Sensory Neurons and NT-3 Research

[Guest guest]

1: Dev Biol 2002 Sep 15;249(2):255-69

(This research was done with chick embryos - some more NT-3 news)

Target-independent specification of proprioceptive sensory neurons.

Oakley RA, Karpinski BA.

Department of Anatomy and Cell Biology, The Washington University

Medical Center, Washington, DC 20037, USA. anarao@...

Previous studies in the chick embryo have shown that sensory neurons

fail to innervate muscle in the absence of motor neurons. Instead, motor

neuron deletion causes more sensory axons to project to the skin. We

used this experimental paradigm to determine when sensory neurons are

specified to become proprioceptive afferents. Experimental embryos were

treated with either saline or exogenous neurotrophin-3 (NT-3) to promote

the survival of proprioceptive afferents. In saline-treated embryos,

motor neuron deletion caused an increase in sensory neuron apoptosis on

the deleted side, an effect

reversed by NT3. Motor neuron deletion also eliminated the sartorious

muscle nerve, as previously reported. In NT3-treated embryos, this

altered nerve pattern was accompanied by the enlargement of the adjacent

cutaneous nerve. These embryos were further analyzed by using

immunohistochemistry for trkC (a receptor for NT3) retrograde and

transganglionic labeling. Our results show that, following motor neuron

deletion, more trkC+ afferents project in cutaneous nerves on the

deleted side of NT3-treated embryos.

Transganglionic labeling demonstrated that at least some of these

neurons made spinal projections that are typical of proprioceptive

afferents. These results therefore indicate that the proprioceptive

phenotype is specified prior to target innervation and that these

neurons can retain their identity despite projecting to inappropriate

(cutaneous) targets.