“…and 5-HT systems in the brain has been obtained by using different methodological approaches such as fluorescence histochemistry, immunocytochemistry of enzymes, amine uptake, radioenzymatic assays, and HPLC (Pares-Herbute et al, 1989, and references cited therein). Similarly, isolated reports of the ontogenetic development of enkephalin and tachykinin neurons using immunocytochemistry or radioimmunoassay for the determination of peptide levels, ligand binding studies for receptors, and Northern blot analysis or in situ hybridization histochemistry for the determination of the abundance of peptide-encoding mRNAs are available (Bayon et al, 1979;Patey et al, 1980;Inagaki et al, 1982;Palmer et al, 1982;Pickel et al, 1982;Tsang et a]., 1982;McDowell and Kitchen, 1987;Schwartz and Simatov, 1988;Yoshikawa and Aizawa, 1988;Diez-Guerra et al, 1989;Tecott et al, 1989;Haverstick et al, 1990). The peptide measurements in the ontogenetic studies were by and large done with immunocytochemical methods, which have the advantage of demonstrating the topographical and structural distribution.…”