Sympathetic sprouting in dorsal root ganglia (DRG): a recent histological finding?

During the nineties it was described, as an original finding, the existence of afferent amyelinic nerve endings in animal dorsal root ganglia (DRG) caused by diverse experimental lesions. These works do not take into account the historical studies carried out by Ehrlich (1886), Ramón y Cajal (1890) and Dogiel (1885) among others. Ramón y Cajal (1899) confirmed the existence of these nerve endings naming them after their discoverer as "Dogiel's arborisations". Ramón y Cajal claims that these endings originate from fibres of sympathetic nature, something supported by later authors devoted to this topic. In any case, the same authors remarked already a possible relationship with pathological phenomena, nonetheless always referring to the frequent occasions in which the same images appeared in healthy animals. In this work we review the bibliography about the classically named "Terminal Dogiel's nests" which in modern literature have been referred to as sprouting of sympathetic axons in dorsal root ganglia likely related with sympathetically maintained pain. Furthermore, we present the finding, not described up to date, of multiple afferent amyelinic nervous endings related with the "Terminal Dogiel's nests" observed in different DRG from young adult healthy rabbits.