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. Author manuscript; available in PMC: 2021 Oct 30.
Published in final edited form as: Cell. 2021 Oct 11;184(22):5608–5621.e18. doi: 10.1016/j.cell.2021.09.023

Figure 5. Aβ-LTMRs that innervate glabrous skin more powerfully excite central tactile neurons in the gracile nucleus than Aβ-LTMRs that innervate hairy skin.

Figure 5.

A. Simultaneous in vivo recording from LTMRs with cell bodies in L4 DRG during optical stimulation of skin with sparse spatiotemporal white noise. Single pulses of focused laser light (300 microseconds, 20 mW) were directed to pseudorandom skin locations every 1.1 msec to excite ReaChR present on the terminals of cutaneous sensory neurons. Spatiotemporal optogenetic receptive fields for each unit were estimated through reverse correlation.

B. Representative single LTMR unit recorded in vivo with a MEA in the L4 DRG. (top) Spiking response to mechanical indentation for an Aβ RA-LTMR. (bottom) The optogenetic spatiotemporal receptive field of the same RA-LTMR computed through reverse correlation. LTMRs have spatiotemporally simple receptive fields in skin that align with mechanical receptive fields. Scale bars are 1 mm and 200 μm.

C. The mean number of spikes evoked by a stimulus to the center of a LTMR’s optogenetic receptive field, computed by integrating the conditional probability of a spike over the 3–6 msec following a light pulse. An equivalent number of LTMR spikes were evoked by stimulating optogenetic RFs in glabrous hindpaw skin, hairy hindpaw skin, and thigh skin (following hair removal), one-way ANOVA p=0.20.

D. Strategy for exploring the functional connectivity of the GN at single LTMR resolution. Optogenetic receptive fields of touch sensitive neurons in the GN postsynaptic to Aβ LTMRs were computed similar to A-C.

E. Two representative units recorded from the GN with receptive fields on the glabrous (left) or hairy hindpaw skin (right). GN units are composed of spatially and temporally separable “hotspots” in their RFs, indicating convergence of multiple LTMRs onto central touch neurons in the GN.

F. The number of spikes evoked in a GN neuron by a single optical pulse to “hotspots” comprising their RFs. Optical stimulation of hindpaw glabrous skin innervating sensory neurons more effectively drives spiking in postsynaptic GN neurons than hindpaw and thigh hairy skin optical stimulation (one-way ANOVA, p < 10−13, *** indicates Bonferroni corrected p < 10−6 via Mann Whitney U-Test).