Figure 3. Y1^Cre Neurons within the Dorsal Horn Transmit Mechanical but Not Chemical Itch.

(A) Ablation of dorsal horn NPY::Cre INs increases spontaneous scratching in NPY::Cre; Lbx1^FlpO; Tau^ds-DTR; Ai65^ds-tdTom mice (n = 16) compared with DT-treated NPY::Cre; Tau^ds-DTR; Ai65^ds-tdTom controls that lack DT-receptor expression (n = 11). Ablation of the Y1^Cre and NPY::Cre IN populations in Y1^Cre; NPY::Cre; Lbx1^FlpO; Tau^ds-DTR; Ai65^ds-tdTom mice abolishes scratching (n = 11). Scratching is unaffected when Sst⁺ neurons are ablated together with the NPY::Cre INs in Sst^Cre; NPY::Cre; Lbx1^FlpO; Tau^ds-DTR; Ai65^ds-tdTom mice (n = 13). One-way ANOVA and Bonferroni post hoc tests were used to assess statistical differences.

(B and C) Reduced scratching in response to stimulation of the nape with a 0.16-g von Frey hair in Y1^Cre; Lbx1^FlpO; Tau^ds-DTR; Ai65^ds-tdTom mice treated with DT (n = 14) compared with saline-treated controls (n = 11; B), and in Y1^Cre; Lbx1^FlpO; R26^ds-hM4D mice treated with clozapine N-oxide (CNO; n = 8) compared with Y1^Cre; R26^ds-hM4D controls, which lack FlpO-dependent hM4D expression (n = 8; C).

(D) Enhanced scratching in response to stimulation of the nape in CNO-treated Y1^Cre; Lbx1^FlpO; R26^ds-hM3D mice (n = 6) compared with Y1^Cre; R26^ds-hM3D controls (n = 6).

(E) Spontaneous scratching in CNO-treated Y1^Cre; Lbx1^FlpO; R26^ds-hM3D mice (n = 8) is enhanced over a 30-min period compared with control mice (n = 6).

(F) Scratching responses are unchanged in wild-type mice treated with bombesin-saporin (BOM-SAP; n = 6) to ablate GRPR⁺ neurons compared with controls injected with saporin (SAP; n = 8).

(G and H) Ablation of GRPR⁺ neurons in Y1^Cre; Lbx1^FlpO; R26^ds-hM3D mice does not alter evoked scratching (G; BOM-SAP, n = 8; SAP, n = 7) or spontaneous scratching (H; BOM-SAP, n = 7; SAP, n = 7) following CNO injection.

(I) Scratching responses are unchanged in wild-type mice treated with [Sar⁹, Met(O₂)¹¹]-substance P-SAP (SSP-SAP; n = 10) to ablate NK1R⁺ neurons compared to SAP-injected controls (n = 11).

(J and K) In Y1^Cre; Lbx1^FlpO; R26^ds-hM3D mice, ablation of NK1R⁺ neurons does not alter evoked (J; SSP-SAP, n = 9; SAP, n = 7) or spontaneous (K; SSP-SAP, n = 10; SAP, n = 7) scratching following CNO injection.

(L) Unchanged scratching in NPY::Cre; Lbx1^FlpO; Tau^ds-DTR; Ai65^ds-tdTom mice 2 weeks after NK1R⁺ neuron ablation and 1 week following DT administration (SSP-SAP, n = 9; SAP, n = 8).

(M) Unchanged scratching over a 30-min period in Y1^Cre neuron-ablated mice following injection of chloroquine (control, n = 9; ablated, n = 11), histamine (control, n = 6; ablated, n = 8), compound 48/80 (control, n = 6; ablated, n = 8), and SLIGRL (control, n = 7; ablated, n = 8).

*p < 0.05, **p < 0.01, ***p < 0.001, NS, not significant. Data: mean ± SEM. See also Figures S4–S6.