Synaptic Modulation by a Neuropeptide Depends on Temperature and Extracellular Calcium

Abstract

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.

Temperature dependent modulation of lobster neuromuscular properties by serotonin

“…Asterisks indicate values that are significantly different from data recorded at 2°C (independent t-test, P<0.05). Florey, 1981;White, 1983), whereas they increase in size over the temperature range 10-20°C in deep abdominal extensor muscle (Dunn and Mercier, 2003).…”

“…Quantal neurotransmission at dactyl opener muscle synapses is asynchronous at cold (<5°C) temperatures Worden et al, 1997) and becomes more synchronous at warmer temperatures. Finally, it is also possible that temperature regulates the relative amount of neurotransmitter released from synaptic terminals, as demonstrated in crayfish (Dunn and Mercier, 2003).…”

“…Interestingly, although 5-HT modulated neurally evoked contractions and relaxations as well as resting muscle tension in temperature-dependent ways, it potentiated excitatory neurotransmission in a temperatureindependent manner. In contrast, the neuromodulatory effect of peptide DF 2 on crayfish phasic abdominal extensor muscles is three times as strong at 7-9°C as it is at 15-17°C (Friedrich et al, 1994), an effect that has been attributed to the greater ability of the peptide to increase calcium influx into presynaptic terminals of the motoneurons at low temperatures (Dunn and Mercier, 2003).…”

Molecular physiology of crustacean and insect neuropeptides

“…[86][87][88][89] The synaptic modulation was shown to dependent on temperature and extracellular calcium. 91,92) DRNFLRFamide also induces contraction of superficial abdominal extensor muscles 93) and enhances hindgut contractions. 94) Receptors for FMRFamide-related peptides (FaRPs) have been cloned in two insect species, Drosophila and Anopheles.…”

“…However, at least one of these peptides enhances synaptic potentials of one motor neuron but not another. 92) Thus, these peptides may modulate different chemical synapses in the larval body wall. In some insects FMRFamides increase the amplitude or frequency of heartbeats and in the blowfly induce salivary secretion.…”