Co-occurrence of substance P and enkephalin-like immunoreactivities in the prosencephalon of two amphibians.

We studied the co-occurrence of substance P-(SP) and leucine (or methionine) enkephalin (ENK)-like immunoreactivities in the prosencephalon of two amphibians: Rana esculenta L. (Anura) and Triturus carnifex Laur. (Urodela) using single and double immunohistochemical methods. The two peptides (SP-ENK) were sometimes found colocalized in neuronal cell bodies and processes. Double-labelled neurons were seen in the nucleus accumbens, lateral septal nucleus, preoptic area, dorsal and ventral hypothalamic nuclei of the frog, whereas in the newt co-occurrence was shown in neurons of the primordium pyriform, corpus striatum, pars ventralis thalami, preoptic area and nucleus infundibularis dorsalis and ventralis. Furthermore, in both amphibians, fibres simultaneously showing SP- and ENK-positivity were observed in the amygdaloid complex, preoptic area and in the posterior hypothalamus, around the infundibulum. Co-occurrence studies in comparative neuroanatomy are relevant, as shown in the present paper regarding the similarities of SP-ENK distribution in the striatopallidal and striatonigral systems of tetrapods.