A Null Mutation for the α3 Nicotinic Acetylcholine (ACh) Receptor Gene Abolishes Fast Synaptic Activity in Sympathetic Ganglia and Reveals That ACh Output from Developing Preganglionic Terminals Is Regulated in an Activity-Dependent Retrograde Manner

Abstract

In vertebrates, synaptic activity exerts an important influence on the formation of neural circuits, yet our understanding of its role in directing presynaptic and postsynaptic differentiation during synaptogenesis is incomplete. This study investigates how activity influences synaptic differentiation as synapses mature during early postnatal life. Specifically, we ask what happens to presynaptic terminals when synapses develop without functional postsynaptic receptors and without fast synaptic transmission.To address this issue, we investigated cholinergic nicotinic synapses in sympathetic ganglia of mice with a null mutation for the ␣3 nicotinic ACh receptor gene. Disrupting the ␣3 gene completely eliminates fast excitatory synaptic potentials on postganglionic sympathetic neurons, establishing a crucial role for ␣3-containing postsynaptic receptors in synaptic transmission. Interestingly, the preganglionic nerve terminals form morphologically normal synapses with sympathetic neurons, and these synapses persist without activity in postnatal animals. Surprisingly, when stimulating the preganglionic nerve at physiological rates, we discovered a significant decrease in ACh output from the presynaptic terminals in these ␣3 Ϫ/Ϫ sympathetic ganglia. We show that this decrease in ACh output from the presynaptic terminals results, in part, from a lack of functional high-affinity choline transporters. We conclude the following: (1) fast synaptic transmission in mammalian SCG requires ␣3 expression; (2) in the absence of activity, the preganglionic nerve forms synapses that appear morphologically normal and persist for several weeks; and (3) to sustain transmitter release, developing presynaptic terminals require an activity-dependent retrograde signal.

PACAP/PAC1R signaling modulates acetylcholine release at neuronal nicotinic synapses

“…Both cAMP and Ca 2+ are known to stimulate NOS (Oess et al, 2006; Ohnishi et al, 2008) an action that would increase somatic NO output and thus be expected to influence presynaptic ACh release in a retrograde fashion. Interestingly, a retrograde signal regulates ACh release at nicotinic synapses in mouse sympathetic ganglia where a disruption in the α3-nAChR subunit gene abolishes synaptic transmission and α3-nAChR mediated currents (Rassadi et al, 2005). In that case, the loss of postsynaptic activity impairs presynaptic ACh release by reducing high-affinity choline transporter (CHT) function and expression (Krishnaswamy and Cooper, 2009).…”

Mitochondrial Reactive Oxygen Species Inactivate Neuronal Nicotinic Acetylcholine Receptors and Induce Long-Term Depression of Fast Nicotinic Synaptic Transmission

“…For extracellular compound action potentials, the postganglionic trunk was connected to an AC differential amplifier (DP-301; Warner Instruments, Hamden, CT) with a suction electrode; the postganglionic compound action potentials were amplified, filtered at 100 Hz (low-pass cutoff) and 1 kHz (high-pass cutoff), digitized at 10 kHz, and stored on a Pentium II-based computer. To record intracellularly from individual SCG neurons, we used 50 -70 M⍀ glass microelectrodes (G150F-4; Warner Instruments) made with a DMZ universal puller (Zeitz Instruments, Munich, Germany) as described previously (Rassadi et al, 2005). Stable intracellular recordings were achieved with a high inertial precision microdrive (Inchworm 8200; EXFO, Vanier, Quebec, Canada) attached to a micromanipulator (SM11; Narshige, Tokyo, Japan) that drove the electrode through the ganglion.…”

Nonsynaptic Chemical Transmission Through Nicotinic Acetylcholine Receptors

“…During highfrequency synaptic stimulation (50 Hz), non-␣7 nAChRs appear to mediate the Ca 2ϩ transients confined to spines, and the sustained Ca 2ϩ signal shows a decrement as an indication of receptor desensitization (150). Synaptic transmission through ␣3 subunit-containing nAChRs has been identified in the sympathetic ganglia (109,129). Both ␣7 and non-␣7 nAChRs contribute to the remaining synaptic currents following the elimination of GABA and glutamatergic transmission, suggesting a synaptic role for nAChRs in dopaminergic neurons of the substantia nigra (108).…”