Journal of Neuroscience, Vol 14, 4147-4158, Copyright © 1994 by Society for Neuroscience
Activity-dependent expression and distribution of M1 muscarinic ACh receptors in visual cortex neuronal cultures
Y Wang, Q Gu, F Mao, RP Haugland and MS Cynader
Department of Ophthalmology, University of British Columbia, Vancouver, Canada.
The fluorescently labeled muscarinic M1 receptor-selective antagonist
BODIPY FL pirenzepine has been employed to study the activity-dependent
distribution and expression of muscarinic M1 ACh receptors (M1AChRs) in
cultured neurons derived from rat visual cortex. Displacement experiments
showed that like pirenzepine, binding of BODIPY FL pirenzepine was specific
to M1 receptors and its K(i) was similar to that of unlabeled pirenzepine.
Using confocal laser scanning microscopy, M1 receptors were predominantly
localized to cell bodies early in development in the culture environment.
After 2 weeks in culture, the receptors showed labeling not only in cell
bodies but also in neuritic processes, especially on the initial segments
of the processes. Chronic membrane depolarization with 40 mM potassium
chloride caused a dramatic increase in M1 receptor expression on these
neurons. Conversely, blockade of neuronal activity with 0.1 microM TTX
decreased expression of the receptors. Receptor expression increased after
cells were treated chronically with 50 nM pirenzepine, whereas it decreased
after exposure to 10 microM carbachol. The results demonstrate for the
first time the exact location of muscarinic receptors in living cultured
neurons and also the activity-dependent expression of M1 receptors on these
neurons. Both chronic membrane depolarization and antagonist application
upregulate receptor expression, whereas blocking bioelectrical activity or
chronic agonist application downregulates expression.