Journal of Neuroscience Methods, 10 (1984) 83-101 83 Elsevier NSM 00361 Research Papers A method for rostrocaudal integration of morphometric information from transmitter-identified cell groups. A morphometrical identification and description of 5-HT cell groups in the medulla oblongata of the rat * L.F. Agnati 1, K. Fuxe 2 L. Calza 1, I. Zini 1 T. H6kfelt 2, A. Steinbusch 2 and A. Verhofstad 3 I Departments of Human PhysioloD' and Endocrinology, Unwersity of Modena, Modena, (Italy), 2 Department of Histology, Karolinska Institutet, Stockholm (Sweden) and 3 Department of Anatomy and Embryology, Catholic University, Nijmegen (The Netherlands) (Received February 4th, 1983) (Revised September 28th, 1983) (Accepted December 23rd, 1983) Key words: morphology--5-HT--morphometry--immunocytochemistry--cell body parameters--cell group parameters--rostro-caudal integration--medulla oblongata A method has been developed to integrate rostrocaudal information from morphometrically char- acterized 5-HT nerve cell groups visualized by means of the indirect immunofluorescence technique in single coronal sections of the neuroaxis. The present method has been applied to the 5-HT positive cells of the medulla oblongata of the rat. 5-HT cell body and cell group parameters were measured by the use of a semiautomatic image analyzer (Kontron, MOP AMO 2) plugged into an Apple II computer. The density distribution of 5-HT positive cells was also studied by dividing the area analyzed into unitary squares (about 120× 120 p,m) and then by considering the number of 5-HT cells falling in each of these squares. The existence of a 5-HT cell group was determined by testing the randomness of the 5-HT profiles per unitary square. The entire population of 5-HT positive cells as well as the 5-HT cell groups were described in terms of gravity center coordinates, mean maximal diameter and homogeneity index. A rostrocaudal representation of the gravity centers and of the dispersion of the 5-HT nerve cell groups around them provided an exact three-dimensional description of the respective locations of the 5-HT cell groups within the medulla oblongata. These methods can be applied to all types of transmitter-identified cell groups and at any level of the neuroaxis. * In memory of Professor Giorgio Montanari, professor at the Medical Faculty of Modena. Correspondence." K. Fuxe, Department of Histology, Karolinska Institutet, Box 60400, S-104 01 Stock- holm, Sweden. 0165-0270/84/$03.00 © 1984 Elsevier Science Publishers B.V.