Decline in Spontaneous Activity of Group Aαβ Sensory Afferents After Sciatic Nerve Axotomy in Rat

Changes are observed in the strength of central synaptic transmission and the firing behavior of primary afferents damaged by peripheral nerve injury. To clarify the relationship between synaptic strength and amount of spontaneous activity, firing behavior was studied in adult, male Sprague–Dawley rats in which sciatic nerve afferents were axotomized. Intra-axonal recordings were taken from Aαβafferents within 7 h (acute, n=309), at 3 days (n=228), or at 10 days (n=230) after sciatic nerve cut. The proportion of spontaneously discharging afferents fell from 22% in the acute group to ≤13% in chronic groups. Thus, neither the progressive decline in the strength of central synaptic transmission from cut primary afferents nor the altered sensation observed after nerve cut can be explained by chronic changes in spontaneous activity of cut Aα/Aβ afferents

Decline in Spontaneous Activity of Group Aαβ Sensory Afferents After Sciatic Nerve Axotomy in Rat

Changes are observed in the strength of central synaptic transmission and the firing behavior of primary afferents damaged by peripheral nerve injury. To clarify the relationship between synaptic strength and amount of spontaneous activity, firing behavior was studied in adult, male Sprague–Dawley rats in which sciatic nerve afferents were axotomized. Intra-axonal recordings were taken from Aαβafferents within 7 h (acute, n=309), at 3 days (n=228), or at 10 days (n=230) after sciatic nerve cut. The proportion of spontaneously discharging afferents fell from 22% in the acute group to ≤13% in chronic groups. Thus, neither the progressive decline in the strength of central synaptic transmission from cut primary afferents nor the altered sensation observed after nerve cut can be explained by chronic changes in spontaneous activity of cut Aα/Aβ afferents

D. pulex.

<p><i>D</i>. <i>pulex</i> were exposed to ethylene blue for 15 min, rinsed thoroughly, and imaged using a Maximum Intensity Projection Z Plane Stack (10x, Leica SP5 Scanning Laser Confocal Microscope). The intensity image presented here was used as proof of concept during the characterization of ethylene blue.</p

<i>D</i>. <i>pulex</i> survival with vitamin D₃.

<p><i>D</i>. <i>pulex</i> (N = 12) exposed to acute UV-A in the presence of vitamin D₃. Blue line = 0 mg D₃; Black line = 5 mg D₃; Red line = 10 mg D₃. No reproduction was observed in any individuals during the experimental period. Error = standard error of the mean across 3 trials.</p

Synthetic route for the preparation of fluorescently labeled vitamin D₃.

<p>The carbodiimidazole (CDI) coupling of vitamin D₃ and the fluorescent dye linker.</p

D. pulex.

<p><i>D</i>. <i>pulex</i> were exposed to ethylene blue for 15 min, rinsed thoroughly, and imaged using a Maximum Intensity Projection Z Plane Stack (10x, Leica SP5 Scanning Laser Confocal Microscope). The intensity image presented here was used as proof of concept during the characterization of ethylene blue.</p

UV-Stressed <i>Daphnia pulex</i> Increase Fitness through Uptake of Vitamin D₃

<div><p>Ultraviolet radiation is known to be highly variable in aquatic ecosystems. It has been suggested that UV-exposed organisms may demonstrate enough phenotypic plasticity to maintain the relative fitness of natural populations. Our long-term objective is to determine the potential photoprotective effect of vitamin D₃ on <i>Daphnia pulex</i> exposed to acute or chronic UV radiation. Herein we report our initial findings in this endeavor. <i>D</i>. <i>pulex</i> survival and reproduction (fitness) was monitored for 5 d as a proof of concept study. Significantly higher fitness was observed in the <i>D</i>. <i>pulex</i> with D₃ than those without (most extreme effects observed were 0% survival in the absence of D₃ and 100% with 10 ppm D₃). Vitamin D₃ was isolated from the culture media, the algal food (<i>Pseudokirchneriella</i>), and the <i>D</i>. <i>pulex</i> and quantified using high performance liquid chromatography (HPLC). Vitamin D₃ was fluorescently labeled using a phenothiazinium dye and added to cultures of <i>D</i>. <i>pulex</i>. Images demonstrating the uptake of D₃ into the tissues and carapace of the <i>D</i>. <i>pulex</i> were acquired. Our initial findings suggest a positive role for D₃ in ecosystems as both UV-stressed algae and <i>Daphnia</i> sequester D₃, and <i>D</i>. <i>pulex</i> demonstrate increased fitness in the presence of D₃.</p></div

Tracking vitamin D₃ in <i>D</i>. <i>pulex</i>.

<p>(A) A live <i>D</i>. <i>pulex</i> was placed in a 1:10 solution of ethylene blue, with no vitamin D₃ (“control”) and images were captured 30 min post exposure (10x, Leica SP5 Scanning Laser Confocal Microscope). Note the presence of the dye in the gut tract (red stain). (B). Live <i>D</i>. <i>pulex</i> were placed in a 1:10 solution of ethylene blue linked vitamin D₃, rinsed thoroughly, and images were captured 120 min post exposure (10x). Image was compiled from a 90-min time lapse to capture sequestration of vitamin D₃ (red) into the tissues of the <i>D</i>. <i>pulex</i> from the intestine. The high intensity red “dots” in the image are concentrated dye on the outside of the carapace that was not removed during the rinsing stages. The yellow circle indicates a region where D₃ sequestration was detected.</p