THE CHOLINESTERASE AND ACETYLCHOLINE CONTENT OF THE CHICK RETINA, WITH ESPECIAL REFERENCE TO FUNCTIONAL ACTIVITY AS INDICATED BY THE PUPILLARY CONSTRICTOR REFLEX

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Abstract
A quantitative study was made of the cholinesterase and acetylcholine content of the developing chick retina for the period of incubation covering the differentiation of the neural units. From the 8th to the 18th day, cholinesterase activity gradually increased with incubation time. Between the 18th and 20th day a significant increase occurred after which no appreciable change took place for the remaining period studied. The acetylcholine content showed a more gradual increase from the 1lth-19th day. Around the 19th day, a very sharp increase occurred, reaching a maximum level of between 12 or 12.5 [gamma]/ g. of tissue. This level was maintained until shortly after hatching when it fell to a new level of between 5 and 6 [gamma]/g. of retina. The pupillary constrictor reflex was first elicited between the 18th and 19th day of incubation. This was taken as evidence that the neural units of the retina are sufficiently developed at that time to function as conductors of impulses. There appears to be a close relationship between the increase in cholinesterase and acetylcholine content and the maturation of the neural units in the developing chick retina. It is suggested that the sharp increase in acetylcholine content may be a "reserve" built up to facilitate the establishment of functional synapses.