Neuropeptides regulate the cardiac activity of a prosobranch mollusc,Rapana thomasiana

Summary Involvement of neuropeptides in the regulation of cardiac activity in a prosobranch mollusc, Rapana thomasiana, was studied physiologically as well as immunohistochemically. A catch-relaxing peptide (CARP) showed strong inhibitory effects on the heart with a lower threshold than acetylcholine. The action of CARP was in contrast to that of another neuropeptide, FMRFamide, which has previously been shown to enhance the heart beat. Benzoquinonium blocked the effects of acetylcholine and stimulation of right cardiac nerves 1 and 3b, but not those of CARP, suggesting that the effects of nerve stimulation are mainly due to the release of acetylcholine. Immunohistochemical examinations demonstrated that FMRFamide-like and CARP-like immunoreactive neurons are distributed in the visceral ganglia. Although a neuron appeared to show weak immunoreactivity to both antisera, evidence for the coexistence of peptides in a single neuron was not exhibited. Positive immunoreactivity to FMRFamide and CARP antisera also appeared in right cardiac nerves 1 and 3. In the heart, FMRFamide- and CARP-like immunoreactive fibers were restricted to the atrium and the aortic end of the ventricle, consistent with the morphological observation of innervation. The present results suggest that FMRFamide- and CARP-like peptides are involved in regulating the heart beat.     

The molluscan neurosecretory peptide FMRFamide: comparative pharmacology and relationship to the enkephalins

The molluscan neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH2) has diverse actions on excitable tissues of molluscs, including hearts, noncardiac muscles, complex organs, and neurons. The intracellular transducing mechanisms are also diverse and are not readily correlated with particular responses. FMRFamide increases cyclic AMP levels concomitant with both cardioexcitation and inhibition, but not with muscle contraction. In the same tissues, the effects of 5-hydroxytryptamine are dissimilar and are always accompanied by a cyclic AMP increase. FMRFamide and acetylcholine cause similar tonic contractions of the Busycon radula protractor muscle and identical catch contractures of the mytilid anterior byssus retractor muscle, but the ionic basis of excitation and the sources of activator calcium for contraction are not the same for the two agonists. A comparative study of structure-activity relations showed that FMRFamide receptors are heterogeneous. Helix aspersa ganglia contain no FMRFamide, but a close analog occurs and has been tentatively identified. Evidence supporting a proposed homology between FMRFamide-like and opioid peptides is summarized. The effects of the amphiactive heptapeptide Tyr-Gly-Gly-Phe-Met-Arg-Phe-NH2 on the venus clam rectum support this hypothesis.     

Localization of FMRFamide- and ACEP-1-like immunoreactivities in the nervous system and heart of a pulmonate mollusc,Achatina fulica

Immunohistochemical localization of two neuropeptides possibly involved in the regulation of cardiac activity in a pulmonate mollusc, Achatina fulica Férussac, was studied. On the ventral surface of the right cerebral ganglion, more than 50 neurons with diameters of 30–50 m showed immunoreactivity to the antiserum of the neuropeptide FMRFamide. Many were also immunoreactive to an antiserum raised against Achatina cardio-excitatory peptide-1 (ACEP-1). Although FMRFamidelike immunoreactive neurons occurred in all components of the subesophageal ganglia, identifiable ACEP-1-like immunoreactive neurons were located only in the visceral ganglion and the right parietal ganglion. In the heart, FMRFamide- and ACEP-1-like immunoreactive fibers were restricted to the atrium and the aortic end of the ventricle, consistent with morphological observations of cardiac innervation. The present results suggest that FMRFamide-and ACEP-1-like peptides are involved in regulating the heart beat of this snail.     

Distribution of catch-relaxing peptide (CARP)-like immunoreactive neurons in the central and peripheral nervous system of Helix pomatia

Immunocytochemistry was performed on the nervous system of Helix by the use of an antibody raised against a myotropic neuropeptide, the catch-relaxing peptide (CARP), isolated from Mytilus edulis. In each ganglion of the central nervous system of Helix pomatia, numerous CARP-immunoreactive cell bodies and a dense immunoreactive fiber system could be observed with a dominancy in the cerebral and pedal ganglia. The majority of the immunoreactive neurons are unipolar, although multipolar neurons also occur. In the neuropil areas, CARP-immunoreactive fibers show extensive arborization, which may indicate a central role of CARP. CARP-immunoreactive elements could be observed in each investigated peripheral nerve and peripheral areas, namely in the intestine, heart, aorta, buccal mass, lips, and foot. However, CARP-immunoreactive cell bodies could only be demonstrated in the intestine and the foot musculature. Thin varicose CARP-immunoreactive fibers were observed over both muscle and gland cells in the different peripheral organs, suggesting a peripheral role of CARP. In vivo CARP injection into the body cavity (10^-3, 10^-4, 10^-5 M) altered the general behavioral state of the animals and induced the relaxation of the musculature of the whole body wall indicating that CARP has a significant role in the regulation of muscle contraction.     

Multilevel inhibition of feeding by a peptidergic pleural interneuron in the mollusc<Emphasis Type="Italic"> Lymnaea stagnalis</Emphasis>

The pleural interneuron PlB is a white neuron in the pleural ganglion of the snail Lymnaea. We test the hypothesis that it inhibits neurons at all levels of the feeding system, using a combination of anatomy, physiology and pharmacology. There is just one PlB in each pleural ganglion. Its axon traverses the pedal and cerebral ganglia, running into the buccal ganglia. It has neuropilar branches in the regions of the cerebral and buccal ganglia where neurons that are active during feeding also branch. Activation of the PlB blocks fictive feeding, whether the feeding rhythm occurs spontaneously or is driven by a modulatory interneuron. The PlB inhibits all the neurons in the feeding network, including protraction and retraction motoneurons, central pattern generator interneurons, buccal modulatory interneurons (SO, OC), and cerebral modulatory interneurons (CV1, CGC). Only the CV1 interneuron shows discrete 1:1 IPSPs; all other effects are slow, smooth hyperpolarizations. All connections persist in Ca²⁺/Mg²⁺-rich saline, which reduces polysynaptic effects. The inhibitory effects are mimicked by 0.5 to 100 mol l^–1 FMRFamide, which the PlB soma contains. We conclude that the PlB inhibits neurons in the feeding system at all levels, probably acting though the peptide transmitter FMRFamide.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00359-004-0503-x     

Small cardioactive peptide-like immunoreactivity and its colocalization with FMRFamide-like immunoreactivity in the central nervous system of the leech Hirudo medicinalis

Summary The distributions of small cardioactive peptide (SCP)- and FMRFamide-like immunoreactivities in the central nervous system of the medicinal leech Hirudo medicinalis were studied. A subset of neurons in the segmental ganglia and brains was immunoreactive to an antibody directed against SCP_B. Immunoreactive cell bodies were regionally distributed throughout the nerve cord, and occurred both as bilaterally paired and unpaired neurons. The majority of the unpaired cells displayed a tendency to alternate from side to side in adjacent ganglia. A small number of neurons were immunoreactive only in a minority of nerve cords investigated. Intracellular injections of Lucifer yellow dye and subsequent processing for immunocytochemistry revealed SCP-like immunoreactivity in heart modulatory neurons but not in heart motor neurons. FMRFamide-like immunoreactivity was also detected in cell bodies throughout the central nervous system. A subset of neurons contained both SCP- and FMRFamide-like immunoreactivities; others stained for only one or the other antigen. These data suggest that an antigen distinct from FMRFamide is responsible for at least part of the SCP-like immunoreactivity. This antigen likely bears some homology to the carboxyl terminal of SCP_A and SCP_B.     

Detection of FMRFamide-like immunoreactivities in the sea scallopPlacopecten magellanicus by immunohistochemistry and Western blot analysis

FMRFamide-like immunoreactivity was detected histochemically in the sea scallopPlacopecten magellanicus. Most immunoreactivity was concentrated in the cerebral, pedal, and parietovisceral ganglia, particularly in the cortical cell bodies and in their fibers which extend into the central neuropile. Whole-mount immunofluorescence studies were used to localize concentrations of immunoreactive cells on the dorsal and ventral surfaces of each ganglion. Immunoreactivity was also detected in nerves emanating from the ganglia. Strong immunoreactivity was localized in peripheral organs, including the gut and gills of juvenile and adult scallops. Weak immunoreactivity was detected in the gonads, heart, and adductor muscle of the adults. A broad FMRFamide-like immunoreactive band of 2.5–8.2 kDa was detected by Western blotting of acetone extracts of the parietovisceral ganglia. In the presence of protease inhibitors, two FMRFamide-like immunoreactive bands (7.2–8.2 kDa and >17 kDa) were obtained. Neither of these bands comigrated with the FMRFamide standard. It is concluded that peptides of the FMRFamide family are probably regulators of numerous central and peripheral functions inP. magellanicus.     

Neuroanatomical,immunocytochemical, and physiological studies of the pharyngeal retractor muscle and its putative regulatory neurons playing a role in withdrawal and feeding in the snail, <Emphasis Type="Italic">Helix pomatia</Emphasis>

We describe the neurons regulating two separate functions of the pharyngeal retractor muscle (PRM), namely sustained contraction during body withdrawal and rhythmic phasic contractions during feeding, in the snail, Helix pomatia. The distribution of central neurons innervating the PRM is organized into two main units; one in the buccal-cerebral ganglion complex, the other in the subesophageal ganglion complex. Serotonin- (5-HT-), FMRFamide- (FMRFa-), and tyrosine-hydroxylase-immunostained neurons are present among the PRM neurons that densely innervate the PRM. 5HT both decreases and increases the amplitude of the electrically evoked contraction between concentrations of 0.1 M and 1 M. Dopamine (DA) only decreases the amplitude of contraction at a 1-M threshold concentration. In contrast, FMRFa increases the amplitude of the contraction and slightly elevates the tone of the PRM but requires a higher threshold (10 M). Assay by high-performance liquid chromatography of 5HT and DA in the PRM has shown that the 5HT level decreases during locomotion but increases during feeding, whereas the DA level increases during locomotion but slightly decreases during feeding. Thus, different segments of the PRM are innervated by neurons from different loci within the central nervous system. The segments of the PRM distal to the pharynx are innervated from loci of the subesophageal ganglion complex suggesting that they mediate withdrawal. The proximal segment of the PRM is innervated from cerebral and buccal loci indicating that these neurons mediate the feeding rhythm produced by buccal and cerebral feeding central pattern generators to induce rhythmic phasic contractions in the PRM during feeding.This work was supported by Hungarian Scientific Research Fund (OTKA) grants (T034106, T037389, T037505), the Wellcome Trust CRIG Programme, and the Wellcome Trust Travel Grant.     

Presence and distribution of immunoreactive and bioactive FMRFamide-like peptides in the nervous system of the horseshoe crab, Limulus polyphemus

FMRFamide immunoreactivity was detected in all regions of the Limulus nervous system, including the brain (6.5 +/- 0.6 pg FMRFamide/mg), cardiac ganglion (2.06 +/- 0.67 pg FMRFamide/mg), and ventral nerve cord (5.8 +/- 0.7 pg FMRFamide/mg). The distribution of immunoreactive FMRFamide (irFMRFamide) was mapped by immunofluorescence and the distribution corresponded to regional RIA data. A good proportion of the CNS and cardiac ganglion neuropile contained irFMRFamide, and fluorescent cell bodies were observed in several areas. High performance liquid chromatography (HPLC) was employed to separate and characterize the FMRFamide-like peptides from extracts of Limulus brains. HPLC fractions were analyzed using coincidental radioimmunoassay and bioassay (the radula protractor muscle of Busycon contrarium). There appear to be at least three FMRFamide-like peptides in the Limulus brain, including one similar to clam FMRFamide. FMRFamide acts on Limulus heart in a biphasic manner at relatively high concentrations (10(-5)M), but has no effect on the activity of the isolated ventral nerve cord. These data suggest that in Limulus FMRFamide-like peptides are acting as neurotransmitters, or neuromodulators.     

Distribution of tyrosine-hydroxylase-immunoreactive and dopamine-immunoreactive neurons in the central nervous system of the snail Helix pomatia

The distribution and characterization of dopamine-containing neurons are described in the different ganglia of the central nervous system of Helix on the basis of the distribution of tyrosine hydroxylase immunoreactive (TH-ir) and dopamine immunoreactive (DA-ir) neurons. Both TH-ir and DA-ir cell bodies of small diameter (10–25 m) can be observed in the buccal, cerebral and pedal ganglia, dominantly on their ventral surface, and concentrated in small groups close to the origin of the peripheral nerves. The viscero-parietal-pleural ganglion complex is free of immunoreactive cell bodies but contains a dense fiber system. The largest number of TH-ir and DA-ir neurons can be detected in the pedal, and cerebral ganglia. The average number of TH-ir and DA-ir neurons significantly differs but all the identifiable groups of TH-ir neurons also show DA-immunoreactivity. Therefore, we consider the TH-ir neurons in those groups as being DA-containing neurons. The amounts of DA in the different ganglia assayed by high performance liquid chromatography correspond to the distribution and number of TH-ir and DA-ir neurons in the different ganglia. The axon processes of the labeled small-diameter neurons send thin proximal branches toward the cell body layer but only rarely surround cell bodics, whereas distally they give off numerous branches in the neuropil and then leave the ganglion through the peripheral nerves. In the cerebral ganglia, the analysis of the TH-ir pathways indicates that the largest groups of labeled neurons send their processes through the peripheral nerves in a topographic order. These results furnish morphological evidence that DA-containing neurons of Helix pomatia have both central and peripheral roles in neuronal regulation.     

Distribution of GABA-like immunoreactive neurons in the slug Limax maximus

Summary Immunohistochemical techniques were used to study the distribution of gamma-amino butyric acid (GABA)-like immunoreactive neurons in the nervous system of the slug Limax maximus. Approximately 170 GABA-like immunoreactive cell bodies were found in the central nervous system. These were located in the cerebral, buccal and pedal ganglia. Most GABA-like immunoreactive neurons had small cell bodies, which were aggregated into discrete clusters within the cerebral and pedal ganglia. Three pairs of longer, uniquely identifiable, GABA-like immunoreactive cells were found in the cerebral ganglion. GABA-like immunoreactive nerve fibres were also found in all of the central ganglia but were absent from peripheral nerves. These results suggest that GABA acts as a central neurotransmitter in the slug. The possible roles of GABA-ergic neurotransmission in the slug are discussed.     

Distribution and anatomy of GABA-like immunoreactive neurons in the central and peripheral nervous system of the snail Helix pomatia

Gamma-aminobutyric acid (GABA)-like immunoreactive neurons were studied in the central and peripheral nervous system of Helix pomatia by applying immunocytochemistry on whole-mount preparations and serial paraffin sections. GABA-immunoreactive cell bodies were found in the buccal, cerebral and pedal ganglia, but only GABA-immunoreactive fibers were found in the viscero-parietal-pleural ganglion complex. The majority of GABA-immunoreactive cell bodies were located in the pedal ganglia but a few could be found in the buccal ganglia. Varicose GABA-ir fibers could be seen in the neuropil areas and in distinct areas of the cell body layer of the ganglia. The majority of GABA-ir axonal processes run into the connectives and commissures of the ganglia, indicating an important central integrative role of GABA-immunoreactive neurons. GABA may also have a peripheral role, since GABA-immunoreactive fibers could be demonstrated in peripheral nerves and the lips. Glutamate injection did not change the number or distribution of GABA-immunoreactive neurons, but induced GABA immunoreactivity in elements of the connective tissue ensheathing the muscle cells and fibers of the buccal musculature. This shows that GABA may be present in different non-neural tissues as a product of general metabolic pathways.     

Fulicin, a novel neuropeptide containing a D-amino acid residue isolated from the ganglia of Achatina fulica

A novel pentapeptide containing a D-amino acid residue was purified from the central ganglia of the African giant snail Achatina fulica Ferussac, and it was named fulicin. The primary structure of the peptide was determined to be Phe-D-Asn-Glu-Phe-Val-NH2. Fulicin potentiated tetanic contraction of the penis retractor muscle of this snail at very low concentrations, and also showed modulatory actions on the activity of the buccal and ventricular muscles and the central ganglionic neurons.     

Ultrastructural immunocytochemical evidence for peptidergic neurotransmission in the pond snail Lymnaea stagnalis

Summary Three neuronal systems of the pond snail Lymnaea stagnalis were immunocytochemically investigated at the ultrastructural level with the unlabeled peroxidase-antiperoxidase technique. Preliminary electrophysiological and cell-filling investigations have shown that a cluster of neurons which reacts positively with an antiserum against the molluscan cardio-active peptide FMRFamide, sends axons to the penis retractor muscle. In this muscle anti-FMRF-amide (aFM) positive axons form neuro-muscular synapses with (smooth) muscle fibers. The morphological observations suggest the aFM immunoreactive system to be involved in peptidergic neurotransmission. In the right parietal ganglion a large neuron (LYAC) is penetrated by aFM positive axons which form synapse-like structures (SLS) with the LYAC. The assumption that the SLS represent the morphological basis for peptidergic transmission is sustained by the observation that iontophoretical application of synthetic FMRFamide depolarizes the LYAC. The axons of a group of pedal anti-vasopressin (aVP) positive cells run in close vicinity to the cerebral ovulation (neuro-)-hormone producing cell system (CDC system) Synapses or SLS between the two systems were not observed. The fact that (bath) application of arg-vasopressin induces bursting in the CDC, may indicate that the vasopressin-like substance of the aVP cells is released non-synaptically.     

Localisation of substance P-like immunoreactivity in the ciliary ganglia of monkey (Macaca fascicularis) and cat: a light- and electron-microscopic study

The present study describes substance P-like immunoreactivity in the ciliary ganglia of monkey (Macaca fascicularis) and cat. About 60% of neurons in the monkey ciliary ganglion and 40% in the cat ciliary ganglion were substance P-like immunoreactive, ranging from faint to moderate staining. Substance P-like immunoreactivity was located in cell bodies, dendritic profiles and axons. In the monkey, substance P-like immunoreactive pericellular arborisations were associated with about 0.5%–3% of the ganglion cells, which were either negatively, faintly or moderately stained. An electron-microscopic study demonstrated the presence of either substance P-like immunoreactive positive or negative axon terminals synapsing or closely associated with positive dendritic profiles in both the monkey and cat ciliary ganglia. The results suggest that substance P plays an important role in the ciliary ganglion, perhaps as a modulator or transmitter.     

Crustacean cardioactive peptide in the nervous system of the locust,Locusta migratoria: an immunocytochemical study on the ventral nerve cord and peripheral innervation

Summary Crustacean cardioactive peptide-immunoreactive neurons occur in the entire central nervous system of Locusta migratoria. The present paper focuses on mapping studies in the ventral nerve cord and on peripheral projection sites. Two types of contralaterally projecting neurons occur in all neuromers from the subesophageal to the seventh abdominal ganglia. One type forms terminals at the surface of the thoracic nerves 6 and 1, the distal perisympathetic organs, the lateral heart nerves, and on ventral and dorsal diaphragm muscles. Two large neurons in the anterior part and several neurons of a different type in the posterior part of the terminal ganglion project into the last tergal nerves. In the abdominal neuromers 1–7, two types of ipsilaterally projecting neurons occur, one of which gives rise to neurosecretory terminals in the distal perisympathetic organs, in peripheral areas of the transverse, stigmata and lateral heart nerves. Four subesophageal neurons have putative terminals in the neurilemma of the nervus corporis allati II, and in the corpora allata and cardiaca. In addition, several immunoreactive putative interneurons and other neurons were mapped in the ventral nerve cord. A new in situ whole-mount technique was essential for elucidation of the peripheral pathways and targets of the identified neurons, which suggest a role of the peptide in the control of heartbeat, abdominal ventilatory and visceral muscle activity.Abbreviations AG abdominal ganglia - AM alary muscle - AMN alary muscle nerve - CA corpus allatum - CC corpus cardiacum - dPSO distal perisympathetic organ - LHN lateral heart nerve - LT CCAP-immunoreactive lateral tract - NCA nervus corporis allati - NCC nervus corporis cardiaci - NM neuromer - PMN paramedian nerve - PSO perisympathetic organ - SOG subesophageal ganglion - VDM ventral diaphragm muscles - VNC ventral nerve cord     

Distribution of FMRFamide-like immunoreactivity in the brain and suboesophageal ganglion of the sphinx mothManduca sexta and colocalization with SCPB-, BPP-, and GABA-like immunoreactivity

Summary Using an antiserum against the tetrapeptide FMRFamide, we have studied the distribution of FMRFamide-like substances in the brain and suboesophageal ganglion of the sphinx mothManduca sexta. More than 2000 neurons per hemisphere exhibit FMRFamide-like immunoreactivity. Most of these cells reside within the optic lobe. Particular types of FMRFamide-immunoreactive neurons can be identified. Among these are neurosecretory cells, putatively centrifugal neurons of the optic lobe, local interneurons of the antennal lobe, mushroom-body Kenyon cells, and small-field neurons of the central complex. In the suboesophageal ganglion, groups of ventral midline neurons exhibit FMRFamide-like immunoreactivity. Some of these cells have axons in the maxillary nerves and apparently give rise to FMRFamide-immunoreactive terminals in the sheath of the suboesophageal ganglion and the maxillary nerves. In local interneurons of the antennal lobe and a particular group of protocerebral neurons, FMRFamide-like immunoreactivity is colocalized with GABA-like immunoreactivity. This suggests that FMRFamide-like peptides may be cotransmitters of these putatively GABAergic interneurons. All FMRFamide-immunoreactive neurons are, furthermore, immunoreactive with an antiserum against bovine pancreatic polypeptide, and the vast majority is also immunoreactive with an antibody against the molluscan small cardioactive peptide SCP_B. Therefore, it is possible that more than one peptide is localized within many FMRFamide-immunoreactive neurons. The results suggest that FMRFamide-related peptides are widespread within the nervous system ofM. sexta and might function as neurohormones and neurotransmitters in a variety of neuronal cell types.Abbreviations AL antennal lobe - BPPLI bovine pancreatic polypeptide-like immunoreactivity - FLI FMRFamide-like immunoreactivity - GLI GABA-like immunoreactivity - NSC neurosecretory cell - SCP _B LI small cardioactive peptide_B-like immunoreactivity - SLI serotonin-like immunoreactivity - SOG suboesophageal ganglion     

PBAN/pyrokinin peptides in the central nervous system of the fire ant, <Emphasis Type="Italic">Solenopsis invicta</Emphasis>

The pyrokinin/pheromone-biosynthesis-activating neuropeptide (PBAN) family of peptides found in insects is characterized by a 5-amino-acid C-terminal sequence, FXPRLamide. The pentapeptide is the active core required for diverse physiological functions, including the stimulation of pheromone biosynthesis in female moths, muscle contraction, induction of embryonic diapause, melanization, acceleration of puparium formation, and termination of pupal diapause. We have used immunocytochemical techniques to demonstrate the presence of pyrokinin/PBAN-like peptides in the central nervous system of the fire ant, Solenopsis invicta. Polyclonal antisera against the C-terminal end of PBAN have revealed the location of the peptide-producing cell bodies and axons in the central nervous system. Immunoreactive material is detectable in at least three groups of neurons in the subesophageal ganglion and corpora cardiaca of all adult sexual forms. The ventral nerve cord of adults consists of two segmented thoracic ganglia and four segmented abdominal ganglia. Two immunoreactive pairs of neurons are present in the thoracic ganglia, and three neuron pairs in each of the first three abdominal ganglia. The terminal abdominal ganglion has no immunoreactive neurons. PBAN immunoreactive material found in abdominal neurons appears to be projected to perisympathetic organs connected to the abdominal ganglia. These results indicate that the fire ant nervous system contains pyrokinin/PBAN-like peptides, and that these peptides are released into the hemolymph. In support of our immunocytochemical results, significant pheromonotropic activity is found in fire ant brain-subesophageal ganglion extracts from all adult fire ant forms (queens, female and male alates, and workers) when extracts are injected into decapitated females of Helicoverpa zea. This is the first demonstration of the presence of pyrokinin/PBAN-like peptides and pheromonotropic activity in an ant species. This research was supported in part by a US-Israel Binational Science Foundation Grant (no. 2003367).     

Morphology and electrophysiological properties of neurons projecting to the retrocerebral complex in the blow fly, <Emphasis Type="Italic">Protophormia terraenovae</Emphasis>

Morphological and electrical properties of neurons with somata in the pars intercerebralis (PI) and pars lateralis (PL) were examined by intracellular recording and staining in the adult blow fly, Protophormia terraenovae. According to the location of somata and fiber distribution, two types of PI neurons (PIa and PIb) and two types of PL neurons (PLa and PLb) were identified. PIb neurons were further divided into two subgroups of PIb₁ and PIb₂ depending on fiber branching patterns in the retrocerebral complex. PIa neurons projected axons to the contralateral nervi corporis cardiaci, whereas PLa and PLb neurons projected axons to the ipsilateral nervi corporis cardiaci. PIb neurons characteristically showed symmetrical morphology with their somata along the midline. PLb neurons had a large branching area in the subesophageal ganglion. In the retrocerebral complex, PIb₂ and PLa neurons sent fibers into the corpus allatum. PIa, PIb₁ and PLb neurons projected not to the corpus allatum but to the corpus cardiacum–hypocerebral complex or visceral muscles in their vicinity. PIa, PIb and PLa neurons showed long spike durations (3–10 ms). PLb neurons were immunoreactive with antisera against corazonin, FMRFamide, or -pigment-dispersing hormone. This is the first report revealing the morphology of individual neurons with somata residing in PI and PL in the adult fly.The authors acknowledge a research grant from the Naito Foundation, a Grant-in-Aid for Scientific Research C (13640686) from the Japan Society for the Promotion of Science, and a Grant-in-Aid for Young Scientists B (15770050) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan