Abstract
Cholinergic mechanism is involved in motor behavior. In songbirds, the robust nucleus of the arcopallium (RA) is a song premotor nucleus in the pallium and receives cholinergic inputs from the basal forebrain. The activity of projection neurons in RA determines song motor behavior. Although many evidences suggest that cholinergic system is implicated in song production, the cholinergic modulation of RA is not clear until now. In the present study, the electrophysiological effects of carbachol, a nonselective cholinergic receptor agonist, were investigated on the RA projection neurons of adult male zebra finches through whole-cell patch-clamp techniques in vitro. Our results show that carbachol produced a significant decrease in the spontaneous and evoked action potential (AP) firing frequency of RA projection neurons, accompanying a hyperpolarization of the membrane potential, an increase in the evoked AP latency, afterhyperpolarization (AHP) peak amplitude, and AHP time to peak, and a decrease in the membrane input resistance, membrane time constant, and membrane capacitance. These results indicate that carbachol reduces the activity of RA projection neurons by hyperpolarizing the resting membrane potential and increasing the AHP and the membrane conductance, suggesting that the cholinergic modulation of RA may play an important role in song production.
Highlights
In order to better understand the cholinergic modulation of RA, we investigated the electrophysiological effects of carbachol, a nonselective cholinergic receptor agonist, on the RA projection neurons of adult male zebra finches using in vitro whole-cell current-clamp recording
We have found that carbachol produced a hyperpolarization of membrane potential and an increase in the AHP peak amplitude, AHP time to peak, and evoked action potential (AP) latency, accompanying a decrease in the spontaneous AP firing frequency, evoked AP firing frequency, membrane input resistance, membrane time constant, and membrane capacitance of RA projection neurons in adult male zebra finches
Our results showed that carbachol produced a hyperpolarization of membrane potential, a lower firing rate, and an increase in the AHP peak amplitude and AHP time to peak in zebra finch RA projection neurons, indicating that carbachol reduced the excitability of RA projection neurons by hyperpolarizing the resting membrane potential and changing AP’s firing rate and firing pattern, which may be due to the regulation of AHP
Summary
Juvenile male songbirds learn their song from adult conspecific tutor songs during the sensitive period of song learning [1]. It has been demonstrated that motor production of song is controlled by the vocal motor pathway (VMP) in the pallium and brainstem [2]. RA receives inputs from HVC (used as a proper name) of the VMP and receives inputs from the lateral magnocellular nucleus of anterior nidopallium (LMAN) of the anterior forebrain pathway (AFP) that is necessary for song learning and adult song variability [3]. RA projection neurons project to brainstem respiratory and vocal control nuclei to form a part of song premotor pathway [4]. Considering the important function of the AFP on song learning, it was supposed that RA may play an important role in the regulation of song learning and song production
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