropin-releasing hormone (cGnRH-I) in reproductively active, male, red-sided garter snakes (Thamnophis sirtalis parietalis). Cell bodies with cGnRH-I immunoreactivity (ir) were found in the terminal nerve ganglion, nucleus of the diagonal band of Broca, medial preoptic area, and the hypothalamus. Fibers containing cGnRH-Iir were distributed in the following brain areas. Within the olfactory bulb, fibers were found in the internal plexiform, mitral and glomerular cell layers, as well as in the terminal nerve; within the forebrain, fibers were observed in the diagonal band of Broca, rostral and lateral septum, lateral pallium, retrobulbar region pars dorsomedialis, nucleus accumbens, medial preoptic area, hippocampal commissure, amygdala, posterior dorsal ventricular ridge, hypothalamus, median eminence, and the thalamus; within the midbrain, fibers were found in the interpeduncular nucleus and the stratum album periventricular of the optic tectum. This study shows that the distribution of cell bodies for cGnRH-Iir in this reptile is consistent with the distribution of immunoreactivity for cGnRH-I in birds and mammalian GnRH in amphibians and mammals. Using antiserum specific to cGnRH-I, the endogenous form of GnRH, this is the first study to show that the terminal nerve in a reptile contains GnRH immunoreactivity.

Radioimmunoassay determination of tachykinin-related peptide in different portions of the central nervous system and intestine of the cockroach Leucophaea maderae

A radioimmunoassay was developed for insect tachykinin-related peptides with the use of an antiserum raised to the locust neuropeptide locustatachykinin I (LomTK I). Determination of tachykinin-related peptide was performed in different tissues of the cockroach Leucophaea maderae. The largest amounts of LomTK-like immunoreactivity (LomTK-LI) reside in the brain and in the midgut. Relatively large amounts were also found in the suboesophageal ganglion and throughout the ganglia of the ventral nerve cord, whereas smaller amounts of LomTK-LI were detected in the corpora cardiaca, foregut and hindgut. Extracts of unfused abdominal ganglia and midguts, respectively, were analysed by a combination of reversed phase high performance liquid chromatography, and radioimmunoassay for LomTK-LI. The extracts of abdominal ganglia and midguts both contain LomTK-LI material which separates in at least two major components. This LomTK-LI material had retention times corresponding approximately to those of synthetic LomTK I and II. Since the cellular source of LomTK-LI material in the foregut and hindgut was not known from earlier studies, we investigated these tissues by immunocytochemistry. We found that the LomTK-LI material associated with the foregut was in arborizing fibres in the oesophageal and gastric nerves and in the ingluvial ganglion. In the hindgut the muscle layer was innervated by immunoreactive fibres derived from cell bodies in the terminal ganglion. The amount of LomTK-LI material in other portions of the nervous system correlates well with previous immunocytochemical data. We conclude that L. maderae have two or more isoforms of tachykinin-related peptides in the nervous system and intestine and that these are present in various amounts in different parts of the central nervous system and intestine. The relative large amounts of LomTK-LI material in the suboesophageal ganglion, oesophageal nerve and associated ganglia and intestine indicate important roles of tachykinin-related peptides in feeding and digestion.

GABA-like immunoreactivity of an identified nonspiking local interneurone in the crayfish terminal abdominal ganglion

Using an antiserum directed against -aminobutyric acid (GABA) to label neurones with GABA-like immunoreactivity, approximately 70 central neurones (68±9; mean ± s.e.m., N=9) were labelled in the terminal abdominal ganglion of the crayfish Procambarus clarkii. This mean number of neurones with GABA-like immunoreactivity represents approximately 10 % of the total number of neurones in the terminal ganglion. A combination of intracellular staining using Lucifer Yellow and immunocytochemical staining revealed that an identified nonspiking local interneurone (the local directionally selective interneurone, LDS) showed GABA-like immunoreactivity.

The initiation of pre-ecdysis and ecdysis behaviors in larval Manduca sexta: the roles of the brain, terminal ganglion and eclosion hormone.

Each larval molt of Manduca sexta culminates in the sequential performance of pre-ecdysis (cuticle loosening) and ecdysis (cuticle shedding) behaviors. Both behaviors are thought to be triggered by the release of a peptide, eclosion hormone (EH), from brain neurons whose axons extend the length of the nervous system. EH bioactivity appears in the hemolymph at the onset of pre-ecdysis behavior, and EH injection can trigger pre-ecdysis and ecdysis behaviors prematurely. The present study examined the effects of removing or disconnecting portions of the central nervous system prior to the time of EH release on the initiation of pre-ecdysis and ecdysis behaviors at the final larval molt. We found that the initiation of pre-ecdysis abdominal compressions at the appropriate time required the terminal abdominal ganglion (AT) but not the brain; the initiation of pre-ecdysis proleg retractions at the appropriate time required neither the AT nor the brain; the initiation of ecdysis at the appropriate time usually required the brain but did not require the AT; and premature pre-ecdysis (but not ecdysis) could be elicited in isolated abdomens by injection of EH. Finally, pre-ecdysis behavior performed by brainless larvae was not associated with the normal elevation of EH bioactivity in the hemolymph or the normal loss of EH immunoreactivity from peripheral neurohemal release sites.

Molecular characterization and expression analysis of Manduca sexta allatotropin.

Juvenile hormones (JH) are a class of regulatory sesquiterpenoids that control metamorphosis in immature insects and reproduction in adult insects. The regulation of JH synthesis by the corpora allata (CA), a pair of endocrine glands with nervous connections to the brain, is achieved by a complex interplay of stimulatory and inhibitory factors mediated in part by the brain. The neuropeptide, allatotropin (Mas AT), was recently isolated and sequenced from the brain of the tobacco hornworm Manduca sexta. Mas AT is a 13-residue amidated peptide that activates JH synthesis in adult, but not larval, lepidopteran CA. A 23-nucleotide degenerate oligonucleotide was designed based on the peptide sequence and was used to isolate the Mas AT genomic clone. The Mas AT gene is expressed as three mRNAs which differ from one another by alternative splicing. These mRNAs are predicted to encode three distinct prohormones, each containing Mas AT. A restriction fragment from the genomic clone was then used to isolate the cDNA clone. In situ hybridization and immunohistochemistry studies show that Mas AT is expressed in both the central and enteric nervous systems. Cells expressing Mas AT were identified in the brain, frontal ganglion and terminal ganglion.

Expression of engrailed in an array of identified sensory neurons: Comparison with position, axonal arborization, and synaptic connectivity

engrailed (en) is expressed in the posterior region of embryonic segments and appendages of the cockroach, Periplaneta americana. By 23% of embryogenesis En immunoreactivity is apparent in the dorsal half of the cercus, appendages of segment A11. By 40% of development, En staining is present in the dorsomedial half of the cercus. The nucleus of the medial filiform hair sensory neuron (M), born in this region, expresses en strongly. Staining is never seen in the lateral neuron (L). En is expressed in M as the sensory axons enter the terminal ganglion and begin to form their different arborizations and synaptic connections. This pattern of expression persists through development to the second instar. In mutant animals with supernumerary filiform hair sensilla, En immunoreactivity is only seen in the medial neurons. In second-instar and adult cerci en expression is also seen in medially located neurons. We compared the levels of En staining in the array of 25 second instar neurons with their position, axonal arbor type, and synaptic connections. Staining intensity correlates with distance from the cercal midline, suggesting that en is regulated by other circumferential positional determinants. The expression of en does not correlate with the formation of an M-type arbor. Although 10 to 12 sensory neurons that express en form synapses with giant interneuron 5, the correlation is not precise. These results suggest that, if En does form part of a combinatorial system of positional information in the cercus, its actions are modulated by other gene products.

Putative neurohemal areas in the peripheral nervous system of an insect, Gryllus bimaculatus, revealed by immunocytochemistry

The morphology and position of putative neurohemal areas in the peripheral nervous system (ventral nerve cord and retrocerebral complex) of the cricket Gryllus bimaculatus are described. By using antisera to the amines dopamine, histamine, octopamine, and serotonin, and the neuropeptides crustacean cardioactive peptide, FMRFamide, leucokinin 1, and proctolin, an extensive system of varicose fibers has been detected throughout the nerves of all neuromeres, except for nerve 2 of the prothoracic ganglion. Immunoreactive varicose fibers occur mainly in a superficial position at the neurilemma, indicating neurosecretory storage and release of neuroactive compounds. The varicose fibers are projections from central or peripheral neurons that may extend over more than one segment. The peripheral fiber varicosities show segment-specific arrangements for each of the substances investigated. Immunoreactivity to histamine and octopamine is mainly found in the nerves of abdominal segments, whereas serotonin immunoreactivity is concentrated in subesophageal and terminal ganglion nerves. Immunoreactivity to FMRFamide and crustacean cardioactive peptide is widespread throughout all segments. Structures immunoreactive to leucokinin 1 are present in abdominal nerves, and proctolin immunostaining is found in the terminal ganglion and thoracic nerves. Codistribution of peripheral varicose fiber plexuses is regularly seen for amines and peptides, whereas the colocalization of substances in neurons has not been detected for any of the neuroactive compounds investigated. The varicose fiber system is regarded as complementary to the classical neurohemal organs.

Abundant distribution of locustatachykinin-like peptide in the nervous system and intestine of the cockroach Leucophaea maderae.

An antiserum raised to the locust neuropeptide locustatachykinin I (LomTK I) was used for analysis of the distribution of tachykinin-related peptide in the cockroach Leucophaea maderae. Extracts of dissected brains, suboesophageal ganglia, thoracic ganglia and midguts were separated by high performance liquid chromatography and the fractions analysed in enzyme-linked immunosorbent assay with use of the LomTK antiserum. Each of the tissues was found to contain LomTK-like immunoreactive (LomTK-LI) components with retention times corresponding approximately to synthetic LomTK I and II and callitachykinins I and II. The LomTK antiserum was also used for immunocytochemical mapping of peptide in the nervous system and intestine of L. maderae. A large number of LomTK-LI interneurons were detected in the proto-, deuto- and tritocerebrum of the brain and in the suboesophaegeal ganglion. The immunoreactive neurons supply processes to most parts of the brain: the central body, protocerebral bridge, mushroom body calyces, antennal lobes, optic lobe and most regions of the non-glomerular neuropil. A few protocerebral neurons send LomTK-LI processes to the glandular lobe of the corpora cardiaca. In each of the thoracic ganglia there are six LomTK-LI interneurons and in each of the unfused abdominal ones there are two interneurons. The fused terminal ganglion contains some additional cell bodies in the posterior neuromers. LomTK-LI cell bodies were detected in the frontal ganglion and fibres were seen in this ganglion as well as in the hypocerebral ganglion. The frontal ganglion supplies LomTK-LI processes to the muscle layer of the pharynx. The muscle layer of the midgut is innervated by LomTK-LI fibres from the stomatogastric system (oesophageal nerve and associated ganglia). Additionally the midgut contains numerous LomTK-LI endocrine cells. A number of the pharyngeal dilator muscles were also found to be innervated by LomTK-LI fibres, probably derived from cell bodies in the suboesophageal ganglion. All the LomTK-LI neurons of the central nervous system appear to be interneurons, suggesting a neuromodulatory role of the endogenous tachykinins. The tachykinin-like peptides from peripheral ganglia may be involved in the control of foregut and midgut contractility and possibly the peptide of the endocrine cells in the midgut has additional actions related to intestinal function.

Expression of the Engrailed Gene Reveals Nine Putative Segment-Anlagen in the Embryonic Pleon of the Freshwater Crayfish Cherax destructor (Crustacea, Malacostraca, Decapoda).

Segment formation in the embryonic pleon of the freshwater crayfish Cherax destructor was analyzed by using the monoclonal antibody mAb 4D9 against the product of the segment-polarity gene engrailed. As in other body regions, engrailed is expressed in transverse stripes in the posterior portion of segments in the pleon. Nine engrailed stripes are formed in the pleon. The anterior six stripes correspond to the six pleon segments of adult eumalacostracan crustaceans. The uropods are clearly the appendages of the sixth pleon segment. The seventh engrailed stripe marks the anlage of a seventh ganglion. Stripes eight and nine are transient and disappear before morphogenesis begins. The engrailed stripes seven to nine are interpreted as vestiges of ancestral segments. The seventh segment anlage is thus a recapitulation of the seventh pleonic segment, which is retained in recent adult leptostracans and is considered to be part of the malacostracan ground plan. The stripes eight and nine might point still further back into the phylogeny of crustaceans or even mandibulates. The use of rhodamine-labeled phalloidin reveals that the terminal ganglion of adult crayfish is the fusion product of the anlagen of the sixth and seventh pleonic ganglia and an eighth hemiganglion that is devoid of engrailed expression.