Background & Aims
Stimulation of the periaqueductal grey (PAG) is known to be anti-nociceptive (Reynolds, 1969; Mayer et al., 1971). A circuit involving PAG projections to the rostral ventral medulla (RVM) has been previously implicated in inhibiting nociception at the level of the spinal cord (Behbehani & Fields, 1979; Fields & Heinricher, 1985). However, whether this inhibition promotes analgesia (a decrease in pain as opposed to simply a decrease in nociceptive behaviors) is unclear. While activation of this pathway has been found to increase withdrawal latencies in assays measuring spinally-mediated reflexes, the role of this pathway in modulating other behaviors that require supraspinal input, is unknown.
Methods
Efferent projections from the PAG to other supraspinal structures were assessed anatomically and behaviorally through the use of viral tracing, RNA fluorescent in situ hybridization, and chemogenetics. Withdrawal latencies and affect were measured across a variety of nociceptive assays to determine the role of these projections in promoting different responses to pain.
Results
Different pain behaviors were modulated by distinct PAG projections. While select pain behaviors were inhibited by activation of the PAG to RVM pathway, other behaviors were not. Additionally, certain behaviors not modulated by this projection were inhibited by activation of other PAG output pathways.
Conclusions
Our preliminary data suggest that the projection from the PAG to the RVM is not the sole pathway underlying PAG stimulation-induced anti-nociception; rather, it is one of several PAG output pathways involved in the modulation of pain behaviors.
References
Behbehani, M. M., & Fields, H. L. (1979). Evidence that an excitatory connection between the
periaqueductal gray and nucleus raphe magnus mediates stimulation produced analgesia. Brain Research, 170(1), 85-93.
Fields, H. L., & Heinricher, M. M. (1985). Anatomy and Physiology of a Nociceptive Modulatory System. Philosophical Transactions of the Royal Society B: Biological Sciences, 308(1136), 361-374.
Mayer, D. T., Wolfe, T. L., Akil, H., Carder, B. & Liebeskind, J. C. (1971). Analgesia from electrical stimulation in the brainstem of the rat. Science, 174(4016), 1351-1354.
Reynolds, D. V. (1969). Surgery in the Rat during Electrical Analgesia Induced by Focal Brain
Stimulation. Science, 164(3878), 444-445.
Presenting Author
Isabel H. Bleimeister
Poster Authors
Isabel Bleimeister
BSc
University of Pittsburgh
Lead Author
Topics
- Mechanisms: Biological-Systems (Physiology/Anatomy)