Spacing of central-peripheral transitional nodes of rat motoneurones

Node of Ranvier distribution is examined in the two basic types of CNS-PNS transitional zone (TZ) related to rat spinal nerves. Type 1 TZ is short and lies at the cord surface. Type 2 is long and lies in the proximal part of the rootlet. Nearest neighbour distance measures the length between adjacent node centres and is a better estimate of node spacing than simple density measurements. Many nearest neighbour distances measure less than 10 microns. The nearest neighbour distance means (ca. 13.5 microns) and distributions are similar in both TZ types, suggesting that developmental influences on node separation are also similar in both locations. Fibres traversing the TZ are separated by large amounts of astrocytic tissue. This may prevent functional interaction between their closely packed nodes.