p75 Nerve Growth Factor Receptor as a Specific Nerve Marker in the Diagnosis of Perineural Invasion of Squamous Cell Carcinoma.

OBJECTIVES: Perineural invasion (PNI) is an important factor in tumor prognosis. We evaluated p75 nerve growth factor receptor (p75NGFR) as a neuromarker for perineural invasion of squamous cell carcinoma. METHODS: A comparison of H&E, and S100 and p75NGFR immunohistochemical staining methods, using sequential sections from 29 samples, for identification nerve bundles and PNI diagnosis, was carried out. RESULTS: p75NGFR and S100 correctly identified more nerve bundles than H&E. Accuracy of p75NGFR was higher than that of S100, but there was no significant difference from H&E. The accuracy of nerve bundle identification by p75NGFR and S100 showed no significant difference among different histopathologic grades of squamous cell carcinomas. p75NGFR gave mild staining of small vessels, while S100 gave strong staining of smooth muscle and glandular tissue. CONCLUSIONS: p75NGFR specifically stains nerve tissue and is better than S100 and H&E in identifying nerve bundles. p75NGFR is expected to become a new neuromarker.

Localization of TrkB and p75 receptors in peritoneal and deep infiltrating endometriosis: an immunohistochemical study.

BACKGROUND: The roles of the neurotrophins NGF (Neurotrophic growth factor) and BDNF (brain-derived neurotrophic factor) in neuronal growth and development are already known. Meanwhile, the neurotrophin receptors TrkA (tropomyosin related kinase A), TrkB, and p75 are important for determining the fate of cells. In endometriosis, this complex system has not been fully elucidated yet. The aim of this study was to evaluate the expression and location of these neurotrophins and their receptors in peritoneal (PE) and deep infiltrating endometriotic (DIE) tissues and to measure and compare the density of nerve fibers in the disease subtypes. METHODS: PE lesions (n = 20) and DIE lesions (n = 22) were immunostained and analyzed on serial slides with anti-BDNF, -NGF, -TrkA, -TrkB, -p75,-protein gene product 9.5 (PGP9.5, intact nerve fibers) and -tyrosine hydroxylase (TH, sympathetic nerve fibers) antibodies. RESULT: There was an equally high percentage (greater than 75 %) of BDNF-positive immunostaining cells in both PE and DIE. TrkB (major BDNF receptor) and p75 showed a higher percentage of immunostaining cells in DIE compared to in PE in stroma only (p < 0.014, p < 0.027, respectively). Both gland and stroma of DIE lesions had a lower percentage of NGF-positive immunostaining cells compared to those in PE lesions (p < 0.01 and p < 0.01, respectively), but there was no significant reduction in immunostaining of TrkA in DIE lesions. There was no difference in the mean density of nerve fibers stained with PGP9.5 between PE (26.27 ± 17.32) and DIE (28.19 ± 33.15, p = 0.8). When we performed sub-group analysis, the density of nerves was significantly higher in the bowel DIE (mean 57.33 ± 43.9) than in PE (mean 26.27 ± 17.32, p < 0.01) and non-bowel DIE (mean 14.6. ± 8.6 p < 0.002). CONCLUSIONS: While the neurotrophin BDNF is equally present in PE and DIE, its receptors TrkB and p75 are more highly expressed in DIE and may have a potential role in the pathophysiology of DIE, especially in promotion of cell growth. BDNF has a stronger binding affinity than NGF to the p75 receptor, likely inducing sympathetic nerve axonal pruning in DIE, resulting in the lower nerve fiber density seen.

Messenger RNA expression patterns of p75 neurotrophin receptor and tropomyosin-receptor-kinase A following spinal cord injury.

BACKGROUND: Induction of p75 neurotrophin receptor (p75NTR) could be one of the first steps that initiate apoptotic cascade after injury, or it may indicate regeneration responses undertaken by the injured system, possibly in collaboration with resident tropomyosin-receptor-kinase (Trk). OBJECTIVE: To measure quantitative changes in messenger RNA (mRNA) expression levels of p75NTR, Trk A, and caspase-9 in rat's injured spinal cord (SCI). The reciprocal interaction between Trk and p75NTR signaling pathways can dictate cellular responses to neurotrophins. p75NTR can regulate Trk-dependent responses, but the role of Trk in regulating p75NTR-dependent signaling is not well documented. DESIGN: Using real-time polymerase chain reaction, this study analyzed changes in the mRNA abundance of the mentioned genes at 6, 24, and 72 hours and 7 and 10 days after SCI in adult male rats. SCI was induced at T9 level by transsection. RESULTS: Results show a complicated temporal and spatial pattern of alteration with different degrees and direction (up- or down-regulation) in p75NTR, Trk A, and caspase-9 mRNA expression levels after SCI. The greatest variation was seen in center regions following SCI. This study shows that alteration in p75NTR, Trk A, and caspase-9 expression starts as early as 6 hours after SCI. Alterations in p75NTR, Trk A, and caspase-9 expression within the spinal cord may play a key role in the apoptotic cell death. CONCLUSION: Results suggest that the role of p75NTR is to eliminate damaged cells by activating the apoptotic machinery, especially at the center of damage and during first week after injury.

Vascular and neuronal protection induced by the ocular administration of nerve growth factor in diabetic-induced rat encephalopathy.

BACKGROUND: Based on our previous findings on the efficacy of ocular applied nerve growth factor as eye drops (oNGF) to act in brain and counteract neuronal damage, we hypothesized that oNGF treatment might revert neuronal atrophy occurring in diabetic brain also by controlling neurotrophin system changes. The major NGF brain target areas, such as the septum and the hippocampus, were used as an experimental paradigma to test this hypothesis. METHODS: Bilateral oNGF treatment was performed twice a day for 2 weeks in full-blown streptozotocin-treated adult male rats. The forebrain distribution of cholinergic and endothelial cell markers and NGF receptors were studied by confocal microscopy. The septo-hippocampal content of NGF mature and precursor form and NGF receptors expression were also analyzed by Elisa and Western blot. RESULTS: oNGF treatment recovers the morphological alterations and the neuronal atrophy in septum and normalized the expression of mature and pro-NGF, as well as NGF receptors in the septum and hippocampus of diabetic rats. In addition, oNGF stimulated brain vascularization and up-regulated the TRKA receptor in vessel endothelium. CONCLUSIONS: Our findings confirm that reduced availability of mature NGF and NGF signaling impairment favors vascular and neuronal alterations in diabetic septo-hippocampal areas and corroborate the ability of oNGF to act as a neuroprotective agent in brain.

Vascular wall cells contribute to tumourigenesis in cutaneous neurofibromas of patients with neurofibromatosis type 1. A comparative histological, ultrastructural and immunohistochemical study.

UNLABELLED: Neurofibromas are benign nerve sheath tumours. They occur sporadically, singly or few in number, and in neurofibromatosis type 1 (NF1), an autosomal inherited disease. These tumours are composed of different cell types, e.g. nerve cells (axons and axon sheaths), Schwann cells, mast cells, and fibroblasts. The local control of tumour growth in NF1 is poorly understood. Identification of cell markers could provide new information on the processes that are involved in tumour growth. MATERIALS AND METHODS: NF1 patients were diagnosed according to the revised NF1 diagnostic criteria proposed by the US National Institute of Health. Fifteen cutaneous neurofibromas from eight patients (origin: trunk and face) were excised, immediately immersion-fixed in Bouin's fixative and embedded in paraffin. Six micrometre thin sections were incubated with a variety of neuronal markers, connective tissue and glial cell markers, neurotrophic factors and their receptors. In addition, material was fixed, embedded and further processed for light and electron microscopic studies. RESULTS: The tumours were composed of different cell types, e.g. nerve cells (axons and axon sheaths), Schwann cells, mast cells, compartmentalising cells and fibroblasts. Neuronal markers were identified in axons (neuron-specific protein gene product 9.5, PGP9.5), in several cell types (neurofilament protein-200 kDa, NF-200) and glial cells (protein S-100, S-100). In glial cells the immunoreactivity for fibroblast surface protein (FSP) was scanty, low for cyclic 2,3-nucleotide 3'-phosphodiesterase (CNPase), strong for glucose transporter 1 (Glut-1) but lacking for glial fibrillary acidic protein (GFAP). Schwann cells and so-called compartmentalising cells exhibited immunoreactivity for neurotrophin receptor protein TrkA (TrkA) and glial cell-derived neurotrophic factor (GDNF). GDNF receptor α-1 (GFR-α1) exhibited distinct immunoreactivity in single axons, in Schwann cells, and with lower intensity in some perineurial sheet cells. No immunoreactivity was observed for the low-affinity neurotrophin receptor protein p75(NTR), high-affinity receptor protein TrkB (TrkB), high-affinity receptor protein TrkC (TrkC), the neurotrophin 3 (NT-3), and the brain-derived neurotrophic factor (BDNF). CONCLUSION: Human cutaneous neurofibromas displayed a pattern of neurotrophic factors and their receptor immunoreactivity, which is characteristic of differentiated non-malignant tumours, and exhibited some differences from that established in developing and differentiated control Schwann cells (probably involved in the pathogenesis of the neurofibromas), as well as tumour cells in the process of differentiation. Neurofibromas are highly vascularized tumours and possess activated endothelial cells and pericytes. We presume that most of the hyperplastic structural components of a neurofibroma are generated from activated pericytes and smooth muscle cells of the small tumour vessels which possess qualities of adult stem cells.

P75 nerve growth factor receptor as a useful marker to distinguish spindle cell melanoma from other spindle cell neoplasms of sun-damaged skin.

P75 nerve growth factor receptor (p75 NGF-R) is a low-affinity receptor expressed on the surface of neural crest-derived cells and in a variety of neural tumors. Strong p75 NGF-R expression has been found in spindle cell melanoma (SCM). We studied spindle cell neoplasms of sun-damaged skin to determine whether this marker can reliably distinguish between SCM and other spindle cell malignancies. We evaluated the staining of p75 NGF-R, S100, and HMB-45 in 11 cases of SCM, 16 cases of spindle cell squamous cell carcinoma (SCSCC), 19 cases of spindle cell atypical fibroxanthoma, 6 cases of cutaneous leiomyosarcoma, and 20 scars. Staining with p75 NGF-R was positive in all 11 of 11 (100%) cases of SCM, whereas S100 stained 10 of 11 (91%) cases, and HMB-45 was negative in all SCMs. In addition, there was superior intensity of the staining for p75 NGF-R in comparison to S100. P75-NGF-R showed focal positivity in 3 of 16 (19%) cases of SCSCC. None of the rest of the cases of SCSCC, and none of the cases of spindle cell atypical fibroxanthoma, cutaneous leiomyosarcoma, and scars expressed p75 NGF-R, S100, or HMB-45. P75 NGF-R is a useful marker to distinguish SCM from other spindle cell neoplasms of sun-damaged skin. This marker exhibits greater sensitivity than S100 in identifying SCM and may be a useful diagnostic and ancillary stain especially in the setting of an S100 negative spindle cell neoplasm.

Design of HIV-1 integrase inhibitors targeting the catalytic domain as well as its interaction with LEDGF/p75: a scaffold hopping approach using salicylate and catechol groups.

HIV-1 integrase (IN) is a validated therapeutic target for antiviral drug design. However, the emergence of viral strains resistant to clinically studied IN inhibitors demands the discovery of novel inhibitors that are structurally as well mechanistically different. Herein, we describe the design and discovery of novel IN inhibitors targeting the catalytic domain as well as its interaction with LEDGF/p75, which is essential for the HIV-1 integration as an IN cofactor. By merging the pharmacophores of salicylate and catechol, the 2,3-dihydroxybenzamide (5a) was identified as a new scaffold to inhibit the strand transfer reaction efficiently. Further structural modifications on the 2,3-dihydroxybenzamide scaffold revealed that the heteroaromatic functionality attached on the carboxamide portion and the piperidin-1-ylsulfonyl substituted at the phenyl ring are beneficial for the activity, resulting in a low micromolar IN inhibitor (5p, IC(50)=5 µM) with more than 40-fold selectivity for the strand transfer over the 3'-processing reaction. More significantly, this active scaffold remarkably inhibited the interaction between IN and LEDGF/p75 cofactor. The prototype example, N-(cyclohexylmethyl)-2,3-dihydroxy-5-(piperidin-1-ylsulfonyl) benzamide (5u) inhibited the IN-LEDGF/p75 interaction with an IC(50) value of 8 µM. Using molecular modeling, the mechanism of action was hypothesized to involve the chelation of the divalent metal ions inside the IN active site. Furthermore, the inhibitor of IN-LEDGF/p75 interaction was properly bound to the LEDGF/p75 binding site on IN. This work provides a new and efficient approach to evolve novel HIV-1 IN inhibitors from rational integration and optimization of previously reported inhibitors.

Nerve growth factor receptor immunohistochemistry has a limited additional value to diagnose Hirschsprung's disease.

PURPOSE: The diagnosis of Hirschsprung's disease (HSCR) is based on the histopathological evaluation of rectal suction biopsies (RSB), using haematoxylin and eosin (H&E) stains and acetylcholinesterase (AChE) histochemistry. The use of different immunohistochemical markers, such as nerve growth factor receptor (NGFR), has been suggested to facilitate the diagnosis of HSCR. The aim of this study was to evaluate the addition of NGFR immunohistochemistry to diagnose HSCR. METHODS: RSB from 23 HSCR patients and 16 patients investigated for, but not diagnosed with, HSCR were retrospectively reviewed. The histopathology report supported or did not support the diagnosis of HSCR. RESULTS: In patients with HSCR, the primary biopsies confirmed the diagnosis in 21 of 23 cases with H&E staining, in 16 of 23 cases with AChE histochemistry, and in 8 of 23 cases with NGFR immunohistochemistry. Due to inadequate biopsies or equivocal interpretation, the biopsies were repeated in seven of the patients with HSCR and two patients underwent biopsies a third time. In the 16 patients investigated for but not diagnosed with HSCR, the three tests were normal in all cases. CONCLUSION: We conclude that NGFR immunohistochemistry has limited additional value to diagnose HSCR.

Immunolocalization of NGF and its receptors trkA and p75 in the oviducts of golden hamsters during the estrous cycle.

To investigate the physiological roles of nerve growth factor (NGF) in the oviduct of golden hamsters during the estrous cycle, the localization of NGF and its receptors, trkA and p75, were determined by immunohistochemistry. Positive staining of NGF, trkA, and p75 was present in epithelial cells and muscle cells of the infundibulum, ampulla, and isthmus in the oviduct. The intensities of the immunohistochemical signals for NGF, trkA, and p75 did not markedly change in any segment of the oviduct during the estrous cycle. These results suggest that NGF may play autocrine/paracrine roles in oviductal transport, fertilization, capacitation of spermatozoa and early embryonic development in the oviduct of golden hamsters.

Basal cells as stem cells of the mouse trachea and human airway epithelium.

The pseudostratified epithelium of the mouse trachea and human airways contains a population of basal cells expressing Trp-63 (p63) and cytokeratins 5 (Krt5) and Krt14. Using a KRT5-CreER(T2) transgenic mouse line for lineage tracing, we show that basal cells generate differentiated cells during postnatal growth and in the adult during both steady state and epithelial repair. We have fractionated mouse basal cells by FACS and identified 627 genes preferentially expressed in a basal subpopulation vs. non-BCs. Analysis reveals potential mechanisms regulating basal cells and allows comparison with other epithelial stem cells. To study basal cell behaviors, we describe a simple in vitro clonal sphere-forming assay in which mouse basal cells self-renew and generate luminal cells, including differentiated ciliated cells, in the absence of stroma. The transcriptional profile identified 2 cell-surface markers, ITGA6 and NGFR, which can be used in combination to purify human lung basal cells by FACS. Like those from the mouse trachea, human airway basal cells both self-renew and generate luminal daughters in the sphere-forming assay.

A possible role of BDNF in prostate cancer detection.

Many studies have demonstrated that both normal and malignant prostate cells respond to a variety of growth factors, while several significant differences were found between normal and tumoural cells. The aim of this study was to focus on the localization and distribution of the immuno-reactivity for neurotrophins (NTs) and neurotrophin receptors (NTRs) in normal, hyperplastic and prostate cancer cells, obtained from 40 subjects. We studied samples obtained from 16 prostate cancer (PC, retropubic radical prostatectomy), 20 benign prostatic hyperplasia (BPH, supra-pubic prostatectomy) and normal peripheral prostate tissue from four fresh male cadavers. Samples were examined via immunohistochemical techniques in order to detect the expression of nerve growth factor (NGF), brain derived neurotrophic factor (BDNF), neurotrophin 3 (NT3) and their own receptors TrkA, p75, TrkB and TrkC. We observed a high expression of BDNF and TrkB in PC and BPH, though no immuno-reactivity was found for p75. Low expression was reported by other NTs and NTRs in the normal peripheral prostate zone, BPH and PC. These data suggest a possible predictive role for NTs and NTRs, especially for BDNF and TrkB, in the diagnosis and/or management of prostate cancer. The absence of p75 expression confirms its supposed role in apoptotic phenomenon.

Age-related structural and neurochemical changes of the human superior cervical ganglion.

The aim of this study was to investigate age-related morphological and neurochemical changes in the human superior cervical ganglion (SCG). Thirty-seven superior sympathetic human cervical ganglia of young, adult, and aged subjects were examined using morphometric analysis, biotin-streptavidin immunohistochemistry for detecting neurofilament, myelin protein, protein gene product 9.5, nerve growth factor receptor p75 in sympathetic neurons and nerve fibers. Morphometric parameters of neurons (area, long and short axis, shape factor of the neuron body, nucleus, cytoplasm, and lipofuscin) were investigated in every sixth serial section of the ganglion. Seven hundred neurons with clearly visible nuclei were measured in each studied group. The present study showed that human SCG of older subjects had larger areas of neuron body, cytoplasm and nucleus, a lower shape factor, an increased amount of lipofuscin, and a greater number of large-size neurons, as compared to SCG obtained from young subjects. Neuronal cytoskeletal alterations manifested themselves through a decreased number of neurofilament-positive neurons were detected in old human SCG. The amount of myelinated fibers decreased with age, although the amount of myelinated fibers in the young and the adult subjects varied from few to a moderate number. PGP 9.5 immunoreactivity varied in different age groups. A marked reduction of nerve growth factor receptor p75 in old human sympathetic neurons was detected. In conclusion, the findings of this study confirm age-related morphological changes in the human SCG. Structural neuronal changes may influence the deterioration of neuronal functional capacity, neuronal plasticity, and regenerative characteristics.

Anatomic site-related expression of cancer-associated molecules in ovarian carcinoma.

Ovarian cancer presents as disseminated disease in the majority of cases. Tumor metastasis to the peritoneal and/or pleural cavity is evident in two-thirds of cases at diagnosis and relapse is most often detected at this anatomic site. Despite the fact that the primary tumor is amenable to surgical removal in the majority of cases, ovarian cancer research, including the evaluation of therapeutic targets, has concentrated on primary disease. In recent years, we analyzed the site-dependent expression of cancer-associated and regulatory molecules in primary tumors, effusions and solid metastases. Our data show that some molecules (e.g., Ets transcription factors) are expressed at all anatomic sites in ovarian carcinoma and that their expression in primary and metastatic disease is associated with poor prognosis. However, the majority of molecules (e.g., cadherins, integrins, and nerve growth factor receptors) are differentially expressed along tumor progression and have different prognostic value depending on the organ sampled. Specifically, cancer-associated molecules with a well-characterized clinical significance in solid tumors (e.g., matrix metalloproteinases) have no such role in effusions. Finally, a growing number of molecules are differentially expressed in primary diagnosis (pre-chemotherapy) and disease recurrence (post-chemotherapy) specimens, reflecting the effect of disease progression and chemotherapy. This review will present the current knowledge in this area.

Localization of bromodeoxyuridine-incorporating, p63- and p75(NGFR)- expressing cells in the human gingival epithelium.

The objective of this study was to find the sites with proliferative activity in the human gingival epithelium, where stem cells are likely to exist. Gingival tissues were excised from 16 adult patients and immunohistochemically examined for the presence of bromodeoxyuridine (BrdU)-incorporating, p63- and low affinity nerve growth factor receptor (p75(NGFR))-expressing cells. BrdU-incorporating cells were rarely present in the junctional epithelium. The number of BrdU-incorporating cells in the sulcular and oral gingival epithelia was significantly higher than that found in the junctional epithelium (ANOVA, P < 0.01). A considerable number of p63-positive nuclei were detected in the basal layer to lower spinous layers in the sulcular and oral gingival epithelia, but only few p63-positive cells were present in the junctional epithelium. p75(NGFR)-positive cells were exclusively located in the basal layer in the sulcular and oral gingival epithelia, and in limited basal area in the junctional epithelium neighboring the sulcular epithelium. In the oral gingival epithelium, intense immunostaining of BrdU, p63 and p75(NGFR) was correspondingly observed on the base and side of the rete ridges. These areas probably exhibit high proliferative activity owing to the presence of stem cells.

Mice lacking the p75 receptor fail to acquire a normal complement of taste buds and geniculate ganglion neurons by adulthood.

Brain-derived neurotrophic factor and neurotrophin-4 are required for normal taste bud development. Although these neurotrophins normally function via the tyrosine kinase receptor, trkB, they also bind to the pan-neurotrophin receptor, p75. The goal of the present study was to determine whether the p75 receptor is required for the development or maintenance of a full complement of adult taste buds. Mice with p75 null mutations lose 34% of their circumvallate taste buds, 36% of their fungiform papillae, and 26% of their fungiform taste buds by adulthood. The reduction of taste buds in the adult circumvallate papilla was similar to that observed previously at postnatal day 7 (Fan et al. Brain Res Dev Brain Res 2004;150:23-39). Taken together, these findings indicate that the p75 receptor is critical for the development of a full complement of taste buds, but is not required for maintenance of circumvallate taste buds in adulthood. Immunolabeling for p75 was not observed in taste buds, indicating that p75 signaling influences taste bud number indirectly. Geniculate ganglion neurons, which provides innervation to fungiform taste buds, express the p75 receptor. Mice with p75 null mutations also have fewer neurons in the geniculate ganglion. Together, these results suggest that the p75 receptor is important for the survival of geniculate neurons and geniculate neuron survival is required for the development of a full complement of taste buds by adulthood.

Immunohistochemical analysis of low-affinity nerve growth factor receptor in the human urinary bladder.

INTRODUCTION: Interest in the regulation of nerve growth factor (NGF) production in the urinary tract derives from its probable involvement in obstructive, inflammatory and developmental disorders. Our aim was to investigate the presence of low-affinity nerve growth factor receptor (LNGFR) in the vesical urothelium of patients with bladder outlet obstruction. SUBJECTS AND METHODS: The study included 20 patients with urodynamically confirmed outflow obstruction and 10 control patients without outflow obstruction. Cold cup biopsies of the posterior wall of the urinary bladder were obtained from all patients. Intensity and distribution of LNGFR in the human urinary bladder were examined immunohistochemically. RESULTS: We detected LNGFR immunostaining in all specimens, and it was observed at the (luminal) epithelial surface and in nerve fibers. In the obstruction group, LNGFR immunoreactivity scores were higher than in the control group, but there was no statistically significant difference (p > 0.05). CONCLUSIONS: The presence of LNGFR was demonstrated in the urothelium of the human urinary bladder, and these findings show that cells in hypertrophied and normal bladder can synthesize NGF. This observation may have a potential role for therapeutic implications. However, further studies are needed for an explanation of the pathophysiology and the role in treatment.

Cellular localization of NGF and its receptors trkA and p75LNGFR in male reproductive organs of the Japanese monkey, Macaca fuscata fuscata.

The actions of neurotropins are not restricted to the nervous system. Immunohistochemical methods were used in the present study to clarify distribution of nerve growth factor (NGF) and its receptors TrkA and p75LNGFR in excurrent ducts of the adult male Japanese monkey (Macaca fuscata fuscata). NGF was found in the seminal vesicle, epididymis, and testis, and has been thought to affect male reproductive functions. Leydig cells, Sertoli cells, and spermatogonia at various stages were positively stained for NGF, as well as for TrkA and p75LNGFR. Signals for these proteins were also found in epithelial cells and stromal tissues of the caudal epididymidis, as well as in the seminal vesicle. In the prostate, smooth muscle cells and basal cells were positively stained for NGF, TrkA, and p75 LNGFR. The results were comparatively discussed.

Effects of increased nerve growth factor plasma levels on the expression of TrkA and p75 in rat testicles.

In addition to their well-known roles within the nervous system, the neurotrophins and their receptors regulate some functions in the reproductive system. In this study we used combined morphological and immunohistochemical techniques to investigate the presence and cellular localization in the rat testicle of the two receptors of nerve growth factor (NGF), i.e. TrkA and p75(NTR). Furthermore, to evaluate whether increased plasma levels of NGF affect the ageing process, 4-methylcathechol (4-MC), an inductor of NGF synthesis, was administered. Both TrkA and p75(NTR) were expressed in rat testicles, but the pattern and intensity of immunoreaction were marginally different between them. In adult rats TrkA was expressed in spermatozoa and spermatids, and p75 was expressed in spermatogonia. In newborn rats TrkA immunoreactivity was found in the Leydig cells, whereas p75 was detected in a cellular layer that surrounds the seminiferous tubules. In adult treated animals the immunoreaction for TrkA and p75(NTR) was also localized in the spermatocytes, whereas in newborn treated rats no changes in the pattern of immunoreaction was observed. The present findings suggest a role of the NGF/TrkA/p75 system in the physiology of reproduction, but the practical relevance of this remains to be established.

Immunocytochemical evidence that most sensory neurons of the rat molar pulp express receptors for both glial cell line-derived neurotrophic factor and nerve growth factor.

Most pulpal afferent neurons have cytochemical features in common with the class of nociceptors that express neuropeptides and respond to NGF, while very few bind the plant lectin IB4, a widely used marker for the class of nociceptors that respond to the GDNF family of neurotrophic factors. The present study was undertaken to determine whether the GDNF receptor, GFRalpha-1, is expressed by pulpal afferents, and, further, to determine whether tooth injury evokes changes in expression of the GDNF and NGF receptors among pulpal afferents. The tracer, fluoro-gold (FG), was applied to shallow cavities in dentin of first and second maxillary molars. After 4 weeks, the molars of one side received a test injury consisting of a deeper cavity that exposed pulp horns. Animals were perfusion fixed 2 days later, and sections of the trigeminal ganglia were double immunostained with combinations of antibodies against GFRalpha-1, and TrkA. Under control conditions, GFRalpha-1 immunostaining was observed in 72% of neurons that projected to the molar pulp, TrkA in 78%, and immunostaining for both receptors was observed in 65% of pulpal afferents. Tooth injury evoked up-regulation of GFRalpha-1 expression (to 93%) and a slight down-regulation of TrkA expression (67%) among tooth afferents, while there was no discernable change in the proportion of pulpal afferents that expressed both TrkA and GFRalpha-1 (to 61%).

Thymocyte depletion affects neurotrophin receptor expression in thymic stromal cells.

Thymocytes and thymic stromal cells cross-talk in a bidirectional manner within the thymus, thus contributing to the generation of mature T-cells. The thymic stromal cells in the rat express the high- (TrkA, TrkB) and low-affinity (p75NTR) receptors for neurotrophins. In this study we analysed the regulation of TrkA, TrkB and p75NTR expression in the rat thymus by thymocytes. We induced thymocyte apoptosis by administration of corticoids in rats, and then analysed the expression and distribution of these receptors 1, 4 and 10 days later. Thymocyte death was assessed by the activation of caspase-3 in cells undergoing apoptosis. We observed massive thymocyte apoptosis 1 day after injection and, to a lesser extent, after 4 days, which was parallel with a reduction in the density of thymic epithelial cells normally expressing TrkA and p75NTR. Furthermore, TrkA expression was found in cortical thymic epithelial cells, which normally lack this receptor. The expression of TrkB was restricted to a subset of macrophage-dendritic cells, and remained unchanged with treatment. The normal pattern of neurotrophin receptor expression was almost completely restored by day 10. The results demonstrate that the expression of neurotrophin receptors by thymic epithelial cells, but not by macrophage-dendritic cells, is regulated by thymocytes.