Temperature sensitivity of the pyloric neuromuscular system and its modulation by dopamine

We report here the effects of temperature on the p1 neuromuscular system of the stomatogastric system of the lobster (Panulirus interruptus). Muscle force generation, in response to both the spontaneously rhythmic in vitro pyloric network neural activity and direct, controlled motor nerve stimulation, dramatically decreased as temperature increased, sufficiently that stomach movements would very unlikely be maintained at warm temperatures. However, animals fed in warm tanks showed statistically identical food digestion to those in cold tanks. Applying dopamine, a circulating hormone in crustacea, increased muscle force production at all temperatures and abolished neuromuscular system temperature dependence. Modulation may thus exist not only to increase the diversity of produced behaviors, but also to maintain individual behaviors when environmental conditions (such as temperature) vary

Choline And NMDG Directly Reduce Outward Currents: Reduced Outward Current when these Substances Replace Na\u3csup\u3e+\u3c/sup\u3e is Alone not Evidence of Na\u3csup\u3e+\u3c/sup\u3e-Activated K\u3csup\u3e+\u3c/sup\u3e Currents

© 2018 the American Physiological Society. Choline chloride is often, and N-methyl-D-glucamine (NMDG) sometimes, used to replace sodium chloride in studies of sodium-activated potassium channels. Given the high concentrations used in sodium replacement protocols, it is essential to test that it is not the replacement substances themselves, as opposed to the lack of sodium, that cause any observed effects. We therefore compared, in lobster stomatogastric neurons and leech Retzius cells, the effects of applying salines in which choline chloride replaced sodium chloride, and in which choline hydroxide or sucrose was added to normal saline. We also tested, in stomatogastric neurons, the effect of adding NMDG to normal saline. These protocols allowed us to measure the direct effects (i.e., effects not due to changes in sodium concentration or saline osmolarity or ionic strength) of choline on stomatogastric and leech currents, and of NMDG on stomatogastric currents. Choline directly reduced transient and sustained depolarization-activated outward currents in both species, and NMDG directly reduced transient depolarization-activated outward currents in stomatogastric neurons. Experiments with lower choline concentrations showed that adding as little as 150 mM (stomatogastric) or 5 mM (leech) choline reduced at least some depolarization-activated outward currents. Reductions in outward current with choline chloride or NMDG replacement alone are thus not evidence of sodium-activated potassium currents. NEW & NOTEWORTHY We show that choline or N-methyl-D-glucamine (NMDG) directly (i.e., not due to changes in extracellular sodium) decrease outward currents. Prior work studying sodium-activated potassium channels in which sodium was replaced with choline or NMDG without an addition control may therefore be artifactual

Cell dialysis by sharp electrodes can cause nonphysiological changes in neuron properties

We recorded from lobster and leech neurons with two sharp electrodes filled with solutions often used with these preparations (lobster: 0.6 M K2SO4 or 2.5 M KAc; leech: 4 M KAc), with solutions approximately matching neuron cytoplasm ion concentrations, and with 6.5 M KAc (lobster, leech) and 0.6 M KAc (lobster). We measured membrane potential, input resistance, and transient and sustained depolarization-activated outward current amplitudes in leech and these neuron properties and hyperpolarization-activated current time constant in lobster, every 10 min for 60 min after electrode penetration. Neuron properties varied with electrode fill. For fills with molarities >= 2.5 M, neuron properties also varied strongly with time after electrode penetration. Depending on the property being examined, these variations could be large. In leech, cell size also increased with noncytoplasmic fills. The changes in neuron properties could be due to the ions being injected from the electrodes during current injection. We tested this possibility in lobster with the 2.5 M KAc electrode fill by making measurements only 10 and 60 min after penetration. Neuron properties still changed, although the changes were less extreme. Making measurements every 2 min showed that the time-dependent variations in neuron properties occurred in concert with each other. Neuron property changes with high molarity electrode-fill solutions were great enough to decrease neuron firing strongly. An experiment with C-14-glucose electrode fill confirmed earlier work showing substantial leak from sharp electrodes. Sharp electrode work should thus be performed with cytoplasm- matched electrode fills

Dopamine blocks temperature sensitivity in an isolated, rhythmically stimulated neuromuscular preparation.

<p>(A) A neuromuscular preparation that has been isolated from the spontaneous activity of the pyloric neural network by severing the lvn. Contractions instead elicited by direct motor nerve stimulation with unvarying input (10 spikes at 27 Hz). Muscle contraction amplitude still declined dramatically in warmer saline. This animal had been acclimated to 15°C for 48 hrs, and thus these data also show that neuromuscular temperature sensitivity is independent of animal housing temperature. (B) Adding dopamine (10⁻⁵) to the saline increased force generation at colder temperatures and allowed the neuromuscular system to continue functioning at warmer temperatures. (C) The dopamine effect reversed upon wash. (D) Dopamine also maintained contraction amplitude in neuromuscular systems from animals held in 9°C aquaria for 48 hrs before the experiment. Data in panels A, B, C all from same animal.</p

Changing available dissolved oxygen does not affect temperature sensitivity.

<p>The preparation was initially perfused with cold, oxygenated saline (top trace) and then switched (arrow) to cold saline containing at least 3 fold less dissolved oxygen. The muscle showed no change in activity (bottom trace) when the reduced oxygen saline was introduced. However, the temperature sensitivity remained and was still reversible despite the much lower oxygen availability. The periodic large decreases in muscle force every 75–100 s are due to the activity of another, much more slowly cycling, stomatogastric network, the gastric mill, which greatly reduces lateral pyloric neuron activity during one phase of gastric mill activity <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0067930#pone.0067930-Morris4" target="_blank">[13]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0067930#pone.0067930-Thuma2" target="_blank">[15]</a>.</p

Dopamine allows the neuromuscular system to generate greater force at cold temperatures and continue functioning at warm temperatures.

<p>(A) Data from six motor nerve stimulation experiments (closed circles, control saline; open circles, dopamine; matching color lines are data from the same experiment; all animals housed at 15°C). Where present, solid lines show that linear fits to the data were significant. (B) Data for each experiment were binned (1°C) and mean contraction force was determined for each bin. Dopamine differed from control and wash conditions both in amplitude and in temperature sensitivity (present in control and wash, absent in dopamine). See text for statistical details.</p

The lobster p1 neuromuscular system is temperature-sensitive.

<p>(A) As temperature (top trace) was decreased the force of muscle contraction (middle trace) increased. The activity of the nerve containing the LP neuron input to the muscle is shown in the bottom trace. (B) and (C) Time expansion from (A) showing muscle force (top trace) and neural input (bottom trace) at 9°C and 15°C. Arrows show that two LP neuron bursts chosen for having essentially identical characteristics induced very different muscle contraction amplitudes at the two temperatures. Inset in (C) is muscle force at an expanded scale to show that even at warm temperatures each motor neuron burst continued to induce (very small) muscle contractions.</p

Detection of Plasmodium falciparum in pregnancy by laser desorption mass spectrometry

Detection of Plasmodium falciparum malaria during pregnancy is complicated by sequestration of parasites in the placenta, which reduces peripheral blood microscopic detection. Laser desorption mass spectrometry (LDMS) has previously demonstrated sensitive detection of hemozoin from P. falciparum blood cultures and the ability to track parasitemia in a Plasmodium yoelii malaria mouse model. Here we use a simple, dilution in water, blood sample preparation protocol for LDMS detection of malaria in 45 asymptomatic, pregnant Zambian women. We compare LDMS to microscopy and polymerase chain reaction (PCR) analysis. All women were microscopy negative. LDMS detected P. falciparum hemozoin in 15 out of 45 women, while PCR results were positive in 25 women. Compared with PCR, which analyzed 20-30 μL of blood, the sensitivity of LDMS, which analyzed \u3c 1 μL of blood, was 52%, with a specificity of 92%. LDMS is a potentially rapid and more sensitive alternate diagnostic method than microscopy. Copyright © 2005 by The American Society of Tropical Medicine and Hygiene