Nicotinic and muscarinic cholinergic receptor binding in the human hippocampal formation during development and aging

Abstract

High-affinity nicotine, α-bungarotoxin ( αBT) and muscarinic receptor binding was measured in the human hippocampal formation in a series of 57 cases aged between 24 weeks gestation and 100 years. Changes in nicotine receptor binding during development and aging were more striking than differences in αBT and muscarinic binding. Nicotine binding was higher at the late foetal stage than at any other subsequent time in all areas investigated. In the hippocampus a fall in binding then occurred within the first six months of life, with little or no subsequent fall during aging, whereas in the entorhinal cortex and the presubiculum the major loss of nicotine binding occurred after the fourth decade. αBT binding was significantly elevated in the CA 1 region, but in no other region of the hippocampus, in the late foetus, and there was also a fall in αBT binding in the entorhinal cortex during aging from the second decade. The modest changes in total muscarinic binding, which appeared to reflect those in M1 and M3+4 rather than M2 binding, were a rise in the entorhinal cortex between the foetal stage and childhood and a tendency for receptors to fall with age in the hippocampus and subicular complex. These findings implicate mechanisms controlling the expression of nicotinic receptors to a greater extent than muscarinic receptors in postnatal development and aging in the human hippocampus.