Influence of peripheral and central targets on subpopulations of sensory neurons expressing calbindin immunoreactivity in the dorsal root ganglion of the chick embryo.

The influence of central and peripheral target tissues on the expression of calbindin D-28k by sensory neurons of the chick dorsal root ganglia was tested under various experimental conditions. Firstly, dorsal root ganglia of chick embryos were transplanted at two stages of development onto the chorioallantoic membrane of a host embryo for a period of 4 or 8 days. In dorsal root ganglia grafted at E12, 20% of the ganglion cell bodies were immunoreactive to calbindin 4 and 8 days later; the percentage of calbindin-immunostained neurons in grafted dorsal root ganglia was similar to that observed in control dorsal root ganglia of the same embryonic age (E16 or 20). In contrast, when grafted dorsal root ganglia were taken from a donor embryo at E8, no calbindin-immunoreactive neuron was found 4 or 8 days later. However, when dorsal root ganglia at E8 were cotransplanted with musculature cells, 14% of the grafted ganglion cell bodies were again immunoreactive to calbindin 4 or 8 days later. Secondly, peripheral targets of sensory neurons were suppressed by excision of one hindlimb. After excision at E6, virtually all the ipsilateral dorsal root ganglia cells were free of calbindin immunoreaction after 6 days of reincubation. In contrast, when the excision was performed at E11, calbindin was expressed in about 9% of the nerve cell bodies. Thirdly, central connections were destroyed by cauterization of the lumbosacral spinal cord at E6 or E11. Six days after deprivation of central connections, the percentage of calbindin-immunoreactive ganglion cells was the same as in control dorsal root ganglia of the same age.(ABSTRACT TRUNCATED AT 250 WORDS)