Ontogenesis of Muscarinic Receptors and Acetylcholinesterase Activity in Various Areas of Chick Brain

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Abstract
Muscarinic receptors, labeled with [3H]quinuclidinyl benzylate ([3H]QNB), and acetylcholinesterase activity were studied in 5 areas of the developing chick brain: hyperstriatum and neostriatum, paleostriatum, optic lobes, mesodiencephalon and cerebellum. Protein content of these areas, expressed as mg/g tissue and total protein, was determined between day -10 and adulthood. Differences in both determinations were observed among the areas. Binding of [3H]QNB was expressed as density (fmol/mg protein) and total number of receptors (fmol/total protein) in the area. Considerable variations were observed among the areas. The cerebellum showed the lowest receptor density and a large decrease in density and total number of receptors in the adult, which may reflect a change in neuronal population. Acetylcholinesterase, in certain areas, accompanied the changes in receptor concentration, but the timing and rate of increase had special features in each case. In the cerebellum, the enzyme increased steadily postnatally, while the muscarinic receptors dropped to very low values.