Enkephalin-, thyrotropin-releasing hormone- and substance P-immunoreactive axonal innervation of the ventrolateral dendritic bundle in the cat sacral spinal cord: An ultrastructural study

Abstract

The distribution and synaptic arrangement of thyrotropin-releasing hormone-, substance P- and enkephalin-immunoreactive axonal boutons have been studied in the ventrolateral nucleus (Onuf's nucleus) of the upper sacral spinal cord segments in the cat. For this purpose, the peroxidase-antiperoxidase immunohistochemical technique was used. Immunoreactive axonal boutons were traced in complete series of sections in order to reveal synaptic contacts with the bundled dendrites of the ventrolateral nucleus. As judged from the cross-sectional diameter of the postsynaptic dendrites, the distribution of immunoreactive boutons was non-random. Enkephalin-immunoreactive axonal boutons, presumed to be mostly of segmental origin, displayed a rather restricted distribution to mainly (> 80%) medium-to-large dendrites. Thyrotropin-releasing hormone-immunoreactive boutons, that derive from supraspinal levels, were also found to impinge on medium-to-large dendrites (> 80%), indicating a proximal location within the dendritic trees. The skewness toward large postsynaptic dendrites was even more marked for thyrotropin-releasing hormone- than for enkephalin-immunoreactive boutons. Substance P-immunoreactive boutons, that are of either supraspinal or spinal origin, showed a more even distribution throughout the dendritic trees, including both thin distal branches and thick proximal dendrites. In view of the well-known fact that virtually all thyrotropin-releasing hormone-immunoreactive boutons in the ventral horn co-contain substance P (and serotonin) it was assumed that substance P-immunoreactive boutons in synaptic contact with the finest-calibre dendrites as well as most of those with a very proximal juxtasomatic location on the dendritic trees were of segmental origin, while those impinging on medium-to-large dendrites could be of either spinal or supraspinal origin. Fine-calibre dendrites (< 1 micron) represent about 25% of the dendritic branches in the ventrolateral nucleus, but receive, with the exception of substance P (8%), very little (< 3%) peptidergic or GABAergic (Ramírez-León and Ulfhake, 1993) input, although the degree of dendritic membrane covering by bouton profiles in the ventrolateral nucleus does not seem to vary much with the calibre of the postsynaptic dendrite (Ramírez-León and Ulfhake, 1993). Both substance P- and enkephalin-immunoreactive axonal boutons established synaptic contact with more than one dendrite. Furthermore, one and the same bouton could be found in contact with two dendrites that were coupled to each other by a dendro-dendritic contact of desmosomal or puncta adherentia type.(ABSTRACT TRUNCATED AT 400 WORDS)

Duloxetine for the treatment of post-prostatectomy stress urinary incontinence

“…[13][14][15] The somatic and autonomic neural innervation of the EUS arise from Onuf's nucleus of the sacral cord. [16][17][18] The postsynaptic autonomic neurons of the EUS have a high density of serotonergic and noradrenergic terminals. Blocking the reuptake of NE and 5-HT in the pre-synaptic adrenergic nerve results in increased EUS contractility secondary to increased stimulation of the post-synaptic 5-HT and NE receptors.…”

The Dual Nature of Onuf’s Nucleus: Neuroanatomical Features and Peculiarities, in Health and Disease

“…It has been demonstrated, in both human and laboratory animals, that Onuf's nucleus is densely innervated by CPON-(C-terminal Flanking Peptide of Neuropeptide Y), enkephalinand somatostatin-immunopositive fibers, suggesting an autonomic nature of these cells. In specific areas of the neuropil, dense aggregates of peptide-immunoreactive fibers are visible in the proximity of Onuf's nucleus (Gibson et al, 1988;Katagiri et al, 1988;Pullen et al, 1997). Indeed, the density of enkephalinimmunopositive varicosities is higher than over somatic neurons (Ramírez-León et al, 1994), and enkephalin fibers outline Onuf's nucleus (Gibson et al, 1988 (Gibson et al, 1988;Katagiri et al, 1988), and dopamine beta-hydroxylase (DBH)-immunoreactive fibers were described in rat Onuf's nucleus by Kojima et al (1985).…”

“…involvement (Kawatani et al, 1986;Pullen et al, 1997). In 1900, Onuf and colleagues (Onuf, 1900) reported that it innervates the only ischiocavernosus (and it's equivalent in females, erector clitoridis) and bulbospongiosus (or bulbocavernosus) muscles.…”

“…Onuf's neurons mainly display an ellipsoid shape (44%), and more rarely a circular (37%) or fusiform (19%) shape (Pullen et al, 1997). As the somatic motor neurons (MNs), Onuf's MNs are multipolar and show large Nissl granules.…”

“…Additionally, electron microscopic studies showed that the surrounding neuropil is characterized by few myelinated fibers and numerous vertical unmyelinated fibers arranged as dendritic bundles (Schrøder, 1981;Mannen, 2000): this could explain the appearance of Onuf's nucleus in a Nissl stain. Pullen et al (1997) performed several morphological analyses that allowed defining its dimension and the number and size of neurons. In some cases, these results (although referring to a few subjects and not statistically significant) highlighted a slight sexual dimorphism.…”