Fine structure of the mesencephalic nucleus of the trigeminal nerve in the rat.

Since Cajal's day, numerous morphological and neurophysiological studies on the mesencephalic nucleus of the trigeminal nerve have accumulated (CAJAL, 1909; MAY and HORSLEY, 1910; WEINBERG, 1928; CORBIN and HARRISON, 1940; SZENTAGOTHAI, 1948; etc.). On the basis of these studies, it is generally accepted that the peripheral processes of the large unipolar cells terminate in the muscles of mastication as proprioceptive afferent fibers, while their collaterals end in the motor nucleus of the trigemin al nerve. Recently, evidence for the bilateral relationships between the mesencephalic nuclei and masticatory muscles has been obtained in an experimental study by SMITH and his co-workers (1967, 1968). After peripheral section of the branches of the trigeminal nerve, DAULT and SMITH (1969) found anatomical evidence of bilateral distribution of peripheral fibers from the mesencephalic nucleus. On the other hand, some histochemical studies (NAKAJIMA, 1965; MAEDA, 1966; etc.) had given new information about enzyme distribution and metabolism of the mesencephalic nucleus, which needed to be correlated with the fine morphological structures. However, electron microscopic studies of this nucleus were lacking except for an observation of the mouse by HINRICHSEN and LARRAMENDI (1968). Under these circumstances, it seemed necessary to perform an electron microscopic study of the nucleus of normal rats with speciall reference to the perikaryal structure and synaptic organization which would serve to advance the functional and biochemical analysis of this nucleus.