Established in 1947 to celebrate neuroanatomy and now promotes all of neuroscience.
In Memoriam: Constantino Sotelo
The Cajal Club mourns the passing of Constantino Sotelo,
a neuroscientist whose distinguished career linked the classical histological tradition of Santiago Ramón y Cajal with the emergence of modern, interdisciplinary neuroscience.
Born in 1937 in La Coruña, Spain, Sotelo studied medicine at the Complutense University of Madrid. He completed his doctoral thesis under the direction of Fernando de Castro (1896-1967), one of the youngest and last direct disciples of Santiago Ramón y Cajal. From 1958 to 1960, Sotelo worked with de Castro first as an external student and later as a fellow of the Instituto Cajal. There he entered a scientific tradition still closely connected to Cajal's methods and conception of the nervous system. De Castro also introduced Sotelo to the work of the French histologists Jean Nageotte and Jean Verne. Connections with both men would become important in the next stage of his career.
Because of the political climate, Sotelo left Spain rather abruptly in 1961, and de Castro helped send him to Paris. He had also received training in pathology at the University of Cologne that year. Sotelo subsequently trained in neurobiology in Jean Verne's laboratory in Paris beginning in 1962. Sotelo studied histochemistry and histoenzymology, particularly in relation to the cerebellum, and he received his doctorate in 1965. Verne was able to secure a modest fellowship for him in part because of his friendship with de Castro.
Sotelo arrived in France at a pivotal moment in the history of neuroscience. Classical histology remained influential, while electron microscopy, electrophysiology, biochemistry, and other emerging approaches were rapidly transforming understanding of the nervous system. Sotelo brought to this environment both the rigorous morphological training he had received in the Cajal tradition and an unusually critical and forward-looking scientific outlook. He was surprised to find remnants of reticular theory still present in French teaching and became closely associated with researchers who were bringing neuroanatomy into a new experimental era.
Carol Mason with Constantino Sotelo.
Photo courtesy of Carol Mason.
In 1965, Sotelo joined the laboratory of René Couteaux, who brought him into the CNRS. Working with Couteaux's collaborator Jacques Taxi, Sotelo learned electron microscopy and became determined to apply its extraordinary resolving power to the fine organization of the brain. Couteaux subsequently sent him to Harvard Medical School to train with Sanford L. Palay, a pioneer of electron microscopic neuroanatomy. There Sotelo contributed to important early observations of the organization of the axon hillock and initial segment.
Soon afterward, Sotelo made a significant discovery: the first mixed synapse, displaying signs of both electrical and chemical transmission, described in the rat vestibular nucleus. This work launched a sustained investigation of electrical transmission and electrotonic coupling. Later, using his typical methods of research, he started working with important physiologists such as Francis Crépel, Henri Korn and Rodolfo Llinás. He correlated neural structure with its function, showing an interdisciplinary approach typical for modern neuroscience.
By the 1970s, Sotelo had established an independent research program. From 1970 to 1976, he led a team at Port-Royal Hospital, where his investigations extended into synaptic degeneration and reinnervation. With Tencho Gentschev, he demonstrated that postsynaptic sites could retain their differentiation following partial degeneration and participate in subsequent reinnervation by attracting nearby synaptic boutons, contributing to the concept of “terminal plasticity.”
The cerebellum became one of the enduring subjects of Sotelo's scientific career. Beginning in the 1970s, he participated in multidisciplinary studies of cerebellar mutant mice, including Staggerer, Weaver, and Reeler. With anatomists, electrophysiologists, biochemists, geneticists and others, Sotelo tried to uncover the rules governing the "set up" of neuronal circuits, and their subsequent reorganization during development. His microscopic study of the structure of neurons thus went hand-in-hand with questions on the function of these elements, on their development, on genetics and on plasticity.
Sotelo later expanded his laboratory at La Salpêtrière Hospital in Paris. His work there spanned the time from his early days as a student at the Instituto Cajal to more than four decades later as a researcher in French institutions. During this time, he studied, among other topics, electrotonic coupling between mammalian neurons, cerebellar development and plasticity, neuronal transplantation, axonal guidance and even neuronal regeneration. From 1964 until his retirement in 2004, he was CNRS researcher and then, as director of INSERM Unit 106 at La Salpêtrière, he enabled his students and future collaborators to continue along many of the lines opened by himself. As an Emeritus researcher at the Vision Institute in Paris, he maintained a research activity until 2023.
Sotelo's career occupies a distinctive place in the history of neuroscience. He belonged to a generation that was close enough to Cajal to receive his intellectual tradition through a direct disciple, yet young enough to participate fully in the technological and conceptual revolution that transformed neurohistology into modern neuroscience. Through Fernando de Castro, there is a direct line from Cajal to Sotelo; through Sotelo's own students, collaborators, and discoveries, that lineage continued into new areas of cellular, developmental, and functional neuroscience.
His scientific life therefore represents more than continuity with a distinguished past. Constantino Sotelo helped carry the morphological tradition of Cajal forward, integrating the study of neuronal form with emerging questions about synaptic function, circuit development, plasticity, and regeneration. In doing so, he became part of the transformation of the discipline itself—from the great European schools of histology in which he was trained to the collaborative and interdisciplinary neuroscience practiced today.
The Cajal Club celebrated Sotelo’s extraordinary achievements in 2001, when he and King Juan Carlos I of Spain became the first recipients of the Club’s Krieg Lifetime Achievement Award. Reflecting on his passing, Cajal Club past president Carol Mason remembered him as “a true inheritor of Ramón y Cajal, with his precise and intuitive cellular anatomy, in one setting among many, of the developing cerebellum.” The Cajal Club will continue to remember Constantino Sotelo with admiration and gratitude for a life devoted to understanding the organization, development, and remarkable plasticity of the nervous system, and for his place in the living scientific legacy of Santiago Ramón y Cajal.
Constantino Sotelo shares a playful moment with Alain Chédotal’s daughter. Chédotal welcomed Sotelo into his laboratory at the Institut de la Vision in Paris, where Sotelo continued his scientific work as an emeritus researcher. Photo courtesy of Alain Chédotal.
By Dawn Hunter, Carol Mason and Alain Chédotal, September 2026
Read More about Constantino Sotelo’s Life and Legacy in El País, by Salvador Martínez Pérez and Fernando de Castro Soubriet, grandson of Sotelo’s mentor Fernando de Castro.
