GIBB, AC; O’NEILL, MW; KRAUS, NJ; Northern Arizona University; NAU; St. Norberts College: Chemical denervation: Using botulinum toxin to test functional hypotheses in teleost fishes

Techniques currently used for testing hypotheses in functional morphology, such as transecting nerves, tendons or ligaments, are highly invasive and may cause unintended structural damage, thereby yielding misleading functional results. Botulinum toxin, when injected into muscles, acts upon the neuromuscular junction and limits the ability of nerves to release neurotransmitter (acetylcholine). Thus, injection of Botulinum toxin (or �Botox�) into a muscle via a syringe acts as a minimally invasive mechanism of chemical denervation for that muscle. Botox has been used by the medical community to disable spastic human muscles for decades. To our knowledge, Botox has never been used to test functional hypotheses about vertebrate skeletal muscle. We pioneer this methodology by using Botox to chemically denevate one of the paired adductor mandibulae muscles in smallmouth bass, Micropterus dolomieui and green sunfish, Lepomis cyanellus. Baseline feeding kinematics and adductor mandibulae electromyographic (EMG) profiles were obtained from unmanipulated fish feeding on non-elusive prey. Type A botulinum complex was obtained from Metabiologics, Inc. (Madison, Wisconsin, USA) and .035 µg toxin in 1.5 µL saline (0.7 mouse units) was injected into the adductor mandibulae (.3 µL of muscle) on the left side of the head of these same individuals. Feeding behavior and muscle activity were recorded at two day intervals for up to two weeks. Results indicate that Type A botulinum complex is an effective and minimally invasive way to denervate vertebrate muscle. We suggest this technique can be widely applied by functional morphologists to test specific hypotheses about muscle function in vertebrates.