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The midgut of 5th instar male African migratory locust, Locusta migratoria, was found to contain endocrine-like cells that stained positively for FMRFamide-like immunoreactivity. These cells have cell bodies which are tear-drop in shape with processes extending from the cell body. FMRFamide-like immunoreactivity has been described in similar cells in adult midgut tissue [16]. The midgut tissue content of FMRFamide-like immunoreactivity is differentially distributed throughout various regions of the midgut (gastric cecae, anterior and posterior midgut) in 5th instar and varied ages of adult. FMRFamide-like immunoreactivity in midgut tissues decreases significantly by 24 h of starvation, whereas locustatachykinin I-like immunoreactivity does not decrease until 48 h of starvation indicating that there are differential timing effects of there two peptide families on midgut content. HPLC analysis, combined with RIA, of different regions of the midgut tissue from both fed and starved locusts revealed that the relative proportions of the members of the two peptide families vary depending upon the feeding state. These results indicate that the contents of these endocrine-like cells appears to be differentially influenced by the feeding state of the locust. (C) 2001 Elsevier Science Inc. All rights reserved.