In vitro frog sciatic nerve as a peripheral nerve model for studies of the mechanism of action of low energy lasers: Part one

Evaluation of low-level laser therapy in the treatment of masticatory muscles spasticity in children with cerebral palsy

Spasticity is a motor disorder frequently present in individuals with cerebral palsy (CP). This study aimed to evaluate the effect of low-level laser therapy (LLLT) on the spasticity of the masseter and anterior temporal muscle fibers in children with CP over three weeks of intermittent laser exposures. The bite force (BF) of the masticatory muscles and the amplitude of mouth opening were evaluated before and after laser irradiation in 30 children with CP. Both sides of the masseter and temporalis muscles were irradiated with low-intensity diode laser pulses of 808-nm wavelength six times over three consecutive weeks. During the subsequent three weeks of postlaser exposures, although no laser treatment was applied, the evaluation parameters were measured and recorded. A significant improvement in the amplitude of mouth opening and a decrease in the BF were observed in the weeks following LLLT (P<0.05 ). However, by the sixth week post-LLLT, the BF and the amplitude of mouth opening reverted to values equivalent to those obtained before the first application of LLLT. Our investigation revealed low-level energy exposures from a 808-nm diode laser to be an effective short-term therapeutic tool. This method increased the amplitude of mouth opening and decreased the muscle tonus of children with spastic CP over a time course of three weeks of intermittent laser applications.

Effects of low level laser treatment on the survival of axotomized retinal ganglion cells in adult Hamsters

Injury to axons close to the neuronal bodies in the mammalian central nervous system causes a large proportion of parenting neurons to degenerate. It is known that optic nerve transection close to the eye in rodents leads to a loss of about half of retinal ganglion cells in 1 week and about 90% in 2 weeks. Using low level laser treatment in the present study, we demonstrated that treatment with helium-neon (660 nm) laser with 15 mW power could delay retinal ganglion cell death after optic nerve axotomy in adult hamsters. The effect was most apparent in the first week with a short period of treatment time (5 minutes) in which 65-66% of retinal ganglion cells survived the optic nerve axotomy whereas 45-47% of retinal ganglion cells did so in optic nerve axotomy controls. We also found that single dose and early commencement of laser irradiation were important in protecting retinal ganglion cells following optic nerve axotomy. These findings thus convincingly show that appropriate laser treatment may be neuroprotective to retinal ganglion cells.

The use of phototherapy in peripheral nerve regeneration: an updated critical review

This review describes the possible factors that may have contributed to the variability of the results between studies that have assessed the effects of phototherapy on peripheral nerve regeneration. Furthermore, it aims to make recommendations to overcome the methodological shortcomings identified. A search of the literature was conducted. In vitro and in vivo experimental studies and clinical trials were included. Twenty five studies were critically reviewed and showed considerable variability in irradiation parameters, techniques, approaches, length of irradiation courses, experimental injury tools and procedures. Many studies that have investigated the use of phototherapy in nerve regeneration produce positive results. However, the majority of these studies suffered from a number of shortcomings: no evidence of blinding and/or randomizing procedures, lack of specification of irradiation parameters, unspecified and/or inadequate tests in their experimental injury procedures, inappropriate irradiation parameters and/or poor experimental conditions.

Treatment of experimentally induced transient cerebral ischemia with low energy laser inhibits nitric oxide synthase activity and up-regulates the expression of transforming growth factor-beta 1

BACKGROUND AND OBJECTIVES

Nitric oxide (NO) has been shown to be neurotoxic while transforming growth factor-beta 1 (TGF-beta1) is neuroprotective in the stroke model. The present study investigates the effects of low energy laser on nitric oxide synthase (NOS) and TGF-beta1 activities after cerebral ischemia and reperfusion injury.

STUDY DESIGN/MATERIALS AND METHODS

Cerebral ischemia was induced for 1 hour in male adult Sprague-Dawley (S.D.) rats with unilateral occlusion of middle cerebral artery (MCAO). Low energy laser irradiation was then applied to the cerebrum at different durations (1, 5, or 10 minutes). The activity of NOS and the expression of TGF-beta1 were evaluated in groups with different durations of laser irradiation.

RESULTS

After ischemia, the activity of NOS was gradually increased from day 3, became significantly higher from day 4 to 6 (P < 0.001), but returned to the normal level after day 7. The activity and expression of the three isoforms of NOS were significantly suppressed (P < 0.001) to different extents after laser irradiation. In addition, laser irradiation was shown to trigger the expression of TGF-beta1 (P < 0.001).

CONCLUSIONS

Low energy laser could suppress the activity of NOS and up-regulate the expression of TGF-beta1 after stroke in rats.

Acute electrophysiologic effect of pulsed gallium-arsenide low energy laser irradiation on configuration of compound nerve action potential and nerve excitability

BACKGROUND AND OBJECTIVES

We evaluated the acute electrophysiologic effects of low-energy pulsed laser irradiation, measured by extracellular recording technique on compound action potential configuration and nerve excitability in the isolated frog sciatic nerve

STUDY DESIGN/MATERIALS AND METHODS

A pulsed gallium-arsenide (GaAs) laser (wavelength, 904 nm; pulse duration, 220 nanoseconds; peak power per pulse, 27 W; spot size, 0.28 cm(2); total applied energy density, 0.005-2.5 J/cm(2)) was used for the experiment. Sixty isolated nerves were divided into six groups (n = 10), each of which received a different repetition frequency. In each group, action potentials were recorded, before laser irradiation, which served as the control data. The extracellular action potentials were recorded for each combination of 1, 3, 5, 7, 10, 13, and 15 minutes of irradiation time and 4, 8, 16, 32, 64, 128 repetition frequency by using a BIOPAC MP 100 Acquisition System Version 3.5.7 (Santa Barbara USA). Action potential latency, duration of depolarization and repolarization, and the stimulating voltage were measured. Statistical evaluation was performed using linear correlation analysis by SPSS 9.05.

RESULTS

Although there was no correlation between applied energy density and action potential latency, the duration of depolarization and repolarization phases (P > 0.05), there was a weak correlation between applied energy density and stimulating voltage.

CONCLUSIONS

The study showed that low-energy GaAs irradiation at 42 different energy density between 0.005 and 2.5 J/cm(2) generates no effect on action potential configuration and nerve excitability.

Importance of using rigorous statistical methods to analyze low energy laser experimental data: Part two

BACKGROUND AND OBJECTIVE

Numerous authors have reported successful alteration of peripheral nerve action potential characteristics through application of low energy laser irradiation (LELI). The statistical analysis that accompanies many of these reports frequently does not account for the special nature of the data generated in typical LELI experiments. The objective of this study was to evaluate the application of repeated measures linear regression techniques to the analysis of this type of data. Issues of analyzing raw versus normalized data, proper accounting for correlation between measurements, and discrete time point hypothesis testing were addressed.

STUDY DESIGN/MATERIALS AND METHODS

The data analyzed in this work were generated from an experiment in which in vitro frog sciatic nerves were irradiated with a helium-neon laser using a variety of treatment protocols. Compound action potential (CAP) amplitude, latency, depolarization rate, and repolarization rate were recorded at 1-minute intervals for 135 minutes for each nerve. Laser-induced changes in CAP parameters were analyzed using various repeated measures linear regression models.

RESULTS

The findings of statistical significance were highly dependent on the rigor of the regression model applied. Application of the same regression model to raw and normalized data produced different findings of significance. Determination of significant contrasts was highly dependent on how well the regression model accounted for the correlation between repeated measurements made on the same nerve. In general, models that failed to account adequately for this correlation produced more findings of significant contrasts than increasingly rigorous models. Finally, discrete time point hypothesis testing on normalized data can suggest improper statistical conclusions if the proper correlation structure is not applied to the data set.

CONCLUSION

Linear regression analysis offers advantages over discrete time point hypothesis testing in the analysis of highly correlated serial data of this type. Trends in the behavior of the measured parameters are evident, rigorous accounting for correlation between measurements is facilitated, and hypothesis testing is highly flexible.

Effect of HeNe and pulsed Nd:YAG laser irradiation on intradental nerve responses to mechanical stimulation of dentine

BACKGROUND AND OBJECTIVE

Our study aimed to determine how lasing affected intradental nerve responses to dentine stimulation. Study Design/Materials and Methods Intradental nerve activity was recorded from canine teeth of anaesthetised ferrets. Dentine exposed at the tip of the tooth was stimulated with a glass probe. After determining baseline responses to mechanical stimulation, dentine was lased using a pulsed Nd:YAG laser at 60-150mJ/pulse and 10-30 pulses/sec (total power = 0.3-3.0 W).

RESULTS

The HeNe aiming beam alone and Nd:YAG laser at 0.3 W (+ HeNe) had no effect on intradental nerve responses to dentine stimulation. Lasing at 0.6-1. 5 W could either enhance or suppress intradental nerve responses. Lasing at more than or equal to 2.0 W or repeated lasing at lower intensities depressed intradental nerve responses. Lasing often induced intradental nerve firing.

CONCLUSION

HeNe lasing had no effect on intradental nerve excitability. The Nd:YAG laser could depress intradental nerve responses to dentine stimulation.