Spinal reflexes in cat after intravenous saxitoxin and tetrodotoxin

Abstract

Solutions of saxitoxin or of tetrodotoxin have been given by slow i.v. infusion to artificially ventilated acute spinal cats. Monosynaptic and polysynaptic hindlimb reflexes were reduced in amplitude when the dose reached 2·4–7·8 μg per kg, but in almost all cases this reflex loss was solely due to a peripheral block in the afferent nerves. No significant changes were found in reflex patterns of post-tetanic potentiation, inhibition or facilitation even after the toxin had partly blocked the responses at the spinal cord roots. Central actions are not likely to be important in cases of acute intoxication, perhaps because the toxins do not easily cross the blood-brain barrier into the central nervous system.