A comparative and quantitative study of small intensely fluorescent (SIF) cells in the sympathetic ganglia of some small mammals.

This comparative study of the number of SIF cells in the ganglions of the rat, cat, rabbit, mouse and hamster has confirmed that the mean number of SIF cells in the same ganglion of different species varies greatly, for instance in the superior cervical ganglion (SCG) of the rat and the cat, in the stellate ganglion of the cat and the mouse, or in the inferior mesenteric ganglion of the hamster and the other species. There is also considerable variability among individuals of the same animal species. In the SCG, the only ganglion for which there are data on the number of neurons, the ratio of SIF cells to neurons is around 1% in the rat, 0.2% in the rabbit, 0.3% in the mouse and 0.05% in the cat, i.e. a twenty-fold difference between the cat and the rat. Williams et al. (1975) distinguished type 1 SIF cells, corresponding to interneurons, from type 2, which are purely endocrine cells. Type 2 appears to be predominant in all ganglia, except the rabbit SCG where type 1 is highly predominant, and in all species, except the rat, in which this distinction is not applicable. The possible implications of these data on ganglionic functioning are discussed.