The distribution of oxytocin- and neurophysin-stained fibers in the spinal cord of the rat and monkey.

Immunohistochemical methods have been used to describe the distribution of neurophysin I- and oxytocin-stained fibers in the spinal cord. In albino rats of either sex, such fibers descend through the dorsal part of the lateral funiculus to the caudal end of the cord. Fibers leave the lateral funiculus to innervate the marginal zone of the dorsal horn at all levels, and the intermediolateral column at thoracic, lumbar and sacral levels. Some fibers course medially through the intermediate gray to end in the central gray, which is innervated at all levels, and also appears to be innervated by fibers descending in the central gray itself. A semiquantitative analysis shows that the density of terminal fields in the intermediolateral column, marginal zone, and central gray varies significantly at different levels. The intermediolateral column is preferentially innervated between T1-T3, T9-T11, and T13-L2. The nucleus intercalatusspinalis and the dorsal commissural nucleus (between T13 and L2), both of which contain preganglionic neurons, are densely innervated. In the monkey (Macaca fascicularis), neurophysin I- and oxytocin-stained fibers descend through the lateral funiculus to the filum terminale, where some of them enter the pia-arachnoid surrounding the filum. The intermediolateral column is not innervated between T1-T3, is sparsely innervated at sacral levels, and is moderately innervated between T4 and L3; the greatest density of fibers occurs at L3. At most levels, few if any fibers are found in the central gray and marginal zone; the central gray is sparsely innervated between T8 and L2 at S2, and between Co3-Co6, and the marginal zone contains a small number of fibers in the region of S2 and Co6. Neurophysin I- and oxytocin-stained fibers were also found in the intermediolateral column, marginal zone, and central gray of homozygous Brattleboro, spontaneously hypertensive, and Egyptian sand rats. The results suggest that the paraventriculo-spinal pathway is particularly related to specific groups of sympathetic and parasympathetic preganglionic neurons, and to the marginal zone, whick is involved in the relay of ascending nociceptive information through the spinothalamic tract.