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

Abstract

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.

Hypothalamic Hypocretin (Orexin): Robust Innervation of the Spinal Cord

“…Whereas the paraventricular nucleus is reported to send only a sparse innervation to the sacral cord (Swanson and McKellar, 1979), a large hypocretin projection is found here. This indicates that although there is some overlap between the descending projections from different fiber systems of the hypothalamus to the cord, there also appear to be some substantial differences.…”

“…Some of the same superficial dorsal horn regions innervated by hypocretin axons receive an innervation from oxytocin-or vasopressin-containing fibers from the paraventricular nucleus (Swanson and McKellar, 1979), in contrast to long descending axons from the cortex, which preferentially innervate the deeper layers of the dorsal horn (Brown, 1981). Whereas the paraventricular nucleus is reported to send only a sparse innervation to the sacral cord (Swanson and McKellar, 1979), a large hypocretin projection is found here.…”

Evidence for the presence and functioning of the spinal generator for ejaculation in the neonatal male rat

“…[11][12][13] These oxytocin receptors in the neonatal spinal cord appear to be functional given that a variety of electrophysiological effects in response to oxytocin have been reported 13 and since a novel role for oxytocin in the activation of spinal locomotor pattern generators has been recently demonstrated. 14 Moreover, the paraventricular hypothalamic nucleus contributes with descending oxytocinergic fibres to the lumbosacral spinal cord 15,16 and it has been shown that the local administration of oxytocin to spinal adult rats exerts prosexual effects. 17 Interestingly, in the present study, we registered facilitated rhythmic ejaculatory motor responses in neonatal male rats during the first 21 postnatal days, and after this developmental period, a significant decrease in motor activity was observed.…”

Spinal effects of oxytocin on uterine motility in anesthetized rats

“…urogenital; lumbosacral spinal cord; sexual reflexes OXYTOCIN (OT) exerts peripheral contractile effects on the uterus after its release into the systemic circulation by magnocellular neurons of the paraventricular nucleus (29). In addition to this endocrine mode of action, OT may also be released at various levels of the brain stem and spinal cord by paraventriculo-spinal projections originating in parvocellular neurons of the paraventricular nucleus (5,25,28,30,31,33). In the brain stem, this pathway activates motoneurons of the dorsal motor nucleus of the vagus to increase gut motility (6).…”