On the Origin of Cortical Dopamine: Is it a Co-Transmitter in Noradrenergic Neurons?

Dopamine (DA) and noradrenaline (NA) in the prefrontal cortex (PFC) modulate superior cognitive functions, and are involved in the aetiology of depressive and psychotic symptoms. Moreover, microdialysis studies in rats have shown how pharmacological treatments that induce modifications of extracellular NA in the medial PFC (mPFC), also produce parallel changes in extracellular DA.To explain the coupling of NA and DA changes, this article reviews the evidence supporting the hypothesis that extracellular DA in the cerebral cortex originates not only from dopaminergic terminals but also from noradrenergic ones, where it acts both as precursor for NA and as a co-transmitter.Accordingly, extracellular DA concentration in the occipital, parietal and cerebellar cortex was found to be much higher than expected in view of the scarce dopaminergic innervation in these areas.Systemic administration or intra-cortical perfusion of alpha(2)-adrenoceptor agonists and antagonists, consistent with their action on noradrenergic neuronal activity, produced concomitant changes not only in extracellular NA but also in DA in the mPFC, occipital and parietal cortex.Chemical modulation of the locus coeruleus by locally applied carbachol, kainate, NMDA or clonidine modified both NA and DA in the mPFC.Electrical stimulation of the locus coeruleus led to an increased efflux of both NA and DA in mPFC, parietal and occipital cortex, while in the striatum, NA efflux alone was enhanced.Atypical antipsychotics, such as clozapine and olanzapine, or antidepressants, including mirtazapine and mianserine, have been found to increase both NA and DA throughout the cerebral cortex, likely through blockade of alpha(2)-adrenoceptors. On the other hand, drugs selectively acting on dopaminergic transmission produced modest changes in extracellular DA in mPFC, and had no effect on the occipital or parietal cortex.Acute administration of morphine did not increase DA levels in the PFC (where NA is diminished), in contrast with augmented dopaminergic neuronal activity; moreover, during morphine withdrawal both DA and NA levels increased, in spite of a diminished dopaminergic activity, both increases being antagonised by clonidine but not quinpirole administration.Extensive 6-hydroxy dopamine lesion of the ventral tegmental area (VTA) decreases below 95% of control both intra- and extracellular DA and DOPAC in the nucleus accumbens, but only partially or not significantly in the mPFC and parietal cortex.The above evidence points to a common origin for NA and DA in the cerebral cortex and suggests the possible utility of noradrenergic system modulation as a target for drugs with potential clinical efficacy on cognitive functions.     

Effects of Rhynchophyline on L-type Calcium Channels in Isolated Rat Cortical Neurons During Acute Hypoxia

目的：研究钩藤碱对急性分离的Ｗｉｓｔａｒ大鼠大脑皮层神经元低氧状态下Ｌ型钙通道的作用。方法：细胞贴附膜片钳技术，从－４０ｍＶ去极化至０ｍＶ激活Ｌ型钙通道。结果：低氧可激活皮层神经元Ｌ型钙通道开放，使平均开放时间延长，平均关闭时间缩短，开放概率增加。钩藤碱（１５和３０μｍｏｌ·Ｌ－１）可浓度依赖性抑制低氧状态下此钙通道的激活，缩短其平均开放时间（从８８７ｍｓ缩至３０３ｍｓ和２２３ｍｓ，Ｐ＜０００１），延长其平均关闭时间（从９２３ｍｓ延至３８８４和５４４３ｍｓ，Ｐ＜０００１）并降低其开放概率（从０１４２降至００３１和００２５，Ｐ＜０００１）此作用与维拉帕米（１５μｍｏｌ·Ｌ－１）相似，但稍弱。结论：钩藤碱对低氧大鼠大脑皮层神经元Ｌ型钙通道有阻滞作用，从而降低细胞内钙超载，此为钩藤碱改善低氧性脑代谢紊乱的机制之一     

Toxicity Studies on Depleted Uranium in Primary Rat Cortical Neurons and in Caenorhabditis Elegans: What Have We Learned?

Depleted uranium (DU) is the major by-product of the uranium enrichment process for its more radioactive isotopes, retaining approximately 60% of its natural radioactivity. Given its properties as a pyrophoric and dense metal, it has been extensively used in armor and ammunitions. Questions have been raised regarding the possible neurotoxic effects of DU in humans based on follow-up studies in Gulf War veterans, where a decrease in neurocognitive behavior in a small population was noted. Additional studies in rodents indicated that DU readily traverses the blood–brain barrier, accumulates in specific brain regions, and results in increased oxidative stress, altered electrophysiological profiles, and sensorimotor deficits. This review summarizes the toxic potential of DU with emphasis on studies on thiol metabolite levels, high-energy phosphate levels, and isoprostane levels in primary rat cortical neurons. Studies in Caenorhabditis elegans detail the role of metallothioneins, small thiol-rich proteins, in protecting against DU exposure. In addition, recent studies also demonstrate that only one of the two forms, metallothionein-1, is important in the accumulation of uranium in worms.     

Aldosterone-Sensitive Nucleus Tractus Solitarius Neurons Regulate Sensitivity of the Baroreceptor Reflex in High Sodium–Loaded Rats

We examined the role of aldosterone-sensitive neurons in the nucleus tractus solitarius (NTS) in the arterial baroreceptor reflex (baroreflex) function. Baroreflex sensitivity was induced by phenylephrine in high sodium–loaded rats and was significantly reduced. This baroreflex sensitivity was reversed by microinjection of the mineralocorticoid receptor (MR) antagonist eplerenone into the NTS. 11β-Hydroxysteroid dehydrogenase type 2 neurons and MR were also identified in the NTS. These data suggest that the aldosterone-sensitive neurons in the NTS may have an important role in baroreflex function.     

A Mouse Model of Sural Nerve Injury–Induced Neuropathy: Gabapentin Inhibits Pain-Related Behaviors and the Hyperactivity of Wide-Dynamic Range Neurons in the Dorsal Horn

This study was conducted to make a new mouse model of neuropathic pain due to injury to a branch of the sciatic nerve. One of three branches (sural, tibial, and common peroneal nerves) of the sciatic nerve was tightly ligated, and mechanical and cool stimuli were applied to the medial part (tibial and common peroneal nerve territories) of the plantar skin. The three types of nerve injuries produced behavioral mechanical hypersensitivities, and the extent of the hypersensitivities after sural and tibial nerve ligation was larger than that of common peroneal nerve ligation. Sural nerve ligation did not affect motor function of the affected hind paw, but tibial and common peroneal nerve ligation produced motor dysfunction. These results suggest that the ligation of the sural nerve is the most suitable for behavioral study. Sural nerve ligation induced behavioral hypersensitivities to mechanical and cool stimuli, which were almost completely inhibited by gabapentin (30 mg/kg). Sural nerve ligation increased spontaneous activity and responses of the wide-dynamic range neurons in the lumbar dorsal horn, which were also almost completely inhibited by gabapentin (30 mg/kg). Sural nerve ligation provides a new mouse model of neuropathic pain, which is easy to prepare and sensitive to gabapentin.     

Population PKPD Modeling of BACE1 Inhibitor-Induced Reduction in Aβ Levels In Vivo and Correlation to In Vitro Potency in Primary Cortical Neurons from Mouse and Guinea Pig

Purpose

The aims were to quantify the in vivo time-course between the oral dose, the plasma and brain exposure and the inhibitory effect on Amyloid β (Aβ) in brain and cerebrospinal fluid, and to establish the correlation between in vitro and in vivo potency of novel β-secretase (BACE1) inhibitors.

Methods

BACE1-mediated inhibition of Aβ was quantified in in vivo dose- and/or time-response studies and in vitro in SH-SY5Y cells, N2A cells, and primary cortical neurons (PCN). An indirect response model with inhibition on Aβ production rate was used to estimate unbound in vivo IC ₅₀ in a population pharmacokinetic-pharmacodynamic modeling approach.

Results

Estimated in vivo inhibitory potencies varied between 1 and 1,000 nM. The turnover half-life of Aβ40 in brain was predicted to be 0.5 h in mouse and 1 h in guinea pig. An excellent correlation between PCN and in vivo potency was observed. Moreover, a strong correlation in potency was found between human SH-SY5Y cells and mouse PCN, being 4.5-fold larger in SH-SY5Y cells.

Conclusion

The strong in vivo-in vitro correlation increased the confidence in using human cell lines for screening and optimization of BACE1 inhibitors. This can optimize the design and reduce the number of preclinical in vivo effect studies.     

Protective Effect of Tetrandrine against Excitatory Amino Acids induced Neuronal Injury in Cortical Culture

兴奋性氨基酸类神经毒剂与粉防己碱（ｔｅｔｒａｎｄｒｉｎｅ，Ｔｅｔ）共同作用于原代培养胎鼠大脑皮层神经元２４小时，发现１０７，１０６ｍｏｌ·Ｌ１Ｔｅｔ明显降低５０μｍｏｌ·Ｌ１谷氨酸（ｇｌｕｔａｍａｔｅ，Ｇｌｕ），３００μｍｏｌ·Ｌ１βＮｍｅｔｈｙｌａｍｉｎｏＬａｌａｎｉｎｅ（ＢＭＡＡ，ＮＭＤＡ受体激动剂）和２０μｍｏｌ·Ｌ１βＮｏｘａｌｙｌａｍｉｎｏＬａｌａｎｉｎｅ（ＢＯＡＡ，ｎｏｎＮＭＤＡ受体激动剂）导致的培养液乳酸脱氢酶（ｌａｃｔａｔｅｄｅｈｙｄｒｏｇｅｎａｓｅ，ＬＤＨ）活性的增高；细胞形态损害减轻，细胞数量增加。对２０μｍｏｌ·Ｌ１ＮＭＤＡ介导的神经元损伤改变无影响。提示Ｔｅｔ对某些Ｇｌｕ类神经毒剂引起的胎鼠大脑皮层神经元损伤有一定保护作用，其机制可能是抑制细胞膜上的Ｎａ＋通道开放，阻止膜去极化而影响电压依赖性Ｃａ２＋通道启动。对ＮＭＤＡ受体可能亦有一定作用。     

Inhibition of the Formation of the Alzheimer's β-Amyloid Peptide

Anorexia and body weight loss are characteristic of many diseases, including cancer and AIDS. Neuropeptides play a pivotal role in the physiological mechanisms regulating food intake and body weight. Neuropeptide Y (NPY) is a key molecule of the orexigenic network for energy intake and for normal adaptive feeding response to energy deficits. Therefore, the NPY receptors (notably, Y1 and Y5) may be one of the most significant target classes for treatment of anorexia and body weight loss. In addition, several anorexigenic peptides including corticotropin-releasing factor (CRF), cholecystokinin (CCK), leptin and melanocortin (MC) are emerging as potential targets for anorexia. Antagonists for CRF 2 receptor, CCK A receptor, MC 4 receptor and leptin receptor may be useful in stimulating food intake. The development of highly specific and selective non-peptide antagonists for these receptors is awaited. Anorexia is a crucial and critical disease. Increasing knowledge of its pathophysiology could lead to innovative new medicines for anorexia-cachexia syndrome.     

Effects of the administration of miconazole by different routes on the biomarkers of the “steroidal module” of the Athlete Biological Passport

This article reports the results obtained from the investigation of the influence of miconazole administration on the physiological fluctuation of the markers of the steroid profile included in the “steroidal module” of the Athlete Biological Passport. Urines collected from male Caucasian subjects before, during, and after either systemic (i.e., oral and buccal) or topical (i.e., dermal) treatment with miconazole were analyzed according to validated procedures based on gas chromatography coupled to tandem mass spectrometry (GC–MS/MS) (to determine the markers of the steroid profile) or liquid chromatography coupled to MS/MS (LC–MS/MS) (to determine miconazole urinary levels). The results indicate that only after systemic administration, the markers of the steroid profile were significantly altered. After oral and buccal administration, we have registered (i) a significant increase of the 5α-androstane-3α,17β-diol/5β-androstane-3α,17β-diol ratio and (ii) a significant decrease of the concentration of androsterone, etiocholanolone, 5β-androstane-3α,17β-diol, and 5α-androstane-3α,17β-diol and of the androsterone/etiocholanolone, androsterone/testosterone, and 5α-androstane-3α,17β-diol/epitestosterone ratios. Limited effects were instead measured after dermal intake. Indeed, the levels of miconazole after systemic administration were in the range of 0.1–12.5 μg/ml, whereas after dermal administration were below the limit of quantification (50 ng/ml). Significant alteration started to be registered at concentrations of miconazole higher than 0.5 μg/ml. These findings were primarily explained by the ability of miconazole in altering the kinetic/efficacy of deglucuronidation of the endogenous steroids by the enzyme β-glucuronidase during the sample preparation process. The increase of both incubation time and amount of β-glucuronidase was demonstrated to be effective countermeasures in the presence of miconazole to reduce the risk of uncorrected interpretation of the results.     

Possible involvement of the opioid receptor gene expression in the mechanisms of the analgesic action of melatonin

In the present study, we attempt to analyse the potential involvement of the opioid receptor gene expression in the mechanisms of the analgesic action of melatonin. A trauma-pain model was established in Wistar rats by combining right - hind limb amputation with 50℃ tail - flick test. Antinociception was determined by tail-flick latency to hot waster at 50℃. Melatonin produced the antinociceptive effect in dose-dependent manner after i. p or i. c.v. administration Injected i. c. v. to rats, naloxone（10μg） obviously antagonized the antinociceptive effect induced by i.p. melatonin.     

Protective Effect of Gabapentin on N-methyl-D-aspartate–Induced Excitotoxicity in Rat Hippocampal CA1 Neurons

Gabapentin was developed as an anticonvulsant, but has also been used to alleviate hyperalgesia in neuropathic pain. In this study, the protective effect of gabapentin against N-methyl-D-aspartate (NMDA)-induced excitotoxicity in rat hippocampal CA1 neurons was investigated. Pre-treatment with gabapentin reduced the degree of neuronal damage induced by NMDA exposure in cultured hippocampal slices. Patch-clamp studies revealed that gabapentin significantly inhibited the NMDA receptor–activated ion current in dissociated hippocampal CA1 neurons, resulting in suppression of glutamate-induced neuronal injury. These results show that gabapentin may exert protective effects against glutamate-induced neuronal injury at least in part by inhibiting the NMDA receptor–activated ion current.     

Proton pump inhibitors: the beginning of the end or the end of the beginning?

Despite the dramatic success of pharmacological acid suppression in healing peptic ulcers (PUs) and managing patients with gastro-esophageal reflux disease (GERD) a number of challenges remain in the management of acid-related disorders. Several new drugs are currently being investigated to provide a significant advance over current treatments. These include new drug formulations, novel proton pump inhibitors (PPIs) as well as potassium-competitive acid blockers (P-CABs), which have already reached clinical testing. Some others (like NO-releasing antisecretory compounds) are still in preclinical development and require proof of concept in humans. While H(2)-receptor antagonists (especially soluble or OTC formulations) will become the 'antacids of the third millennium' and will be particularly useful for on-demand symptom relief, clinicians will continue to rely on PPIs to control acid secretion in GERD and other acid-related diseases. Since an increasing proportion of patients fail to respond to the best PPI treatment, more potent and long-acting drugs and more effective regimens are needed.     

Hydrogen sulfide: from the smell of the past to the mediator of the future?

Gases such as nitric oxide and carbon monoxide play important roles both in normal physiology and in disease. In recent years, interest has been directed towards other naturally occurring gases, notably hydrogen sulfide (H₂S), which is both a potent vasodilator and a mediator of long-term potentiation in the brain. This article focuses on recent work that suggests a role for H₂S, and perhaps other gases, in the CNS and cardiovascular system.     

A Gαs DREADD Mouse for Selective Modulation of cAMP Production in Striatopallidal Neurons

Here, we describe a newly generated transgenic mouse in which the Gs DREADD (rM3Ds), an engineered G protein-coupled receptor, is selectively expressed in striatopallidal medium spiny neurons (MSNs). We first show that in vitro, rM3Ds can couple to Gα_olf and induce cAMP accumulation in cultured neurons and HEK-T cells. The rM3Ds was then selectively and stably expressed in striatopallidal neurons by creating a transgenic mouse in which an adenosine2A (adora2a) receptor-containing bacterial artificial chromosome was employed to drive rM3Ds expression. In the adora2A-rM3Ds mouse, activation of rM3Ds by clozapine-N-oxide (CNO) induces DARPP-32 phosphorylation, consistent with the known consequence of activation of endogenous striatal Gα_s-coupled GPCRs. We then tested whether CNO administration would produce behavioral responses associated with striatopallidal G_s signaling and in this regard CNO dose-dependently decreases spontaneous locomotor activity and inhibits novelty induced locomotor activity. Last, we show that CNO prevented behavioral sensitization to amphetamine and increased AMPAR/NMDAR ratios in transgene-expressing neurons of the nucleus accumbens shell. These studies demonstrate the utility of adora2a-rM3Ds transgenic mice for the selective and noninvasive modulation of Gα_s signaling in specific neuronal populations in vivo.This unique tool provides a new resource for elucidating the roles of striatopallidal MSN Gα_s signaling in other neurobehavioral contexts.     

Protection of Dopaminergic Neurons in a Mouse Model of Parkinson’s Disease by a Physically-Modified Saline Containing Charge-Stabilized Nanobubbles

Neuroinflammation underlies the pathogenesis of various neurodegenerative disorders including Parkinson’s disease (PD). Despite intense investigations, no effective therapy is available to stop its onset or halt its progression. RNS60 is a novel therapeutic containing charge-stabilized nanobubbles in saline, generated by subjecting normal saline to Taylor-Couette-Poiseuille flow under elevated oxygen pressure. Recently, we have delineated that RNS60 inhibits the expression of proinflammatory molecules in glial cells via type 1A phosphatidylinositol-3 kinase (PI3K)-mediated upregulation of IκBα. In this study, we demonstrate that RNS60 inhibited the expression of proinflammatory molecules in cultured microglial cells stimulated by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridium ion (MPP⁺) and in vivo in the nigra of MPTP-intoxicated mice. While investigating the underlying mechanisms, we found that MPTP intoxication rapidly stimulated the activation of type IB PI3K p110γ in the nigra, while suppressing the activation of type IA PI3K p110α/β. Interestingly, RNS60 treatment suppressed the activation of p110γ PI3K, while inducing the activation of p110α/β PI3K in the nigra of MPTP-intoxicated mice. Accordingly, RNS60 treatment increased the level of IκBα and inhibited the activation of NF-κB in the SNpc of MPTP-intoxicated mice. These findings paralleled dopaminergic neuronal protection, normalized striatal neurotransmitters, and improved motor functions in MPTP-intoxicated mice. These results strongly suggest a promising therapeutic role of this simple modified saline in PD and other neuroinflammatory disorders.     

A review of the fate of inhaled α-quartz in the lungs of rats

The distribution of dust particles within the lungs and their excretion are highly associated with their pulmonary toxicity. Literature was reviewed to discern pulmonary translocation pathways for inhaled α-quartz compared to those for inhaled TiO₂. Accordingly, it was hypothesized α-quartz particles in the alveoli were phagocytized by alveolar macrophages but silica-containing macrophages remained in the alveoli for longer time in contrast to the rapid elimination from the alveoli seen for TiO₂-containing macrophages. In addition, it was presumed that free silica particles are translocated in the interstitium, possibly through the cytoplasm of Type I epithelial cells, as observed with TiO₂. Free silica particles are presumed to be phagocytized by interstitial macrophages soon after the particles penetrate the interstitium; these dust cells are then translocated to the ciliated airway regions in the lumen through bronchus-associated lymphoid tissue (BALT). The pulmonary retention half-time of dust particles in rats exposed to α-quartz is several times longer than that of rats exposed to TiO₂, as long as the lung dust burden is ≈ 3?mg. The reduced pulmonary particle clearance ability in rats exposed to α-quartz aerosol is presumably attributed to the long-term retention of dust cells both in the alveoli and in the interstitium; this retention may be caused by the reduced chemotactic abilities of α-quartz-containing dust cells. However, the accumulation of α-quartz-containing dust cells in the lungs is not associated with the occurrence of pulmonary inflammation.     

Blockade of γ-aminobutyric acid-receptors of the B-subtype inhibits the dopamine-induced enhancement of the release of cholecystokinin-like immunoreactivity from slices of rat dorsal caudatoputamen

Summary When slices of rat dorsal caudatoputamen (= neostriatum) are incubated in vitro, Choecystokinin-like immunoreactivity (CCK-LI) is released upon addition of veratridine (3.75 mol/l). This release is affected by dopamine and by -aminobutyric acid (GABA)-receptor agonists. Dopamine enhances the release by stimulating dopamine D₂-receptors and decreases it via D₁-receptors. GABA_A-receptor agonists enhance the veratridine-induced release of CCK-LI, while GABA_B-receptor agonists decrease it. In the present investigation, it was examined whether GABA-receptors are involved in the effect which dopamine exerts via D₂-receptors. The GABA_A-receptor antagonist bicuculline (10 mol/l)and the blocker of the GABA_A-receptor ionophore picrotoxin (1 mol/l) did not affect the dopamine (0.1 mol/1)-induced increase in the release of CCK-LI. However, the GABA_A-receptor agonist muscimol (1 mol/l) not only enhanced the release of CCK-LI, but also prevented a further enhancement by dopamine (0.1 mol/l). This effect of muscimol was blocked by bicuculline (10 mol/l). In the presence of -amino-n-valeric acid (0.1 mmol/l), which has been described to block GABA_B-receptors, dopamine no longer enhanced the veratridine-induced release of CCK-LI. -Amino-n-valeric acid also inhibited the pronounced enhancement of the release of CCK-LI caused by dopamine (0.1 mol/l) and 1 mol/l in the presence of the preferential D₁-receptor antagonist SCH 23390. The effect of -amino-n-valeric acid persisted in the presence of bicuculline (10 mol/l and 100 mol/l). (+)-Baclofen, a partial agonist at GABA_B-receptors, and the stereoisomer (–)-baclofen, a full agonist, also prevented the effect of dopamine on the veratridine-induced release of CCK-LI. The effects of both drugs may be due to desensitization of GABA_B-receptors, which has been described to develop quite rapidly. It is concluded that -amino-n-valeric acid blocks GABA_B-receptors and in this way prevents the enhancement of the veratridine-induced release of CCK-LI caused by dopamine via D₂-receptors. These data are interpreted as evidence that dopamine and GABA-neurons can directly or indirectly interact in the rat neostriatum. Send offprint requests to D. K. Meyer at the above address