Radiation Exposure Reduction by Digital Variance Angiography in Lower Limb Angiography: A Randomized Controlled Trial.

BACKGROUND: digital variance angiography (DVA) provides higher image quality than digital subtraction angiography (DSA). This study investigates whether the quality reserve of DVA allows for radiation dose reduction during lower limb angiography (LLA), and compares the performance of two DVA algorithms. METHODS: this prospective block-randomized controlled study enrolled 114 peripheral arterial disease patients undergoing LLA into normal dose (ND, 1.2 µGy/frame, n = 57) or low-dose (LD, 0.36 µGy/frame, n = 57) groups. DSA images were generated in both groups, DVA1 and DVA2 images were generated in the LD group. Total and DSA-related radiation dose area product (DAP) were analyzed. Image quality was assessed on a 5-grade Likert scale by six readers. RESULTS: the total and DSA-related DAP were reduced by 38% and 61% in the LD group. The overall visual evaluation scores (median (IQR)) of LD-DSA (3.50 (1.17)) were significantly lower than the ND-DSA scores (3.83 (1.00), p < 0.001). There was no difference between ND-DSA and LD-DVA1 (3.83 (1.17)), but the LD-DVA2 scores were significantly higher (4.00 (0.83), p < 0.01). The difference between LD-DVA2 and LD-DVA1 was also significant (p < 0.001). CONCLUSIONS: DVA significantly reduced the total and DSA-related radiation dose in LLA, without affecting the image quality. LD-DVA2 images outperformed LD-DVA1, therefore DVA2 might be especially beneficial in lower limb interventions.

Possible use of Digital Variance Angiography in Liver Transarterial Chemoembolization: A Retrospective Observational Study.

PURPOSE: Digital variance angiography (DVA), a recently developed image processing technology, provided higher contrast-to-noise ratio (CNR) and better image quality (IQ) during lower limb interventions than digital subtraction angiography (DSA). Our aim was to investigate whether this quality improvement can be observed also during liver transarterial chemoembolization (TACE). MATERIALS AND METHODS: We retrospectively compared the CNR and IQ parameters of DSA and DVA images from 25 patients (65% male, mean ± SD age: 67.5 ± 11.2 years) underwent TACE intervention at our institute. CNR was calculated on 50 images. IQ of every image set was evaluated by 5 experts using 4-grade Likert scales. Both single image evaluation and paired image comparison were performed in a blinded and randomized manner. The diagnostic value was evaluated based on the possibility to identify lesions and feeding arteries. RESULTS: DVA provided significantly higher CNR (mean CNRDVA/CNRDSA was 1.33). DVA images received significantly higher individual Likert score (mean ± SEM 3.34 ± 0,08 vs. 2.89 ± 0.11, Wilcoxon signed-rank p < 0.001) and proved to be superior also in paired comparisons (median comparison score 1.60 [IQR:2.40], one sample Wilcoxon p < 0.001 compared to equal quality level). DSA could not detect lesion and feeding artery in 28 and 36% of cases, and allowed clear detection only in 22% and 16%, respectively. In contrast, DVA failed only in 8 and 18% and clearly revealed lesions and feeding arteries in 32 and 26%, respectively. CONCLUSION: In our study, DVA provided higher quality images and better diagnostic insight than DSA; therefore, DVA could represent a useful tool in liver TACE interventions. LEVEL OF EVIDENCE: III Non-consecutive study.

Initial Experience Using Digital Variance Angiography in Context of Prostatic Artery Embolization in Comparison with Digital Subtraction Angiography.

RATIONALE AND OBJECTIVES: In previous clinical studies digital variance angiography (DVA) provided higher contrast-to-noise ratio (CNR) and better image quality in lower extremity angiography than digital subtraction angiography (DSA). Our aim was to investigate whether DVA has similar quality reserve in prostatic artery embolization (PAE). The secondary aim was to explore the potential advantages of the color-coded DVA (ccDVA) technology in PAE. MATERIAL AND METHODS: This retrospective study evaluated 108 angiographic acquisitions from 30 patients (mean ± SD age 68.0 ± 8.9, range 41-87) undergoing PAE between May and October 2020. DSA and DVA images were generated from the same unsubtracted acquisition, and their CNR was calculated. Visual evaluation of DVA and DSA image quality was performed by four experienced interventional radiologists in a randomized, blinded manner. The diagnostic value of DSA and ccDVA images was also evaluated using clinically relevant criteria (visibility of small [< 2.5 mm] and large arteries [> 2.5 mm], feeding arteries and tissue blush) in a paired comparison. Data were analysed by the Wilcoxon signed rank test or the binomial test, the interrater agreement was determined by the Kendall W or Fleiss Kappa analysis. RESULTS: DVA provided 4.11 times higher median CNR than DSA (IQR: 1.72). The visual score of DVA images (4.40 ± 0.05) was significantly higher than that of DSA (3.39 ± 0.07, p < 0.001). The Kendall W analysis showed moderate but significant agreement (WDVA = 0.38, WDSA = 0.53). The preference of ccDVA images was significantly higher in all criteria (63-89%) with an interrater agreement of 58-79%. The Fleiss Kappa range was 0.02-0.18, significant in all criteria except large vessels. CONCLUSION: Our data show that DVA provides higher CNR and better image quality in PAE. This quality reserve might be used for dose management (reduction of radiation dose and contrast agent volume), and ccDVA technology has also a high potential to assist PAE interventions in the future.

Digital Variance Angiography in Selective Lower Limb Interventions.

PURPOSE: To evaluate the potential benefits of digital variance angiography (DVA) in selective lower limb angiography and to compare the performance of 2 DVA algorithms (conventional DVA1 and the recently developed DVA2) to that of digital subtraction angiography (DSA). MATERIALS AND METHODS: From November 2019 to May 2020, 112 iodinated contrast media (ICM) and 40 carbon dioxide (CO2) angiograms were collected from 15 and 13 peripheral artery disease patients, respectively. The DVA files were retrospectively generated from the same unsubtracted source file as DSA. The objectively calculated contrast-to-noise ratio (CNR) and the subjective visual image quality of DSA, DVA1, and DVA2 images were statistically compared using the Wilcoxon signed-rank test. The images were evaluated by 6 radiologists (R.P.T., S.V., A.M.K., S.S.A., O.E., and J.S.) from 2 centers using a 5-grade Likert scale. RESULTS: Both DVA algorithms produced similar increase (at least 2-fold) in CNR values (P < .001) and significantly higher image quality scores than DSA, independent of the contrast agent used. The overall scores with ICM were 3.61 ± 0.05 for DSA, 4.30 ± 0.04 for DVA1, and 4.33 ± 0.04 for DVA2 (each P < .001 vs DSA). The scores for CO2 were 3.10 ± 0.14 for DSA, 3.63 ± 0.13 for DVA1 (P < .001 vs DSA), and 3.38 ± 0.13 for DVA2 (P < .05 vs DSA). CONCLUSIONS: DVA provides higher CNR and significantly better image quality in selective lower limb interventions irrespective of the contrast agent used. Between DVA algorithms, DVA1 is preferred because of its identical or better image quality than DVA2. DVA can potentially help the interventional decision process and its quality reserve might allow dose management (radiation/ICM reduction) in the future.

Digital variance angiography allows about 70% decrease of DSA-related radiation exposure in lower limb X-ray angiography.

Our aim was to investigate whether the previously observed higher contrast-to-noise ratio (CNR) and better image quality of Digital Variance Angiography (DVA) - compared to Digital Subtraction Angiography (DSA) - can be used to reduce radiation exposure in lower limb X-ray angiography. This prospective study enrolled 30 peripheral artery disease patients (mean ± SD age 70 ± 8 years) undergoing diagnostic angiography. In all patients, both normal (1.2 µGy/frame; 100%) and low-dose (0.36 µGy/frame; 30%) protocols were used for the acquisition of images in three anatomical regions (abdominal, femoral, crural). The CNR of DSA and DVA images were calculated, and the visual quality was evaluated by seven specialists using a 5-grade Likert scale. For investigating non-inferiority, the difference of low-dose DVA and normal dose DSA scores (DVA30-DSA100) was analyzed. DVA produced two- to three-fold CNR and significantly higher visual score than DSA. DVA30 proved to be superior to DSA100 in the crural region (difference 0.25 ± 0.07, p < 0.001), and there was no significant difference in the femoral (- 0.08 ± 0.06, p = 0.435) and abdominal (- 0.10 ± 0.09, p = 0.350) regions. Our data show that DVA allows about 70% reduction of DSA-related radiation exposure in lower limb X-ray angiography, providing a potential new radiation protection tool for the patients and the medical staff.

Initial evidence of a 50% reduction of contrast media using digital variance angiography in endovascular carotid interventions.

PURPOSE: In previous clinical studies Digital Variance Angiography (DVA) provided higher signal-to-noise ratio (SNR) and better image quality than Digital Subtraction Angiography (DSA). Our aim was to investigate whether this quality reserve of DVA provides an opportunity for the reduction of iodinated contrast media (ICM) in carotid X-ray angiography (CXA). METHOD: Our prospective study enrolled 26 patients (67.0 ±â€¯8.1 years) undergoing carotid percutaneous transluminal angioplasty. The SNR of DSA and DVA image pairs obtained by a standard (100 %, 6 mL ICM) or a low-dose (50 %, 3 mL ICM) protocol were compared. Visual evaluation of all images was performed by five specialists using a 5-grade rating scale. The quality of DSA100 and DVA50 videos was also compared. RESULTS: DVA provided more than two-fold SNR, the median SNRDVA/SNRDSA ratio was 2.06 (100 %) and 2.25 (50 %). In the visual evaluation, the DVA100 score (3.73 ±â€¯0.06) was significantly higher than the DSA100 score (3.52 ±â€¯0.07, Wilcoxon p < 0.001), and the DVA50 score (3.64 ±â€¯0.13) was also significantly higher than the DSA50 score (3.01 ±â€¯0.17, Wilcoxon p < 0.001). While the low-dose protocol significantly decreased the DSA score (Mann-Whitney p < 0.01, DSA100 vs DSA50), it had no effect on the DVA score (DVA100 vs DVA50). There was no statistical difference between the DSA100 and DVA50 scores. Evaluators preferred the diagnostic value of DVA50 to DSA100 videos in 61% of comparisons, the interrater agreement was 69 % (Fleiss' kappa 0.35, p < 0.001). CONCLUSIONS: Our data show that DVA allows a substantial (50 %) ICM reduction in CXA without affecting the quality and diagnostic value of angiograms.

Initial Operating Room Experience with Digital Variance Angiography in Carbon Dioxide-Assisted Lower Limb Interventions: A Pilot Study.

PURPOSE: In retrospective clinical studies digital variance angiography (DVA) provided higher contrast-to-noise ratio and better image quality than digital subtraction angiography (DSA). Our aim was to verify the clinical usefulness and benefits of DVA in carbon dioxide (CO2)-assisted lower limb interventions. MATERIALS AND METHODS: A workstation running the DVA software was integrated into a Siemens Artis Zee with Pure angiography system, and this new image processing technology was used in four patients (3 male, 1 female, age: 76.2 ± 4.2 years) with peripheral artery disease (PAD, Rutherford 2-3) and impaired renal function (average eGFR 25.5 ± 11.2 ml/min/1.73 m2). The DSA and DVA images of 46 CO2-assisted runs were visually evaluated by five experts in single-image evaluation using a 5-grade Likert scale and in paired comparisons. RESULTS: DVA images received significantly higher score (3.84 ± 0.10) than DSA images (3.31 ± 0.10, p < 0.001). Raters preferred DVA images in terms of diagnostic value and usefulness for therapeutic decisions in 85.2% and 83.9% of all comparisons, respectively. These benefits were achieved at lower frame rates (1-3 FPS) than usually recommended for CO2 angiography (4-6 FPS). No adverse events were recorded during or after the procedures. CONCLUSIONS: Our initial experience shows that DVA might facilitate the correct diagnostic and therapeutic decisions, and potentially help to reduce radiation exposure in lower limb CO2 angiography. Although the dose management capabilities of DVA have to be validated in further clinical studies, this technology might be a useful new tool in the operating room and contributes to the safety and efficacy of CO2-enhanced endovascular interventions. LEVEL OF EVIDENCE: Level IV.

Digital Variance Angiography as a Paradigm Shift in Carbon Dioxide Angiography.

OBJECTIVES: Our aim was to investigate the feasibility of digital variance angiography (DVA) in lower extremity CO2 angiography and to compare the quantitative and qualitative performance of the new image processing technique with that of the current reference standard digital subtraction angiography (DSA). MATERIALS AND METHODS: This prospective study enrolled 24 patients (mean age ± SD, 65.5 ± 9.2 years; 14 males, 65.1 ± 7.5 years; 10 females, 66.1 ± 11.6 years) undergoing lower-limb CO2 angiography between December 2017 and April 2018 at 2 clinical centers: The Heart and Vascular Center (HVC) of Semmelweis University, Budapest (7 patients), and the Bács-Kiskun County Hospital (BKCH) in Kecskemét (17 patients). The interventional protocol was similar at both sites, but the image acquisition instruments and protocols were different, which allowed us to investigate DVA in different settings. For comparison, the signal-to-noise ratio (SNR) of DSA and DVA images were calculated. The visual quality of DSA and DVA images were compared by independent clinical specialists using an online questionnaire. Interrater agreement was characterized by percent agreement and Fleiss kappa. The specialists also evaluated in a random and blinded manner the individual DSA and DVA images on a 5-grade scale ranging from poor (1) to outstanding (5) image quality, and the mean ± standard error of mean (SEM) was calculated. RESULTS: A total of 4912 regions of interest were carefully selected in 110 image pairs to determine the SNRs. The ratio of SNRDVA/SNRDSA was calculated. At HVC, it ranged between 2.58 and 4.16 in the anatomical regions (abdominal, iliac, femoral, popliteal, crural, talar), and the overall median value was 3.53, whereas at BKCH the range was 2.71 to 4.92 and the overall median value was 4.52. During the visual evaluation, 120 DSA and DVA image pairs were compared. At HVC in 78%, although at BKCH in 90% of comparisons, it was judged that DVA provided higher quality images. The interrater agreement was 88% (P < 0.001) and 90% (P < 0.01), respectively. DVA images received consistently higher individual rating than DSA images, regardless of the research site and anatomical region. At HVC, the overall DSA and DVA scores (mean ± SEM) were 2.75 ± 0.12 and 3.23 ± 0.16, respectively (P < 0.05), whereas at BKCH these values were 2.49 ± 0.10 and 3.03 ± 0.09, respectively (P < 0.001). CONCLUSIONS: These data show that lower-limb CO2 angiography DVA, regardless of the image acquisition instruments and protocols, produces higher SNR and significantly better image quality than DSA; therefore this new image processing technique might help the widespread use of CO2 as a safer contrast agent in clinical practice.

The tricyclic antidepressant desipramine inhibited the neurotoxic, kainate-induced [Ca(2+)]i increases in CA1 pyramidal cells in acute hippocampal slices.

Kainate (KA), used for modelling neurodegenerative diseases, evokes excitotoxicity. However, the precise mechanism of KA-evoked [Ca(2+)]i increase is unexplored, especially in acute brain slice preparations. We used [Ca(2+)]i imaging and patch clamp electrophysiology to decipher the mechanism of KA-evoked [Ca(2+)]i rise and its inhibition by the tricyclic antidepressant desipramine (DMI) in CA1 pyramidal cells in rat hippocampal slices and in cultured hippocampal cells. The effect of KA was dose-dependent and relied totally on extracellular Ca(2+). The lack of effect of dl-2-amino-5-phosphonopentanoic acid (AP-5) and abolishment of the response by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) suggested the involvement of non-N-methyl-d-aspartate receptors (non-NMDARs). The predominant role of the Ca(2+)-impermeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPARs) in the initiation of the Ca(2+) response was supported by the inhibitory effect of the selective AMPAR antagonist GYKI 53655 and the ineffectiveness of 1-naphthyl acetylspermine (NASPM), an inhibitor of the Ca(2+)-permeable AMPARs. The voltage-gated Ca(2+) channels (VGCC), blocked by ω-Conotoxin MVIIC+nifedipine+NiCl2, contributed to the [Ca(2+)]i rise. VGCCs were also involved, similarly to AMPAR current, in the KA-evoked depolarisation. Inhibition of voltage-gated Na(+) channels (VGSCs; tetrodotoxin, TTX) did not affect the depolarisation of pyramidal cells but blocked the depolarisation-evoked action potential bursts and reduced the Ca(2+) response. The tricyclic antidepressant DMI inhibited the KA-evoked [Ca(2+)]i rise in a dose-dependent manner. It directly attenuated the AMPA-/KAR current, but its more potent inhibition on the Ca(2+) response supports additional effect on VGCCs, VGSCs and Na(+)/Ca(2+) exchangers. The multitarget action on decisive players of excitotoxicity holds out more promise in clinical therapy of neurodegenerative diseases.

The hippocampal-prefrontal pathway: the weak link in psychiatric disorders?

While the hippocampal formation and the prefrontal cortex each have a well-established role in cognitive and mnemonic processes, the extent and manner in which these structures interact to achieve these functions has not been fully delineated. Recent research in rodents compellingly supports the idea that the projection of neurons extending from the CA1 region of the hippocampus and from the subiculum to the prefrontal cortex, referred to here as the H-PFC pathway, is critically involved in aspects of cognition related to executive function and to emotional regulation. Concurrently, it is becoming evident that persons suffering from schizophrenia, depression, and post-traumatic stress disorder display structural anomalies and aberrant functional coupling within the hippocampal-prefrontal circuit. Considering that these disorders involve varying degrees of cognitive impairment and emotional dysregulation, dysfunction in the H-PFC pathway might therefore be the common element of their pathophysiology. This overlap might also be intertwined with the pathway's evident susceptibility to stress and with its relationship to the amygdala. In consequence, the H-PFC pathway is a potentially crucial element of the pathophysiology of several psychiatric diseases, and it offers a specific target for therapeutic intervention, which is consistent with the recent emphasis on reframing psychiatric diseases in terms of brain circuits.

Brain-derived neurotrophic factor-mediated effects on mitochondrial respiratory coupling and neuroprotection share the same molecular signalling pathways.

Intracerebral injection of ibotenate into mouse pups induced grey matter lesions and white matter cysts; co-administration of brain-derived neurotrophic factor (BDNF) produced a dose-dependent reduction in these lesions. In contrast, glial cell line-derived neurotrophic factor (GDNF) had no significant effect, whereas nerve growth factor (NGF) or interleukin-1ß (IL-1ß) resulted in dose-dependent exacerbation. The neuroprotective effects of BDNF were abolished by co-administration of anti-BDNF antibody or MEK inhibitors, or ABT-737, a BH3 mimetic and Bcl-2 antagonist. The actions of BDNF, GDNF and NGF were measured in a parallel in vitro study on the oxidative metabolism of mouse brain mitochondria. BDNF produced a concentration-dependent increase in the respiratory control index (RCI, a measure of respiratory coupling efficiency, ATP synthesis, and organelle integrity) when co-incubated with synaptosomes containing signal transduction pathways; but GDNF failed to modify RCI, and NGF had only weak effects. BDNF had no effect on pure mitochondria, and enhanced oxidation only when complex I substrates were used. The effect of BDNF was inhibited by anti-BDNF antibody, MEK inhibitors or ABT-737, and also by IL-1ß, indicating that the mitochondrial effects are mediated via the same MEK-Bcl-2 pathway as the neuroprotection. The complex I inhibitor rotenone, a compound implicated in the aetiology of Parkinson's disease, inhibited both the in vitro mitochondrial and in vivo neuroprotective effects of BDNF. The ability of BDNF to modify brain metabolism and the efficiency of oxygen utilization via a MEK-Bcl-2 pathway may be an important component of the neuroprotective action observed with this neurotrophin.

GluN2B-containing NMDA receptors as possible targets for the neuroprotective and antidepressant effects of fluoxetine.

Accumulating evidence has indicated the involvement of glutamatergic neurotransmission in the pathophysiology of excitotoxicity and in the mechanism of action of antidepressants. We have previously shown that tricyclic desipramine and the selective serotonin reuptake inhibitor fluoxetine inhibit NMDA receptors (NMDARs) in the clinically relevant, low micromolar concentration range. As the different subtypes of NMDARs are markedly different in their physiological and pathological functions, our aim was to investigate whether the effect of antidepressants is subtype-specific. Using whole-cell patch-clamp recordings in rat cortical cell cultures, we studied the age-dependence of inhibition of NMDA-induced currents after treatment with desipramine and fluoxetine, as the expression profile of the NMDAR subtypes changes as a function of days in vitro. We also investigated the inhibitory effect of these antidepressants on NMDA-induced currents in HEK 293 cell lines that stably expressed rat recombinant NMDARs with GluN1a/GluN2A or GluN1a/GluN2B subunit compositions. The inhibitory effect of desipramine was not age-dependent, whereas fluoxetine displayed a continuously decreasing inhibitory profile, which was similar to the GluN1/GluN2B subtype-selective antagonist ifenprodil. In HEK 293 cells, desipramine equally inhibited NMDA currents in both cell lines, whereas fluoxetine showed an inhibitory effect only in cells that expressed the GluN1/GluN2B subtype. Our data show that fluoxetine is a selective inhibitor of GluN2B-containing NMDARs, whereas desipramine inhibits both GluN1/GluN2A and GluN1/GluN2B subtypes. As the clinical efficacy of these drugs is very similar, the putative NMDAR-associated therapeutic effect of antidepressants may be mediated only via inhibition of the GluN2B-containing subtype. The manifestation of the GluN1/GluN2B-selectivity of fluoxetine suggests the neuroprotective potential for this drug in both acute and chronic neurodegenerative disorders.

Inhibitory effect of antidepressants on the NMDA-evoked [(3)H]noradrenaline release from rat hippocampal slices.

We have previously shown that monoamine uptake blocker-type antidepressants with different chemical structure and selectivity are able to inhibit neuronal nicotinic acetylcholine receptors (nAChRs) in concentrations observed during antidepressant treatment. The mechanism of action of these drugs is similar to that of mecamylamine, a channel blocker-type antagonist of nAChRs. Since mecamylamine has been shown to block also NMDA receptors, our aim was to investigate whether the monoamine uptake blockers may affect the function of these ionotropic glutamate receptors. We studied, therefore the effect of the two most potent nicotinic antagonist antidepressants, the tricyclic desipramine and the selective serotonin reuptake inhibitor fluoxetine on the NMDA-induced [(3)H]noradrenaline ([(3)H]NA) release from rat hippocampal slices. The NMDA-induced hippocampal [(3)H]NA release was effectively blocked by the selective, non-competitive NMDA antagonist MK-801 (IC(50)=0.54 microM), indicating that the [(3)H]NA release was mediated through NMDA receptors. This response was also dose-dependently inhibited by desipramine (IC(50)=14.57 microM) and fluoxetine (IC(50)=41.06 microM). The Na(+)-channel blocker TTX equally inhibited both the electrical stimulation- and the NMDA-evoked [(3)H]NA release (the IC(50) was 55 nM and 66 nM, respectively), whereas the antidepressants inhibited only the NMDA-evoked response. These data suggest that the inhibitory effect of fluoxetine and desipramine on the NMDA-evoked [(3)H]NA release is exerted directly on NMDA receptors rather than indirectly on Na(+)-channels. Due to accumulation processes the concentration of desipramine and fluoxetine in the brain might be in the same range as the observed IC(50) values, thus our data indicate that monoamine uptake blocker-type antidepressants are able to influence the function of NMDA receptors during antidepressant treatment, and the inhibitory effect on NMDA receptors might contribute to the therapeutic effects of these drugs.

Theory of active antidepressants: a nonsynaptic approach to the treatment of depression.

Although depression is one of the major neuropsychiatric disorders, the success rate of medication for any drug is about 60%, which means that approximately 40% of the patients does not respond to the initial treatment. The major aim of this review is to provide a possible explanation for the relative inefficacy of currently used antidepressants and to propose a novel mechanism of action, which might improve the success rate of clinical treatment. According to the monoamine theory the most important neurochemical process in depression is the impairment of monoaminergic neurotransmission and the concomitant decrease of extracellular concentration of noradrenaline and/or serotonin. Since the vast majority of monoaminergic varicosities makes no synaptic contact but is able to release transmitters directly into the extrasynaptic space, the monoaminergic neurotransmission is predominantly nonsynaptic in nature. Depression can be regarded, therefore, as a disease, which is developed (at least in part) on the basis of the impairment of nonsynaptic interactions and the effective treatment has to improve this non-conventional communication in the nervous system. The currently used antidepressants (reuptake inhibitors, negative feedback inhibitors, monoamino oxidase inhibitors) can increase the monoamine levels in the extracellular space only if the monoaminergic cells are electrically active and without an action potential-induced vesicular exocytosis these compounds are ineffective. It is proposed that a selective and moderate induction of the carrier-mediated release of NA and 5-HT might be a better therapeutic approach to the treatment of depression, since this new class of antidepressants, the so-called 'active antidepressants' have a mechanism of action, which is independent from the electrical activity of monoaminergic cells, therefore the extrasynaptic concentration of monoamines and thereby the nonsynaptic communication can be enhanced more efficiently.

Direct inhibitory effect of fluoxetine on N-methyl-D-aspartate receptors in the central nervous system.

BACKGROUND: Data accumulated in the last decade indicate that N-methyl-D-aspartate (NMDA) receptors might be involved in the pathophysiology of depression and the mechanism of action of antidepressants, although a direct inhibitory effect has been reported only in connection with tricyclic compounds, which interact with a wide range of receptors. METHODS: Using whole-cell patch-clamp recording in rat cortical cell cultures, we investigated whether the selective serotonin reuptake inhibitor fluoxetine, which has a much better adverse effect profile, has a direct effect on NMDA receptors, and we compared its action to that of the tricyclic desipramine. RESULTS: Both desipramine (concentration that causes 50% inhibition (IC(50)) = 3.13 microM) and fluoxetine (IC(50) = 10.51 microM) inhibited NMDA-evoked currents with similar efficacy in the clinically relevant low micromolar concentration range. However, in contrast to desipramine, the inhibition by fluoxetine was not voltage-dependent, and fluoxetine partially preserved its ability to associate with NMDA receptor in the presence of Mg(2+), suggesting different binding sites for the two drugs. CONCLUSIONS: The fact that different classes of antidepressants were found to be low-affinity NMDA antagonists suggests that direct inhibition of NMDA receptors may contribute to the clinical effects of antidepressants.

Inhibitory effect of hemicholinium-3 on presynaptic nicotinic acetylcholine receptors located on the terminal region of myenteric motoneurons.

Previously we have demonstrated the presence of presynaptic nicotinic acetylcholine receptors on the terminals of myenteric neurons in Auerbach's plexus of guinea-pig ileum. During these studies we observed, that the presence of hemicholinium-3, an inhibitor of the high affinity choline uptake significantly influences the contraction of the longitudinal muscle strip preparation. Our aim was to investigate the neurochemical background of this effect and quantitatively characterize the action of HC-3. We studied the effect of HC-3 on epibatidine- and electrical stimulation-evoked contraction and release of [3H]acetylcholine from the guinea-pig longitudinal muscle strip preparation. We found that in the presence of tetrodotoxin, when the contribution of somatodendritic nicotinic acetylcholine receptors to the response was prevented due to the inhibition of axonal conduction, HC-3 inhibited the epibatidine-evoked contraction and [3H]acetylcholine release in the submicromolar range (IC50 = 897 nM and IC50 = 693 nM, respectively), whereas the electrical stimulation-evoked contraction was not affected by HC-3, and the release of [3H]acetylcholine was apparently enhanced. Our data indicate that HC-3 inhibits the presynaptic nicotinic acetylcholine receptors of myenteric neurons. Since these receptors play an important role in the regulation of cholinergic neurotransmission in the enteric nervous system, the use of HC-3 in [3H]acetylcholine release experiments might bias the interpretation of data.

Carrier-mediated release of monoamines induced by the nicotinic acetylcholine receptor agonist DMPP.

We have previously shown that dimethylphenylpiperazinium (DMPP) increases the release of noradrenaline (NA) from rat hippocampal slices via two distinct mechanisms: a nicotinic acetylcholine receptor (nAChR)-mediated exocytosis and a carrier-mediated release induced by the reversal of NA transporters. Our aim was to investigate whether other monoaminergic systems are also affected by the multiple actions of DMPP. In our experiments DMPP dose-dependently increased the release of dopamine (DA) and serotonin (5-HT) from rat striatal and hippocampal slices, respectively. The dual effect was observed, however, only in case of DA at a lower DMPP concentration (30 microM), where the response was partly inhibited by mecamylamine, TTX and Ca2+-free medium (nAChR-mediated exocytosis) while the other part of the response was blocked only by the DA uptake inhibitor nomifensine (carrier-mediated release). In contrast, the DMPP-evoked 5-HT release and the DA release induced by high concentration DMPP was not inhibited by nicotinic antagonists, TTX and Ca2+-free medium but only by selective uptake inhibitors. In addition, DMPP dose-dependently inhibited the [3H]DA and [3H]5-HT uptake in striatal and hippocampal synaptosome preparation with an IC50 of 3.18 and 0.49 microM, respectively. Our data show that DMPP interacts with monoamine transporters and induces a substantial carrier-mediated release of DA and 5-HT, therefore caution is needed for the interpretation of data, when this drug is used as a nAChR agonist.

Further evidence for the functional role of nonsynaptic nicotinic acetylcholine receptors.

The function of nicotinic acetylcholine receptors in the main central systems has been documented in the past decade. These studies focused mostly on the synaptic functions, although acetylcholine is released dominantly into the extrasynaptic space and the majority of nicotinic acetylcholine receptors on remote neurons are found on extrasynaptic membranes. Here, we show further evidence for the role of nonsynaptic nicotinic functions in the cognitive and the reward system. Dendrites of gamma-amino-n-butyric acid (GABA)-containing interneurons of the hippocampus are densely equipped with nicotinic acetylcholine receptors. These cells play an important role in memory processing. We analysed the effects of nicotinic acetylcholine receptor stimulation on the Ca(2+) dynamics of interneurons in different dendritic compartments. We also investigated the role of nicotinic receptors in the nucleus accumbens where nicotine stimulated vesicular dopamine release via activation of receptors located on varicosities. Nicotine produced comparable effects with 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) on dopamine release. These examples demonstrate that nonsynaptic nicotinic acetylcholine receptors can effectively influence activity pattern of neural networks in key structures of central systems.

Uptake and release of norepinephrine by serotonergic terminals in norepinephrine transporter knock-out mice: implications for the action of selective serotonin reuptake inhibitors.

Our aim was to investigate the functional properties of the noradrenergic system in genetically modified mice lacking the norepinephrine transporter (NET). We measured the uptake and release of [(3)H]norepinephrine ([(3)H]NE) from hippocampal and cortical slices of NET(-/-) knock-out (KO) and NET(+/+) wild-type (WT) mice and investigated the presynaptic alpha2-adenoceptor-mediated modulation of NE release in vitro and in vivo. The [(3)H]NE uptake was reduced to 12.6% (hippocampus) and 33.5% (frontal cortex) of WT control in KO mice. The neuronal component of this residual uptake was decreased by 79.4 and 100%, respectively, when a selective serotonin reuptake inhibitor (SSRI) citalopram was present during the loading. The more preserved neuronal release of [(3)H]NE (hippocampus, 28.1%; frontal cortex, 74.4%; compared with WT) almost completely disappeared in both regions (94.1 and 95.3% decrease compared with KO, respectively) in the presence of citalopram, suggesting that [(3)H]NE was taken up and released by serotonergic varicosities. This was further supported by the finding that the release of [(3)H]NE from hippocampal slices of KO mice was not modulated by the alpha2-adrenoceptor antagonist 7,8-(methylenedioxy)-14-alpha-hydroxyalloberbane HCl, whereas the endogenous release of NE measured by microdialysis was even more efficiently enhanced by this drug in NET-deficient mice. These experiments indicate that serotonergic varicosities can accumulate and release NE as a result of the heterologous uptake of transmitters. Because the diffusion of NE may be spatially limited by serotonin transporters, the SSRIs, despite their selectivity, might enhance not only serotonergic but also noradrenergic neurotransmission, which might contribute to their antidepressant action.