Expression of dopamine by chick primary sensory neurons and their related targets.

The expression of dopamine by primary sensory neurons and their peripheral projections was studied in the chick dorsal root ganglion by means of immunocytochemical procedures. Within the sensory neurons, dopamine immunoreactivity is first expressed by 0.8% of cells at E10 and reaches a percentage of 5.6% before hatching. After hatching, 8.6% of neurons, belonging to both the A and B classes of sensory neurons, exhibit a clear immunostaining. According to the immunostaining of nerve terminals located in various peripheral target tissues, these immunoreactive neurons are responsible, at least in part, for the sensory innervation of the skin and paravertebral ganglia. The results provide evidence that different classic neurotransmitters may be expressed by specific subpopulations of primary sensory neurons expressing various somatic and autonomic sensory functions in relation to specific targets.