Genesis of anxiety, depression, and ongoing abdominal discomfort in ulcerative colitis-like colon inflammation

Abstract

Psychological disorders are prevalent in patients with inflammatory bowel disease; the underlying mechanisms remain unknown. We tested the hypothesis that ulcerative colitis-like inflammation induced by dextran sodium sulfate (DSS) exacerbates the ongoing spontaneous activity in colon-projecting afferent neurons that induces abdominal discomfort and anxiety, and depressive-like behaviors in rats. In this study, we used the conditioned place preference and standard tests for anxiety- and depression-like behaviors. DSS rats developed anxiety- and depression-like behaviors 10 to 20 days after the start of inflammation. Single-fiber recordings showed an increase in the frequency of spontaneous activity in L6-S1 dorsal root ganglion (DRG) roots. Prolonged desensitization of transient receptor potential vanilloid 1 (TRPV1)-expressing colonic afferents by resiniferatoxin (RTX) suppressed the spontaneous activity, as well as the anxiety- and depressive-like behaviors. Reduction in spontaneous activity in colon afferents by intracolonic administration of lidocaine produced robust conditioned place preference (CPP) in DSS rats, but not in control rats. Patch-clamp studies demonstrated a significant decrease in the resting membrane potential, lower rheobase, and sensitization of colon-projecting L6-S1 DRG neurons to generate trains of action potentials in response to current injection in DSS rats. DSS inflammation upregulated the mRNA levels of transient receptor potential ankyrin 1 and TRPV1 channels and downregulated that of Kv1.1 and Kv1.4 channels. Ulcerative colitis-like inflammation in rats induces anxiety- and depression-like behaviors, as well as ongoing abdominal discomfort by exacerbating the spontaneous activity in the colon-projecting afferent neurons. Alterations in the expression of voltage- and ligand-gated channels are associated with the induction of mood disorders following colon inflammation.

Keywords: anxiety; depression; inflammatory bowel disease; spontaneous activity in visceral afferent neurons; visceral hypersensitivity.

Fig. 1.

Dextran sodium sulfate (DSS) rats exhibited greater anxiety- and depression-like behaviors compared with controls. DSS rats made significantly fewer entries (A) and spent significantly less time in the open arms of the elevated plus-maze (EPM) (B). C: there was no significant difference between Ctr. and DSS in the average total distance traveled in EPM. In the sucrose preference test, sucrose consumption as a percentage of total liquid consumed was lower in DSS vs. the control rats (D), DSS rats spent significantly more time immobile in the forced swim test (E), and engaged in significantly fewer social contacts compared with controls (F). *P < 0.05 DSS vs. control rats.

Fig. 2.

Colonic spontaneous activity and sensitization to colorectal distension (CRD) increased in DSS rats. A: wave mark tracings show multiunit afferent fiber activity from S1 dorsal roots from a Ctr. and a DSS rat during graded CRD, on day 20. B, C, and D: mean frequencies of spontaneous activity in CRD-responsive single afferent fibers from control and DSS rats: all active fibers, Ctr. (B; n = 54), DSS (n = 89), low threshold (LT) fibers Ctr. (n = 34), DSS, (n = 58) (C), high-threshold (HT) fibers Ctr. (n = 21), DSS, (n = 32) (D). E: average distention-evoked fiber activity was significantly higher in fibers from DSS (n = 89) vs. those from control rats (n = 54). F: visceromotor response to graded CRD was significantly greater in DSS (n = 5 rats) vs. control rats (n = 6). *P < 0.05, DSS vs. rats. EMG, electromyographic activity.

Fig. 3.

Reduction of colon afferent fiber activity by intracolonic application of lidocaine produces a conditioned place preference in DSS, but not in control rats. A: time spent in the lidocaine- or vehicle-paired chambers before conditioning and during the postconditioning test in DSS and control rats (n = 15 and 12, respectively). Lidocaine-treated DSS rats spent a significantly greater time in the lidocaine-paired chamber, whereas controls showed no significant difference. B: after conditioning, lidocaine-conditioned DSS rats exhibited a significantly greater increase in average change in preference for the lidocaine-paired chamber than the lidocaine-conditioned control rats. C: intracolonic lidocaine produced significant decrease in average single fiber activity recorded during a 20-s 80-mmHg colon distention delivered at 10-min intervals in DSS rats. D: lidocaine treatment significantly decreased spontaneous activity of CRD-responsive fibers in DSS rats. E: lidocaine significantly inhibited distention evoked single fiber activity in DSS rats at all distention pressures tested. *P < 0.05 DSS vs. control (Ctr.) rats.

Fig. 4.

Resiniferatoxin (RTX) treatment reduced afferent nerve activity, as well as anxiety- and depression-like behaviors in DSS rats. A: number of open arm entries made by DSS+RTX rats in the EPM was not significantly different from Ctr. + Veh. However, DSS+Veh. rats made significantly fewer open arm entries vs. Ctr.+Veh. rats. The number of immobile episodes (B) and the time spent immobile (C) in the forced swim test by DSS+RTX rats were not significantly different from those in Ctr.+Veh. However, DSS+Veh. rats had significantly more immobile episodes and spent more time immobile vs. Ctr.+Veh rats. D: RTX treatment significantly reduced the frequency of spontaneous activity in DSS rats vs. DSS+Veh. rats. E: RTX treatment significantly reduced colon afferent firing frequencies in response to graded CRD in DSS rats. *P < 0.05, DSS vs. control (Ctr.) rats.

Fig. 5.

Evaluation of excitability of acutely dissociated DiI-labeled colon projecting lumbar-sacral dorsal root ganglion (DRG) neurons in patch-clamp experiments. A: representative traces show action potentials evoked by 30-s constant current injection recorded from a DiI-labeled neuron from a Ctr. (top) or DSS (bottom) rat. B: bar graph shows the percent of DiI-labeled neurons from control and DSS rats that exhibited sustained action potential firing in response to current injection. Average resting membrane potential (C; RMP) was significantly depolarized and rheobase (D) was significantly less in neurons from DSS vs. control. The average number of action potentials evoked in neurons during a 400-ms current pulse from DSS rats was significantly greater than in Ctr. rats at 2× rheobase (E) and 3× rheobase (F). *P < 0.05 DSS vs. control (Ctr.) rats.

Fig. 6.

Bar graphs show quantitative RT-PCR. mRNA levels of brain-derived neurotrophic factor (BDNF) (A) and five cation channels, K_v1.1, K_v1.4, Na_v1.8, transient receptor potential vanilloid 1 (TRPV1), and transient receptor potential ankyrin 1 (TRPA1) (B) in colon projecting S1 DRG neurons from DSS and Ctr. rats. *P < 0.05 DSS vs. control (Ctr.) rats.

Fig. 7.

Inflammation is restricted to the colon in DSS rats on day 7 and day 15. A: myeloperoxidase (MPO) in extracts from the colon muscularis externa (ME) and mucosa/submucosa (MSM) from DSS and Ctr. rats on day 7 and day 15. B–D: bar graphs comparing IL-1β concentrations in colon ME and MSM, cerebrospinal fluid (CSF), and plasma from control and DSS rats on day 7 and day 15. *P < 0.05 DSS vs. control (Ctr.) rats.