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In JoVE (2)
- Inspelning Behavioral Svar på Reflektion i Kräftor
- Fysiologiska experiment med Kräftor hindgut: En student laboration
Other Publications (8)
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Articles by A. Joffre Mercier in JoVE
JoVE Neuroscience
Inspelning Behavioral Svar på Reflektion i Kräftor
Department of Biological Sciences, Brock University
Vi har utvecklat två metoder för att studera effekter av visuella referenser på beteendet i avsaknad av taktila och kemiska signaler. En metod innebär videofilmning svar kräftor till reflekterande väggar i ett akvarium, den andra undersöker effekterna av visuell input från en levande kräftor bakom en genomskinlig partition.
JoVE Neuroscience
Fysiologiska experiment med Kräftor hindgut: En student laboration
1Department of Biology, University of Kentucky, 2Department of Biological Sciences, Brock University
I denna rapport visar vi tekniker som kan användas för att undersöka biologi kräftor hindgut. Vi visar hur man kan dissekera en kräfta buken och studera tillhörande anatomi, fysiologi och modulering av aktivitet. Den peristaltiska aktiviteten och styrka sammandragningar mäts med en kraftgivare.
Other articles by A. Joffre Mercier on PubMed
Physiological Functions of FMRFamide-like Peptides (FLPs) in Crustaceans
Neuropeptides play important roles in chemical signalling in the central and peripheral nervous systems. One of the largest families of neuropeptides is that of the FMRFamide-like peptides (FLPs). This paper reviews what is known about the physiological functions of FLPs in crustaceans, focussing on the cardiovascular, digestive and neuromuscular systems.
Synaptic Modulation by a Neuropeptide Depends on Temperature and Extracellular Calcium
The crayfish neuropeptide DRNFLRFamide increases transmitter release from synaptic terminals onto muscle cells. As temperature decreases from 20 to 8 degrees C, the size of excitatory junctional potentials (EJPs) decreases, and the peptide becomes more effective at increasing EJP amplitude. The goal of the present study was to determine whether the enhanced effectiveness of the peptide is strictly a temperature-related effect, or whether it is related to the fact that the EJPs are smaller at low temperature, allowing a greater range for EJP amplitude to increase. Decreasing temperature reduced the number of quanta of transmitter released per nerve impulse (assessed by recording synaptic currents) and increased input resistance in muscle fibers. As in earlier work, the ability of the peptide to increase EJP amplitude was enhanced by decreasing temperature. However, the peptide was also more effective at increasing EJP amplitude when transmitter output was lowered by reducing the ratio of calcium to magnesium ions in the bath. Thus the effectiveness of the peptide may be related to the level of output from the synaptic terminals.
Synaptic Modulation by a Drosophila Neuropeptide is Motor Neuron-specific and Requires CaMKII Activity
The Drosophila FMRFamide-related peptide, DPKQDFMRFamide modulates synaptic transmission at the larval neuromuscular junction. The amplitude of excitatory junctional potentials (EJPs) produced by the selective stimulation of motor neuron MN6/7-Ib increases following application of 1 microM DPKQDFMRFamide. EJPs elicited by stimulating motor neuron MNSNb/d-Is, however, exhibit no significant increase with the same concentration of neuropeptide. The mechanisms underlying the modulatory effects of DPKQDFMRFamide were examined using a combination of pharmacological and genetic methods. Three independent lines of evidence implicate CaMKII as an essential effector protein or part of the signal transduction pathway. The effect of the neuropeptide is suppressed by 1 microM KN-93 (CaMKII inhibitor) and by heat-shock induced expression of a CaMKII inhibitor. A heterozygous CaM kinase mutant responds poorly to the peptide.
A Role for Cyclic Nucleotide Monophosphates in Synaptic Modulation by a Crayfish Neuropeptide
DF2 (DRNFLRFamide), a FMRFamide-like peptide, has been shown to increase the amount of transmitter released at crayfish neuromuscular junctions. Here, we examined a possible role for the cyclic nucleotide monophosphates, cAMP and cGMP, in DF2's effects on synaptic transmission. The effects of DF2 on synaptic transmission were monitored by recording excitatory postsynaptic potentials (EPSPs) in the deep abdominal extensor muscles of the crayfish, Procambarus clarkii. A number of activators and inhibitors were used to determine whether or not cAMP, cGMP, protein kinase A (PKA) and protein kinase G (PKG) mediate the effect of this neuropeptide. Phosphodiesterase inhibitors, known to inhibit the breakdown of cAMP (IBMX) and/or cGMP (mdBAMQ), potentiate the effect of DF2 on synaptic transmission. Activators of PKA (Sp-cAMPS) and PKG (8-pCPT-cGMP) increase EPSP amplitude, mimicking the effects of DF2. Inhibitors of PKA (Rp-cAMPS) and PKG (Rp-8-pCPT-cGMPS) each block a portion of the response to the peptide, and when applied together these two inhibitors completely block the response. Taken together, these results indicate that cyclic nucleotides and cyclic nucleotide-dependent protein kinases are necessary components of the pathway underlying modulation by this neuropeptide.
Duration of Socialization Influences Responses to a Mirror: Responses of Dominant and Subordinate Crayfish Diverge with Time of Pairing
Reflective surfaces have been shown previously to modify behaviour in socialized crayfish. Socializing crayfish by pairing them for two weeks established a hierarchy with one dominant and one subordinate crayfish per pair. Dominant crayfish exhibited specific behaviours, such as cornering, turning and crossing, more frequently in a reflective environment than in a non-reflective environment. After 2 weeks of pairing, subordinate crayfish did not respond in this manner but, instead, performed more reverse walking in a reflective environment. The present study investigated how the length of social pairing affects the response to mirrors. Crayfish from a communal tank were paired for 30 min or for 3 days, and their activity was videotaped for 20 min in a test aquarium lined with mirrors on one half and a non-reflective matte lining on the other half. Crayfish housed in the communal tank were used as a comparison group. After 30 min of pairing, dominant and subordinate crayfish responded similarly to the reflection, showing essentially the same pattern for seven of nine behaviours examined. After 3 days of pairing, dominant crayfish continued to respond to the reflection in essentially the same way, but subordinate crayfish behaved differently, showing differences in seven out of nine behaviours. Thus, the pattern of responses of dominant and subordinate crayfish to reflection diverged with time of pairing.
Evidence for Postsynaptic Modulation of Muscle Contraction by a Drosophila Neuropeptide
DPKQDFMRFamide, the most abundant FMRFamide-like peptide in Drosophila melanogaster, has been shown previously to enhance contractions of larval body wall muscles elicited by nerve stimulation and to increase excitatory junction potentials (EJPs). The present work investigated the possibility that this peptide can also stimulate muscle contraction by a direct action on muscle fibers. DPKQDFMRFamide induced slow contractions and increased tonus in body wall muscles of Drosophila larvae from which the central nervous system had been removed. The threshold for this effect was approximately 10(-8)M. The increase in tonus persisted in the presence of 7x10(-3)M glutamate, which desensitized postsynaptic glutamate receptors. Thus, the effect on tonus could not be explained by enhanced release of glutamate from synaptic terminals and, thus, may represent a postsynaptic effect. The effect on tonus was abolished in calcium-free saline and by treatment with L-type calcium channel blockers, nifedipine and nicardipine, but not by T-type blockers, amiloride and flunarizine. The present results provide evidence that this Drosophila peptide can act postsynaptically in addition to its apparent presynaptic effects, and that the postsynaptic effect requires influx through L-type calcium channels.
Distribution of Dopamine and Octopamine in the Central Nervous System and Ovary During the Ovarian Maturation Cycle of the Giant Freshwater Prawn, Macrobrachium Rosenbergii
Dopamine (DA), octopamine (OA) and serotonin (5-HT) are the key neurotransmitters that control gonadal development in decapod crustaceans. 5-HT stimulates, while DA and OA delay gonadal development in Macrobrachium rosenbergii. In the present study, we have further investigated the distribution patterns of DA and OA in the central nervous system (CNS) and ovary during various stages of the ovarian maturation cycle of this giant freshwater prawn. DA- and OA-immunoreactive neurons and fibers were distributed extensively in several regions of the brain, subesophageal ganglion (SEG), thoracic ganglia and abdominal ganglia. In the brain, the two neurotransmitters were present in neurons of clusters 6, 7, 11, 17, and nearby neuropil regions. In the SEG, thoracic ganglia and abdominal ganglia, immunoreactive neurons and fibers were found along the midline and in several neuronal clusters around each neuropil region. Staining for DA and OA was more intense in the thoracic ganglia than in other parts of the CNS. In the ovary, DA- and OA-immunoreactivities were present at high intensity in early oocytes. The presence of DA- and OA-immunoreactivities in neural ganglia as well as ovary suggests that DA and OA may also be involved in the reproductive process, particularly ovarian development and differentiation of oocytes in this species.
Peptide-induced Modulation of Synaptic Transmission and Escape Response in Drosophila Requires Two G-protein-coupled Receptors
Neuropeptides are found in both mammals and invertebrates and can modulate neural function through activation of G-protein-coupled receptors (GPCRS). The precise mechanisms by which many of these GPCRs modulate specific signaling cascades to regulate neural function are not well defined. We used Drosophila melanogaster as a model to examine both the cellular and behavioral effects of DPKQDFMRFamide, the most abundant peptide encoded by the dFMRF gene. We show that DPKQDFMRFamide enhanced synaptic transmission through activation of two G-protein-coupled receptors, Fmrf Receptor (FR) and Dromyosupressin Receptor-2 (DmsR-2). The peptide increased both the presynaptic Ca(2+) response and the quantal content of released transmitter. Peptide-induced modulation of synaptic function could be abrogated by depleting intracellular Ca(2+) stores or by interfering with Ca(2+) release from the endoplasmic reticulum through disruption of either the ryanodine receptor or the inositol 1,4,5-trisphosphate receptor. The peptide also altered behavior. Exogenous DPKQDFMRFamide enhanced fictive locomotion; this required both the FR and DmsR-2. Likewise, both receptors were required for an escape response to intense light exposure. Thus, coincident detection of a peptide by two GPCRs modulates synaptic function through effects of Ca(2+)-induced Ca(2+) release, and we hypothesize that these mechanisms are involved in behavioral responses to environmental stress.
