Published online Aug 14, 2021. doi: 10.3748/wjg.v27.i30.5060
Peer-review started: March 4, 2021
First decision: May 5, 2021
Revised: May 19, 2021
Accepted: July 5, 2021
Article in press: July 5, 2021
Published online: August 14, 2021
Processing time: 159 Days and 1 Hours
Chronic stress during pregnancy may increase visceral hyperalgesia in the offspring. Combining adult stress in offspring will increase this sensitivity. Therefore, based on the evidence implicating estrogen exacerbates visceral hypersensitivity in female rodents in preclinical models, we predicted that chronic prenatal stress (CPS) + chronic adult stress (CAS) would maximize visceral hyperalgesia and that estrogen has an important role in colonic hyperalgesia.
The mechanisms of visceral hypersensitivity are not well defined. Understanding the neurophysiological mechanisms driving visceral hypersensitivity will spur the development of female pain-specific therapies.
The objective was to identify the enhancement of visceral hypersensitivity in a CPS + CAS model and explain the role of estrogen in that process.
A CPS + CAS rodent model was established. Single fiber recording in vivo and patch clamp experiments in vitro were used to monitor the activity of colonic neurons. Reverse transcription-polymerase chain reaction (RT-PCR), western blots, and immunofluorescence were used to study the effects of CPS and CAS on colon primary afferent sensitivity. We used ovariectomy (OVX) and letrozole to reduce estrogen levels in female rats in order to assess the role of estrogen in female-specific enhanced primary afferent sensitization.
A CPS + CAS rodent model was established. Single fiber recording in vivo and patch clamp experiments were used to monitor the colonic neuron activity in vitro. RT-PCR, western blots, and immunofluorescence were used to study the effects of CPS and CAS on colon primary afferent sensitivity. We used OVX and letrozole to reduce estrogen levels of female rats in order to assess the role of estrogen in female-specific enhanced primary afferent sensitization.
Spontaneous activity and single fiber activity were significantly greater in females than in males. The enhanced sensitization in female rats mainly came from the low-threshold neurons. CPS significantly increased single-unit afferent fiber activity in the L6-S2 dorsal roots in response. Activity was further enhanced by CAS. In addition, the increased excitability of colon-projecting DRG neurons in CPS + CAS rats was associated with a decrease in transient A-type K+ currents. Compared with OVX, letrozole treatment further reduced the estrogen levels of female rats, which confirmed the gender difference. Moreover, rats treated with letrozole had decreased colonic DRG neuron excitability. The intrathecal infusion of estrogen increased BDNF protein levels and contributed to the response to visceral pain. Western blots showed that nerve growth factor protein was upregulated in CPS + CAS rats.
This study adds to the evidence of the development of chronic stress-induced visceral hypersensitivity in females, and that it involves estrogen-dependent sensitization of primary afferent colon neurons.
This study demonstrated that CAS + CPS induced visceral hypersensitivity and that estrogen played a role in the process. Understanding the molecular and neuro