DIFFERENTIAL DISTRIBUTION OF CALCIUM-BINDING PROTEINS IN THE DORSAL COLUMN NUCLEI OF RATS - A COMBINED IMMUNOHISTOCHEMICAL AND RETROGRADE TRACT TRACING STUDY

This study aimed to investigate whether different calcium-binding prot eins are present in morphologically and functionally separate cell gro ups in the dorsal column nuclei of rats. Thalamic-projecting neurons w ere identified by iontophoretic injection of an intraaxonal tracer sub stance, choleragenoid, into the ventroposterolateral thalamic nucleus, which was localized by extracellular recordings of the responses to n atural peripheral stimulation. The presence of the calcium-binding pro teins calbindin and paravalbumin in the projection neurons was detecte d by a double labelling immunofluorescent method. The vast majority of the thalamic-projecting neurons contained paravalbumin, but not all p arvalbumin-immunoreactive cells were retrogradely labelled. Calbindin- immunoreactive neurons were also found in the dorsal column nuclei, bu t only a small minority of these neurons projected to the thalamus. Th ese findings are generally consistent with the notion that the differe nt calcium-binding proteins represent functionally separate neuronal p opulations. Taken together with previous observations that parvalbumin is present in large dorsal root ganglion cells, which project to the dorsal column nuclei, and in the thalamocortical relay cells that rece ive dorsal column nuclear input, the present findings suggest that par valbumin is associated with neurons that transmit modality-specific lo w-threshold mechanoreceptive information from the periphery to the som atosensory cortex. However, the presence of parvalbumin-immunoreactive cells that appeared not to project to the thalamus, as well as the oc currence of thalamic-projecting calbindin-immunoreactive neurons, indi cate that parvalbumin and calbindin are present within several, functi onally different, groups of neurons in the dorsal column nuclei. Copyr ight (C) 1996 IBRO.