The pharmacological properties of some crustacean neuronal acetylcholine, gamma‐aminobutyric acid, and L‐glutamate responses.

Abstract

L-glutamate, GABA, and acetylcholine (ACh) responses of cells in the stomatogastric ganglion of the crab, Cancer pagurus were studied. Ionophoretic or pressure application of L-glutamate revealed 3 classes of responses: a K+-dependent inhibition which reversed at 15-20 mV more negative than the resting potential; a Cl- dependent inhibitory response which was at equilibrium at the resting potential; and a depolarizing response. Ionophoretic or pressure applications of GABA likewise produced 3 kinds of responses: an increase in K+ conductance, an increase in Cl- conductance and a depolarizing response. Picrotoxin (10-6-10-5 M) was effective in blocking both the glutamate inhibitory responses. 10-4 M-picrotoxin, necessary to produce a 50% block of the GABA-K+-dependent response, had no effect on the GABA-Cl- response. .beta.-Guanidinopropionic acid (.beta.-GP) was an agonist for the GABA-K+ response, but was ineffective in mimicking or blocking the GABA-Cl- response. ACh applications produced large depolarizing responses with a pharmacological profile similar to that of the nicotinic ganglionic response in vertebrates. The muscarinic agonist, acetyl-.beta.-methyl choline (MeCh), produced depolarizations which decreased in amplitude as the membrane was hyperpolarized from -40 to -100 mV. Pilocarpine and oxotremorine produced changes in the endogenous activity of ganglionic neurons. Implications of these results for identification of synaptic transmitters in the stomatogastric ganglion are discussed.