Overexpression of EphB2 in the basolateral amygdala is crucial for inducing visceral pain sensitization in rats subjected to water avoidance stress

Activation of EphrinB2/EphB2 signaling in the spine cord alters glia-neuron interactions in mice with visceral hyperalgesia following maternal separation

Background

Sress early in life has been linked to visceral hyperalgesia and associated functional gastrointestinal disorders. In a mouse model of visceral hyperalgesia, we investigated whether the EphB2 receptor and its EphrinB2 ligand in spinal cord contribute to dysregulation of glia-neuron interactions.

Methods

An established mouse model of stress due to maternal separation (MS). Pups were separated from their mothers for 14 days during early development, then analyzed several weeks later in terms of visceral sensitivity based on the abdominal withdrawal reflex score and in terms of expression of c-fos, EphrinB2, EphB2, and phosphorylated MAP kinases (ERK, p38, JNK).

Results

Visceral hyperalgesia due to MS upregulated EphB2, EphrinB2 and c-fos in the spinal cord, and c-fos levels positively correlated with those of EphB2 and EphrinB2. Spinal astrocytes, microglia, and neurons showed upregulation of EphB2, EphrinB2 and phosphorylated MAP kinases. Blocking EphrinB2/EphB2 signaling in MS mice reduced visceral sensitivity, activation of neurons and glia, and phosphorylation of NMDA receptor. Activating EphrinB2/EphB2 signaling in unstressed mice induced visceral hyperalgesia, upregulation of c-fos, and activation of NMDA receptor similar to maternal separation.

Conclusion

The stress of MS during early development may lead to visceral hyperalgesia by upregulating EphrinB2/EphB2 in the spinal cord and thereby altering neuron-glia interactions.

Overexpression of EphB2 in the basolateral amygdala is crucial for inducing visceral pain sensitization in rats subjected to water avoidance stress

AIMS

Basolateral amygdala (BLA), as a center for stress responses and emotional regulation, is involved in visceral hypersensitivity of irritable bowel syndrome (IBS) induced by stress. In the present study, we aimed to investigate the role of EphB2 receptor (EphB2) in BLA and explore the underlying mechanisms in this process.

METHODS

Visceral hypersensitivity was induced by water avoidance stress (WAS). Elevated plus maze test, forced swimming test, and sucrose preference test were applied to assess anxiety- and depression-like behaviors. Ibotenic acid or lentivirus was used to inactivate BLA in either the induction or maintenance stage of visceral hypersensitivity. The expression of protein was determined by quantitative PCR, immunofluorescence, and western blot.

RESULTS

EphB2 expression was increased in BLA in WAS rats. Inactivation of BLA or downregulation of EphB2 in BLA failed to induce visceral hypersensitivity as well as anxiety-like behaviors. However, during the maintenance stage of visceral pain, visceral hypersensitivity was only partially relieved but anxiety-like behaviors were abolished by inactivation of BLA or downregulation of EphB2 in BLA. Chronic WAS increased the expression of EphB2, N-methyl-D-aspartate receptors (NMDARs), and postsynaptic density protein (PSD95) in BLA. Downregulation of EphB2 in BLA reduced NMDARs and PSD95 expression in WAS rats. However, activation of NMDARs after the knockdown of EphB2 expression still triggered visceral hypersensitivity and anxiety-like behaviors.

CONCLUSIONS

Taken together, the results suggest that EphB2 in BLA plays an essential role in inducing visceral hypersensitivity. In the maintenance stage, the involvement of EphB2 is crucial but not sufficient. The increase in EphB2 induced by WAS may enhance synaptic plasticity in BLA through upregulating NMDARs, which results in IBS-like symptoms. These findings may give insight into the treatment of IBS and related psychological distress.