Pictorial History of the Early Microscopic Study of Vagal Sensory Neurons

Vagal sensory neurons play a central role in monitoring internal organ physiology and maintaining homeostasis. Although now recognized as key mediators of brain-body communication and promising therapeutic targets, their characterization emerged gradually over centuries of anatomical and microscopic investigation. This review provides a focused historical perspective on the study of vagal sensory neurons, emphasizing morphological and histological developments prior to the molecular era. Drawing on a collection of images from historical literature, this article traces the evolution of ideas and techniques, highlighting how early anatomical and histological studies established the foundation for modern investigations into vagal sensory function in health and disease. The review features the contributions of both well-known pioneers, including Adolph Hannover, Albert von Kölliker, Santiago Ramón y Cajal, and Fernando de Castro, as well as lesser-known investigators such as Adam Ploschko, Sergey Izhevesky, and Margaret Brown, whose work helped advance the field but has received comparatively little historical attention.