Role of tissue plasminogen activator in the rewarding effect of morphine]

Tissue plasminogen activator (tPA) is a serine protease that catalyzes the conversion of plasminogen (plg) to plasmin. The tPA-plasmin system plays a role in synaptic plasticity and remodeling. In this review, we focused on the role of tPA-plasmin system in the rewarding effect of morphine. A single morphine treatment induced tPA mRNA and protein expression in a naloxone-sensitive manner, which was associated with an increase in the enzyme activity in the nucleus accumbens (NAc). The acute effect of morphine in inducing tPA expression was diminished after repeated administration. No differences were observed in the morphine-induced antinociceptive effect between wild-type and tPA knockout (tPA-/-) mice. Morphine-induced conditioned place preference and hyperlocomotion were significantly reduced in tPA-/- and pLg-/- mice, being accompanied by a loss of morphine-induced dopamine release in the NAc. Microinjection of either exogenous tPA or plasmin into the NAc significantly potentiated morphine-induced dopamine release in the NAc of ICR mice. In contrast, plasminogen activator inhibitor-1 (PAI-1) dose-dependently reduced morphine-induced dopamine release. Furthermore, the defect of morphine-induced dopamine release and hyperlocomotion in tPA-/- mice was reversed by microinjections of either exogenous tPA or plasmin into the NAc. Our findings demonstrate a novel function of the tPA-plasmin system in regulating dopamine release in the NAc, which is involved in the morphine reward.     

Role of tissue plasminogen activator in the rewarding effect of nicotine

Nicotine, a primary component of tobacco, is one of the most abused drugs worldwide. Approximately four million people die a year because of diseases associated with tobacco smoking. Nicotine rapidly reaches the brain through smoking and this leads to nicotine dependence. Drugs of abuse including nicotine acutely modulate the activity of mesolimbic dopaminergic neurons, projecting from the ventral tegmental area of the midbrain to the nucleus accumbens (NAc). Recently, it has been proposed that activity-dependent synaptic plasticity and remodeling of the mesolimbic dopaminergic system play a crucial role in the development of drug dependence. Tissue plasminogen activator (tPA) is a serine protease that catalyzes the conversion of plasminogen to plasmin. In our previous study, we have demonstrated that the tPA-plasmin system participates in the rewarding effect of morphine and methamphetamine. Here we show that the tPA-plasmin system regulates nicotine-induced reward and dopamine release. In vivo microdialysis revealed that microinjection of either tPA or plasmin into the NAc significantly potentiated whereas plasminogen activator inhibitor-1 reduced the nicotine-induced dopamine release in the NAc in a dose-dependent manner. Nicotine-induced dopamine release was markedly diminished in tPA-deficient (tPA-/-) mice, and the defect of dopamine release in tPA-/- mice was restored by microinjection of either exogenous tPA or plasmin into the NAc. Nicotine increased tPA protein levels and promoted the release of tPA into the extracellular space in the NAc. Immunohistochemistry revealed that protease activated receptor-1 (PAR1)-immunoreactivity was localized to the nerve terminals positive for tyrosine hydroxylase in the NAc. Furthermore, we demonstrated that plasmin activated PAR1 and that nicotine-induced place preference and dopamine release were diminished in PAR1-deficient (PAR1-/-) mice. Our findings suggest that targeting the tPA-plasmin-PAR1 system would provide new therapeutic approaches to the treatment of nicotine dependence.     

Regulation by tissue plasminogen activator of rewarding effects of drugs of abuse]

Drugs of abuse acutely modulate the activity of mesolimbic dopaminergic neurons, projecting from the ventral tegmental area of the midbrain to the nucleus accumbens (NAc). Tissue plasminogen activator (tPA) is a serine protease that catalyzes the conversion of plasminogen (plg) to plasmin. Here we show that this protease system participates in the rewarding effects of morphine, methamphetamine (METH) and nicotine. A single morphine treatment induces tPA mRNA and protein expression in the NAc. Morphine-induced conditioned place preference and hyperlocomotion are significantly reduced in tPA-deficient (tPA-/-) and plg-deficient (plg-/-) mice, being accompanied by a loss of morphine-induced dopamine release in the NAc. Repeated METH treatment also induces tPA mRNA expression in the NAc. METH-induced conditioned place preference and behavioral sensitization after repeated METH treatment are significantly reduced in tPA-/- mice compared with those in wild-type mice. Finally, we show that the tPA-plasmin system regulates nicotine-induced reward and dopamine release by activating protease activated receptor-1 (PAR1). Nicotine-induced dopamine release is markedly diminished in tPA-/- mice. Furthermore, plasmin activates PAR1 and nicotine-induced conditioned place preference and dopamine release are diminished in PAR1-deficient mice. Our findings suggest that targeting the tPA-plasmin-PAR1 system would provide new therapeutic approaches to the treatment of drug dependence.     

Drug dependence, synaptic plasticity, and tissue plasminogen activator

The mesocorticolimbic dopaminergic system plays an important role in the reinforcing effects of drugs of abuse, and the activity-dependent synaptic plasticity of the system is involved in drug dependence. A DNA microarray screening revealed that the expression levels of tissue plasminogen activator (tPA) mRNA in the nucleus accumbens of morphine- or methamphetamine-dependent rats were significantly increased compared with those in control animals. Since tPA plays a role in synaptic plasticity, we hypothesized that tPA may contribute to the development of drug dependence. Single and repeated morphine treatment as well as repeated methamphetamine treatment induced tPA mRNA expression in the nucleus accumbens, which was associated with an increase in the enzyme activity. Conditioned place preference induced by morphine was markedly reduced in mice with a targeted deletion of the tPA gene (tPA-/- mice), being accompanied by a loss of morphine-induced dopamine release. Similarly, methamphetamine-induced conditioned place preference and locomotor sensitization were reduced in tPA-/- mice. The defects of morphine-induced hyperlocomotion as well as methamphetamine-induced locomotor sensitization in tPA-/- mice were reversed by microinjection of exogenous tPA or plasmin into the nucleus accumbens. These results support our hypothesis that tPA plays a role in long-lasting neuronal changes related to drug dependence.     

Pharmacological characterization of nicotine-induced acetylcholine release in the rat hippocampus in vivo: evidence for a permissive dopamine synapse.

In this study, the mechanism of nicotine-induced hippocampal acetylcholine (ACh) release in awake, freely moving rats was examined using in vivo microdialysis. Systemic administration of nicotine (0.4 mg kg(-1), s.c.) increased the levels of ACh in hippocampal dialysates. The nicotine-induced hippocampal ACh release was sensitive to the pretreatment of neuronal nicotinic acetylcholine receptor (nAChR) antagonists mecamylamine (3.0 mg kg(-1), s.c.) and dihydro-beta-erythrodine (DHbetaE; 4.0 mg kg(-1), s.c.) as well as systemic administration of the dopamine (DA) D1 receptor antagonist SCH-23390 (R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-benzaz epine; 0.3 mg kg(-1), s.c.). Local perfusion of mecamylamine (100 microM), DHbetaE (100 microM) or SCH-23390 (10 microM) through microdialysis probe did not increase basal hippocampal ACh release. Hippocampal ACh release elicited by systemic administration of nicotine (0.4 mg kg(-1), s.c.) was antagonized by local perfusion of SCH-23390 (10 microM), but not by MEC (100 microM) or DHbetaE (100 microM). Direct perfusion of nicotine (1 mM, but not 0.1 mM) increased hippocampal ACh levels; however, this effect was relatively insensitive to blockade by co-perfusion of either mecamylamine (100 microM) or SCH-23390 (10 microM). These results suggest that nicotine-induced hippocampal ACh release occurs by two distinct mechanisms: (1) activation of nAChRs outside the hippocampus leading to DA release and subsequent ACh release involving a permissive DA synapse, and (2) direct action of nicotine within the hippocampus leading to ACh release via non-DA-ergic mechanism.     

Modulation of Delta(9)-THC-induced increase of cortical and hippocampal acetylcholine release by micro opioid and D(1) dopamine receptors

The administration of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and synthetic cannabinoids stimulates acetylcholine (ACh) release in the rat prefrontal cortex (PFCx) and hippocampus as estimated by brain microdialysis. The present study was aimed at assessing whether the ability of Delta(9)-THC to stimulate ACh release is dependent upon opioid and dopamine (DA) receptors. Administration of the micro opioid receptor antagonists naloxone and naltrexone prevented the Delta(9)-THC-induced release of ACh in the PFCx and hippocampus. Similarly, bilateral infusion in the ventral tegmental area (VTA), 24h before Delta(9)-THC, of the pseudo-irreversible micro(1) antagonist naloxonazine completely prevented the increase of ACh release by Delta(9)-THC. Pre-treatment with the D(1) receptor antagonist SCH 39,166 reduced Delta(9)-THC-induced ACh release both in the PFCx and in the hippocampus. Since Delta(9)-THC has been shown to increase DA release in the nucleus accumbens (NAc) shell via a micro(1)-opioid receptor mediated mechanism located in the VTA (Tanda, G., Pontieri, F.E., Di Chiara, G., 1997. Cannabinoid and heroin activation of mesolimbic dopamine transmission by a common micro(1) opioid receptor mechanism. Science 276, 2048-2050.), we hypothesize that Delta(9)-THC-induced stimulation of ACh release in the PFCx and hippocampus is related to stimulation of endogenous opioids release in the VTA with secondary activation of DA neurons projecting to the NAc shell.     

Tissue plasminogen activator is not involved in methamphetamine-induced neurotoxicity

To investigate the role of tissue plasminogen activator (tPA) in methamphetamine (METH)-induced dopaminergic neurotoxicity, we compared the changes in tyrosine hydroxylase (TH) and dopamine transporter (DAT) levels in the striatum after repetitive treatment of METH at 4 mg/kg among wild-type, tPA-deficient (tPA-/-), and protease activated receptor-1-deficient (PAR-1-/-) mice. METH treatment caused a marked decrease in TH and DAT levels in the striatum of those mice with a similar magnitude. No difference in METH-induced abnormal behavior and hyperthermia was observed among the three types of mice. These results suggest that neither tPA nor PAR-1 is involved in METH-induced dopaminergic neurotoxicity in vivo.     

Choline transporter hemizygosity results in diminished basal extracellular dopamine levels in nucleus accumbens and blunts dopamine elevations following cocaine or nicotine

Dopamine (DA) signaling in the central nervous system mediates the addictive capacities of multiple commonly abused substances, including cocaine, amphetamine, heroin and nicotine. The firing of DA neurons residing in the ventral tegmental area (VTA), and the release of DA by the projections of these neurons in the nucleus accumbens (NAc), is under tight control by cholinergic signaling mediated by nicotinic acetylcholine (ACh) receptors (nAChRs). The capacity for cholinergic signaling is dictated by the availability and activity of the presynaptic, high-affinity, choline transporter (CHT, SLC5A7) that acquires choline in an activity-dependent matter to sustain ACh synthesis. Here, we present evidence that a constitutive loss of CHT expression, mediated by genetic elimination of one copy of the Slc5a7 gene in mice (CHT+/−), leads to a significant reduction in basal extracellular DA levels in the NAc, as measured by in vivo microdialysis. Moreover, CHT heterozygosity results in blunted DA elevations following systemic nicotine or cocaine administration. These findings reinforce a critical role of ACh signaling capacity in both tonic and drug-modulated DA signaling and argue that genetically imposed reductions in CHT that lead to diminished DA signaling may lead to poor responses to reinforcing stimuli, possibly contributing to disorders linked to perturbed cholinergic signaling including depression and attention-deficit hyperactivity disorder (ADHD).     

Acamprosate blocks the increase in dopamine extracellular levels in nucleus accumbens evoked by chemical stimulation of the ventral hippocampus

Recently, we have shown that acamprosate is able to modulate extracellular dopamine (DA) levels in the nucleus accumbens (NAc) and may act as an antagonist of N-methyl-D-aspartate (NMDA) receptors. Neurochemical studies show that chemical stimulation (using NMDA) of the ventral subiculum (vSub) of the hippocampus produces robust and sustained increases in extracellular DA levels in the NAc, an effect mediated through ionotropic glutamate (iGlu) receptors. The present study examines whether acamprosate locally infused in the NAc of rats could block or attenuate the increase in NAc extracellular DA elicited by chemical stimulation (with 5 mM NMDA) of the ventral subiculum of the hippocampus. The stimulation of the vSub during perfusion of artificial cerebrospinal fluid in NAc induced a significant and persistent increase in NAc DA levels. Reverse dialysis of 0.05 mM acamprosate in NAc blocked the increase in DA evoked by the chemical stimulation of the vSub. These data support the possibility that the antagonism at the NMDA receptors in NAc can explain, at least in part, the mechanism of action of this drug.     

Effects of nicotine and mecamylamine-induced withdrawal on extracellular dopamine and acetylcholine in the rat nucleus accumbens

RATIONALE: Prior research suggests that high levels of acetylcholine (ACh) in the nucleus accumbens (NAc) are associated with aversive states such as morphine withdrawal, but this has not been tested for nicotine withdrawal. OBJECTIVES: The goal was to test the hypothesis that acute nicotine decreases extracellular ACh and increases extracellular dopamine (DA) in the NAc, while withdrawal from nicotine causes an opposite neurochemical imbalance with high extracellular ACh and low DA. METHODS: Rats were prepared with a microdialysis probe in the NAc (primarily the shell region). They received one injection of nicotine (0.5 mg/kg, s.c.) or chronic nicotine (9 mg/kg per day via osmotic minipump). RESULTS: Naive animals receiving acute nicotine showed a mild, significant increase in both ACh (122% of baseline) and DA (124%). After chronic nicotine administration for 7 days, the nicotinic antagonist mecamylamine (1.0 mg/kg, s.c.) precipitated withdrawal with the appearance of somatic signs (teeth chattering and shakes/tremors) and a significant increase in extracellular ACh to 125% of baseline, while extracellular DA decreased to 65%. Control groups receiving saline in place of nicotine or mecamylamine did not show these effects. CONCLUSIONS: Earlier work suggests that the observed release of accumbens ACh and DA in response to acute nicotine administration may be a factor in nicotine-induced suppression of appetite. ACh release during withdrawal, coupled with the decrease in extracellular DA may play a role in the aversive aspects of nicotine withdrawal that contribute to dependency.     

The interaction between components of the fibrinolytic system and GPIb/V/IX of platelets thrombus formation in mice

The interaction of fibrinolytic components with GPIb/V/IX of platelets on thrombus formation, was investigated in mice deficient in tissue type (tPA-/-), urokinase type plasminogen activator (uPA-/-) or plasminogen activator inhibitor-1 (PAI-1-/-) and in their wild type control (tPA+/+, uPA+/+, PAI-1+/+). A thrombus was induced in the murine carotid artery using a photochemical reaction. The times to occlusion after the initiation of endothelial injury in all wild type mice was within 12 min, and no significant changes in occlusion delay were observed in uPA-/- and tPA-/- mice compared to wild type mice, whereas that of PAI-1 mice were significantly prolonged (16.9+/-2.9 min, P<0.05). When high molecular weight aurintricarboxylic acid (ATA), an inhibitor of platelet glycoprotein Ib/V/IX, was administered, the time to occlusion was prolonged in a dose-dependent manner in all types of mice. However, when this compound was injected in tPA-/- mice, the most significant changes were observed: i.e. the estimated ED(50) was 20.2 times higher than that in tPA+/+ mice, but the estimated ED(50) in uPA-/- mice was not changed as compared with that of wild type mice. On the other hand, when ATA was injected in PAI-1-/- mice, the estimated ED(50) was significantly decreased (P<0.05). Platelet aggregation induced by botrocetin was not significantly different among all types of mice. The bleeding time was prolonged in a dose dependent-manner when ATA was injected in all types of mice. In conclusion, the antithrombotic effect of inhibition of platelet GPIb/V/IX is severely affected by the absence or presence of tPA-production on thrombus formation and the inhibition of PAI-1 could enhance this antithrombotic effect.     

Alpha6-containing nicotinic acetylcholine receptors dominate the nicotine control of dopamine neurotransmission in nucleus accumbens.

Modulation of striatal dopamine (DA) neurotransmission plays a fundamental role in the reinforcing and ultimately addictive effects of nicotine. Nicotine, by desensitizing beta2 subunit-containing (beta2*) nicotinic acetylcholine receptors (nAChRs) on striatal DA axons, significantly enhances how DA is released by reward-related burst activity compared to nonreward-related tonic activity. This action provides a synaptic mechanism for nicotine to facilitate the DA-dependent reinforcement. The subfamily of beta2*-nAChRs responsible for these potent synaptic effects could offer a molecular target for therapeutic strategies in nicotine addiction. We explored the role of alpha6beta2*-nAChRs in the nucleus accumbens (NAc) and caudate-putamen (CPu) by observing action potential-dependent DA release from synapses in real-time using fast-scan cyclic voltammetry at carbon-fiber microelectrodes in mouse striatal slices. The alpha6-specific antagonist alpha-conotoxin-MII suppressed DA release evoked by single and low-frequency action potentials and concurrently enhanced release by high-frequency bursts in a manner similar to the beta2*-selective antagonist dihydro-beta-erythroidine (DHbetaE) in NAc, but less so in CPu. The greater role for alpha6*-nAChRs in NAc was not due to any confounding regional difference in ACh tone since elevated ACh levels (after the acetylcholinesterase inhibitor ambenonium) had similar outcomes in NAc and CPu. Rather, there appear to be underlying differences in nAChR subtype function in NAc and CPu. In summary, we reveal that alpha6beta2*-nAChRs dominate the effects of nicotine on DA release in NAc, whereas in CPu their role is minor alongside other beta2*-nAChRs (eg alpha4*), These data offer new insights to suggest striatal alpha6*-nAChRs as a molecular target for a therapeutic strategy for nicotine addiction.     

Accumbens dopamine-acetylcholine balance in approach and avoidance

Understanding systems for approach and avoidance is basic for behavioral neuroscience. Research on the neural organization and functions of the dorsal striatum in movement disorders, such as Huntington's and Parkinson's Disease, can inform the study of the nucleus accumbens (NAc) in motivational disorders, such as addiction and depression. We propose opposing roles for dopamine (DA) and acetylcholine (ACh) in the NAc in the control of GABA output systems for approach and avoidance. Contrary to DA, which fosters approach, ACh release is a correlate or cause of meal satiation, conditioned taste aversion and aversive brain stimulation. ACh may also counteract excessive DA-mediated approach behavior as revealed during withdrawal from drugs of abuse or sugar when the animal enters an ACh-mediated state of anxiety and behavioral depression. This review summarizes evidence that ACh is important in the inhibition of behavior when extracellular DA is high and the generation of an anxious or depressed state when DA is relatively low.     

Hippocampal dopamine receptors modulate the motor activation and the increase in dopamine levels in the rat nucleus accumbens evoked by chemical stimulation of the ventral hippocampus.

A number of studies have shown that chemical stimulation (using N-methyl-D-aspartate (NMDA) infusions) or electrical stimulation of the ventral hippocampus (VH) elicits locomotor activation and sustained increases in nucleus accumbens (NAc) dopamine (DA) levels in rodents. How DA neurotransmission in NAc is involved in these effects has also been well established. However, the modulatory role of the DA receptors located in VH is not yet fully understood. The purpose of this study was to characterize the role played by VH D1 and D2 subtype receptors in both the locomotor activation and NAc DA increases induced by NMDA stimulation of the VH. This was assessed by studying how retrodialysis application of NMDA (50 mM, 10 min) affects motor activity and NAc DA levels during simultaneous retrodialysis administration of the D1/D5 receptor antagonist SCH 23390 (100 and 250 microM, 60 min) or the D2 receptor antagonist raclopride (100 and 250 microM, 60 min). SCH 23390 attenuated or completely abolished NMDA-evoked locomotor activation and the concurrent increase in NAc DA levels. On the other hand, raclopride was initially able to attenuate the effects of VH NMDA stimulation. However, in the last phase of the experiments, animals showed an important increase in clonic seizure activity with a simultaneous and dramatic increase in NAc DA levels. Our results show that the NMDA receptor-mediated effects in the VH require both D1 and, probably, D2 receptors and suggest that DA in VH strongly modulates the excitatory outputs from this brain area.     

Ethanol enhances the calcium-dependent stimulus-induced release of endogenous dopamine from slices of rat striatum and nucleus accumbens in vitro

When slices of striatum from the rat were preincubated for 40 min in calcium-free medium in vitro, the subsequent release of endogenous dopamine (DA) induced by 40 mM KCl was completely calcium-dependent, showing a maximal response in the presence of 1.5 mM CaCl2, and a half-maximal response in the presence of 0.5 mM CaCl2. In this calcium-dependent preparation, ethanol, at concentrations of 80-120 mM, significantly increased the KCl-induced release of endogenous DA from the striatum by 19-29%. This effect was not reproducible in calcium-replete incubation medium (2.0 mM CaCl2), suggesting that the phenomenon was calcium-dependent. Preliminary studies in the nucleus accumbens of the rat showed a similar increase (30%) in the calcium-dependent, KCl-induced release of endogenous DA in the presence of 100 mM ethanol.     

Attenuation of basal and cocaine-enhanced locomotion and nucleus accumbens dopamine in cannabinoid CB1-receptor-knockout mice

Rationale  Effect of cannabinoid CB1 receptor deletion on cocaine’s actions is controversial. This is partly based on findings in CB1-receptor-knockout (CB1^−/−) mice with CD1 genetic background. Objectives  In the present study, we used CB1^−/− mice with a C57BL/6J genetic background to further investigate the role of CB1 receptors in cocaine’s action. Materials and methods  Locomotor activity was assessed using AccuScan locomotor chambers. Brain extracellular dopamine (DA) levels were measured by in vivo microdialysis and by fast-scan cyclic voltammetry in the nucleus accumbens (NAc). Results  CB1^−/− mice displayed a significant reduction in basal levels of locomotion and extracellular DA, as well as in cocaine-enhanced locomotion and extracellular DA, as compared to their wild-type (CB1^+/+) littermates. The reduction in basal and cocaine-enhanced DA appears to be related to a reduction in basal DA release, not to an increase in DA clearance, as indicated by fast-scan cyclic voltammetry in brain slices. Pharmacological blockade of CB1 receptors by SR141716 inhibited locomotion and NAc DA release in CB1^+/+ mice. Conclusions  The present findings suggest an important role for CB1 receptors in mediating cocaine’s behavioral and neurochemical effects.     

Hippocampal dopamine receptors modulate cFos expression in the rat nucleus accumbens evoked by chemical stimulation of the ventral hippocampus

Recently, we have shown that D1 and D2 receptors in the ventral hippocampus (VH) modulate both the locomotor activation and the increase in dopamine (DA) levels in the rat nucleus accumbens (NAc) induced by NMDA stimulation of the VH. In the present study we analyze the possible role of VH D1 and D2 receptors in the modulation of the cFos expression in NAc (core and shell subregions) and in dorsal striatum. This was assessed by immunohistochemical analysis of cFos expression in the rat brains after retro-dialysis application of NMDA (50mM, 10 min) into VH, in absence and in presence of either the D1/D5 receptor antagonist SCH 23390 (100 and 250 microM, 60 min) or the D2 receptor antagonist raclopride (100 and 250 microM, 60 min). NMDA induced a robust increase in the cFos expression in the NAc shell, both in the ipsilateral and contralateral side. No statistically significant increases were observed in the NAc core and in the dorsal striatum. Simultaneous application of SCH 23390 and NMDA into the VH attenuated the NMDA-evoked cFos expression in NAc shell. In contrast, raclopride had no significant effect. Our present results show that the NMDA receptor mediated effects in the VH require D1 receptors and suggest that DA in VH strongly modulates the excitatory outputs from this brain area.     

Administration of exogenous tissue plasminogen activator reduces oedema in mice lacking the tissue plasminogen activator gene

It has recently become apparent that tissue plasminogen activator (tPA) modulates inflammation in diseases such as rheumatoid arthritis (RA) and acute respiratory distress syndrome (ARDS). We have shown previously that tPA has anti-inflammatory activity in in vivo models of oedema or inflammation. The present study investigated the ability of exogenous recombinant tPA (rtPA) to reduce carrageenan-mediated oedema in mice lacking the tPA gene, testing the hypothesis that rtPA treatment may be beneficial in diseases such as RA and ARDS in which there is a paucity of endogenous tPA. Knockout mice deficient in the tPA gene and matching wild-type mice received an intraplantar injection (25 micro L) of carrageenan (1.5%, w/v) following either vehicle (sterile water for injection) or tPA (12 mg/kg). Footpad oedema was measured, an oedema index was calculated and tissue myeloperoxidase (MPO) activity was determined. Mean oedema indices were higher in untreated tPA (-/-) mice than untreated wild-type mice. Pretreatment with rtPA in either tPA (-/-) or wild-type mice reduced the mean measured peak footpad oedema index by 63 and 48%, respectively. Tissue MPO activity was not different between treatment groups. We conclude that exogenous rtPA has the ability to reduce acute oedema without altering neutrophil infiltration into the site of injury in both tPA (-/-) and wild-type mice and that endogenous tPA may participate in the inflammatory process, as evidenced by higher oedema indices in untreated tPA (-/-) mice. These data provide support for the potential clinical utility of exogenous rtPA in the treatment of inflammatory diseases, such as RA and ARDS, in which there is a paucity of tPA.     

3,4-Methylenedioxymethamphetamine enhances the release of acetylcholine in the prefrontal cortex and dorsal hippocampus of the rat

Rationale The neurochemical effects produced by acute administration of 3,4-methylenedioxymethamphetamine (MDMA) on the monoaminergic systems in the brain are well documented; however, there has been little consideration of the potential effects of MDMA on other neurotransmitter systems. Objective The present study was designed to investigate the acute effect of MDMA on cholinergic neurons by measuring acetylcholine (ACh) release in the medial prefrontal cortex (PFC) and dorsal hippocampus, terminal regions of cholinergic projection neurons originating in the basal forebrain. Methods In vivo microdialysis and high-performance liquid chromatography with electrochemical detection (HPLC-ED) were used to assess the effects of MDMA on the extracellular concentration of ACh in the PFC and dorsal hippocampus of the rat. Results The systemic administration of MDMA (3–20 mg/kg, i.p.) resulted in an increased extracellular concentration of ACh in the PFC and dorsal hippocampus. Reverse dialysis of MDMA (100 μM) into the PFC and hippocampus also increased ACh release in these brain regions. Treatment with parachlorophenylalanine and α-methyl-para-tyrosine, inhibitors of serotonin (5-HT) and dopamine (DA) synthesis, respectively, significantly attenuated the release of ACh stimulated by MDMA in the PFC, but not in the dorsal hippocampus. Conclusions MDMA exerts a stimulatory effect on the release of ACh in the PFC and dorsal hippocampus in vivo, possibly by mechanisms localized within these brain regions. In addition, these results suggest that the MDMA-induced release of ACh in the PFC involves both serotonergic and dopaminergic mechanisms.     

Effects of nicotine on levels of acetylcholine and biogenic amines in rat cortex

Transcortical dialysis was employed to investigate the effects of systemic nicotine (3.6 μmol/kg, sc) administration on cortical extracellular levels of acetylcholine (ACh), norepinephrine (NE), dopamine (DA), and serotonin (5-HT). Systemic administration of [–]-nicotine produced a 106% increase of cortical ACh release over basal levels that persisted for approximately 2 h. Concurrently, NE levels were increased 86% over basal values for 60 min. The effects appear to be stereoselective, as systemic injections of [+]-nicotine significantly increased cortical ACh levels only 48% over basal levels for 30 min, and NE levels in the dialysate only 43% over control levels for 60 min. No significant changes of basal dopamine (DA) or serotonin (5-HT) levels were observed, although DA did appear to increase in response to systemic nicotine. In addition, striatal total endogenous ACh increased significantly over control levels 15 min after [–]-nicotine administration (3.6 μmol/kg, sc), and then significantly declined after 3 h, suggesting that nicotine may influence synthesis as well as release. Analysis of total ACh levels in cortical tissue revealed a similar trend. At the dose utilized in this study, no changes in the cortical electroencephalogram (EEG) were observed. © 1994 Wiley-Liss, Inc.