Dental pulp cells produce neurotrophic factors, interact with trigeminal neurons in vitro, and rescue motoneurons after spinal cord injury

Interactions between ingrowing nerve fibers and their target tissues form t he basis for functional connectivity with the central nervous system. Studi es of the developing dental pulp innervation by nerve fibers from the trige minal ganglion is an excellent example of nerve-target tissue interactions and will allow specific questions regarding development of the dental pulp nerve system to be addressed. Dental pulp cells (DPC) produce an array of n eurotrophic factors during development, suggesting that these proteins migh t be involved in supporting trigeminal nerve fibers that innervate the dent al pulp. We have established an in vitro culture system to study the intera ctions between the dental pulp cells and trigeminal neurons. We show that d ental pulp cells produce several neurotrophic factors in culture. When DPC are cocultured with trigeminal neurons, they promote survival and a specifi c and elaborate neurite outgrowth pattern from trigeminal neurons, whereas skin fibroblasts do not provide a similar support. in addition, we show tha t dental pulp tissue becomes innervated when transplanted ectopically into the anterior chamber of the eye in rats, and upregulates the catecholaminer gic nerve fiber density of the irises. Interestingly, grafting the dental p ulp tissue into hemisected spinal cord increases the number of surviving mo toneurons, indicating a functional bioactivity of the dental pulp-derived n eurotrophic factors in vivo by rescuing motoneurons. Based on these finding s, we propose that dental pulp-derived neurotrophic factors play an importa nt role in orchestrating the dental pulp innervation. (C) 2001 Academic Pre ss.