Dendrobine, an antagonist of beta-alanine, taurine and of presynaptic inhibition in the frog spinal cord.
1 The effects of dendrobine and nobiline, alkaloids isolated from Dendrobium nobile, on the electrical activity and on amino acid-induced depolarizations of primary afferent terminals were tested on the frog isolated spinal cord and were compared with those of picrotoxinin and strychnine. 2 Dendrobine (3 X 10(-5) M) caused a slight hyperpolarization in both dorsal and ventral roots and this hyperpolarization was accompanied by the augmentation of the dorsal root potential (DR-DRP) and the ventral root potential and reflex (DR-VRP and DR-VRR). The amplitude of the dorsal root reflex (DR-DRR) however, was reduced significantly. Nobiline (3 X 10(-5) M) had no significant effect on either the root potentials or the reflexes. 3 Dendrobine (3 X 10(-5) M) reduced the dorsal root potential induced by repetitive antidromic stimulation of ventral root (VR-DRP) as well as diminishing the maximum rate of rise of the dorsal root potential induced by the stimulation of adjacent dorsal roots (DR-DRP), during which time the amplitude of the DR-DRP was seen to be augmented. 4 Dendrobine (3 X 10(-5) M) reduced the beta-alanine- and taurine-induced depolarizations of primary afferent terminals, while having little effect upon GABA- and glycine-induced depolarizations. 5 Dendrobine (10(-5) M) reversibly blocked the presynaptic inhibition caused by antidromic conditioning stimulation of the ventral root. 6 These effects of dendrobine were qualitatively similar to those of strychnine but were somewhat different from those of picrotoxinin, a molecule having the same picrotoxane skeleton. 7 The present results are discussed with reference to the likely neurotransmitters involved in presynaptic inhibition in the frog spinal cord, and with respect to the structure-activity relationship of picrotoxane compounds as amino acid antagonists.
D000200:Action Potentials / Q000187:drug effects; D000409:Alanine / Q000037:antagonists & inhibitors*; D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D004558:Electric Stimulation; D066298:In Vitro Techniques; D009433:Neural Inhibition / Q000187:drug effects; D011892:Rana catesbeiana; D013116:Spinal Cord / Q000187:drug effects*; D013569:Synapses; D013654:Taurine / Q000037:antagonists & inhibitors*; D013997:Time Factors; D015091:beta-Alanine / Q000037:antagonists & inhibitors*
D000470:Alkaloids; D015091:beta-Alanine; D013654:Taurine; C002077:dendrobine; D000409:Alanine