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An early somatosensory map in the zebrafish hindbrain as revealed by in vivo two-photon calcium imaging

›σμ ˜aG / Kazuhide Asakawa:1@μγ _ˆκ / Koichi Kawakami:1,2
1:‘—§ˆβ“`Œ€ŒΒ‘Μˆβ“`‰Šϊ”­Ά / National Institute of Genetics@2:‘Œ€‘ε‰@ˆβ“`Šw / SOKENDAI@

Diverse behavioral responses are controlled by the hindbrain through its ability to convert sensory stimuli into motor commands. The hindbrain receives the axons of the somatosensory cells and forms point-to-point connectivity maps to discriminate nature and positional origin of a stimulus in the skin. However, how a somatosensory stimulus is represented as an activity in the hindbrain neural network is not fully understood at cellular level. Here, by performing in vivo two-photon calcium imaging of larval zebrafish, we show that the hindbrain contains at least two spatially segregated cell populations with distinct response properties against touch stimulation. The first population, aligned longitudinally in the mediolateral hindbrain area, was differentially activated depending on the touch position in the body surface. Single cell labeling experiments revealed that these neurons in the mediolateral longitudinal stripe were glutamatergic, and projected to the spinal cord. These observations imply that the spatial response properties of these spinal projection neurons contribute to transform the positional information of touch into the intensity of the touch evoked-lateral body bending (C-turn), which determines the direction of escape locomotion. The second population, which resided in the medial part of the hindbrain, was activated for a long duration irrespective of stimulus position, suggesting that their activity is associated with the swimming movements during the escape. The cellular-level somatosensory and somatomotor maps in the hindbrain revealed here provide an insight into how an image of the body and its movement emerges in the vertebrate brain.