Characterization of cardiac innervation in the nudibranch, Archidoris montereyensis

The heart of the nudibranch mollusc Archidoris montereyensis is regulated by a small number of powerful effector neurons located in the right pleural and visceral ganglia. Two identifiable neurons in the pleural ganglion, a heart excitor (PlHE) and a heart inhibitor (PlHI), are especially important regulators of cardiac function in that low levels of spontaneous activity in either cell significantly alters the amplitude and rate of heart contractions. These neurons have extensive dendritic arbors within the right pleural ganglion and branching axonal processes within the visceral ganglion. The visceral ganglion also contains a heart excitor neuron (VHE) and at least two heart inhibitor neurons (VHI cells), but their influence on cardiac activity is weaker than that of the pleural ganglion cells. All of these heart effector cells appear to be motor neurons with axons that terminate predominantly in the atrio-ventricular valve region of the heart via the pericardial nerve. The simplicity and strength of these neuronal connections to the heart of Archidoris make this a favorable preparation for studies of cardiac regulation.     

The whole-body shortening reflex of the medicinal leech: motor pattern,sensory basis,and interneuronal pathways

The leech whole-body shortening reflex consists of a rapid contraction of the body elicited by a mechanical stimulus to the anterior of the animal. We used a variety of reduced preparations — semi-intact, body wall, and isolated nerve cord — to begin to elucidate the neural basis of this reflex in the medicinal leech Hirudo medicinalis. The motor pattern of the reflex involved an activation of excitatory motor neurons innervating dorsal and ventral longitudinal muscles (dorsal excitors and ventral excitors respectively), as well as the L cell, a motor neuron innervating both dorsal and ventral longitudinal muscles. The sensory input for the reflex was provided primarily by the T (touch) and P (pressure) types of identified mechanosensory neuron. The S cell network, a set of electrically-coupled interneurons which makes up a fast conducting pathway in the leech nerve cord, was active during shortening and accounted for the shortest-latency excitation of the L cells. Other, parallel, interneuronal pathways contributed to shortening as well. The whole-body shortening reflex was shown to be distinct from the previously described local shortening behavior of the leech in its sensory threshold, motor pattern, and (at least partially) in its interneuronal basis.Abbreviations conn connective - DE dorsal excitor motor neuron - DI dorsal inhibitor motor neuron - DP dorsal posterior nerve - DP:B1 dorsal posterior nerve branch 1 - DP:B2 dorsal posterior nerve branch 2 - MG midbody ganglion - VE ventral excitor motor neuron - VI ventral inhibitor motor neuron     

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.     

Excitatory neural control of posterograde heartbeat by the frontal ganglion in the last instar larva of a lepidopteran, Bombyx mori

The frontal ganglion of the silkworm (Bombyx mori) gives rise to a visceral nerve, branches of which include a pair of anterior cardiac nerves and a pair of the posterior cardiac nerves. Forward-fill of the visceral nerve with dextran labeled with tetramethyl rhodamine shows the anterior cardiac nerves innervate the anterior region of the dorsal vessel. Back-fill of the anterior cardiac nerves with Co²⁺ and Ni²⁺ ions and the fluorescent dye reveals that the cell bodies of two motor neurons are located in the frontal ganglion. Injection of 5, 6-carboxyfluorescein into the cell body of an identified motor neuron shows that the neuron gives rise to an axon running to the visceral nerve. Unitary excitatory junctional potentials (EJPs) were recorded from a myocardial cell at the anterior end of the heart. They responded in a one-to-one manner to electrical stimuli applied to the visceral nerve, or to impulses generated by a depolarizing current injected into the cell body. EJPs induced by stimuli at higher than 0.5 Hz showed facilitation while those induced at higher than 2 Hz showed summation. Individual EJPs without summation, or a train of EJPs with summation, caused acceleration in the phase of posterograde heartbeat and heart reversal from anterograde heartbeat to posterograde heartbeat. It is likely that the innervation of the anterior region of the dorsal vessel by the motor neurons, through the anterior cardiac nerves is responsible for the control of heartbeat in Lepidoptera, at least in part.     

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.     

Modulation of swimming behavior in the medicinal leech

Expression of swimming in the medicinal leech (Hirudo medicinalis) is modulated by serotonin, a naturally occurring neurohormone. Exogenous application of serotonin engenders spontaneous swimming activity in nerve-cord preparations. We examined whether this activity is due to enhanced participation of swim motor neurons (MNs) in generating the swimming rhythm. We found that depolarizing current injections into MNs during fictive swimming are more effective in shifting cycle phase in nerve cords following serotonin exposure. In such preparations, the dynamics of membrane potential excursions following current injection into neuronal somata are substantially altered. We observed: 1) a delayed outward rectification (relaxation) during depolarizing current injection, most marked in inhibitory MNs; and 2) in excitor MNs, an enhancement of postinhibitory rebound (PIR) and afterhyperpolarizing potentials (AHPs) following hyperpolarizing and depolarizing current pulses, respectively. In contrast, we found little alteration in MN properties in leech nerve cords depleted of amines. We propose that enhanced expression of swimming activity in leeches exposed to elevated serotonin is due, partly, to enhancement of relaxation, PIR and AHP in MNs. We believe that as a consequence of alterations in cellular properties and synaptic interactions (subsequent paper) by serotonin, MNs are reconfigured to more effectively participate in generating and expressing the leech swimming rhythm.Abbreviations AHP Afterhyperpolarizing potential - DCC Discontinuous current clamp - DE Dorsal excitor motor neuron - DI Dorsal inhibitor motor neuron - IPSP Inhibitory postsynaptic potential - MN Motor neuron - PIR Postinhibitory rebound - VE Ventral excitor motor neuron - VI Ventral inhibitor motor neuron     

Single neurone responses to tactile stimulation of the heart in the snail,Helix pomatia L.

Summary The electrical activity of the heart nerve and of single neurons in the suboesophageal ganglia were recorded during tactile stimulation of the heart. 15 neurons were identified which responded to heart stimulation by inhibiting or accelerating activity. Cells influenced by heart afferents are scattered in the visceral and in the right and left parietal ganglia.In most of the cases both decrease and increase of cell activity are caused by synaptic potentials, in some cases, however, the neuron is assumed to have a sensory character.The activity of three neurons influenced by heart stimulation was conducted into the heart nerve. These cells are central neurons of a heart-CNS-heart reflex.Some of the neurons located in the right parietal and visceral ganglia have no connection with the mechanoreceptors of the heart. Since their spikes propagate into the heart nerve, they probably take part in the extracardial regulation of heart activity.One of the neurons located in the visceral ganglion (cell V12) sends its axon into the heart nerve. The response of this neuron to heart stimulation was an increase in activity and an inhibition of the heart rate. This is an inhibitory neuron of the extracardial heart regulatory system.     

Localization of ovulation hormone-like neuropeptide in the central nervous system of the snail Lymnaea stagnalis by means of immunocytochemistry and in situ hybridization

Summary The caudo-dorsal cells (CDC) in the cerebral ganglia of the pond snail Lymnaea stagnalis synthesize the 36-amino acid ovulation hormone (CDCH). We have used immuno-cytochemistry and in situ hybridization to reveal the localization of neurons and axons containing CDCH-like material.A monoclonal antibody to a fragment of CDCH and a cDNA probe encoding CDCH reacted with the CDC-system, with specific cell groups in the cerebral and pleural ganglia, and with individually occurring neurons throughout the central nervous system. The cells in the pleural ganglia, which were found in about 50% of the preparations studied, are considered as ectopic CDC. They are morphologically similar to CDC in their somal dimensions and axonal organization. By means of immuno-electron microscopy it was shown that these neurons contain secretory vesicles that are similar to those of the CDC. The neurons of the bilateral groups occurring in the cerebral ganglia in addition to the CDC are smaller and more intensely stained than the CDC. Axons of these small neurons probably have varicosities located on the CDC axons in the neuropil of the cerebral ganglion, indicating synaptic contacts. Two major axon tracts could be followed from (or toward) the neuropil of the cerebral ganglion. One tract runs from the cerebral gangion via the pleural and parietal ganglia to the visceral ganglion, giving off branches to most nerves emanating from these ganglia. The other tract could be traced through the cerebro-pedal connective to the pedal ganglia. Only in the right pedal ganglion was extensive axonal branching observed. The nerves emanating from this ganglion contained many more immunoreactive axons than those from the left pedal ganglion. A polyclonal antibody raised against the synthetic fragment of CDCH stained, in addition to the neurons and axons revealed with the monoclonal antibody and the cDNA probe, three other major groups of neurons. Two are located in the cerebral ganglion, the other in the left pedal ganglion.The present findings suggest the presence of a system of neurons that contain CDCH or CDCH-like peptides. The role this system may play in the control of egg-laying and egg-laying behaviour is discussed.     

The morphology of suboesophageal ganglion cells innervating the nervus corporis cardiaci III of the locust

Summary The nervus corporis cardiaci III (NCC III) of the locust Locust migratoria was investigated with intracellular and extracellular cobalt staining techniques in order to elucidate the morphology of neurons within the suboesophageal ganglion, which send axons into this nerve. Six neurons have many features in common with the dorsal, unpaired, median (DUM) neurons of thoracic and abdominal ganglia. Three other cells have cell bodies contralateral to their axons (contralateral neuron 1–3; CN 1–3). Two of these neurons (CN2 and CN3) appear to degenerate after imaginal ecdysis. CN3 innervates pharyngeal dilator muscles via its anterior axon in the NCC III, and a neck muscle via an additional posterior axon within the intersegmental nerve between the suboesophageal and prothoracic ganglia. A large cell with a ventral posterior cell body is located close to the sagittal plane of the ganglion (ventral, posterior, median neuron; VPMN). Staining of the NCC III towards the periphery reveals that the branching pattern of this nerve is extremely variable. It innervates the retrocerebral glandular complex, the antennal heart and pharyngeal dilator muscles, and has a connection to the frontal ganglion.Abbreviations AH antennal heart - AN antennal nerves - AO aorta - AV antennal vessel - CA corpus allatum - CC corpus cardiacum - CN1, CN2, CN3 contralateral neuron 1–3 - DIT dorsal intermediate tract - DMT dorsal median tract - DUM dorsal, unpaired, median - FC frontal connective - FG frontal ganglion - HG hypocerebral ganglion - LDT lateral dorsal tract - LMN, LSN labral motor and sensory nerves - LN+FC common root of labral nerves and frontal connective - LO lateral ocellus - MDT median dorsal tract - MDVR ventral root of mandibular nerve - MVT median ventral tract - NCA I, II nervus corporis allati I, II - NCC I, II, III nervus corporis cardiaci I, III - NR nervus recurrens - NTD nervus tegumentarius dorsalis - N8 nerve 8 of SOG - OE oesophagus - OEN oesophageal nerve - PH pharynx - SOG suboesophageal ganglion - T tentorium - TVN tritocerebral ventral nerve - VLT ventral lateral tract - VIT ventral intermediate tract - VMT ventral median tract - VPMN ventral, posterior, median neuron - 1–7 peripheral nerves of the SOG - 36, 37, 40–45 pharyngeal dilator muscles     

The morphology,innervation and neural control of the anterior arterial system of Aplysia californica

Summary The morphology, innervation, and neural control of the anterior arterial system of Aplysia californica were investigated. Immunocytochemical and histochemical techniques generated positive reactions in the anterior arterial system for several neuroactive substances, including SCP_B, FMRFamide, R151 peptide, dopamine and serotonin. Three neurons were found to innervate the rostral portions of the anterior arterial tree. One is the identified peptidergic neuron R15 in the abdominal ganglion, and the other two are a pair of previously unidentified neurons, one in each pedal ganglion, named pedal arterial shorteners (P_AS)- The endogeneously bursting neuron R15 was found to innervate the proximal anterior aorta. It also innervates a branch of the distal anterior aorta, the left pedal-parapodial artery. Activity in R15 causes constriction of the left pedal-parapodial artery. This effect is presumed to direct hemolymph towards the genital groove and penis on the right side in vivo. This vasoconstrictor action of R15 is mimicked by the R151 peptide. The P_AS neuron pair causes longitudinal contraction of the rostral anterior aorta and the pedal-parapodial arteries. In vivo, the pair is active during behaviors involving head withdrawal and turning. By adjusting the length of the arteries during postural changes, the P_AS neurons may prevent disturbances in blood flow due to bending or kinking of the arterial walls.     

Termination of leech swimming activity by a previously identified swim trigger neuron

Cell Tr2 is a neuron in the subesophageal ganglion of the leech that can trigger swim episodes. In this report, we describe the ability of Tr2 to terminate ongoing swim episodes as well as to trigger swimming. Stimulation of Tr2 terminated ongoing swim episodes in nearly every preparation tested, while Tr2 stimulation triggered swim episodes in only a minority of the preparations. We suggest that the primary role of Tr2 is in the termination rather than the initiation of swimming activity.The swim trigger neuron Tr3 and a swim-gating neuron, cell 21, hyperpolarized during Tr2-induced swim termination. Another swim-gating neuron, cell 204 was sometimes slightly excited, but more often, hyperpolarized during Tr2-induced swim termination. In contrast to these cells, Tr2 stimulation excited another swim-gating neuron, cell 61. The responses of the swimgating cells were variable in amplitude and sometimes not evident during Tr2-induced swim termination. Hence, the effects of Tr2 stimulation on swim-gating neurons seem unlikely to be the direct cause of swim termination.Oscillator cells examined during Tr2-induced swim termination include: 27, 28, 33, 60, 115, and 208. The largest effect seen in an oscillator neuron was in cell 208, which was repolarized by up to 10 mV during Tr2 stimulation. Tr2 stimulation did not produce any obvious synaptic effects in motor neurons DI-1, VI-1, and DE-3. Our findings indicate that other, yet undiscovered, connections are likely to be important in Tr2-induced swim termination. Therefore, we propose that cell Tr2 is probably a member of a distributed neural network involved in swim termination.Abbreviations DP dorsal posterior nerve - Mx midbody ganglion x - Rx neuromere x of the subsesophageal (rostral) ganglion - DE dorsal excitatory motor neuron - DI dorsal inhibitory motor neuron - VI ventral inhibitory motor neuron     

Acceleratory nervous regulation of juvenile myogenic hearts in the isopod crustacean Ligia exotica

We examined regulation of the myogenic heart by two identified cardioacceleratory neurons (CA1, CA2) in early juveniles of the isopod Ligia exotica. Repetitive stimulation of either the CA1 or CA2 axon increased the frequency and plateau amplitude of the action potential and decreased the maximum hyperpolarization of the cardiac muscle. These effects were larger with increasing stimulus frequency. The rate of increase in the frequency caused by CA1 stimulation was significantly larger than that by CA2. No impulse activity of the cardiac ganglion was induced by acceleratory nerve stimulation. The frequency of the muscle activity was decreased by injection of a hyperpolarizing current into the muscle during stimulation of the acceleratory nerve. In a quiescent heart, acceleratory nerve stimulation caused an overall depolarization in the muscle membrane and the amplitude of the depolarization induced by CA1 stimulation was significantly larger than that by CA2. These results suggest that CA1 and CA2 neurons regulate the myogenic heart affecting directly the cardiac muscle; the CA1 neuron produces more potent effects than does the CA2 neuron.     

Activity-dependent induction of facilitation,depression, and post-tetanic potentiation at an insect central synapse

Summary In Manduca sexta larvae, sensory neurons innervating planta hairs on the tips of the prolegs make monosynaptic excitatory connections with motoneurons innervating proleg retractor muscles. Tactile stimulation of the hairs evokes reflex retraction of the proleg. In this study we examined activity-dependent changes in the amplitude of the excitatory postsynaptic potentials (EPSPs) evoked in a proleg motoneuron by stimulation of individual planta hair sensory neurons. Deflection of a planta hair caused a phasic-tonic response in the sensory neuron, with a mean peak instantaneous firing frequency of >300 Hz, and a tonic firing rate of 10–20 Hz. Direct electrical stimulation was used to activate individual sensory neurons to fire at a range of frequencies including those observed during natural stimulation of the hair. At relatively low firing rates (e.g., 1 Hz), EPSP amplitude was stable indefinitely. At higher instantaneous firing frequencies (>10 Hz), EPSPs were initially facilitated, but continuous stimulation led rapidly to synaptic depression. High-frequency activation of a sensory neuron could also produce post-tetanic potentiation, in which EPSP amplitude remained elevated for several min following a stimulus train. Facilitation, depression, and post-tetanic potentiation all appeared to be presynaptic phenomena. These activity-dependent changes in sensory transmission may contribute to the behavioral plasticity of the proleg withdrawal reflex observed in intact insects.Abbreviations ACh acetylcholine - AChE acetylcholine esterase - CNS central nervous system - EPSP excitatory postsynaptic potential - I _h injected hyperpolarizing current - LTP long-term potentiation - PPR principal planta retractor motoneuron - PTP post-tetanic potentiation - R _in input resistance - V _h hyperpolarized potential - V _m membrane potential - VN ventral nerve - VNA anterior branch of the ventral nerve - V _r resting potential.     

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     

The innervation of the pyloric region of the crab,Cancer borealis: Homologous muscles in decapod species are differently innervated

Summary The muscles of the pyloric region of the stomach of the crab,Cancer borealis, are innervated by motorneurons found in the stomatogastric ganglion (STG). Electrophysiological recording and stimulating techniques were used to study the detailed pattern of innervation of the pyloric region muscles. Although there are two Pyloric Dilator (PD) motorneurons in lobsters, previous work reported four PD motorneurons in the crab STG (Dando et al. 1974; Hermann 1979a, b). We now find that only two of the crab PD neurons innervate muscles homologous to those innervated by the PD neurons in the lobster,Panulirus interrruptus. The remaining two PD neurons innervate muscles that are innervated by pyloric (PY) neurons inP. interruptus. The innervation patterns of the Lateral Pyloric (LP), Ventricular Dilator (VD), Inferior Cardiac (IC), and PY neurons were also determined and compared with those previously reported in lobsters. Responses of the muscles of the pyloric region to the neurotransmitters, acetylcholine (ACh) and glutamate, were determined by application of exogenous cholinergic agonists and glutamate. The effect of the cholinergic antagonist, curare, on the amplitude of the excitatory junctional potentials (EJPs) evoked by stimulation of the pyloric motor nerves was measured. These experiments suggest that the differences in innervation pattern of the pyloric muscles seen in crab and lobsters are also associated with a change in the neurotransmitter active on these muscles. Possible implications of these findings for phylogenetic relations of decapod crustaceans and for the evolution of neural circuits are discussed.Abbreviations ACh acetylcholine - Carb carbamylcholine - cpv muscles of the cardio-pyloric valve - cpv7n nerve innervating muscle cpv7 - cv muscles of the ventral cardiac ossicles - cv1n nerve innervating muscle cvl - cv2n nerve innervating muscle cv2 - EJP excitatory junctional potential - IC inferior cardiac neuron - IV inferior ventricular neuron - IVN inferior ventricular nerve - LP lateral pyloric neuron - LPG lateral posterior gastric neuron - lvn lateral ventricular nerve - mvn medial ventricular nerve - p muscles of the pylorus - PD pyloric dilator neuron - PD _in intrinsic PD neuron - PD _ex extrinsic PD neuron - pdn pyloric dilator nerve - PY pyloric neuron - pyn pyloric nerve - STG stomatogastric ganglion - VD ventricular dilator neuron     

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     

Multimodal distribution and discontinuous variation in period of interacting oscillators in the crustacean stomatogastric nervous system

Summary In the stomatogastric ganglion (STG) of Homarus gammarus, pacemaker neurons of the pyloric central pattern generator are entrained by a network oscillator (CPO) contained in the commissural ganglion. A consequence of CPO's influence is that the spontaneous pyloric period can take one of several absolute values, most commonly displaying a bimodal distribution. These discrete values correspond to different coordination modes with the CPO rhythm. Moreover, the oscillation period of pyloric pacemaker neurons varies discontinuously with their membrane potential. This behavior persists when the mean pyloric period is modified by different perfusion salines but disappears when the STG is disconnected from the anterior ganglia. Under these conditions, pyloric pacemaker neurons are deprived of CPO inputs and behave like independent oscillators whose period varies continuously as a function of the membrane potential. The modulatory pyloric suppressor neurons (PS), which are known to decrease the oscillatory capabilities of the pyloric pacemakers, can change the coordination mode between these neurons and the CPO. PS can provoke discontinuous variations in the pyloric period as a function of their firing frequency. Finally, the nonlinear behavior of the pyloric pattern generator described in Homarus also occurs in Jasus lalandii, in which the existence of a CPO has not yet been demonstrated.Abbreviations AB anterior burster neuron - ASW artificial seawater - COG commissural ganglion - CP commissural pyloric neuron - CPG central pattern generator - CPO commissural pyloric oscillator - IC inferior cardiac neuron - ivn inferior ventricular nerve - LP lateral pyloric neuron - OG esophageal ganglion - PD pyloric dilator neuron - PDn pyloric dilator nerve - PS pyloric suppressor neuron - son superior esophageal nerve - PY pylonic neuron - STG stomatogastric ganglion - stn stomatogastric nerve - vlvn ventral branch of the lateral ventricular nerve Maître de conférence à l'U.E.R. de Médecine et de Pharmacie, 2 rue Dr Marcland, 87025 Limoges Cedex, France.     

Morphological and electrophysiological aspects of dorsal median paired neurons generating plateau action potentials in the terminal abdominal ganglion of the insect central nervous system

Among the three clusters of dorsal unpaired median neurons of the Periplaneta americana terminal abdominal ganglion, another type of neuron has been characterized by anterograde cobalt stainings and microelectrode technique. These neurons are bilaterally distributed in the ganglion. Their axons ipsilaterally exit the ganglion via the anterior proctodeal nerves, to innervate the proctodeum. They are characterized by a long-duration overshooting action potentials and a low firing frequency. Most often the depolarizing phase is composed of two peaks: a fast spike followed by a slow phase. Tetrodotoxin suppressed the fast peak and blocked the spontaneous activity suggesting that sodium channels are involved in the depolarizing phase as well as in the initiation of the action potential. Calcium channel blockers induced a disappearing of the slow depolarizing phase indicating the participation of calcium ions and a reduction of the afterhyperpolarization reflecting the participation of calcium-activated potassium channels. Furthermore, cadmium, as lanthanum or barium, induced a long-lasting plateau potential, which would be due to a persistent sodium conductance. Tetraethylammonium increased the duration of the action potential indicating that potassium channels are implicated in the falling phase. The results demonstrate that these neurons are different from other cells, especially dorsal unpaired median neurons, of the central nervous system of the cockroach.Abbreviations DUM dorsal unpaired median - SDP slow depolarizing phase - AP action potential - PAP plateau action potential - TAG terminal abdominal ganglion - CNS central nervous system     

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