Memantine inhibits α3β2-nAChRs-mediated nitrergic neurogenic vasodilation in porcine basilar arteries

Acute and chronic glutamate NMDA antagonist treatment attenuates dopamine D1 antagonist-induced reduction of nicotine self-administration in female rats

Multiple interacting neural systems are involved in sustaining nicotine reinforcement. We and others have shown that dopamine D1 receptors and glutamate NMDA receptors both play important roles in nicotine reinforcement. Blockade of D1 receptors with the antagonist SCH-23390 (0.02 mg/kg) both acutely and chronically significantly decreased nicotine self-administration in rats. Blockade of NMDA receptors (10 mg/kg) acutely with memantine significantly increased nicotine self-administration, but chronic blockade of NMDA receptors with memantine significantly decreased nicotine self-administration. The current study examined the interactions of acute and chronic administration of SCH-23390 and memantine on nicotine self-administration in female rats. Replicating earlier studies, acute and chronic SCH-23390 significantly decreased nicotine self-administration and memantine had a biphasic effect with acute administration increasing nicotine self-administration and chronic memantine showed a non-significant trend toward decreasing it. However, chronic interaction study showed that memantine significantly attenuated the decrease in nicotine self-administration caused by chronic SCH-23390. These studies provide important information that memantine attenuates the efficacy of D1 antagonist SCH 23390 in reducing nicotine-self-administration. These two drugs do not appear to have mutually potentiating effects to aid tobacco cessation.

Cognitive- and memory-enhancing effects of Augmentin in Alzheimer’s rats through regulation of gene expression and neuronal cell apoptosis

Introduction: Alzheimer’s disease (AD) is the most common type of dementia among older persons. This study looked at how Augmentin affected behavior, gene expression, and apoptosis in rats in which AD had been induced by scopolamine.

Methods: The rats were divided into five groups: control, sham, memantine, Augmentin, and pre-Augmentin (the last group received Augmentin before scopolamine administration and was treated with memantine). A Morris water maze was utilized to measure spatial memory in the animals, and real-time quantitative reverse transcription PCR (qRT-PCR) and flow cytometry were employed to analyze gene expression and neuronal cell apoptosis, respectively.

Results: Memantine and Augmentin increased spatial memory in healthy rats. The use of scopolamine impaired spatial memory. Both Augmentin and memantine improved spatial memory in AD rats, particularly in the group that received memantine; however, the outcomes were more substantial when Augmentin was administered before scopolamine was given to induce AD. Furthermore, the expression of presenilin-2 (PSEN2) and inositol-trisphosphate 3-kinase B (ITPKB) increased, whereas the expression of DEAD-box helicase 5 (DDX5) fell in the AD-treated groups; however, the results were more substantial after combination therapy. According to flow cytometry studies, Augmentin pre-treatment reduced apoptosis in AD rats.

Discussion: The results showed that administering Augmentin to AD rats before memantine improved their spatial memory, reduced neuronal cell death, upregulated protective genes, and suppressed genes involved in AD pathogenesis.

Indoor Secondary Pollutants Cannot Be Ignored: Third-Hand Smoke

Smoking has been recognized by the World Health Organization (WHO) as the fifth highest threat to humanity. Smoking, a leading disease promoter, is a major risk factor for non-communicable diseases (NCDs) such as cancer, cardiovascular disease, diabetes, and chronic respiratory diseases. NCDs account for 63% of all deaths worldwide. Passive smoking is also a health risk. Globally, more than a third of all people are regularly exposed to harmful smoke. Air pollution is a common global problem in which pollutants emitted into the atmosphere undergo a series of physical or chemical reactions to produce various oxidation products, which are often referred to as secondary pollutants. Secondary pollutants include ozone (O₃), sulfur trioxide (SO₃), nitrogen dioxide (NO₂), and respirable particulate matter (PM). It is worth mentioning that third-hand smoke (THS), formed by the reaction of nicotine with second-hand smoke (SHS) caused by indoor O₃ or nitrous acid (HONO), is a major indoor secondary pollutant that cannot be ignored. As a form of indoor air pollution that is relatively difficult to avoid, THS exists in any corner of the environment where smokers live. In this paper, we summarize the important research progress on the main components, detection, and toxicity of THS and look forward to future research directions. Scientific understanding of THS and its hazards will facilitate smoking bans in indoor and public places and raise public concern for how to prevent and remove THS.

Protective Felix-Culpa Effect of Superior Sympathetic Cervical Ganglion Degenerations on Prevention of Basilar Artery Spasm Following Subarachnoid Hemorrhage: A Preliminary Experimental Study

BACKGROUND

Posterior cerebral blood flow is regulated by the basilar arteries (BA). Its vasospasm of basilar arteries (BA) can occur following subarachnoid hemorrhage (SAH). Superior cervical sympathetic ganglia (SCG) fibers have a vasoconstrictor effect on the BA. We aimed to investigate the relationship between the degenerated neuron density of the SCG and the severity of BA vasospasm after experimental subarachnoid hemorrhage.

METHODS

Twenty-four rabbits were used. Five of them were used as the control group, and five of them were used as the SHAM group. Experimental subarachnoid hemorrhages were performed in the remaining fourteen animals (study group) by injecting homologous blood into cisterna magna. After three weeks of injection, neuron densities of SCG and the severity of BA vasospasm index values (VSI) were examined histopathologically and compared statistically.

RESULTS

The mean VSI was 0.669±0.1129 in the control group, 0.981±0.159 in the SHAM group, and 1.512±0.298 in the study group. The mean degenerated neuronal density of SCG was 436±79/mm³ in severe vasospasm (n=3), 841±101/mm³ in moderate vasospasm (n=4), and 1.921±849/mm³ in the less vasospasm detected animals (n=6).

CONCLUSION

This study shows an inverse relationship between the degenerated neuronal density in the SCG and VSI values. This finding indicates a diminished sympathetic input from the superior cervical ganglion (SCG) resulting in a beneficial (the Felix-culpa) effect by dilating the lumen diameter of the basilar artery (BA), so superior sympathetic cervical ganglion degeneration following SAH protects the basilar artery spasm.

Activation of Neuropeptide Y2 Receptor Can Inhibit Global Cerebral Ischemia-Induced Brain Injury

Cardiopulmonary arrest (CA) can greatly impact a patient's life, causing long-term disability and death. Although multi-faceted treatment strategies against CA have improved survival rates, the prognosis of CA remains poor. We previously reported asphyxial cardiac arrest (ACA) can cause excessive activation of the sympathetic nervous system (SNS) in the brain, which contributes to cerebral blood flow (CBF) derangements such as hypoperfusion and, consequently, neurological deficits. Here, we report excessive activation of the SNS can cause enhanced neuropeptide Y levels. In fact, mRNA and protein levels of neuropeptide Y (NPY, a 36-amino acid neuropeptide) in the hippocampus were elevated after ACA-induced SNS activation, resulting in a reduced blood supply to the brain. Post-treatment with peptide YY_3-36 (PYY_3-36), a pre-synaptic NPY2 receptor agonist, after ACA inhibited NPY release and restored brain circulation. Moreover, PYY_3-36 decreased neuroinflammatory cytokines, alleviated mitochondrial dysfunction, and improved neuronal survival and neurological outcomes. Overall, NPY is detrimental during/after ACA, but attenuation of NPY release via PYY_3-36 affords neuroprotection. The consequences of PYY_3-36 inhibit ACA-induced 1) hypoperfusion, 2) neuroinflammation, 3) mitochondrial dysfunction, 4) neuronal cell death, and 5) neurological deficits. The present study provides novel insights to further our understanding of NPY's role in ischemic brain injury.

Pharmacological Characterizations of anti-Dementia Memantine Nitrate via Neuroprotection and Vasodilation in Vitro and in Vivo

We have previously designed and synthesized a series of novel memantine nitrates, and some of them have shown neuroprotective effects; however, the detailed mechanisms remain unknown. In this study, we demonstrated that MN-12, one of the memantine nitrates, concentration-dependently protected against glutamate-induced neurotoxicity in rat primary cultured cerebellar granule neurons (CGNs). Western blotting assays revealed that MN-12 might possess neuroprotective effects through the inhibition of ERK pathway and activation of PI3K/Akt pathway concurrently. Moreover, MN-12 concentration-dependently dilated precontracted rat middle cerebral artery through activation of NO-cGMP pathway ex vivo. In the 2-vessel occlusion (2VO) rat model, MN-12 alleviated the impairments of spatial memory and motor dysfunction possibly via neuroprotection and improvement of the cerebral blood flow. Furthermore, the results of preliminary pharmacokinetic studies showed that MN-12 might quickly distribute to the major organs including the brain, indicating that MN-12 could penetrate the blood-brain barrier. Taken together, MN-12 might provide multifunctional therapeutic benefits for dementia associated with Alzheimer's disease, vascular dementia, and ischemic stroke, via neuroprotection and vessel dilation to improve the cerebral blood flow.

Daily memantine treatment blunts hedonic response to sucrose in rats

RATIONALE

Preclinical and clinical studies suggest the potential use of memantine in the treatment of binge eating disorder. The aim of this study was to further investigate the mechanisms by which memantine influences the motivational aspects of ingestion through the analysis of licking microstructure. To interpret treatment effects in relation to drug action at specific functionally relevant times, we compared the effect of two different administration schedules.

METHODS

Memantine was administered daily for a week, either 1 h before or immediately after a 30-min daily session. The effects on the microstructure of licking for a 10% sucrose solution in rats were examined in the course of treatment and for 15 days after treatment discontinuation.

RESULTS

Treatment before testing reduced ingestion due to reduced burst size and increased latency in the first session. However, a progressive increase in burst number across sessions led to a full recovery of ingestion levels by the end of treatment. Daily post-session administration induced a dramatic decrease of activation of licking behaviour, indicated by reduced burst number, accompanied to reduced burst size. A slow recovery of ingestion took place after treatment discontinuation.

CONCLUSION

These results suggest a reduced hedonic/reward evaluation response, an effect likely due to NMDA receptor blockade occurring during the testing time and support the hypothesis that memantine interferes with the hedonic/non-homeostatic mechanisms regulating food intake and food-seeking. The effect of post-session administration might be explained by the development of conditioned taste aversion.

Alzheimer's Disease Therapeutic Approaches

Alzheimer's disease (AD) was first described and diagnosed by Dr. Alois Alzheimer in 1906 (Hippius and Neundorfer, Dialogues Clin Neurosc 5:101-108, 2003). According to World Health Organization (WHO), AD is the most common cause of dementia, accounting for as many as 60-70% of senile dementia cases and affecting 47.5 million people worldwide (data from 2015) (Dementia Fact Sheet No 362. http://who.int/mediacentre/factsheets/fs362/en/ ). The median survival time after the onset of dementia ranges from 3.3 to 11.7 years (Todd et al. Int J Geriatr Psychiatry 28:1109-1124, 2013). AD is characterized as a severe, chronic, incurable, and progressive neurodegenerative disorder, associated with memory loss and cognition impairment accompanied by abnormal behavior and personality changes (Godyn et al. Pharmacol Rep 68:127-138, 2016). AD is characterized by neuronal death, which usually correlates with the appearance of key neuropathological changes, including acetylcholine deficiency, glutamate excitotoxicity, extracellular deposition of β-amyloid (Aβ plaques), intracellular neurofibrillary tangles by hyperphosphorylated tau protein deposits, neuroinflammation, and widespread neuronal loss (Godyn et al. Pharmacol Rep 68:127-138, 2016; Graham et al. Annu Rev. Med 68:413-430, 2017). The discovery of the degeneration of cholinergic neurons and the reduction of acetylcholine levels in postmortem studies of patients resulted in the use of drugs that leads to the increase of acetylcholine levels in brain (Dubois et al. Lacet Neurol 13:614-629, 2014). At present there is no preventative or curative treatment that interferes with the development of the disease. However, in recent years progress was made in the development of cholinergic drugs which have a positive effect on disease progression. Nowadays, specific drugs that can inhibit the enzyme that degrades acetylcholine are used. The development of new effective drugs involves a difficult and time-consuming process, accompanied by a very high failure rate. In the absence of effective therapies, the estimated number of people with dementia will reach 115 to 131, five million by 2050 (Dubois et al. Lacet Neurol 13:614-629, 2014; Cummings et al. Alzheimers Res Ther 6:37, 2014). Novel therapies and new targets required for developing more effective drugs for the treatment of AD patients are urgently needed.

Biosensors Show the Pharmacokinetics of S-Ketamine in the Endoplasmic Reticulum

The target for the “rapid” (<24 h) antidepressant effects of S-ketamine is unknown, vitiating programs to rationally develop more effective rapid antidepressants. To describe a drug’s target, one must first understand the compartments entered by the drug, at all levels—the organ, the cell, and the organelle. We have, therefore, developed molecular tools to measure the subcellular, organellar pharmacokinetics of S-ketamine. The tools are genetically encoded intensity-based S-ketamine-sensing fluorescent reporters, iSKetSnFR1 and iSKetSnFR2. In solution, these biosensors respond to S-ketamine with a sensitivity, S-slope = delta(F/F₀)/(delta[S-ketamine]) of 0.23 and 1.9/μM, respectively. The iSKetSnFR2 construct allows measurements at <0.3 μM S-ketamine. The iSKetSnFR1 and iSKetSnFR2 biosensors display >100-fold selectivity over other ligands tested, including R-ketamine. We targeted each of the sensors to either the plasma membrane (PM) or the endoplasmic reticulum (ER). Measurements on these biosensors expressed in Neuro2a cells and in human dopaminergic neurons differentiated from induced pluripotent stem cells (iPSCs) show that S-ketamine enters the ER within a few seconds after appearing in the external solution near the PM, then leaves as rapidly after S-ketamine is removed from the extracellular solution. In cells, S-slopes for the ER and PM-targeted sensors differ by <2-fold, indicating that the ER [S-ketamine] is less than 2-fold different from the extracellular [S-ketamine]. Organelles represent potential compartments for the engagement of S-ketamine with its antidepressant target, and potential S-ketamine targets include organellar ion channels, receptors, and transporters.

Therapeutics of Neurotransmitters in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease, characterized by the loss of memory, multiple cognitive impairments and changes in the personality and behavior. Several decades of intense research have revealed that multiple cellular changes are involved in disease process, including synaptic damage, mitochondrial abnormalities and inflammatory responses, in addition to formation and accumulation of amyloid-β (Aβ) and phosphorylated tau. Although tremendous progress has been made in understanding the impact of neurotransmitters in the progression and pathogenesis of AD, we still do not have a drug molecule associated with neurotransmitter(s) that can delay disease process in elderly individuals and/or restore cognitive functions in AD patients. The purpose of our article is to assess the latest developments in neurotransmitters research using cell and mouse models of AD. We also updated the current status of clinical trials using neurotransmitters' agonists/antagonists in AD.

Interruption of perivascular sympathetic nerves of cerebral arteries offers neuroprotection against ischemia

Sympathetic nervous system activity is increased after cardiopulmonary arrest, resulting in vasoconstrictor release from the perivascular sympathetic nerves of cerebral arteries. However, the pathophysiological function of the perivascular sympathetic nerves in the ischemic brain remains unclear. A rat model of global cerebral ischemia (asphyxial cardiac arrest, ACA) was used to investigate perivascular sympathetic nerves of cerebral arteries via bilateral decentralization (preganglionic lesion) of the superior cervical ganglion (SCG). Decentralization of the SCG 5 days before ACA alleviated hypoperfusion and afforded hippocampal neuroprotection and improved functional outcomes. These studies can provide further insights into the functional mechanism(s) of the sympathetic nervous system during ischemia.

NEW & NOTEWORTHY

Interruption of the perivascular sympathetic nerves can alleviate CA-induced hypoperfusion and neuronal cell death in the CA1 region of the hippocampus to enhance functional learning and memory.

Synthesis and biological evaluation of memantine nitrates as a potential treatment for neurodegenerative diseases

A series of memantine nitrate derivatives, as dual functional compounds with neuroprotective and vasodilatory activity for neurodegenerative diseases, was designed and synthesized. These compounds combined the memantine skeleton and a nitrate moiety, and thus inhibited the N-methyl-d-aspartic acid receptor and released NO in the central nervous system. The biological evaluation results revealed that the new memantine nitrates were effective in protecting neurons against glutamate-induced injury in vitro. Moreover, memantine nitrates dilated aortic rings against phenylephrine-induced contraction. The structure-activity relationships of neuroprotection and vasodilation were both analyzed. In further studies, compound MN-05 significantly protected cortical neurons by inhibiting Ca²⁺ influx, reducing free radical production and maintaining the mitochondrial membrane potential. Further research on MN-05 is warranted.

Recent insights into the mode of action of memantine and ketamine

The clinical benefits of the glutamate receptor antagonists memantine and ketamine have helped sustain optimism that glutamate receptors represent viable targets for development of therapeutic drugs. Both memantine and ketamine antagonize N-methyl-D-aspartate receptors (NMDARs), a glutamate receptor subfamily, by blocking the receptor-associated ion channel. Although many of the basic characteristics of NMDAR inhibition by memantine and ketamine appear similar, their effects on humans and to a lesser extent on rodents are strongly divergent. Some recent research suggests that preferential inhibition by memantine and ketamine of distinct NMDAR subpopulations may contribute to the drugs' differential clinical effects. Here we review studies that shed light on possible explanations for differences between the effects of memantine and ketamine.

L-type calcium channels in sympathetic α3β2-nAChR-mediated cerebral nitrergic neurogenic vasodilation

AIM

Nicotine stimulation of α3β2-nicotinic acetylcholine receptors (α3β2-nAChRs) located on sympathetic nerves innervating basilar arteries causes calcium-dependent noradrenaline release, leading to activation of parasympathetic nitrergic nerves and dilation of basilar arteries. This study aimed to investigate the major subtype of calcium channels located on cerebral peri-vascular sympathetic nerves, which is involved in nicotine-induced α3β2-nAChR-mediated nitrergic vasodilation in basilar arteries.

METHODS

Nicotine- and transmural nerve stimulation (TNS)-induced dilation of isolated porcine basilar arteries was examined using in vitro tissue bath. Nicotine-induced calcium influx, nicotine-induced noradrenaline release and nicotine-induced inward currents were evaluated in rat superior cervical ganglion (SCG) neurones, peri-vascular sympathetic nerves of porcine basilar arteries and α3β2-nAChRs-expressing oocytes respectively. mRNA and protein expression of Cav 1.2 and Cav 1.3 channels were detected by RT-PCR, Western blotting and immunohistochemistry.

RESULTS

Nicotine-induced vasodilation was not affected by ω-agatoxin TK (selective P/Q-type calcium channel blocker) or ω-conotoxin GVIA (N-type calcium channel blocker). The vasodilation, however, was inhibited by nicardipine (L-type calcium channel blocker) in concentrations which did not affect TNS-induced vasodilation, suggesting the specific blockade. Nicardipine concentration-dependently inhibited nicotine-induced calcium influx in rat SCG neurones and reduced nicotine-induced noradrenaline release from peri-vascular sympathetic nerves of porcine basilar arteries. Nicardipine (10 μm), which significantly blocked nicotine-induced vasorelaxation by 70%, did not appreciably affect nicotine-induced inward currents in α3β2-nAChRs-expressing oocytes. Furthermore, the mRNAs and proteins of Cav 1.2 and Cav 1.3 channels were expressed in porcine SCG and peri-vascular nerve terminals.

CONCLUSION

The sympathetic neuronal calcium influx through L-type calcium channels is modulated by α3β2-nAChRs. This calcium influx causes noradrenaline release, initiating sympathetic-parasympathetic (axo-axonal) interaction-induced nitrergic dilation of porcine basilar arteries.

Therapeutics of Alzheimer's disease: Past, present and future

Alzheimer's disease (AD) is the most common cause of dementia worldwide. The etiology is multifactorial, and pathophysiology of the disease is complex. Data indicate an exponential rise in the number of cases of AD, emphasizing the need for developing an effective treatment. AD also imposes tremendous emotional and financial burden to the patient's family and community. The disease has been studied over a century, but acetylcholinesterase inhibitors and memantine are the only drugs currently approved for its management. These drugs provide symptomatic improvement alone but do less to modify the disease process. The extensive insight into the molecular and cellular pathomechanism in AD over the past few decades has provided us significant progress in the understanding of the disease. A number of novel strategies that seek to modify the disease process have been developed. The major developments in this direction are the amyloid and tau based therapeutics, which could hold the key to treatment of AD in the near future. Several putative drugs have been thoroughly investigated in preclinical studies, but many of them have failed to produce results in the clinical scenario; therefore it is only prudent that lessons be learnt from the past mistakes. The current rationales and targets evaluated for therapeutic benefit in AD are reviewed in this article. This article is part of the Special Issue entitled 'The Synaptic Basis of Neurodegenerative Disorders'.