Representations of hindlimb digits in rat dorsal root ganglia

The distribution in dorsal root ganglia of neurones that innervate the dist al tips of the hindlimb digits in the rat were mapped after subcutaneous in jections of the fluorescent tracers Fast Blue, Diamidino Yellow, and Fluoro -Gold into different digits. Three-dimensional reconstruction was used to d escribe the intraganglionic distribution of neurones labelled from differen t digits. Labelled neurones were found mainly in the L3-L5 ganglia. The dis tribution in ganglia and the number of neurones labelled from each digit va ried considerably between cases, but mean numbers of labelled neurones were similar for the different digits. Neurones in L3 tended to innervate media l digits and neurones in L5 tended to innervate lateral digits, but most ne urones from any digit were found in L4. Although overlap was considerable, the three-dimensional reconstruction showed tendencies of neurones to be di stributed in restricted territories within the dorsal root ganglia. This wa s especially clear in ganglion L5, where digit TV was found to be represent ed more rostrally than digit V. The results indicate that primary afferent neurones that innervate the hindlimb digits are represented by a crude rost rocaudal somatotopic organisation both among and within lumbar dorsal root ganglia. (C) 1999 Wiley-Liss, Inc.