Both presynaptic nicotinic-like and muscarinic-like autoreceptors regulate acetylcholine release at an identified neuro-neuronal synapse of Aplysia.
The possible involvement of cholinergic presynaptic receptors regulating evoked quantal acetylcholine (ACh) release was investigated at an identified cholinergic neuro-neuronal synapse in the buccal ganglion of Aplysia, using cholinergic agonists (carbachol, pilocarpine, oxotremorine) and/or antagonists (curare, atropine, hexamethonium). Bath applied carbachol or pilocarpine (10(-8) M to 10(-4) M) induced a decrease in the evoked quantal release of ACh. As the effects of carbachol were prevented by atropine (5.10(-6) M) and not by curare (10(-5) M), it was concluded that carbachol activated presynaptic muscarinic-like receptors implicated in a negative feed-back on ACh release. On the contrary, oxotremorine (up to 10(-4) M) induced a potentiation of ACh release which was suppressed by curare (4.10(-6) M) or hexamethonium (10(-5) M) but not by atropine (5.10(-6) M) pointing to the activation of presynaptic nicotinic-like receptors implicated in a positive feed-back on ACh release. Moreover, in the presence of curare, oxotremorine decreased ACh release: this suggested that oxotremorine also activated the presynaptic muscarinic-like receptors. These results revealed the conjoint presence, on the same terminal, of both muscarinic-like and nicotinic-like autoreceptors.
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D001048:Aplysia / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology; D003472:Curare / Q000494:pharmacology; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D009116:Muscarine / Q000502:physiology; D010095:Oxotremorine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010862:Pilocarpine / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000502:physiology*; D011978:Receptors, Nicotinic / Q000502:physiology*; D013569:Synapses / Q000378:metabolism*
D006584:Hexamethonium Compounds; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D010862:Pilocarpine; D018738:Hexamethonium; D010095:Oxotremorine; D009116:Muscarine; D003472:Curare; D002217:Carbachol; D000109:Acetylcholine