The neurotoxic mechanism of Jack Bean Urease in insects involves the interplay between octopaminergic and dopaminergic pathways

In the last decades, the entomotoxicity of JBU and its derived peptides became an object of study, due mainly to the ubiquitous interaction of these compounds with different species of insects and their potential as natural insecticides. In this work, we investigated the neurotoxic effects of JBU in Nauphoeta cinerea cockroaches by dissecting pharmacologically the monoaminergic pathways involved. Selective pharmacological modulators for monoaminergic pathways in in vivo and ex vivo experimental models were employed. Thus, the analysis of N. cinerea neurolocomotory behavior demonstrated that JBU (1.5 and 3 μg/g) induces a significant decrease in the exploratory activity. In these assays, pretreatment of animals with phentolamine, SCH23390 or reserpine, interfered significantly with the response of JBU. Using in vivo abductor metathoracic preparations JBU (1.5 μg/g) induced progressive neuromuscular blockade, in 120 min recordings. In this set of experiments, the previous treatment of the animals with phentolamine, SCH23390 or reserpine, completely inhibited JBU-induced neuromuscular blockade. The recordings of spontaneous compound neural action potentials in N. cinerea legs showed that JBU, only in the smallest dose, significantly decreased the number of potentials in 60 min recordings. When the animals were pretreated with phentolamine, SCH23390, or reserpine, but not with mianserin, there was a significant prevention of the JBU-inhibitory responses on the action potentials firing. Meanwhile, the treatment of the animals with mianserin did not affect JBU's inhibitory activity. The data presented in this work strongly suggest that the neurotoxic response of JBU in N. cinerea involves a cross talking between OCTOPAMIN-ergic and DOPAMIN-ergic nerve systems, but not the SEROTONIN-ergic neurotransmission. Further molecular biology studies with expression of insect receptors associated with voltage clamp techniques will help to discriminate the selectivity of JBU over the monoaminergic transmission.

Fluoksetinin sıçan torasik aort düz kasındaki vazoaktif etkileri

Amaç: Literatürdeki çalışmaların çoğu fluoksetinin kardiyo/serebrovasküler sistemler üzerindeki etkilerine odaklanmış olsa da, vazomotor etkisi hakkında bilinenler hala sınırlıdır. Bu çalışma, fluoksetinin sıçan torasik aort halkalarında düz kas üzerindeki vazoaktif etkilerini deneysel bir düzende araştırmak için planlanmıştır. Gereç ve Yöntem: 24 adet yetişkin Wistar albino rat iki gruba ayrıldı. Grup1-Endotel sağlam grup, Grup2-Endotel hasarlı grup. Servikal dislokasyon sonrası torasik aort izole edildi. Aort halkaları hemen Krebs solüsyonu içeren organ banyosu haznelerine yerleştirildi. Aort halkalarının izometrik gerimindeki değişiklikler kaydedildi. Fenilefrin 10-6M uygulandı ve kasılmalar kaydedildi. Daha sonra Grup 1'e kümülatif dozlarda (0.01, 0.1, 1, 2 mM) fluoksetin uygulandı. Grup 2'de endotel hasarı oluşturuldu. Asetilkolin 10-6M ile endotel hasarı kontrol edildikten sonra, halkalar bir saat yıkanarak ikinci doz fenilefrin hazneye eklendi. Ardından Grup 2'ye kümülatif olarak fluoksetin uygulanıp kasılmalar kaydedildi. Bulgular: Fluoksetinin doza bağımlı ana vazodilatör etkisi anlamlı olarak farklıyken [F (5.110) =72.740, p

Antidepressants Rescue Stress-Induced Disruption of Synaptic Plasticity via Serotonin Transporter-Independent Inhibition of L-Type Calcium Channels

BACKGROUND

Long-term synaptic plasticity is a basic ability of the brain to dynamically adapt to external stimuli and regulate synaptic strength and ultimately network function. It is dysregulated by behavioral stress in animal models of depression and in humans with major depressive disorder. Antidepressants have been shown to restore disrupted synaptic plasticity in both animal models and humans; however, the underlying mechanism is unclear.

METHODS

We examined modulation of synaptic plasticity by selective serotonin reuptake inhibitors (SSRIs) in hippocampal brain slices from wild-type rats and serotonin transporter (SERT) knockout mice. Recombinant voltage-gated calcium (Ca²⁺) channels in heterologous expression systems were used to determine the modulation of Ca²⁺ channels by SSRIs. We tested the behavioral effects of SSRIs in the chronic behavioral despair model of depression both in the presence and in the absence of SERT.

RESULTS

SSRIs selectively inhibited hippocampal long-term depression. The inhibition of long-term depression by SSRIs was mediated by a direct block of voltage-activated L-type Ca²⁺ channels and was independent of SERT. Furthermore, SSRIs protected both wild-type and SERT knockout mice from behavioral despair induced by chronic stress. Finally, long-term depression was facilitated in animals subjected to the behavioral despair model, which was prevented by SSRI treatment.

CONCLUSIONS

These results showed that antidepressants protected synaptic plasticity and neuronal circuitry from the effects of stress via a modulation of Ca²⁺ channels and synaptic plasticity independent of SERT. Thus, L-type Ca²⁺ channels might constitute an important signaling hub for stress response and for pathophysiology and treatment of depression.

Psychostimulants, antidepressants and neurokinin-1 receptor antagonists ('motor disinhibitors') have overlapping, but distinct, effects on monoamine transmission: the involvement of L-type Ca2+ channels and implications for the treatment of ADHD

Both psychostimulants and antidepressants target monoamine transporters and, as a consequence, augment monoamine transmission. These two groups of drugs also increase motor activity in preclinical behavioural screens for antidepressants. Substance P-preferring receptor (NK1R) antagonists similarly increase both motor activity in these tests and monoamine transmission in the brain. In this article, the neurochemical and behavioural responses to these three groups of drugs are compared. It becomes evident that NK1R antagonists represent a distinct class of compounds ('motor disinhibitors') that differ substantially from both psychostimulants and antidepressants, especially during states of heightened arousal or stress. Also, all three groups of drugs influence the activation of voltage-gated Ca(v)1.2 and Ca(v)1.3 L-type channels (LTCCs) in the brain, albeit in different ways. This article discusses evidence that points to disruption of these functional interactions between NK1R and LTCCs as a contributing factor in the cognitive and behavioural abnormalities that are prominent features of Attention Deficit Hyperactivity Disorder (ADHD). Arising from this is the interesting possibility that the hyperactivity and impulsivity (as in ADHD) and psychomotor retardation (as in depression) reflect opposite poles of a behavioural continuum. A better understanding of this pharmacological network could help explain why psychostimulants augment motor behaviour during stress (e.g., in preclinical screens for antidepressants) and yet reduce locomotor activity and impulsivity in ADHD. This article is part of the Special Issue entitled 'CNS Stimulants'.

Antidepressants for the treatment of chronic pain

Chronic pain represents one of the most important public health problems and, in addition to classical analgesics, antidepressants are an essential part of the therapeutic strategy. This article reviews available evidence on the efficacy and safety of antidepressants in major chronic pain conditions; namely, neuropathic pain, headaches, low back pain, fibromyalgia, irritable bowel syndrome (IBS) and cancer pain. Studies, reviews and meta-analyses published from 1991 to March 2008 were retrieved through MEDLINE, PsycINFO and the Cochrane database using numerous key words for pain and antidepressants. In summary, evidence supports the use of tricyclic antidepressants in neuropathic pain, headaches, low back pain, fibromyalgia and IBS. The efficacy of the newer serotonin and norepinephrine reuptake inhibitors is less supported by evidence, but can be recommended in neuropathic pain, migraines and fibromyalgia. To date, evidence does not support an analgesic effect of serotonin reuptake inhibitors, but beneficial effects on well-being were reported in several chronic pain conditions. These results are discussed in the light of current insights in the neurobiology of pain, the reciprocal relationship between pain and depression, and future developments in this field of research.

Effect of antidepressants on ATP-dependent calcium uptake by neuronal endoplasmic reticulum

This study investigated the effect of tricyclic and atypical antidepressants on adenosine triphosphate (ATP) dependent calcium uptake by the endoplasmic reticulum of lysed synaptosomes from rat brain cortex. Tricyclic antidepressants (imipramine, desipramine, clomipramine, amitriptyline) exhibited no effect in the lower range (0.06 to 2 µM) of drug concentrations, and a concentration-dependent inhibition of calcium uptake in the upper range (6 to 200 µM). A concentration-dependent inhibition was observed for atypical antidepressants (mianserin, desmethylmianserin, venlafaxine, desmethylvenlafaxine, fluoxetine) in both the lower and the upper range of drug concentrations. Since no stimulation of calcium uptake was observed in either concentration range, it appears that the tricyclic and atypical antidepressants tested are not capable of normalizing, through their effect on the endoplasmic reticulum, an overactive calcium signal, which is possibly implicated in the etiology of affective disorders. Also, although only marginal inhibition of calcium uptake is expected at brain concentrations of tricyclics and mianserin–desmethylmianserin that are likely to be encountered during clinical use, a more substantial inhibition could occur with fluoxetine.Key words: adenosine triphosphate-dependent calcium uptake, neuronal endoplasmic reticulum, lysed brain synaptosomes, tricyclic antidepressants, atypical antidepressants.

Serotonin reuptake inhibitors fluoxetine and citalopram relax intestinal smooth muscle

Selective serotonin reuptake inhibitor antidepressants (SSRIs) exert depressant effects on cardiac myocytes and vascular smooth muscle cells by inhibiting Ca2+ channels. We hypothesized that the SSRIs fluoxetine and citalopram affect the contractile activity of intestinal smooth muscle by interfering with Ca2+ entry and (or) signaling pathways. The effects of fluoxetine and citalopram on contractions of guinea-pig ileum longitudinal muscle-myenteric plexus preparations (LMMP) were compared with the effects of the voltage-operated Ca2+ channel inhibitors nifedipine and diltiazem. In a concentration-dependent manner, nifedipine, diltiazem, fluoxetine, and citalopram elicited relaxation of LMMPs contracted by electrical field stimulation (EC50 values of 4 × 10–7 M, 1.4 × 10–6 M, 1.4 × 10–5, and 6.8 × 10–6 M, respectively). Nifedipine, diltiazem, fluoxetine, and citalopram also relaxed LMMPs contracted with a depolarizing concentration of KCl (48 mM; EC50 values of 1.8 × 10–8 M, 1.4 × 10–7 M, 3.7 × 10–6 M, and 6.3 × 10–6, respectively), a response that could be reversed by increasing the extracellular Ca2+ concentration (2.5–30 mM). These data suggest that fluoxetine and citalopram elicit relaxation of intestinal smooth muscle, likely by inhibiting Ca2+ channel(s). This effect may be of clinical importance.Key words: fluoxetine (Prozac(r)), citalopram (Seropram(r)), nifedipine, diltiazem, L-type Ca2+ channels, intestinal smooth muscle.

Effect of fluoxetine on intracellular Ca2+ levels in bladder female transitional carcinoma (BFTC) cells

The effect of the antidepressant fluoxetine on Ca2+ signaling in cultured cells was largely unknown. The effect of various concentrations of fluoxetine on [Ca 2+] i in populations of bladder female transitional cancer (BFTC) cells was evaluated by using fura-2 as a Ca2+ probe. Fluoxetine increased [Ca 2+] i concentration dependently (20-100 microM) with an EC50 value of 30 microM. The response was inhibited by 50-60% on extracellular Ca2+ removal. In Ca2+ -free medium, pretreatment with 1 microM thapsigargin (an inhibitor of the endoplasmic reticulum Ca2+ pump) abolished 50 microM fluoxetine-induced Ca2+ release; whereas pretreatment with fluoxetine did not alter the thapsigargin-induced Ca2+ response. Addition of 3 mM Ca2+ increased [Ca 2+] i after pretreatment with 50 microM fluoxetine in Ca2+ -free medium, suggestive of fluoxetine-induced capacitative Ca2+ entry. Suppression of inositol 1,4,5-trisphosphate formation by 2 microM U73122 (a phospholipase C inhibitor) did not affect 50 microM fluoxetine-induced Ca2+ release. Collectively, this study shows that fluoxetine increased [Ca 2+] i in bladder cancer cells in a concentration-dependent fashion, by releasing Ca2+ from thapsigargin-sensitive Ca2+ stores in an IP3-independent manner, and by inducing Ca2+ influx from extracellular medium.

Inhibition of voltage-gated calcium channels by fluoxetine in rat hippocampal pyramidal cells

Fluoxetine, an antidepressant which is used world-wide, is a prominent member of the class of selective serotonin re-uptake inhibitors. Recently, inhibition of voltage-gated Na(+) and K(+) channels by fluoxetine has also been reported. We examined the effect of fluoxetine on voltage-gated calcium channels using the patch-clamp technique in the whole-cell configuration. In hippocampal pyramidal cells, fluoxetine inhibited the low-voltage-activated (T-type) calcium current with an IC(50) of 6.8 microM. Fluoxetine decreased the high-voltage-activated (HVA) calcium current with an IC(50) between 1 and 2 microM. Nifedipine and omega-conotoxin GVIA inhibited the HVA current by 24% and 43%, respectively. Fluoxetine (3 microM), applied in addition to nifedipine or omega-conotoxin, further reduced the current. When fluoxetine (3 microM) was applied first neither nifedipine nor omega-conotoxin attenuated the remaining component of the HVA current. This observation indicates that fluoxetine inhibits both L- and N-type currents. In addition, fluoxetine inhibited the HVA calcium current in carotid body type I chemoreceptor cells and pyramidal neurons prepared from prefrontal cortex. In hippocampal pyramidal cells high K(+)-induced seizure-like activity was inhibited by 1 microM fluoxetine; the mean burst duration was shortened by an average of 44%. These results provide evidence for inhibition of T-, N- and L-type voltage-gated calcium channels by fluoxetine at therapeutically relevant concentrations.

Second messenger-regulated protein kinases in the brain: their functional role and the action of antidepressant drugs

Depression has been treated pharmacologically for over three decades, but the views regarding the mechanism of action of antidepressant drugs have registered recently a major change. It was increasingly appreciated that adaptive changes in postreceptor signaling pathways, rather than primary action of drugs on monoamine transporters, metabolic enzymes, and receptors, are connected to therapeutic effect. For some of the various signaling pathways affected by antidepressant treatment, it was shown that protein phosphorylation, which represents an obligate step for most pathways, is markedly affected by long-term treatment. Changes were reported to be induced in the function of protein kinase C, cyclic AMP-dependent protein kinase, and calcium/calmodulin-dependent protein kinase. For two of these kinases (cyclic AMP- and calcium/calmodulin-dependent), the changes have been studied in isolated neuronal compartments (microtubules and presynaptic terminals). Antidepressant treatment activates the two kinases and increases the endogenous phosphorylation of selected substrates (microtubule-associated protein 2 and synaptotagmin). These modifications may be partly responsible for the changes induced by antidepressants in neurotransmission. The changes in protein phosphorylation induced by long-term antidepressant treatment may contribute to explain the therapeutic action of antidepressants and suggest new strategies of pharmacological intervention.

Inhibition of neuronal KV potassium currents by the antidepressant drug, fluoxetine

1. The effect of the antidepressant drug, fluoxetine on neuronal delayed rectifier (KV) potassium (K) currents was investigated using perforated-patch whole-cell electrophysiological recording methods. 2. Fluoxetine was an effective inhibitor of KV currents in cerebellar granule neurons (CGNs) and also inhibited recombinant KV1.1 channels expressed in Chinese hamster ovary (CHO) cells. 3. Fluoxetine had an IC50 of 11 microM in CGNs but was slightly less potent on KV1.1 channels (IC50=55 microM). Interestingly, fluoxetine was a much more potent inhibitor of KV1.1 expressed in mammalian cells than has been found previously for the same homomeric channel expressed in Xenopus oocytes. 4. At concentrations that produced around 50% block, the shape of the KV currents in the presence of fluoxetine was simply scaled down when compared to control currents. 5. The effect of fluoxetine on KV currents in CGNs was neither voltage-dependent nor dependent on the channels being in their open state. Both of these observations suggest that fluoxetine does not act as a simple open channel blocking agent. 6. It is concluded that block of KV currents in mammalian neurons can occur at therapeutic levels of fluoxetine. This could lead to an increase in neuronal excitability and this effect may contribute to the therapeutic antidepressant action of fluoxetine.

Fluoxetine dilates isolated small cerebral arteries of rats and attenuates constrictions to serotonin, norepinephrine, and a voltage-dependent Ca(2+) channel opener

BACKGROUND AND PURPOSE

Recent clinical observations question that the antidepressant effect of fluoxetine (Prozac) can be explained solely with serotonin reuptake inhibition in the central nervous system. We hypothesized that fluoxetine affects the tone of vessels and thereby modulates cerebral blood flow.

METHODS

A small branch of rat anterior cerebral artery (195+/-15 microm in diameter at 80 mm Hg perfusion pressure) was isolated, cannulated, and pressurized (at 80 mm Hg), and changes in diameter were measured by videomicroscopy.

RESULTS

Fluoxetine dilated small cerebral arteries with an EC(50) of 7.7+/-1.0x10(-6) mol/L, a response that was not affected by removal of the endothelium or application of 4-aminopyridine (an inhibitor of aminopyridine-sensitive K(+) channels), glibenclamide (an inhibitor of ATP-sensitive K(+) channels), or tetraethylammonium (a nonspecific inhibitor of K(+) channels). The presence of fluoxetine (10(-6) to 3x10(-5) mol/L) significantly attenuated constrictions to serotonin (10(-9) to 10(-5) mol/L) and norepinephrine (10(-9) to 10(-5) mol/L). Increasing concentrations of Bay K 8644 (a voltage-dependent Ca(2+) channel opener, 10(-10) to 10(-6) mol/L) elicited constrictions, which were markedly reduced by 2x10(-6) and 10(-5) mol/L fluoxetine, whereas 3x10(-5) mol/L fluoxetine practically abolished the responses.

CONCLUSIONS

Fluoxetine elicits substantial dilation of isolated small cerebral arteries, a response that is not mediated by endothelium-derived dilator factors or activation of K(+) channels. The finding that fluoxetine inhibits constrictor responses to Ca(2+) channel opener, as well as serotonin and norepinephrine, suggests that fluoxetine interferes with the Ca(2+) signaling mechanisms in the vascular smooth muscle. We speculate that fluoxetine increases cerebral blood flow in vivo, which contributes to its previously described beneficial actions in the treatment of mental disorders.

Serotonin reuptake inhibitor, fluoxetine, dilates isolated skeletal muscle arterioles. Possible role of altered Ca2+ sensitivity

1. Inhibitors of serotonin reuptake in the central nervous system, such as fluoxetine, may also affect the function of vascular tissues. Thus, we investigated the effect of fluoxetine on the vasomotor responses of isolated, pressurized arterioles of rat gracilis muscle (98 +/- 4 microns in diameter at 80 mmHg perfusion pressure). 2. We have found that increasing concentrations of fluoxetine dilated arterioles up to 155 +/- 5 microns with an EC50 of 2.5 +/- 0.5 x 10(-6) M. 3. Removal of the endothelium, application of 4-aminopyridine (4-AP, an inhibitor of aminopyridine sensitive K+ channels), or use of glibenclamide (an inhibitor of ATP-sensitive K+ channels) did not affect the vasodilator response to fluoxetine. 4. In the presence of 10(-6), 2 x 10(-6) or 10(-5) M fluoxetine noradrenaline (NA, 10(-9)-10(-5) M) and 5-hydroxytryptamine (5-HT, 10(-9)-10(-5)M)-induced constrictions were significantly attenuated resulting in concentration-dependent parallel rightward shifts of their dose-response curves (pA2 = 6.1 +/- 0.1 and 6.9 +/- 0.1, respectively). 5. Increasing concentrations of Ca2+ (10(-4) 3 x 10(-2) M) elicited arteriolar constrictions (up to approximately 30%), which were markedly reduced by 2 x 10(-6)M fluoxetine, whereas 10(-5)M fluoxetine practically abolished these responses. 6. In conclusion, fluoxetine, elicits substantial dilations of isolated skeletal muscle arterioles, a response which is not mediated by 4-AP- and ATP-sensitive K+ channels or endothelium-derived dilator factors. The findings that fluoxetine had a greater inhibitory effect on Ca2+ elicited constrictions than on responses to NA and 5-HT suggest that fluoxetine may inhibit Ca2+ channel(s) or interfere with the signal transduction by Ca2+ in the vascular smooth muscle cells.

Inhibition of K+-induced Ca2+ uptake in rat hippocampus synaptosomes by mianserin enantiomers

In order to test potential links with other stereospecific neurobiological effects of mianserin, the present study explored the stereospecificity for inhibition of depolarization-induced Ca2+ uptake by mianserin. Synaptosomes from rat hippocampus were incubated with 45Ca2+ in either resting or depolarizing (60 mM K+) choline medium, in the absence or presence (0.6-200 microM) of a mianserin enantiomer. The enantiomers were equipotent (IC50 approximating 50 microM) at inhibiting net depolarization-induced Ca2+ uptake. This finding, therefore, cannot help to explain the stereoselective enhancement of noradrenaline release by S(+)-mianserin; it is also not in keeping with the stereospecificity exhibited by mianserin in acute tests predictive of antidepressant activity, thus suggesting that the calcium-channel blocking activity of mianserin is not linked to its antidepressant effect.

Monoamine oxidase A inhibition by fluoxetine: an in vitro and in vivo study

Monoamine oxidase A (MAO-A) inhibition was investigated both in vitro and in vivo in rat brains by using the radioligand, 18F-fluoroclorgyline (N-[3-(2',4'-dichlorophenoxy)-2-18F-fluoropropyl]-N-methylpropa rgylamine). In vitro binding affinities of six compounds, clorgyline, Ro 41-1049, deprenyl, fluoxetine, norfluoxetine and citalopram, were studied. Fluoxetine and norfluoxetine showed in vitro affinities of 36.5 and 68 microM for MAO-A, respectively. Fluoxetine and norfluoxetine also significantly inhibited (more than 20%) the binding of the radioligand in vivo while citalopram and deprenyl showed very poor affinities in vitro for MAO-A and had no effect in vivo. The in vivo effects of the various drugs were directly comparable to their in vitro affinities for binding to MAO-A as seen in the correlation plot of percent control in vivo binding of 18F-fluoroclorgyline and binding affinity, -log IC50 (R2 = 0.979). An acute dose of 20 mg/kg of fluoxetine inhibited binding of 18F-fluoroclorgyline by more than 20%, while lower doses had some significant effects. These results provide evidence on the in vitro and in vivo inhibition of monoamine oxidase A by fluoxetine.