Two populations of serotonin-immunoreactive neurons in the frog (Rana esculenta) retina

Serotonin immunocytochemical staining in retina whole-mounts of Rana esculenta revealed two differently stained amacrine cell populations. Statistical investigations using nearest neighbor analysis and comparison with different theoretical cell distributions suggested that the two serotonin-immunoreactive cell populations are related to functionally different types. The analysis of type A (intensely stained somata, less numerous) revealed a good coincidence with the normal Gaussian distribution indicating a functionally homogeneous population. The distribution of the neurons of type B (weakly stained somata, more numerous) reflects rather a random dot pattern than a regular arrangement. Thus there is evidence that this last type is a heterogeneous cell population consisting of several functionally different types.