title: The topographic distribution of the efferents from neocortical neurons is not only dependent upon where in the neocortex the cells develop. A transplantation study within one single neocortical region.
abstract: It has been proposed that the distribution of efferents developed by neocortical neurons depends upon where in the neocortex the cells develop, not where they were generated. However, the capacity of diverse isocortical areas to differentiate connectional characteristics belonging to other isocortical areas has recently been questioned in several experiments using heterotopic transplantation paradigms. The present study was designed to determine whether the principle of multipotentiality is still valid within one single isocortical region. Mediolateral bands of embryonic (E16) frontal neocortex were dissected out and grafted into the left frontal cortex of neonate hosts according to either correct or inverted mediolateral orientation. Five to six months after grafting, a retrograde tracer was injected into the dorsomedial or ventrolateral left neostriatum of the host. The mediolateral distribution of the cell labeling within the transplant was then compared to that of an equivalent frontal cortical area (ECA) in control cases. The results indicate that strips of embryonic frontal neocortex transplanted according to a correct mediolateral orientation are able to develop a projection towards the host striatum whose mediolateral topographical distribution is not significantly different from that arising from the frontal neocortex of control animals. The percentages of transplant cells labeled in the medial or lateral division of the grafts were not significantly different from those found medially or laterally in the ECA in control cases. Following inversion of the mediolateral orientation of the grafts at the time of transplantation, the percentages of cells labeled in the medial or lateral division of the grafts were nearly equal whatever the site of tracer deposit within the host neostriatum. These results indicate that even within one single neocortical region the principle of areal interchangeability is not entirely validated and that the development of neocortical efferents is not only guided by extrinsic factors.
authors.affiliation: CNRS: URA 1869, Département des Neurosciences, Université de Poitiers, France.
authors.forename: C
authors.initials: C
authors.lastname: Garnier
authors.forename: P
authors.initials: P
authors.lastname: Arnault
authors.forename: A
authors.initials: A
authors.lastname: Ebrahimi-Gaillard
authors.forename: J
authors.initials: J
authors.lastname: Létang
authors.forename: M
authors.initials: M
authors.lastname: Roger
mesh_terms: D000818:Animals; D001931:Brain Mapping; D004525:Efferent Pathways / Q000502:physiology; D005260:Female; D016332:Fetal Tissue Transplantation / Q000502:physiology*; D005625:Frontal Lobe / Q000166:cytology / Q000196:embryology / Q000637:transplantation*; D008297:Male; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012016:Reference Values