ANATOMICAL DISTRIBUTION OF THE CHEMOREPELLENT SEMAPHORIN-III COLLAPSIN-1 IN THE ADULT-RAT AND HUMAN BRAIN - PREDOMINANT EXPRESSION IN STRUCTURES OF THE OLFACTORY-HIPPOCAMPAL PATHWAY AND THE MOTOR SYSTEM

Alterations in neuronal connectivity of the mature central nervous sys tem (CNS) appear to depend on a delicate balance between growth-promot ing and growth-inhibiting molecules, To begin to address a potential r ole of the secreted chemorepulsive protein semaphorin(D)III/collapsin- 1 (semaIII/coll-1) in structural plasticity during adulthood, we used high resolution nonradioactive in situ hybridization to identify neura l structures that express semaIII/coll-1 mRNA in the mature rat and hu man brain, SemaIII/ coll-1 was expressed in distinct but anatomically and functionally linked structures of the adult nervous system, The ol factory-hippocampal pathway displayed semaIII/coll-1 expression in a c ontinuum of neuronal structures, including mitral and tufted cells of the olfactory bulb, olfactory tubercle, and piriform cortex; and disti nct nuclei of the amygdaloid complex, the superficial layers of the en torhinal cortex, and the subiculum of the hippocampal formation, In ad dition, prominent labeling was found in neuronal components of the mot or system, particularly in cerebellar Purkinje cells and in subpopulat ions of cranial and spinal motoneurons. Retrograde tracing combined wi th in situ hybridization also revealed that the staining of semaIII/co ll-1 within the entorhinal cortex was present in the stellate neurons that project via the perforant path to the molecular layer of the dent ate gyrus, Like in the rat, the human brain displayed discrete express ion of semaIII/coll-1. Among the structures examined, the most promine nt staining was observed in the cellular islands of the superficial la yers of the human entorhinal cortex, The constitutive expression of th e chemorepellent semaIII/coll-1 in discrete populations of neurons in the mature rat and human CNS raises the possibility that, in addition to its function as repulsive axon guidance cue during development, sem aIII/coll-1 might be involved in restricting structural changes that o ccur in the wiring of the intact CNS. (C) 1998 Wiley-Liss, Inc.