Abstract The distribution of FMRFamide (FMRFa)-like peptides in caiman (Caiman crocodilus) and turtle (Trachemys scripta elegans) brains was studied by im- munohistochemistry. In both species, distinct groups of FMRFa-like immunoreactive (ir) perikarya were present in the medial septal nucleus, accumbens nucleus, nucleus of the diagonal band of Broca, suprachiasmatic area, lat- eral hypothalamic area, and periventricular hypothalamic nucleus. A few FMRFa-ir neurons in the hypothalamic area were located in the neuroepithelial cell lining of the third ventricle. FMRFa-ir fibers were scattered in all ma- jor areas of the brain, from the olfactory bulbs to the rhombencephalon. They formed dense aggregates in the medial septal area, basal telencephalon, median emi- nence, and infundibulum, and adjacent to the fourth ven- tricle. The most obvious difference between the FMRFa- ir systems in caimans and turtles concerned the number of nuclei that contained neurons with this immunoreac- tivity. Eight such clusters were present in the caiman brain, whereas thirteen clusters were found in the turtle brain. The turtle also displayed scattered FMRFa-ir som- ata in the anterior olfactory nucleus, striatum, lateral sep- tal nucleus, medial and lateral cortex, medial forebrain bundle, lateral preoptic area, and lateral geniculate nu- cleus. In the caiman brain, a few FMRFa-ir neurons were noted in the ventrolateral area of the pallial commissure and an even smaller number of ir neurons was found dis- persed in the optic tracts. Neither formed nuclear aggre- gates. The results are compared with those described for other vertebrates. Key words Reptiles · Brain · Evolution · FMRFamide · Immunohistochemistry · Caiman, Caiman crocodilus (Crocodiliä) · Red-eared turtle, Trachemys scripta elegans (Chelonia) Introduction The tetrapeptide FMRFamide (FMRFa: Phe-Met-Arg- Phe-NH 2 ) was originally isolated and characterized from central ganglia of the clam Macrocallista nimbosa (Price and Greenberg 1977). Since then, the presence of FMRFa-like or FMRFa-related peptides has been de- scribed in the nervous system of vertebrates and inverte- brates (Price and Greenberg 1989; Greenberg and Price 1992; Santacana et al. 1995). FMRFa-immunoreactive (ir) neuronal systems have been described in all verte- brate classes, from cyclostomes to mammals (see Dockray et al. 1986; Vallarino et al. 1991, 1994, 1995; Wicht and Northcutt 1992; Boersma et al. 1993; Pestarino and Vallarino 1996; D’Aniello et al. 1996; Wright and Demski 1996; Oelschläger et al. 1998; Pinelli et al. 1999, and references therein). These investigations have shown that FMRFa-like ir material is widely distributed within the brain. It is thus plausible to assume that FMRFa-like peptides play a variety of roles acting as neurotransmitters, neuromodulators, or neurohormones. There is experimental evidence in mammals to indicate a number of physiological and behavioral roles (nocicept- ion, cardiovascular activity, modulation of central pro- cesses related to social behavior) for this tetrapeptide (Tang et al. 1984; Wong et al. 1985; Raffa et al. 1986; Roth et al. 1987; Raffa 1988; Yang and Majane 1990). However, specific functional roles of FMRFa-like pep- tides in the reptile brain are still obscure. This study was supported by an EC-fellowship (B.D’A.), fellow- ships by the Alexander von Humboldt Foundation and the DFG- GK “Organisation und Dynamik neuronaler Netzwerke” (A.G.J.), grants from MURST and the University of Napoli Federico II (R.K.R.), and the DFG (D.L.M.) D.L. Meyer is deceased (22.12.1947–8.6.1999) B. D’Aniello · A.G. Jadhao · D.L. Meyer Department of Neuroanatomy, School of Medicine, University of Göttingen, Kreuzbergring 36, D-37075 Göttingen, Germany C. Pinelli · B. D’Aniello · R.K. Rastogi ( ✉ ) Dipartimento di Zoologia, Università di Napoli Federico II, Via Mezzocannone 8, I-80134 Naples, Italy e-mail: rastogi@unina.it Fax: +39–0–81–7903342 Cell Tissue Res (1999) 298:549–559 © Springer-Verlag 1999 Digital Object Identifier (DOI) 10.1007/s004419900112 REGULAR ARTICLE Biagio D’Aniello · Claudia Pinelli · Arun G. Jadhao Rakesh K. Rastogi · Dietrich L. Meyer Comparative analysis of FMRFamide-like immunoreactivity in caiman (Caiman crocodilus) and turtle (Trachemys scripta elegans) brains Received: 12 March 1999 / Accepted: 30 July 1999 / Published online: 19 October 1999