GABA, glutamate, dopamine and serotonin transporters expression on memory formation and amnesia

Comprehensive Neurotoxicity of Lead Halide Perovskite Nanocrystals in Nematode Caenorhabditis elegans

To date, all-inorganic lead halide perovskite quantum dots have emerged as promising materials for photonic, optoelectronic devices, and biological applications, especially in solar cells, raising numerous concerns about their biosafety. Most of the studies related to the toxicity of perovskite quantum dots (PeQDs) have focused on the potential risks of hybrid perovskites by using zebrafish or human cells. So far, the neurotoxic effects and fundamental mechanisms of PeQDs remain unknown. Herein, a comprehensive methodology is designed to investigate the neurotoxicity of PeQDs by using Caenorhabditis elegans as a model organism. The results show that the accumulation of PeQDs mainly focuses on the alimentary system and head region. Acute exposure to PeQDs results in a decrease in locomotor behaviors and pharyngeal pumping, whereas chronic exposure to PeQDs causes brood decline and shortens lifespan. In addition, some abnormal issues occur in the uterus during reproduction assays, such as vulva protrusion, impaired eggs left in the vulva, and egg hatching inside the mother. Excessive reactive oxygen species formation is also observed. The neurotoxicity of PeQDs is explained by gene expression. This study provides a complete insight into the neurotoxicity of PeQD and encourages the development of novel nontoxic PeQDs.

The effects of ruminant milk treatments on hippocampal, striatal, and prefrontal cortex gene expression in pigs as a model for the human infant

While infant formula is usually bovine milk-based, interest in other ruminant milk-based formulas is growing. However, whether different ruminant milk treatments with varying nutrient compositions influence the infant’s brain development remains unknown. The aim was to determine the effects of consuming bovine, caprine, or ovine milk on brain gene expression in the early postnatal period using a pig model of the human infant. Starting at postnatal day 7 or 8, pigs were exclusively fed bovine, ovine, or caprine milk for 15 days. The mRNA abundance of 77 genes in the prefrontal cortex, hippocampus, and striatum regions was measured at postnatal day 21 or 22 using NanoString. The expression level of two hippocampal and nine striatal genes was most affected by milk treatments, particularly ovine milk. These modulatory genes are involved in glutamate, gamma-aminobutyric acid, serotonin, adrenaline and neurotrophin signaling and the synaptic vesicle cycle. The expression level of genes involved in gamma-aminobutyric acid signaling was associated with pigs’ lactose intake. In contrast, milk treatments did not affect the mRNA abundance of the genes in the prefrontal cortex. This study provides the first evidence of the association of different ruminant milk treatments with brain gene expression related to cognitive function in the first 3 months of postnatal life.

Effects of lanthanum nitrate on behavioral disorder, neuronal damage and gene expression in different developmental stages of Caenorhabditis elegans

Rare earth elements (REEs) are widely used in the industry, agriculture, biomedicine, aerospace, etc, and have been shown to pose toxic effects on animals, as such, studies focusing on their biomedical properties are gaining wide attention. However, environmental and population health risks of REEs are still not very clear. Also, the REEs damage to the nervous system and related molecular mechanisms needs further research. In this study, the L1 and L4 stages of the model organism Caenorhabditis elegans were used to evaluate the effects and possible neurotoxic mechanism of lanthanum(III) nitrate hexahydrate (La(NO₃)₃·6H₂O). For the L1 and L4 stage worms, the 48-h median lethal concentrations (LC₅₀s) of La(NO₃)₃·6H₂O were 93.163 and 648.0 mg/L respectively. Our results show that La(NO₃)₃·6H₂O induces growth inhibition and defects in behavior such as body length, body width, body bending frequency, head thrashing frequency and pharyngeal pumping frequency at the L1 and L4 stages in C. elegans. The L1 stage is more sensitive to the toxicity of lanthanum than the L4 stage worms. Using transgenic strains (BZ555, EG1285 and NL5901), we found that La(NO₃)₃·6H₂O caused the loss or break of soma and dendrite neurons in L1 and L4 stages; and α-synuclein aggregation in L1 stage, indicating that Lanthanum can cause toxic damage to dopaminergic and GABAergic neurons. Mechanistically, La(NO₃)₃·6H₂O exposure inhibited or activated the neurotransmitter transporters and receptors (glutamate, serotonin and dopamine) in C. elegans, which regulate behavior and movement functions. Furthermore, significant increase in the production of reactive oxygen species (ROS) was found in the L4 stage C. elegans exposed to La(NO₃)₃·6H₂O. Altogether, our data show that exposure to lanthanum can cause neuronal toxic damage and behavioral defects in C. elegans, and provide basic information for understanding the neurotoxic effect mechanism and environmental health risks of rare earth elements.

Bidirectional role of dopamine in learning and memory-active forgetting

Dopaminergic neurons projecting from the Substantia Nigra to the Striatum play a critical role in motor functions while dopaminergic neurons originating in the Ventral Tegmental Area (VTA) and projecting to the Nucleus Accumbens, Hippocampus and other cortical structures regulate rewarding learning. While VTA mainly consists of dopaminergic neurons, excitatory (glutamate) and inhibitory (GABA) VTA-neurons have also been described: these neurons may also modulate and contribute to shape the final dopaminergic response, which is critical for memory formation. However, given the large amount of information that is handled daily by our brain, it is essential that irrelevant information be deleted. Recently, apart from the well-established role of dopamine (DA) in learning, it has been shown that DA plays a critical role in the intrinsic active forgetting mechanisms that control storage information, contributing to the deletion of a consolidated memory. These new insights may be instrumental to identify therapies for those disorders that involve memory alterations.

Chronic exposure to UV-aged microplastics induces neurotoxicity by affecting dopamine, glutamate, and serotonin neurotransmission in Caenorhabditis elegans

Microplastics are ubiquitous in all environments and exert toxic effects in various organisms. However, the neurotoxicity and underlying mechanisms of long-term exposure to MPs aged under UV radiation remain largely unclear. In this study, Caenorhabditis elegans was treated with 0.1-100 μg/L virgin and aged polystyrene microplastics (PS-MPs) for 10 d, with locomotion behavior, neuronal development, neurotransmitter content, and neurotransmission-related to gene expression as endpoints. Using locomotion behavior as an endpoint, chronic exposure to aged PS-MPs at low concentrations (1 μg/L) caused more severe neurotoxicity than that to virgin PS-MPs. In transgenic nematodes, exposure to 10-100 μg/L aged PS-MPs significantly influenced the fluorescence intensity and percentage of worms with neurodegeneration of dopaminergic, glutamatergic, and serotonergic neurons compared with control. Further investigations showed that the content of glutamate, serotonin, and dopamine was significantly influenced in nematodes chronically exposed to 100 μg/L of aged PS-MPs. Similarly, neurotransmission-related gene (e.g., eat-4, dat-1, and tph-1) expression was also altered in nematodes. These results indicate that aged PS-MPs exert neurotoxicity owing to their effects on dopamine, glutamate, and serotonin neurotransmission. This study provides insights into the underlying mechanisms and potential risks of PS-MPs after UV radiation.

Forgetting Unwanted Memories: Active Forgetting and Implications for the Development of Psychological Disorders

Intrusive memories are a common feature of many psychopathologies, and suppression-induced forgetting of unwanted memories appears as a critical ability to preserve mental health. In recent years, biological and cognitive studies converged in revealing that forgetting is due to active processes. Recent neurobiological studies provide evidence on the active role of main neurotransmitter systems in forgetting, suggesting that the brain actively works to suppress retrieval of unwanted memories. On the cognitive side, there is evidence that voluntary and involuntary processes (here termed "intentional" and "incidental" forgetting, respectively) contribute to active forgetting. In intentional forgetting, an inhibitory control mechanism suppresses awareness of unwanted memories at encoding or retrieval. In incidental forgetting, retrieval practice of some memories involuntarily suppresses the retrieval of other related memories. In this review we describe recent findings on deficits in active forgetting observed in psychopathologies, like post-traumatic stress disorder, depression, schizophrenia, and obsessive-compulsive disorder. Moreover, we report studies in which the role of neurotransmitter systems, known to be involved in the pathogenesis of mental disorders, has been investigated in active forgetting paradigms. The possibility that biological and cognitive mechanisms of active forgetting could be considered as hallmarks of the early onset of psychopathologies is also discussed.

The multi-faceted impact of methamphetamine on Alzheimer's disease: From a triggering role to a possible therapeutic use

Although it has been initially synthesized for therapeutic purposes and currently FDA-approved and prescribed for obesity, attention-deficit/hyperactivity disorder, narcolepsy and depression, methamphetamine became a recreational drug that is nowadays massively manufactured illegally. Because it is a powerful and extremely addictive psychotropic agent, its abuse has turned out to become a major health problem worldwide. Importantly, the numerous effects triggered by this drug induce neurotoxicity in the brain ultimately leading to serious neurological impairments, tissue damage and neuropsychological disturbances that are reminiscent to most of the symptoms observed in Alzheimer's disease and other pathological manifestations in aging brain. In this context, there is a growing number of compelling evidence linking methamphetamine abuse with a higher probability of developing premature Alzheimer's disease and consequent neurodegeneration. This review proposes to establish a broad assessment of the effects that this drug can generate at the cellular and molecular levels in connection with the development of the age-related Alzheimer's disease. Altogether, the objective is to warn against the long-term effects that methamphetamine abuse may convey on young consumers and the increased risk of developing this devastating brain disorder at later stages of their lives, but also to discuss a more recently emerging concept suggesting a possible use of methamphetamine for treating this pathology under proper and strictly controlled conditions.

Voltammetric evidence for discrete serotonin circuits, linked to specific reuptake domains, in the mouse medial prefrontal cortex

The medial prefrontal cortex (mPFC) is an important brain region, that controls a variety of behavioral and functional outputs. As an important step in characterizing mPFC functionality, in this paper we focus on chemically defining serotonin transmission in this area. We apply cutting-edge analytical methods, fast-scan cyclic voltammetry (FSCV) and fast-scan controlled adsorption cyclic voltammetry (FSCAV), pioneered in our laboratory, for the first real-time in vivo analysis of serotonin in the mPFC. In prior in vivo work in the substantia nigra, pars reticulata, we found that our sub-second measurements of a single evoked serotonin release were subject to two clearance mechanisms. These mechanisms were readily modeled via Uptake 1, mediated by the serotonin transporters (SERTs), and Uptake 2, mediated by monoamine transporters (dopamine transporters (DATs), norepinephrine transporters (NETs), and organic cation transporters (OCTs)). Here in the mPFC, for the first time to our knowledge, we observe two release events in response to a single stimulation of the medial forebrain bundle (MFB). Of particular note is that each response is tied to a discrete reuptake profile comprising both Uptake 1 and 2. We hypothesize that two distinct populations of serotonin axons traverse the MFB and terminate in different domains with specific reuptake profiles. We test and confirm this hypothesis using a multifaceted pharmacological, histological and mathematical approach. We thus present evidence for a highly elaborate biochemical organization that regulates serotonin chemistry in the mPFC. This knowledge provides a solid foundation on which to base future studies of the involvement of the mPFC in brain function and behavior.

Effects of 5-HT5A receptor blockade on amnesia or forgetting

Previously the effects (0.01-3.0 mg/kg) of post-training SB-699551 (a 5-HT_5A receptor antagonist) were reported in the associative learning task of autoshaping, showing that SB-699551 (0.1 mg/kg) decreased lever-press conditioned responses (CR) during short-term (STM; 1.5-h) or (3.0 mg/kg) long-term memory (LTM; 24-h); relative to the vehicle animals. Moreover, as pro-cognitive efficacy of SB-699551 was reported in the ketamine-model of schizophrenia. Hence, firstly aiming improving performance (conditioned response, CR), in this work autoshaping lever-press vs. nose-poke response was compared; secondly, new set of animals were randomly assigned to SB-699551 plus forgetting or amnesia protocols. Results show that the nose-poke operandum reduced inter-individual variance, increased CR and produced a progressive CR until 48-h. After one week of no training/testing sessions (i.e., interruption of 216 h), the forgetting was observed; i.e., the CR% of control-saline group significantly decreased. In contrast, SB-699551 at 0.3 and 3.0 mg/kg prevents forgetting. Additionally, as previously reported the non-competitive NMDA receptor antagonist dizocilpine (0.2 mg/kg) or the non-selective cholinergic antagonist scopolamine (0.3 mg/kg) decreased CR in STM. SB-699551 (0.3 mg/kg) alone also produced amnesia-like effect. Co-administration of SB-699551-dizocilpine or SB-699551-scopolamine reversed the SB-699551 induced-amnesic effects in LTM (24-h). Nose-poke seems to be a reliable operandum. The anti-amnesic and anti-forgetting mechanisms of amnesic SB-699551-dose remain unclear. The present findings are consistent with the notion that low doses of 5-HT_5A receptor antagonists might be useful for reversing memory deficits associated to forgetting and amnesia. Of course, further experiments are necessary.

Frameworking memory and serotonergic markers

The evidence for neural markers and memory is continuously being revised, and as evidence continues to accumulate, herein, we frame earlier and new evidence. Hence, in this work, the aim is to provide an appropriate conceptual framework of serotonergic markers associated with neural activity and memory. Serotonin (5-hydroxytryptamine [5-HT]) has multiple pharmacological tools, well-characterized downstream signaling in mammals’ species, and established 5-HT neural markers showing new insights about memory functions and dysfunctions, including receptors (5-HT1A/1B/1D, 5-HT2A/2B/2C, and 5-HT3-7), transporter (serotonin transporter [SERT]) and volume transmission present in brain areas involved in memory. Bidirectional influence occurs between 5-HT markers and memory/amnesia. A growing number of researchers report that memory, amnesia, or forgetting modifies neural markers. Diverse approaches support the translatability of using neural markers and cerebral functions/dysfunctions, including memory formation and amnesia. At least, 5-HT1A, 5-HT4, 5-HT6, and 5-HT7receptors and SERT seem to be useful neural markers and therapeutic targets. Hence, several mechanisms cooperate to achieve synaptic plasticity or memory, including changes in the expression of neurotransmitter receptors and transporters.

Parthenolide, an NF-κB Inhibitor Ameliorates Diabetes-Induced Behavioural Deficit, Neurotransmitter Imbalance and Neuroinflammation in Type 2 Diabetes Rat Model

Diabetes is associated with behavioural and neurochemical alterations. In this manuscript, we are reporting the beneficial effects of parthenolide, an NF-κB inhibitor on behavioural and neurochemical deficits in type 2 diabetic rat model. Diabetes was induced by high-fat diet followed by low dose of streptozotocin (35 mg/kg). Elevated plus maze, open-field, MWM and passive avoidance test paradigm were used to assess behavioural and cognitive deficits. Three-week treatment of parthenolide (0.25 and 0.50 mg/kg; i.p.) attenuated diabetes-induced alteration in cognitive function in Morris water maze and passive avoidance test. Anxiety-like behaviour was also reduced by parthenolide treatment. Moreover, TNF-α and IL-6 levels were significantly decreased in cortex and hippocampus of parthenolide-treated rats. Three-week parthenolide treatment also toned down the alteration of GABA and glutamate homoeostasis. Results of this study corroborate the involvement of neuroinflammation in the development of behavioural and neurochemical deficits in diabetic animals and point towards the therapeutic potential of parthenolide in diabetes-induced alteration of learning, memory and anxiety behaviour.

The interaction of central nitrergic and GABAergic systems on food intake in neonatal layer-type chicks

Most physiological behaviors such as food intake are controlled by the hypothalamus and its nuclei. It has been demonstrated that injection of the paraventricular nucleus of the hypothalamus with nitric oxide (NO) donors elicited changes in the concentration of some amino acids, including GABA. Also, central nitrergic and GABAergic systems are known to provide inputs to the paraventricular nucleus and are involved in food intake control. Therefore, the present study examines the probable interaction of central nitrergic and GABAergic systems on food intake in neonatal layer-type chicks. The results of this study showed that intracerebroventricular (ICV) injection of L-arginine (400 and 800 nmol), as a NO donor, significantly decreased food intake (P < 0.001), but ICV injection of Nω-Nitro-L-arginine methyl ester (L-NAME) (200 and 400 nmol), a NO synthesis inhibitor, increased food intake (P < 0.001). In addition, the orexigenic effect of gaboxadol (0.2 µg), a GABAA agonist, was significantly attenuated in ICV co-injection of L-arginine (200 nmol) and gaboxadol (0.2 µg) (P < 0.001), but it was significantly amplified in ICV co-injection of L-NAME (100 nmol) and gaboxadol (0.2 µg) (P < 0.001). On the other hand, the orexigenic effect of baclofen (0.2 µg), a GABAB agonist, did not change in ICV co-injection of L-arginine (200 nmol) or L-NAME (100 nmol) with baclofen (0.2 µg) (P > 0.05). Also, the hypophagic effect of L-arginine (800 nmol) was significantly amplified in ICV co-injection of picrotoxin (0.5 µg), a GABAA antagonist, or CGP54626 (21 ng), a GABAB antagonist, with L-arginine (800 nmol) (P < 0.001). These results probably suggest an interaction of central nitrergic and GABAergic systems on food intake in neonatal layer-type chicks and GABAA receptors play a major role in this interaction.

MPA-capped CdTe quantum dots exposure causes neurotoxic effects in nematode Caenorhabditis elegans by affecting the transporters and receptors of glutamate, serotonin and dopamine at the genetic level, or by increasing ROS, or both

As quantum dots (QDs) are widely used in biomedical applications, the number of studies focusing on their biological properties is increasing. While several studies have attempted to evaluate the toxicity of QDs towards neural cells, the in vivo toxic effects on the nervous system and the molecular mechanisms are unclear. The aim of the present study was to investigate the neurotoxic effects and the underlying mechanisms of water-soluble cadmium telluride (CdTe) QDs capped with 3-mercaptopropionic acid (MPA) in Caenorhabditis elegans (C. elegans). Our results showed that exposure to MPA-capped CdTe QDs induced behavioral defects, including alterations to body bending, head thrashing, pharyngeal pumping and defecation intervals, as well as impaired learning and memory behavior plasticity, based on chemotaxis or thermotaxis, in a dose-, time- and size-dependent manner. Further investigations suggested that MPA-capped CdTe QDs exposure inhibited the transporters and receptors of glutamate, serotonin and dopamine in C. elegans at the genetic level within 24 h, while opposite results were observed after 72 h. Additionally, excessive reactive oxygen species (ROS) generation was observed in the CdTe QD-treated worms, which confirmed the common nanotoxicity mechanism of oxidative stress damage, and might overcome the increased gene expression of neurotransmitter transporters and receptors in C. elegans induced by long-term QD exposure, resulting in more severe behavioral impairments.

Cronobacter sakazakii infection alters serotonin transporter and improved fear memory retention in the rat

It is well established that Cronobacter sakazakii infection cause septicemia, necrotizing enterocolitis and meningitis. In the present study, we tested whether the C. sakazakii infection alter the learning and memory through serotonin transporter (SERT). To investigate the possible effect on SERT, on postnatal day-15 (PND-15), wistar rat pups were administered with single dose of C. sakazakii culture (infected group; 10⁷ CFU) or 100 μL of Luria-Bertani broth (medium control) or without any treatment (naïve control). All the individuals were subjected to passive avoidance test on PND-30 to test their fear memory. We show that single dose of C. sakazakii infection improved fear memory retention. Subsequently, we show that C. sakazakii infection induced the activation of toll-like receptor-3 and heat-shock proteins-90 (Hsp-90). On the other hand, level of serotonin (5-hydroxytryptamine) and SERT protein was down-regulated. Furthermore, we show that C. sakazakii infection up-regulate microRNA-16 (miR-16) expression. The observed results highlight that C. sakazakii infections was responsible for improved fear memory retention and may have reduced the level of SERT protein, which is possibly associated with the interaction of up-regulated Hsp-90 with SERT protein or miR-16 with SERT mRNA. Taken together, observed results suggest that C. sakazakii infection alter the fear memory possibly through SERT. Hence, this model may be effective to test the C. sakazakii infection induced changes in synaptic plasticity through SERT and effect of other pharmacological agents against pathogen induced memory disorder.

Serotonin, neural markers, and memory

Diverse neuropsychiatric disorders present dysfunctional memory and no effective treatment exits for them; likely as result of the absence of neural markers associated to memory. Neurotransmitter systems and signaling pathways have been implicated in memory and dysfunctional memory; however, their role is poorly understood. Hence, neural markers and cerebral functions and dysfunctions are revised. To our knowledge no previous systematic works have been published addressing these issues. The interactions among behavioral tasks, control groups and molecular changes and/or pharmacological effects are mentioned. Neurotransmitter receptors and signaling pathways, during normal and abnormally functioning memory with an emphasis on the behavioral aspects of memory are revised. With focus on serotonin, since as it is a well characterized neurotransmitter, with multiple pharmacological tools, and well characterized downstream signaling in mammals' species. 5-HT_1A, 5-HT₄, 5-HT₅, 5-HT₆, and 5-HT₇ receptors as well as SERT (serotonin transporter) seem to be useful neural markers and/or therapeutic targets. Certainly, if the mentioned evidence is replicated, then the translatability from preclinical and clinical studies to neural changes might be confirmed. Hypothesis and theories might provide appropriate limits and perspectives of evidence.

The effect of GABA transporter 1 (GAT1) inhibitor, tiagabine, on scopolamine-induced memory impairments in mice

BACKGROUND

GABAergic neurotransmission is involved in long-term potentiation, a neurophysiological basis for learning and memory. On the other hand, GABA-enhancing drugs may impair memory and learning in humans and animals. The present study aims at investigating the effect of GAT1 inhibitor tiagabine on memory and learning.

METHODS

Albino Swiss (CD-1) and C57BL/6J mice were used in the passive avoidance (PA), Morris water maze (MWM) and radial arm water maze (RAWM) tasks. Scopolamine (1mg/kg ip) was applied to induce cognitive deficits.

RESULTS

In the retention trial of PA scopolamine reduced step-through latency as compared to vehicle-treated mice, and pretreatment with tiagabine did not have any influence on this effect. In MWM the results obtained for vehicle-treated mice, scopolamine-treated group and combined scopolamine+tiagabine-treated mice revealed variable learning abilities in these groups. Tiagabine did not impair learning in the acquisition trial. In RAWM on day 1 scopolamine-treated group made nearly two-fold more errors than vehicle-treated mice and mice that received combined scopolamine and tiagabine. Learning abilities in the latter group were similar to those of vehicle-treated mice in the corresponding trial block on day 1, except for the last trial block, during which tiagabine+scopolamine-injected mice made more errors than control mice and the scopolamine-treated group. In all groups a complete reversal of memory deficits was observed in the last trial block of day 2.

CONCLUSIONS

The lack of negative influence of tiagabine on cognitive functions in animals with scopolamine-induced memory impairments may be relevant for patients treated with this drug.

Ameliorative effect of gastrodin on 3,3'-iminodipropionitrile-induced memory impairment in rats

3,3'-Iminodipropionitrile (IDPN), one of the nitrile derivatives inducing neurotoxicity, causes the dyskinetic syndrome and cognitive impairment. Gastrodin is widely used to treat neurological disorders and showed to improve cognitive functions. The present study aimed to determine whether treatment with gastrodin can attenuate IDPN-induced impairment of memory consolidation in the passive avoidance (PA) task, and to explore the possible neural mechanisms. Our results showed that intragastric administration of gastrodin (200mg/kg) reversed the IDPN-induced impairment of memory consolidation as indicated by the prolonged retention latency in the PA task. Furthermore, gastrodin reverted IDPN-induced reduction of serotonin (5-HT) and elevation of serotonin turnover ratio. Gastrodin treatment prevented the increase of serotonin transporter (SERT) and the decrease of serotonin 1A (5-HT1A) receptor expression in the hippocampus of IDPN-treated rats. These results suggest that long-term gastrodin treatment could represent a novel pharmacological strategy for IDPN-induced memory impairment, as well that its protective effect is mediated through normalization of the serotoninergic system.

Neurochemical changes observed by in vivo proton magnetic resonance spectroscopy in the mouse brain postadministration of scopolamine

RATIONALE AND OBJECTIVES

This study is aimed at investigating neurochemical changes in scopolamine (SCP)-induced memory impairment using spatially localized in vivo magnetic resonance spectroscopy (MRS) of the hippocampus.

MATERIALS AND METHODS

Four groups of mice (eight mice per group) were scanned after the injection of different SCP doses: 0, 1, 3, and 5 mg/kg (intraperitoneally). All the animals received (1)H MRS of their hippocampus at two time intervals: 30 minutes and 72 hours after SCP injection.

RESULTS

This work demonstrated that the doses of 3 mg/kg SCP or higher reduce the concentration of total choline-containing compounds, and these levels returned to baseline after 72 hours. These results are consistent with observations made by others using more invasive brain dialysis approaches. The levels of glutamate and glutamic compounds (glutamate + glutamine) were slightly changed at 3 and 5 mg/kg SCP dose, but the differences were not statistically significant (P > .05). These findings suggest that SCP produces transient, in vivo measurable alterations in the cholinergic system in the hippocampus.

CONCLUSIONS

On this basis, we conclude that in vivo MRS is a feasible noninvasive method to probe aspects of the alterations induced by SCP in the cholinergic neurotransmission pathways in both animal models and human studies of memory impairment.

Gastrodin ameliorates memory deficits in 3,3'-iminodipropionitrile-induced rats: possible involvement of dopaminergic system

3,3'-Iminodipropionitrile (IDPN), one of the nitrile derivatives, can induce neurotoxicity, and therefore cause motor dysfunction and cognitive deficits. Gastrodin is a main bioactive constituent of a Chinese herbal medicine (Gastrodia elata Blume) widely used for treating various neurological disorders and showed greatly improved mental function. This study was designed to determine whether administration of gastrodin attenuates IDPN-induced working memory deficits in Y-maze task, and to explore the underlying mechanisms. Results showed that exposure to IDPN (150 mg/kg/day, v.o.) significantly impaired working memory and that long-term gastrodin (200 mg/kg/day, v.o.) could effectively rescue these IDPN-induced memory impairments as indicated by increased spontaneous alternation in the Y-maze test. Additionally, gastrodin treatment prevented IDPN-induced reductions of dopamine (DA) and its metabolites, as well as elevation of dopamine turnover ratio (DOPAC + HVA)/DA. Gastrodin treatment also prevented alterations in dopamine D2 receptor and dopamine transporter protein levels in the rat hippocampus. Our results suggest that long-term gastrodin treatment may have potential therapeutic values for IDPN-induced cognitive impairments, which was mediated, in part, by normalizing the dopaminergic system.

Different transporter systems regulate extracellular GABA from vesicular and non-vesicular sources

Tonic GABA type A (GABA_A) conductance is a key factor regulating neuronal excitability and computation in neuronal networks. The magnitude of the tonic GABA_A conductance depends on the concentration of ambient GABA originating from vesicular and non-vesicular sources and is tightly regulated by GABA uptake. Here we show that the transport system regulating ambient GABA responsible for tonic GABA_A conductances in hippocampal CA1 interneurons depends on its source. In mice, GABA from vesicular sources is regulated by mouse GABA transporter 1 (mGAT1), while that from non-vesicular sources by mouse GABA transporters 3/4 (mGAT3/4). This finding suggests that the two transporter systems do not just provide backup for each other, but regulate distinct signaling pathways. This allows individual tuning of the two signaling systems and indicates that drugs designed to act at specific transporters will have distinct therapeutic actions.

A DKP cyclo(L-Phe-L-Phe) found in chicken essence is a dual inhibitor of the serotonin transporter and acetylcholinesterase

Diketopiperazines (DKPs) are naturally-occurring cyclic dipeptides with a small structure and are found in many organisms and in large amounts in some foods and beverages. We found that a chicken essence beverage, which is popular among Southeast Asians as a traditional remedy and a rich source of DKPs, inhibited the serotonin transporter (SERT) and suppressed serotonin uptake from rat brain synaptosomes, which prompted us to isolate and identify the active substance(s). We purified a SERT inhibitor from the chicken essence beverage and identified it as the DKP cyclo(L-Phe-L-Phe). Interestingly, it was a naturally occurring dual inhibitor that inhibited both SERT and acetylcholinesterase (AChE) in vitro. The DKP increased extracellular levels of the cerebral monoamines serotonin, norepinephrine, and dopamine in the medial prefrontal cortex and acetylcholine in the ventral hippocampus of freely moving rats when administered orally. Moreover, cyclo(L-Phe-L-Phe) significantly shortened escape latency in the water maze test in depressed mice previously subjected to a repeated open-space swimming task, which induces a depression-like state. Cyclo(L-Phe-L-Phe) also significantly improved accuracy rates in a radial maze test in rats and increased step-through latencies in a passive avoidance test in mice with scopolamine-induced amnesia. These animal test results suggest that cyclo(L-Phe-L-Phe), which is present abundantly in some foods such as chicken essence, may abrogate the onset of depression and, thus, contribute to preventing the development of Alzheimer's disease and other dementia, because senile depression is a risk factor for dementia.