Partial coexistence of neuropeptide Y and calbindin D28k in the trigeminal ganglion following peripheral axotomy of the inferior alveolar nerve in the rat

Effects of peripheral nerve injury on parvalbumin expression in adult rat dorsal root ganglion neurons

Background

Parvalbumin (PV) is a calcium binding protein that identifies a subpopulation of proprioceptive dorsal root ganglion (DRG) neurons. Calcitonin gene-related peptide (CGRP) is also expressed in a high proportion of muscle afferents but its relationship to PV is unclear. Little is known of the phenotypic responses of muscle afferents to nerve injury. Sciatic nerve axotomy or L5 spinal nerve ligation and section (SNL) lesions were used to explore these issues in adult rats using immunocytochemistry.

Results

In naive animals, the mean PV expression was 25 % of L4 or L5 dorsal root ganglion (DRG) neurons, and this was unchanged 2 weeks after sciatic nerve axotomy. Colocalization studies with the injury marker activating transcription factor 3 (ATF3) showed that approximately 24 % of PV neurons expressed ATF3 after sciatic nerve axotomy suggesting that PV may show a phenotypic switch from injured to uninjured neurons. This possibility was further assessed using the spinal nerve ligation (SNL) injury model where injured and uninjured neurons are located in different DRGs. Two weeks after L5 SNL there was no change in total PV staining and essentially all L5 PV neurons expressed ATF3. Additionally, there was no increase in PV-ir in the adjacent uninjured L4 DRG cells. Co-labelling of DRG neurons revealed that less than 2 % of PV neurons normally expressed CGRP and no colocalization was seen after injury.

Conclusion

These experiments clearly show that axotomy does not produce down regulation of PV protein in the DRG. Moreover, this lack of change is not due to a phenotypic switch in PV immunoreactive (ir) neurons, or de novo expression of PV-ir in uninjured neurons after nerve injury. These results further illustrate differences that occur when muscle afferents are injured as compared to cutaneous afferents.

Primary sensory neurons containing choline acetyltransferase of the peripheral type in the rat trigeminal ganglion and their relation to neuropeptides-, calbindin- and nitric oxide synthase-containing cells

We have previously demonstrated that a variant form of choline acetyltransferase (pChAT) is expressed in rat trigeminal neurons. To assess the significance of pChAT in sensory functions, we characterized immunohistochemically pChAT-positive trigeminal neurons in the rat. pChAT-immunoreactivity was observed in a rather uniform pattern in about half of all trigeminal neurons throughout the trigeminal ganglion. The majority of pChAT-positive neurons had small to medium-sized cell bodies. Double immunofluorescent study showed that more than 90% of substance P (SP)-positive trigeminal cells and about 80% of calcitonin gene-related peptide (CGRP)-positive cells exhibited pChAT-immunoreactivity. pChAT-positive cells formed a larger population of neurons than SP-positive or CGRP-positive cells, but they were a different population from calbindin-D(28k)-positive neurons. In addition, pChAT-immunoreactivity was present in a subset of neurons positive for neuronal nitric oxide synthase. The present results suggest that pChAT plays roles not only in nociception, but also in other sensory functions such as mechanoreception mediating tactile sensation.

Changes in P2X3 purinoceptors in sensory ganglia of the mouse during embryonic and postnatal development

The expression of the P2X(3) nucleotide receptor in embryonic day 14-18, postnatal day 1-14 and adult mouse sensory ganglia was examined using immunohistochemistry. Nearly all sensory neurons in dorsal root ganglia, trigeminal ganglia and nodose ganglia in embryos at embryonic day 14 expressed P2X(3) receptors, but after birth there was a gradual decline to about 50% of neurons showing positive immunostaining for P2X(3). In embryos there were only small neurons, while from postnatal day 7 both large and small neurons were present. Isolectin B(4) (IB(4))-positive neurons in dorsal, trigeminal and nodose ganglia did not appear until birth, but the numbers increased to about 50% by postnatal day 14 when a high proportion of IB(4)-positive neurons were also positively labelled for the P2X(3) receptor. About 10% of neurons in dorsal, trigeminal and nodose ganglia were positive for calcitonin gene-related peptide in embryos, nearly all of which stained for P2X(3) receptors. This increased postnatally to about 35-40% in adults, although only a few colocalised with P2X(3) receptors. Neurofilament 200 was expressed in about 50% of neurons in trigeminal ganglia in the embryo, and this level persisted postnatally. All neurofilament 200-positive neurons stained for P2X(3) in embryonic dorsal root ganglia, trigeminal ganglia and nodose ganglia, but by adulthood this was significantly reduced. The neurons that were positive for calbindin in embryonic dorsal, trigeminal and nodose ganglia showed colocalisation with P2X(3) receptors, but few showed colocalisation postnatally.

Comparative immunohistochemical analysis of the peptidergic innervation of human primary and permanent tooth pulp

This immunohistochemical study sought to determine whether there are any differences in the peptidergic innervation of these pulps and whether dental caries is associated with changes in neuropeptide expression. Mandibular first permanent molars and second primary molars (n=120) were obtained from children requiring dental extractions under general anaesthesia. Extracted teeth were split longitudinally, placed in fixative, and categorized as intact, moderately carious or grossly carious. The coronal pulps were removed and 10-microm frozen sections were processed for indirect immunofluorescence. Double labelling employed combinations of the following antisera: (1) protein gene product 9.5, a general neuronal marker; (2) one of the neuropeptides calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), galanin (GAL), enkephalin (ENK) and somatostatin (SOM). Image analysis was then used to determine the percentage area of immunostaining for each label within different anatomical regions of the coronal pulp. Sparse or absent immunoreactivity for GAL, ENK and SOM made analysis impossible. Analysis of CGRP, SP and VIP revealed significant interdentition differences, with their expression being significantly greater in permanent teeth, but this was not the case for NPY, with primary and permanent teeth demonstrating a similar amount of label for this peptide. Both dentitions showed significant increases in CGRP, SP, VIP and NPY expression with caries progression. These findings could have biological and clinical importance in connection with nociception, inflammation and healing.

Comparative analysis of the chemical neuroanatomy of the mammalian trigeminal ganglion and mesencephalic trigeminal nucleus

A characteristic peculiarity of the trigeminal sensory system is the presence of two distinct populations of primary afferent neurons. Most of their cell bodies are located in the trigeminal ganglion (TG) but part of them lie in the mesencephalic trigeminal nucleus (MTN). This review compares the neurochemical content of central versus peripheral trigeminal primary afferent neurons. In the TG, two subpopulations of primary sensory neurons, containing immunoreactive (IR) material, are identified: a number of glutamate (Glu)-, substance P (SP)-, neurokinin A (NKA)-, calcitonin gene-related peptide (CGRP)-, cholecystokinin (CCK)-, somatostatin (SOM)-, vasoactive intestinal polypeptide (VIP)- and galanin (GAL)-IR ganglion cells with small and medium-sized somata, and relatively less numerous larger-sized neuropeptide Y (NPY)- and peptide 19 (PEP 19)-IR trigeminal neurons. In addition, many nitric oxide synthase (NOS)- and parvalbumin (PV)-IR cells of all sizes as well as fewer, mostly large, calbindin D-28k (CB)-containing neurons are seen. The majority of the large ganglion cells are surrounded by SP-, CGRP-, SOM-, CCK-, VIP-, NOS- and serotonin (SER)-IR perisomatic networks. In the MTN, the main subpopulation of large-sized neurons display Glu-immunoreactivity. Additionally, numerous large MTN neurons exhibit PV- and CB-immunostaining. On the other hand, certain small MTN neurons, most likely interneurons, are found to be GABAergic. Furthermore, NOS-containing neurons can be detected in the caudal and the mesencephalic-pontine junction portions of the nucleus. Conversely, no immunoreactivity to any of the examined neuropeptides is observed in the cell bodies of MTN neurons but these are encircled by peptidergic, catecholaminergic, serotonergic and nitrergic perineuronal arborizations in a basket-like manner. Such a discrepancy in the neurochemical features suggests that the differently fated embryonic migration, synaptogenesis, and peripheral and central target field innervation can possibly affect the individual neurochemical phenotypes of trigeminal primary afferent neurons.

Calbindin-D28k in cerebrovascular extrinsic innervation system of the rat

Calbindin-D28k, one of the calcium-binding proteins, belongs to the EF hand family and is commonly found in neurons. It serves as a representative neuronal marker for neuroanatomical investigations. The authors' knowledge of its precise function, however, is yet very limited. In this study, we examined the existence of nerve fibers with calbindin-D28k immunoreactivity in the cerebral blood vessels and ganglia that innervate the cerebral blood vessels in the rat. Numerous nerve fibers with calbindin-D28k immunoreactivity were observed on the walls of the major extracerebral arteries forming the circle of Willis and its branches. Calbindin-D28k immunoreactivity was seen in many neurons of the trigeminal, dorsal root and jugular ganglia. A small number of neurons showed calbindin-D28k immunoreactivity in the otic and superior cervical ganglia. Calbindin-D28k immunoreactivity was not detected in the sphenopalatine or internal carotid ganglia. Pericellular basket-like formations of nerve terminals with calbindin-D28k immunoreactivity were observed in the sphenopalatine, otic, internal carotid and superior cervical ganglia. The present study demonstrated calbindin-D28k immunoreactivity in the cerebrovascular nerve fibers as well as in their origins--the cranial ganglia. These findings are significant in understanding the calcium-mediated mechanism of the neural control of the cerebral blood vessels.

Peripheral nerve regeneration and neurotrophic factors

The role of neurotrophic factors in the maintenance and survival of peripheral neuronal cells has been the subject of numerous studies. Administration of exogenous neurotrophic factors after nerve injury has been shown to mimic the effect of target organ-derived trophic factors on neuronal cells. After axotomy and during peripheral nerve regeneration, the neurotrophins NGF, NT-3 and BDNF show a well defined and selective beneficial effect on the survival and phenotypic expression of primary sensory neurons in dorsal root ganglia and of motoneurons in spinal cord. Other neurotrophic factors such as CNTF, GDNF and LIF also exert a variety of actions on neuronal cells, which appear to overlap and complement those of the neurotrophins. In addition, there is an indirect contribution of GGF to nerve regeneration. GGF is produced by neurons and stimulates proliferation of Schwann cells, underlining the close interaction between neuronal and glial cells during peripheral nerve regeneration. Different possibilities have been investigated for the delivery of growth factors to the injured neurons, in search of a suitable system for clinical applications. The studies reviewed in this article show the therapeutic potential of neurotrophic factors for the treatment of peripheral nerve injury and for neuropathies.

Neurotrophin-3 delivered locally via fibronectin mats enhances peripheral nerve regeneration

A better understanding of the mechanisms of nerve regeneration could improve the outcome of surgical nerve repair. We have previously shown that axonal regeneration is increased by nerve growth factor. Neurotrophin-3 (NT-3) belongs to the same family as nerve growth factor but acts on a distinct neuron subpopulation. As little is known about its role following nerve injury, we have investigated the effect of NT-3 delivered via fibronectin mats, previously shown to support nerve regeneration comparable to nerve grafts. NT-3 stimulation (0.1-1000 ng/ml) of neurite extension from embryonic chick dorsal root ganglia in vitro has shown that fibronectin can bind and release bioactive NT-3. Fibronectin mats impregnated with NT-3 (500 ng/ml) were grafted into 1 cm sciatic nerve defects in adult Lewis rats. Plain mats were used as controls. Computerized quantification of penetration distance, volume of axonal regeneration and myelinated fibre counts was undertaken using immunostaining for axonal markers (growth-associated protein 43, calcitonin gene-related peptide, substance P, vasoactive intestinal peptide and neuropeptide tyrosine), or S100 or thionine blue staining up to 8 months postoperatively. The maximal effect of NT-3 occurred at day 15, when for GAP43-immunostained axons both penetration distance (NT-3, 6.10 +/- 0.42 mm; control, 4.11 +/- 0.41 mm; P < 0.01) and staining area (NT-3, 0.137 +/- 0.012 mm2; control, 0.077 +/- 0.018 mm2; P < 0.05) were significantly increased. Similar results were found for each neuronal subpopulation investigated. By 8 months after repair, the NT-3 group supported a significantly greater number of myelinated axons (NT-3, 7003 +/- 402; control, 4932 +/- 725; P < 0.05) of similar diameter and g-ratio to controls. These results demonstrate the contribution of NT-3 to the increase of nerve regeneration promoted by growth factors.

Immunohistochemical localization of calbindin D28k in the periodontal Ruffini endings of rat incisors

It was examined whether calbindin D28k (CB) might be located in the rat incisor periodontal Ruffini ending, an essential mechanoreceptor in periodontal ligament, by light- and electron-microscopic immunohistochemistry. Some thick nerve fibers showing CB-like immunoreactivity (LI) entered the lingual half of the periodontal ligament of the incisor and showed the dendritic terminal arborization. Electron-dense immunoreaction products indicating CB-LI were distributed diffusely in axoplasm of the axon terminals, no mitochondria, however, were not labeled. Neither cell bodies nor cytoplasmic extensions of the terminal Schwann cells exhibited CB-LI. CB was presumed to be involved in the maintenance of Ca2+ homeostasis in the mechano-electric transduction in mechanoreceptors in the periodontal ligament.

The effects of peripheral nerve injury of the masseteric nerve on the levels of calcium binding proteins and neuropeptide Y, and their correlation in the mesencephalic trigeminal nucleus of the rat

Combined retrograde neuronal tracing with FluoroGold (FG) and a double immunofluorescence method was performed to examine the effects of peripheral nerve injury of the masseteric nerve (MassN) on the levels of two calcium binding proteins (CaBPs), parvalbumin (PV) and calbindin D28k (CB), and neuropeptide Y (NPY) in the mesencephalic trigeminal nucleus (MesV) in the rat. In the normal MesV, many medium- to large-sized unipolar PV-like immunoreactive (-IR) cells were detected through the entire rostrocaudal extent, but CB-IR cells were rarely observed. No NPY-IR cells were observed in the normal MesV. The distributions of these three neurochemical markers in the MesV contralateral to the transection of Mass were almost identical to those observed in the normal MesV. Four days following transection and application of FG to the MassN, approximately 52% (572/1104) and 38% (414/1104) of FG-labeled cells (FG cells) in the MesV displayed PV-like immunoreactivity (-LI) and NPY-LI, respectively; Approximately 24% (265/1104) of FG cells showed both PV-LI and NPY-LI. Approximately 47% (265/572) of FG cells with PV-LI showed NPY-LI or 64% (265/414) of FG cells with NPY-LI displayed PV-LI. Fourteen days following transection and application of FG, the percentage of FG cells with PV-LI significantly decreased to 36% (365/1024) compared to that observed 4 days post-injury; approximately 44% (448/1024) of FG cells displayed NPY-LI; approximately 38% (141/365) of FG cells with PV-LI showed NPY-LI and approximately 31% (141/448) of FG cells with NPY-LI displayed PV-LI. In contrast, FG cells showing CB-LI were very rare on 4 days (1%; 15/1182) or 14 days (1%; 16/1085) following MassN transection. The present results indicate that the levels of PV in the MesV decreased 14 days following the MassN injury compared to those observed 4 days post-injury and rapid induction of NPY in the injured MesV neurons, and that the correlation between CaBP and NPY in the MesV following the MassN transection is different from that observed in the trigeminal ganglion, which is equivalent to the MesV, following peripheral nerve injury of the inferior alveolar nerve.