(A) Experimental protocol. Time course of EMG activity (B) and behavioral pain posturing (C) before and during colorectal distension (CRD) in female and male rats (n = 10 - 12). (D) Area under curve computed over the 40-s period after the onset of CRD for EMG activity normalized to the 40-s baseline before CRD. Two-way ANOVA revealed significant main effect of CRD (F_1,41 = 63.6, P < 0.0005), but not of Sex (F_1,41 = 0.6, P = 0.5) or of the Sex × CRD interaction (F_1,41 = 0.5, P = 0.5). (D) Percentage of time animals spent in pain postures during the 40-s period after CRD onset. Rats exposed to 60-mmHg CRD spent significantly more time in pain postures than 0-mmHg controls (CRD effect: F_1,42 = 299.0, P < 0.0005, two-way ANOVA). Pain scores were significantly higher in female than in male rats (Sex effect: F_1,42 = 5.1, P < 0.05). There was no significant Sex × CRD interaction (F_1,42 = 0.5, P = 0.5). Results of the two male groups were reproduced from Wang et al. [50] with permission.

Statistically significant positive (red scale) and negative (blue scale) differences of the 60-mmHg distension groups compared to 0-mmHg controls (voxel level P < 0.05, cluster > 100 contiguous voxels) as determined by statistical parametric mapping are shown on representative coronal slices with anterior-posterior coordinates given relative to bregma (n = 11 for female control, n = 12 for the other groups). Abbreviations [34]: ACo/PLCo (anterior/posterolateral cortical amygdala), Au (auditory cortex), BMA (basomedial amygdala), CA1 (hippocampus CA1 region), CeA (central n. of the amygdala), Cg1, Cg2 (cingulate cortex, areas 1 and 2), dCPu, vCPu (dorsal and ventral caudate-putamen), Ect (ectorhinal cortex), EGP (external globus pallidus), En (endopiriform n.), Hb (habenula), aIns, pIns (anterior, mid/posterior insular cortex), LaA (lateral n. of the amygdala), LC (locus coeruleus), LL (lateral lemniscus), M1, M2 (primary and secondary motor cortex), MD (mediodorsal thalamic n.), Me (medial amygdala), mfb (medial forebrain bundle), MG (medial geniculate), MnPO (medial preoptic n.), MnR/PMnR (median, paramedian raphe), MS (medial septum), Acb (n. accumbens), PBP (parabrachial pigmented n.), PeFLH (perifornical lateral hypothalamus), Pir (piriform cortex), PrL (prelimbic cortex), PnC (pontine reticular caudal n.), Po (posterior thalamic n.), PtA (parietal association area), Re, Rh (reuinens, rhomoboid thalamic n.), RLi (rostral linear raphe), SC (superior colliculus), Sim (simple lobule), S1BF, S1FL, S1HL, S1Tr (primary somatosensory cortex: barrel field, forelimb, hindlimb, trunk), S2 (secondary somatosensory cortex), TeA (temporal association cortex), VA, VL, VM, VPL, VPM, (ventral anterior, ventrolateral, ventromedial, ventral posterolateral, ventral posteromedial thalamic n.), V1, V2 (primary, secondary visual cortex), Pr5 (trigeminal n.). The male results were reproduced from Wang et al. [50] with permission. Rat brain atlas figures were reproduced with modification from Paxinos and Watson [34] with permission.

Regions are highlighted as showing significant increases (red), decreases (blue) or no significant change (white) in regional cerebral blood flow during 60-mmHg CRD. Abbreviations: aIns (anterior insula), Cg1 (cingulate cortex, area 1, BA24b [49]), Cg2 (cingulate cortex, area 2, BA24a [49]), dACC (dorsal anterior cingulate cortex in human), dlPFC (dorsolateral prefrontal cortex in human), iACC (infragenual anterior cingulate cortex in human), IL (infralimbic cortex, BA25 [49]), LCC (locus coeruleus complex), MD (mediodorsal thalamic nucleus), mOFC (medial orbital frontal cortex), PAG (periaqueductal gray), PBN (parabrachial nucleus), pIns (mid/posterior insula), PrL (prelimbic cortex, BA32 [49]), sACC (supragenual anterior cingulate cortex in human), VM (ventromedial thalamic nucleus). Rat brain atlas figures were reproduced with modification from Paxinos and Watson [34] with permission.