Estrogen augmented visceral pain and colonic neuron modulation in a double-hit model of prenatal and adult stress

Abstract

BACKGROUND

Chronic stress during pregnancy may increase visceral hyperalgesia of offspring in a sex-dependent way. Combining adult stress in offspring will increase this sensitivity. Based on the evidence implicating estrogen in exacerbating visceral hypersensitivity in female rodents in preclinical models, we predicted that chronic prenatal stress (CPS) + chronic adult stress (CAS) will maximize visceral hyperalgesia; and that estrogen plays an important role in colonic hyperalgesia.

AIM

The aim was to illuminate the role of estrogen in colonic hyperalgesia and its underlying mechanisms.

METHODS

We established a CPS plus CAS rodent model in which the balloon was used to distend the colorectum. The single-fiber recording in vivo and patch clamp experiments in vitro were used to monitor the colonic neuron’s activity. The reverse transcription-polymerase chain reaction, western blot, and immunofluorescence were used to study the effects of CPS and CAS on colon primary afferent sensitivity. We used ovariectomy and letrozole to reduce estrogen levels of female rats respectively in order to assess the role of estrogen in female-specific enhanced primary afferent sensitization.

RESULTS

Spontaneous activity and single fiber activity were significantly greater in females than in males. The enhanced sensitization in female rats mainly came from low-threshold neurons. CPS significantly increased single-unit afferent fiber activity in L6-S2 dorsal roots in response. Activity was further enhanced by CAS. In addition, the excitability of colon-projecting dorsal root ganglion (DRG) neurons increased in CPS + CAS rats and was associated with a decrease in transient A-type K⁺ currents. Compared with ovariectomy, treatment with the aromatase inhibitor letrozole significantly reduced estrogen levels in female rats, confirming the gender difference. Moreover, mice treated with letrozole had decreased colonic DRG neuron excitability. The intrathecal infusion of estrogen increased brain-derived neurotrophic factor (BDNF) protein levels and contributed to the response to visceral pain. Western blotting showed that nerve growth factor protein was upregulated in CPS + CAS mice.

CONCLUSION

This study adds to the evidence that estrogen-dependent sensitization of primary afferent colon neurons is involved in the development of chronic stress-induced visceral hypersensitivity in female rats.

Keywords: Chronic prenatal stress; Estrogen; Visceral pain; Neuronal sensitization; Excitability; Letrozole

Core Tip: We investigated whether estrogen re-enhanced visceral hyperalgesia in chronic prenatal stress plus chronic adult stress models. After using physical ovariectomy or chemical inhibition with letrozole to reduce estrogen levels, we found that visceral hyperalgesia, colonic afferent neuronal excitability, nerve growth factor and brain-derived neurotrophic factor, and estrogen were all increased. The findings indicate that chronic stress-induced visceral hypersensitivity was estrogen dependent and that the hypersensitivity was mediated by estrogen-dependent sensitization of primary afferent colon neurons. The preclinical models provide key scientific evidence in support of developing gender-based visceral pain management.