DIFFERENTIAL DISTRIBUTION OF CALBINDIN-D-28K AND PARVALBUMIN IN SOMATIC AND VISCERAL SENSORY NEURONS

The purpose of the present investigation was to determine whether calb indin-D-28k and parvalbumin are distributed to different subpopulation s of somatic and visceral sensory neurons. Immunofluorescent and retro grade techniques were combined to examine the distribution of calbindi n- and parvalbumin-like immunoreactivity in the cell bodies of somatic and visceral primary afferent neurons in dorsal root ganglia L1-S1 of rats. Calbindin and parvalbumin were differentially distributed to es sentially non-overlapping subpopulations of primary sensory neurons th at could be distinguished by their segmental and size distributions, a s well as by their innervation of somatic and visceral structures. Cal bindin-like immunoreactivity was found in a population of smaller-size d cell bodies comprising approximately 14% of all dorsal root ganglion cells examined, with the proportions being greatest in L6 and S1. In contrast, parvalbumin was found In a population of larger-sized cells that made up about 11% of dorsal root ganglion cells and that were mos t concentrated in L4 and L5. Sensory neurons were further characterize d by retrograde transport following the application of the neuroanatom ical tracer FluoroGold to somatic (sural and gastrocnemius) and viscer al (hypogastric and pelvic) nerves. Somatic tissues were innervated by a population of calbindin-containing as well as a separate population of parvalbumin-containing sensory neurons. In contrast, afferent neur ons innervating visceral structures contained only a subpopulation of calbindin-containing neurons and very few parvalbumin-positive cells.