Microplastics as Contaminants in Water Bodies and Their Threat to the Aquatic Animals: A Mini-Review.

Microplastics (MPs), which are particles with a diameter of less than 5 mm, have been extensively studied due to their serious global pollution. Typically, MPs in water originate from terrestrial input. A number of studies have reported the presence of MPs as a stressor in water environments worldwide, and their potential threat to the aquatic animals, affecting the growth, oxidative stress responses, body composition, histopathology, intestinal flora, and immune and reproduction systems. During the plastic degradation process, a large variety of toxic substances are released. MPs have been proposed to be the carriers of toxic chemicals and harmful microorganisms. A study of the literature on MP pollution and stress on the aquatic animals associated with MPs was carried out.

Effect of dithiocyano-methane on hexose monophosphate pathway in the respiratory metabolism of Escherichia coli.

This paper studied the inhibitory effects of dithiocyano-methane (DM) on the glucose decomposition pathway in the respiratory metabolism of Escherichia coli. We investigated the effects of DM on the activities of key enzymes (ATPase and glucose-6-phosphate dehydrogenase, G6PDH), the levels of key product (nicotinamide adenosine denucleotide hydro-phosphoric acid, NADPH), and gene expression in the hexose monophosphate pathway (HMP). The results showed that the minimum inhibitory concentration (MIC) and the minimum bactericide concentration (MBC) of DM against the tested strains were 5.86 mg/L and 11.72 mg/L, respectively. Bacteria exposed to DM at MIC demonstrated an increase in bacterial ATPase and G6PDH activities, NADPH levels, and gene expression in the HMP pathway compared to bacteria in the control group, which could be interpreted as a behavioral response to stress introduced by DM. However, DM at a lethal concentration of 10 × MIC affected glucose decomposition by inhibiting mainly the HMP pathway in E. coli.

Erratum to "The Role of a Selective P2Y6 Receptor Antagonist, MRS2578, on the Formation of Angiotensin II-Induced Abdominal Aortic Aneurysms".

[This corrects the article DOI: 10.1155/2020/1983940.].

The Role of a Selective P2Y6 Receptor Antagonist, MRS2578, on the Formation of Angiotensin II-Induced Abdominal Aortic Aneurysms.

OBJECTIVE: The P2Y6 receptor has been shown to be involved in many cardiovascular diseases, including hypertension and atherosclerosis. The study is aimed at exploring the role of the P2Y6 receptor in Ang II-induced abdominal aortic aneurysm (AAA) formation in apolipoprotein E-deficient (apoE-/-) mice by using its selective antagonist. METHODS: Male apoE-/- mice were fed with high-fat diet and infused with angiotensin (Ang) II (1000 ng/kg/min) for 4 weeks to induce AAA or saline as controls. Mice were divided into four groups: normal saline (NS, placebo control) group (n = 8), Ang II+vehicle (Ang II) group (n = 14), Ang II-low dose MRS2578 (Ang II+MRS-16 mg) group (n = 14), and Ang II-high dose MRS2578 (Ang II+MRS-32 mg) group (n = 14). Daily intraperitoneal injection with vehicle or MRS2578 was pretreated one week before Ang II infusion. On postoperative day 10, aorta imaging of each group was taken by ultrasonography. After 4 weeks of Ang II infusion, the excised aortas were processed for diameter measurement and quantification of aneurysm severity and tissue characteristics; the blood samples were collected for measurement of the lipid profile and levels of cytokines. Verhoeff's Van Gieson (EVG) staining and immunochemistry staining were performed to evaluate disruption of the extracellular matrix (ECM) and infiltration of macrophages. Expression and activity of matrix metalloproteinases (MMPs) was measured by gelatin zymography. RESULTS: Treatment with MRS2578 made no significant difference in AAA formation, and maximal aortic diameter yet caused higher AAA rupture-induced mortality from 7% (Ang II) to 21.4% (Ang II+MRS-16 mg) or 42.9% (Ang II+MRS-32 mg), respectively (p < 0.05). Consistently, the severity of aneurysm tended to be more deteriorated in MRS2578-treated groups, especially the high-dosage group. The ratios of type III and IV aneurysm were much higher in the MRS2578-coadministered groups (p < 0.05). Furthermore, histological analyses showed that administration of MRS2578 significantly increased infiltration of macrophages, expression of monocyte chemotactic protein 1 (MCP-1) and vascular cell adhesion molecule-1 (VCAM-1), and activities of MMP-2 and MMP-9 followed by aggravating degradation elastin in vivo (p < 0.05). However, the multiple effects of MRS2578 on the development of AAA are independent of changes in systolic blood pressure and lipid profiles. CONCLUSIONS: The present study demonstrated that administration of MRS2578 exacerbated the progression and rupture of experimental AAA through promoting proinflammatory response and MMP expression and activity, which indicated a crucial role of the P2Y6 receptor in AAA development. Clinical Relevance. Purinergic P2Y receptors have attracted much attention since the P2Y12 receptor antagonist had been successfully applied in clinical practice. Elucidating the underlying mechanisms of AAA and exploring potential therapeutic strategies are essential to prevent its progression and reduce the mortality rate.

MicroRNA-186 promotes cell proliferation and inhibits cell apoptosis in cutaneous squamous cell carcinoma by targeting RETREG1.

MicroRNAs (miRs), a class of small non-coding RNAs, have been demonstrated to be involved in the development and progression of human malignancies, including cutaneous squamous cell carcinoma (CSCC). miR-186 serves a suppressive role in certain common types of human cancer; however, its exact function in CSCC has not been reported previously. In the present study, the expression of miR-186 was significantly increased in CSCC tissues compared with adjacent non-tumour tissues. Overexpression of miR-186 significantly promoted CSCC cell proliferation while inhibiting cell apoptosis. Reticulophagy regulator 1 (RETREG1), a gene that is significantly downregulated in CSCC tissues and cell lines, was identified as a novel target of miR-186. In addition, the expression of RETREG1 was inversely correlated with miR-186 expression in CSCC tissues. Furthermore, the expression of RETREG1 was negatively regulated by miR-186 in CSCC cells, and restoration of RETREG1 attenuated the effects of miR-186 on CSCC cells. Taken together, the results of the current study suggest that miR-186 serves an oncogenic role in CSCC and may be used as a potential therapeutic target for the treatment of this disease.

Isoliquiritigenin alleviated the Ang II-induced hypertensive renal injury through suppressing inflammation cytokines and oxidative stress-induced apoptosis via Nrf2 and NF-κB pathways.

PURPOSE: Hypertensive renal injury plays important role in the pathogenesis of end-stage nephropathy and the need for dialysis. Isoliquiritigenin (ISL) is a natural compound with antioxidant and anti-inflammatory activities. In this study, the protective effects of ISL on Angiotensin II (Ang II)- induced apoptosis, inflammation and extracellular matrix production in HK-2 cells were observed and its mechanisms were elucidated. METHODS: Cell survival was determined with MTT assay. Cell cycle and apoptosis was assessed with flow cytometric analysis. The production of cytokines including IL-1ß and TNF-α were evaluated with Elisa. Western blotting assay was used to determine protein levels of apoptosis related signaling, oxidative stress, NF-κB and ECM related molecules. mRNA levels of fibronectin and collagen Ⅳ were detected by RT-qPCR. RESULTS: Ang II significantly inhibited cell survival, induced cell cycle arrest and enhanced cell apoptosis. However, the above effects were markedly alleviated by ISL treatment in a dose-dependent manner. In addition, Ang II significantly induced oxidative stress and NF-κB signaling activation, as well as inflammatory cytokines release. In contrast, these effects were remarkably reversed by ISL via regulation of Nrf2. Notably, Ang II also triggered generation of extracellular matrix, including fibronectin and collagen Ⅳ, which was abolished upon ISL treatment. CONCLUSIONS: Taken together, ISL alleviated the Ang II-induced hypertensive renal injury through suppressing inflammation cytokines, excessive deposition of extracellular matrix and oxidative stress-induced apoptosis via Nrf2 and NF-κB pathways. Our findings provided the evidences for exploring the possible mechanism of hypertensive renal injury pathogenesis and identifying novel therapeutic targets.

[Explore mechanism of Compound Uncaria Hypotensive Tablet for hypertension based on network pharmacology].

This paper aimed to predict the active ingredients and action targets of Compound Uncaria Hypotensive Tablet for hypertension based on network pharmacology, and discuss its possible "multi-components, multi-targets, and multi-pathways" mechanism for treatment of hypertension. The integrative pharmacological platform of traditional Chinese medicine (TCM-IP) was used to construct the component target-disease target network of Compound Uncaria Hypotensive Tablet, and the internet analysis method was used to screen the key nodes, on which the pathway enrichment analysis was carried out to explore its possible biological process in the treatment of hypertension. Target network analysis showed that, 35 predicted active ingredients of Compound Uncaria Hypotensive Tablet had a strong interaction with the prostaglandin endogenous peroxidase synthase (PTGS1, PTGS2), ATP synthetase (ATP1A1, ATP5A1, ATP5C1, ATP5B) and other 29 major proteins. Network enriched analysis showed that Compound Uncaria Hypotensive Tablet participated in the regulation of hypertension in different processes of pathology, through 15 pathways such as regulating blood pressure, G protein coupled receptor activation, adrenergic myocardial cell signal transduction and platelet activation. This study revealed the potential active compounds and possible mechanism of Compound Uncaria Hypotensive Tablet for treatment of hypertension, providing theoretical references for further systematic laboratory experiments on effective compounds and action mechanism of Compound Uncaria Hypotensive Tablet.

Potential Medication Treatment According to Pathological Mechanisms in Abdominal Aortic Aneurysm.

Abdominal aortic aneurysm (AAA) is a vascular disease with high mortality. Because of the lack of effective medications to stop or reverse the progression of AAA, surgical operation has become the most predominant recommendation of treatment for patients. There are many potential mechanisms, including inflammation, smooth muscle cell apoptosis, extracellular matrix degradation, oxidative stress, and so on, involving in AAA pathogenesis. According to those mechanisms, some potential therapeutic drugs have been proposed and tested in animal models and even in clinical trials. This review focuses on recent advances in both pathogenic mechanisms and potential pharmacologic therapies of AAA.

miR-185/P2Y6 Axis Inhibits Angiotensin II-Induced Human Aortic Vascular Smooth Muscle Cell Proliferation.

The abnormal proliferation and apoptosis of human aortic vascular smooth muscle cells (HAVSMCs) play an important role in the pathogenesis of hypertension. Recent study revealed that angiotensin II (Ang II) could elicit HAVSMC dysfunction, to induce or aggravate hypertension. Purinergic receptor P2Y6, an inflammation-inducible G protein-coupled receptor, promoted Ang II-induced hypertension. In the present study, we revealed that Ang II induced HAVSMC proliferation and upregulated P2Y6 protein levels. After knockdown of P2Y6, the promotive effect of Ang II on HAVSMC proliferation was restored. microRNAs (miRNAs) involve in most biological processes. In this study, we scanned out seven candidate miRNAs, which were predicted to contain binding site of P2Y6's 3'-UTR by online tools. Among them, miR-185 was significantly downregulated by Ang II treatment. miR-185 reduced P2Y6 protein levels by direct binding to the 3'UTR of P2Y6. miR-185 overexpression suppressed HAVSMC proliferation; P2Y6 overexpression or Ang II treatment promoted HAVSMC proliferation, and restored the suppressive effect of miR-185 on HAVSMC proliferation. Besides, miR-185/P2Y6 axis also affected pERK1/2 protein levels. Taken together, the present study indicated that miR-185/P2Y6 axis might inhibit Ang II-induced HAVSMC proliferation through miR-185 negatively regulating P2Y6 expression and the downstream ERK pathway; rescuing miR-185 expression to inhibit P2Y6 may represent a therapeutic strategy against HAVSMC dysfunction and hypertension.

Acupuncture Treatment of Lateral Elbow Pain: A Nonrandomized Pilot Study.

In planning for a large-scale multicenter trial to evaluate the effect of acupuncture for the treatment of lateral elbow pain, a pilot study was conducted. This was a prospective, investigator- and patient-blinded, nonrandomized, placebo controlled trial. Subjects were evaluated at baseline, before fourth, seventh, and ninth treatment, and at a two-week posttreatment follow-up. The treatment group received unilateral acupuncture at LI 10 and LI 11 at the affected side with manual needle manipulation; the control group received sham-laser acupuncture at the same acupoints. Measures included (i) disabilities of the arm, shoulder, and hand (DASH) questionnaire, (ii) pain-free grip strength (PFGS), and (iii) a visual analogue scale (VAS) for pain. Significant differences in DASH score, PFGS, and VAS between treatment and control group were found at the ninth treatment (n = 20 for each group, P < 0.05). Only DASH showed significant differences compared to the control for all the measurement time points after treatment commenced and appears to be a sensitive and appropriate primary outcome measure for the future multisite trial. Results from this pilot study provided relevant information about treatment efficacy, credibility of control treatment, and sensitivity of different outcome measures for the planning of the future trial.

[Chinese Medicine in Overall Modern Scientific Technologies].

Chinese medicine (CM) develops with the survival, reproduction, growth, and progressing of the Chinese nation. Scientific technologies not only promote continual progressing of human societies, but also provide new ideas and methods for the development of CM. In recent years, great changes have taken place in CM complying with developing modern scientific technologies, mainly manifested in the depth of CM theories at molecular levels, the combination of syndrome differentiation and disease identification, continuous innovation and development of clinical diagnosis and treatment techniques, diversified dosages of Chinese materia medica, the academic tendency of education patterns, occupational refinement, diversified medical practice modes, and so on.

Zuogui Jiangtang Jieyu Formulation Prevents Hyperglycaemia and Depressive-Like Behaviour in Rats by Reducing the Glucocorticoid Level in Plasma and Hippocampus.

Aim. To determine whether Zuogui Jiangtang Jieyu prescription (ZGJTJY) has hypoglycemic and antidepressant effects which are mediated by corticosterone through adjustment of 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) and glucocorticoid (GR) levels. Materials and Methods. The diabetes-related depression rats were randomly divided into four groups: the model group, metformin (1.8 mg/kg) combined with fluoxetine (10.8 mg/kg) group, and ZGJTJY high and low dose groups. Four weeks after modeling, blood glucose, behavior, and cognitive function of depression were detected. The expressions of 11ß-HSD1 and GR in hippocampus were measured by western blotting and immunohistochemical experiments. Results. We found that (1) the treatment with ZGJTJY (10.26 g/kg) increases the motor activities and improves cognition ability. (2) ZGJTJY (10.26 g/kg) significantly relieves the disorder in blood and the relative indexes. (3) ZGJTJY (10.26 g/kg) can reduce hippocampal corticosterone expression levels and further improve hippocampus pathological changes. (4) ZGJTJY increased the expression of GR accompanied with decreasing 11ß-HSD1 in hippocampus. Conclusions. ZGJTJY inhibits the expression of 11ß-HSD1 and increases GR in hippocampus and subsequently modulates blood glucose levels, and therefore it is potential property that ZGJTJY could be of benefit for the treatment of behavior and cognitive function of diabetes-related depression.

Acupuncture and moxibustion for lateral elbow pain: a systematic review of randomized controlled trials.

BACKGROUND: Acupuncture and moxibustion have widely been used to treat lateral elbow pain (LEP). A comprehensive systematic review of randomized controlled trials (RCTs) including both English and Chinese databases was conducted to assess the efficacy of acupuncture and moxibustion in the treatment of LEP. METHODS: Revised STRICTA (2010) criteria were used to appraise the acupuncture procedures, the Cochrane risk of bias tool was used to assess the methodological quality of the studies. A total of 19 RCTs that compared acupuncture and/or moxibustion with sham acupuncture, another form of acupuncture, or conventional treatment were included. RESULTS: All studies had at least one domain rated as high risk or uncertain risk of bias in the Cochrane risk of bias tool. Results from three RCTs of moderate quality showed that acupuncture was more effective than sham acupuncture. Results from 10 RCTs of mostly low quality showed that acupuncture or moxibustion was superior or equal to conventional treatment, such as local anesthetic injection, local steroid injection, non-steroidal anti- inflammatory drugs, or ultrasound. There were six low quality RCTs that compared acupuncture and moxibustion combined with manual acupuncture alone, and all showed that acupuncture and moxibustion combined was superior to manual acupuncture alone. CONCLUSION: Moderate quality studies suggest that acupuncture is more effective than sham acupuncture. Interpretations of findings regarding acupuncture vs. conventional treatment, and acupuncture and moxibustion combined vs. manual acupuncture alone are limited by the methodological qualities of these studies. Future studies with improved methodological design are warranted to confirm the efficacy of acupuncture and moxibustion for LEP.

Cryopreservation of precision-cut tissue slices.

1.Cryopreservation of precision-cut tissue slices (PCTS) would have many advantages for drug development and would encourage more extensive use of the PCTS preparation. 2.Three methods have been studied to date: slow freezing, fast freezing, and vitrification. 3.Slow freezing can be very effective for some PCTS but is devastating to rat liver PCTS. Fast freezing can be successful for rat liver PCTS but is devastating to renal PCTS and has given inconsistent results even for rat liver PCTS. Vitrification has been effective for some slice systems but less effective for rat liver PCTS. Rat liver PCTS appear to be particularly difficult to cryopreserve well. 4.The general cryobiological principles of slow freezing, rapid freezing, and vitrification are reviewed. The empirical literature on the cryopreservation of PCTS has not taken sufficient account of these principles, and may, for example, include the effects of easily preventable osmotic injury. 5.More attention is needed to the effects of cryopreservation on specific cell types within PCTS and to the general integrity and viability of cryopreserved PCTS. Drug metabolism as a sole endpoint of study can be highly misleading. 6.Better application of cryobiological principles may enable improved results in the future.

[Editorial explanation on the state standard The Name and Location of Acupoints (2006, edition)].

To tie in with extension and application of The Name and Location of Acupoints (GB 12346-2006), the present paper introduces the difference between The Name and Location of Acupoints (GB 12346-2006) and Location of Points (GB 12346-90), and expounds the changes of standard name, body position and term of direction when locating the acupoint and stylistic rules, and introduces the revision of concrete contents which include setting of primary standard acupoints, regulation of bone-length measurement, regulation of the nomenclature of some meridians and meridian acupoints, the location of some meridian acupoints and regulation of some acupoints, some main problems which needed to be further studied are also explores.

Ortho-substituted PCBs kill cells by altering membrane structure.

Our previous studies have demonstrated that ortho-substituted PCBs cause a rapid cell death in both thymocytes and cerebellar granule cell neurons, whereas coplanar congeners are without effect at comparable concentrations and exposure times. We have demonstrated that multiple membrane components are altered by these exposures, including the plasma membrane, mitochondria, and endoplasmic reticulum. The present experiments were designed to test the hypothesis that because of their stereochemistry, ortho-substituted congeners cause a greater disruption of membrane integrity than do coplanar congeners, and that this membrane disruption results in altered cellular function and to cell death. To test this hypothesis we have measured fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) in thymocytes, cerebellar granule cells, and lipid bilayer vesicles upon exposure to an ortho-substituted PCB congener (PCB 52) and a coplanar congener (PCB 77), and compared results obtained in these studies to those from flow cytometric studies of plasma membrane permeability to large molecules and elevations of intracellular calcium in living cells. The fluorescence polarization of the DPH probe, which inserts into the lipid bilayer, reflects changes in membrane fluidity. In all three preparations we found that whereas fluorescence polarization was unchanged upon exposure to PCB 77, it was reduced significantly by PCB 52, reflecting an increase in membrane fluidity. These observations are consistent with the hypothesis that ortho-substituted PCBs disrupt membrane structure, which alters the function of membrane proteins. In the two cell types we have studied, the disruption is sufficient to cause death of the cell within a brief time.

Ortho-substituted but not coplanar PCBs rapidly kill cerebellar granule cells.

Several PCB congeners were assessed for their cytotoxicity on cerebellar granule cells in an attempt to compare their structure-activity relationship as potential neurotoxicants and to assess the mechanisms associated with their toxicity. Flow cytometry was used to monitor the changes of a number of biochemical endpoints: membrane integrity, intracellular free calcium concentration ([Ca(2+)](i)), reactive oxygen species (ROS) production, mitochondrial membrane potential (Delta psi(m)), and cell size. The non-coplanar, ortho-substituted congeners, PCB 8 (2,4'-dichlorobiphenyl), PCB 28 (2,4,4'-trichlorobiphenyl), PCB 47 (2,4,2',4'-tetrachlorobiphenyl), and PCB 52 (2,5,2',5'-tetrachlorobiphenyl) (10 microM) killed neurons to different degrees within 30 min. Loss of viability was accompanied by increased [Ca(2+)](i) and decreased Delta psi(m). No significant changes of ROS level were observed during exposure. The coplanar congeners, PCB 77 (3,4,3',4'-tetrachlorobiphenyl), PCB 80 (3,5,3',5'-tetrachlorobiphenyl), and PCB 81 (3,4,5,4'-tetrachlorobiphenyl) (10 microM), had no effects on membrane integrity, [Ca(2+)](i) or Delta psi(m) in this time period of exposure. In Ca(2+)-free Tyrode's medium, there was no [Ca(2+)](i) increase after exposure to the ortho-substituted congeners, but also no reduction in loss of membrane integrity, suggesting Ca(2+) influx was not the cause of viability loss. The mitochondrial uncoupler, carbonyl cyanide m-chlorophenyl hydrazone (CCCP) (1-2 microM), caused a large decrease of Delta psi(m), but only a slight loss of viability, which suggested that Delta psi(m) is not the primary cause of PCB 52-induced cell death. These studies show that ortho-substituted PCBs are toxic to cerebellar granule cells; however, their toxic action is not secondary to elevation of intracellular calcium, a change in mitochondrial membrane potential, or free radical generation.

Inducible and reversible NR1 knockout reveals crucial role of the NMDA receptor in preserving remote memories in the brain.

Long-term storage of information is a hallmark feature of the brain, yet routine turnover of synaptic receptors appears to be intrinsically paradoxical to this capability. To investigate how the brain preserves its delicate synaptic efficacies, we generated inducible and reversible knockout mice in which the NMDA receptor can be temporarily switched off in the forebrain specifically during the storage stage. Retention of 9-month contextual and cued fear memories is severely disrupted by prolonged, but not transient, loss of the NMDA receptor that occurs 6 months after initial training and at least 2 months prior to memory retrieval. Normal learning and memory function in subsequent tasks following the 9-month retention tests suggest that the observed retention deficits did not result from recall or performance impairment. Thus, our study reveals a hitherto unrecognized role of the NMDA receptor in dynamically maintaining the long-term synaptic stability of memory storage circuits in the brain.

Ortho-substituted PCBs kill thymocytes.

The effects of exposure of acutely dissociated rat thymocytes to various polychlorinated biphenyl (PCB) congeners were examined using flow cytometry. Non-planar, ortho-substituted congeners caused a rapid cell death at low micromolar concentrations, while coplanar, dioxin-like congeners at the same concentration were without significant effect. The most potent of the congeners studied was PCB 52 (2,2',5,5'-tetrachlorobiphenyl), which had an IC50 of 3.96 microM at 20 min. Prior to loss of viability there was a decrease in mitochondrial membrane potential Delta Psi m, an accumulation of intracellular calcium, and a progressive leakiness of the plasma membrane. Application of PCB 52 in calcium-free medium reduced the calcium accumulation, but did not reduce cell death. Agents that depolarized mitochondria also did not induce the same degree of cell death caused by PCB 52. Cyclosporin A, which prevents opening of the mitochondria permeability transition channel, protected against cell death but did not protect against mitochondrial depolarization or calcium accumulation. Rapamycin and FK 506 at high concentration provided partial protection against cell death. These observations indicate that the ortho-substituted PCB 52 disrupts plasma, mitochondrial and endoplasmic reticulum membranes. We hypothesize that PCB 52 incorporates into lipid bilayers and with its bulky, three-dimensional ortho-substituted congener structure disrupts membrane function to a greater degree than coplanar congeners.

The mechanism of presynaptic long-term depression mediated by group I metabotropic glutamate receptors.

1. Metabotropic glutamate receptors (mGluRs) are known to play a role in synaptic plasticity. In a study of rat hippocampal brain slices, we find that a brief perfusion of a group I mGluR agonist, (S)-3,5-dihydroxyphenylglycine (DHPG), induced a robust long-term depression (DHPG-LTD) in area CA1. 2. The action was accompanied by an enhancement of the paired-pulse facilitation (PPF) ratio. 3. At the same time DHPG enhanced ionophoretic responses to alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA), kainic acid (KA), and N-methyl-D-aspartate (NMDA) in CA1 pyramidal neurons. This was only partially reversed by washing. 4. These observations indicate that DHPG exerts two opposing actions, suppression of the synaptic transmission and facilitation of postsynaptic responses. However, the presynaptic action dominates, since the net effect of monosynaptic activation is a reduction of response. 5. Perfusion of DHPG reduced three calcium-dependent responses in CA3 pyramidal neurons, which are presynaptic to CA1 neurons. These are calcium spike width and amplitude, after-hyperpolarization (AHP), and spike frequency adaptation (SFA). 6. These results suggest that the DHPG-LTD results from modulation of the presynaptic calcium currents by group I mGluRs.