Cutaneous Allodynia of the Withers in Cattle: An Experimental<em> In Vivo</em> Neuroanatomical Preliminary Investigation of the Dichotomizing Sensory Neurons Projecting into the <em>Reticulum </em>and Skin of the Withers

The presence of dichotomizing neurons in the dorsal root ganglia (DRG) of cattle, innervating both the reticulum and the withers, may indicate a pre-spinal convergence of visceral and cutaneous sensory information. This anatomical feature could be the underlying basis for the cutaneous allodynia observed in traumatic reticuloperitonitis, also known as the &quot;Kalchschmidt pain test.&quot; In two anesthetized calves, two retrograde fluorescent tracers, Fast Blue (FB, affinity for cytoplasm) and Diamidino Yellow (DY, affinity for nucleus), were injected into the reticulum and skin of the withers, respectively. At the end of the experimental period, the calves were deeply anesthetized and then euthanatized. The thoracic (T1-T8) DRG were collected and processed to obtain cryosections which were examined on a fluorescent microscope. A large number of neurons localized, especially in the T7 DRG, presented nuclei labeled with DY. On the contrary, only a few neurons localized exclusively in T6 and T7 DRG presented the cytoplasm labeled with FB. No neurons displayed FB and DY simultaneously within the cytoplasm and nucleus, respectively. The absence of double-labeled DRG neurons suggested the involvement of higher integration centers which integrate the afferent information to coordinate respiratory movements of the diaphragm, intercostal muscles and larynx