NORADRENALINE RELEASE BY NERVE STIMULATION OF THE SPINAL CORD

Broccoli-shaped biosensor hierarchy for electrochemical screening of noradrenaline in living cells

Monitoring and determination of ultra-trace concentrations of monoamine neurotransmitter such as noradrenaline (NA) in living cells with simple, sensitive and selective assays are significantly interesting. We design NA-electrode sensing system based on C-, N-doped NiO broccoli-like hierarchy (CNNB). The spherical broccoli-head umbrella architectures associated with nano-tubular arrangements enabled to tailor NA biosensor design. The homogenous doping and anisotropic dispersion of CN nanospheres along the entire NB head nanotubes lead to creating of abundant electroactive sites in the interior tubular vessels and outer surfaces for ultrasensitive detection of NA in living cells such as PC12. The CNNB biosensor electrodes showed efficient electrocatalytic activity, enhanced kinetics for electrooxidation of NA, and fast electron-transfer between electrode-electrolyte interface surfaces, enabling synergistic enhancement in sensitivity, and selectivity at a low-detectable concentration of ∼ 6nM and reproducibility of broccoli-shaped NA-electrodes. The integrated CNNB biosensor electrodes showed evidence of monitoring and screening of NA released from PC12 cells under K⁺ ion-extracellular stimulation process. The unique features of CNNB in terms of NA-selectivity among multi-competitive components, long-term stability during the detection of NA may open their practical, in-vitro application for extracellular monoamine neurotransmitters detection in living cells.

The role of serotonin in reflex modulation and locomotor rhythm production in the mammalian spinal cord

Over the past 40 years, much has been learned about the role of serotonin in spinal cord reflex modulation and locomotor pattern generation. This review presents an historical overview and current perspective of this literature. The primary focus is on the mammalian nervous system. However, where relevant, major insights provided by lower vertebrate models are presented. Recent studies suggest that serotonin-sensitive locomotor network components are distributed throughout the spinal cord and the supralumbar regions are of particular importance. In addition, different serotonin receptor subtypes appear to have different rostrocaudal distributions within the locomotor network. It is speculated that serotonin may influence pattern generation at the cellular level through modulation of plateau properties, an interplay with N-methyl-D-aspartate receptor actions, and afterhyperpolarization regulation. This review also summarizes the origin and maturation of bulbospinal serotonergic projections, serotonin receptor distribution in the spinal cord, the complex actions of serotonin on segmental neurons and reflex pathways, the potential role of serotonergic systems in promoting spinal cord maturation, and evidence suggesting serotonin may influence functional recovery after spinal cord injury.

Mechanisms of norepinephrine accumulation within sites of spinal cord injury

✓ Vascularity and blood-brain barrier (BBB) function within spinal cord were studied with fluorescent microscopy at 14 intervals following 300 gm-cm injuries to the thoracolumbar spinal cord in 32 dogs. Histochemical staining with formaldehyde brought out a yellow-green fluorescence of vascular origin that was unrelated to tracer dye. This fluorescence accumulated in perivascular sites and is possibly related to catecholamine elevation within damaged spinal cord. Intrinsic CNS mechanisms for catecholamine build-up (increased transport, increased synthesis, increased release) are reviewed as well as the pharmacological action of alpha methyl tyrosine. It is hypothesized that an intrinsic CNS source of norepinephrine build-up is unlikely and that elevation of circulating catecholamine levels following stress and trauma leads to the extravasation of this material across injured BBBs within contused spinal cord.

Altered norepinephrine metabolism following experimental spinal cord injury. 1. Relationship to hemorrhagic necrosis and post-wounding neurological deficits

✓ Experimentally injured spinal cord tissues were chemically examined for changes in norepinephrine (NE), serotonin, and dopamine; remarkable NE metabolic alterations were found. The amine doubled in 30 minutes, quadrupled in 1 hour, and thereafter slowly declined to approach control values at 4 hours. Comparisons between injured tissue NE content and the presence of central gray hemorrhages and necrosis were consistently found, and profound increases in NE were universally associated with massive central hemorrhages. Within 2 hours of injection of minute quantities of pure NE into the spinal gray matter, large central hemorrhages appeared that closely resembled the lesions associated with severe spinal cord injury. We have hypothesized that toxic quantities of tissue NE induce intense vasospasm which impedes or arrests cord perfusion and causes the neuronal necrosis, vascular rupture, and parenchymal self-destruction manifest as central hemorrhagic necrosis. Thus, excess NE liberated within traumatized tissue may act to depress or halt electrical activity of adjacent fibers and neurons, producing the neuronal response of transient weakness or paralysis. Permanent loss of function ensues as the electrically depressed spinal cord tissue also undergoes hemorrhagic autodestruction.

Some factors influencing the release of 5-hydroxyindol-3-ylacetic acid in the forebrain

1. Electrical stimulation of the mid-brain raphé in anaesthetized adrenalectomized rats produced a significant decrease in the forebrain content of 5-hydroxytryptamine (5-HT) and an increase in the concentration of 5-hydroxyindol-3-ylacetic acid (5-HIAA).2. Stimulation of peripheral sensory nerves did not influence either the forebrain content of 5-HIAA or the efflux of 5-HIAA from the cerebral cortex.3. Probenecid (200 mg/kg) caused a twofold increase in 5-HIAA content of the rat's forebrain, while the efflux of 5-HIAA from the cerebral cortex remained unchanged.4. Stimulation of the mid-brain raphé in animals pretreated with probenecid does not produce the rise in the forebrain levels of 5-HIAA seen in stimulated untreated controls and does not affect the efflux of 5-HIAA from the cerebral cortex.5. In preliminary experiments, lysergic acid diethylamide (LSD 25) substantially reduced and/or prevented the increase in the release of 5-HIAA in the forebrain observed in untreated animals with raphé stimulation.