Effect of halothane anesthesia on responses from primary endings of muscle spindles in the cat

The effect of halothane anesthesia was tested on the responses from primary endings of deefferented muscle spindles. Recordings from spindles of the tenuissimus muscle during constant velocity stretches of the muscle revealed that halothane augments the response during stretch. The static or dynamic action of single fusimotor fibers, although being modified, was not fundamentally altered in the presence of the gas. Whereas the increase in phasic sensitivity of a spindle produced by stimulation of a dynamic fusimotor fiber was less marked during halothane anesthesia, the decrease in phasic sensitivity during static fusimotor stimulation remained unaffected or was slightly raised.