Electron microscopic observations of the trigeminal mesencephalic nucleus in the frog, Rana ridibunda

The trigeminal mesencephalic nucleus (Mes V) of the frog Rana ridibunda, has been studied by means of electron microscopic techniques. Mes V neurons are large (20-30 microns in diameter). They are dispersed in the optic tectum and show round to oval cell bodies. Both multipolar and unipolar cells were observed. Their cytoplasm is very rich in organelles with well-developed rough endoplasmic reticulum that forms prominent and scattered Nissl bodies. Numerous small mitochondria, Golgi dyctiosomes, neurotubules and neurofilaments are distributed among the granular endoplasmic reticulum. A striking feature is the existence of abundant lysosome-like particles throughout the cytoplasm. In the surface of Mes V neurons spinous processes are absent and synaptic contacts on the perikarya are scarce. Two types of synapses, one with spherical translucent vesicles and the other with elongated translucent vesicles, contact on either the cell body or the dendrites of Mes V cells.