Citations

Spinal cord hemisection at C2 (SH) disrupts descending drive to ipsilateral phrenic motoneurons (PMNs) causing unilateral diaphragm muscle (DIAm) paralysis. Previously, we found a decrease in motoneuron size at 2 weeks post‐SH. Recently, we found neuregulin (NRG) in synaptic boutons surrounding PMNs. NRG is a trophic factor known to regulate development of the neuromuscular junction, but the effect of NRG on motoneurons is unknown. We hypothesized that 1) NRG input to PMNs is supraspinal in origin, and 2) SH disrupts NRG input to PMNs. Adult male Sprague‐Dawley rats underwent SH or sham‐surgery. PMNs were retrogradely labeled by intramuscular injection of Alexa488‐conjugated cholera toxin B. Using laser capture microdissection, we found that PMNs express mRNA for the NRG receptors ErbB2 and ErbB3, providing a functional substrate for a NRG effect. Two weeks post‐SH, labeled PMNs and NRG boutons were imaged using confocal microscopy. PMN morphology and the number of NRG boutons in the vicinity of PMNs were determined using a computerized, semi‐automated reconstruction algorithm. NRG boutons were fairly homogeneously distributed on motoneurons independent of size. Following SH, few NRG boutons were observed. We conclude that 1) NRG input to PMNs derives from a supraspinal source; and 2) SH removes NRG input to PMNs. It is possible that NRG input exerts a trophic influence on PMNs. Supported by NIH grants HL37680, AR51173 and Mayo Clinic

Intracellular Ca 2+ ([Ca 2+ ] i ) levels are increased in inflamed airway smooth muscle (ASM). Sarcoplasmic reticulum (SR) Ca 2+ release and reuptake are key components of ASM [Ca 2+ ] i regulation. Ca 2+ reuptake occurs via the ATPase SERCA. We hypothesized that inflammation disrupts SERCA function, contributing to increased [Ca 2+ ] i . We examined SERCA expression and regulation in human ASM exposed to pro‐inflammatory cytokines TNFα and IL‐13. Western blot analysis showed significantly decreased SERCA expression following overnight cytokine exposure. In other tissues, SERCA is regulated by the inhibitory protein phospholamban (PLB). We found that human ASM does not express PLB protein (although mRNA is detectable). Cytokine exposure did not induce PLB expression, raising the issue of how SERCA is regulated. We then found that direct SERCA phosphorylation (potentially via CaMKII) occurs in human ASM. In fura‐2 loaded human ASM cells, we examined [Ca 2+ ] i responses to ACh or bradykinin (zero extracellular Ca 2+ ) and found significant reduction in rates of fall of [Ca 2+ ] i transients in cells exposed to TNF‐α or IL‐13. We further found that CaMKII antagonist KN‐93 significantly slowed the fall of [Ca 2+ ] i transients in both controls and cytokine‐exposed human ASM cells. These data suggest that a) SERCA in human ASM is regulated by mechanisms such as CaMKII; and b) airway inflammation decreases SR refilling by blunting SERCA expression and function. Supported by NIH grants HL74309, the Flight Attendants Medical Research Institute (FAMRI), and the Department of Anesthesiology, Mayo Clinic.