PACAP/PAC1R signaling modulates acetylcholine release at neuronal nicotinic synapses.
Neuropeptides collaborate with conventional neurotransmitters to regulate synaptic output. Pituitary adenylate cyclase-activating polypeptide (PACAP) co-localizes with acetylcholine in presynaptic nerve terminals, is released by stimulation, and enhances nicotinic acetylcholine receptor- (nAChR-) mediated responses. Such findings implicate PACAP in modulating nicotinic neurotransmission, but relevant synaptic mechanisms have not been explored. We show here that PACAP acts via selective high-affinity G-protein coupled receptors (PAC(1)Rs) to enhance transmission at nicotinic synapses on parasympathetic ciliary ganglion (CG) neurons by rapidly and persistently increasing the frequency and amplitude of spontaneous, impulse-dependent nicotinic excitatory postsynaptic currents (sEPSCs). Of the canonical adenylate cyclase (AC) and phospholipase-C (PLC) transduction cascades stimulated by PACAP/PAC(1)R signaling, only AC-generated signals are critical for synaptic modulation since the increases in sEPSC frequency and amplitude were mimicked by 8-Bromo-cAMP, blocked by inhibiting AC or cAMP-dependent protein kinase (PKA), and unaffected by inhibiting PLC. Despite its ability to increase agonist-induced nAChR currents, PACAP failed to influence nAChR-mediated impulse-independent miniature EPSC amplitudes (quantal size). Instead, evoked transmission assays reveal that PACAP/PAC(1)R signaling increased quantal content, indicating that it modulates synaptic function by increasing vesicular ACh release from presynaptic terminals. Lastly, signals generated by the retrograde messenger, nitric oxide- (NO-) are critical for the synaptic modulation since the PACAP-induced increases in spontaneous EPSC frequency, amplitude and quantal content were mimicked by NO donor and absent after inhibiting NO synthase (NOS). These results indicate that PACAP/PAC(1)R activation recruits AC-dependent signaling that stimulates NOS to increase NO production and control presynaptic transmitter output at neuronal nicotinic synapses.
Pugh
Phyllis C
PC
University of Toledo College of Medicine, Department of Neurosciences, Toledo, OH 43614-5804, USA.
Jayakar
Selwyn S
SS
Margiotta
Joseph F
JF
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000109:Acetylcholine / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D001703:Biophysics; D002478:Cells, Cultured; D002642:Chick Embryo; D018678:Cholinergic Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005728:Ganglia, Sympathetic / Q000166:cytology; D009116:Muscarine / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009538:Nicotine / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000494:pharmacology; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000378:metabolism*; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*; D016704:Synapsins / Q000378:metabolism; D013997:Time Factors
D018678:Cholinergic Agents; D004791:Enzyme Inhibitors; D010446:Peptide Fragments; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D011978:Receptors, Nicotinic; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; D016704:Synapsins; D015124:8-Bromo Cyclic Adenosine Monophosphate; D009569:Nitric Oxide; D011189:Potassium Chloride; D009538:Nicotine; D009116:Muscarine; D000109:Acetylcholine