Regulation And Receptor Mechanism Of Cholinergic Signaling On Inhibitory Synaptic Transmission Of RA In The Motor Nucleus Before Singing In Adult Songbirds

The central cholinergic system is one of the important neurotransmitter systems in the brain and is closely related to learning memory and sensorimotor activity.Songbirds are an important model animal for studying vocal learning memory and sensorimotor,and their song behavior is a unique and complex vocal-motor learning behavior,similar to human speech behavior.The robust nucleus of the arcopallium(RA)is a premotor nucleus of the songbird forebrain that controls songbird vocal behavior and plays an important role in the production and control of songbirds.Our previous study confirmed that cholinergic signaling can modulate RA associated with birdsong characteristics through muscarinic acetylcholine receptors(mACh Rs),but not nicotinic acetylcholine receptor(n ACh Rs)projection neuron activity and excitatory synaptic transmission associated with song characteristics.However,the mechanisms by which the inhibitory synaptic transmission received by RA projection neurons is regulated by cholinergic signals and receptors are unclear,and it remains to be shown whether cholinergic signals can influence song behavior by modulating the activity of RA neurons in adult songbirds.We investigated the effect of cholinergic signaling on inhibitory synaptic afferents in adult male Spotted-breasted Nuthatch RA projection neurons at the ex vivo level using the whole-cell membrane clamp technique,and the effect of exogenous cholinergic signaling on song behavior in adult male Spotted-breasted Nuthatch RA at the in vivo level using the microdialysis-targeted drug delivery technique.The results of the study showed that:1.The non-selective acetylcholine receptor agonist carbachol reduces the frequency and amplitude of mini-inhibitory postsynaptic currents(m IPSCs)in RA projection neurons and decreases the amplitude and paired-pulse ratio(PPR)of evoked-inhibitory postsynaptic currents(e IPSCs)in RA projection neurons.The amplitude and paired-pulse ratio(PPR)of evoked-inhibitory postsynaptic currents(e IPSCs)in RA projection neurons were reduced.2.The mAChRs agonist oxotremorine M(OM)had similar effects to carbachol on inhibitory synaptic transmission in RA projection neurons,also reducing the frequency and amplitude of m IPSCs and the amplitude and PPR of e IPSCs in RA projection neurons.mACh Rs blocker atropine abolished the inhibitory synaptic transmission reduction of RA projection neurons by carbachol.3.The n AChRs agonist DMPP did not affect inhibitory synaptic transmission in RA projection neurons,changing neither the frequency and amplitude of m IPSCs nor the amplitude and PPR of e IPSCs in RA projection neurons.n ACh R blocker mecamylamine also failed to block the inhibitory synaptic transmission of carbachol in RA projection neurons.The modulatory effect of carbachol on inhibitory synaptic transmission in RA projection neurons was also not blocked.4.Microdialysis of carbachol within the in vivo RA was effective in reducing the entropy of the song syllable and increasing the similarity of the song.While microdialysis of the mACh R agonist OM had similar effects to carbachol on the song,the n ACh R agonist DMPP did not affect the song.The above results suggest that cholinergic signaling reduces inhibitory synaptic transmission received by RA projection neurons and reveal that the effect works mainly through mACh Rs,while n ACh Rs may not be involved and both presynaptic and postsynaptic mechanisms are involved.Furthermore,at the same time,cholinergic signaling enhances the stability of the birdsong through mACh Rs,consistent with electrophysiological data yielding receptor mechanisms.The text provides a potential mechanism by which cholinergic signaling modulates inhibitory synaptic transmission received by RA neurons,which in turn affects song behavior.