Microneurography in anesthetized rats for the measurement of sympathetic nerve activity in the sciatic nerve

Microneurography is widely used for the measurement of human peripheral sympathetic nerve activity (SNA) in conscious subjects by virtue of its low invasive nature, but has rarely been employed in animal experiments. Because the low invasive nature sometimes is very useful even in animal experiments, we tested its feasibility for the measurement of SNA in the sciatic nerve of the anesthetized rat, aiming in particular to establish a methodology for measurement. A tungsten microelectrode was inserted into the nerve exposed at the thigh level to detect the "spontaneous, intermittent burst" signal that is one of the main characteristics of compound SNA. Such signals were found in more than 70% of experiments after surgical operators became accustomed to the method. Whenever such signals were detected, electrical stimulation of the sympathetic chain resulted in induced action potentials detected with the microelectrode after a reasonable conduction period. The spikes were successfully reduced after administration of hexamethonium bromide, a sympathetic ganglion blocker. On the other hand, induced spikes were never observed when we failed to find the "spontaneous, intermittent burst" signal. The results demonstrate the feasibility of microneurography in evaluating SNA in anesthetized small animals, and that the "spontaneous, intermittent burst" signal may be sufficient to identify SNA.