New research provides insight into a long-observed, but little-understood connection between chronic pain and anxiety and offers a potential target for treatment.
The findings, published in Biological Psychiatry, showed that increased expression of a peptide neurotransmitter the body releases in response to stress — pituitary adenylate cyclase activating polypeptide (PACAP) — is also increased in response to neuropathic pain and contributes to these symptoms.
The researchers examined the expression of PACAP along the spino-parabrachiomygdaloid tract, which travels from the spinal cord to the amygdala.
Using models for chronic pain and anxiety, as well as models that can trace PACAP neurocircuits, the team members were able to observe where the stress and chronic pain pathways intersected.
“Chronic pain and anxiety-related disorders frequently go hand-in-hand,” said senior author Victor May, PhD, University of Vermont, Burlington, Vermont.
In a 2011 study, he and members of the research team found that PACAP was highly expressed in women exhibiting PTSD symptoms.
While Dr. May and colleagues saw an increase in anxiety-related behaviours in models of chronic pain, the anxious behaviour and pain hypersensitivity were significantly reduced when a PACAP receptor antagonist was applied.
“By targeting this regulator and pathway, we have opportunities to block both chronic pain and anxiety disorders,” said Dr. May. “This would be a completely different approach to using benzodiazepine and opioids — it’s another tool in the arsenal to battle chronic pain and stress-related behavioural disorders.”