Abstract
BackgroundSensory input is generally thought to be necessary for refining and consolidating neuronal connections during brain development. We here report that cortical callosal axons in somatosensory cortex require sensory input for their target selection in contralateral cortex.ResultsEliminating sensory input to either hemisphere by unilateral transection of infraorbital nerve (ION) prevents target selection of callosal axons in contralateral cortex. Strikingly, blocking sensory input bilaterally, by simultaneously transecting both IONs, results in rescued callosal projection. In contrast, non-simultaneous bilateral ION transection has the same effect as unilateral transection. Similar results are obtained by lesion of whisker hair follicles. c-Fos-positive neurons in brain slices treated with KCl is decreased more in contralateral cortex with unilateral removal of sensory input, but decreased similarly in both cortices in mice with simultaneous bilateral removal of sensory input. Frequency of sEPSC of cortical neurons is also reduced in contralateral cortex with the unilateral removal of sensory input, but equally reduced on both sides with the bilateral removal of sensory input, suggesting that unbalanced bilateral sensory input might lead to mismatched neuronal activity between the two cortices and contribute to the formation of callosal projection.ConclusionOur data demonstrate a critical role of balanced bilateral somatosensory input in the formation of callosal connections, and thus reveal a new role of sensory input in wiring brain circuits.
Highlights
Sensory input is generally thought to be necessary for refining and consolidating neuronal connections during brain development
Our results show the requirement of sensory input in wiring of callosal connection, and reveal the critical role of balanced bilateral sensory input in this developmental process
Consistent with our previous finding [5], callosal axons of layer II-III cortical pyramidal neurons enter the white matter beneath the contralateral somatosensory cortex at postnatal day (P) 5, and initiate dense projections to the border region between the primary somatosensory cortex (S1) and secondary somatosensory cortex (S2) during P6-P9
Summary
Sensory input is generally thought to be necessary for refining and consolidating neuronal connections during brain development. We here report that cortical callosal axons in somatosensory cortex require sensory input for their target selection in contralateral cortex. The corpus callosum is the largest commissural system in the mammalian brain and responsible for communication between the two cerebral hemispheres, which is highlighted by the findings from “split brain” patients with corpus callosotomy [1,2]. Callosal axons cross the midline region and find correct cortical areas in opposite hemisphere to establish callosal connection [3]. The early-born layer V callosal neurons cross the midline before birth, while the late-born layer II-III. How callosal axons select the correct target in the contralateral cortex is unclear
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