Effect of Dendroaspis neurotoxins on synaptic transmission in the spinal cord of the frog

Abstract

Six neurotoxins from Dendroaspis venom, and α -bungarotoxin, were tested on a cholinergic synaptic pathway in the isolated spinal cord of the frog. Four dendrotoxins, which block neuromuscular transmission, also blocked the cholinergic pathway in the spinal cord. In both cases the block is slowly reversible and not due to presynaptic action. The dendrotoxins appear to act by blocking acetylcholine receptors and are therefore potentially useful for the localization and isolation of acetylcholine receptors in the central nervous system of vertebrates.

Effects of some divalent cations on synaptic transmission in frog spinal neurones.

“…Experiments were performed on the isolated and heinisected spinal cord of the frog, Rana temporaria. The method of isolating the cord and recording the root potentials was essentially that used in previous work (Katz & Miledi, 1963;Miledi & Szczepaniak, 1975). After sagittal hemisection, the hemi-cord was transferred to a chamber (3 5 ml.…”

A Re‐evaluation of Acetylcholine Receptors on Feline Renshaw Cells

“…a-Bungarotoxin is ineffective in blocking the early discharge or ACh-evoked excitation of cat Renshaw cells (Duggan, Hall & Lee, 1976) and it does not block a cholinergically-mediated dorsal root potential in the frog spinal cord (Miledi & Szczepaniak, 1975), which demonstrates a further difference between nicotinic receptors on Renshaw cells and at the neuromuscular junction.…”

Convulsant and Possible Anticholinergic Actions of Dendrotoxin in the Amphibian Spinal Cord

“…Since Miledi & Szczepaniak (1975) blocked by a-bungarotoxin (25,ug/ml) or atropine (1.4 p,M). Neither mecamylamine, a-bungarotoxin nor atropine showed any tendency to induce DTOXlike convulsant activity.…”

“…Since dendrotoxins (DTOX) are known to block neuromuscular transmission (Banks, Miledi & Shipolini, 1974) and the polysynaptic VR-DRP pathway contains a cholinergic synapse (Kiraly & Phillis, 1961;Mitchell & Phillis, 1962;Barker, Nicoll & Padjen, 1975b;Kudo, 1978), the blockade of this response has been attributed to a central antinicotinic action of the toxin (Szczepaniak, 1974;Miledi & Szczepaniak, 1975; see also, Patrick, Stallcup, Zavanelli & Ravdin, 1980). The mechanism whereby the toxin induces convulsant activity is not known.…”

“…Toxin fractions isolated from the venom of the green mamba, Dendroaspis viridis promote convulsant activity and antagonize the ventral root-dorsal root potential (VR-DRP) of the amphibian isolated hemisected spinal cord (Miledi & Szczepaniak, 1975;Smith, Padjen, Quik & Collier, 1980;Quik, Smith, Padjen & Collier, 1980). Since dendrotoxins (DTOX) are known to block neuromuscular transmission (Banks, Miledi & Shipolini, 1974) and the polysynaptic VR-DRP pathway contains a cholinergic synapse (Kiraly & Phillis, 1961;Mitchell & Phillis, 1962;Barker, Nicoll & Padjen, 1975b;Kudo, 1978), the blockade of this response has been attributed to a central antinicotinic action of the toxin (Szczepaniak, 1974;Miledi & Szczepaniak, 1975; see also, Patrick, Stallcup, Zavanelli & Ravdin, 1980).…”