Neuroinflammation and ß amyloid deposition in Alzheimer's disease: in vivo quantification with molecular imaging.

BACKGROUND/AIMS: Neuroinflammation plays a crucial role in the pathogenesis of Alzheimer's disease (AD). Its relationship with underlying ß amyloid deposition remains unclear. In vivo visualization of microglial activation has become possible with the development of molecular imaging ligands when used with positron emission tomography (PET). The translocator protein (TSPO) is upregulated during neuroinflammation. Consequently, targeting TSPO with radiolabeled ligands for PET is an attractive biomarker for neuroinflammation. METHODS: A review of the research literature on PET imaging which studied in vivo neuroinflammation in AD subjects and its relationship with amyloid load was performed, including papers published between 2001 and 2012. RESULTS: Six studies were included using either [(11)C]PK-11195 or another non-TSPO radioligand that binds to the monoaminooxidase B. All the studies evaluated amyloid load with [(11)C]PIB. Microglial activation and astrocytosis are potentially early phenomena in AD. However, the individual levels of amyloid deposition and microglial activation were not correlated. CONCLUSION: Noninvasive in vivo molecular imaging to visualize neuroinflammation in AD may contribute to our understanding of the kinetics of neuroinflammation and its relationship to the hallmarks of the disease. Both are important for the development of future therapeutic modalities and for quantifying the efficacy of future disease-modifying treatments.

Basal ganglia neuroprotection with anticonvulsants after energy stress: a comparative study.

The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model provides a valuable paradigm of the energy deficiency disorders found in childhood. In such disorders, anticonvulsants may provide neuroprotection by modulating cellular energy consumption and by exerting favorable pleiotropic effects on neuronal survival. To verify such hypothesis, we tested the effects of levetiracetam, vigabatrin, gabapentine, pregabaline, tiagabine, clonazepam and lamotrigine on neuroprotection in the MPTP mouse model. The membrane dopamine transporter (DAT) density, which provides a reliable index of dopaminergic neurons survival in the basal ganglia, was assessed by semi-quantitative autoradiography of the striatum. Unlike all other anticonvulsants tested, lamotrigine provided a significant and dose-dependent neuroprotection in these experimental conditions. Lamotrigine, a widely used and well-tolerated molecule in children, could provide neuroprotection in various energy deficiency disorders.

MPTP intoxication in mice: a useful model of Leigh syndrome to study mitochondrial diseases in childhood.

The basal ganglia, which are interconnected in the striato-nigral dopaminergic network, are affected in several childhood diseases including Leigh syndrome (LS). LS is the most common mitochondrial disorder affecting children and usually arise from inhibition of the respiratory chain. This vulnerability is attributed to a particular susceptibility to energetic stress, with mitochondrial inhibition as a common pathogenic pathway. In this study we developed a LS model for neuroprotection trials in mice by using the complex I inhibitor MPTP. We first verified that MPTP significantly inhibits the mitochondrial complex I in the brain (p = 0.018). This model also reproduced the biochemical and pathological features of LS: MPTP increased plasmatic lactate levels (p = 0.023) and triggered basal ganglia degeneration, as evaluated through dopamine transporter (DAT) autoradiography, tyrosine hydroxylase (TH) immunohistochemistry, and dopamine dosage. Striatal DAT levels were markedly decreased after MPTP treatment (p = 0.003). TH immunoreactivity was reduced in the striatum and substantia nigra (p = 0.005), and striatal dopamine was significantly reduced (p < 0.01). Taken together, these results confirm that acute MPTP intoxication in young mice provides a reproducible pharmacological paradigm of LS, thus opening new avenues for neuroprotection research.

Multiple-dose plasma pharmacokinetic and safety study of LY450108 and LY451395 (AMPA receptor potentiators) and their concentration in cerebrospinal fluid in healthy human subjects.

The objective of this study was to measure the steady-state cerebrospinal fluid (CSF) concentration of LY450108 and LY451395 (positive modulators of AMPA receptors) in healthy subjects after the administration of 1 mg and 5 mg. Secondary objectives included the evaluation of safety, pharmacokinetics, and steady-state ratio of plasma:CSF concentrations of LY450108 and LY451395 after multiple dosing. This study was an open-label, multiple oral dose study evaluating 1 mg and 5 mg LY450108 and 1 mg and 5 mg LY451395 in 12 (3 subjects per dosing group) healthy subjects, aged 18 to 49 years. Twelve healthy male subjects completed the study. LY450108 and LY451395 were quantifiable in CSF after 1-mg and 5-mg multiple-dose administrations with plasma:CSF ratio of 82:1 and 44:1, respectively. LY450108 and LY451395 1 mg and 5 mg were measured in the CSF. Single and multiple oral doses of LY450108 and LY451395 were determined to be safe and well tolerated in healthy subjects.

Relationship between the appearance of symptoms and the level of nigrostriatal degeneration in a progressive 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned macaque model of Parkinson's disease.

The concept of a threshold of dopamine (DA) depletion for onset of Parkinson's disease symptoms, although widely accepted, has, to date, not been determined experimentally in nonhuman primates in which a more rigorous definition of the mechanisms responsible for the threshold effect might be obtained. The present study was thus designed to determine (1) the relationship between Parkinsonian symptom appearance and level of degeneration of the nigrostriatal pathway and (2) the concomitant presynaptic and postsynaptic striatal response to the denervation, in monkeys treated chronically with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine according to a regimen that produces a progressive Parkinsonian state. The kinetics of the nigrostriatal degeneration described allow the determination of the critical thresholds associated to symptom appearance, these were a loss of 43.2% of tyrosine hydroxylase-immunopositive neurons at the nigral level and losses of 80.3 and 81.6% DA transporter binding and DA content, respectively, at the striatal level. Our data argue against the concept that an increase in DA metabolism could act as an efficient adaptive mechanism early in the disease progress. Surprisingly, the D(2)-like DA receptor binding showed a biphasic regulation in relation to the level of striatal dopaminergic denervation, i.e., an initial decrease in the presymptomatic period was followed by an upregulation of postsynaptic receptors commencing when striatal dopaminergic homeostasis is broken. Further in vivo follow-up of the kinetics of striatal denervation in this, and similar, experimental models is now needed with a view to developing early diagnosis tools and symptomatic therapies that might enhance endogenous compensatory mechanisms.

PET and SPECT exploration of central monoaminergic transporters for the development of new drugs and treatments in brain disorders.

Membrane and vesicular monoaminergic transporters, responsible for the homeostasis of neurotransmitter pools at nerve endings, are very involved in the physiology and diseases of central nervous system. Recent progresses of cerebral molecular imaging using SPECT and PET methods allow the extend of in vivo exploration of these transporters. For this aim, an increasing number of radiopharmaceuticals labelled with [123I], [99mTc], [11C] or [18F] have been developed such as cocaine derivatives for the DAT, compounds from the diphenyl sulfide family for the SERT, and dihydrotetrabenazine derivatives for the VMAT2. These functional imaging methods can be very useful in several neurological and psychiatric disorders which involve the monoaminergic neurotransmission systems such as Parkinson's disease, ADHD, depression and autism. For example, the DAT is a specific index of the density of dopaminergic endings which progressively degenerate in Parkinson's disease. In vivo exploration of this transporter can therefore be a relevant way (i) to realize an early detection of the loss of dopaminergic neurons, (ii) to assess the progression of the disease, (iii) to validate and improve the efficacy of new therapeutic strategies such as neuroprotection and neuroreparation. In all, the extend of in vivo exploration of monoamine transporters will allow great progress for (1) knowledge of physiopathological mechanisms of brain disorders, (2) early diagnosis of cerebral dysfunctions, allowing early use of new therapies, (3) selection of homogenous classes of subjects for therapeutic assays, (4) objectiveness of drug-molecular target interaction, (5) follow-up of disease evolution and treatment.

PET tracers for imaging brain α7 nicotinic receptors: an update.

Positron emission tomography (PET) molecular imaging of brain targets is a powerful tool to diagnose, follow up, and develop treatments and personalized medicine for a number of acute and chronic brain disorders. The availability of ß+ emitter tracers labelled with [(11)C] or [(18)F] having optimal characteristics of affinity and selectivity for alpha-7 nicotinic receptors (α7R) has received considerable attention, due to the major implication of these receptors in brain functions. The aim of this review is to identify the interest and need for the in vivo exploration of α7R by PET molecular imaging, which tools are currently available for this and how to progress.

Angiotensin-converting enzyme inhibition improves venous endothelial dysfunction in chronic smokers.

OBJECTIVE: In arteries and veins smoking is associated with impaired nitric oxide-mediated relaxation to endothelium-dependent agonists such as bradykinin. We investigated whether acute local angiotensin-converting enzyme (ACE) inhibition, achieved by enalaprilat, could influence bradykinin-induced vasodilation in veins of smokers. METHODS: We studied 7 smokers and 7 nonsmokers with the hand vein technique. After preconstriction with phenylephrine was performed, endothelium-dependent and independent relaxations were assessed by infusing bradykinin (1 to 278 ng/min) and sodium nitroprusside (0.0001 to 3166 ng/min), respectively. Dose-response curves were constructed before and during enalaprilat coinfusion (1 microg/min for 40 minutes). RESULTS: Smokers had impaired venodilation to bradykinin compared with nonsmokers (P < .01). Apparent maximal relaxation induced by bradykinin was 78%+/-9% in the control group and 48%+/-9% in smokers (mean +/- SD). ACE inhibition shifted the bradykinin dose-response curve to the left in both groups (P < .001) and was associated with a minimal increase in apparent maximal venodilation in nonsmokers (78%+/-9% to 83%+/-18%). In contrast, in smokers ACE inhibition augmented the magnitude of apparent maximal venodilation to values comparable to those observed in the control group (48%+/-9% to 102%+/-21%). In both groups the response to sodium nitroprusside was not affected by enalaprilat. CONCLUSIONS: This study shows that acute local ACE inhibition restores bradykinin-induced relaxation in smokers to values found in nonsmokers. This observation suggests that increased vascular metabolism of bradykinin exists in veins of smokers and that the vascular renin-angiotensin system may play a key role in smoking-induced endothelial dysfunction.

Nicotine impairs endothelium-dependent dilatation in human veins in vivo.

BACKGROUND: Cigarette smoking is associated with impaired endothelium-dependent dilatation in human veins and arteries. An in vivo study in animals suggests that nicotine may contribute to this abnormality. We tested the hypothesis that local administration of nicotine at a dose reproducing the plasma concentration observed during smoking would impair endothelium-dependent vasodilatation in human veins in vivo. METHODS: We studied 11 healthy nonsmokers with the dorsal hand vein compliance technique. After 70% to 80% preconstriction with phenylephrine, endothelium-dependent venous relaxation was assessed by infusion of bradykinin (1 to 278 ng/min), a potent vasodilator acting primarily in this model through endothelial release of nitric oxide and prostanoids. Sodium nitroprusside (0.0001 to 3166 ng/min) was used to test endothelium-independent relaxation. Dose-response curves were constructed before and during nicotine coinfusion at a rate of 40 ng/min, reproducing a plasma concentration of 15 ng/mL. RESULTS: After a 10-minute preinfusion, nicotine administration was associated with a loss in sensitivity to bradykinin (P < .001). After 30 and 60 minutes of preinfusion with nicotine, the venorelaxant effect of bradykinin was further reduced (P < .001). A similar inhibition of the response to bradykinin by nicotine persisted in the presence of indomethacin (INN, indomethacin). Coinfusion of nicotine did not attenuate sodium nitroprusside-induced venodiiation. CONCLUSION: The results show that acute local exposure to nicotine in vivo is associated with an impaired response to endothelium-derived nitric oxide in human veins. This finding may provide further insight into the pathophysiology of smoking-induced endothelial dysfunction.

Heparin-induced vasodilation in human hand veins.

OBJECTIVE: To investigate whether heparin produces vasodilation in human veins and to explore the underlying mechanisms. METHODS: Eleven healthy volunteers were studied with the dorsal hand vein compliance technique. Dose-response curves to heparin and enoxaparin were generated. Dose-response curves to heparin were also constructed before and after heparin was infused with the nitric oxide synthase inhibitor N(G)-monomethyl-l-arginine (L-NMMA) or combined histamine H1- and H2-receptor blockade. RESULTS: Heparin but not enoxaparin caused significant dose-dependent relaxation with an average apparent maximal response (at an infusion rate of 20 IU/min) of 47% +/- 23%. L-NMMA attenuated heparin-induced relaxation (P < .001). The combination of H1-and H2-receptor antagonists attenuated heparin-induced relaxation to a lesser extent (P < .05). Heparin-induced relaxation decreased by 52%, 73%, and 35% in the presence of L-NMMA, indomethacin (INN, indometacin) plus L-NMMA, and combined H1- and H2-receptor blockade, respectively. CONCLUSION: Heparin is an endothelium-dependent venodilator in humans. The mechanism of heparin-induced relaxation involves an increased availability of nitric oxide, possibly partially related to local release of histamine.

Reduction of hyperglycemia after oral glucose load by the new alpha 2-adrenergic receptor antagonist SL 84.0418 in healthy subjects.

OBJECTIVE: To assess the antihyperglycemic activity of a new peripherally acting alpha 2-adrenergic receptor antagonist, SL 84.0418 in healthy volunteers METHODS: This was a randomized, double-blind crossover study. The effects of 10, 50, and 100 mg SL 84.0418 on blood glucose, plasma insulin, C-peptide, glucagon, epinephrine, and norepinephrine were investigated in comparison with placebo and 5 mg glipizide before and after an oral glucose challenge (75 gm). RESULTS: Peak blood glucose and area under the blood-glucose curve were dose-dependently reduced by SL 84.0418; the extent of this reduction was similar with 100 mg SL 84.0418 and glipizide. Glipizide but not SL 84.0418 decreased nadir blood glucose. Plasma insulin and C-peptide were increased by glipizide but not by SL 84.0418. Treatments did not modify plasma glucagon. Plasma epinephrine increased during glipizide treatment and plasma norepinephrine increased during treatment with 50 and 100 mg SL 84.0418. Systolic and diastolic blood pressure were moderately enhanced by 50 and 100 mg SL 84.0418. Adverse effects reflecting alpha 2-adrenergic receptor blockade occurred more frequently with 100 mg SL 84.0418. The adverse effect profile of 50 mg SL 84.0418 was not different from that observed with glipizide. CONCLUSION: The alpha 2-adrenergic receptor antagonist SL 84.0418 dose dependently reduced the increase in blood glucose after glucose load without modification of plasma insulin. It may represent an alternative to sulfonylureas in the treatment of non-insulin-dependent diabetes mellitus. Further studies are needed to assess its efficacy and tolerability in non-insulin-dependent patients.

Inhibition of angiotensin-converting enzyme in human hand veins.

Conversion of angiotensin I to angiotensin II likely occurs in human veins, supporting the existence of endothelial angiotensin-converting enzyme (ACE) activity in these vessels. Using the dorsal hand vein technique, we investigated the effects of 2 ACE inhibitors, captopril (single oral dose of 6.25 mg) and enalaprilat (local infusion of 1 microgram/min), on venous responsiveness in healthy subjects. Orally administered captopril induced a marked decrease in angiotensin I- but not angiotensin II-induced venoconstriction. This blunted response persisted for at least 4 hours. Enalaprilat and captopril increased the sensitivity to bradykinin, decreasing the dose producing half-maximal response (ED50) of bradykinin 18-fold and 5-fold, respectively, without changing the maximal venodilatory response. These results confirm that there is substantial rapid metabolism of angiotensin I in human veins and suggest that a single dose of locally infused angiotensin I can be used with the dorsal hand vein technique to assess the time-course effect of vascular ACE inhibition after oral administration. Our findings also extend previous in vitro observations in human veins by showing that these agents potentiate the venodilatory effects of bradykinin in vivo.

Synthesis and ligand binding of nortropane derivatives: N-substituted 2beta-carbomethoxy-3beta-(4'-iodophenyl)nortropane and N-(3-iodoprop-(2E)-enyl)-2beta-carbomethoxy-3beta-(3',4'-disubstituted phenyl)nortropane. New high-affinity and selective compounds for the dopamine transporter.

Two novel series of iodinated N-substituted analogs of 2beta-carbomethoxy-3beta-(4'-iodophenyl)tropane (beta-CIT) and N-(3-iodoprop-(2E)-enyl)-2beta-carbomethoxy-3beta-(3',4'-dis ubstituted phenyl)nortropane were synthesized. They were evaluated for their inhibitory properties on dopamine (DA(T)), serotonin (5-HT(T)), and norepinephrine (NE(T)) transporters in rat brain homogenates using [3H]GBR-12935, [3H]paroxetine, and [3H]nisoxetine as specific ligands. All new N-substituted analogs of beta-CIT exhibited higher DAT selectivity over both 5-HT(T) and NE(T) than beta-CIT. Moreover compounds with the N-substituents propynyl (6), crotyl (4), 2-bromoprop-(2E)-enyl (5), and 3-iodoprop-(2E)-enyl (3d) showed similar to higher DA(T) affinities than beta-CIT (respectively 14, 15, 30, and 30 nM vs 27 nM). Compound 3d was found to be the most selective DA(T) agent of this series (5-HTT/DA(T) = 32.0 vs 0.1 for beta-CIT). The N-(3-iodoprop-(2E)-enyl) chain linked to the tropane nitrogen was therefore maintained on the tropane structure, and phenyl substitution was carried out in order to improve DA(T) affinity. K(i) values of N-(3-iodoprop-(2E)-enyl)-2beta-carbomethoxy-3beta-(3',4'-dis ubstituted phenyl)nortropanes revealed that phenyl, 4'-isopropyl, and 4'-n-propyl derivatives weakly inhibited specific binding to DA(T), whereas phenyl substitution with 4'-methyl (3c), 3',4'-dichloro (3b), and 4'-iodo (3d) yielded high-DA(T) reuptake agents with increased DA(T) selectivity compared to beta-CIT. These results demonstrate that the combination of a nitrogen and a phenyl substitution yields compounds with high affinity and selectivity for the dopamine transporter which are usable as SPECT markers for DA neurons.

Motor behaviour deficits and their histopathological and functional correlates in the nigrostriatal system of dopamine transporter knockout mice.

Chronic dysregulation of dopamine homeostasis has been shown to induce behavioural impairment in dopamine transporter knockout mutant mice arising from the dysfunction of the mesolimbic and hypothalamo-infundibular system. Here, we assessed whether there are also any motor consequences of a chronic and constitutive hyperdopaminergia in the nigrostriatal system in dopamine transporter knockout mutant mice. For this, we analysed motor performances using tests assessing balance, coordinated motor skills (rotarod, pole test), stride lengths and locomotor activity. Dopamine transporter knockout mutant mice were markedly hyperactive in the open field with central compartment avoidance, as previously shown. However, sensorimotor integration was also found to be altered in dopamine transporter knockout mutant mice which displayed a reduced fore- and hind-limb mean stride length, impaired motor coordination on the pole test and reduced rearings in the open field. Moreover, dopamine transporter knockout mutant mice showed a slower task acquisition on the rotarod. Six-week-old dopamine transporter knockout wild type mice having the same femur size as adult dopamine transporter knockout mutant mice ruled out a possible size-effect bias. Whilst there was no significant difference in the striatal volume, we found a slight but significant reduction in neuronal density in the striatum but not in the nucleus accumbens of dopamine transporter knockout mutant mice. There was a reduced binding in the striatum and nucleus accumbens of dopamine(1) receptors ([(3)H]SCH 23390) and dopamine(2) receptors ([(3)H]YM-09151-2). There was no significant difference in the number of dopaminergic neurons in the substantia nigra between dopamine transporter knockout mutant mice and dopamine transporter knockout wild type mice. These results suggest an impaired functioning of the nigrostriatal system in dopamine transporter knockout mutant hyperdopaminergic mice, as illustrated by motor and sensorimotor integration deficits, despite their apparent hyperactivity. These dysfunctions may arise from combined striatal cell loss and/or functional changes of dopaminergic neurotransmission.

Pallidal border cells: an anatomical and electrophysiological study in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated monkey.

A dopamine transporter-radioligand binding study demonstrated a dopaminergic innervation around the pallidal complex in the normal monkey (n=5), i.e. where a subpopulation of pallidal neurons known as "border cells" is classically identified. Surprisingly, this peripallidal binding persists in monkeys rendered parkinsonian (n=5) with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment. The border cell electrophysiological activity was then analysed in normal and parkinsonian monkeys (n=2), either in the untreated state or following administration of levodopa. Pallidal border cell firing frequency was significantly decreased after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment (8.9+/-0.7 vs 31.4+/-1.6Hz, P<0.05). This decrease was partly corrected by levodopa administration (19.2+/-1.0Hz, P<0.05 vs both normal and parkinsonian situations). The peripallidal dopaminergic innervation suggests that pallidal border cells are under a direct dopaminergic control, arising from the ventral tegmental area and/or the basal forebrain magnocellular complex, the role of which remains unknown. Moreover, the relative sparing of these dopaminergic fibers in parkinsonian monkeys suggests that they would exhibit specific adaptive properties totally different from those described in the nigrostriatal pathway.

Characterization of both dopamine uptake systems in rat striatal slices by specific pharmacological tools.

Previous results have shown that modifications of dopamine (DA) high-affinity uptake1 and those of DA low-affinity uptake2 in rat striatal slices were different after autoxidation of this model and in the presence of antioxidants. The aim of this study was to determine whether these two DA uptake systems correspond to two different dopamine transporters or rather to a single one. A lesion into the substantia nigra of animals by injection of 6-hydroxydopamine, a neurotoxic substance of nigrostriatal dopaminergic neurons led to the suppression of both DA uptake systems. These two DA uptake systems were not modified when animals were treated by reserpine or tetrabenazine, which inhibit the vesicular monoamine transporter. Moreover, they were sodium- and temperature-dependent. Experiments with specific inhibitors showed that 1-[2-(diphenylmethoxy) ethyl]-4-(3-phenylpropyl)-piperazine dihydrochloride (GBR-12935) and (E)-N-(3-iodoprop-2-enyl)-2beta-carbomethoxy-3beta-(4'-tolyl ) nortropane chloride (PE2I), two selective DA uptake inhibitors, were significantly more potent than fluoxetine and nisoxetine (selective serotonin and norepinephrine uptake inhibitors respectively) in both DA uptake systems. However, the concentrations of these products inhibiting low-affinity uptake2 by 50% were much greater than those for high-affinity uptake1. Our data indicate that both DA uptake systems are neuronal, independent of the vesicular monoamine transporter, active and specific for dopamine. Our results suggest that high-affinity uptake1 and low-affinity uptake2 correspond to the same dopamine transporter, but would be situated at different levels in the striatal slice model. Uptake1 could take place at the periphery of the slice whereas uptake2 in the depth of the slice.

Plasma fatty acid levels in autistic children.

Phospholipid fatty acids are major structural components of neuronal cell membranes, which modulate membrane fluidity and hence function. Evidence from clinical and biochemical sources have indicated changes in the metabolism of fatty acids in several psychiatric disorders. We examined the phospholipid fatty acids in the plasma of a population of autistic subjects compared to mentally retarded controls. Our results showed a marked reduction in the levels of 22: 6n-3 (23%) in the autistic subjects, resulting in significantly lower levels of total (n-3) polyunsaturated fatty acids (PUFA) (20%), without significant reduction in the (n-6) PUFA series, and consequently a significant increase in the (n-6)/(n-3) ratio (25%). These variations are discussed in terms of potential differences in PUFA dietary intake, metabolism, or incorporation into cellular membranes between the two groups of subjects. These results open up interesting perspectives for the investigation of new biological indices in autism. Moreover, this might have new therapeutic implications in terms of child nutrition.

Microdialysis as a tool for in vivo study of dopamine transporter function in rat brains.

The role of dopamine as a major modulator of CNS function is well-known, and the homeostasis of dopamine is considered to be of major importance in the pathogenesis of several psychiatric and neurological diseases. Few methods are currently available for in vivo study of dopamine transporter function, which regulates extracellular levels of dopamine. Adapting the 'indicator diffusion' method applied to the microdialysis technique, we present here a suitable method for this functional investigation. We measured the cellular extraction of [3H]-MPP+, which is known to accumulate in the dopaminergic neurones through the DAT in the rat striatum, using [14C]-mannitol as reference substance characterized by absence of cellular accumulation. The cellular extraction was 0.41 and was almost abolished in the presence of the dopamine-uptake inhibitor cocaine, reaching 0.07. This suggested that extraction of [3H]-MPP+ was due to cellular uptake by dopamine transporters. Tissue analysis confirmed that [3H]-MPP+ was internalized in cells and that such transport was stopped by cocaine. Moreover, [3H]-MPP+ extraction was dramatically decreased after lesioning the nigro-striatal pathway with 6-hydroxydopamine, whereas [14C]-mannitol extraction was unchanged. It is concluded that the presented method can be used to study the functioning of the dopamine transporter in live animals.

Chronic n-3 polyunsaturated fatty acid diet-deficiency acts on dopamine metabolism in the rat frontal cortex: a microdialysis study.

The effects of alpha-linolenic acid diet deficiency on rat dopaminergic metabolism were investigated in the frontal cortex of male 2-3 month-old rats using the microdialysis method. Increased basal levels of dopamine metabolites were observed in the frontal cortex of awake deficient rats, without modification of dopamine levels. Moreover, using KCl perfusion which releases newly synthesized dopamine, no difference was observed in anaesthetized deficient rats versus control rats. In addition, a decrease in dopamine release was observed in anaesthetized deficient rats versus control rats after tyramine stimulation, which is known to induce release of dopamine from vesicular stores. A working model is proposed which suggests that a chronic n-3 polyunsaturated fatty acids (PUFA) deficiency may lead to modifications in the internalization of dopamine in the storage pool in the frontal cortex.

Chronic n-3 polyunsaturated fatty acid deficiency alters dopamine vesicle density in the rat frontal cortex.

We studied the effects of a chronic deficiency in n-3 polyunsaturated fatty acids (n-3 PUFA) on the vesicle dopaminergic compartment in the frontal cortex of rats. Electronic micrographic analysis showed that the synaptic density and the clear vesicle density were similar in deficient and control rats. However, dopaminergic immunolabeling revealed a significantly decreased number of gold-labeled vesicles in the dopaminergic presynaptic terminals of the deficient rats. These findings demonstrate that dopamine cortical vesicles are specifically decreased in n-3 PUFA deficiency. The mechanism leading to this modification could involve several abnormalities (vesicle turn-over, membrane fluidity, vesicular monoamine transporter). This reduction in the dopaminergic vesicle pool constitutes the first structural support for the previously described modifications of dopamine metabolism in the frontal cortex. Such changes in dopamine neurotransmission could be involved in behavioral abnormalities occurring in n-3 PUFA deficient rats.