TOPOGRAPHY OF PRIMARY AFFERENT-PROJECTIONS IN THE TRIGEMINAL SENSORY NUCLEI OF RATS

The afferent projection pattern from individual vibrissae follicles wa s related to the distribution of cytochrome oxidase (CO) dark cell clu sters in the trigeminal sensory nuclei of adult rats to determine whet her segregated primary afferent projections limit the extent of the to pographic reorganizations that can occur at the level of the brainstem on a short term basis after changes in sensory driven activity. The r esults indicate that the projections to all the brain stem trigeminal subnuclei, including the principal sensory nucleus and the three subdi visions of the spinal trigeminal nucleus, are topographic; however, th e extent to which label from different whisker rows overlap appears to differ from subdivision to subdivision. In the principal sensory nucl eus there is nearly a one to one relationship between the inputs from the vibrissae follicles and the corresponding GO-dense clusters. Thus, little overlap of inputs from different vibrissae rows is likely. In contrast, in the pars interpolaris and, to a lesser extent, in the par s caudalis, inputs from individual vibrissae follicles extend beyond t he appropriate GO-dark patch into adjacent whisker patches; thus, inpu ts to these subdivisions from different vibrissae likely overlap more extensively.