Low-level laser therapy (810 nm) protects primary cortical neurons against excitotoxicity in vitro.

Excitotoxicity describes a pathogenic process whereby death of neurons releases large amounts of the excitatory neurotransmitter glutamate, which then proceeds to activate a set of glutamatergic receptors on neighboring neurons (glutamate, N-methyl-D-aspartate (NMDA), and kainate), opening ion channels leading to an influx of calcium ions producing mitochondrial dysfunction and cell death. Excitotoxicity contributes to brain damage after stroke, traumatic brain injury, and neurodegenerative diseases, and is also involved in spinal cord injury. We tested whether low level laser (light) therapy (LLLT) at 810-nm could protect primary murine cultured cortical neurons against excitotoxicity in vitro produced by addition of glutamate, NMDA or kainate. Although the prevention of cell death was modest but significant, LLLT (3 J/cm2 delivered at 25 mW/cm2 over 2 min) gave highly significant benefits in increasing ATP, raising mitochondrial membrane potential, reducing intracellular calcium concentrations, reducing oxidative stress and reducing nitric oxide. The action of LLLT in abrogating excitotoxicity may play a role in explaining its beneficial effects in diverse central nervous system pathologies. ((Figure: 5a)) Effect of 810-nm laser on intracellular reactive oxygen species (ROS) in cortical neurons with excitotoxicity Figure 5 Effect of 810-nm laser on intracellular reactive oxygen species (ROS) in cortical neurons with excitotoxicity Keywords: low-level laser therapy, cultured cortical neurons, excitotoxicity, reactive oxygen species, mitochondrial membrane potential glutamate, NMDA, kainic acid 1. INTRODUCTION Excitotoxicity is a pathological process by which neurons are damaged and killed by the excessive stimulation of receptors for the excitatory amino acid neurotransmitter glutamate (Glu) in the central nervous system (CNS). Excitotoxicity may be involved in CNS pathologies such as stroke, traumatic brain injury and spinal cord injury, and is also implicated in neurodegenerative diseases such as multiple sclerosis, Alzheimer's disease, amyotrophic lateral sclerosis (ALS), Parkinson's disease, and Huntington's disease. Low level light (laser) therapy (LLLT) consists of non-thermal red and/or near infrared light (600–1000 nm) delivered from a laser or from a non-coherent light source, shown to have beneficial effects on a wide range of diseases. A growing number of reports have shown a positive outcome for LLLT in diseases and injuries related to the nervous system (both peripheral and central). The exact cellular and molecular mechanisms of LLLT are still under investigation. The most acceptable hypothesis at the cellular level is based on the absorption of red and/or NIR light by cytochrome c oxidase of the cellular respiratory chain localized in mitochondria [1]. The light may either be monochromatic from a laser or broad band from a LED or even a filtered lamp. LLLT promoted axonal growth and nerve regeneration in both rat spinal cord [2, 3] and peripheral nerve injuries [4]. The efficacy of LLLT in the nervous system has been further demonstrated in animal studies showing improved neurological and functional outcome post-stroke [5–7] and post-traumatic brain injury (TBI) [8–13]. LLLT also enhanced emotional response and memory function of middle aged CD-1 mice [14]. Recently, promising results of human studies have been shown in patients with long-term peripheral nerve injury and ischemic stroke [15, 16]. Although the exact mechanisms are yet to be fully understood, LLLT has been used to help tissue repair and wound healing in animal models [17] and rescue neurons from neurotoxic injuries [18–20]. It has been reported that visible light can change the redox state of the cell by producing ROS or by increasing the cellular reduction capability [21]. Previous studies from our laboratory have shown that LLLT (810 nm) increased cellular ATP synthesis, raised mitochondrial membrane potential (MMP) and raised intracellular calcium levels, with a biphasic pattern in murine primary cultured cortical neurons [22]. ROS production and NO release had two peaks, one at low fluence and another at high fluence. We also studied [23] the effect of LLLT (810 nm) on murine primary cultured cortical neurons that had been subjected to oxidative stress-induced by three different agents (hydrogen peroxide, cobalt chloride and rotenone). MMP was raised by LLLT in both stressed and control cells, while ROS was reduced in stressed cells but raised in control cells. In the present work, we report that LLLT protects primary cortical neurons from excitotoxicity caused by three different excitotoxins.