Journal of Neuroscience, Vol 15, 7012-7023, Copyright © 1995 by Society for Neuroscience
Pronounced cellular diversity and extrasynaptic location of nicotinic acetylcholine receptor subunit immunoreactivities in the chicken pretectum
EM Ullian and PB Sargent
Neuroscience Graduate Program, University of California, San Francisco 94143, USA.
The diversity of nicotinic ACh receptor (AChR) expression in the chick
lateral spiriform nucleus (SpL) was assessed using subunit-specific
monoclonal antibodies (mAbs) and laser scanning confocal microscopy. The
late embryonic SpL was immunoreactive for mAbs against the alpha 2, alpha
5, alpha 7, alpha 8, and beta 2 AChR subunits. Distinct neuronal cell
classes were determined using pair-wise staining of mAbs. Approximately 90%
of the neurons in the SpL contained both alpha 5-like immunoreactivity (LI)
and beta 2-LI, with no neurons having only one of these subunit-LIs.
Approximately 70% of the neurons contained alpha 2- LI. All alpha 2-LI
neurons contained alpha 5/beta 2-LI; thus, neurons having alpha 2-LI are a
subset of those having alpha 5- and beta 2-LI. Fewer neurons, approximately
20%, contained alpha 7-LI. A subset of alpha 7-positive neurons were
immunoreactive for other subunits; for example, some alpha 7-positive
neurons also contained alpha 2-LI. Fewer than 15% of the neurons contained
alpha 8-LI. Some of the alpha 8-LI- containing neurons contained alpha
7-LI. The 14 week post-hatch SpL resembles the late embryonic nucleus in
the percentage of neurons immunoreactive for alpha 2, alpha 5, alpha 7,
alpha 8, and beta 2 AChR subunits, and in the presence of multiple classes
based on AChR subunit immunoreactivity. In addition, alpha 4-LI was found
in about 20% of the 14 week SpL neurons. Double-label immunofluorescence
experiments with mAbs to AChRs and to synaptic vesicle antigens showed that
most clusters of alpha 5-LI and beta 2-LI are extrasynaptic. The pronounced
diversity of AChR subunit expression and the extrasynaptic location of
AChR-LI suggest that AChR-like molecules in the SpL do not function solely
to respond to transmitter focally released from presynaptic terminals.