IMMUNOCYTOCHEMICAL STUDY OF PHENOTYPIC PLASTICITY OF CULTURED DORSAL-ROOT GANGLION NEURONS DURING DEVELOPMENT

Rat dorsal root ganglia (DRG) were cultured from different stages of d evelopment ranging from embryonic day-14 to adult. The expression of e ight neurotransmitter phenotypes was examined with immunocytochemical detection and the percentages of each phenotype were calculated with r eference to the whole neuronal population defined by the expression of neuron specific enolase (NSE). The expression of peptides, calcitonin gene-related peptide (CGRP), substance P (SP), cholecystokinin (CCK) and neuropeptide Y (NPY) was always present whatever the age at onset of the cultures. Although the percentage of CGRP remained stable, that of the other peptides declined progressively. Their in-vitro expressi on did not differ markedly from that found in vivo. Another group of n eurotransmitters, including 5-hydroxytryptamine (5-HT), thyrotropin-re leasing hormone (TRH) and gamma-aminobutyric acid (GABA) was never exp ressed in situ in DRG neurons. In culture, they were expressed in a hi gh percentage of neurons, especially for 5-HT and TRH, and they showed a similar evolution, with a decrease at early postnatal ages followed by a further increase. This profile suggests that the expression of t hese transmitters is strongly environment-dependent and may be repress ed in situ. Finally, somatostatin (SOM) was found only in cultures pre pared from adult tissues, whereas it was present in situ from the embr yo onwards. The expression of this peptide would thus require a stabil ization by a long exposure to environmental factors. We can conclude t hat the great diversity of phenotypic expression found in DRG neurons in situ is the result of a wide variety of influences occurring at dif ferent stages of development in a large potential repertory present in these neurons.