Surgical management of dentigerous cyst arises from ectopic tooth: A report of three consecutive cases and literature review.

BACKGROUND: Dentigerous cysts are slow-growing, asymptomatic lesions that typically form around the crowns of impacted teeth. They are not detected until they start to harm the tissues around the teeth. AIM: The present study aimed to describe surgical techniques for treating dentigerous cysts associated with ectopic teeth. CASES: Three patients with dentigerous cysts associated with ectopic teeth, their surgical approaches, and the supporting literature are presented herein. In two cases, the surgical technique used was intra-oral, and in one case was extra-oral. Under general anesthesia, dentigerous cyst enucleation and ectopic tooth removal were carried out. DISCUSSION: In the present study, the ectopic tooth cases were all linked to dentigerous cysts. Enucleation or marsupialization treatments could be used to treat dentigerous cysts. Enucleation with the removal of the impacted tooth is the preferred treatment for dentigerous cysts. CONCLUSION: To perform minimally invasive surgery, the position of the ectopic teeth, the accessibility of the surgical site, the degree of bone reduction, and the simplicity of instrumentation should all be considered.

Unilateral hypoglossal nerve palsy following orthognathic surgery: A case report and literature review.

INTRODUCTION: Hypoglossal nerve palsy (HNP) can be caused by nerve damage from the central nerve to a peripheral nerve, and individuals with multiple factors could be predisposed to HNP. We report a case of isolated unilateral HNP after orthognathic surgery. CASE PRESENTATION: A 56-year-old Japanese woman complained of jaw distortion and malocclusion. She had undergone a Le Fort I osteotomy and bilateral sagittal split ramus osteotomy (BSSRO) under general anesthesia in August 2021. On postoperative day 3, she experienced tongue motility, and when the tongue protruded forward, the tongue tip shifted to the right, and swelling of the right lateral pharyngeal wall was observed. An additional blood test revealed increased antibody titer levels (40×), cytomegalovirus IgG EIA titer (16.9 U/mL), HSV-IgG EIA titer (40 U/mL), and EBV-viral capsid antigen (VCA) IgG EIA titer (1.4 U/mL). We administered valacyclovir hydrochloride 1000 mg/day for 7 days, prednisolone (PSL) 60 mg/day, mecobalamin 1500 µg/day, and adenosine triphosphate (ATP) disodium hydrate 300 mg/day. A neurological examination revealed no central lesions, and we continued the patient's tongue-function training and oral hygiene guidance. The tongue apex deviation was resolved approx. 3 months postoperatively. DISCUSSION: There are no major reports on the etiology of HNP after orthognathic surgery. The possibility of HNP triggered by endotracheal intubation or through packing gauze under general anesthesia and viral infection cannot be ruled out. CONCLUSION: Clinicians should be aware of the possibility of unilateral HNP following orthognathic surgery.

Bone formation ability of Gli1+ cells in the periodontal ligament after tooth extraction.

During the process of socket healing after tooth extraction, osteoblasts appear in the tooth socket and form alveolar bone; however, the source of these osteoblasts is still uncertain. Recently, it has been demonstrated that cells expressing Gli1, a downstream factor of sonic hedgehog signaling, exhibit stem cell properties in the periodontal ligament (PDL). Therefore, in the present study, the differentiation ability of Gli1+-PDL cells after tooth extraction was analyzed using Gli1-CreERT2/ROSA26-loxP-stop-loxP-tdTomato (iGli1/Tomato) mice. After the final administration of tamoxifen to iGli1/Tomato mice, Gli1/Tomato+ cells were rarely detected in the PDL. One day after the tooth extraction, although inflammatory cells appeared in the tooth socket, Periostin+ PDL-like tissues having a few Gli1/Tomato+ cells remained near the alveolar bone. Three days after the extraction, the number of Gli1/Tomato+ cells increased as evidenced by numerous PCNA+ cells in the socket. Some of these Gli1/Tomato+ cells expressed BMP4 and Phosphorylated (P)-Smad1/5/8. After seven days, the Osteopontin+ bone matrix was formed in the tooth socket apart from the alveolar bone. Many Gli1/Tomato+ osteoblasts that were positive for Runx2+ were arranged on the surface of the newly formed bone matrix. In the absence of Gli1+-PDL cells in Gli1-CreERT2/Rosa26-loxP-stop-loxP-tdDTA (iGli1/DTA) mice, the amount of newly formed bone matrix was significantly reduced in the tooth socket. Therefore, these results collectively suggest that Gli1+-PDL cells differentiate into osteoblasts to form the bone matrix in the tooth socket; thus, this differentiation might be regulated, at least in part, by bone morphogenetic protein (BMP) signaling.

The Role of Hedgehog Signaling in the Melanoma Tumor Bone Microenvironment.

A crucial regulator in melanoma progression and treatment resistance is tumor microenvironments, and Hedgehog (Hh) signals activated in a tumor bone microenvironment are a potential new therapeutic target. The mechanism of bone destruction by melanomas involving Hh/Gli signaling in such a tumor microenvironment is unknown. Here, we analyzed surgically resected oral malignant melanoma specimens and observed that Sonic Hedgehog, Gli1, and Gli2 were highly expressed in tumor cells, vasculatures, and osteoclasts. We established a tumor bone destruction mouse model by inoculating B16 cells into the bone marrow space of the right tibial metaphysis of 5-week-old female C57BL mice. An intraperitoneal administration of GANT61 (40 mg/kg), a small-molecule inhibitor of Gli1 and Gli2, resulted in significant inhibition of cortical bone destruction, TRAP-positive osteoclasts within the cortical bone, and endomucin-positive tumor vessels. The gene set enrichment analysis suggested that genes involved in apoptosis, angiogenesis, and the PD-L1 expression pathway in cancer were significantly altered by the GANT61 treatment. A flow cytometry analysis revealed that PD-L1 expression was significantly decreased in cells in which late apoptosis was induced by the GANT61 treatment. These results suggest that molecular targeting of Gli1 and Gli2 may release immunosuppression of the tumor bone microenvironment through normalization of abnormal angiogenesis and bone remodeling in advanced melanoma with jaw bone invasion.

Effects of prolonged stimulation with heated tobacco products (Ploom TECH+ ) on gingival epithelial cells.

OBJECTIVE AND BACKGROUND: Heated tobacco products have recently become commercially available. These products, as well as combustible cigarettes, produce aerosols; the risk of various diseases associated with heated tobacco products may be the same or higher than that with combustible cigarettes. In this study, we examined the effect of Ploom TECH+ extract on gingival epithelial cells. METHODS: Tobacco leaves from Ploom TECH+ tobacco capsules and water were mixed and heated; the supernatant subsequently collected was the heated tobacco product (HTP; control: HTP not added). Normal human gingival epithelial progenitors were cultured alternately with or without HTP for a total of 1 month. Subsequently, RNA, DNA, and proteins were isolated from these samples and comprehensively analyzed using RNA sequencing (RNA-seq), reduced representation bisulfite sequencing (RRBS), and western blotting, respectively. RESULTS: RNA-seq revealed that 284 genes showed a twofold increase and 145 genes showed a twofold decrease in gene expression. A heat map showed genetic differences between the control and HTP groups. A principal component analysis plot showed a clear genetic distribution between the control and HTP. Gene Ontology (GO) analysis showed that genes related to seven GO terms, including cornification and keratinization, were induced by long-term HTP stimulation. By contrast, GO pathways with a significant decrease in component expression were not detected. RRBS revealed that CpG island methylation increased more than twofold in 158 genes and decreased to less than twofold in 171 genes. Methylation of these CpG islands was not correlated with changes in gene expression levels. HTP treatment increased S100A7 expression. CONCLUSION: Long-term HTP stimulation affected epithelial differentiation and keratinization of gingival epithelial cells. Thus, habitual use of Ploom TECH+ may be a risk factor for tobacco-related oral mucosal diseases.

Angiogenesis Assays for the Analysis of CCN Proteins.

Angiogenesis, the process of generating new blood vessels from an existing vasculature, is essential in normal developmental processes such as endochondral ossification and in numerous kinds of pathogenesis including tumor growth. A part from the actin of angiogenic factor or antiangiogenic factor, it is still unknown at which stage of the angiogenic cascade these agents affect angiogenesis. Here, we describe methods for the use of cellular communication network factor/connective tissue growth factor (CTGF/CCN2) and CCN2-neutralizing antibody in the currently used principal angiogenesis assays, including those in vitro ones for the proliferation, migration, adhesion, and tube formation of endothelial cells and in vivo assays such as those utilizing type I collagen implantation and the chick chorioallantoic membrane (CAM). In addition, we introduce an autofluorescence imaging of blood vessels in the subcutaneous tumor xenograft mouse model. These assays can be applied to studies on roles of CCN proteins in tumor metastasis and development of treatment strategies targeting CCN proteins.

Immunohistochemical Analysis of CCN2 in Experimental Fracture Healing Models.

Skeletal fractures are most common large-organ traumatic injuries that impact the functions and esthetic outcomes and quality of life. Unfortunately, infection during the fracture healing process and inadequate blood supply to the bone impede reduced ability to produce cartilage and effective bone callus formation, leading to nonunion or delayed union fracture. Therefore, studying the mechanism of fracture healing is an important task in solving the problem of fracture healing failure. Animal models of bone fracture healing are important tools to investigate the pathogenesis and develop treatment strategies. This protocol introduces researchers to a bone repair model utilizing the ribs of rats and the immunohistological expression of cellular communication network factor/connective tissue growth factor (CTGF/CCN2) during the fracture healing processes.

Mouse Models of Tumor Bone Metastasis and Invasion for Studying CCN Proteins.

Bone metastasis and bone destruction are common occurrences in human malignancies, including breast, prostate, and lung cancer, and are associated with a high morbidity rate because of intractable bone pain, pathological fractures, hypercalcemia, and nerve compression. Animal models of bone metastasis and bone destruction are important tools to investigate the pathogenesis and develop treatment strategies. However, there are few models of spontaneous bone metastasis despite the fact that animals often spontaneously develop cancer. Here, we describe methods for developing a mouse model of breast cancer bone metastasis achieved by injection of MDA-MB-231 breast cancer cells into the left cardiac ventricle. In addition, we introduce mouse model of the bone destruction by injection of SAS oral squamous cell carcinoma cells into the bone marrow space of the right tibial metaphysis. These assays can be applied to studies on roles of cellular communication network factor/connective tissue growth factor (CTGF/CCN2) protein in tumor metastasis and development of treatment strategies targeting CCN proteins.

Association between impaired healing after orthognathic surgery and irritable bowel syndrome: A case report and literature review.

INTRODUCTION: In the disease irritable bowel syndrome (IBS), gastrointestinal function is worsened even though no organic abnormalities are observed in the gastrointestinal mucosa. We report the case of an orthognathic surgery patient with suspected irritable bowel syndrome. CASE: In September 2017, a 15-year-old Japanese female was referred to us with dental crowding, malocclusion, and mandibular protrusion. In June 2019, a disagreement with classmates led to abdominal pain, diarrhea, and hemorrhage; in August 2019, a preoperative blood test showed sudden anemia, and her surgery was thus postponed. Subsequent upper and lower gastrointestinal endoscopy revealed no organic abnormality, and no definitive diagnosis was made. In March 2020, after an improvement in anemia was observed, a segmental Le Fort I osteotomy and bilateral sagittal split ramus osteotomy (BSSRO) were performed under general anesthesia. On the third post-operative day, due to the mucosal dehiscence adjacent to the suture part, the titanium plate was exposed, and irrigation of the wound with normal saline solution and oral hygiene instruction was continued daily for 2 weeks. Two years and eight months have passed since the surgery, and the healing of the oral mucosa and bone has been uneventful. DISCUSSION: The relationship between IBS and post-operative impaired healing associated with the fragility of the oral mucosa is unknown. However, psychological stress has been reported as a cause of IBS and to be related to oral microorganisms. CONCLUSION: Reducing risk factors for IBS and maintaining proper perioperative oral hygiene is essential in managing similar cases.

Surgical procedures for correcting vertical maxillary excess: A review.

INTRODUCTION: Vertical maxillary excess, a common orthodontic problem that leads to long faces and open bites, can be repositioned with a Le Fort I osteotomy. However, the Le Fort I osteotomy poses the risk of a variety of complications including descending palatine artery (DPA) injury. Although several Le Fort I osteotomy modifications were reported to avoid complications associated with this osteotomy, only a few of such studies were conducted in Japan, and details remain scarce. PATIENTS AND METHODS: We performed a literature review regarding modifications of Le Fort I osteotomies, including Le Fort I with a horseshoe osteotomy, modified horseshoe osteotomy, unilateral horseshoe osteotomy, pyramidal osteotomy, and U-shaped osteotomy. We identified eight relevant studies conducted in Japan; one study did not provide the number of patients examined. The 77 patients (seven studies) with vertical maxillary excess who underwent orthognathic surgery were ≥17 years old. DISCUSSION: There were no severe complications after the modified Le Fort I osteotomies. The postoperative maxillary changes obtained by the conventional horseshoe, modified horseshoe, unilateral type of horseshoe, pyramidal, and U-shaped osteotomies were nearly repositioned to the planned position and remained stable for ≥12 months post-surgery. CONCLUSION: Our review indicates that preserving the DPA can lower the incidence of intra- and post-operative complications. Each modification of the Le Fort I osteotomy (i.e., conventional horseshoe, modified horseshoe, unilateral horseshoe, pyramidal, and U-shaped osteotomy) has its respective advantages and indications.

Intraosseous clear cell mucoepidermoid carcinoma in the maxilla: A case report and review of literature.

We reported an extremely rare case regarding intraosseous clear cell variant of mucoepidermoid carcinoma in maxilla.

Expression of Neurokinin B Receptor in the Gingival Squamous Cell Carcinoma Bone Microenvironment.

Gingival squamous cell carcinoma (SCC) frequently invades the maxillary or mandibular bone, and bone destruction is known as a key prognostic factor in gingival SCCs. Recently, Neurokinin 3 receptor (NK-3R), the receptor ligand for NK-3, which is a member of the tachykinin family expressed in the central nervous system, was identified through pathway analysis as a molecule expressed in osteoclasts induced by the hedgehog signal. Although the expression of NK-3R has been detected in osteoclast and SCC cells at the bone invasion front, the relationship between NK-3R expression and the prognosis of gingival SCC patients remains unclear. In the present study, we retrospectively reviewed 27 patients with gingival SCC who had undergone surgery with curative intent. Significantly higher NK-3R expression in tumor cells was found in a case of jawbone invasion than in a case of exophytic poor jawbone invasion. On the other hand, no significant association was observed between NK-3R tumor-positive cases and tumor size, TNM stage, or tumor differentiation. The survival rate tended to be lower in NK-3R tumor-positive cases, but not significantly. However, the disease-specific survival rate was significantly lower in patients with a large number of NK-3R-positive osteoclasts than in those with a small number of them at the tumor bone invasion front. Our results suggest that NK-3R signaling in the gingival SCC bone microenvironment plays an important role in tumor bone destruction and should be considered a potential therapeutic target in advanced gingival SCC with bone destruction.

A challenging diagnosis of a mucocele in the maxillary gingiva: Case report and literature review.

INTRODUCTION: Mucoceles are mucous extravasation phenomena resulting from spontaneous ductal rupture or, less commonly, a traumatic cutting of a salivary excretory duct. Occasionally, the appearance of a mucocele closely resembles a neoplastic lesion, and it can be difficult to diagnose. PRESENTATION OF CASE: A 74-year-old Japanese male patient was referred to our clinic with painless swelling related to the upper right canine-premolar area. Preoperative imaging of the lesion revealed that it was fluid-filled and the histopathological biopsy suggested a myxoid tumor. We excised the lesion with the patient under general anesthesia, using safety margins based on the histology of the biopsy specimen to reach the definitive diagnosis and treatment. The final pathological diagnosis was a mucocele in the vicinity with an aberrant small salivary gland. Follow-up visits showed complete healing of the epithelium, and no recurrence has been observed during the subsequent 30 months. DISCUSSION: In cases with a difficult definitive diagnosis based on medical history, diagnostic imaging and pathological examination, it is important to proceed carefully with the possibility of a tumor in mind. CONCLUSION: This case emphasizes that some mucous cysts are challenging for clinicians in terms of diagnosis and treatment due to an uncommon presentation.

Masticatory muscle tendon-aponeurosis hyperplasia diagnosed as temporomandibular joint disorder: A case report and review of literature.

INTRODUCTION: Masticatory muscle tendon-aponeurosis hyperplasia (MMTAH) is a new clinical entity that presents mainly with trismus due to hyperplasia of the masseter aponeurosis and temporalis muscle tendon. However, the etiological factors of this disease are unknown; it is often mistreated as temporomandibular joint disorder (TMD). PRESENTATION OF CASE: We report a 32-year-old female patient complaining of bilateral pain in her jaw and difficulty opening her mouth. She was first diagnosed as TMD and treated with a splint; however, her symptoms did not improve. Clinical examination revealed a square mandible, tenderness in the left and right temporalis muscles and masseter muscles, and tenderness along the anterior border of the masseter muscle. Her maximum mouth-opening was 30 mm. Short TI inversion recovery magnetic resonance imaging showed areas of low intensity at the anterior border of the masseter muscle and around the coronoid process where the temporalis muscle tendon attaches. Consequently, the diagnosis made based on the clinical and radiographic findings was MMTAH. Bilateral coronoidectomy was performed, followed by a rehabilitation program for six months. The maximum opening was maintained at 48 mm two years after the operation. DISCUSSION: MMTAH was treated as type 1 TMD until it was recognized as a new disease at the conference for the Japanese Society for Oral and Maxillofacial Surgeons. Since then, many clinicians have become aware of this particular condition, and different treatment modalities have been proposed. CONCLUSION: Clinicians should consider MMTAH as a differential diagnosis when the patient's chief complaint is gradually decreasing mouth-opening.

High mobility group box 1 induces bone pain associated with bone invasion in a mouse model of advanced head and neck cancer.

Advanced head and neck cancer (HNC) can invade facial bone and cause bone pain, thus posing a significant challenge to the quality of life of patients presenting with advanced HNC. The present study was designed to investigate HNC bone pain (HNC­BP) in an intratibial mouse xenograft model that utilized an HNC cell line (SAS cells). These mice develop HNC­BP that is associated with an expression of phosphorylated ERK1/2 (pERK1/2), which is a molecular indicator of neuron excitation in dorsal root ganglia (DRG) sensory neurons. Our experiments demonstrated that the inhibition of high mobility group box 1 (HMGB1) by short hairpin (shRNA) transduction, HMGB1 neutralizing antibody, and HMGB1 receptor antagonist suppressed the HNC­BP and the pERK1/2 expression in DRG. It was also observed that HNC­derived HMGB1 increased the expression of the acid­sensing nociceptor, transient receptor potential vanilloid 1 (TRPV1), which is a major cause of osteoclastic HNC­BP in DRG. Collectively, our results demonstrated that HMGB1 originating in HNC evokes HNC­BP via direct HMGB1 signaling and hypersensitization for the acid environment in sensory neurons.

Disuse atrophy of masticatory muscles after intracranial trigeminal schwannoma resection: A case report and review of literature.

INTRODUCTION: Temporomandibular disorders (TMD) are diseases of the temporomandibular joint and masticatory muscles, and are often difficult to be diagnosed because they have various symptoms, pathological conditions and causes. PRESENTATION OF CASE: Herein, we report a 78-year-old male referred to our hospital with a diagnosis of TMD and presenting with facial asymmetry, marked deviation to the right side on vertical mandibular movement and complaints of abnormal perception at the right oral and buccal region. Past medical history revealed that he had undergone a right intracranial trigeminal schwannoma resection 9 years prior. Computed tomography (CT) showed disuse atrophy of the right side of 4 masticatory muscles and 2 suprahyoid muscles controlled by the motor component of the mandibular division (V3) of the trigeminal nerve (TGN). Together with the neurosurgeon, we confirmed that there was no recurrence of the tumor and explained to the patient that the oral and maxillofacial symptoms are after-effects of the operation, and we provided oral hygiene instructions and coordinated cleaning of the inside of the oral cavity. DISCUSSION: Although it is difficult to compare treatment methods from case to case, we believe that in our case, the patient's understanding of the cause of his discomfort contributed significantly to the improvement of his quality of life. CONCLUSION: We experienced a case of masticatory muscle disuse atrophy during long-term follow-up after resection of intracranial trigeminal schwannoma. Further studies are needed to develop the diagnostic and therapeutic protocols for disuse atrophy.

Stem cell properties of Gli1-positive cells in the periodontal ligament.

BACKGROUND: The periodontal ligament (PDL), which surrounds the tooth root, contains mesenchymal stem cells (MSCs) capable of differentiating into osteoblasts, cementoblasts, and fibroblasts under normal conditions. These MSCs are thought to have important roles in the repair and regeneration of injured periodontal tissues. However, since there is no useful marker for MSCs in the PDL, the characteristics and distributions of these cells remain unclear. Gli1, an essential hedgehog signaling transcription factor, functions in undifferentiated cells during embryogenesis. Previous studies have demonstrated that the dental epithelial and mesenchymal cells positive for Gli1 in developing teeth have stem cell properties, including the ability to form colonies and pluripotency. Therefore, the focus of this review is the stem cell properties of Gli1-positive cells in the PDL, with an emphasis on the differentiation ability of osteoblasts for the regeneration of periodontal tissues. HIGHLIGHT: Lineage tracing analysis identified Gli1-positive PDL cells as MSCs that contribute to the formation of periodontal tissues and can regenerate alveolar bone. CONCLUSION: Gli1 is a potential stem cell marker in the PDL. A more definitive understanding of the functions of Gli1-positive cells could be useful for the development of regenerative methods using the MSCs in the PDL.

High-mobility group box 1 induces bone destruction associated with advanced oral squamous cancer via RAGE and TLR4.

Bone destruction of maxillary and mandibular bone by invasive oral squamous cell cancer (OSCC) raises various problems in the management of patients, resulting in poor outcomes and survival. However, the mechanism behind bone destruction by OSCC remains unclear. High-mobility group box 1 (HMGB1), a highly conserved ubiquitous nuclear non-histone DNA-binding protein, has been demonstrated to be secreted by aggressive cancers and regulate osteoclastogenesis, a central player during bone destruction. We therefore reasoned that HMGB1 secreted by OSCCs contributes to bone destruction. Our results showed that HMGB1 is produced by human cell lines of OSCC and promotes osteoclastogenesis via up-regulation of the expression of receptor activator of nuclear factor kappa-Β ligand in osteoblasts and osteocytes, and consequently osteoclastic bone destruction in mice. Further, we found that these actions of HMGB1 are mediated via the receptor for advanced glycation end products and toll-like receptors. These findings suggest that HMGB1 of OSCC and its down-stream signal pathways are potential targets for the treatment of bone destruction associated with advanced OSCC.

Hedgehog Signaling in Organogenesis and the Tumor Microenvironment.

The Hedgehog signaling pathway was first discovered in 1980 during a large-scale genetic screening seeking to find mutations that affect larval body segment development in the fruit fly, Drosophila melanogaster [...].

Expression and Role of IL-1ß Signaling in Chondrocytes Associated with Retinoid Signaling during Fracture Healing.

The process of fracture healing consists of an inflammatory reaction and cartilage and bone tissue reconstruction. The inflammatory cytokine interleukin-1ß (IL-1ß) signal is an important major factor in fracture healing, whereas its relevance to retinoid receptor (an RAR inverse agonist, which promotes endochondral bone formation) remains unclear. Herein, we investigated the expressions of IL-1ß and retinoic acid receptor gamma (RARγ) in a rat fracture model and the effects of IL-1ß in the presence of one of several RAR inverse agonists on chondrocytes. An immunohistochemical analysis revealed that IL-1ß and RARγ were expressed in chondrocytes at the fracture site in the rat ribs on day 7 post-fracture. In chondrogenic ATDC5 cells, IL-1ß decreases the levels of aggrecan and type II collagen but significantly increased the metalloproteinase-13 (Mmp13) mRNA by real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis. An RAR inverse agonist (AGN194310) inhibited IL-1ß-stimulated Mmp13 and Ccn2 mRNA in a dose-dependent manner. Phosphorylated extracellular signal regulated-kinases (pERK1/2) and p-p38 mitogen-activated protein kinase (MAPK) were increased time-dependently by IL-1ß treatment, and the IL-1ß-induced p-p38 MAPK was inhibited by AGN194310. Experimental p38 inhibition led to a drop in the IL-1ß-stimulated expressions of Mmp13 and Ccn2 mRNA. MMP13, CCN2, and p-p38 MAPK were expressed in hypertrophic chondrocytes near the invaded vascular endothelial cells. As a whole, these results point to role of the IL-1ß via p38 MAPK as important signaling in the regulation of the endochondral bone formation in fracture healing, and to the actions of RAR inverse agonists as potentially relevant modulators of this process.