Subpopulation Of Nerve Fibers Research Articles

Innervation Changes Induced by Inflammation in the Murine Vagina

Vulvodynia is a prevalent chronic pain disorder associated with high medical costs and often ineffective treatments. The major pathological feature is proliferation of vaginal nerve fibers. This study aimed to develop a highly reproducible animal model to study neuroproliferation in the vagina and aid the identification of appropriately targeted treatments for conditions such as vulvodynia. Mild chronic inflammation was induced using microinjection of complete Freund’s adjuvant in the distal vagina of C57Bl/6 mice. Control mice received saline. Inflammation and innervation density were assessed at 7 and 28 days after a single administration or 14 days following repeated administration of complete Freund’s adjuvant or saline. Histochemistry and blinded-analysis of images were used to assess vaginal morphology (H & E) and abundance of macrophages (CD68-labeling), mast cells (toluidine blue staining, mast cell tryptase-immunoreactivity), blood vessels (αSMA-immunoreactivity) and nerve fibers immunoreactive for the pan-neuronal marker PGP9.5. Subpopulations of nerve fibers were identified using immunoreactivity for calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY). Single administration of complete Freund’s adjuvant resulted in vaginal swelling, macrophage infiltration, vascular proliferation and increased abundance of nerve fibers immunoreactive for CGRP, SP, VIP and/or PGP9.5 but not NPY, evident at seven days. Inflammation further increased following repeated administration of complete Freund’s adjuvant but nerve fiber proliferation did not. Nerve fiber proliferation continued to be evident at 28 days. The inter-individual differences within each treatment group were small, indicating that this model may be useful to study mechanisms underlying vaginal nerve fiber proliferation associated with inflammation.

CGRP and substance P in intraepithelial neuronal structures of the human upper respiratory system

The distribution of intraepithelial nerve fibres and neuroendocrine cells within the surface and glandular epithelium of human nasal mucosa and larynx was examined using immunohistochemical techniques. Neuronal structures were immunostained for the general neuroendocrine marker protein gene-product (PGP) 9.5, and the two neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) using immunofluorescence and streptavidin–biotin-peroxidase complex (S-ABC) methods. Intraepithelial nerve fibres with free nerve endings contained PGP 9.5 and were found within the respiratory surface epithelium of the nasal mucosa and the squamous epithelium of the larynx. A subpopulation of these nerve fibres showed positive immunoreactivties with antibodies against SP and CGRP. Nerve fibres within the ductal epithelium of subepithelial excretory ducts passing the basal membrane and reaching the luminal part were detected. These nerve fibres showed CGRP-like immunoreactivity but not for SP. A dense network of nerve fibres within the squamous surface epithelium was detected in the subglottic and epiglottic region containing CGRP and SP in a small subpopulation of nerve fibres. Single intraepithelial taste buds in the epiglottic region and neuroendocrine cells within the subglottic epithelium expressed PGP 9.5.

Hair cycle-dependent plasticity of skin and hair follicle innervation in normal murine skin.

The innervation of normal, mature mammalian skin is widely thought to be constant. However, the extensive skin remodeling accompanying the transformation of hair follicles from resting stage through growth and regression back to resting (telogen-anagen-catagen-telogen) may also be associated with alteration of skin innervation. We, therefore, have investigated the innervation of the back skin of adolescent C57BL/6 mice at various stages of the depilation-induced hair cycle. By using antisera against neuronal (protein gene product 9.5 [PGP 9.5], neurofilament 150) and Schwann cell (S-100, myelin basic protein) markers, as well as against neural cell adhesion molecule (NCAM) and growth-associated protein-43 (GAP-43), we found a dramatic increase of single fibers within the dermis and subcutis during early anagen. This was paralleled by an increase in the number of anastomoses between the cutaneous nerve plexuses and by distinct changes in the nerve fiber supply of anagen vs. telogen hair follicles. The follicular isthmus, including the bulge, the seat of epithelial follicle stem cells, was found to be the most densely innervated skin area. Here, a defined subpopulation of nerve fibers increased in number during anagen and declined during catagen, accompanied by dynamic alterations in the expression of NCAM and GAP-43. Thus, our study provides evidence for a surprising degree of plasticity of murine skin innervation. Because hair cycle-associated tissue remodeling evidently is associated with tightly regulated sprouting and regression of nerve fibers, hair cycle-dependent alterations in murine skin and hair follicle innervation offer an intriguing model for studying the controlled rearrangement of neuronal networks in peripheral tissues under physiological conditions.

Pituitary adenylate cyclase-activating peptide-immunoreactive nerve fibers in the cat eye.

To study the occurrence and distribution of the neuropeptide pituitary adenylate cyclase-activating peptide (PACAP) in ocular and orbital structures of the cat. Immunocyto-chemistry to localize PACAP and double immunostaining to detect co-localization of PACAP with other neuropeptides. Numerous PACAP-immunoreactive nerve fibers were observed in the lacrimal gland, choroid and retroocular arteries. There was a sparse supply of PACAP-containing nerve fibers in the iris, ciliary body and conjunctiva. Subpopulations of PACAP-containing nerve fibers stored vasoactive intestinal peptide (VIP) or calcitonin gene-related peptide (CGRP). Around 10% of the ganglion cells in the sphenopalatine ganglion harbored PACAP immunoreactivity. In the trigeminal ganglion around 5% of the neuronal cell bodies and in the ciliary ganglion only occasional ganglion cells contained PACAP immunoreactivity. PACAP immunoreactivity co-localized with VIP in the sphenopalatine ganglion and with CGRP in the trigeminal ganglion. PACAP-containing nerves in the eye and associated structures demonstrate a distribution pattern resembling that of VIP. Subpopulations of nerve fibers containing PACAP immunoreactivity store VIP or CGRP immunoreactivity. Neuronal PACAP in the eye and orbit may take part in regulation of smooth muscle tone, glandular secretion and sensory processing.

The innervation of taste buds in the soft palate of the rat as revealed by methylene blue staining.

Light microscopic data on the innervation of taste buds in the soft palate of the rat obtained by methylene blue (MB) supravital staining are presented here for the first time. The taste pore including subpopulations of taste bud cells and nerve fibers were stained. Intragemmal nerve fibers were detected ascending up to the taste pore; this suggests the possibility of additional paracellular pathways in taste transduction directly via nerve fibers. Moreover, relatively large bulbous or laminar enlargements of the intragemmal nerve fibers were found. The branches of these nerve fibers, showing minute spiny protuberances, appeared to anastomose. Some perigemmal nerve fibers were also seen in close apposition to the taste pore. The basal plexus in the vicinity of the taste buds showed enlargements which resembled the Merkel's discs, but were significantly smaller. These structures did not occur in the subgemmal part of the basal plexus. Regarding the oxygen-dependency of the staining reaction, it was speculated that both MB and oxygen were attracted by iron-containing enzymes. Therefore, the strong affinities for MB shown by subpopulations of nerve fibers and taste bud cells were explained by their high requirements for oxygen. Furthermore due to its selectivity for intraepithelial nerve fibers and sensory cells, the method applied here is well-suited for routine use in light microscopy.

Pharmacological characterization of serotonin synthesis and uptake suggest a false transmitter role for serotonin in the pituitary intermediate lobe

A subpopulation of nerve fibers in the rat pituitary intermediate lobe (IL) have been shown to exhibit colocalization of serotonin (5-HT-IR) and tyrosine hydroxylase immunoreactivities and they are sensitive to neurotoxins specific to catecholamine neurons. This study was set out to examine the uptake and synthesis mechanisms of serotonin in these fibers. We developed an in vitro technique in which the neurointermediate lobe explants were incubated (14 and 48 h) in the presence of various drugs and serotonin was subsequently visualized by immunohistochemistry. Control incubation in the presence of serotonin (10 −6 M) resulted in a rich plexus of 5-HT-IR fibers in both posterior and intermediate lobes. Fluoxetine and citalopram (10 −6 M and 10 −5 M), inhibitors of 5-HT transporter, did not affect 5-HT-IR in the IL fibers, unless they were used in concentrations high enough (10 −4 M and 10 −3 M) to block unspecifically a number of monoamine transporters. The same applied for desipramine (10 −5–10 −7 M), an inhibitor of the noradrenaline transporter. However, cocaine (10 −5–10 −6 M) blocked serotonin uptake into these terminals, suggesting that serotonin uptake occurs through a dopamine transporter. Incubation of the IL in presence of l-tryptophan (10 −4 M) did not result in 5-HT-IR in the IL fibers showing colocalization of 5-HT-IR and tyrosine hydroxylase, which suggests that these fibers do not synthesize serotonin. The present results suggest that serotonin is taken up into the IL terminals by a dopamine transporter and is not synthesized in them, at least in vitro. Thus, serotonin may act as a false transmitter in some of the IL fibers, which may prove to be a valuable model tissue for studying serotonin's role as an exogenously synthesized cotransmitter.

Carbonic anhydrase activity in the peripheral nervous system of rat: the enzyme as a marker for muscle afferents

The distribution of carbonic anhydrase (CA) activity was determined histochemically using Hansson's cobalt phosphate method in cross-sections of peripheral nerves from rats. As the studied nerves contain either efferent, proprioceptive or exteroceptive myelinated fibres, our survey particularly focused on the question whether CA-reactive nerve fibres are functionally related. Intense CA activity was detected in all large diameter (8–12 μm) muscle afferents. The amount of similarly reactive cutaneous afferents was negligibly low (3.6%). Efferent fibres displayed only weak CA activity, which was confined to the small myelinated fibres (3–6 μm). Moderate staining could be assessed in medium-sized (4–11 μm) proprioceptive fibres. The same reactivity occurred in a sizeable percentage (11.4%) of exteroceptive afferents. Their diameters ranged from 4 to 11 μm. These results indicated, that high enzyme activity is found predominantly in large-calibre proprioceptive afferents, which according to Hunt's classification were identified as group IA and IB fibres. Further confirmation for our observations was obtained by demonstrating high levels of enzyme activity in primary nerve endings of muscle spindles (IA fibres) and in axon terminals of Golgi tendon organs (IB fibres) constantly. Finally possible functions for neuronal CA are discussed with respect to its high activity in a functionally related subpopulation of nerve fibres.