Abstract
The rodent whisker-barrel system has been an ideal model for studying somatosensory representations in the cortex. However, it remains a challenge to experimentally stimulate whiskers with a given pattern under spatiotemporal precision. Recently the optogenetic manipulation of neuronal activity has made possible the analysis of the neuronal network with precise spatiotemporal resolution. Here we identified the selective expression of channelrhodopsin-2 (ChR2), an algal light-driven cation channel, in the large mechanoreceptive neurons in the trigeminal ganglion (TG) as well as their peripheral nerve endings innervating the whisker follicles of a transgenic rat. The spatiotemporal pattern of whisker irradiation thus produced a barrel-cortical response with a specific spatiotemporal pattern as evidenced by electrophysiological and functional MRI (fMRI) studies. Our methods of generating an optogenetic tactile pattern (OTP) can be expected to facilitate studies on how the spatiotemporal pattern of touch is represented in the somatosensory cortex, as Hubel and Wiesel did in the visual cortex.
Highlights
Animals perceive the external world through sensory systems consisting of the peripheral sensory organs, sensory nerves and the central nervous system (CNS)
There was no significant difference in size between the calcitonin gene-related peptide (CGRP)- and the P2X3-positive groups
Each whisker follicle is innervated by a single, relatively large deep vibrissal nerve (DVN), and several smaller superficial vibrissal nerves (SVNs) [7]. To test whether these nerves expressed ChR2V, we examined the follicle-sinus complexes (FSCs) of the whiskers at three levels: (1) the superficial layer consisting of the rete ridge collar (RRC) and outer conical body (OCB); (2) the middle layer including the inner conical body (ICB); (3) the deep layer surrounded by the ring sinus (RS)
Summary
Animals perceive the external world through sensory systems consisting of the peripheral sensory organs, sensory nerves and the central nervous system (CNS). Rodents use their whiskers/vibrissae to collect information about objects: position, size, shape and texture [1,2,3]. The principal whiskers/vibrissae are two-dimensionally arrayed on the snout and innervated by the maxillary branch of the trigeminal nerve. The trigeminal ganglion (TG) neurons innervating the whisker follicles transmit the afferent signal to the primary somatosensory cortex called ‘‘barrels’’ through the brainstem and thalamus. The layer IV projection is somatotopically patterned so as to map the whisker arrangement of the contralateral side, some thalamo-cortical projections have broad receptive fields. The rodent whiskerbarrel system has been an ideal model for studying somatosensory representations in the cortex
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