Figure 1.
Simplified scheme showing pain pathway. The ascending pathway (red) is physiologically modulated by the descending inhibitory tracts (blue). Also represented are medications that can modify the sensory input of each of the four processes (green) [23,24]. Proposed H4R presence on neuronal cells in DRG, spinal cord [21,22] and in the brain [21,25] (pink) and non-neuron cells involved in pain [26] (orange). Abbreviations: 5-HT, serotonin, DRG, dorsal root ganglion; NE, norepinephrine; NMDA, N-methyl-d-aspartate receptor, NSAIDs, nonsteroidal anti-inflammatory drugs; Parts of Figure were drawn in Inkscape 1.1 using images from Servier Medical Art, which is licenced under a Creative Commons Attribution 3.0 Unported Licence (https://creativecommons.org/licenses/by/3.0/ accessed on 18 January 2023).