Time-dependent sensory nerve ingrowth into a bone conduction chamber

We studied time-dependent ingrowth of sensory nerve fibers into a bone defect in a rat bone conduction chamber model. In 10 male Sprague Dawley rats, a titanium chamber was implanted bilaterally in the proximal tibiae, representing an experimental bone defect. To mimic a clinical situation, the chambers were filled with a fresh blood clot. After 1, 2, 4, 6 and 8 weeks, 2 rats were fixed in vivo at each time before removal of specimens, and histological and immunohistochemical analyses. We used antisera against protein gene product 9.5, neural growth-associated protein 43/B-50, calcitonin gene-related peptide, and substance P, to locate regenerating sensory nerve fibers in the chamber. During bone defect healing, hematoxylin/eosin sections showed that new bone grew in through the ingrowth openings in the chamber, gradually filling it and replacing the blood clot. At 1 and 2 weeks after implantation, no nerve fibers could be detected. At 4, 6 and 8 weeks, however, small numbers of nerve fibers were seen in 8 of 11 specimens. The nerve fibers were located mainly in the dense fibrous tissue in close proximity to the new bone, and in some cases within the new forming bone. In this chamber model, the periosteum is not in contact with the bone ingrowth openings, and all ingrowing nerve fibers thus originated from the cortical bone, endosteum or bone marrow. We speculated that these late ingrowing sensory nerve fibers may actively participate in bone repair.     

Time-dependent sensory nerve ingrowth into a bone conduction chamber

We studied time-dependent ingrowth of sensory nerve fibers into a bone defect in a rat bone conduction chamber model. In 10 male Sprague Dawley rats, a titanium chamber was implanted bilaterally in the proximal tibiae, representing an experimental bone defect. To mimic a clinical situation, the chambers were filled with a fresh blood clot After 1, 2, 4, 6 and 8 weeks, 2 rats were fixed in vivo at each time before removal of specimens, and histological and immunohistochemical analyses. We used antisera against protein gene product 9.5, neural growth-associated protein 43/B-50, calcitonin gene-related peptide, and substance P, to locate regenerating sensory nerve fibers in the chamber. During bone defect healing, hematoxylin/eosin sections showed that new bone grew in through the ingrowth openings in the chamber, gradually filling it and replacing the blood clot. At 1 and 2 weeks after implantation, no nerve fibers could be detected. At 4, 6 and 8 weeks, however, small numbers of nerve fibers were seen in 8 of 11 specimens. The nerve fibers were located mainly in the dense fibrous tissue in close proximity to the new bone, and in some cases within the new forming bone. In this chamber model, the periosteum is not in contact with the bone ingrowth openings, and all ingrowing nerve fibers thus originated from the cortical bone, endosteum or bone marrow. We speculated that these late ingrowing sensory nerve fibers may actively participate in bone repair.     

Cartilage induction by controlled mechanical stimulation in vivo.

To study mechanical control of tissue differentiation, we designed a new version of the previously described bone conduction chamber. The bone conduction chamber consists of a cylindrical titanium chamber for implantation in the rat tibia. It has tissue ingrowth openings at one end, located subcortically, and the other end protrudes into the subcutis. The newly developed load chamber has a mobile piston so that an external compressive load can be transferred to the tissue within the chamber. Sprague-Dawley rats had a regular bone conduction chamber implanted in one tibia and a load chamber implanted in the other. Mesenchymal tissue was allowed to grow into the chamber for 3 weeks before the mechanical loading was started. Thereafter, twice a day, 20 cycles of compressive load were applied with a frequency of 0.17 Hz to the load chamber. This was estimated to produce a compressive hydrostatic stress of 2 MPa. The chambers, harvested after 7 weeks of loading, all contained newly formed bone. The bone ingrowth distance into the chamber was decreased in the loaded specimens compared with the contralateral unloaded controls (p = 0.01). Instead, cartilage was found in the loaded chambers next to the piston. Beneath the cartilage was a dense bone plate under which a marrow cavity had formed. No cartilage was found in the unloaded controls, but the architecture of the bone and marrow cavity was similar to that of the loaded specimens. We conclude that this model allows load to be transmitted onto the ingrowing tissue and that the load parameters used cause this tissue to differentiate into cartilage close to the piston.     

Sensory nerve ingrowth during bone graft incorporation in the rat

We studied nerve ingrowth into a cancellous bone graft in a bone conduction chamber model in the rat. Before implantation of the chamber bilaterally in the proximal tibiae of 8 Sprague-Dawley rats, a defatted cancellous bone graft from separate donor rats was fitted snugly into each chamber. After 6 weeks, the animals were perfused with Zamboni's fixative and the chambers were harvested. Immunohistochemi-cal detection of nerve fibers was performed in cry-ostat sections, using antisera to protein gene product 9.5 (PGP 9.5), neural growth-associated protein GAP-43/B-50, calcitonin gene-related peptide (CGRP), substance P and C- flanking peptide of neuropeptide Y (CPON). Nerve fibers were found in 10 out of 16 samples in the newly formed bone, and also in the fibrous tissue which had penetrated deeper into the graft. The nerve fibers were mainly of sensory origin, as they showed immunoreactivity for CGRP and GAP-43/B-50. We speculate that the nerve fibers may act as transmitters of nociceptive impulses from the graft, and as transport pathways for neuropeptides that are actively involved in angio-genesis and in the recruitment and activity of osteogenic cell populations from the graft recipient.     

Basic fibroblast growth factor enhances bone-graft incorporation: Dose and time dependence in rats

In a previous study, we found that basic fibroblast growth factor could stimulate bone-graft incorporation. In the present study, the effects of different doses and implantation times were further studied, using the bone conduction chamber, in rats. Inside the chamber, the graft is isolated from the surrounding tissues except at one end, where small openings embedded in host bone allow ingrowth of tissue. The distance that new tissues had reached from the openings into the graft was measured on histological slides. Bone grafts were obtained from the proximal tibiae of donor rats, frozen at ?70°C, and lipid-extracted. Before implantation, they were soaked overnight in a hyaluronate gel with or without basic fibroblast growth factor and then were fitted into the chambers, which were implanted in the proximal tibiae of recipient rats. In a doseresponse experiment, grafts containing 0.3, 8, 40, 200, or 1,000 ng of basic fibroblast growth factor were compared with grafts treated with carrier gel only, after an implantation time of 6 weeks. Fibrous tissue always penetrated the grafts further than the ingrown bone; the distance that it reached from the ingrowth openings (total ingrowth distance) was increased by all of the doses except 0.3 ng per implant. The distance of bone ingrowth was increased by 8, 40, and 200 ng. The increased total ingrowth with 1,000 ng was due to an increased amount of fibrous tissue ahead of the bone, whereas with the lower doses the increase was due to more bone. Thus, the dose had an effect on the type of ingrown tissue found in the graft. In a time-effect study, grafts treated with 40 ng of basic fibroblast growth factor had a higher uptake of [^99mTc]MDP at 2 and 4 weeks and an increased bone ingrowth distance at 10 weeks. The radioactivity from [¹²⁵I]basic fibroblast growth factor declined with a half-life of 17 hours. The results suggest that basic fibroblast growth factor may be beneficial for the incorporation of contained bone grafts; studies using more clinically relevant models are required.     

Basic fibroblast growth factor infused at different times during bone graft incorporation Titanium chamber study in rats

We investigated the effect of applying basic fibroblast growth factor (bFGF) to a bone graft during different stages of incorporation in an infusion bone chamber model. Bone chambers were implanted bilaterally into rat tibiae. Both chambers were connected to an implanted osmotic minipump. Ingrowing bone could enter the cylindrical interior of the chamber only at one end. The distance which ingrowing bone had reached into the bone graft was then measured on histological slides. Specimens were also analyzed by ^99mTc-MDP scintimetry. The infusion of buffer during 2 weeks from implantation had no effects on tissue ingrowth distance or quality. bFGF was infused during 2 weeks from implantation in a dose of either 1.2 or 12 ng/day. Bone ingrowth was measured 6 weeks after implantation. The higher dose had a more marked effect and was used for studying the effect of application at different times.The maximum stimulation of bFGF as measured at 6 weeks postimplantation was found after infusion during the first postimplantation week. Infusion during the third and fourth weeks had no effect at 6 weeks, but tended to increase the bone ingrowth distance at 8 weeks postimplantation. These findings suggest that bFGF infusion increases bone ingrowth into bone grafts when infused at both an early and a later stage, but the effect can be measured only several weeks later.     

酸性成纤维细胞生长因子促进引导性骨再生的实验研究

目的　研究酸性成纤维细胞生长因子（α Ｆ Ｇ Ｆ）对引导性骨再生（ Ｇ Ｂ Ｒ）的作用,增强 Ｇ Ｂ Ｒ 修复骨缺损的能力。方法　１６ 只新西兰白兔分为四组,每组 ４ 只,造成兔双侧桡骨干１０ ｍ ｍ 节段性骨缺损,以硅胶管桥接骨缺损,实验侧管内置入人基因重组酸性成纤维细胞生长因子（ｈｒａ Ｆ Ｇ Ｆ）２４ μｇ,对侧管内注入生理盐水作对照。于术后２、４、６ 及８ 周各处死一组兔,作 Ｘ 线、大体、组织学观察。结果　实验侧术后２ 周即在骨断端髓腔、骨内膜及皮质断面处有新骨形成,并长入管内血肿,术后４ 周新骨长入血肿中心,８ 周完全骨愈合。对照侧在各阶段新骨形成均不如实验侧,８ 周时仅出现部分骨愈合。结论　酸性成纤维细胞生长因子（ａ Ｆ Ｇ Ｆ）可促进 Ｇ Ｂ Ｒ,增强其修复骨缺损的能力。     

Reinnervation of syngeneic pancreatico-duodenal grafts in rats

BACKGROUND: Knowledge on the reinnervation of transplanted organs is scarce, and the aim of the study was therefore to evaluate to what degree syngeneic pancreas grafts were reinnervated in rats. METHODS: Syngeneic pancreatico-duodenal transplantations were performed in normoglycemic Wistar-Furth rats. Native and transplanted pancreas and duodenum were removed 4 or 40 weeks after implantation, and processed for indirect immunofluorescence using antibodies directed against vasoactive intestinal peptide, substance P (SP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), tyrosine hydroxylase (TH), or the general neuronal marker protein gene product 9.5. RESULTS: Four weeks after transplantation a moderate to rich number of protein gene product 9.5-positive nerve fibers were found homogeneously distributed through the pancreas, probably representing the intrapancreatic nervous system, because the grafted pancreas lacked both a sympathetic (TH/NPY) and sensory (SP/CGRP) innervation 4 weeks after implantation. In a few of the animals there was a marked increase in SP-immunoreactive nerves (lacking CGRP), most conspicuous in the duodenal portion, both 4 and 40 weeks after transplantation probably secondary to a chronic pancreatitis. The fibers seemed to emanate from intrapancreatic ganglia and possibly also from enteric neurons in adjacent parts of the duodenum. A few scattered vasoactive intestinal peptide-containing nerve fibers probably also emanating from local ganglia could be seen throughout the grafted pancreas both 4 and 40 weeks after transplantation. At 40 weeks after transplantation sympathetic (TH- and NPY-positive) nerve fibers were regularly seen, whereas CGRP-positive nerve fibers were still virtually lacking in the pancreas. To trace the origin of the ingrowing nerve fibers, the tracer True Blue was injected into the grafted pancreas of some rats 38 weeks after transplantation, i.e., 2 weeks before killing. True Blue-labeled nerve cell bodies were numerous in the celiac ganglion (presumably sympathetic nerves) and few in dorsal root ganglia (sensory nerves). CONCLUSIONS: The data suggest that the transplanted rat pancreas becomes reinnervated by mainly sympathetic nerve fibers.     

Reinnervation of syngeneic mouse pancreatic islets transplanted into renal subcapsular space.

A syngeneic transplantation of 150 islets into the subcapsular renal space was performed on normoglycemic or alloxan-induced diabetic male C57BL/6 mice. Six, 8, 14, or 20-21 wk after transplantation, the graft-bearing kidney was removed and processed for microscopical examinations with indirect immunofluorescence for neuropeptides and tyrosine hydroxylase, and with acetylcholinesterase staining to visualize nerve fibers within the graft. Six weeks after implantation, only a few scattered nerve fibers were observed within the grafts. A progressive increase in the number of nerves was observed until 14 wk after transplantation, after which, a stable level was reached. Alloxan-induced diabetic mice showed quantitatively and qualitatively similar reinnervation to normoglycemic mice 20 wk after transplantation. The findings demonstrate the presence of sympathetic nerve fibers (containing tyrosine hydroxylase and neuropeptide Y), mainly accompanying ingrowing blood vessels; parasympathetic nerve fibers (containing acetylcholinesterase and vasoactive intestinal peptide), possibly reaching the graft from the adjacent renal capsule; and afferent nerve fibers (containing substance P and calcitonin gene-related peptide), which were less numerous. The data suggest that transplanted islets become reinnervated by ingrowth of nerve fibers from the implantation organ and that several types of nerves are present.     

静电纺纳米聚乳酸己内酮共聚物导管修复周围神经缺损的实验研究

目的 探讨应用同轴静电纺丝技术制备的聚乳酸己内酮共聚物[Poly(1-lactide-co-epsilon-caprolactone),P(LLA-CL)]导管,移植修复大鼠周围神经缺损的效果.方法 选取健康SD大鼠54只,随机分成3组,每组18只.先造成坐骨神经1.5cm缺损段,然后分别采用P(LLA-CL)导管桥接(A组)、硅胶管桥接(B组)、自体神经逆行原位移植(C组).分别在术后4、8、12周对大鼠进行大体观察、坐骨神经功能指数检查、神经电生理检查、肌肉湿重、再生有髓神经纤维计数、电镜观察,评价各组神经再生.结果 术后4周时A组再生神经已部分生长到导管的中部;8周时再生神经已通过神经导管,但再生的神经纤细;12周时再生神经粘连较轻,直径较粗.A组的坐骨神经功能指数、神经电生理、肌肉湿重和组织学观察等各项指标均略差于C组,但明显优于B组.结论 纳米聚乳酸己内酮神经导管具有促进神经轴突再生的作用,有望成为自体神经移植的替代材料应用于周围神经缺损的修复.     

Intermittent micromotion inhibits bone ingrowth. Titanium implants in rabbits.

We studied the effects of micromotion on bone ingrowth into a 1-mm canal through a titanium chamber implanted in the proximal tibia of rabbits. The implant surface became "osseointegrated," but an interior core was movable, allowing the central portion of the canal to be moved in relation to the ends. Thus, the ingrowing bone in the canal had to pass an area of ad latus motion. When implanted in rabbit tibiae, the canal became filled with ingrown cancellous bone. Bone ingrowth was inhibited by 20 cycles of 0.5-mm movement applied during a 30-second period once daily. With this regimen, the canal was usually filled with vascularized fibrous tissue and significantly less bone. The micromotion chamber may enable detailed studies of the effects of different motion variables on ingrowth of bone.     

Fibrous tissue armoring increases the mechanical strength of an impacted bone graft

Impacted, morselized bone allografts are used with good clinical results in revision of hip prostheses with loosening and osteolysis. The impacted bone graft appears radiographically to remodel, but histological analyses have shown a heterogeneous picture with a mixture of living and dead bone. Thus, complete remodeling of the graft may be neither a prerequisite nor a cause of the good clinical results. The present study concerns the mechanical effect of the mere armoring of the bone graft by ingrowing fibrous tissue. We compared the compression strength of freshly-impacted grafts to grafts that had been inserted into a bone chamber and thus were penetrated by fibrous tissue growing in between the graft trabeculae. The compressive strength was doubled after 4 weeks of fibrous ingrowth. We conclude that the mechanical properties of an impacted graft are enhanced by armoring with ingrowing fibrous tissue. Strengthening of the parts of the impacted grafts which have not yet remodeled, would be clinically relevant for the outcome of the operation, since these parts are at high stress during the whole remodeling period. Complete osseous remodeling may not be necessary to obtain a good clinical result with a morselized impacted graft.     

Increased bone ingrowth distance into lipid-extracted bank bone at 6 weeks

In previous rabbit chamber experiments, lipid extraction has been shown to increase bank bone incorporation, as measured by scintimetric activity at 3 weeks. In the present study, the new bone ingrowth distance was measured by histomorphometry at 6 weeks using a titanium chamber model in rats. By insertion into bilateral bone conduction chambers, frozen grafts were compared with grafts that had been processed by lipid extraction. To evaluate the effects of lipid extraction further, the group of 26 rats was divided into three subgroups according to MHC haplotype, namely a heterogeneous group (outbred Sprague-Dawley rats), a mismatched group, and a syngeneic group. In the total material, defatted grafts showed a 58% greater new bone ingrowth distance and a 31% higher scintimetric activity over controls. The effect of defatting was not shown to be due to immunologic factors. In general, rats with a lower capacity to incorporate bone grafts showed a larger positive effect of defatting.     

Fibrous tissue armoring increases the mechanical strength of an impacted bone graft

Impacted, morselized bone allografts are used with good clinical results in revision of hip prostheses with loosening and osteolysis. The impacted bone graft appears radiographically to remodel, but histological analyses have shown a heterogeneous picture with a mixture of living and dead bone. Thus, complete remodeling of the graft may be neither a prerequisite nor a cause of the good clinical results. The present study concerns the mechanical effect of the mere armoring of the bone graft by ingrowing fibrous tissue. We compared the compression strength of freshly-impacted grafts to grafts that had been inserted into a bone chamber and thus were penetrated by fibrous tissue growing in between the graft trabeculae. The compressive strength was doubled after 4 weeks of fibrous ingrowth. We conclude that the mechanical properties of an impacted graft are enhanced by armoring with ingrowing fibrous tissue. Strengthening of the parts of the impacted grafts which have not yet remodeled, would be clinically relevant for the outcome of the operation, since these parts are at high stress during the whole remodeling period. Complete osseous remodeling may not be necessary to obtain a good clinical result with a morselized impacted graft.     

Fibrous tissue armoring increases the mechanical strength of an impacted bone graft

Impacted, morselized bone allografts are used with good clinical results in revision of hip prostheses with loosening and osteolysis. The impacted bone graft appears radiographically to remodel, but histological analyses have shown a heterogeneous picture with a mixture of living and dead bone. Thus, complete remodeling of the graft may be neither a prerequisite nor a cause of the good clinical results. The present study concerns the mechanical effect of the mere armoring of the bone graft by ingrowing fibrous tissue. We compared the compression strength of freshly-impacted grafts to grafts that had been inserted into a bone chamber and thus were penetrated by fibrous tissue growing in between the graft trabeculae. The compressive strength was doubled after 4 weeks of fibrous ingrowth. We conclude that the mechanical properties of an impacted graft are enhanced by armoring with ingrowing fibrous tissue. Strengthening of the parts of the impacted grafts which have not yet remodeled, would be clinically relevant for the outcome of the operation, since these parts are at high stress during the whole remodeling period. Complete osseous remodeling may not be necessary to obtain a good clinical result with a morselized impacted graft.     

Basic fibroblast growth factor increases allograf incorporation: Bone chamber study in rats

We found increased penetration of new bone into a frozen bone allograft which had been pretreated with basic fibroblast growth factor (bFGF). Pairs of grafts were placed in newly designed titanium bone chambers implanted bilaterally in rat tibiae. The ingrowing bone can enter the cylindrical interior of the chamber only at one end. It then penetrates the graft inside the chamber but, due to the length of the cylinder, it never reaches the other end. The distance which the ingrown bone has reached into the graft can then be measured on histological slides. With bFGF there was a 51 percent increase in the bone penetration distance at 6 weeks in this model. It also appeared that further penetration had almost ceased in the controls, whereas in the bFGF-treated specimens, membranous ossification was still going on.     

Bone graft incorporation. Effects of osteogenic protein-1 and impaction

Impaction of cancellous bone grafts in a bone chamber in rats in a previous study led to decreased ingrowth of new bone after 6 weeks compared with unimpacted grafts. The current study analyzes whether this decrease represented a final loss of ingrowth or just a delay, if the decrease was influenced by immunologic factors, and if it was possible to influence the inhibitory effect by adding a bone morphogenetic protein. Bone chambers with impacted or unimpacted bone grafts were implanted bilaterally in rat tibias. The mean bone ingrowth distance into the graft was measured on histologic sections. Three experiments were done: (1) the bone ingrowth into impacted and unimpacted grafts was studied at 6 and 12 weeks; (2) the immunologic influence was studied by comparing isogeneic grafts with allogeneic grafts; and (3) the authors tried to influence the decrease in bone ingrowth in impacted grafts by adding osteogenic protein-1. Bone ingrowth into the impacted graft was decreased at 6 weeks but not at 12 weeks. No difference was found between isografts and allografts at 6 weeks. With the addition of osteogenic protein-1, the impacted grafts showed dramatically increased bone ingrowth. Impacted bone grafts are incorporated at a slower rate than were structural grafts. The delay can be reversed by adding osteogenic protein-1, making ingrowth faster than in structural bone.     

BMP‐2 but not VEGF or PDGF in fibrin matrix supports bone healing in a delayed‐union rat model

Treatment of delayed bone healing and non‐unions after fractures, osteotomies or arthrodesis still is a relevant clinical challenge. Artificially applied growth factors can increase bone healing and progressively gain importance in clinical routine. The aim of this study was to determine the effects of rhPDGF‐BB, rhVEGF‐165, and rhBMP‐2 in fibrin matrix on bone healing in a delayed‐union rat model. Thirty‐seven rats underwent a first operation where a standardized femoral critical size defect was created. A silicone spacer was implanted to impair vascularization within the defect. At 4 weeks the spacer was removed in a second operation and rhPDGF‐BB, rhVEGF‐165, or rhBMP‐2 were applied in a fibrin clot. Animals in a fourth group received a fibrin clot without growth factors. At 8 weeks fibrin bound rhBMP‐2 treated animals showed a significantly increased union rate and bone volume within the defect compared to the other groups. Single application of fibrin bound rhPDGF‐BB and rhVEGF‐165 failed to increase bone healing in our atrophic non‐union model. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1563–1569, 2012     

Intraosseous incorporation of composite collagen prostheses designed for ligament reconstruction

Composite collagen prostheses are potentially useful for reconstruction of the anterior cruciate ligament (ACL). We evaluated the intraosseous response to composite collagen prostheses to determine if “biological fixation” could be used to secure the prostheses within surgical bone tunnels. The rate of degradation of the prosthesis and the response of the tissue were evaluated, as a function of collagen crosslinking agent and time, in nonloaded bone tunnels in rabbits. Prostheses were fabricated by the alignment of 200 reconstituted type-I collagen fibers (60 μm in diameter) and the embedding of the fibers within a collagen matrix. The prostheses degraded rapidly within the bone tunnels in comparison with soft-tissue implantation sites. Dehydrothermal-cyanamide crosslinked collagen fibers were completely degraded by 8 weeks. Only 10% of glutaraldehyde crosslinked collagen fibers remained intact at 12 weeks. Fibrous tissue and inflammatory cells rapidly infiltrated the prostheses, and new bone surrounded the circumference of the prostheses, advancing toward the center at longer times. At the lateral cortex, where fibrous tissue emerged, the bone/soft-tissue interface was delineated by a tidemark, similar to that observed in a normal ligament insertion site. Preliminary pull-out testing of the soft tissue; this suggests rapid incorporation of the prostheses within the bone tunnels. Composite collagen prostheses designed for ACL reconstruction degrade rapidly in bone and induce rapid ingrowth of fibrous tissue and bone. These results suggest that tissue ingrowth in the bone tunnels might provide biological fixation for collagen prostheses used for ACL reconstruction.     

Cell relationship in a Wistar rat model of spontaneous prostatitis.

PURPOSE: Prostatitis in men is a painful, noninfectious inflammatory condition. It is similar to interstitial cystitis which is associated with increased bladder mast cell and sensory nerve fiber density as well as suprapubic pain. Certain strains of rats may provide a useful model for studies of the development of spontaneous prostatitis. We evaluated the time course, and involvement of mast cells and sensory nerve fibers in this process using Wistar rats. MATERIALS AND METHODS: The prostates of 4, 6, 8, 10 and 13-week-old male Wistar rats were examined for the degree of inflammation, innervation, mast cell density and nerve mast cell relationship using histochemical and immunocytochemical studies. Bacterial cultures of tissue were performed at 13 weeks. RESULTS: The inflammatory cell index increased progressively with age. Inflammation was moderate and consisted mostly of lymphocytes and macrophages associated with occasional glandular epithelial necrosis and edema. The density of nerve fibers immunoreacting with the neuronal marker protein gene produce 9.5 increased gradually with age and fibers immuno-positive for the sensory neuropeptide calcitonin gene-related peptide more than doubled by 13 weeks compared with by 4 weeks. The density of visible mast cells declined after 4 weeks in a pattern that corresponded with the increased percent of mast cells undergoing degranulation. For the mast cells with calcitonin gene-related peptide immuno-positive nerve fibers within a distance of 40 microm. distance correlated significantly with the degree of degranulation. Bacterial cultures were negative at 13 weeks. CONCLUSIONS: Our results confirm previous reports of spontaneous prostatitis in Wistar rats and indicate that moderate inflammation may occur in 80% of rats at as early as age 13 weeks. While the correlation of the nerve mast cell axis with mast cell degranulation does not prove our hypothesis of mast cell mediated inflammatory mediator release in the development of nonbacterial prostatitis, it suggests that such a relationship is possible.