P₂Y₂ Receptors Mediate Masseter Muscle Mechanical Hypersensitivity in Rats

Figures & data

Figure 1 Experimental design timelines. (A) Phase one of the experiment – evaluation of CFA injection on nocifensive behavior, masseter muscle (MM) tissue histopathology and TRG tissue qRT-PCR. (B) Phase two – evaluation of AR-C118925/DMSO injection on nocifensive behavior in sham rats. (C) Phase two – evaluation of AR-C118925/DMSO administration on nocifensive behavior in unilateral MM inflammation-induced rats.

Abbreviations: CFA, complete Freund’s adjuvant; HWT, head withdrawal threshold; MM, masseter muscle; TRG, trigeminal ganglion; qRT-PCR, quantitative real-time polymerase chain reaction; DMSO, dimethyl sulfoxide.f

Figure 2 Histopathological analysis of the masseter muscle (MM) tissue (hematoxylin and eosin staining, 20x). (A) Complete Freund’s adjuvant (CFA)-injected MM presents signs of inflammation. (B) MM contralateral to CFA injection shows no signs of inflammation. (C) MM of control rats shows no signs of inflammation.

Abbreviations: CFA, complete Freund’s adjuvant; MM, masseter muscle.

Figure 3 Relative levels of P₂Y₂ mRNA expression in the trigeminal ganglion (TRG). (A) Relative levels of P₂Y₂ mRNA expression in the TRG ipsilateral to complete Freund’s adjuvant (CFA) injection. (B) Relative levels of P₂Y₂ mRNA expression relative levels in the TRG contralateral to CFA administration.

Note: *p˂0.05.

Abbreviations: TRG, trigeminal ganglion; CFA, complete Freund’s adjuvant.

Figure 4 The effect of unilateral intramasseteric administration of AR-C118925 or dimethyl sulfoxide (DMSO) on baseline head withdrawal threshold (HWT). (A) The effect on baseline HWT of AR-C118925/DMSO ipsilateral injection. (B) The effect on baseline HWT of AR-C118925/DMSO contralateral injection.

Abbreviations: DMSO, dimethyl sulfoxide; HWT, head withdrawal threshold.

Figure 5 The effect of unilateral administration of AR-C118925 or dimethyl sulfoxide (DMSO) on head withdrawal threshold (HWT) in rats injected with complete Freund’s adjuvant (CFA). (A) The effect on HWT of ipsilateral CFA and AR-C118925/DMSO injection. (B) The effect on HWT of contralateral CFA and AR-C118925/DMSO injection.

Notes: *p˂0.05, ***p≤0.001 for D^low group, ^p˂0.05, ^^p≤0.01, ^^^p≤0.001 for D^high group.

Abbreviations: DMSO, dimethyl sulfoxide; HWT, head withdrawal threshold; CFA, complete Freund’s adjuvant; D^low, 0.2 mg/100 μL dose of AR-C118925; D^high, 1 mg/100 μL dose of AR-C118925.