Modulation of 5-HT and proctolin receptors by FMRFamide in the foregut of the locust Schistocerca gregaria

Abstract

Initial studies demonstrated that FMRFamide (10 −6M-2 × 10 −4M) caused contraction of the in vitro locust foregut. 2. FMRFamide (2 × 10 −6M) potentiated 5-HT induced relaxation of the foregut. This effect was blocked completely by 5 × 10 −5 M ketanserin. 3. FMRFamide (2 × 10 −6M) inhibited proctolin induced contraction of the foregut. The proctolin response was restored partially in the presence of ketanserin (5 × 10 −5M). 4. FMRFamide induced potentiation of 5-HT relaxation and inhibition of contraction caused by proctolin were abolished by naloxone (10 −5M). 5. It is proposed that FMRFamide sensitizes the foregut 5-HT 2-like receptor and to a lesser extent desensitizes the proctolin receptor by activation of distinct naloxone-sensitive FMRFamide receptors.