Diversity of neuronal nicotinic acetylcholine receptor expression and function

Nicotinic acetylcholine receptor (AChR) expression and function was assessed in two model systems. The diversity of 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 {dollar}alpha{dollar}2, {dollar}alpha{dollar}5, {dollar}alpha{dollar}7, {dollar}alpha{dollar}8 and {dollar}beta{dollar}2 AChR subunits. Distinct neuronal cell classes were determined using pair-wise staining of mAbs. Double-label immunofluorescence experiments using mAbs to AChRs and to synaptic vesicle antigens showed that most clusters of {dollar}alpha{dollar}5-like immunoreactivity (LI) and {dollar}beta{dollar}2-LI are extrasynaptic. The pronounced diversity of AChR subunit expression and extrasynaptic location of AChR-LI suggest that AChRs in the SpL do not function solely to respond to transmitter focally released from presynaptic terminals.; The kinetics and pharmacology of excitatory postsynaptic currents (EPSCs) in two kinds of neurons in the embryonic avian ciliary ganglion were also assessed. Whole-cell voltage-clamp recordings revealed that the singly innervated ciliary neurons had large-amplitude (1.5-8 nA) EPSCs that could be classified according to the kinetics of their falling phases. Most neurons responded with an EPSC whose falling phase followed a double exponential time course with time constants of {dollar}sim{dollar}1 and 10 msec. The EPSCs of the remaining ciliary neurons followed a single time constant ({dollar}sim{dollar}8 msec). Multiply 1.5 nA) that appeared to contain only a slowly decaying component ({dollar}sim{dollar}12 msec). The fast and slow components of EPSC decay could be pharmacologically isolated with two toxins against AChRs. 50 nM {dollar}alpha{dollar}-bungarotoxin, which binds {dollar}alpha{dollar}7-subunit containing AChRs, blocked the fast component. 50 nM {dollar}alpha{dollar}-conotoxin-MII, which blocks {dollar}alpha 3beta 2{dollar} containing AChRs, blocked the slow component. in the presence of both toxins nearly all of the EPSC was abolished. Similar pharmacological results were found for monoexponential ciliary and choroid neurons. These results suggest that nerve-evoked transmitter acts on at least two different populations of AChRs in ciliary motor neurons.