Oral bacterial insights from a comparative study between healthy and comorbid diseased human individuals

The human oral cavity is colonized by a diverse microbial community, which includes both native and transient colonizers. The microbial composition is crucial for maintaining oral homeostasis, but due to overgrowth or imbalances of these microbial communities, dysbiosis can occur. There is a lack of understanding of the research of native and transient colonizers in the oral cavity of the Indian subpopulation Therefore, in our present study, we explored the role and prevalence of transient and native colonizers between healthy and comorbid oral diseased human individuals. Culture-dependent techniques and culture-independent 16S r DNA metagenomic analyses were employed to isolate and study the interactions of native and transient colonizers from human oral samples. Among the 66 human individuals of both healthy and comorbid individuals, the most abundant isolate was found to be Bacillus amyloliquefaciens MCC 4424. In addition, the more prevalent culturable isolate from the healthy samples was Streptococcus salivarius MTCC 13009, whereas in comorbid samples Staphylococcus pasteuri MTCC 13076, Rothia dentocariosa MTCC 13010 and Pseudomonas aeruginosa MTCC 13077 were prevalent to a greater extent. 16S rDNA metagenomic analyses revealed the prevalence and abundance of genera such as Bacteroidetes and Proteobacteria in healthy individuals; consequently, Fusobacteria and Firmicutes were observed mostly in comorbid individuals. The significant differences in bacterial population density were observed in terms of the Shannon index (p = 0.5145) and Simpson index (p = 0.9061) between the healthy and comorbid groups. B. amyloliquefaciens MCC 4424 exhibits antagonistic behavior when grown as a dual-species with native and transient colonizers. This result is very consistent with the findings of antibiofilm studies using confocal laser scanning microscopy, which revealed a significant reduction in biofilm biovolume (73 %) and maximum thickness (80 %) and an increase in the rough coefficient of biofilms (30 %). Our data suggested that B. amyloliquefaciens MCC 4424 can be a native colonizer of Indian sub-populations. It may act as a novel candidate for oral healthcare applications and greatly aids in the regulation of transient species in the oral cavity.

Mechanisms by which Porphyromonas gingivalis evades innate immunity

The oral cavity is home to unique resident microbial communities whose interactions with host immunity are less frequently studied than those of the intestinal microbiome. We examined the stimulatory capacity and the interactions of two oral bacteria, Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum), on Dendritic Cell (DC) activation, comparing them to the effects of the well-studied intestinal microbe Escherichia coli (E. coli). Unlike F. nucleatum and E. coli, P. gingivalis failed to activate DCs, and in fact silenced DC responses induced by F. nucleatum or E. coli. We identified a variant strain of P. gingivalis (W50) that lacked this immunomodulatory activity. Using biochemical approaches and whole genome sequencing to compare the two substrains, we found a point mutation in the hagA gene. This protein is though to be involved in the alteration of the PorSS/gingipain pathway, which regulates protein secretion into the extracellular environment. A proteomic comparison of the secreted products of the two substrains revealed enzymatic differences corresponding to this phenotype. We found that P. gingivalis secretes gingipain(s) that inactivate several key proinflammatory mediators made by DCs and/or T cells, but spare Interleukin-1 (IL-1) and GM-CSF, which can cause capillary leaks that serve as a source of the heme that P. gingivalis requires for its survival, and GM-CSF, which can cause epithelial-cell growth. Taken together, our results suggest that P. gingivalis has evolved potent mechanisms to modulate its virulence factors and dampen the innate immune response by selectively inactivating most proinflammatory cytokines.

Real Time, Spatial, and Temporal Mapping of the Distribution of c-di-GMP during Biofilm Development

Bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) is a dynamic intracellular signaling molecule that plays a central role in the biofilm life cycle. Current methodologies for the quantification of c-di-GMP are typically based on chemical extraction, representing end point measurements. Chemical methodologies also fail to take into consideration the physiological heterogeneity of the biofilm and thus represent an average c-di-GMP concentration across the entire biofilm. To address these problems, a ratiometric, image-based quantification method has been developed based on expression of the green fluorescence protein (GFP) under the control of the c-di-GMP-responsive cdrA promoter (Rybtke, M. T., Borlee, B. R., Murakami, K., Irie, Y., Hentzer, M., Nielsen, T. E., Givskov, M., Parsek, M. R., and Tolker-Nielsen, T. (2012) Appl. Environ. Microbiol. 78, 5060-5069). The methodology uses the cyan fluorescent protein (CFP) as a biomass indicator and the GFP as a c-di-GMP reporter. Thus, the CFP/GFP ratio gives the effective c-di-GMP per biomass. A binary mask was applied to alleviate background fluorescence, and fluorescence was calibrated against known c-di-GMP concentrations. Using flow cells for biofilm formation, c-di-GMP showed a non-uniform distribution across the biofilm, with concentrated hot spots of c-di-GMP. Additionally, c-di-GMP was found to be localized at the outer boundary of mature colonies in contrast to a uniform distribution in early stage, small colonies. These data demonstrate the application of a method for the in situ, real time quantification of c-di-GMP and show that the amount of this biofilm-regulating second messenger was dynamic with time and colony size, reflecting the extent of biofilm heterogeneity in real time.

Flagellin FliC Phosphorylation Affects Type 2 Protease Secretion and Biofilm Dispersal in Pseudomonas aeruginosa PAO1

Protein phosphorylation has a major role in controlling the life-cycle and infection stages of bacteria. Proteome-wide occurrence of S/T/Y phosphorylation has been reported for many prokaryotic systems. Previously, we reported the phosphoproteome of Pseudomonas aeruginosa and Pseudomonas putida. In this study, we show the role of S/T phosphorylation of one motility protein, FliC, in regulating multiple surface-associated phenomena of P. aeruginosa PAO1. This is the first report of occurrence of phosphorylation in the flagellar protein, flagellin FliC in its highly conserved N-terminal NDO domain across several Gram negative bacteria. This phosphorylation is likely a well-regulated phenomenon as it is growth phase dependent in planktonic cells. The absence of phosphorylation in the conserved T27 and S28 residues of FliC, interestingly, did not affect swimming motility, but affected the secretome of type 2 secretion system (T2SS) and biofilm formation of PAO1. FliC phosphomutants had increased levels and activities of type 2 secretome proteins. The secretion efficiency of T2SS machinery is associated with flagellin phosphorylation. FliC phosphomutants also formed reduced biofilms at 24 h under static conditions and had delayed biofilm dispersal under dynamic flow conditions, respectively. The levels of type 2 secretome and biofilm formation under static conditions had an inverse correlation. Hence, increase in type 2 secretome levels was accompanied by reduced biofilm formation in the FliC phosphomutants. As T2SS is involved in nutrient acquisition and biofilm dispersal during survival and spread of P. aeruginosa, we propose that FliC phosphorylation has a role in ecological adaptation of this opportunistic environmental pathogen. Altogether, we found a system of phosphorylation that affects key surface related processes such as proteases secretion by T2SS, biofilm formation and dispersal.

A novel technique for detoxification of phenol from wastewater: Nanoparticle Assisted Nano Filtration (NANF)

BACKGROUND

Phenol is one of the most versatile and important organic compound. It is also a growing concern as water pollutants due to its high persistence and toxicity. Removal of Phenol from wastewaters was investigated using a novel nanoparticle adsorption and nanofiltration technique named as Nanoparticle Assisted Nano Filtration (NANF).

METHODS

The nanoparticle used for NANF study were silver nanoparticles and synthesized to three distinct average particle sizes of 10 nm, 40 nm and 70 nm. The effect of nanoparticle size, their concentrations and their tri and diparticle combinations upon phenol removal were studied.

RESULTS

Total surface areas (TSA) for various particle size and concentrations have been calculated and the highest was 4710 × 10(12 )nm(2 )for 10 nm particles and 180 ppm concentration while the lowest was for 2461 × 10(11) for 70 nm and 60 ppm concentrations. Tri and diparticle studies showed more phenol removal % than that of their individual particles, particularly for using small particles on large membrane pore size and large particles at low concentrations. These results have also been confirmed with COD and toxicity removal studies.

CONCLUSIONS

The combination of nanoparticles adsorption and nanofiltration results in high phenol removal and mineralization, leading to the conclusion that NANF has very high potential for treating toxic chemical wastewaters.

The horizontally-acquired response regulator SsrB drives a Salmonella lifestyle switch by relieving biofilm silencing

A common strategy by which bacterial pathogens reside in humans is by shifting from a virulent lifestyle, (systemic infection), to a dormant carrier state. Two major serovars of Salmonella enterica, Typhi and Typhimurium, have evolved a two-component regulatory system to exist inside Salmonella-containing vacuoles in the macrophage, as well as to persist as asymptomatic biofilms in the gallbladder. Here we present evidence that SsrB, a transcriptional regulator encoded on the SPI-2 pathogenicity-island, determines the switch between these two lifestyles by controlling ancestral and horizontally-acquired genes. In the acidic macrophage vacuole, the kinase SsrA phosphorylates SsrB, and SsrB~P relieves silencing of virulence genes and activates their transcription. In the absence of SsrA, unphosphorylated SsrB directs transcription of factors required for biofilm formation specifically by activating csgD (agfD), the master biofilm regulator by disrupting the silenced, H-NS-bound promoter. Anti-silencing mechanisms thus control the switch between opposing lifestyles.

DOI:http://dx.doi.org/10.7554/eLife.10747.001

Salmonella bacteria can infect a range of hosts, including humans and poultry, and cause sickness and diseases such as typhoid fever. Disease-causing Salmonella evolved from harmless bacteria in part by acquiring new genes from other organisms through a process called horizontal gene transfer. However, some strains of disease-causing Salmonella can also survive inside hosts as communities called biofilms without causing any illness to their hosts, who act as carriers of the disease and are able to pass their infection on to others.

So how do Salmonella bacteria ‘decide’ between these two lifestyles? Previous studies have uncovered a regulatory system that controls the decision in Salmonella, which is made up of two proteins called SsrA and SsrB. To trigger the disease-causing lifestyle, SsrA is activated and adds a phosphate group onto SsrB. This in turn causes SsrB to bind to and switch on disease-associated genes in the bacterium. However, it was less clear how the biofilm lifestyle was triggered.

Desai et al. now reveal that the phosphate-free form of SsrB – which was considered to be the inactive form of this protein – plays an important role in the formation of biofilms. Experiments involving an approach called atomic force microscopy showed that the unmodified SsrB acts to stop a major gene that controls biofilm formation from being switched off by a so-called repressor protein.

Salmonella acquired SsrB through horizontal gene transfer, and these findings show how this protein now acts as a molecular switch between disease-causing and biofilm-based lifestyles. SsrB protein is also involved in the decision to switch between these states, but how it does so remains a question for future work.

DOI:http://dx.doi.org/10.7554/eLife.10747.002

Pseudomonas aeruginosa PAO1 exopolysaccharides are important for mixed species biofilm community development and stress tolerance

Pseudomonas aeruginosa PAO1 produces three polysaccharides, alginate, Psl, and Pel that play distinct roles in attachment and biofilm formation for monospecies biofilms. Considerably less is known about their role in the development of mixed species biofilm communities. This study has investigated the roles of alginate, Psl, and Pel during biofilm formation of P. aeruginosa in a defined and experimentally informative mixed species biofilm community, consisting of P. aeruginosa, Pseudomonas protegens, and Klebsiella pneumoniae. Loss of the Psl polysaccharide had the biggest impact on the integration of P. aeruginosa in the mixed species biofilms, where the percent composition of the psl mutant was significantly lower (0.06%) than its wild-type (WT) parent (2.44%). In contrast, loss of the Pel polysaccharide had no impact on mixed species biofilm development. Loss of alginate or its overproduction resulted in P. aeruginosa representing 8.4 and 18.11%, respectively, of the mixed species biofilm. Dual species biofilms of P. aeruginosa and K. pneumoniae were not affected by loss of alginate, Pel, or Psl, while the mucoid P. aeruginosa strain achieved a greater biomass than its parent strain. When P. aeruginosa was grown with P. protegens, loss of the Pel or alginate polysaccharides resulted in biofilms that were not significantly different from biofilms formed by the WT PAO1. In contrast, overproduction of alginate resulted in biofilms that were comprised of 35-40% of P. aeruginosa, which was significantly higher than the WT (5-20%). Loss of the Psl polysaccharide significantly reduced the percentage composition of P. aeruginosa in dual species biofilms with P. protegens (<1%). Loss of the Psl polysaccharide significantly disrupted the communal stress resistance of the three species biofilms. Thus, the polysaccharide composition of an individual species significantly impacts mixed species biofilm development and the emergent properties of such communities.

Neutrophil recruitment to lymph nodes limits local humoral response to Staphylococcus aureus

Neutrophils form the first line of host defense against bacterial pathogens. They are rapidly mobilized to sites of infection where they help marshal host defenses and remove bacteria by phagocytosis. While splenic neutrophils promote marginal zone B cell antibody production in response to administered T cell independent antigens, whether neutrophils shape humoral immunity in other lymphoid organs is controversial. Here we investigate the neutrophil influx following the local injection of Staphylococcus aureus adjacent to the inguinal lymph node and determine neutrophil impact on the lymph node humoral response. Using intravital microscopy we show that local immunization or infection recruits neutrophils from the blood to lymph nodes in waves. The second wave occurs temporally with neutrophils mobilized from the bone marrow. Within lymph nodes neutrophils infiltrate the medulla and interfollicular areas, but avoid crossing follicle borders. In vivo neutrophils form transient and long-lived interactions with B cells and plasma cells, and their depletion augments production of antigen-specific IgG and IgM in the lymph node. In vitro activated neutrophils establish synapse- and nanotube-like interactions with B cells and reduce B cell IgM production in a TGF- β1 dependent manner. Our data reveal that neutrophils mobilized from the bone marrow in response to a local bacterial challenge dampen the early humoral response in the lymph node.

Highly antibiotic resistant Staphylococcus aureus (S. aureus) are an important human pathogen and major cause of hospital acquired infections. An early host defense mechanism against bacterial infection is neutrophil recruitment, which helps eliminate the bacteria at the site of invasion. However, unless quickly neutralized, pathogens such as S. aureus can gain access to nearby lymph nodes via draining lymphatics. Lymph nodes protect the host by mobilizing additional resources that limit further pathogen dissemination. These include recruitment of neutrophils to the lymph node to directly target pathogens and the initiation of adaptive immune mechanisms, such as the humoral immune response, which transforms B lymphocytes capable of making pathogen specific antibodies into antibody producing plasma cells. Using a mouse model that allows direct visualization of lymphocytes, neutrophils, and fluorescently-labeled S. aureus in lymph nodes, we document the rapid appearance of bacteria in the lymph node following local S. aureus infection. We characterize the dynamic influx of neutrophils that occurs as a consequence and reveal direct B cell-neutrophil interactions within the lymph node parenchyma. We find that while lymph node neutrophils rapidly engage bacteria, they limit the subsequent humoral immune response likely by producing Transforming Growth Factor-β1, a factor known to limit B cell responses. These finding have important implication for our understanding of B cell responses against potent pathogens such as S. aureus and for the design of effective vaccines.

Anastomotic Recurrence of Colon Cancer-is it a Local Recurrence, a Second Primary, or a Metastatic Disease (Local Manifestation of Systemic Disease)?

The aim of this study is to review the literature to find out the exact etiology of anastomotic cancers of colon post resection and differentiate them between a recurrence, second primary, and metastatic disease (local manifestation of systemic disease). Web-based literature search was done, and datas collected. We searched PubMed for papers using the keywords colon cancer recurrence, anastomotic recurrence, and recurrent colon carcinoma. We also searched for systematic review in the same topic. In addition, we used our personal referrence archive. Anastomotic recurrences of colon are postulated to arise due to inadequate margins, tumor implantation by exfoliated cells, altered biological properties of bowel anastomosis, and missed synchronous lesions. Some tumors are unique with repeated recurrence after repeated resection. Duration after primary surgery plays a major role in differentiating recurrent and second primary lesions. Repeated recurrences after repeated resections have to be considered a manifestation of systemic disease or metastatic disease due to the virulence of the disease. A detailed analysis and study of patients with colonic anastomotic lesion are required to differentiate it between a recurrent, a second primary lesion, and a metastatic disease (local manifestation of a systemic disease). The nomenclature is significant to study the survival of these patients, as a second primary lesion will have different survival compared to that of recurrent lesions.

Pathology of experimental infection by Pasteurella multocida serotype A: 1 in buffalo calves

Pasteurella multocida serotype A:3 has been mostly implicated in pneumonic pasteurellosis in ruminants. In contrast, our previous studies have reported that both serotypes A:1 and A:3 were responsible for respiratory diseases in cattle and buffaloes. However, the pathology and pathogenesis of P. multocida serotype A:1 (Pm A:1) infection have not been studied in ruminants. In the present study, 12- to 15-week-old buffalo calves (Bubalus bubalis) infected by Pm A:1 had fibrinous and suppurative bronchopneumonia with focal areas of coagulation necrosis typical of pneumonic pasteurellosis. For the first time, this study reports the lung pathology and pathogenecity of Pm A:1 infection in calves.

Biofilm development and enhanced stress resistance of a model, mixed-species community biofilm

Most studies of biofilm biology have taken a reductionist approach, where single-species biofilms have been extensively investigated. However, biofilms in nature mostly comprise multiple species, where interspecies interactions can shape the development, structure and function of these communities differently from biofilm populations. Hence, a reproducible mixed-species biofilm comprising Pseudomonas aeruginosa, Pseudomonas protegens and Klebsiella pneumoniae was adapted to study how interspecies interactions affect biofilm development, structure and stress responses. Each species was fluorescently tagged to determine its abundance and spatial localization within the biofilm. The mixed-species biofilm exhibited distinct structures that were not observed in comparable single-species biofilms. In addition, development of the mixed-species biofilm was delayed 1-2 days compared with the single-species biofilms. Composition and spatial organization of the mixed-species biofilm also changed along the flow cell channel, where nutrient conditions and growth rate of each species could have a part in community assembly. Intriguingly, the mixed-species biofilm was more resistant to the antimicrobials sodium dodecyl sulfate and tobramycin than the single-species biofilms. Crucially, such community level resilience was found to be a protection offered by the resistant species to the whole community rather than selection for the resistant species. In contrast, community-level resilience was not observed for mixed-species planktonic cultures. These findings suggest that community-level interactions, such as sharing of public goods, are unique to the structured biofilm community, where the members are closely associated with each other.

Expression of angiotensin II and its receptors in cyclosporine-induced gingival overgrowth

BACKGROUND AND OBJECTIVES

The renin-angiotensin system (RAS) is considered as a hormonal circulatory system involved in maintaining blood pressure, electrolyte and fluid homeostasis. RAS components can be synthesized in local tissues and are found to play a role in gingival overgrowth. The drug-induced gingival overgrowth (DIGO) is a fibrotic condition, which is associated with multiple factors, including inflammation and adverse drug effects such as cyclosporine A. This study was directed forward to the identification of the angiotensinogen, angiotensin II (Ang II) and its receptors AT₁ /AT₂ expression in DIGO tissues and cyclosporine-treated human gingival fibroblast cells.

MATERIAL AND METHODS

Gingival samples were obtained from patients with cyclosporine-induced gingival overgrowth, chronic periodontitis and normal healthy subjects. The total RNA was isolated and reverse transcription-polymerase chain reaction was performed for angiotensinogen, Ang II and AT₁ /AT₂ receptor. Ang II protein was estimated from tissue by enzyme immunoassay. The expression of Ang II and its receptors were also examined in gingival fibroblast cells treated with cyclosporine.

RESULTS

Ang II mRNA and protein expression was significantly higher in patients with DIGO than in patients with periodontitis and healthy subjects. The AT₁ mRNA was expressed more than AT₂ in all examined tissues. In gingival fibroblasts, Ang II and AT₁ expressions were increased with cyclosporine incorporation compared to controls.

CONCLUSION

These results suggest that cyclosporine can modulate local expression of RAS components such as angiotensinogen, Ang II and its receptors in gingival tissues and gingival fibroblast cells.

Phenol-soluble modulins in staphylococci: What are they originally for?

Phenol-soluble modulins (PSMs) are amphipathic peptides produced by staphylococci that have multiple functions in pathogenesis. For example, they may function as cytotoxins and pro-inflammatory agents. Additionally, in a recent study we demonstrated that Staphylococcus aureus PSMs structure biofilms and cause dissemination during biofilm infection. Based on those results suggesting a surfactant-like mechanism by which PSMs work, we here propose that all PSM functions in pathogenesis arose from an original role in non-pathogenic surface colonization. This original role may have included overcoming surface tension in environments of strongly varying hydrophobicity and emulsification of hydrophobic molecules for use as food sources.

Primary malignancy of seminal vesicle: A rare entity

We report a rare case of seminal vesicle malignancy (primitive neuro ectodermal tumor) in a 40-year-old male patient. He was treated with enbloc resection of the tumor and ureteric reimplantation. In view of the rarity of this entity, management of these tumors should be individualized.

Effect of cryopreservation on apoptotic-like events and its relationship with cryocapacitation of buffalo (Bubalus bubalis) sperm

This study investigated the apoptosis-like events associated with cryopreservation process and their relationship with cryocapacitation in buffalo (Bubalus bubalis) sperm. A total of 49 semen ejaculates from seven bulls were studied for structural changes in sperm following cryopreservation. Apoptotic changes were detected by assays specific for translocation of phosphatidylserine (PS) to the cell surface, alterations in membrane permeability and mitochondrial membrane potential (MMP), and DNA integrity. A significant (p < 0.01) percentage of cryopreserved sperm showed externalization of PS and early apoptotic changes and lowered MMP when compared with the fresh sperm. Freezing and thawing of sperm increased permeability to YOPRO-1, an impermeant fluorescent dye. However, on TUNEL staining, cryopreserved sperm showed no breach in DNA integrity. The sperm capacitation status was evaluated by chlortetracycline (CTC) fluorescence pattern, in which a significant (p < 0.01) percentage of cryopreserved sperm were found to be capacitated. The capacitated sperm (Pattern B) was positively correlated with the aforementioned apoptotic events. In conclusion, cryopreservation process induced early apoptosis-like changes in buffalo sperm, and a close link exists between cryocapacitation and apoptosis during cryopreservation of sperm.

Limb conservation in extremity soft tissue sarcomas with vascular involvement

BACKGROUND

The major neurovascular involvement and large primary tumors are indication of amputation. The present study is an attempt to explore the feasibility of a limb salvage surgery in extremity sarcoma cases with major vessel involvement. Oncological outcomes and surgery-related morbidities are compared with those reported in literature.

MATERIALS AND METHODS

A retrospective review of all limb salvage surgeries done in our department between 2005 and 2008 was done and four cases of extremity sarcoma of lower limb involving femoral vessels analyzed. Interpretation of data from these cases, along with review of literature, is done.

RESULTS

In all these cases a wide monobloc excision was done adhering to oncological principles. This required resection of superficial femoral artery alone in two cases, resection of superficial femoral artery along with common femoral vein and femoral nerve in another, and of common femoral vein alone in yet another. Reconstruction was done in all these cases with reversed long saphenous vein graft. Histopathology of resected margins was free of tumor in all the four patients. One patient developed local recurrence and one developed distant metastsis. Two were disease free for one year with good functional limb, one has been disease-free for three years and another was disease-free at two years, after which he defaulted further follow-up. One patient developed arterial blowout which required ligation of common femoral artery which resulted in gangrene of the limb. He underwent amputation.

CONCLUSION

Major neurovascular involvement in extremity sarcoma is not considered a contraindication for limb salvage surgery. Review of literature also supports our view. Post-operative wound related complications are more in this group of patients. However, long term functional outcome is good. Literature suggests a good long term local control after vascular resection and reconstruction.

Presynaptic dopamine D(4) receptor localization in the rat nucleus accumbens shell

Dopamine D(4) receptors in the nucleus accumbens shell (AcbSh) are thought to play a key role in mediating the locomotor and sensitizing affects of psychostimulants, as well as the therapeutic efficacy of atypical antipsychotic drugs. We used electron microscopic immunocytochemistry to determine the functional sites for endogenous and exogenous D(4) receptor activation in this region. Of 1,090 D(4) receptor-labeled profiles observed in the AcbSh of rat brain, 65% were axons and axon terminals, while 22% were dendrites and dendritic spines. Within axons and terminals, D(4) receptor immunoreactivity was localized to segments of the plasma membrane and membranes of nearby vesicles. The axon terminals were morphologically heterogenous, varying in size and content of either all small synaptic vesicles (ssv), or ssv and large dense-core vesicles. The labeled terminals occasionally formed asymmetric excitatory-type axospinous synapses, but the majority were without recognizable synaptic specializations. In a separate series of tissue sections that were processed for dual-labeling of the D(4) receptor and the catecholamine synthesizing enzyme, tyrosine hydroxylase (TH), 56% of all observed associations were appositions between differentially labeled axonal profiles, and 17% were terminals that contained immunoreactivity for both antigens. Dendritic spines containing D(4) receptor-labeling also received convergent input from TH-immunoreactive terminals and unlabeled terminals forming asymmetric synapses. These results provide the first ultrastructural evidence for a major presynaptic, and a more minor postsynaptic, involvement of D(4) receptors in dopaminergic modulation of excitatory transmission in the AcbSh.