Injections of Algesic Solutions into Muscle Activate the Lateral Reticular Formation: A Nociceptive Relay of the Spinoreticulothalamic Tract.

Panneton WM, Gan Q, Ariel M.
PLoS One. 2015 Jul 8;10(7).

I wanted to take a look at this paper mainly because it is fairly similar to some of what we have done in our lab. Instead of stimulating the sciatic nerve, the injected algesic solutions (capsaicin, 6% NaCl, or low pH) into the gastrocnemius muscle, perfused the rats, and then compared the number of Fos+ cells in a number of regions involved in processing and responding to noxious stimuli. The number of Fos+ neurons in these regions was compared to the Fos+ neurons found in saline-injected rats. They analyzed the rostral and cuadal pons, rostral and caudal medulla, and the spinal cord.

Focusing on their results that correspond to our areas of research, they found that algesia caused more Fos+ neurons in both the RVLM and the CVLM, and not much in the RVMM (compare this to facial air puffs causing activation in the RVMM, but not in the RVLM, in last year's paper from the Dampney group), and that some of them were catecholaminergic neurons. Interestingly, even though the algesic solutions were injected unilaterally, Fos+ were not significantly different between sides of the brainstem - this either conflicts with other results (Pillowski group), or adds support to the idea of differential control. -DH