A Reversible Low Frequency Alternating Current Nerve Conduction Block Applied to Mammalian Autonomic Nerves

Electrical stimulation can be used to modulate activity within the nervous system in one of two modes: (1) Activation, where activity is added to the neural signalling pathways, or (2) Block, where activity in the nerve is reduced or eliminated. In principle, electrical nerve conduction block has many attractive properties compared to pharmaceutical or surgical interventions. These include reversibility, localization, and tunability for nerve caliber and type. However, methods to effect electrical nerve block are relatively new. Some methods can have associated drawbacks, such as the need for large currents, the production of irreversible chemical byproducts, and onset responses. These can lead to irreversible nerve damage or undesirable neural responses. In the present study we describe a novel low frequency alternating current blocking waveform (LFACb) and measure its efficacy to reversibly block the bradycardic effect elicited by vagal stimulation in anaesthetised rat model. The waveform is a sinusoidal, zero mean(charge balanced), current waveform presented at 1 Hz to bipolar electrodes. Standard pulse stimulation was delivered through Pt-Black coated PtIr bipolar hook electrodes to evoke bradycardia. The conditioning LFAC waveform was presented either through a set of CorTec® bipolar cuff electrodes with Amplicoat® coated Pt contacts, or a second set of Pt Black coated PtIr hook electrodes. The conditioning electrodes were placed caudal to the pulse stimulation hook electrodes. Block of bradycardic effect was assessed by quantifying changes in heart rate during the stimulation stages of LFAC alone, LFAC-and-vagal, and vagal alone. The LFAC achieved 86.2±11.1% and 84.3±4.6% block using hook (N = 7) and cuff (N = 5) electrodes, respectively, at current levels less than 110 µAp (current to peak). The potential across the LFAC delivering electrodes were continuously monitored to verify that the blocking effect was immediately reversed upon discontinuing the LFAC. Thus, LFACb produced a high degree of nerve block at current levels comparable to pulse stimulation amplitudes to activate nerves, resulting in a measurable functional change of a biomarker in the mammalian nervous system

The loss of STAT3 in mature osteoclasts has detrimental effects on bone structure

Signal Transducer and Activator of Transcription 3 (STAT3) has recently been shown to be involved in bone development and has been implicated in bone diseases, such as Job’s Syndrome. Bone growth and changes have been known for many years to differ between sexes with male bones tending to have higher bone mass than female bones and older females tending to lose bone mass at faster rates than older males. Previous studies using conditional knock mice with Stat3 specifically deleted from the osteoblasts showed both sexes exhibited decreased bone mineral density (BMD) and strength. Using the Cre-Lox system with Cathepsin K promotor driving Cre to target the deletion of the Stat3 gene in mature osteoclasts (STAT3-cKO mice), we observed that 8-week old STAT3-cKO female femurs exhibited significantly lower BMD and bone mineral content (BMC) compared to littermate control (CN) females. There were no differences in BMD and BMC observed between male knock-out and male CN femurs. However, micro-computed tomography (μCT) analysis showed that both male and female STAT3-cKO mice had significant decreases in bone volume/tissue volume (BV/TV). Bone histomorphometry analysis of the distal femur, further revealed a decrease in bone formation rate and mineralizing surface/bone surface (MS/BS) with a significant decrease in osteoclast surface in female, but not male, STAT3-cKO mice. Profiling gene expression in an osteoclastic cell line with a knockdown of STAT3 showed an upregulation of a number of genes that are directly regulated by estrogen receptors. These data collectively suggest that regulation of STAT3 differs in male and female osteoclasts and that inactivation of STAT3 in osteoclasts affects bone turnover more in females than males, demonstrating the complicated nature of STAT3 signaling pathways in osteoclastogenesis. Drugs targeting the STAT3 pathway may be used for treatment of diseases such as Job’s Syndrome and osteoporosis

Stat3 in osteocytes mediates osteogenic response to loading

Signal transducer and activator of transcription 3 (Stat3) is a member of the Stat family of proteins involved in signaling in many different cell types, including osteocytes. Osteocytes are considered major mechanosensing cells in bone due to their intricate dendritic networks able to sense changes in physical force and to orchestrate the response of osteoclasts and osteoblasts. We examined the role of Stat3 in osteocytes by generating mice lacking Stat3 in these cells using the Dmp-1(8kb)-Cre promoter (Stat3cKO mice). Compared to age-matched littermate controls, Stat3cKO mice of either sex (18 weeks old) exhibit reduced bone formation indices, decreased osteoblasts and increased osteoclasts, and altered material properties, without detectable changes in bone mineral density (BMD) or content of either trabecular or cortical bone. In addition, Stat3cKO mice of either sex show significantly decreased load-induced bone formation. Furthermore, pharmacologic inhibition of Stat3 in osteocytes in vitro with WP1066 blocked the increase in cytosolic calcium induced by ATP, a mediator of the cellular responses to sheer stress. WP1066 also increased reactive oxygen species (ROS) production in cultured MLO-Y4 osteocytes. These data demonstrate that Stat3 is a critical mediator of mechanical signals received by osteocytes and suggest that osteocytic Stat3 is a potential therapeutic target to stimulate bone anabolism