Presence Of Proctolin Research Articles

Identification and localisation of selected myotropic neuropeptides in the ventral nerve cord of tenebrionid beetles

MALDI-TOF MS and MS/MS techniques were used for the isolation and identification of neuropeptides from the ventral nerve cord (VNC) of two beetle species Tenebrio molitor and Zophobas atratus. Two peptides, proctolin and myosuppressin (Zopat-MS), with well-established myotropic properties were identified as well as Trica-NVPL-4trunc. The presence of proctolin and myosuppressin was confirmed by immunocytochemical studies in adults and larvae of both beetles. In addition, the myosuppressin gene in Z. atratus was sequenced and expression analyses showed that it is present in all parts of the beetle central nervous system. Results suggest that the identified peptides act as neurotransmitters/neuromodulators in beetles, regulate visceral muscle contractions and indirectly influence important physiological processes such as feeding and reproduction.

Proctolin affects gut functions in lepidopteran larvae

AbstractWe examined if the pentapeptide proctolin, a well‐investigated myotropic neutrotrasmitter/neuromodulator for which a possible role in insect control has been suggested, affected the gastrointestinal function in lepidopteran larvae. We verified in the model species Bombyx mori (Lepidoptera, Bombicidae) if the visceral muscles of the larval gut expressed receptors for the peptide, by monitoring the spontaneous contractions of the hindgut in the absence or in the presence of proctolin. The frequency of the peristaltic contractions increased only at a very high concentration of the peptide, suggesting that proctolin could effectively bind with low affinity to non‐specific receptors. The outcome on larval fitness of increasing doses of proctolin orally administered to fourth instar larvae were investigated by recording the standard nutritional indices. A significant decrease of the Efficiency of Conversion of Ingested and Digested food to body substance with a concomitant reduction of the Relative Growth Rate (RGR) was observed at the lowest dose tested (0.18 mg/g larva). The amount of peptide administered appeared critical, because a 10‐fold higher dose of proctolin abolished the negative effect on RGR by a stimulation of the feeding behaviour, possibly as a result of the activation of compensatory mechanisms. A similar decrease of larval RGR with a low concentration of proctolin was observed also in the polyphagous pest Spodoptera littoralis (Lepidoptera, Noctuidae).

A mechanism underlying short-term synaptic dynamics regulated by neuromodulator based on kinetics of Ca currents

The crustacean stomatogastric nervous system (STNS) is one of the most extensively researched neural systems in studying the effects of neuromodulation. Previous studies have reported the actions of neuromodulators on intrinsic neuronal properties and synaptic strength in the STNS [2], but little is known about neuromodulatory effects on the short-term synaptic dynamics. We investigated the effect of the neuropeptide proctolin on the dynamics of the inhibitory synapse from the lateral pyloric (LP) to the pyloric dilator (PD) neuron in the crab pyloric network. Synaptic transmission between these neurons consists of spike-mediated and non-spike-mediated (graded) components. The graded component of this synapse shows short-term depression in control saline, but in the presence of proctolin, low-amplitude ( 30 mV) stimulation causes depression.

Effects of leucomyosuppressin on the excitation-concentration coupling of insect Leucophaea maderae visceral muscle

Abstract 1. Leucomyosuppressin (LMS) inhibited neurally evoked contractions of the hindgut of the cockroach Leucophaea maderae . The threshold for this inhibition of LMS was in the range of 1 × 10 −10 M. 2. LMS caused a sharp reduction in both l -glutamate and proctolin induced contractions. Dose-response profiles of the effect of LMS (held constant at 10 −8 M) on variable amounts of proctolin showed an inhibitory effect at 10 −9 M proctolin and below, but at 5 × 10 −9 M proctolin and above, LMS caused no inhibition. 3. Potassium (158 mM) depolarized hindguts treated with LMS (10 −8 M) showed a marked reduction (76% ± 2.1) in the proctolin (10 −8 M) response. 4. When calcium depleted preparations were returned to normal calcium levels (2 mM) in the presence of proctolin (10 −8 M) a contraction occurred that was 45% ± 4 of the maximum in normal saline solution. However, LMS (10 −8 M) reduced this response to only 28% ± 2 of the maximum. 5. Proctolin (10 −8 M) induced contractions in the presence of the manganous ions (2mM) fell to 63% ± 4 of the maximum but on the addition of LMS (10 −8 M), such responses fell to only 16% ± 5 of the maximum. 6. These results offer evidence for a non-synaptic site of action for LMS and a perturbation of key calcium dependent events in the excitation-contraction coupling sequence of visceral muscle by this peptide.

Some effects of octopamine, proctolin and serotonin on dorsal unpaired median neurones of cockroach ( Periplaneta americana) thoracic ganglia

Effects of neuromodulators, two monoamines, octopamine and serotonin, and the pentapeptide, proctolin, known to be present in the cockroach central nervous system, on the excitability of dorsal unpaired median neurones in the thoracic ganglia of the cockroach, Periplaneta americana, were investigated using intracellular recording technique. Octopamine had a marked excitatory effect on these neurones. Bath application of octopamine increased the frequency of spontaneous spikes in a dose-dependent manner associated with an increase in membrane input resistance. Serotonin increased the frequency and the resistance, but much less than octopamine. Proctolin also had an excitatory effect on the dorsal unpaired median somata, but the effect was somewhat equivocal. No appreciable change in the membrane input resistance occurred in the presence of proctolin. Among these neuromodulators tested, octopamine may alter the intrinsic properties of the above somata, resulting in the modulation of neural networks.

Modulatory action of proctolin in the locust ( Locusta migratoria) antennal motor system

Previous investigations of locust antennal muscles suggested the involvement of a peptidergic cotransmitter in the excitation-contraction coupling. The presence and action of proctolin in the antennal motor system were therefore investigated with physiological and immunohistochemical techniques. In experiments with the scape muscles, application of synthetic proctolin enhanced electrically-induced single contractions as well as tetanic contractures. In the presence of proctolin, electrical nerve stimulation additionally evoked an underlying slow contraction with a refractory period of several seconds. Neither the membrane potential of scape muscle fibres nor the amplitude of intracellularly recorded junction potentials were altered by proctolin indicating a predominantly postsynaptic action of the pentapeptide. Even in the absence of motoneuronal activity, proctolin was found to induce concentration-dependent increases in muscle tension of the scape and the tentorio-scapal muscles. Proctolin-like immunoreactivity was found to be present on all four antennal muscles and in the nerves containing antennal motoneurones. Up to 12 proctolin-like immunoreactive somata were found on each side of the deutocerebrum within the same region where the somata of antennal motoneurones are located. These results suggest that proctolin is an endogenous modulator within the locust antennal motor system.

Identification of proctolin in the central nervous system of the horseshoe crab, Limulus polyphemus

A proctolin-like peptide was isolated from the prosomal CNS of the chelicerate arthropod, Limulus, and purified using size exclusion, ion exchange and high performance liquid chromatography. Coincident bioassay (cockroach hindgut) and radioimmunoassay were employed to identify fractions which contained proctolin-like material. Proctolin-like activity coeluted with synthetic proctolin with all three chromatographic techniques employed. When applied to either the Limulus heart or hindgut preparations, purified Limulus proctolin produced excitatory responses which were indistinguishable from those produced by the synthetic peptide. Purified samples of the Limulus proctolin-like peptide were subjected to Edman degradation and tandem mass spectrometry and the amino acid sequence of the Limulus peptide was determined to be identical to that of cockroach proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH). The presence of proctolin in the Limulus CNS and its biological action on the isolated heart and hindgut suggest a physiological role for this peptide in the regulation of cardiac output and hindgut motility.

The presence of proctolin in the reproductive system of Rhodnius prolixus

The distribution of proctolin throughout the reproductive system of female Rhodnius prolixus has been studied using reversed-phase high-performance liquid chromatography (RP-HPLC) together with a sensitive bioassay for proctolin. The spermathecae contained the largest amount of proctolin per mg protein, followed by the common oviduct, the bursa and lateral oviducts, with the ovaries containing the lowest amount. Immunohistochemistry of the reproductive structures revealed proctolin-like immunoreactivity in terminal aborisations extending from the lateral oviducts across the common oviduct, spermathecae and along to the bursa. No immunostaining was evident on the ovaries or cement gland. The oviducts of Rhodnius are sensitive to proctolin, with exposure to proctolin producing a dose-dependent increase in muscle tonus as well as an increase in amplitude and frequency of phasic contractions. Proctolin also produces an increase in the frequency of the rhythmical contractions of the spermathecae. The results indicate that proctolin is probably involved in the regulation of events associated with reproduction in this hemipteran.

Modulation of the crayfish swimmeret rhythm by octopamine and the neuropeptide proctolin.

1. The swimmeret system can be excited by perfusing the neuropeptide proctolin through the isolated ventral nerve cord of the crayfish. Previously silent preparations begin to generate a characteristic motor pattern, the swimmeret rhythm, in the nerves that innervate the swimmerets. The response to proctolin is dose dependent and reversible. The threshold concentration of proctolin perfused through the ventral artery is approximately 10(-8) M. The EC50 is 1.6 X 10(-6) M. 2. Proctolin-induced motor patterns have periods and phases similar to those of spontaneously generated motor patterns. The durations of the bursts of impulses in power-stroke motor neurons generated in the presence of proctolin are, however, significantly longer than those that occur during spontaneous activity. 3. DL-Octopamine inhibits the swimmeret system, both when the system is spontaneously active and when it has been excited by proctolin. The inhibition by octopamine is dose dependent and reversible. The threshold for inhibition is approximately 10(-6) M, and the EC50 is approximately 5 X 10(-5) M. 4. Octopamine's effect is mimicked by its agonists, synephrine and norepinephrine. Synephrine has a lower threshold concentration than does octopamine, but norepinephrine is much less effective than octopamine. 5. Octopamine's inhibition is partially blocked by an antagonist, phentolamine. 6. Phentolamine also blocks inhibition of the swimmeret system by inhibitory command interneurons. This block is dose dependent and can be partially overcome by stimulating the command interneurons at higher frequencies. 7. Perfusion with 11 other suspected crustacean neurotransmitters and transmitter analogues did not similarly excite or inhibit the swimmeret system, so we suggest that proctolin and octopamine are transmitters used by the neurons that normally control expression of the swimmeret rhythm.

Neuropeptide proctolin associated with an identified skeletal motoneuron

Our objective was to find large and identifiable peptide-containing neurons and their postsynaptic targets. For this, a whole mount immunohistochemical method was used to locate cell bodies of neurons in the cockroach central nervous system immunoreactive to antibodies raised against the pentapeptide proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH). The morphology and projections of the immunoreactive neurons were investigated by combining intracellular dye injection and electrophysiological and immunochemical procedures. The presence of proctolin in specific immunoreactive neurons was check by high pressure liquid chromatography combined with bioassay applied to extracts made from individually identified and isolated cell bodies. Using these approaches, we have identified a large proctolin-containing motoneuron which innervates muscles in a proximal segment of the cockroach leg. This study establishes a well characterized cellular preparation in which the physiological actions and functions of a peptide-containing neuron can be studied in vivo.