THE PUPILLOCONSTRICTOR AND PUPILLODILATATOR RESPONSE AREA IN THE PRETECTAL REGION, MESENCEPHALIC CENTRAL GRAY MATTER AND ITS PERIPHERY IN CATS.
Authors: Matsushita Taizo 
Published: March 2008

For the purpose of determining the pupillary light reflex pathway, there were given on 47 adult cats the electrical stimulation of alternating current and square wave on the pretectal region, mesencephalic central gray matter and its periphery. Observation went focused on the constrictor and dilator responses, eventually with accompanying symptoms. The stimulated regions were examined on the serial sections subsequently.

The chief result thereof are as follows:

1. The alternating current and the square wave were used as means of stimulation, but there was little to choose between them in this stimulation experiment, as it was chief aim here to get determined the pupillary light reflex pathway.

2. Bilateral constriction was producible from the brachium of the superior colliculus, the nuclei of the pretectal region, the posterior commissure and its interstitial nucleus and the medial longitudinal bundle and ipsilateral constriction from the constrictor nucleus and the root fiber of the oculomotor nerve. There was little difference between either sides concerning the degree of bilateral constriction.

3. The constrictor response areas in the pretectal region were found in Area pretectalis, Nucl. lentiformis mesencephali pars parvocellularis and Nucl. sublentiformis.

4. The constrictor responses in the midline part of the posterior commissure occurred much strong in the dorsal zone composed of the fine medullated fibers, thus rendering much suggestive of passing of the light reflex pathway through the said zone.

5. Also the medial longitudinal bundle reacted as bilateral constrictor, thus passing of the light reflex pathway to the constrictor nucleus made much presumable in the way: partly through direct adjoining from the descending peduncles of the posterior commissure and partly after a reversal turn through the said bundle.

6. From the fact that all the above mentioned constrictions occur always bilaterally, conclusion is drawn now that partial decussation of the light reflex pathway takes place once in the posterior commissure.

7. The constrictor nucleus is composed of a pair of medium‐sized cell groups located within the central gray matter lying dorsoanteriorily to the main oculomotor nerve nucleus. Its rostral part nearly coincides with the extent described by Yoshioka, the caudal part reaches the middle level of the main oculomtor nucleus while the more caudally lying region gives hardly reaction as constrictor but rather as dilatator.

8. The fact that bilateral constriction is producible from the descending peduncle of the posterior commissure and the medial longitudinal bundle whereas ipsilateral constriction is produced at the constrictor nucleus does quite positively favor the view speaking for presence of secondary prenuclear decussation in the ventral side beneath the primary decussation on the posterior commissure in cat.

9. On the basis of the above mentiond results, the pupillary light reflex fiber of cat is supposed to start from the optic tract, to run through the brachium of the superior colliculus, then proceed scatteredly into the nuclei of the pretectal region. At the synapses of the region, it switches over the second neuron and the latter reaches the constrictor nucleus located at dorsoanterior to the main oculomotor nerve nuclei. This terminal is reached through 3 routes: viz. one part of the fiber reaches it after crossing on the posterior commissure (chiefly at its dorsal zone), another part uncrossed just after trespassing of the descending peduncle of the posterior commissure and still another part after passing the medial longitudinal bundle. Besides, though still lacking of an anatomical evidenece, the secondary decussation is higly expectable at its ventral side.

10. From the comparative study of the light reflex pathway concerning both rabbit and cat, the chief points of difference are to be mentioned as follows: the pathway of cat builds up the brachium of the superior collicus and reaches the pretectal region under relatively dense flocking, while it builds up in rabbit the dorsolateral archiform fiber and tractus sublentiformis and reaches the terminal relatively scattering; the primary decussation of the pathway in the posterior commissure is done only partly in cat, while comletely in rabbit, the secondary decussation at the ventral side prior to the terminal nucleus must be expected in cat while an ipsilateral connection takes really place in rabbit between the constrictor nucleus and the descending peducnle of the posterior commissure.

11. The dilator response areas are so widely distributed in the thalamus, hypothalamus and midbrain whithout showing definite localization.

12. Nystagmus and nystagmoid movement are observed upon stimulation of Fasciculus longitudinalis medialis and its periphery, the midline part of the posterior commissure and its proximity. Besides, the stimulation on such tegmental bundles as Fasciculus tegmentalis centralis et medialis caused forced posture such as decline of head to the stimulated side as well as concave bending of body axis towards the same side.