Caudal end of the rat spinal dorsal horn.

We have previously demonstrated that the transformation of the caudal spinal cord through the conus medullaris to the filum terminale takes place in three steps. In the conus medullaris the twin layers of CGRP-immunoreactive and IB4-labeled primary afferent fibers as well as the translucent portion of the superficial dorsal horn equivalent to the substantia gelatinosa discontinue before the complete removal of the dorsal horn. Parallel with these changes VGLUT1-immunoreactive myelinated primary afferent fibers arborize not only in the deep layers but also in the entire extension of the remaining dorsal horn, while scattered CGRP fibers still remains at the margin of and deep in the dorsal horn. PKCgamma-immunoreactive dorsal horn neurons discontinue parallel with the disappearance of the IB4-labeled nerve fibers. These observations suggest that in the dorsal horn certain neurons are linked to the substantia gelatinosa, while others are substantia gelatinosa-independent neurons.

Neurochemical architecture of the filum terminale in the rat.

Contrary to the widespread assumption, the filum terminale in the rat possesses a precise glial and neuronal organization. The processes of glial fibrillary acidic protein-stained astrocytes form a rich, three dimensional array. The crescent shaped white matter could be outlined with antibody detecting oligodendrocytes. The neurons in the filum terminale, labeled with neuron-specific nuclear protein, are distributed in a small midline group (dorsal nucleus) dorsal to and in two symmetrical clusters at both sides of the central canal (lateral nuclei). Nitric oxide synthase-, calretinin-, choline acetyltransferase-, substance P- and neurokinin receptor-1-immunoreactive neurons were detected in the lateral nuclei. Axons were classified based on their course and termination. Small number of calcitonin gene-related peptide-immunoreactive fibers was found exclusively in the dorsal nucleus. Nitric oxide synthase-, substance P-, and neurokinin receptor-1-stained axon arborizations were detected mainly in the lateral nucleus. A dense array of extremely fine vesicular glutamate transporter 2- and fine, synaptophysin-immunoreactive varicosities covered densely the lateral nuclei. Fine glycine-transporter 2-immunoreactive axon arborization like structures were seen also in the lateral nucleus. Vesicular glutamate transporter 1- and choline acetyltransferase-immunoreactive axons arborized in the entire gray matter. Serotonin- and enkephalin-immunoreactive fibers congregated in the dorsolateral portion of the white matter, called "shoulder region", while calretinin- and thick, varicose neurokinin receptor-1-stained axons were also seen in the same area of the white matter. Synaptophysin-immunoreactive fine varicosities colocalized only with vesicular glutamate transporter 2 immunoreaction. Substance P and glycine-transporter 2-immunoreactive puncta were found in close contact with neurokinin receptor-1-immunostained perikarya and dendrites.