The pharmacology of the isolated foregut of the locust schistocerca gregaria—I. the effect of a range of putative neurotransmitters

Abstract 1. Isolated locust foreguts exhibited little or no spontaneous contractile activity. 2. Proctolin (10 −9 m-10 −6 m) caused rapid and powerful contraction of the tissue while the response to similar doses of l -glutamate was much weaker. 3. 5-HT (10 −8 M-5 × 10 −6 M), acting at ketanserin-sensitive receptors, was the most powerful tissue relaxant tested. 4. Relaxation caused by octopamine (10 −7 M-10 −5 M), acting at ketanserin-insensitive receptors was less than 50% of that caused by similar concentrations of 5-HT. 5. ACh (10 −5 M-10 −3 M) induced relaxation, mimicked by nicotine and antagonised by d -tubocurarine, was seen only in the presence of the anti-cholinesterase neostigmine.