Abstract
Synaptic plasticity is the cellular basis of learning and memory. When animals learn a novel motor skill, synaptic modifications are induced in the primary motor cortex (M1), and new postsynaptic dendritic spines relevant to motor memory are formed in the early stage of learning. However, it is poorly understood how presynaptic axonal boutons are formed, eliminated, and maintained during motor learning, and whether long-range corticocortical and thalamocortical axonal boutons show distinct structural changes during learning. In this study, we conducted two-photon imaging of presynaptic boutons of long-range axons in layer 1 (L1) of the mouse M1 during the 7-day learning of an accelerating rotarod task. The training-period-averaged rate of formation of boutons on axons projecting from the secondary motor cortical area increased, while the average rate of elimination of those from the motor thalamus (thalamic boutons) decreased. In particular, the elimination rate of thalamic boutons during days 4–7 was lower than that in untrained mice, and the fraction of pre-existing thalamic boutons that survived until day 7 was higher than that in untrained mice. Our results suggest that the late stabilization of thalamic boutons in M1 contributes to motor skill learning.
Highlights
Synapses consist of presynaptic and postsynaptic sites, and are indispensable prerequisites for communication between neurons
The anteromedial nucleus, which mainly receives projections from the medial mammillary nucleus, prelimbic, infralimbic, and anterior cingulate cortices [50, 51], was labeled with the tracer. Given that both M2 and the motor thalamus send synaptic inputs onto apical tuft dendrites of layer 5 (L5) corticospinal neurons [29], we hypothesized that these brain areas could be candidates for the presynaptic counterpart of the newly formed learningrelated spines of L5 pyramidal neurons that have been reported in previous studies [15, 16]
We examined the structural dynamics of boutons on long-range axons in layer 1 (L1) of M1 that originated either from M2 or the thalamus throughout a motor learning
Summary
Synapses consist of presynaptic and postsynaptic sites, and are indispensable prerequisites for communication between neurons. Synapses can change the strength of their chemical transmission by processes such as modification of the probability of transmitter release and varying the number of postsynaptic glutamate receptors [1, 2]. Synapses can be newly formed, eliminated, or undergo a change in size [3,4,5]. Decision to publish, or preparation of the manuscript
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