The data regarding the identity of motilin like immunoreactivity in the central nervous system are controversial. The aim of the present study was to clarify whether motilin mRNA is present in the brain of rabbit and man. Total RNA, prepared from several regions of the rabbit brain, was subjected to RT-PCR aimed at amplifying a 294 bp cDNA fragment of the rabbit motilin precursor. The amplified product was subcloned and sequenced. The sequence showed 7 differences compared to the one reported for the duodenal precursor (1). However the duodenal precursor from the rabbit used in the present study revealed identical substitutions. One of these, involving amino acid -11 of the signal peptide, was shown to be due to gene polymorphism, as has also been described at this site in man. By radioimmunoassay the highest concentration of motilin (fmol/mg protein) was detected in the hippocampus (4788 +/- 295), the lowest in the telencephalon (2127 +/- 221). Using a similar approach, but starting from commercial human brain mRNA, the sequence of a comparable cDNA fragment of the human brain motilin precursor was obtained. Its sequence was identical with the one published for the human intestinal precursor (41). Our study demonstrates that motilin mRNA is present in the brain of man and rabbit. Together with our recent findings of central motilin receptors, they suggest a central role for motilin. (C) 1997 Elsevier Science Inc.