PMC

Characterization of the nature of the cuneate nucleus relay projecting relay neurons. (a) Confocal images of cuneate nucleus neurons (red) double-labeled with markers for glutaminase (purple). Quantification of the % of cuneate nucleus projecting neurons immunoreactive for glutaminase contacted by DRG fibers (left) and quantification of the number of contacts onto glutaminase positive cuneate projecting neurons (right). (b) Confocal images of cuneate nucleus projecting neurons (red) double-labeled with markers for parvalbumin (purple). Quantification of the % of cuneate nucleus projecting neurons immunoreactive for parvalbumin contacted by DRG fibers (left) and quantification of the number of contacts onto parvalbumin positive cuneate projecting neurons (right). ***: p = 0.0003 & **: p = 0.0012 (left) and *: p = 0.0209 & *: p = 0.0125 (right) (c) Confocal images of cuneate nucleus projecting neurons (red) and transgenic labeling for glycinergic neurons (GlyT2: green). Quantification of the % of cuneate nucleus projecting neurons immunoreactive for glycine contacted by DRG fibers (left) and quantification of the number of contacts onto glycine positive cuneate projecting neurons (right). ***: p = 0.0003 (left, both comparisons). Areas boxed in the low magnification images are magnified 4 times in the left inset. All DRG fibers appear yellow on the pictures. Data were tested for normality and analyzed then with a one-way ANOVA followed by Dunnett’s post-hoc test. N = 9 sections per group and n = 3 animal per group. Scale bar equal 40 µm in (a–e). For insets scale bar equals 10 µm in (a–e).

Comparisons between cuneate and external cuneate cells. A: schematic showing approximate locations of recording sites for monkey M. Only cells with clear proprioceptive or cutaneous receptive fields are shown. Shaded areas show approximate locations of the main cuneate (Main cun; yellow) and external cuneate (Ext cun; light blue). B: scatter plot of response amplitude versus width for cells facilitated by median or ulnar nerve stimulation. C: as in B for cells suppressed by median or ulnar nerve stimulation. D: average PSTHs for cells in B. PSTHs for external and main cuneate cells have been overlaid. E: average PSTHs for cells in C. PSTHs for external and main cuneate cells have been overlaid. F: coherence spectra between stimulus train and cell firing for cells in B. Dotted line shows significant level (P < 0.05). G: coherence spectra between stimulus train and cell firing for cells in C. Dotted line shows significance level (P < 0.05).

Cells possessing strychnine-sensitive glycine receptors were evenly distributed throughout the main cuneate nucleus. A, B, Two coronal sections (expanded at right), one 2 mm caudal (A) and another 2 mm rostral (B) to the obex showing dark-colored glycine receptor-immunoreactive neurons. The patchy distribution of immunoreactivity in the dorsal area corresponded to the cluster region of the cuneate nucleus (see A). Cuneate neurons show moderate to high levels of immunoreactivity for the strychnine-sensitive glycine receptor. DMV, Dorsal motor nucleus of the vagus; ExtCN, external cuneate nucleus; rCN, rostral cuneate nucleus; Sp5, spinal trigeminal nucleus; VIN, inferior vestibular nucleus.

Dorsal column lesion triggers the formation of relays circuits between DRG exiting collaterals and relay neurons originating from the cuneate nucleus. (a) Experimental setup of the analysis of the formation of relay circuits. (b) Confocal image of cuneate nucleus projecting neurons in the cervical spinal cord following dorsal column lesion and quantification of the percentage of cuneate nucleus projecting neurons contacted by DRG collaterals in unlesioned (control) of lesioned mice at 21 and 84dpi (left panel). Quantification of the localization of cuneate nucleus projecting neurons in unlesioned (control) of lesioned mice at 21 and 84dpi (right panel). (c) Representative confocal images of appositions between cuneate nucleus projecting neurons and DRG collaterals in the cervical spinal cord (arrows point to appositions). Quantifications of the % of contacted cuneate nucleus projecting neurons (left) in unlesioned (control) of lesioned mice at 21 and 84dpi (left panel, p = 0.0378) and quantifications of the localization of contacted cuneate nucleus projecting neurons (%, right p = 0.0408 dorsal laminae control vs 12 weeks). (d) Representative confocal images of appositions between relay neurons and DRG collaterals and quantifications (left) of the number of contacts per cuneate nucleus projecting neuron (p = 0.0041 control vs 3 weeks and p = 0.00002 control vs 12 weeks). Quantification of the total number of contacts per time points (**: p < 0.01 control vs 3 weeks and *p < 0.05 control vs 12 weeks). Data distribute normally and were analyzed using 1-way ANOVA followed by Dunnett’s multiple comparisons test. Scale bars equal 300 µm in (b), 50 µm in ((c); right panel is a 3-times magnification of the boxed area) and 15 µm in (d).