The pupilloconstrictor and pupillodilatator response area in rabbits' pretectal region, in the central gray matter of midbrain and its periphery.

Abstract

Summary Using 61 rabbits, we made an observation on the papillary reaction. After exposing the surface of the cerebral cortex or the dorsal surface of the midbrain, concentric electrodes were inserted, and the alternative current of 0.5-5 volt and 60 cycle was given on the pretectal region, the central gray matter and its periphery, the stimulated points amounting to 3,500 in total. The pupillary responses areas were histologically determined afterwards by means of Nissl stain and myelin stain series tracing rabbit's pupillary reflex afferent pathway. The result thereof is as follows: 1. The minimum voltage to cause constrictor response and dilatator response with the alternative current stimulation by needle electrode is 0.5 volt. In certain portions, mere insertion of the electrode produced the responses. Pupillo-constriction concurred in many cases with blephalo-ptosis and pupillo-dilstation with the reopening of eyelids. 2. Wheress the pupillo-constrictor response area was founs localized in the pretectal region, the posterior commissure, the descending peduncle of the posterior commirsure and the central gray matter, the pupillo-dilatator response area was lesser delimited, as widely distributed over the whole midbrain as covering. the radiatio optical, pretectal region, posterior commissure and its descending peduncle, tectum, tegmentum and the central gray matter. 3. The stimulation on the dorsolateral archiform fiber system in connection with the optic tract and the tractus sublentifomis (Kuhlenbeck) caused contralateral pupillo-constricticn and the same was caused by the stimulation on the lateral and medial geniculate body, the latter represen ting the pathway of these two fiber systems and also the pretectal arza (Nucl. praetectalis, Nucl. lentifonnis mesencephali, Nucl. sublentiformis), the locus of termination of the pathway, whereas Area praetectalis lying just adjacent to the lateral surface of the posterior commissure yielded both bilateral and contralateral constriction. 4. Bilateral constriction was producible from the median of posterior commissure; bilateral, homolateral and contralateral constriction from the lateral surface of the posterior commissure; lastly, homolateral constriction from the descending peduncle of posterior commissure, respectively. 5. Regarding the interstitial nuclei, there were obtained both homolateral and contralateral constrictions from Nucl. interstitialis principalis com-missurae posterioris and Nucl. interstitialis supra-commissuralis commis-surae posteroris, while only homolateral constriction was obtainable from the interstitial nuclei located in the lateral part of the descending peduncle of posterior commissure. 6. So far as we could roughly determine the scope of the constrictor nucleus in the central gray matter, a small-cell group found between fasciculus longitudinalis dorsalis and faxiculus longitudinalis medialis lying in the dorsal part of Darkschewitsch nucleus (Kuhlenbeck) and about 200 μ anterior to the main oculomotor nucleus produced the constriction. It runs farther about 1,200 μ along the dorso-oral to the dorsal side of the oculomotor nucleus downward to the middle of the same. 7. Homolateral constriction was obtained from the main oculomotor nucleus and oculomotor fibers. 8. Besides homolateral constriction. dilatation was also obtainable from the fasciculus longitudinalis medialie. 9. Dilatation was obtained from the radiatio optica, ventromedial archiform fiber system (Kuhlenbeck) and tractus praetectalis descendens (Kuhlenbeck). Also, there was obtained dilatation from the lateral and medial geniculate body and pretectal region, which serve as the pathway of those fiber systems. 10. Dilatation was also obtained from the posterior commissure, its descending peduncle and the interstitial nuclei. 11. Dilatation only could be obtained from Nucl. olivaris colliculi supe-rioris (Fuse). 12. Dilatation tends to occur as the result of the stimulation on the fasciculus longitudinalis dorsalis and periventricular system (Kuhlenbeck). 13. Our assumption iegarding the pupillary light reflex afferent pathway of rabbits on the basis of the result of the stimulation experiment on the pretectal region, posterior commissure, central gray matter, and its periphery, the pathway makes a complete central decussation at the optic chiasma and enters the pretectal region scatterringly running through dorsolateral archiform fiber system and tractus sublentiformis of Kuhlen beck. The pupillo-constrictor fibers change the neuron at the pretectal ragion; the secondary neuron starting hers undergoes a cornpletc central decussation again at the median of the posterior comrnissure, then turns to the ventrocaudal direction and joins with the descending peduncle of posterior commissure. Then, running farther around the lateral surface of the central gray matter and by way of the ventrocaudal part hereof, it reacheo the small-celled constrictor nucleus on the dorso-lateral side of the main oculomotor nucleus at the ventral part of the central gray matter of midbrain. The course of the pupillary light reflex afferent pathway differs according to different animal species. Therefore, it is not right to apply the findings concerning rabbits to animal species in general.