Low-energy He-Ne laser irradiation (LELI) was found to affect the electric activity and morphology in both intact and severely injured peripheral nerves in rats. Action potential (AP) in the healthy nerve increased by 33% following a single transcutaneous irradiation. Similar irradiation in crushed nerves caused AP to increase significantly over the AP of nonirradiated crushed nerve. Morphological observations revealed that a laser-irradiated injured nerve had diminished scar tissue as compared to an injured but not an irradiated nerve.

The effect of low energy CW HeNe laser irradiation on normal and dissected nerves in the rat was examined. The methods are described. Results are compared to the laser effect on other living tissues. HeNe irradiation was found to increase significantly the action potentials of the nerves. It was found to be a long-lasting effect, keeping an increase in the nerves action potential for more than eight months after irradiation has been stopped. A possible explanation for the way the irradiation acts on the nerve is suggested.

To study the in-vivo effects of direct Low-Energy Laser Irradiation (LELI) on the Peripheral Nervous System, the sciatic nerve in rats was surgically exposed, crushed and then subjected to the direct irradiation of either of two continuous-wave HeNe lasers--0.3 mW or 17 mW. We found that the 0.3 mW laser significantly boosts the electrical activity in both the injured and non-injured nerves. The temperature changes of the nerve were measured during irradiation, and no thermal effect was detected. These findings could have direct therapeutic applications in various surgical situations.

Injury to a mammalian peripheral nerve is accompanied by a restorative process that is manifested after a delay. This process is expressed morphologically by the emergence of new nerve fibers. Restoration of function occurs when the regenerating fibers reconnect with the target organ. Because of the low rate of fiber elongation, the denervated target is partially degenerated by the time that the regenerating fibers approach it. To prevent such an atrophy, one must find a way to prevent the degeneration of the nerve, to speed up regeneration, or to maintain the target during the period of nerve degeneration. In the present work, we examined the potential of treatment with low energy laser radiation for improving regeneration or preventing degeneration of mammalian peripheral nerve after injury. After repeated injury for 20 consecutive days, treatment of the sciatic nerve of the rat with low energy laser (He-Ne, 17 mW) caused a significant increase in the amplitude of the action potential recorded in the corresponding gastrocnemius relative to the action potential of injured but not treated nerves. The action potential of the injured sciatic nerves that were laser-irradiated increased to values close to that of a noninjured nerve. The studies include follow-up for 1 year after the injury. This electrophysiological manifestation of the effect of laser treatment on injured nerves was accompanied by a diminution of the size of the scar tissue from these nerves. Yet to be resolved is whether these two phenomena (i.e., electrophysiological and morphological responses) coincide or whether they relate to each other.(ABSTRACT TRUNCATED AT 250 WORDS)

For our study of the effect of low energy laser irradiation (LELI) on living tissue we used HeNe laser on rats. The exponential absorption was reaffirmed in the living tissues overlying the sciatic nerve. An optimal range of energy between 3.5 and 7 J--associated with energy concentration of 4-10 J/cm2 delivered transcutaneously--was found to cause a significant increase in action potential in the sciatic nerve. The effect lasted for more than 8 months after the irradiation session.