Afferents of cranial sensory ganglia pathfind to their target inadependentof the site of entry into the hindbrain

In vertebrates, sensory neurons interconnect a variety of peripheral tissue s and central targets, conveying sensory information from different types o f sensory receptors to appropriate second-order neurons in the central nerv ous system:(CNS). To explore the possibility that the different rhombomere environments where sensory neurons enter into the hindbrain affect the path finding capability of growth cones, We studied the development of the VIIIt h ganglion afferent both in vivo and in vitro. We focused on the vestibular nerve because it is the only cranial nerve projecting to the cerebellum, a llowing: for ready identification from its pattern of projection. Embryonic rat brain was cut along the dorsal midline and, with the VIIIth and Vth ga nglia still attached, flat mounted and visualized with antibodies specific for sensory ganglia. Axons reached the cerebellar primordium: at embryonic day (E) 13, then splayed out towards the edges of the rhombic lip of rostra l hindbrain. In vitro, the VIIIth ganglion showed development similar to th at in vivo and innervated the cerebellum, an appropriate target, indicating that mechanisms for axon guidance and target recognition are preserved in vitro. When the VIIIth ganglion was transplanted to the position of the Vth ganglion, axons from the transplanted ganglion entered the cerebellar prim ordium with a trajectory characteristic of the VIIIth nerve. These results indicate that the central projection pattern of the VIIIth nerve is not aff ected by the environment of nerve entry into the brainstem, suggesting that axons of sensory cranial ganglion intrinsically possess the capacity to fi nd their target correctly. (C) 2000 Wiley-Liss, Inc.