The pineal organ of the pike esox lucius 3. intra pineal pathways for conduction of photo sensory messages

Falcon, J.; Mocquard, J.P.

Annales de Biologie Animale Biochimie Biophysique 19(4A): 1043-1062


ISSN/ISBN: 0003-388X
Accession: 006735705

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To elucidate the sensory function of the pineal organ of the pike, E. lucius, the acetylcholinesterase (AChE) reaction was used to demonstrate the pineal neurons. Thirty to 40 sensory neurons (6-20 .mu.m in diameter), more numerous in the ventral than in the dorsal wall (ratio:3/1), were evidenced in the rostral (distal) part of the pineal vesicle (distal pineal). No or very few AChE-positive neurons were observed in the middle pineal. Two hundred to 744 neurons (4-11 .mu.m in diameter) were identified in the proximal pineal (pineal stalk). Multipolar elements were generally observed in the distal pineal, while those in the proximal region were mainly pseudounipolar; bipolar neurons were seen in the distal and proximal pineal. At the level of the subcommissural organ, the pineal tract running towards the posterior commissure was accompanied by some AChE-positive neurons whose axons also ran towards the posterior commissure or the pineal organ. The ultrastructural features of sensory neurons were similar to those already described in other vertebrates. Typical photoreceptor cells, mainly in the proximal region, showed ribbon synaptic connections with dendritic processes of sensory neurons. The pineal tract was composed of 2 types of axons differing in structure and diameter. Some of the fibers of 1 type were myelinated at the middle of the pineal stalk, but most were myelinated at the caudal part. The photosensory function of the pike pineal organ was mainly developed in the proximal and then the distal regions, and regressed (or was lost?) in the middle pineal.