O’NEILL, M. W.*; GIBB, A. C.; Northern Arizona University; NAU: Selective chemical denervation of pectoral fin muscles using botulinum toxin

Recent use of botulinum toxin in mammals suggests that it could be used to chemically denervate specific muscles to test functional hypotheses without regional or systemic effects. We used Type A botulinum toxin complex to denervate one of two adjacent pectoral fin adductors in the green sunfish, Lempomis cyanellus: the abductor profundus and the abductor superficialis. We injected the right side a. superficialis with 2 MU of botulinum toxin diluted in 2 &mu L of saline using a 5 &mu L Hamilton syringe. The left side a. superficialis was injected with the same volume of saline solution. No injections were made into the a. profundus. After a recovery period of 7 to 10 days, we implanted EMG electrodes into the right and left side a. superficialis and a. profundus and recorded muscle activity during station holding. Normal activity was recorded for both a. profundus muscles and the a. superficialis that received the sham injection; little or no activity was recorded for the a. superficialis that received the injection of botulinum toxin. This demonstrates that the toxin can be used to eliminate the contribution of a particular muscle to test functional hypotheses, without fear of the toxin also reducing the activity of adjacent muscles. Several differences from botulium toxin denervation studies in mammalian systems were noted. First, a higher concentration of toxin is required for denervation. Second, denervation does not last as long as in mammalian studies; the muscle recovers in 2-3 weeks, instead of the expected 2 or more months. Additionally, we suggest that this technique might be difficult for very small or deep muscles; though the toxin does not appear to diffuse across muscle fascia, it might enter non-target muscles through the hole created during the injection process.