Neuropeptide proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH): immunological detection and neuronal localization in insect central nervous system

Purification, partial sequencing and characterization of an insect membrane dipeptidyl aminopeptidase that degrades the insect neuropeptide proctolin

Two proctolin-binding proteins solubilized from 1600 cockroach hindgut membranes were purified 1000-fold using five chromatography steps. Twenty-five micrograms of protein were recovered from the final size-exclusion chromatography as a single peak eluting at 74 kDa, whereas two major bands at 80 and 76 kDa were identified after silver staining of electrophoresis gels. The fragments, sequenced by tandem mass spectrometry and the Edman method, revealed a high homology with rat liver dipeptidyl aminopeptidase (DPP) III and a significant homology between the cockroach-purified proteins. From analysis of the Drosophila genome sequence database, it was possible to identify a putative DPP sharing high homology with the sequences obtained from the cockroach purified proteins and with the rat DPP III. Anti-(rat liver DPP III) Ig reacted specifically with both cockroach-purified proteins in Western blot analysis. The purified proteins removed the N-terminal dipeptide from the insect myotropic neuropeptide proctolin (Arg-Tyr-Leu-Pro-Thr) with a Km value of 3.8 +/- 1.1 microM. The specific DPP III inhibitor tynorphin prevented the degradation of proctolin by the purified insect DPP (IC50 = 0.68 microM). These results provide strong evidence that the cockroach-purified proteins represent an insect membrane DPP, presumably present in Drosophila, and that it is closely related to vertebrate DPP III.

Different proctolin neurons elicit distinct motor patterns from a multifunctional neuronal network

Distinct motor patterns are selected from a multifunctional neuronal network by activation of different modulatory projection neurons. Subsets of these projection neurons can contain the same neuromodulator(s), yet little is known about the relative influence of such neurons on network activity. We have addressed this issue in the stomatogastric nervous system of the crab Cancer borealis. Within this system, there is a neuronal network in the stomatogastric ganglion (STG) that produces many versions of the pyloric and gastric mill rhythms. These different rhythms result from activation of different projection neurons that innervate the STG from neighboring ganglia and modulate STG network activity. Three pairs of these projection neurons contain the neuropeptide proctolin. These include the previously identified modulatory proctolin neuron and modulatory commissural neuron 1 (MCN1) and the newly identified modulatory commissural neuron 7 (MCN7). We document here that each of these neurons contains a unique complement of cotransmitters and that each of these neurons elicits a distinct version of the pyloric motor pattern. Moreover, only one of them (MCN1) also elicits a gastric mill rhythm. The MCN7-elicited pyloric rhythm includes a pivotal switch by one STG network neuron from playing a minor to a major role in motor pattern generation. Therefore, modulatory neurons that share a peptide transmitter can elicit distinct motor patterns from a common target network.

Different proctolin neurons elicit distinct motor patterns from a multifunctional neuronal network

Distinct motor patterns are selected from a multifunctional neuronal network by activation of different modulatory projection neurons. Subsets of these projection neurons can contain the same neuromodulator(s), yet little is known about the relative influence of such neurons on network activity. We have addressed this issue in the stomatogastric nervous system of the crab Cancer borealis. Within this system, there is a neuronal network in the stomatogastric ganglion (STG) that produces many versions of the pyloric and gastric mill rhythms. These different rhythms result from activation of different projection neurons that innervate the STG from neighboring ganglia and modulate STG network activity. Three pairs of these projection neurons contain the neuropeptide proctolin. These include the previously identified modulatory proctolin neuron and modulatory commissural neuron 1 (MCN1) and the newly identified modulatory commissural neuron 7 (MCN7). We document here that each of these neurons contains a unique complement of cotransmitters and that each of these neurons elicits a distinct version of the pyloric motor pattern. Moreover, only one of them (MCN1) also elicits a gastric mill rhythm. The MCN7-elicited pyloric rhythm includes a pivotal switch by one STG network neuron from playing a minor to a major role in motor pattern generation. Therefore, modulatory neurons that share a peptide transmitter can elicit distinct motor patterns from a common target network.

Proctolinlike immunoreactivity and identified neurosecretory cells as putative substrates for modulation of courtship display behavior in the blue crab, Callinectes sapidus

Pheromonally stimulated courtship display (CD) behavior in male blue crabs (Callinectes sapidus) is characterized by rhythmic waving of the fifth legs. The waving of the fifth legs is modulated by proctolin in freely moving crabs and in reduced preparations. To begin to identify an anatomical substrate for CD behavior we have localized putative proctolinergic cells and described the morphology of neurosecretory neurons known to oscillate during pheromonal stimulation of reduced preparations. Proctolin-induced CD occurs with developmental and seasonal dependence. Male crabs altered hormonally by eyestalk ligation spontaneously produce CD behavior. We have localized proctolinlike immunoreactivity (PIR) in the central nervous system (CNS) and compared this immunoreactivity across sexes, developmental stage, eyestalk ligation, and seasonal conditions to determine whether or not expression of PIR is correlated with CD behavior. PIR was found in most areas of the CNS. Clusters of PIR-positive cells were found in the sinus gland and eyestalk ganglia, olfactory neuropil with associated cell bodies, and in a large cell cluster in the subesophageal region of the ventral nerve cord. Three pairs of cell bodies in different cell body groups in the brains of adult crabs stained positively for PIR but did not stain in the youngest juvenile animals. Comparison of PIR distribution with toluidine blue studies of the ventral nerve cord indicated a high likelihood that cells in the PIR-positive cluster of the subesophageal ganglia were also members of the cluster of neurons identified as oscillatory neurosecretory neurons.

Localization of the heptapeptide GFSKLYFamide in the sea cucumber Holothuria glaberrima (Echinodermata): a light and electron microscopic study

Two peptides, Gly-Phe-Ser-Lys-Leu-Tyr-Phe-NH2 (GFSKLYFamide) and Ser-Gly-Tyr-Ser-Val-Leu-Tyr-Phe-NH2 (SGYSVLYFamide), recently isolated from the sea cucumber Holothuria glaberrima [Díaz-Miranda et al. (1992) Biol. Bull. 182:241-247] represent the first neuropeptides isolated from holothurians. Using an antibody against GFSKLYFa, we describe here the localization and distribution pattern of GFSKLYFa-like immunoreactivity in H. glaberrima, where immunoreactive fibers form a prominent and extensive peptidergic nervous system component. Neuron-like cells and nerve fibers expressing GFSKLYFa-like immunoreactivity are found in the ectoneural and hyponeural divisions of the radial nerve cords as well as in the digestive, haemal, respiratory, and reproductive systems; in the tentacles; and in tube feet. Neuroendocrine-like cells are found in the mucosal layer of the intestine. Ultrastructure immunocytochemical analysis revealed that, in nerve cells and fibers in the serosal layer of the intestine, the immunoreactivity is concentrated in vesicles. The immunoreactive nerve fibers are found mainly within a dense nerve plexus overlying and in close contact with smooth muscle cells of the intestine. The exclusive expression of GFSKLYFa-like immunoreactivity in neuronal or neuroendocrine tissue together with the close apposition of some fibers to muscle cells suggests that GFSKLYFa acts as a neuromuscular transmitter or neuromodulator in H. glaberrima. The wide occurrence of GFSKLYFa-like immunoreactivity throughout the nervous system of the sea cucumber suggests that GFSKLYFa plays an important role in the control of multiple action systems, including digestion, respiration, circulation, reproduction, and locomotion.

Proctolin and excitation of the crayfish swimmeret system

The ventral nerve cord of crayfish contains axons of five pairs of excitatory interneurons, each of which can activate the swimmeret system. Perfusion of the ventral nerve cord with the neuropeptide proctolin also activates the swimmeret system. The experiments reported here were conducted to test the hypothesis that one or more of these excitatory interneurons uses proctolin as a transmitter. Each of the five excitatory axons was located and stimulated separately in an individual crayfish, and similar motor activity was elicited by stimulating each of them. Quantitative comparison of spontaneous swimmeret motor patterns with activity caused by stimulating one of these excitatory axons, EC, or by perfusing with proctolin solutions showed that the motor patterns produced under these three conditions were not significantly different (P > 0.05). By using a new, affinity-purified proctolin antiserum, we labeled axons in the connective tissue between the last thoracic and first abdominal ganglion and compared the positions of labeled axons with the previously described positions of the excitatory axons. About 0.3% of the axons in these connective tissues showed proctolin-like immunoreactivity, but heavily labeled pairs of axons did occur bilaterally in the regions of excitatory swimmeret axons. The projections of these labeled axons into the abdominal ganglia were traced in serial plastic sections. Labeled processes were abundant in the lateral neuropils, the loci of the swimmeret pattern-generating circuitry. From this evidence, we propose that three of these excitatory swimmeret interneurons use proctolin as a transmitter, but that a fourth does not. The evidence for the fifth axon is ambiguous.

Immunohistochemical localisation of the hypertrehalosaemic hormone II (Cam-HrTH-II) and related peptides in the nervous system of Carausius morosus and Sarcophaga bullata

A polyclonal antiserum was prepared against an N-terminal modified Cam-HrTH-II (Leu-Asn-Phe-...), one of the members of the large AKH/RPCH peptide family, first isolated from Carausius morosus. The localisation of this peptide was performed by means of immunocytochemical methods in the brain and corpora cardiaca-corpora allata complex of the stick insect, Carausius morosus and the grey fleshfly, Sarcophaga bullata. The distribution patterns of molecules reactive to the Cam-HrTH-II and the Lom-AKH-I antisera in both insect species were compared. In Carausius, both antisera reacted in the same cell bodies. In Sarcophaga, some neurons were stained by both, others only by one of the two antisera. By combining two different antisera, we demonstrated that there are no Lom-AKH-I-like molecules present in Carausius and that there must occur at least three different AKH-like molecules in the brain of Sarcophaga. One is similar to Cam-HrTH-II, the second to Lom-AKH-I and the third is an AKH/RPCH-like peptide, different from Lom-AKH-I and Cam-HrTH-II.

Proctolin: a review with emphasis on insects

The distribution, physiological role, mode of action, and pharmacology of the pentapeptide neuroregulator proctolin are reviewed, with special emphasis on insects. Whereas proctolin is distributed extensively throughout arthropods, its presence in molluscs, annelids, or chordates is not well established. In the arthropods, proctolin acts as a neuromodulator and possibly as a neurohormone. It does not appear to function as a conventional neurotransmitter. Two model proctolinergic systems are highlighted: motor control of the visceral muscles of the locust oviduct and of the skeletal muscles of the locust ovipositor. In these preparations proctolin is a cotransmitter acting to enhance neuromuscular transmission and muscular contraction. The mode of action of proctolin is not well understood, although the second messengers cAMP, phosphatidyl inositol, and calcium have been implicated in various systems. Pharmacologically, the proctolin receptor has been examined with structure/activity studies, and the effects of a variety of amino acid substitutions and deletions of the pentapeptide are described. It is unfortunate that no specific antagonists of the proctolin receptor appear to be available and that no receptor-binding studies have been reported. The prospects are good for advances in our understanding of modulatory mechanisms, since proctolin appears to be emerging as the model for studies of this type.

Identification and distribution of a proctolin-like neuropeptide in the nervous system of the gypsy moth, Lymantria dispar, and in other Lepidoptera

Although the neuropeptide proctolin has important functions in many arthropods, it is reported to be absent in Lepidoptera. Its possible occurrence in these insects was reinvestigated by bioassays of HPLC fractions and immunocytochemistry. A proctolin-like substance was recovered from the frontal and subesophageal ganglia of Lymantria dispar. This substance has the same chromatographic retention time as proctolin; enzymatic degradation indicates that it is a peptide; it is bound by proctolin antisera; and thus it is indistinguishable from authentic proctolin. A small subpopulation of proctolin-like immunoreactive (PLI) neurons was stained in the larval CNS of L. dispar, Manduca sexta, Trichoplusia ni, Galleria mellonella, and Vanessa cardui. Most prominent of these cells are median neurosecretory neurons in the brain, paired neurons in the frontal ganglion, two clusters of neurons in the subesophageal ganglion, paired lateral neurons in the thoracic ganglia, and dorsomedial neurons in the abdominal ganglia. Also, varicose PLI axons are found in the corpora cardiaca and perivisceral organs. In L. dispar, PLI cells also were found in the corpora cardiaca. The results of this study indicate that proctolin is of general occurrence in the Lepidoptera, that it has an important role in the stomatogastric nervous system, and that it may be released as a local neurohormone from various neurohemal organs.

Light- and electron-microscopic immunocytochemistry of peptidergic neurons innervating thoracico-abdominal neurohaemal areas in the blowfly

Ventral thoracic neurosecretory cells (VTNCs) of the blowflies, Calliphora erythrocephala and C. vomitoria, innervating thoracic neuropil and the dorsal neural sheath of the thoracico-abdominal ganglion have been shown to be immunoreactive to a variety of mammalian peptide antisera. In the neural sheath the VTNC terminals form an extensive neurohaemal network that is especially dense over the abdominal ganglia. The same areas are invaded by separate, but overlapping serotonin-immunoreactive (5-HT-IR) projections derived from neuronal cell bodies in the suboesophageal ganglion. Immunocytochemical studies with different antisera, applied to adjacent sections at the light-microscopic level, combined with extensive cross-absorption tests, suggest that the perikarya of the VTNCs contain co-localized peptides related to gastrin/cholecystokinin (CCK), bovine pancreatic polypeptide (PP), Met- and Leu-enkephalin and Met-enk-Arg6-Phe7 (Met-enk-RF). Electron-microscopic immunogold-labeling shows that some of the terminals in the dorsal sheath react with several of the individual peptide antisera, whilst others with similar cytology are non-immunoreactive. In the same region, separate terminals with different cytological characteristics contain 5-HT-IR. Both 5-HT-IR and peptidergic terminals are localized outside the cellular perineurium beneath the acellular permeable sheath adjacent to the haemocoel. Hence, we propose that various bioactive substances may be released from thoracic neurosecretory neurons into the circulating haemolymph to act on peripheral targets. The same neurons may also interact by synaptic or modulatory action in the CNS in different neuropil regions of the thoracic ganglion.

Proctolin-like immunoreactive neurons in the blowfly central nervous system

The pentapeptide proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH) is a well-studied bioactive substance in insects. With an antiserum against proctolin we have mapped proctolinlike-immunoreactive (PLI) neurons in the nervous system of the blowfly Calliphora erythrocephala. In the brain, including the suboesophageal ganglia, 80-90 neurons were found to be PLI. A further 200-250 PLI neurons innervate the lobula of the optic lobe. The thoracic ganglia contain 100-130, and the abdominal ca. 60 PLI neurons. In the brain and ventral ganglia the immunoreactive neurons are of different types: interneurons, efferents (possibly some motorneurons), and neurosecretory cells. Some of these neurons are individually identifiable; others can be identified collectively as clusters. Identifiable neurons innervate protocerebral neuropil associated with the pars intercerebralis and the beta-lobes of the mushroom bodies as well as tritocerebral neuropil. Some of the prominent clusters innervate the central body of the protocerebrum, tritocerebrum, and possibly leg motor neurons. One abdominal cluster is of special interest because it consist of efferent neurons with processes in the lateral abdominal nerves. Some of these processes are located in the neural sheath in neurohaemal regions, and electron microscopy demonstrates that their terminals are outside the blood-brain barrier. The PLI processes in the protocerebrum contain large granular vesicles and form chemical synapses with different kinds of nonimmunoreactive neural elements. Thus, in Calliphora the proctolinlike substance may be used as a central transmitter/modulator, a neuromuscular transmitter, and a neurohormone released into the circulation.

Proctolin degradation by membrane peptidases from nervous tissues of the desert locust (Schistocerca gregaria)

The hydrolysis of the insect neuropeptide proctolin (Arg-Tyr-Leu-Pro-Thr) by enzyme preparations from the nervous tissue of the desert locust (Schistocerca gregaria) was investigated. Neural homogenate degraded proctolin (100 microM) at neutral pH by cleavage of the Arg-Tyr and Tyr-Leu bonds to yield Tyr-Leu-Pro-Thr, Arg-Tyr and free tyrosine. Arg-Tyr was detected as a major metabolite when the aminopeptidase inhibitors amastatin and bestatin were present to prevent Arg-Tyr breakdown. Around 50% of the proctolin-degrading activity was isolated in a 30,000 g membrane fraction and was shown to be almost entirely due to aminopeptidase activity. The aminopeptidase had an apparent Km of 23 microM, a pH optimum of 7.0 and was inhibited by 1 mM-EDTA and amastatin [IC50 = 0.3 microM], but was relatively insensitive to bestatin, actinonin and puromycin. Phenylmethanesulphonyl fluoride (1 mM) and p-chloromercuriphenylsulphonic acid (1 mM) had no effect on this enzyme activity. Although the bulk of the Tyr-Leu hydrolytic activity was located in the 30,000 g supernatant, some weak activity was detected in a washed membrane preparation. This peptidase displayed a high affinity for proctolin (Km = 0.35 microM) and optimal activity at around pH 7.0. Synaptosome- and mitochondria-rich fractions were prepared from crude neural membranes. The aminopeptidase activity was concentrated in the synaptic-membrane preparation, whereas activity giving rise to Arg-Tyr was predominantly localized in the mitochondrial fraction. The subcellular localization of the membrane aminopeptidase is consistent with a possible physiological role for this enzyme in the inactivation of synaptically released proctolin.

Immunocytochemical identification and localization of peptide hormones in the gastro-entero-pancreatic (GEP) endocrine system of the mouse and a stomachless fish, Barbus conchonius

A large number of antisera mainly raised against mammalian hormones are tested immunocytochemically on the GEP-endocrine system of mouse and fish (Barbus conchonius). The endocrine pancreas of mouse and fish appeared to contain the same four endocrine cell types; insulin-, glucagon-, PP- and somatostatin-immunoreactive cells. In mouse about 13 GEP endocrine cell types are distinguished: 1. insulin-, 2. somatostatin-, 3. glucagon-, 4. PP-, 5. (entero)glucagon-/PP-like, 6. CCK-like, 7. substance P-, 8. neurotensin-, 9. VIP-, 10. gastrin-, 11. secretin-, 12. beta-endorphin-, 13. serotonin-immunoreactive cells. Based on this and a previous study at least 13 GEP endocrine cell types seems to be present in stomachless fish: 1-9 as described for mouse, 10. (entero)glucagon-like, 11. met-enkephalin, 12. VIP-like, 13. unspecific immunoreactive endocrine cells. Coexistence of glucagon and PP-like peptides is found in the gut and pancreas of mice and in the gut of B. conchonius. In mouse pancreas and fish gut, endocrine cells showing only PP- or glucagon-like immunoreactivity are found too. In mouse stomach some endocrine cells showing only PP-immunoreactivity are demonstrated. In the same region coexistence of C-t-gastrin- and FMRF-amide-immunoreactivity is found in endocrine cells. The importance of these phenomena are discussed. Enteric nerves immunoreactive with antisera raised against substance P and GRP are found in mouse, against somatostatin and met-enkephalin in both mouse and fish and against VIP in fish.

Modulatory action and distribution of the neuropeptide proctolin in the crustacean stomatogastric nervous system

Immunocytochemical methods were used to map the distribution of proctolinlike immunoreactivity in the stomatogastric nervous systems (stomatogastric ganglion (STG), paired commissural ganglia (CG), oesophageal ganglion (OG), and connecting nerves) of three crustacean species: Panulirus interruptus, Cancer borealis, and Homarus americanus. Although the patterns of proctolinlike staining were similar among the three species, some differences were also observed. Over 70% of the proctolinlike material in STGs, as measured by radioimmunoassay, was indistinguishable from authentic proctolin in reverse-phase high-performance liquid chromatography. Bath application of proctolin to STGs from Cancer and Panulirus induced characteristic and robust (though somewhat different) changes in their motor patterns. The threshold concentration was approximately 10(-9)M proctolin, and the effects were dose-dependent. These data suggest that the neuropeptide proctolin serves as a neuromodulator of the stomatogastric ganglion.

Mapping of proctolinlike immunoreactivity in the nervous systems of lobster and crayfish

Whole-mount immunocytochemical techniques have been used to map candidate proctolin-containing cells in the central nervous systems of the lobster, Homarus americanus, and the crayfish, Procambarus clarkii. Proctolinlike immunoreactivity was detected in cell bodies and neuropil regions in all central ganglia, and immunoreactive axons were detected in most interganglionic connectives and nerve roots. Cell body staining was confined to fewer than 2% of all cells. Immunoreactive neurons include motoneurons, sensory neurons, neurosecretory cells, and interneurons. Colocalization of the proctolinlike antigen with other neurotransmitters was indicated in a number of cases. Many aspects of the distribution of immunoreactivity were similar in lobster and crayfish; however, staining differences were detected in a number of identified neurons and neural groups, including neurons that innervate the pericardial organs and hindgut motoneurons. Further studies of such neurons might provide interesting clues about the physiological functions of proctolin and the evolution of peptide transmission.

Peptidergic innervation of insect skeletal muscle: immunochemical observations

Proctolin (Arg-Tyr-Leu-Pro-Thr) is a pentapeptide present in the hindgut or proctodeum of the cockroach Periplaneta americana where it may be a transmitter. Its widespread distribution among peripherally projecting neurons in the CNS (Bishop and O'Shea, '82) suggested that proctolin's motor function is not restricted to the hindgut, but has a variety of peripheral targets. This idea was further supported when proctolin was localized to an identified skeletal motoneuron, the slow coxal depressor, where it acts as a cotransmitter (O'Shea and Bishop, '82; Adams and O'Shea, '83). Our objective was to investigate the proctolinergic innervation of a variety of skeletal muscles of the cockroach Periplaneta americana. We used immunohistochemical and radioimmunochemical methods to map the distribution of proctolin immunoreactivity. This survey revealed that a subpopulation of skeletal muscles are innervated by proctolinergic motoneurons. The anatomical features of the peptidergic innervation and the levels of proctolinlike immunoreactivity of one muscle group, the coxal depressor system, are here described in detail. The source of the proctolin innervation to the metathoracic coxal depressor group is identified as the slow coxal depressor motoneuron. The results of a survey of fast and slow skeletal muscles revealed that proctolin is associated with slow motor function. The functional implications of the association of a peptide with motoneurons are discussed in relationship to the organization of the insect motor pool.

Modulatory effects of proctolin on a crab ventilatory muscle

Proctolin enhances nerve-evoked, phasic contractions of a selected respiratory muscle of the shore crab, Carcinus maenas, but has no effect on muscle tonus. Proctolin also increases the work and power output of this muscle. These effects are functionally appropriate in view of previous reports that proctolin stimulates the ventilatory rhythm. They also suggest that proctolin exerts coordinated modulatory control at the central and peripheral levels of the gill ventilatory system. In contrast, serotonin, dopamine and octopamine have no effect on this muscle.

The distribution of bovine pancreatic polypeptide/FMRFamide-like immunoreactivity in the ventral nervous system of the locust

The distribution of bovine pancreatic polypeptide (BPP) FMRFamide-like immunoreactivity is described in the ganglia of the ventral nerve cord and in the peripheral median nervous system of the locust, Schistocerca gregaria. Immunoreactive cell bodies occur in three regions of the thoracic ganglia: 1) two pairs of cells lie in the anterior of the ganglion ventral to the root of nerve 1 and the anterior ventral association centre; 2) a group of cells lies in the ventral midline at the level at which nerves 3 and 4 leave the ganglion; 3) and two bilaterally symmetrical, posterior lateral groups lie between nerves 5 and 6 at the edge of the ganglion. Immunoreactive cell bodies in the suboesophageal and abdominal ganglia are confined to the midline and are distributed along the anterior-posterior axis both dorsally and ventrally. The processes of the posterior lateral groups have been traced into the neurohaemal organs of the median nerve and beyond. In the periphery such processes innervate the salivary glands and various muscles. The nature of the endogenous antigen contained in the immunoreactive cells has been investigated with the use of antisera against other peptides of the pancreatic polypeptide family, namely avian pancreatic polypeptide, neuropeptide Y, and peptide YY. In addition, BPP antisera not specific for the C terminal hexapeptide have been tested. Liquid preabsorption experiments with BPP and FMRFamide (the molluscan cardioacceleratory peptide) suggest that the endogenous peptide antigen contained in the stained neurones may belong to the pancreatic polypeptide family or to the FMRFamide family.

Evidence for proctolin-like substances in the central nervous system of the leech Hirudo medicinalis

The distribution of proctolin-like immunoreactive (PLI) cells was mapped in the central nervous system of the leech Hirudo medicinalis. In segmental ganglia, PLI cells can be divided into two groups: cells that stain repeatedly in every successive ganglion, and cells that stain only in specific segmental ganglia. The number of PLI cells, therefore, ranged from eight to 20 cells per ganglion. One bilateral pair of PLI cells (cells PLI-1) was further characterized morphologically by Lucifer yellow and horseradish peroxidase cell injections. Cell PLI-1 conforms in soma position, morphology, and physiological properties with cell 101, which has been previously classified as an inhibitory motoneuron to the flattener muscles. A locust bioassay (O'Shea and Adams, Science 213:567-569, 1981) was used to detect the presence of proctolin-like bioactivity. Extracts of leech ganglia when applied to the extensor tibialis muscle of the locust leg induced a proctolin-like response similar to the responses induced by proctolin standards. This work extends the finding of proctolin-like substances to the annelid phylum.

Anatomy and electrophysiology of individual neurosecretory cells of an insect brain

The structure and electrophysiological properties of individual neurosecretory cells of the pars intercerebralis, medial neurosecretory cells (MNSCs), in the brain of an insect, the cricket Teleogryllus commodus, were investigated by means of intracellular injections of the dye Lucifer Yellow and electrophysiological recordings. Action potentials recorded from these cells were of long duration, 8-50 msec. In the pars intercerebralis there are both neurosecretory cells with axons that join one of the tracts of the nervi corpori cardiaci I (NCC I) and cells without an axon or collateral that leaves the brain, local neurosecretory cells. MNSCs with axons that join NCC I and terminate in the anterior corpus cardiacum arborize extensively in the protocerebrum and to a lesser degree in the deutocerebrum. Other MNSCs have axons that pass through the corpus cardiacum and hypocerebral ganglion and join one of the oesophageal nerves. These MNSCs have sparse collateral arborizations in the protocerebrum but do have extensive terminal arborizations in the tritocerebrum. This type of cell is dye-coupled to other MNSCs. Among the local MNSCs, some have an unusual loop shape. These cells branch extensively in the protocerebrum and have massive terminal arborizations in a posterior ventromedial region of the brain. Both the long curved axons of the loop-shaped cells and their ventromedial branches are of large diameter, suitable for storage of neurosecretory material.

Neuropeptide proctolin (H-Arg-Try-Leu-Pro-Thr-OH): immunocytochemical mapping of neurons in the central nervous system of the cockroach

Proctolinlike immunoreactivity was mapped in the central nervous system of the cockroach, Periplaneta americana, by using whole-ganglion immunoreacted preparations. The procedure for this immunohistochemical staining of whole-mounts is described. Immunoreactivity was confined to neuronal cell bodies and and processes. These were found in all ganglia of the CNS. The cells varied in the consistency and intensity of their staining. The occurrence and variability of staining is described in detail. Cell bodies were found in the dorsal, ventral, and lateral regions of the ganglia. The highest number of cell bodies was found in the terminal ganglion and the lowest number in the cerebral ganglion. Those in the cerebral ganglion occurred mainly in the tritocerebral lobes. The distribution of immunoreactive cell bodies correlated with results previously obtained by radioimmunoassay. Immunoreactive processes were detected in all interganglionic connectives and many ganglionic nerve roots. Dense ramifications of immunoreactive processes and variocosities were detected in many of the ganglia. The widespread presence of immunoreactivity suggests that proctolin has diverse central and peripheral functions. The mapping immunoreactive neuronal somata provides a valuable step in the identification of putative proctolin-containing neurons suitable for further biochemical, anatomical, and physiological analysis.