NEUROMUSCULAR EFFECTS OF TOXINS ISOLATED FROM SOUTHERN PRICKLY ASH (ZANTHOXYLUM-CLAVA-HERCULIS) BARK

Objective-To define the nature and mechanisms of neuromuscular effects of toxic principles in bark of Southern Prickly Ash tree (Zanthoxylum clava-herculis) that might contribute to its clinical toxicity in cat tle. Animals-31 rats, 1 dog, and 4 rabbits. Procedures-Extracts were p repared from bark samples, using 2 extraction methods, Contractile res ponses, resting potentials, miniature end-plate potentials (MEPP), and end-plate potentials of rat phrenic nerve-hemidiaphragm preparations were recorded. Blood pressure and contractile responses of the cranial tibial muscle to nerve stimulation were recorded in an anesthetized d og. Topical anesthetic activity in rabbits was determined by evaluatio n of the corneal reflex. Results-One extract usually stimulated muscle contractile response, whereas the other inhibited this response when evoked by nerve stimulation, but not when evoked by direct muscle stim ulation. Inhibitory extract (X(I)) had a hypotensive effect, but lacke d topical anesthetic activity and effect on resting potentials. This e xtract also reduced amplitude of MEPP and end-plate potentials, but di d not affect their time course or the frequency of MEPP. Stimulatory e xtract was not active in presence of neuromuscular blocking agent tubo curarine. Conclusion-Active principles in Southern Prickly Ash extract s appear to exert their action on neuromuscular transmission probably through blockade of postjunctional, end-plate receptors (X(I)) or enha nced release of neurotransmitter (stimulatory extract). Clinical Relev ance-Signs of clinical toxicity in cattle were best correlated with ef fects of X(I), which can be antagonized by Ca2+ and neostigmine.