Effect of temperature change on synaptic transmission at crayfish neuromuscular junctions

Abstract

Ectothermic animals in areas characterised by seasonal changes are susceptible to extreme fluctuations in temperature. To survive through varied temperatures, ectotherms have developed unique strategies. This study focuses on synaptic transmission function at cold temperatures, as it is a vital component of ectothermic animals' survival. For determining how synaptic transmission is influenced by an acute change in temperature (20°C to 10°C within a minute) and chronic cold (10°C), the crayfish (Procambarus clarkii) neuromuscular junction (NMJ) was used as a model. To simulate chronic cold conditions, crayfish were acclimated to 15°C for 1 week and then to 10°C for 1 week. They were then used to examine the synaptic properties associated with the low output nerve terminals on the opener muscle in the walking legs and high output innervation on the abdominal deep extensor muscle. The excitatory postsynaptic potentials (EPSPs) of the opener NMJs increased in amplitude with acute warming (20°C) after being acclimated to cold; however, the deep extensor muscles showed varied changes in EPSP amplitude. Synaptic transmission at both NMJs was enhanced with exposure to the modulators serotonin or octopamine. The membrane resistance of the muscles decreased 33% and the resting membrane potential hyperpolarised upon warm exposure. Analysis of haemolymph indicated that octopamine increases during cold exposure. These results suggest bioamine modulation as a possible mechanism for ensuring that synaptic transmission remains functional at low temperatures.

Physiological Changes as a Measure of Crustacean Welfare under Different Standardized Stunning Techniques: Cooling and Electroshock

“…The concentration of the biogenic amines serotonin and octopamine are higher in crabs than crayfish and shrimp. The decrease in octopamine in the crayfish with rapid cold exposure was unexpected since an earlier study showed an increase in octopamine in crayfish during a prolonged cold exposure of 2 weeks [ 46 ]. Perhaps a longer time is needed for the levels to demonstrate changes.…”

“…Even insects show changes in levels of biogenic amines with environmental stressors and/or exercise [ 43 , 44 , 45 ]. In cold (10 °C) exposed Drosophila melanogaster both serotonin and octopamine concentrations decreased in the hemolymph [ 46 ]. Crayfish gradually exposed to cold (20–21 °C to 15 °C for 1 week and one week at 10 °C) increased hemolymph concentration of octopamine 4-fold [ 46 ].…”

“…In cold (10 °C) exposed Drosophila melanogaster both serotonin and octopamine concentrations decreased in the hemolymph [ 46 ]. Crayfish gradually exposed to cold (20–21 °C to 15 °C for 1 week and one week at 10 °C) increased hemolymph concentration of octopamine 4-fold [ 46 ]. No studies that we are aware of have addressed if a rapid exposure to cold would also raise octopamine or alter levels of serotonin.…”

Grp94 Regulates the Recruitment of Aneural AChR Clusters for the Assembly of Postsynaptic Specializations by Modulating ADF/Cofilin Activity and Turnover

“…Temperature has long been considered as a physiological factor that affects neuronal growth and maintains synaptic homeostasis by modulating presynaptic and postsynaptic elements at the invertebrate NMJs (Tsai et al, 2012;Yeates et al, 2017;Zhu et al, 2018). South African clawed toad, Xenopus laevis, is an ectotherm vertebrate that has been widely used as an excellent animal model for embryology studies (Hobson, 1965).…”

Physiological and Behavioral Indicators to Measure Crustacean Welfare

“…The relative change is approximately 1 mV to 1.3 mV/1 °C change [25,26,27,28]. However, in an earlier study, hyperpolarization of the muscle membrane potential in P. clarkii occurred when cooling the tissue from 20 °C to 10 °C [29,30]. The reason for this change in membrane potential has not been explicitly addressed in prior reports, but it is likely related to the more negative equilibrium potential of potassium (E K ), since the membrane is more permeable to K + and the resting potential is driven mostly by the E K .…”