Morphometric characterization of transmitter-identified nerve cell groups: analysis of mesencephalic 5-HT nerve cell...

Morphometric techniques have been used to introduce criteria to objectively define transmitter-identified nerve cell groups and subpopulations of nerve cells within such groups. The present method is exemplified on two coronal sections of the midbrain, in which 5-HT immunoreactive nerve cell bodies have been visualized. The reliability of the method is shown by the fact that it makes it possible not only to recognize groups B7, B8 and B9 of Dahlström and Fuxe [5] but also to assess the existence of two subpopulations within group B7 as previously suggested by Fuxe and Jonsson [11] based on subjective evaluations. Furthermore, the suggestion could be made that a small assembly of 5-HT nerve cell bodies in the dorsal part of the mesencephalic tegmentum may form a new 5-HT cell group. Hence, the present method offers the advantage of assessing the existence of transmitter-identified nerve cell groups on the basis of objective criteria and to describe them in a quantitative fashion. Therefore, it allows quantitation of morphological changes occurring in transmitter-identified neurons under different experimental and pathological conditions.