FMRF-NH2-like factor from neurohaemal organ modulates neuromuscular transmission in the locust.

YGGFMRFamide, FMRFamide and related peptides potentiate transmission at locust slow motor synapses. Since immunohistochemical evidence points to neurohaemal organs (NHO) as potential sources for endogenous RFamide-like peptides we have applied extracts from the metathoracic NHO, equivalent to 1/3 NHO, to the metathoracic extensor tibiae muscle. NHO-extract depolarizes the muscle fibre and increases its membrane resistance; enhances transmitter release; and increases the amplitude of contraction and the rate of relaxation. These effects are in good qualitative and quantitative agreement with those of YGGFMRFamide (5 X 10(-8) to 10(-7) M). Octopamine which partly acts like YGGFMRFamide cannot account for the NHO-effects.