The nucleus of the optic tract (NOT) is the visuo-motor relay between
the retina and preoculomotor structures in the pathway mediating optok
inetic nystagmus (OKN). NOT lesions in monkeys produce no OKN toward t
he lesioned side. Then, efferent fibers from the NOT course through th
e brainstem and may reach the vestibular nucleus, which is proposed to
be the final nucleus to the motor nucleus. In the present study, the
tracer was injected through a micropipette in the NOT in four monkeys.
Labeled terminals were observed ipsilaterally in the parabigeminal nu
cleus, superficial layers of the superior colliculus, dorsal and later
al terminal nuclei of the accessory optic system and pretectal nuclei
and contralaterally in the NOT and superficial layers of the superior
colliculus. Descending fibers from the NOT consisted of two major path
ways: (1) fibers descended medially from the injection site through th
e reticularis pontis oralis to reach the lateral part of the ipsilater
al nucleus reticularis tegmenti pontis; (2) fibers projecting into the
dorsal cap of inferior olive, by far the greatest number of labeled f
ibers, descended ventrally along the lateral border of the reticularis
pontis oralis and reached the medial lemniscus where they descended f
urther and branched into the dorsolateral pontine nucleus, the lateral
part of the nucleus reticularis tegmenti pontis, the peduncular ponti
ne nucleus, the lateral pontine nucleus, the nucleus prepositus hypogl
ossi, the medial vestibular nucleus and finally the dorsal cap of the
inferior olive. Consistent with the physiological data, the direct ter
minals to the medial vestibular nucleus could serve to drive the stora
ge mechanisms and to produce OKN in the monkey.