Abstract
This investigation integrated intracellular recording techniques with a fiber optic laser delivery system to examine the relationship between laser energy irradiation and the ventral nerve cord (VNC) motor neurons excitability of the crayfish. The VNC was used as a model system analogous to motor neurons of vertebrates. Helium-neon laser energy (He-Ne λ 632.8 nm at 3.5 mW) was delivered via fiber optic material directly to point of contact with the nerve cord. The activity of 18 spontaneously active motorneurons from 13 animals was monitored during laser irradiation by means of glass microelectrodes individually placed within each motorneuron. The resultant signal from each individual motor neuron was digitalized and recorded on a MacIntosh LC II computer. Analyzed data demonstrated statistically significant changes, p < this 0.05, in motor neuron membrane potentials following laser irradiation. Observed changes in frequency, amplitude, and duration of spontaneous potentials illustrated a stimulation effect of laser energy on the VNC motor neurons. Individual variations of response to laser irradiation were analyzed in specific specimens. The degree of response variability within separate specimens illustrated evidence of membrane threshold variability. The threshold level of laser energy necessary to evoke an artificial action potential was not seen in this investigation. Increased activity in specific experiments demonstrated a close proximity to membrane threshold levels. Indications were that threshold levels of activation begin above the delivered energy of 3.5 mW. Spontaneously active motorneurons demonstrated photosensitivity to laser irradiation. All indications were that an artificially generated action potential may be produced given adequate energy at the 632.8 nm wavelength; however, delivered energy must exceed 3.5 mW. Further investigation could lead to establishing a threshold level of motor neuron activation.
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