Cross talk between neurometals and amyloidogenic proteins at the synapse and the pathogenesis of neurodegenerative diseases.

Increasing evidence suggests that disruption of metal homeostasis contributes to the pathogenesis of various neurodegenerative diseases, including Alzheimer's disease, prion diseases, Lewy body diseases, and vascular dementia. Conformational changes of disease-related proteins (amyloidogenic proteins), such as ß-amyloid protein, prion proteins, and α-synuclein, are well-established contributors to neurotoxicity and to the pathogenesis of these diseases. Recent studies have demonstrated that these amyloidogenic proteins are metalloproteins that bind trace elements, including zinc, iron, copper, and manganese, and play significant roles in the maintenance of metal homeostasis. We present a current review of the role of trace elements in the functions and toxicity of amyloidogenic proteins, and propose a hypothesis integrating metal homeostasis and the pathogenesis of neurodegenerative diseases that is focused on the interactions among metals and between metals and amyloidogenic proteins at the synapse, considering that these amyloidogenic proteins and metals are co-localized at the synapse.

Self-awareness of fast eating and its impact on diagnostic components of metabolic syndrome among middle-aged Japanese males and females.

OBJECTIVE: The aim of the present study was to examine the association between subjects with self-awareness of fast eating and diagnostic components of metabolic syndrome in Japanese middle-aged male and female. PATIENTS AND METHODS: Subjects consisted of 3208 males (average age 50.6 years) and 2055 females (average age 50.0 years). Associations between subjects with self-awareness of fast eating and multiple components of metabolic syndrome (waist circumference, body mass index [BMI], blood pressure, and related blood sample tests) were evaluated. RESULTS: Significantly more males (57.7%) acknowledged themselves as "fast eater" than females (46.5%). Self-reported fast eaters showed significantly elevated body weight, BMI, and waist circumference in both genders. However, only male self-reported fast eaters showed high levels of blood pressure, fasting blood glucose, uric acid, and low-density lipoprotein (LDL)-cholesterol. CONCLUSION: Fast eating is associated with diagnostic components of metabolic syndrome. The effect of acknowledging themselves as fast eater presents a higher impact on males than on females in the middle-aged Japanese population. The present study indicates that finding subjects with self-awareness of fast eating may lead to the prevention of developing metabolic syndrome.

Prophylactic procedure for inguinal hernia after radical retropubic prostatectomy.

PURPOSE: The incidence of inguinal hernias (IH) after radical retropubic prostatectomy (RRP) has been reported to range from 10 to 50 %, but no prophylaxis for IH has yet been established. We proposed a prophylaxis for IH after RRP. METHODS: A total of 180 patients underwent RRP at our hospital between 2000 and 2011. In January 2008, we started to perform a prophylaxis involving the dissection of the processus vaginalis. This procedure was performed in 73 patients. We then compared the incidence of IH between the patients that did (prophylaxis group) and did not (no prophylaxis group) undergo the prophylaxis. We also studied the risk factors for IH after RRP. RESULTS: In the no prophylaxis group, 25 (23 %) of the 107 patients developed IH, and the IH-free rate at one postoperative year was 86 %. In contrast, only 3 (4.1 %) of the 73 patients in the prophylaxis group developed IH, resulting in IH-free rate of 96 % at one postoperative year (P = 0.0235). Among the patients in the no prophylaxis group, the mean body mass index of the hernia group was significantly lower than that of the no hernia group (P = 0.006). CONCLUSION: Our results suggest that our prophylaxis is useful for preventing IH after RRP.

Experimental study on the aetiology of benign paroxysmal positional vertigo due to canalolithiasis: comparison between normal and vestibular dysfunction models.

OBJECTIVES: Using American bullfrog models under normal conditions and under vestibular dysfunction, we investigated whether mechanical vibration applied to the ear could induce otoconial dislodgement. METHODS: Vibration was applied to the labyrinth of the bullfrog using a surgical drill. The time required for the otoconia to dislodge from the utricular macula was measured. Vestibular dysfunction models were created and the dislodgement time was compared with the normal models. The morphology of the utricular macula was also investigated. RESULTS: In the normal models, the average time for otoconial dislodgement to occur was 7 min and 36 s; in the vestibular dysfunction models, it was 2 min and 11 s. Pathological investigation revealed that the sensory hairs of the utricle were reduced in number and that the sensory cells became atrophic in the vestibular dysfunction models. CONCLUSION: The otoconia of the utricle were dislodged into the semicircular canal after applying vibration. The time to dislodgement was significantly shorter in the vestibular dysfunction models than in the normal models; the utricular macula sustained significant morphological damage.

Regulation of several androgen-induced genes through the repression of the miR-99a/let-7c/miR-125b-2 miRNA cluster in prostate cancer cells.

The androgen receptor (AR) stimulates and represses gene expression to promote the initiation and progression of prostate cancer. Here, we report that androgen represses the miR-99a/let7c/125b-2 cluster through AR and anti-androgen drugs block the androgen-repression of the miRNA cluster. AR directly binds to the host gene of the miR-99a/let7c/125b-2 cluster, LINC00478. Expression of the cluster is repressed or activated by chromatin remodelers EZH2 or JMJD3 in the presence or absence of androgen, respectively. Bioinformatics analysis reveals a significant enrichment of targets of miR-99a, let-7c and miR-125b in androgen-induced gene sets, suggesting that downregulation of the miR-99a/let7c/125b-2 cluster by androgen protects many of their target mRNAs from degradation and indirectly assists in the gene induction. We validated the hypothesis with 12 potential targets of the miR-99a/let7c/125b-2 cluster induced by androgen: 9 out of the 12 mRNAs are downregulated by the microRNA cluster. To ascertain the biological significance of this hypothesis, we focused on IGF1R, a known prostate cancer growth factor that is induced by androgen and directly targeted by the miR-99a/let7c/125b-2 cluster. The androgen-induced cell proliferation is ameliorated to a similar extent as anti-androgen drugs by preventing the repression of the microRNAs or induction of IGF1R in androgen-dependent prostate cancer cells. Expression of a microRNA-resistant form of IGF1R protects these cells from inhibition by the miR-99a/let7c/125b-2 cluster. These results indicate that a thorough understanding of how androgen stimulates prostate cancer growth requires not only an understanding of genes directly induced/repressed by AR, but also of genes indirectly induced by AR through the repression of key microRNAs.

Efficacy of physical therapy for intractable cupulolithiasis in an experimental model.

OBJECTIVE: To investigate what kinds of stimuli are effective in detaching otoconia from the cupula in three experimental models of cupulolithiasis. METHODS: Three experimental models of cupulolithiasis were prepared using bullfrog labyrinths. Three kinds of stimuli were applied to the experimental models. In experiment one (gravity), the labyrinth preparation was placed so that the cupula-to-crista axis was in the horizontal plane with the canal side in the downward position. In experiment two (sinusoidal oscillation), the labyrinth preparation was placed 3 cm from the rotational centre of a turntable, which was sinusoidally rotated with a rotational cycle of 1 Hz and a rotational angle of 30°. In experiment three (vibration), mechanical vibration was applied to the surface of the bony capsule around the labyrinth using a surgical drill. RESULTS: In experiments one, two and three, the otoconial mass was respectively detached in 2 out of 10 labyrinth preparations, none of the labyrinth preparations, and all of the labyrinth preparations. CONCLUSION: Vibration was the most effective stimulus for detaching the otoconia from the cupula in these experimental models of cupulolithiasis.

Resting functional connectivity between the hemispheres in childhood absence epilepsy.

OBJECTIVE: The fundamental mechanisms by which childhood absence epilepsy (CAE) changes neural networks even between seizures remain poorly understood. During seizures, cortical and subcortical networks exhibit bihemspheric synchronous activity based on prior EEG-fMRI studies. Our aim was to investigate whether this abnormal bisynchrony may extend to the interictal period, using a blood oxygen level-dependent (BOLD) resting functional connectivity approach. METHODS: EEG-fMRI data were recorded from 16 patients with CAE and 16 age- and gender-matched controls. Three analyses were performed. 1) Using 16 pairs of seizure-related regions of interest (ROI), we compared the between-hemisphere interictal resting functional connectivity of patients and controls. 2) For regions showing significantly increased interhemispheric connectivity in CAE, we then calculated connectivity to the entire brain. 3) A paired-voxel approach was performed to calculate resting functional connectivity between hemispheres without the constraint of predefined ROIs. RESULTS: We found significantly increased resting functional connectivity between hemispheres in the lateral orbitofrontal cortex of patients with CAE compared to normal controls. Enhanced between-hemisphere connectivity localized to the lateral orbitofrontal cortex was confirmed by all 3 analysis methods. CONCLUSIONS: Our results demonstrate abnormal increased connectivity between the hemispheres in patients with CAE in seizure-related regions, even when seizures were not occurring. These findings suggest that the lateral orbitofrontal cortex may play an important role in CAE pathophysiology, warranting further investigation. In addition, resting functional connectivity analysis may provide a promising biomarker to improve our understanding of altered brain function in CAE during the interictal period.

Bmi1 is essential for leukemic reprogramming of myeloid progenitor cells.

The polycomb group (PcG) proteins, particularly Bmi1, have an essential role in maintaining the self-renewing capacity of leukemic stem cells (LSCs). Although one of their major targets in LSCs is known to be the Ink4a/Arf tumor suppressor gene locus, the role of PcG proteins in the leukemic reprogramming of target cells into LSCs is not well characterized. In this study, Bmi1(-/-) granulocyte/macrophage progenitors (GMPs) were transformed with the leukemic fusion gene MLL-AF9. Although Bmi1 was not essential to the immortalization of GMPs in vitro, Bmi1(-/-) cells showed enhanced differentiation and retained less LSCs. A number of genes were derepressed in the absence of Bmi1 including potential tumor suppressor genes. Transplantation assays demonstrated that Bmi1 was indispensable for the development of leukemia in vivo and deletion of both the Ink4a and Arf genes only partially restored the leukemogenic capacity of Bmi1(-/-) LSCs. Of note, the complementation of immortalized Bmi1(-/-)Ink4a-Arf(-/-) GMPs with Bmi1 failed to restore the expression of the majority of deregulated genes and leukemogenic activity in vivo. These findings indicate that Bmi1 is essential for the faithful reprogramming of myeloid progenitors into LSCs and unveil that leukemic fusion genes require PcG proteins exerting an effect in concert to establish LSC-specific transcriptional profiles, which confer full leukemogenic activity on LSCs.

Maternal screening and postpartum vaccination for measles infection in Japan: a cohort study.

We investigated the prevalence of measles-sensitive pregnant women and the clinical usefulness of measles vaccination in postpartum women. Measles antibody levels were measured in 751 pregnant women. Forty-four women were vaccinated postpartum, and screened for antibody levels and adverse effects 1 month after vaccination. The prevalence of measles-sensitive pregnant women was 10-20%, with the highest prevalence in those under 24 years of age. Almost all (97.7%) vaccinated women acquired immunity, and did not show any adverse effects. Serum measles antibody levels should be determined in all pregnant women as a screening tool,and sensitive women should be vaccinated immediately after delivery.

Mechanism of disopyramide-induced hypoglycaemia in a patient with Type 2 diabetes.

BACKGROUND: Disopyramide, an antiarrhythmia drug, has been reported to cause hypoglycaemia. Pre-existing factors that increase the concentration of the drug in the blood increase the risk of hypoglycaemia. Furthermore, other factors can also increase the risk of hypoglycaemia even when disopyramide levels are in the therapeutic range. It has been proposed that disopyramide-induced hypoglycaemia is caused by inhibition of the pancreatic B-cell K(ATP) channels. CASE REPORT: We report a case of severe disopyramide-induced hypoglycaemia in a 62-year-old woman with Type 2 diabetes taking low-dose glimepiride treatment. She had not experienced hypoglycaemia prior to the start of disopyramide therapy. No further hypoglycaemic episodes occurred following withdrawal of disopyramide therapy. FUNCTIONAL STUDY: Current recordings of K(ATP) channels expressed in Xenopus oocytes showed that at their estimated therapeutic concentrations, disopyramide and glimepiride inhibited K(ATP) channels by about 50-60%. However, when both drugs were applied together, K(ATP) channels were almost completely closed (approximately 95%). Such dramatic inhibition of K(ATP) channels is sufficient to cause B-cell membrane depolarization and stimulate insulin secretion. CONCLUSIONS: Disopyramide therapy is not recommended for patients treated with K(ATP) channel inhibitors.

Nuclear receptors CAR and PXR in the regulation of hepatic metabolism.

The nuclear receptors CAR and PXR were first characterized as xenosensing transcription factors regulating the induction of phase I and II xenobiotic-metabolizing enzymes as well as transporters in response to exogenous stimuli. It has now become clear, however, that these receptors cross-talk with endogenous stimuli as well, which extends their regulation to various physiological processes such as energy metabolism and cell growth. As recognition of the function of these receptors has widened, the molecular mechanism of their regulation has evolved from simple protein-DNA binding to regulation by complex protein-protein interactions. Novel mechanisms as to how xenobiotic exposure alters hepatic metabolic pathways such as gluconeogenesis and beta-oxidation have emerged. At the same time, the molecular mechanism of how endogenous stimuli, such as insulin, regulate xenobiotc metabolism via CAR and PXR have also become evident.

Induction of genes for metabolism and transport by trans-stilbene oxide in livers of Sprague-Dawley and Wistar-Kyoto rats.

trans-Stilbene oxide (TSO) is a synthetic proestrogen that induces phase I and II drug-metabolizing enzymes in rat liver. The purpose of this study was to determine whether TSO also induces transporter expression in rat liver and whether gene induction in rat liver after TSO occurs in a constitutive androstane receptor (CAR)-dependent manner. Total RNA was isolated from male rat livers after treatment with TSO for up to 4 days (200 mg/kg, i.p., twice daily), and the mRNA levels for each gene were quantified. CYP2B1/2, CYP3A1, epoxide hydrolase, heme oxygenase-1, UGT1A6, UGT2B1, multiple drug resistance protein (Mdr) 1a and 1b, as well as multidrug resistance-associated protein (Mrp) 2, 3, and 4 mRNA were increased in livers after TSO treatment. To determine whether TSO activates gene expression in a CAR-dependent manner, male and female Wistar-Kyoto (WKY) rats were treated with TSO for 3 days. TSO induced CYP2B1/2, UGT2B1, and Mdr1b in males more than in females, suggesting that TSO could increase their expression via CAR. Conversely, TSO induced CYP3A1, epoxide hydrolase, UGT1A6, and Mrp3 similarly in both genders, indicating that induction of these genes occurs independently of CAR. TSO treatment also increased the activity of a CAR binding element luciferase reporter construct in HepG2 cells transfected with rat CAR and in mouse liver. Additionally, TSO increased antioxidant response element/electrophile response element luciferase reporter construct activity in HepG2 cells. In conclusion, in WKY rat liver, TSO increases CYP2B1/2, UGT2B1, and Mdr1b mRNA expression in a gender-dependent manner and CYP3A1, epoxide hydrolase, UGT1A6, and Mrp3 in a gender-independent manner.

Serine 202 regulates the nuclear translocation of constitutive active/androstane receptor.

The constitutive active receptor (CAR) in mouse primary hepatocytes undergoes okadaic acid (OA)-sensitive nuclear translocation after activation by xenobiotics such as phenobarbital (PB) and 1,4 bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP). We have now mimicked this TCPOBOP-dependent and OA-sensitive translocation of mouse CAR (mCAR) in HepG2 cells and have demonstrated that protein phosphatase 2A regulates this nuclear translocation. Site-directed mutagenesis analysis of various Ser and Thr residues delineated the translocation activity to Ser-202. Mutation of Ser-202 to Asp (S202D) prevented mCAR translocation into the nucleus of TCPOBOP-treated HepG2 cells. In addition, in the livers of Car-/- mice, the YFP-tagged S202D mutant did not translocate into the nucleus after PB treatment. To examine whether Ser-202 can be phosphorylated, flag-tagged wild-type mCAR or flag-tagged S202A mutant was expressed in HepG2 cells and subjected to Western blot analysis using an antibody specific to a peptide containing phospho-Ser-202. A high molecular weight phosphorylated form of CAR was detected only with the wild-type mCAR. These results are consistent with the conclusion that the dephosphorylation of Ser-202 is a required step that regulates the xenobiotic-dependent nuclear translocation of mCAR.

Polycomb gene product Bmi-1 regulates stem cell self-renewal.

The Polycomb group (PcG) gene Bmi-1 has recently been implicated in the maintenance of hematopoietic stem cells (HSCs). However, the role of each component of PcG complex in HSCs and the impact of forced expression of PcG genes on stem cell self-renewal remain to be elucidated. To address these issues, we performed both loss-of-function and gain-of-function analysis on various PcG proteins. Expression analysis revealed that not only Bmi-1 but also other PcG genes are predominantly expressed in HSCs. Loss-of-function analyses, however, demonstrated that absence of Bmi-1 is preferentially linked with a profound defect in HSC self-renewal, indicating a central role for Bmi-1, but not the other components, in the maintenance of HSC self-renewal. Over-expression analysis of PcG genes also confirmed an important role of Bmi-1 in HSC self-renewal. Our findings indicate that the expression level of Bmi-1 is the critical determinant for the self-renewal capacity of HSCs. These findings uncover novel aspects of stem cell regulation exerted through epigenetic modifications by the PcG proteins.

Plexins: axon guidance and signal transduction.

Axon guidance represents a key stage in the formation of neuronal network. Axons are guided by a variety of guidance factors, such as semaphorins, ephrins and netrin. Plexins function as receptors for the repulsive axonal guidance molecules semaphorins. Intracellular domains of plexins are responsible for initiating cellular signal transduction inducing axon repulsion. Recent advances have revealed molecular mechanisms for plexin-mediated cytoskeletal reorganization, leading to repulsive responses, and small GTPases play important roles in this signaling. Plexin-B1 activates Rho through Rho-specific guanine nucleotide exchange factors, leading to neurite retraction. Plexin-B1 possesses an intrinsic GTPase-activating protein activity for R-Ras and induces growth cone collapse through R-Ras inactivation. In this review we survey current understanding of the signaling mechanisms of plexins.

Association of interleukin-18 gene single-nucleotide polymorphisms with susceptibility to inflammatory bowel disease.

Interleukin-18 (IL-18) is believed to be one of the most important cytokines in the pathogenesis of inflammatory bowel disease (IBD). The aim of the study was to clarify the significance of single-nucleotide polymorphisms (SNPs) at the 5'-end of the IL-18 gene in the development of IBD. DNA was obtained from peripheral blood of 99 patients with ulcerative colitis (UC), 79 patients with Crohn's disease (CD), and 102 healthy controls. All participants were Japanese. SNPs at -656G/T, -607C/A, -137G/C, +113T/G, and +127C/T were determined by means of direct sequencing, and a genetic association with IBD was examined. The frequencies of the G allele at +113 and the T allele at +127 were significantly higher in patients with CD and UC compared with controls. The differences in allelic frequencies were more striking in patients with CD than in patients with UC, and at position +127 than at position +113. The haplotype estimation, according to the E-M algorithm, suggested that TACGT is closely associated with IBD, especially with CD. It was concluded that SNPs at the 5'-end of IL-18 gene might be closely related to the etiology of IBD.

Downregulation of prostaglandin E receptor subtype EP3 during colon cancer development.

BACKGROUND AND AIMS: Involvement of prostaglandin E(2) (PGE(2)) receptors EP(1), EP(2), and EP(4) in the formation of aberrant crypt foci (ACF) and/or intestinal polyps has been suggested. In contrast, EP(3) appears to have no influence on the early stages of colon carcinogenesis. In the present study, we examined expression of PGE(2) receptor subtypes EP(1), EP(2), EP(3), and EP(4) in normal colon mucosa and colon cancers, and assessed the contribution of EP(3) to colon cancer development. METHODS: mRNA expression of PGE(2) receptor subtypes EP(1), EP(2), EP(3), and EP(4) in normal colon mucosa and colon cancers in azoxymethane (AOM) treated mice and rats, and in humans, were examined by reverse transcription-polymerase chain reaction (RT-PCR), quantitative real time RT-PCR, and immunohistochemical analyses. Evaluation of the role of EP(3) was performed by intraperitoneal injection of AOM, using EP(3) receptor knockout mice. Effects of EP(3) receptor activation on cell growth of human colon cancer cell lines were examined using ONO-AE-248, an EP(3) selective agonist. Moreover, EP(3) expression in colon cancer cell lines was analysed with or without 5-aza-2'-deoxycytidine (5-aza-dC) treatment. RESULTS: Expression levels of EP(1) and EP(2) mRNA were increased in cancer tissues. EP(4) mRNA was constantly expressed in normal mucosa and cancers. In contrast, expression of EP(3) mRNA was markedly decreased in colon cancer tissues, being 5% in mice, 9% in rats, and 28% in humans compared with normal colon mucosa, analysed by quantitative real time RT-PCR. Immunohistochemical staining demonstrated the rat EP(3) receptor protein to be expressed in epithelial cells of normal mucosa and some parts of small carcinomas but hardly detectable in large carcinomas of the colon. Colon cancer development induced by AOM in EP(3) receptor knockout mice was enhanced compared with wild-type mice, with a higher incidence of colon tumours (78% v 57%) and mean number of tumours per mouse (2.17 (0.51) v 0.75 (0.15); p<0.05). Expression of EP(3) mRNA was detected in only one of 11 human colon cancer cell lines tested. Treatment with 5 microM of an EP(3) selective agonist, ONO-AE-248, resulted in a 30% decrease in viable cell numbers in the HCA-7 human colon cancer cell line in which EP(3) was expressed. Treatment with 5-aza-dC restored EP(3) expression in CACO-2, CW-2, and DLD-1 cells but not in WiDr cells, suggesting involvement of hypermethylation in the downregulation of EP(3) to some extent. CONCLUSION: The PGE(2) receptor subtype EP(3) plays an important role in suppression of cell growth and its downregulation enhances colon carcinogenesis at a later stage. Hypermethylation of the EP(3) receptor gene could occur and may contribute towards downregulating EP(3) expression to some extent in colon cancers.

Heparan sulphate N-sulphotransferase activity: reaction mechanism and substrate recognition.

Human heparan sulphate N-deacetylase/N-sulphotransferase 1 sulphates the NH(3) (+) group of the glucosamine moiety of the heparan chain in heparan sulphate/heparin biosynthesis. An open cleft that runs perpendicular to the sulphate donor 3'-phosphoadenosine 5'-phosphosulphate may constitute the acceptor substrate-binding site of the sulphotransferase domain (hNST1) [Kakuta, Sueyoshi, Negishi and Pedersen (1999) J. Biol. Chem. 274, 10673-10676]. When a hexasaccharide model chain is docked into the active site, only a trisaccharide (-IdoA-GlcN-IdoA-) portion interacts directly with the cleft residues: Trp-713, His-716 and His-720 from alpha helix 6, and Phe-640, Glu-641, Glu-642, Gln-644 and Asn-647 from random coil (residues 640-647). Mutation of these residues either abolishes or greatly reduces hNST1 activity. Glu-642 may play the critical role of catalytic base in the sulphuryl group transfer reaction, as indicated by its hydrogen-bonding distance to the NH(3) (+) group of the glucosamine moiety in the model and by mutational data.

Increase in the number of tyrosine hydroxylase-containing neurons in a primary culture system of the rat accessory olfactory bulb by co-culture with vomeronasal pockets.

Previously, we established a culture system of the accessory olfactory bulb in order to investigate the functional role of each accessory olfactory bulb neurons in pheromonal signal processing. In the present study, we developed a co-culture system of cultured accessory olfactory bulb neurons with partially dissociated cells of the vomeronasal organ. The dissociated cells of the vomeronasal organ form spherical structures surrounding a central cavity in culture, referred to as the vomeronasal pockets. The projection and activity of olfactory receptor neurons affect the differentiation and maturation of main olfactory bulb neurons. It was also reported induction of tyrosine hydroxylase expression in main olfactory bulb neurons when they were co-cultured with explants of the olfactory epithelium. Thus, we investigated the effects of co-culture with vomeronasal pockets on the differentiation and/or maturation of cultured accessory olfactory bulb neurons in relation to tyrosine hydroxylase expression. The number of tyrosine hydroxylase-containing neurons developmentally increased over time in the accessory olfactory bulb culture. This increase was significantly enhanced by coculture with vomeronasal pockets. Interestingly, a significant change in tyrosine hydroxylase expression was not observed when main olfactory bulb neurons were co-cultured with vomeronasal pockets. Moreover, significant changes in tyrosine hydroxylase expression were not observed when accessory olfactory bulb neurons were co-cultured with olfactory epithelium explants, as was previously observed in co-culture of main olfactory bulb neurons and olfactory epithelium explants. These results suggest that the differentiation and/or maturation of accessory olfactory bulb neurons is modified by vomeronasal organ neurons via specific interactions between the sensory organ and its target.