Putative cholinergic elements in the photosensory pineal organ and retina of a teleost, Phoxinus phoxinus L. (Cyprinidae). Distribution of choline acetyltransferase immunoreactivity, acetylcholinesterase-positive elements and pinealofugally projecting neurons.
Putative cholinergic neurons in the photosensory pineal organ of a cyprinid teleost, the European minnow, were studied by use of choline acetyltransferase (ChAT) immunocytochemistry and acetylcholinesterase (AChE) histochemistry. Pinealofugally projecting neurons were visualized using retrograde HRP-filling through their cut axons. For comparison, the distribution of choline acetyltransferase immunoreactivity (ChAT-IR) and AChE-positive elements in the retina was investigated. While the distributional patterns of ChAT-IR and strongly AChE-positive perikarya in the retina are similar and may represent the same neuronal population, ChAT-IR and AChE-positive elements in the pineal organ appear to belong to separate populations. In the retina, small- to medium-sized perikarya in the inner nuclear layer, and small perikarya in the ganglion cell layer are ChAT-IR and AChE positive. The entire inner plexiform layer is AChE positive, while only sublaminae 1, 2 and 4 are ChAT-IR. No indication of cholinergic activity was observed in the optic axon layer. In the pineal organ, ChAT-IR is restricted to small perikarya situated rostrally and dorsally in the pineal end-vesicle. AChE-positive neurons are present throughout the pineal end-vesicle and the pineal stalk. The pineal tract (the pinealofugally projecting axons of intrapineal neurons) is strongly AChE positive, but displays no ChAT-IR. The distribution of pinealofugally projecting neurons, labeled with retrogradely transported HRP, is markedly dissimilar to that of the ChAT-IR elements. It is proposed that the photosensory pineal organ transmits photic information to the brain via a non-cholinergic pathway.(ABSTRACT TRUNCATED AT 250 WORDS)
D000110:Acetylcholinesterase / Q000378:metabolism; D000818:Animals; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D003530:Cyprinidae / Q000033:anatomy & histology*; D005260:Female; D006651:Histocytochemistry; D008297:Male; D009474:Neurons / Q000166:cytology / Q000201:enzymology; D010870:Pineal Gland / Q000166:cytology* / Q000201:enzymology; D012160:Retina / Q000166:cytology* / Q000201:enzymology
D002795:Choline O-Acetyltransferase; D000110:Acetylcholinesterase