Stimulation of Fusobacterium nucleatum biofilm formation by Porphyromonas gingivalis

BACKGROUND/AIMS

Bacterial infection is a major cause of periapical periodontitis. Eradication of these microorganisms from apical lesions is essential to the success of endodontic treatment. The aim of this study was to clarify the molecular interaction between Fusobacterium nucleatum, Porphyromonas gingivalis and other microorganisms associated with periapical periodontitis.

METHODS

Microorganisms isolated from periapical lesions were inoculated into type-I collagen-coated polystyrene microtiter plates and maintained at 37 degrees C under anaerobic conditions for 2 days, after which, the quantity of organized biofilm on the plates was evaluated by crystal violet staining. Growth enhancement via soluble factor was evaluated by separated coculture using a 0.4-mum membrane filter.

RESULTS

F. nucleatum exhibited strong adherence to type-I collagen-coated polystyrene microplates. Biofilm formation by F. nucleatum was significantly enhanced by P. gingivalis. It was complemented by compartmentalized coculture with P. gingivalis. Enhancement of biofilm formation by P. gingivalis was only slightly reduced by inactivation of its autoinducer-2-producing gene luxS.

CONCLUSION

The results suggest that P. gingivalis enhances biofilm formation by F. nucleatum by releasing diffusible signaling molecules other than autoinducer-2.

FTY720 suppresses CD4+CD44highCD62L- effector memory T cell-mediated colitis

FTY720, a sphingosine-derived immunomodulator, causes immunosuppression via enhancement of lymphocyte sequestration into secondary lymphoid organs, thereby preventing their antigen-activated T cell egress to sites of inflammation. FTY720 is highly effective in inhibiting autoimmunity in various animal models. However, there is little known about how FTY720 controls the migration property of memory T cells. Here, we demonstrated that FTY720 prevents the development of colitis induced by the adoptive transfer of lamina propria (LP) colitogenic effector memory CD4+ T cells (TEM cells; CD45RB(low)CD44(high)CD62L-) into severe combined immunodeficiency (SCID) mice and suppresses interferon-gamma, interleukin-2, and tumor necrosis factor-alpha production by LP CD4+ T cells. The numbers of spleen, peripheral blood, mesenteric lymph node, and LP CD4+ T cells in FTY720-treated mice were significantly reduced compared with those in control mice. Notably, LP CD4+ TEM cells as well as splenic CD4+CD45RBhigh T cells expressed several spingosine-1-phosphate receptors that are targets for FTY720. Furthermore, FTY720 also prevented the development of colitis induced by the adoptive transfer of splenic CD4+CD45RBhigh T cells into SCID mice. Collectively, the present data indicate that FTY720 treatment may offer the potential not only to prevent the onset of disease but also to treat memory T cell-mediated autoimmune diseases including inflammatory bowel diseases.

Naturally arising CD4+CD25+ regulatory T cells suppress the expansion of colitogenic CD4+CD44highCD62L- effector memory T cells

Naturally arising CD4+CD25+ regulatory T (T(R)) cells have been shown to prevent and cure murine T cell-mediated colitis. However, their exact mechanism of controlling colitogenic memory CD4+ T cells in in vivo systems excluding the initial process of naive T cell activation and differentiation has not been examined to date. Using the colitogenic effector memory (T(EM)) CD4+ cell-mediated colitis model induced by adoptive transfer of colitogenic CD4+CD44(high)CD62L(-) lamina propria (LP) T cells obtained from colitic CD4+CD45RB(high) T cell-transferred mice, we have shown in the present study that CD4+CD25+ T(R) cells are able not only to suppress the development of colitis, Th1 cytokine production, and the expansion of colitogenic LP CD4+ T(EM) cells but also to expand these cells by themselves extensively in vivo. An in vitro coculture assay revealed that CD4+CD25+ T(R) cells proliferated in the presence of IL-2-producing colitogenic LP CD4+ T(EM) cells at the early time point (48 h after culture), followed by the acquisition of suppressive activity at the late time point (96 h after culture). Collectively, these data suggest the distinct timing of the IL-2-dependent expansion of CD4+CD25+ T(R) cells and the their suppressive activity on colitogenic LP CD4+ T(EM) cells.

C3-6 laminoplasty takes over C3-7 laminoplasty with significantly lower incidence of axial neck pain

Five-lamina (C3-7) procedure is the most popular cervical laminoplasty and there have been no studies on the most appropriate number of laminae to be opened. We prospectively reduced the range of laminoplasty from C3-7 to C3-6 in 2002 and compared the outcome of C3-6 laminoplasty (n=37) to that of C3-7 laminoplasty (n=28). In both groups, neurological gain was satisfactory, radiographic changes were minimal, and postoperative MRI indicated sufficient expansion of the dura and the spinal cord. Average operating period was significantly shorter, and length of the operative wound was significantly less in the C3-6 group than in the C3-7 group. Postoperative axial neck pain was significantly rarer after C3-6 laminoplasty than after C3-7 laminoplasty (5.4% vs. 29%, P=0.015). Due to its simplicity and various benefits, C3-6 laminoplasty is a promising alternative to conventional C3-7 laminoplasty for treatment of multisegmental compression myelopathy.

Dissolved organic carbon and disinfection by-product precursor release from managed peat soils

A wetland restoration demonstration project examined the effects of a permanently flooded wetland on subsidence of peat soils. The project, started in 1997, was done on Twitchell Island, in the Sacramento-San Joaquin Delta of California. Conversion of agricultural land to a wetland has changed many of the biogeochemical processes controlling dissolved organic carbon (DOC) release from the peat soils, relative to the previous land use. Dissolved organic C in delta waters is a concern because it reacts with chlorine, added as a disinfectant in municipal drinking waters, to form carcinogenic disinfection byproducts (DBPs), including trihalomethanes (THMs) and haloacetic acids (HAAs). This study explores the effects of peat soil biogeochemistry on DOC and DBP release under agricultural and wetland management. Results indicate that organic matter source, extent of soil organic matter decomposition, and decomposition pathways all are factors in THM formation. The results show that historical management practices dominate the release of DOC and THM precursors. However, within-site differences indicate that recent management decisions can contribute to changes in DOC quality and THM precursor formation. Not all aromatic forms of carbon are highly reactive and certain environmental conditions produce the specific carbon structures that form THMs. Both HAA and THM precursors are elevated in the DOC released under wetland conditions. The findings of this study emphasize the need to further investigate the roles of organic matter sources, microbial decomposition pathways, and decomposition status of soil organic matter in the release of DOC and DBP precursors from delta soils under varying land-use practices.

Hemodynamic response of ovarian artery after hCG injection

We have analyzed ovarian hemodynamics immediately after human chorionic gonadotropin (hCG) administration in patients treated by clomiphene-hCG and human menopausal gonadotropin-hCG. This study involved 40 infertile women who signed consents to participate in this study. After intramuscular injection of 10000 IU hCG, the change of ovarian arterial blood flow (BF) was evaluated by color Doppler. Pulsatility index, resistance index, maximum velocity (V(max)), mean velocity, minimum velocity, cross-sectional area of ovarian artery (Area) and BF were measured before and 15-180 min after hCG administration. In the 36 subjects in which ovulation was induced successfully, V(max) and BF increased significantly even at 15 min after hCG administration and thereafter. In the 4 non-ovulatory subjects, no significant changes in any of indices at any of measured time points were observed. Comparative study of non-ovulatory and ovulatory subjects suggested that ovulation may be predicted by the ovarian hemodynamic analysis immediately after hCG administration.

Cyclic changes of granulocyte colony-stimulating factor (G-CSF) mRNA in the human follicle during the normal menstrual cycle and immunolocalization of G-CSF protein

BACKGROUND

Ovulation has several similarities with inflammation and is closely connected to the activity of leukocytes and inflammatory cytokines. Since granulocytes are one of the major leukocytes, we focused our attention on the presence and local production of granulocyte colony-stimulating factor (G-CSF) in the human ovary.

METHODS

The presence of G-CSF protein in the follicular fluid and perifollicular tissues was examined by Western blot analysis (n = 5) and immunohistochemical staining (n = 10). The relative expression levels of G-CSF mRNA in relation to GAPDH in granulosa, theca and luteal cells during the menstrual cycle were measured by quantitative RT-PCR using TaqMan technology (n = 15).

RESULTS

G-CSF protein was detected in all follicular fluid and located mainly in granulosa cells of the follicle and luteal cells. The expression level of G-CSF mRNA in the late follicular phase was 137.6 +/- 18.5, which was approximately 10-fold greater than other phases during the menstrual cycle (P < 0.05).

CONCLUSIONS

These results demonstrate that G-CSF is produced in the human follicle shortly before the ovulatory phase and may play an important role in the mechanism of ovulation.

Possible involvement of nitric oxide in signaling pigment dispersion in teleostean melanophores

The possible involvement of nitric oxide (NO) in regulating the motile activities of teleostean melanophores was studied in the dark chub Zacco temmincki (Cyprinidae, Cypriniformes) and in the translucent glass catfish Kryptopterus bicirrhis (Siluridae, Siluriformes). NO donors, including (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexaneamide (NOR1), molsidomine (MSD), sodium nitroprusside (SNP) and glyceryl trinitrate (GTN), had no pigment-aggregating action on melanophores, but actively dispersed melanosomes in those cells. Among those reagents, NOR 1, a spontaneous releaser of NO, was the most effective. Inhibitors for nitric oxide synthase (NOS), i.e. N omega-nitro-L-arginine methyl ester (L-NNA), N omega-nitro-L-arginine (L-NAME) and N omega-monomethyl-L-arginine (L-NMMA), showed melanosome-aggregating effects. A membrane-permeable analogue of cyclic guanosine-3',5'-monophosphate (8-Br-cGMP) was effective in dispersing melanosomes. The sum of these results suggests that NO plays an active role in the elaborate control of color changes in teleosts by dispersing pigment in melanophores via activation of soluble guanylyl cyclase to increase cytosolic levels of cGMP.

Characteristics and distribution of endogenous RFamide-related peptide-1

We have recently identified RFamide-related peptide (RFRP) gene that would encode three peptides (i.e., RFRP-1, -2, and -3) in human and bovine, and demonstrated that synthetic RFRP-1 and -3 act as specific agonists for a G protein-coupled receptor OT7T022. However, molecular characteristics and tissue distribution of endogenous RFRPs have not been determined yet. In this study, we prepared a monoclonal antibody for the C-terminal portion of rat RFRP-1. As this antibody could recognize a consensus sequence among the C-terminal portions of rat, human, and bovine RFRP-1, we purified endogenous RFRP-1 from bovine hypothalamus on the basis of immunoreactivity to the antibody. The purified bovine endogenous RFRP-1 was found to have 35-amino-acid length that corresponds to 37-amino-acid length in human and rat. We subsequently constructed a sandwich enzyme immunoassay using the monoclonal antibody and a polyclonal antibody for the N-terminal portion of rat RFRP-1, and analyzed the tissue distribution of endogenous RFRP-1 in rats. Significant levels of RFRP-1 were detected only in the central nervous system, and the highest concentration of RFRP-1 was detected in the hypothalamus. RFRP-1-positive nerve cells were detected in the rat hypothalamus by immunohistochemical analyses using the monoclonal antibody. In culture, RFRP-1 lowered cAMP production in Chinese hamster ovary cells expressing OT7T022 and it was abolished by pre-treatment with pertussis toxin, suggesting that OT7T022 couples G(i)/G(o) in the signal transduction pathway.

Time-dependent changes in the carotenoid composition and preferential binding of spirilloxanthin to the reaction center and anhydrorhodovibrin to the LH1 antenna complex in Rhodobium marinum

Carotenoids were isolated from the cells of Rhodobium marinum, and their structures were determined by mass spectrometry and 1H nuclear magnetic resonance spectroscopy; the carotenoids include lycopene, rhodopin, anhydrorhodovibrin, rhodovibrin and spirilloxanthin. Time-dependent changes in the carotenoid composition in the reaction center (RC) and the light-harvesting complex 1 (LH1) were traced by high-performance liquid chromatography analysis of the extracts. The carotenoid composition changed according to the spirilloxanthin biosynthetic pathway. However, spirilloxanthin having the longest conjugated chain was always preferentially bound to the RC, and anhydrorhodovibrin and other precursors to the LH1.

Dual roles of RNA helicase A in CREB-dependent transcription

RNA helicase A (RHA) is a member of an ATPase/DNA and RNA helicase family and is a homologue of Drosophila maleless protein (MLE), which regulates X-linked gene expression. RHA is also a component of holo-RNA polymerase II (Pol II) complexes and recruits Pol II to the CREB binding protein (CBP). The ATPase and/or helicase activity of RHA is required for CREB-dependent transcription. To further understand the role of RHA on gene expression, we have identified a 50-amino-acid transactivation domain that interacts with Pol II and termed it the minimal transactivation domain (MTAD). The protein sequence of this region contains six hydrophobic residues and is unique to RHA homologues and well conserved. A mutant with this region deleted from full-length RHA decreased transcriptional activity in CREB-dependent transcription. In addition, mutational analyses revealed that several tryptophan residues in MTAD are important for the interaction with Pol II and transactivation. These mutants had ATP binding and ATPase activities comparable to those of wild-type RHA. A mutant lacking ATP binding activity was still able to interact with Pol II. In CREB-dependent transcription, the transcriptional activity of each of these mutants was less than that of wild-type RHA. The activity of the double mutant lacking both functions was significantly lower than that of each mutant alone, and the double mutant had a dominant negative effect. These results suggest that RHA could independently regulate CREB-dependent transcription either through recruitment of Pol II or by ATP-dependent mechanisms.

Molecular properties of apelin: tissue distribution and receptor binding

We analyzed the tissue distribution of apelin mRNA in rats by a quantitative reverse transcription-polymerase chain reaction and that of immunoreactive apelin (ir-apelin) by an enzyme immunoassay (EIA) using a monoclonal antibody. The expression levels of apelin mRNA and ir-apelin seemed to be consistent among tissues: they were highly expressed in the lung and mammary gland. By the combination of gel filtration and EIA, we found that the molecular forms of apelin differ among respective tissues: apelin molecules with sizes close to apelin-36 (long forms) were major components in the lung, testis, and uterus, but both long and short (whose sizes were close to [<Glu(65)]apelin-13) forms were detected in the mammary gland. In Scatchard analyses, the radioiodinated apelin-36 analogue bound to the receptor, APJ, with high affinity. In competitive binding assays, apelin-36 and apelin-19 far more efficiently inhibited the binding of the labeled apelin-36 analogue with APJ than [<Glu(65)]apelin-13. In analyses for the dissociation of apelin from APJ, unlabeled apelin-36 replaced more rapidly the labeled apelin-36 analogue bound with APJ than [<Glu(65)]apelin-13. Our results demonstrate that the long and short forms of apelin differently interact with APJ.

Regulation of dharma/bozozok by the Wnt pathway

The zebrafish homeobox gene dharma/bozozok (boz) is required for the formation and/or function of the Nieuwkoop center and the subsequent induction of the Spemann organizer. dharma is expressed soon after the midblastula transition in the dorsal blastomeres and the dorsal yolk syncytial layer (YSL). We found that the expression of dharma was upregulated or ectopically induced by misexpression of a Wnt protein and cytoplasmic components of the Wnt signaling pathway and downregulated by the expression of dominant-negative Tcf3. A 1.4-kbp fragment of the dharma promoter region contains consensus sequences for Tcf/Lef binding sites. This promoter region recapitulated the Wnt-dependent and dorsal dharma expression pattern when it was fused to luciferase or GFP. Deletion and point mutant analyses revealed that the Tcf/Lef binding sites were required to drive this expression pattern. These data established that dharma/boz functions between the dorsal determinants-mediated Wnt signals and the formation of the Nieuwkoop center.

Transient absorption from the 1Bu+ state of all-trans-beta-carotene newly identified in the near-infrared region

We have attempted subpicosecond time-resolved absorption spectroscopy of all-trans-beta-carotene in organic solvents in the 820-1060 nm region and found novel transient absorption features which lived in subpicosecond time scales. A first component that appeared immediately after excitation showed a lifetime of 190 +/- 10 fs in n-hexane in agreement with the 1Bu+ lifetime that had been determined by fluorescence upconversion spectroscopy (195 +/- 10 fs). (Kandori et al. [1994] J. Am. Chem. Soc. 116, 2671-2672.) Therefore, this component is assigned to a transient absorption from the 1Bu+ state.

A Role of RNA Helicase A in cis-Acting Transactivation Response Element-mediated Transcriptional Regulation of Human Immunodeficiency Virus Type 1

RNA helicase A (RHA) has two double-stranded (ds) RNA-binding domains (dsRBD1 and dsRBD2). These domains are conserved with the cis-acting transactivation response element (TAR)-binding protein (TRBP) and dsRNA-activated protein kinase (PKR). TRBP and PKR are involved in the regulation of HIV-1 gene expression through their binding to TAR RNA. This study shows that RHA also plays an important role in TAR-mediated HIV-1 gene expression. Wild-type RHA preferably bound to TAR RNA in vitro and in vivo. Overexpression of wild type RHA strongly enhanced viral mRNA synthesis and virion production as well as HIV-1 long terminal repeat-directed reporter (luciferase) gene expression. Substitution of lysine for glutamate at residue 236 in dsRBD2 (RHA(K236E)) reduced its affinity for TAR RNA and impaired HIV-1 transcriptional activity. These results indicate that TAR RNA is a preferred target of RHA dsRBDs and that RHA enhances HIV-1 transcription in vivo in part through the TAR-binding of RHA.

Seroepidemiology of human group C rotavirus in Japan based on a blocking enzyme-linked immunosorbent assay

A novel blocking enzyme-linked immunosorbent assay (BL-ELISA) was developed for detection of antibodies to human group C rotavirus (CHRV). The specificity of the BL-ELISA was confirmed by using animal sera hyperimmunized to group A and group C rotaviruses and paired sera from five patients with acute CHRV gastroenteritis. Furthermore, there was concordance between the BL-ELISA and a neutralization assay for CHRV in 226 (95%) of 238 samples. By using the BL-ELISA, we determined the seroprevalence of CHRV in 704 serum samples obtained from nine different age groups of inhabitants of Okayama Prefecture, Japan, in 1992, 1994, and 1996. As a result, 211 sera (30%) were found to be positive for CHRV antibodies. The seroprevalence gradually increased with age and reached 52.7% in the oldest individuals. A further analysis of the youngest age group suggested that CHRVs predominantly prevail in persons older than 3 years of age in Japan. When comparing the three sampling years, a larger percentage of antibody-positive sera was detected in 1994 than in either 1992 or 1996 in individuals between 6 and 15 years of age, reflecting the occurrence of a CHRV outbreak among children during the winter of 1992 to 1993 that was previously documented. These results indicate that CHRV infections may occur more frequently in spite of the relatively low detection rate of the virus.

Visualization of myocardial phosphoinositide turnover with 1-[1-(11)C]-butyryl-2-palmitoyl-rac-glycerol in rats with myocardial infarction

Phosphoinositide turnover mediates the signaling of angiotensin II, which plays a pivotal role in ventricular remodeling after myocardial infarction (MI). We tested the hypothesis that phosphoinositide turnover can be visualized by 1-[1 -(11)C]butyryl-2-palmitoyl-rac-glycerol (11C-DAG) in both infarcted and noninfarcted myocardium after MI in rats.

METHODS

Rats received an injection of 11C-DAG 7 d after left coronary artery ligation, and myocardial lipids were extracted from both infarcted and noninfarcted areas of myocardium (n = 3). Metabolites of 11C-DAG were determined by thin-layer chromatography. Quantitative autoradiography of hearts was performed to visualize myocardial phosphoinositide turnover in rats that received an injection of 11C-DAG 1 d (n = 3) and 7 d (n = 5) after MI and 7 d after a sham operation (n = 3). Quantitative autoradiography with 201TlCl was also performed to evaluate myocardial blood flow in rats 7 d after MI (n = 3). Cells occupying the infarcted myocardium were identified by immunohistochemistry.

RESULTS

The radioactivity incorporated into the intermediates of phosphoinositide turnover was predominant in both the infarcted (67.1% +/- 5.2% of the total activity) and the noninfarcted (57.4% +/- 3.2%) myocardium. 11C-DAG radioactivity in the infarcted region normalized to that in the noninfarcted region was 1.09 +/- 0.04 in rats 7 d after MI, which was significantly higher than that in rats 1 d after MI (0.38 +/- 0.03, P < 0.001). 201Tl radioactivity in the infarcted region normalized to that in the noninfarcted region was only 0.19 +/- 0.01 7 d after MI. 11C-DAG radioactivity in the noninfarcted region normalized to that in the right ventricular free wall tended to be increased in rats 1 and 7 d after MI compared with the sham-operated rats; the differences, however, were not statistically significant (1.30 +/- 0.15, 1.20 +/- 0.07, and 1.13 +/- 0.02, respectively). Immunohistochemistry revealed that abundant fibroblasts, myofibroblasts, and macrophages occupied the infarcted myocardium 7 d after MI, but the cellularity was low during the first day after MI.

CONCLUSION

These data suggest that 11C-DAG may be useful for visualizing regions with activated phosphoinositide turnover after MI. Because wound healing and fibrogenic processes are important factors of ventricular remodeling, 11C-DAG and PET may offer new information benefiting patient management after MI.

Regulation of Lef-mediated transcription and p53-dependent pathway by associating beta-catenin with CBP/p300

CBP and its homologue p300 play significant roles in cell differentiation, cell cycle, and anti-oncogenesis. We demonstrated that beta-catenin, recently known as a potent oncogene, and CBP/p300 are associated through its CH3 region, which is a primary target of adenoviral oncoprotein E1A and various nuclear proteins, such as p53, cyclin E, and AP-1, and both are colocalized in the nuclear bodies. CBP/p300 potentiated Lef-mediated transactivation of beta-catenin, and E1A, a potent inhibitor of CBP/p300, repressed its transactivation. Furthermore, overexpression of stable beta-catenin mutant competitively suppressed the p53-dependent pathway. These may be a key mechanism of beta-catenin involved in oncogenic events underlying disruption of tumor suppressor function through CBP/p300.

New neuropeptides containing carboxy-terminal RFamide and their receptor in mammals

Only a few RFamide peptides have been identified in mammals, although they have been abundantly found in invertebrates. Here we report the identification of a human gene that encodes at least three RFamide-related peptides, hRFRP-1-3. Cells transfected with a seven-transmembrane-domain receptor, OT7T022, specifically respond to synthetic hRFRP-1 and hRFRP-3 but not to hRFRP-2. RFRP and OT7T022 mRNAs are expressed in particular regions of the rat hypothalamus, and intracerebroventricular administration of hRFRP-1 increases prolactin secretion in rats. Our results indicate that a variety of RFamide-related peptides may exist and function in mammals.

The regulation of motile activity in fish chromatophores

Chromatophores, including melanophores, xanthophores, erythrophores, leucophores and iridophores, are responsible for the revelation of integumentary coloration in fish. Recently, blue chromatophores, also called cyanophores, were added to the list of chromatophores. Many of them are also known to possess cellular motility, by which fish are able to change their integumentary hues and patterns, thus enabling them to execute remarkable or subtle chromatic adaptation to environmental hues and patterns, and to cope with various ethological encounters. Such physiological color changes are indeed crucial for them to survive, either by protecting themselves from predators or by increasing their chances of feeding. Sometimes, they are also useful in courtship and mutual communications among individuals of the same species, leading to an increased rate of species survival. Such strategies are realized by complex mechanisms existing in the endocrine and/or nervous systems. Current studies further indicate that some paracrine factors such as endothelins (ETs) are involved in these processes. In this review, the elaborate mechanisms regulating chromatophores in these lovely aquatic animals are described.

Identification and functional characterization of a novel subtype of neuromedin U receptor

Neuromedin U is a bioactive peptide isolated originally from the porcine spinal cord. We recently identified neuromedin U as the cognate ligand for the orphan G protein-coupled receptor FM-3. In this study, we isolated cDNA coding for a novel G protein-coupled receptor, TGR-1, which was highly homologous with FM-3. We found that neuromedin U specifically and clearly elevated the extracellular acidification rates, arachidonic acid metabolite release, and intracellular Ca(2+) mobilization in Chinese hamster ovary cells expressing TGR-1. Radiolabeled neuromedin U specifically bound with high affinity to membrane fractions prepared from these cells. These results show that TGR-1, like FM-3, is a specific and functional receptor for neuromedin U. We analyzed TGR-1 mRNA tissue distribution in rats using quantitative reverse transcription-polymerase chain reaction and found it to considerably differ from that of FM-3 mRNA. TGR-1 mRNA was primarily expressed in the uterus, suggesting that TGR-1 mediates the contractile activity of neuromedin U in this tissue. The identification of specific and functional receptor subtypes for neuromedin U will facilitate the study of their physiological roles and the search for their specific agonists and antagonists.