Differing patterns of neurotrophin-receptor expressing neurons allow distinction of the transient Frorieps' ganglia from normal DRG before morphological differences appear

BDNF and NGF signals originating from sensory ganglia promote cranial motor axon growth

After exiting the hindbrain, branchial motor axons reach their targets in association with sensory ganglia. The trigeminal ganglion has been shown to promote motor axon growth from rhombomeres 2/3 and 4/5, but it is unknown whether this effect is ganglion specific and through which signals it is mediated. Here, we addressed these questions by co-cultures of ventral rhombomere 8 explants with cranial and spinal sensory ganglia in a collagen gel matrix. Our results show that all cranial sensory ganglia and even a trunk dorsal root ganglion can promote motor axon growth and that ganglia isolated from older embryos had a stronger effect on the axonal growth than younger ones. We found that brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) are necessary and sufficient for this effect. Altogether, our results demonstrate that the promoting effect of sensory ganglia on cranial motor axon growth is stage dependent, but not ganglion specific and is mediated by BDNF and NGF signals.

Occipital somites guide motor axons of the accessory nerve in the avian embryo

The accessory nerve (nervus accessorius) displays a unique organization in that its axons ascend along the rostrocaudal axis after exiting the cervical spinal cord and medulla oblongata and thereafter project ventrally into the periphery at the first somite level. Little is known about how this organization is achieved. We have investigated the role of somites in the guidance of motor axons of the accessory nerve using heterotopic transplantations of somites in avian embryos. The formation of not only accessory nerve but also the vagal nerve was affected, when a more caudal occipital somite (somites 2-4) was grafted to the position of the first occipital somite. Our study reveals that only the first occipital somite permits the development of ventral projection of accessory axons, a process that is inhibited by more caudal occipital somites.

Expression of seven members of the ADAM family in developing chicken spinal cord

The expression patterns of seven members of the ADAM (a disintegrin and metalloprotease) family, including ADAM9, ADAM10, ADAM12, ADAM13, ADAM17, ADAM22, and ADAM23, were analyzed in the developing chicken lumbar spinal cord by in situ hybridization and immunohistochemistry. Results show that each individual ADAM is expressed and regulated spatiotemporally in the lumbar cord and its surrounding tissues. ADAM9, ADAM10, ADAM22, and ADAM23 are expressed predominantly by motoneurons in the motor column and by sensory neurons in the dorsal root ganglia, each with a different expression pattern. ADAM12 and ADAM13 are mainly expressed in the meninges around the lumbar cord and in the condensed sheets of chondroblasts around the vertebrae. ADAM17 expression is strong in the ventricular layer and limited to early stages. The differential expression of the ADAMs in the lumbar cord suggests that the ADAMs play a regulatory role in development of the spinal cord.