Presynaptic modulation of acetylcholine, noradrenaline, and serotonin release in the hippocampus of aged rats with various levels of memory impairments

Unraveling the Complexity of Human Brain: Structure, Function in Healthy and Disease States

The human brain stands as an intricate organ, embodying a nexus of structure, function, development, and diversity. This review delves into the multifaceted landscape of the brain, spanning its anatomical intricacies, diverse functional capacities, dynamic developmental trajectories, and inherent variability across individuals. The dynamic process of brain development, from early embryonic stages to adulthood, highlights the nuanced changes that occur throughout the lifespan. The brain, a remarkably complex organ, is composed of various anatomical regions, each contributing uniquely to its overall functionality. Through an exploration of neuroanatomy, neurophysiology, and electrophysiology, this review elucidates how different brain structures interact to support a wide array of cognitive processes, sensory perception, motor control, and emotional regulation. Moreover, it addresses the impact of age, sex, and ethnic background on brain structure and function, and gender differences profoundly influence the onset, progression, and manifestation of brain disorders shaped by genetic, hormonal, environmental, and social factors. Delving into the complexities of the human brain, it investigates how variations in anatomical configuration correspond to diverse functional capacities across individuals. Furthermore, it examines the impact of neurodegenerative diseases on the structural and functional integrity of the brain. Specifically, our article explores the pathological processes underlying neurodegenerative diseases, such as Alzheimer's, Parkinson's, and Huntington's diseases, shedding light on the structural alterations and functional impairments that accompany these conditions. We will also explore the current research trends in neurodegenerative diseases and identify the existing gaps in the literature. Overall, this article deepens our understanding of the fundamental principles governing brain structure and function and paves the way for a deeper understanding of individual differences and tailored approaches in neuroscience and clinical practice-additionally, a comprehensive understanding of structural and functional changes that manifest in neurodegenerative diseases.

Activation of 5-HT1A Receptors Normalizes the Overexpression of Presynaptic 5-HT1A Receptors and Alleviates Diabetic Neuropathic Pain

Neuropathic pain is a well-documented phenomenon in experimental and clinical diabetes; however, current treatment is unsatisfactory. Serotoninergic-containing neurons are key components of the descending autoinhibitory pathway, and a decrease in their activity may contribute at least in part to diabetic neuropathic pain (DNP). A streptozotocin (STZ)-treated rat was used as a model for type 1 diabetes mellitus (T1DM). Pain transmission was evaluated using well-established nociceptive-based techniques, including the Hargreaves apparatus, cold plate and dynamic plantar aesthesiometer. Using qRT-PCR, Western blotting, immunohistochemistry, and HPLC-based techniques, we also measured in the central nervous system and peripheral nervous system of diabetic animals the expression and localization of 5-HT1A receptors (5-HT1AR), levels of key enzymes involved in the synthesis and degradation of tryptophan and 5-HT, including tryptophan hydroxylase-2 (Tph-2), tryptophan 2,3-dioxygenase (Tdo), indoleamine 2,3-dioxygenase 1 (Ido1) and Ido2. Moreover, spinal concentrations of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA, a metabolite of 5-HT) and quinolinic acid (QA, a metabolite of tryptophan) were also quantified. Diabetic rats developed thermal hyperalgesia and cold/mechanical allodynia, and these behavioral abnormalities appear to be associated with the upregulation in the levels of expression of critical molecules related to the serotoninergic nervous system, including presynaptic 5-HT1AR and the enzymes Tph-2, Tdo, Ido1 and Ido2. Interestingly, the level of postsynaptic 5-HT1AR remains unaltered in STZ-induced T1DM. Chronic treatment of diabetic animals with 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT), a selective 5-HT1AR agonist, downregulated the upregulation of neuronal presynaptic 5-HT1AR, increased spinal release of 5-HT (↑ 5-HIAA/5-HT) and reduced the concentration of QA, decreased mRNA expression of Tdo, Ido1 and Ido2, arrested neuronal degeneration and ameliorated pain-related behavior as exemplified by thermal hyperalgesia and cold/mechanical allodynia. These data show that 8-OH-DPAT alleviates DNP and other components of the serotoninergic system, including the ratio of 5-HIAA/5-HT and 5-HT1AR, and could be a useful therapeutic agent for managing DNP.

Advanced age has dissociable effects on hippocampal CA1 ripples and CA3 high frequency events in male rats

Sharp wave/ripples/high frequency events (HFEs) are transient bursts of depolarization in hippocampal subregions CA3 and CA1 that occur during rest and pauses in behavior. Previous studies have reported that CA1 ripples in aged rats have lower frequency than those detected in young animals. While CA1 ripples are thought to be driven by CA3, HFEs in CA3 have not been examined in aged animals. The current study obtained simultaneous recordings from CA1 and CA3 in young and aged rats to examine sharp wave/ripples/HFEs in relation to age. While CA1 ripple frequency was reduced with age, there were no age differences in the frequency of CA3 HFEs, although power and length were lower in old animals. While there was a proportion of CA1 ripples that co-occurred with a CA3 HFE, none of the age-related differences in CA1 ripples could be explained by alterations in CA3 HFE characteristics. These findings suggest that age differences in CA1 are not due to altered CA3 activity, but instead reflect distinct mechanisms of ripple generation with age.

Effects of an Armillaria mellea Polysaccharide on Learning and Memory of D-Galactose-Induced Aging Mice

Armillaria mellea has been known and used in traditional medicine in East Asia for hundreds of years. It has already been reported that A. mellea extracts have various pharmacological effects, and the polysaccharides of A. mellea exhibit antioxidant and anti-apoptotic activities. In this study, a water-soluble polysaccharide (AMP-N-a-1), with an average molecular weight of 17 kD, was isolated and purified from the water extract of A. mellea using DEAE-52, Sepharose CL-4B, and Sephadex G-100 column chromatography. AMP-N-a-1 was mainly composed of Man (1.65%), Glca (1.64%), Rha (1.82%), Gala (2.49%), Glc (90.48%), Gal (0.89%), Xyl (0.42%), and Ara (0.61%). AMP-N-a-1 was used to study the effect on the learning and memory of mice and its underlying mechanisms. The results showed that AMP-N-a-1 could significantly increase the activities of catalase (CAT) and superoxide dismutase (SOD) and reduce the content of nitric oxide (NO) in mouse brain tissue. Meanwhile, AMP-N-a-1 could reduce the contents of norepinephrine (NE) and dopamine (DA) but could increase the content of 5-hydroxytryptamine (5-HT) in mouse brain tissue. In addition, the immunofluorescence experiment showed that AMP-N-a-1 could promote the proliferation of hippocampal dentate gyrus neurons. The above results indicate that AMP-N-a-1 can significantly improve the learning and memory of mice, and the mechanism may be that AMP-N-a-1 can participate in the regulation of learning and memory through a variety of ways.

Protective Effects of a synthetic glycosaminoglycan mimetic (OTR4132) in a rat immunotoxic lesion model of septohippocampal cholinergic degeneration

Using a partial hippocampal cholinergic denervation model, we assessed the effects of the RGTA^® named OTR4132, a synthetic heparan-mimetic biopolymer with neuroprotective/neurotrophic properties. Long-Evans male rats were injected with the cholinergic immunotoxin 192 IgG-saporin into the medial septum/diagonal band of Broca (0.37 µg); vehicle injections served as controls. Immediately after surgery, OTR4132 was injected into the lateral ventricles (0.25 µg/5 µl/rat) or intramuscularly (1.5 mg/kg). To determine whether OTR4132 reached the lesion site, some rats received intracerebroventricular (ICV) or intramuscular (I.M.) injections of fluorescent OTR4132. Rats were sacrificed at 4, 10, 20, or 60 days post-lesion (DPL). Fluorescein-labeled OTR4132 injected ICV or I.M. was found in the lesion from 4 to 20 DPL. Rats with partial hippocampal cholinergic denervation showed decreases in hippocampal acetylcholinesterase reaction products and in choline acetyltransferase-positive neurons in the medial septum. These lesions were the largest at 10 DPL and then remained stable until 60 DPL. Both hippocampal acetylcholinesterase reaction products and choline acetyltransferase-positive neurons in the medial septum effects were significantly attenuated in OTR4132-treated rats. These effects were not related to competition between OTR4132 and 192 IgG-saporin for the neurotrophin receptor P75 (p75^NTR), as OTR4132 treatment did not alter the internalization of Cy3-labelled 192 IgG. OTR4132 was more efficient at reducing the acetylcholinesterase reaction products and choline acetyltransferase-positive neurons than a comparable heparin dose used as a comparator. Using the slice superfusion technique, we found that the lesion-induced decrease in muscarinic autoreceptor sensitivity was abolished by intramuscular OTR4132. After partial cholinergic damage, OTR4132 was able to concentrate at the brain lesion site possibly due to the disruption of the blood-brain barrier and to exert structural and functional effects that hold promises for neuroprotection/neurotrophism.

Age-Dependent and Pathway-Specific Bimodal Action of Nicotine on Synaptic Plasticity in the Hippocampus of Mice Lacking the miR-132/212 Genes

Nicotine addiction develops predominantly during human adolescence through smoking. Self-administration experiments in rodents verify this biological preponderance to adolescence, suggesting evolutionary-conserved and age-defined mechanisms which influence the susceptibility to nicotine addiction. The hippocampus, a brain region linked to drug-related memory storage, undergoes major morpho-functional restructuring during adolescence and is strongly affected by nicotine stimulation. However, the signaling mechanisms shaping the effects of nicotine in young vs. adult brains remain unclear. MicroRNAs (miRNAs) emerged recently as modulators of brain neuroplasticity, learning and memory, and addiction. Nevertheless, the age-dependent interplay between miRNAs regulation and hippocampal nicotinergic signaling remains poorly explored. We here combined biophysical and pharmacological methods to examine the impact of miRNA-132/212 gene-deletion (miRNA-132/212-/-) and nicotine stimulation on synaptic functions in adolescent and mature adult mice at two hippocampal synaptic circuits: the medial perforant pathway (MPP) to dentate yrus (DG) synapses (MPP-DG) and CA3 Schaffer collaterals to CA1 synapses (CA3-CA1). Basal synaptic transmission and short-term (paired-pulse-induced) synaptic plasticity was unaltered in adolescent and adult miRNA-132/212-/- mice hippocampi, compared with wild-type controls. However, nicotine stimulation promoted CA3-CA1 synaptic potentiation in mature adult (not adolescent) wild-type and suppressed MPP-DG synaptic potentiation in miRNA-132/212-/- mice. Altered levels of CREB, Phospho-CREB, and acetylcholinesterase (AChE) expression were further detected in adult miRNA-132/212-/- mice hippocampi. These observations propose miRNAs as age-sensitive bimodal regulators of hippocampal nicotinergic signaling and, given the relevance of the hippocampus for drug-related memory storage, encourage further research on the influence of miRNAs 132 and 212 in nicotine addiction in the young and the adult brain.

((E)-N-(4-(((2-Amino-5-phenylpyridin-3-yl)imino)methyl)pyridin-2-yl)cyclopropanecarboxamide) Ameliorated Aβ1-42-Induced Alzheimer's Disease in SD Rats by Inhibiting Oxidative Stress and Apoptosis

Our study investigated the protective effects of ((E)-N-(4-(((2-amino-5-phenylpyridin-3-yl)imino)methyl)pyridin-2-yl)cyclopropanecarboxamide) 9b, a novel glycogen synthase kinase-3β (GSK-3β) inhibitor, on the learning and memory function of rats with amyloid-β_1-42 (Aβ_1-42)-induced Alzheimer's disease (AD) and explored the possible mechanisms. Sixty male Sprague-Dawley (SD) rats were randomly divided into five groups: the control, Aβ, donepezil, and low-dose and high-dose 9b groups. The rats in the Aβ, donepezil, and two 9b intervention groups received a single microinjection of 10 μg of Aβ_1-42 into the hippocampus followed by intragastric administration of 0.5% sodium carboxymethyl cellulose (CMC-Na), 12 (mg/kg)/d donepezil hydrochloride and 6 or 18 (mg/kg)/d compound 9b for 28 days, while the rats in the control group were treated with the vehicles. Learning and memory impairment were attenuated, the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), acetylcholinesterase (AChE), and adenosine triphosphatase (ATPase) in the brain tissue were significantly increased (p < 0.05), and the concentrations of Aβ_1-42, phospho-tau (p-tau), and malondialdehyde (MDA) in the brain tissue were significantly decreased (p < 0.05) in the compound 9b group compared to the Aβ group. In addition, compound 9b regulated the imbalance in the concentrations of neurotransmitters and alleviated severe damage and apoptosis in the brains of the rats exposed to Aβ_1-42. The novel GSK-3β inhibitor 9b could improve learning and memory dysfunction caused by Aβ_1-42 through its antioxidant and antiapoptotic effects.

Contributions of the Nucleus Accumbens Shell in Mediating the Enhancement in Memory Following Noradrenergic Activation of Either the Amygdala or Hippocampus

The nucleus accumbens shell is a site of converging inputs during memory processing for emotional events. The accumbens receives input from the nucleus of the solitary tract (NTS) regarding changes in peripheral autonomic functioning following emotional arousal. The shell also receives input from the amygdala and hippocampus regarding affective and contextual attributes of new learning experiences. The successful encoding of affect or context is facilitated by activating noradrenergic systems in either the amygdala or hippocampus. Recent findings indicate that memory enhancement produced by activating NTS neurons, is attenuated by suppressing accumbens functioning after learning. This finding illustrates the significance of the shell in integrating information from the periphery to modulate memory for arousing events. However, it is not known if the accumbens shell plays an equally important role in consolidating information that is initially processed in the amygdala and hippocampus. The present study determined if the convergence of inputs from these limbic regions within the nucleus accumbens contributes to successful encoding of emotional events into memory. Male Sprague-Dawley rats received bilateral cannula implants 2 mm above the accumbens shell and a second bilateral implant 2 mm above either the amygdala or hippocampus. The subjects were trained for 6 days to drink from a water spout. On day 7, a 0.35 mA footshock was initiated as the rat approached the spout and was terminated once the rat escaped into a white compartment. Subjects were then given intra-amygdala or hippocampal infusions of PBS or a dose of norepinephrine (0.2 μg) previously shown to enhance memory. Later, all subjects were given intra-accumbens infusion of muscimol to functionally inactivate the shell. Muscimol inactivation of the accumbens shell was delayed to allow sufficient time for norepinephrine to activate intracellular cascades that lead to long-term synaptic modifications involved in forming new memories. Results show that memory improvement produced by infusing norepinephrine in either the amygdala or hippocampus is attenuated by interrupting neuronal activity in the shell 1 or 7 7 h following amygdala or hippocampus activation. These findings suggest that the accumbens shell plays an integral role modulating information initially processed by the amygdala and hippocampus following exposure to emotionally arousing events. Additionally, results demonstrate that the accumbens is involved in the long-term consolidation processes lasting over 7 h.

Repeated treatment with the α2-adrenoceptor agonist UK-14304 improves cognitive performance in middle-age rats: Role of hippocampal Fas-associated death domain

The cell fate regulator Fas-associated death domain (FADD) balances cell death with non-apoptotic actions via its phosphorylated form. A recent study associated loss of cortical FADD with cognitive decline and increased risk of clinical dementia. Since the activation of cortical α_2A-adrenoceptors improved memory deficits in various animal models of working memory loss, the present study evaluated whether UK-14304, an α₂-adrenoceptor agonist known to acutely regulate brain FADD forms, would improve cognitive function in middle-aged rats. Sprague-Dawley rats were treated with UK-14304 (0.3 or 1 mg/kg) or saline (1 mL/kg) for seven days. Cognitive performance was evaluated in the eight-arm radial maze. FADD protein content was measured in the prefrontal cortex and hippocampus by Western blot analysis. The results showed that UK-14304 (1 mg/kg) improved cognitive performance (less time: -310±45 s, p=0.025 and fewer errors: -2.75±1.06, p=0.043 to complete the maze) and increased FADD selectively in the hippocampus (+35±11%, p=0.029). Interestingly, hippocampal FADD content negatively correlated with the time ( r=-0.651, p<0.01) needed to complete the maze. Thus, better cognitive scores were associated with higher FADD hippocampal content. These results support a role for α₂-adrenoceptors in ameliorating cognition and suggest FADD protein content as a possible correlate for cognitive performance.

Differential Effects of Nicotine Exposure on the Hippocampus Across Lifespan

BACKGROUND

Nicotine exposure affects the hippocampus through activation of hippocampal nicotinic acetylcholine receptors (nAChRs), which are present throughout excitatory and inhibitory hippocampal circuitry. The role of cholinergic functioning in the hippocampus varies across developmental stages so that nicotine exposure differentially affects this region depending upon timing of exposure, producing developmentally distinct changes in structure, function, and behavior.

METHODS

We synthesize findings across literature in this area to comprehensively review current understanding of the unique effects of nicotine exposure on the hippocampus throughout the lifespan with a focus on hippocampal morphology, cholinergic functioning, and hippocampusdependent learning and memory.

CONCLUSIONS

Chronic and acute nicotine exposure differentially affect hippocampus structure, functioning, and related learning and memory in the perinatal period, adolescence, and aging. Age-related differences in sensitivity to nicotine exposure should be considered in the research of nicotine addiction and the development of nicotine addiction treatments.

Effect of Zhuang Jing Decoction on Learning and Memory Ability in Aging Rats

With the average life span of humans on the rise, aging in the world has drawn considerable attentions. The monoamine neurotransmitters and neurotrophic factors in brain areas are involved in learning and memory processes and are an essential part of normal synaptic neurotransmission and plasticity. In the present study, the effect of Zhuang Jing Decoction (ZJD) on the learning and memory ability in aging rats was examined in vivo using Morris water maze. Furthermore, the levels of monoamine neurotransmitters and neurotrophic factors in brain were detected by high-performance liquid chromatography with a fluorescence detector and enzyme-linked immunosorbent assay, respectively. These data showed that oral administration with ZJD at the dose of 30 g·kg(-1) exerted an improved effect on learning and memory ability in aging rats. The results revealed that ZJD could effectively adjust the monoamine neurotransmitters and neurotrophic factors, restore the balance of the level of monoamine neurotransmitters and neurotrophic factors in brain, and finally attenuate the degeneration of learning and memory ability. These findings suggested that ZJD might be a potential agent as cognitive-enhancing drug in improving learning and memory ability. It may exert through regulating the levels of monoamine neurotransmitters and neurotrophic factors in brain, which demonstrated that ZJD had certain antiaging effects.

Aerobic training as a means to enhance inhibition: what's yet to be studied?

Some of the neurodegenerative processes in healthy aging, including changes in structural and biochemical properties of the brain, are argued to affect cortical inhibitory functions. Age-related deficits in the ability to control cerebral inhibition may explain wide range of motor and cognitive deficits that healthy older adults experience in daily life such as impaired coordination skills and declines in attention, concentration, and learning abilities. Importantly, evidence from many studies suggests that impaired inhibitory control in advancing age can be delayed or even alleviated by aerobic exercise training. Findings from a recent study by Duchesne and colleagues (2015) may provide insights into this process. First, observations from Duchesne et al. indicated that aerobic exercise training program improved cognitive inhibitory functioning in both patients with Parkinson’s disease (PD) and matched older controls. Second, Duchesne et al. showed that cognitive inhibition and motor skills were highly correlated both pre- and post-exercise in PD but not in controls. Based on the aforementioned findings we highlight possible mechanisms that may play a role in the interactions between cognitive and motor inhibitory functions in healthy elderly that could benefit from aerobic exercise training: specifically, the brain neurotransmission systems and the frontal-basal ganglia network. In conclusion, we raise two fundamental questions which are yet to be addressed: (1) the extent to which different brain neurotransmitter systems are affected by aerobic exercise training; (2) the extent to which neurotransmitter levels prior to the onset of intervention may facilitate (or impede) training-induced neuroplasticity in the aging brain.

Reversal of aging-related emotional memory deficits by norepinephrine via regulating the stability of surface AMPA receptors

Aging-related emotional memory deficit is a well-known complication in Alzheimer's disease and normal aging. However, little is known about its molecular mechanism. To address this issue, we examined the role of norepinephrine (NE) and its relevant drug desipramine in the regulation of hippocampal long-term potentiation (LTP), surface expression of AMPA receptor, and associative fear memory in rats. We found that there was a defective regulation of NE content and AMPA receptor trafficking during fear conditioning, which were accompanied by impaired emotional memory and LTP in aged rats. Furthermore, we also found that the exogenous upregulation of NE ameliorated the impairment of LTP and emotional memory via enhancing AMPA receptor trafficking in aged rats, and the downregulation of NE impaired LTP in adult rats. Finally, acute treatment with NE or desipramine rescued the impaired emotional memory in aged rats. These results imply a pivotal role for NE in synaptic plasticity and associative fear memory in aging rats and suggest that desipramine is a potential candidate for treating aging-related emotional memory deficit.

Effect of Kangshuai Yizhi Formula I on learning and memory dysfunction induced by scopolamine in mice

OBJECTIVE

To evaluate the improvement of Kangshuai Yizhi Formula I ( I, KYF I) on: the learning and memory dysfunction in mice, and on the mechanism of the hippocampal cholinergic system and the nervous system of monoamine which are closely related to learning and memory function.

METHODS

Mice: in the low-, middle-, and high-dose KYF I groups were given low-, middle-, and high-dose KYF, respectively, by gastrogavage for 35 successive days. Animals in the control group and the model group were treated with distilled water. The acute learning and memory dysfunction model was established by injection of scopolamine from day 31, and Morris water maze was used to assess the behavior performance of scopolamine-induced model mice for five days. The activities of acetylcholinesterase (AChE), choline acetyl transferase (ChaT) and the content of monoamine neurotransmitters in hippocampus were measured. The activity of monoamine oxidase (MAO) in hippocampus and serum was also detected.

RESULTS

(1) Compared with the control group, the: mean escape latency was shortened, and the frequency across the platform and the staying time at the platform area on the 5th day were decreased in the model group by Morris water maze test. The activities of AChE and MAO were increased, and the ChaT activity and monoamine neurotransmitter content were decreased as well. (2) The escape latency for 4 days in the low-, middle-, and high-dose KYF I groups was significantly shortened than that in the model group, with the shortest latency in the high-dose KYF I group (P<0.05, P<0.01). The frequency across the platform was significantly increased and the staying time at the platform was significantly prolonged in the middle- and high-dose KYF I groups (P<0.05, P<0.01). (3) As compared with the model group, the activity of ChaT and the content of monoamine neurotransmitters in the hippocampus were significantly increased, and the activities of AchE and MAO were significantly decreased in the hippocampus in the high-dose KYF I group (P<0.01).

CONCLUSIONS

High-dose KYF I can significantly improve the learning and memory dysfunction: induced by scopolamine in mice. Its mechanism may be related to improving the central cholinergic system and regulating the hippocampal monoamine neurotransmitters.

Motor control and aging: links to age-related brain structural, functional, and biochemical effects

Although connections between cognitive deficits and age-associated brain differences have been elucidated, relationships with motor performance are less well understood. Here, we broadly review age-related brain differences and motor deficits in older adults in addition to cognition-action theories. Age-related atrophy of the motor cortical regions and corpus callosum may precipitate or coincide with motor declines such as balance and gait deficits, coordination deficits, and movement slowing. Correspondingly, degeneration of neurotransmitter systems-primarily the dopaminergic system-may contribute to age-related gross and fine motor declines, as well as to higher cognitive deficits. In general, older adults exhibit involvement of more widespread brain regions for motor control than young adults, particularly the prefrontal cortex and basal ganglia networks. Unfortunately these same regions are the most vulnerable to age-related effects, resulting in an imbalance of "supply and demand". Existing exercise, pharmaceutical, and motor training interventions may ameliorate motor deficits in older adults.

The septo-hippocampal system, learning and recovery of function

We understand this review as an attempt to summarize recent advances in the understanding of cholinergic function in cognition. Such a role has been highlighted in the 1970s by the discovery that dementia patients have greatly reduced cholinergic activity in cortex and hippocampus. A brief anatomical description of the major cholinergic pathways focuses on the basal forebrain and its projections to cortex and hippocampus. From this distinction, compelling evidence suggests that the basal forebrain --> cortex projection regulates the excitability of principal cortical neurons and is thereby critically involved in attention, stimulus detection and memory function, although the biological conditions for these functions are still debated. Similar uncertainties remain for the septo-hippocampal cholinergic system. Although initial lesions of the septum caused memory deficits reminiscent of hippocampal ablations, recent and more refined neurotoxic lesion studies which spared non-cholinergic cells of the basal forebrain failed to confirm these memory impairments in experimental animals despite a near total loss of cholinergic labeling. Yet, a decline in cholinergic markers in aging and dementia still stands as the most central piece of evidence for a link between the cholinergic system and cognition and appear to provide valuable targets for therapeutic approaches.

Age-associated changes in synaptic lipid raft proteins revealed by two-dimensional fluorescence difference gel electrophoresis

Brain aging is associated with a progressive decline in cognitive function though the molecular mechanisms remain unknown. Functional changes in brain neurons could be due to age-related alterations in levels of specific proteins critical for information processing. Specialized membrane microdomains known as 'lipid rafts' contain protein complexes involved in many signal transduction processes. This study was undertaken to determine if two-dimensional fluorescence difference gel electrophoresis (2D DIGE) analysis of proteins in synaptic membrane lipid rafts revealed age-dependent alterations in levels of raft proteins. Five pairs of young and aged rat synaptic membrane rafts were subjected to DIGE separation, followed by image analysis and identification of significantly altered proteins. Of 1046 matched spots on DIGE gels, 94 showed statistically significant differences in levels between old and young rafts, and 87 of these were decreased in aged rafts. The 41 most significantly altered (p<0.03) proteins included several synaptic proteins involved in energy metabolism, redox homeostasis, and cytoskeletal structure. This may indicate a disruption in bioenergetic balance and redox homeostasis in synaptic rafts with brain aging. Differential levels of representative identified proteins were confirmed by immunoblot analysis. Our findings provide novel pathways in investigations of mechanisms that may contribute to altered neuronal function in aging brain.

Effects of ethanol and 3,4-methylenedioxymethamphetamine (MDMA) alone or in combination on spontaneous and evoked overflow of dopamine, serotonin and acetylcholine in striatal slices of the rat brain

Ethanol (EtOH) potentiates the locomotor effects of 3,4-methylenedioxymetamphetamine (MDMA) in rats. This potentiation might involve pharmacokinetic and/or pharmacodynamic mechanisms. We explored whether the latter could be local. Using a slice superfusion approach, we assessed the effects of MDMA (0.3, 3microm) and/or EtOH (2mm) on the spontaneous outflow and electrically evoked release of serotonin (5-HT), dopamine (DA) and acetylcholine (ACh) in the striatum, and for comparison, on 5-HT release in hippocampal and neocortical tissue. MDMA and less effectively EtOH, augmented the outflow of 5-HT in all regions. The electrically evoked 5-HT release was increased by MDMA at 3microm in striatal slices only. With nomifensine throughout, EtOH significantly potentiated the 0.3microm MDMA-induced outflow of 5-HT, but only in striatal slices. EtOH or MDMA also enhanced the spontaneous outflow of DA, but MDMA reduced the electrically evoked DA release. With fluvoxamine throughout superfusion, EtOH potentiated the effect of MDMA on the spontaneous outflow of DA. Finally, 3microm MDMA diminished the electrically evoked release of ACh, an effect involving several receptors (D2, 5-HT2, NMDA, nicotinic, NK1), with some interactions with EtOH. Among other results, we show for the first time a local synergistic interaction of EtOH and MDMA on the spontaneous outflow of striatal DA and 5-HT, which could be relevant to the EtOH-induced potentiation of hyperlocomotion in MDMA-treated rats. These data do not preclude the contribution of other pharmacodynamic and/or pharmacokinetic mechanisms in vivo but support the hypothesis that EtOH may affect the abuse liability of MDMA.

Effects of tenuifolin extracted from radix polygalae on learning and memory: a behavioral and biochemical study on aged and amnesic mice

Although normal cognitive changes take place when a person becomes older, aging in humans is generally associated with deterioration of cognitive performance and, in particular, of learning and memory. These cognitive deficits can cause debilitating consequences due to aging. There are a number of herbal medicines which are reported to improve brain function including intelligence. In the present study, improving effects of tenuifolin, extracted from Radix Polygalae (RP), on learning and memory in aged and dysmnesia mice were determined using step-down type passive avoidance test or Y type maze trial. Oral administration of tenuifolin (0.02, 0.04, 0.08 g/kgd(-1), for 15 d) evidently improved the latency and number of errors in aged and dysmnesia mice. The levels of cortical acetylcholine esterase (AChE) activity and hippocampal neurotransmitters in aged mice given tenuifolin (0.02, 0.04, 0.08 g/kgd(-1), for 15 d) were also investigated, and increased levels of norepinephrine (NE), dopamine (DA), decreased activity of AChE were found. However, serotonin (5-HT) had no significant difference from that of aged mice given distilled water. The evident improvement of learning and memory of aged mice is carried out by the effects of tenuifolin on the three stages of memory process, that is, acquisition, consolidation and retrieval. This may do so by relatively increasing the levels of NE, DA in the hippocampus and by decreasing the activity of AChE in the cortex.

Spatial reference- (not working- or procedural-) memory performance of aged rats in the water maze predicts the magnitude of sulpiride-induced facilitation of acetylcholine release by striatal slices

Cluster analysis of water-maze reference-memory performance distinguished subpopulations of young adult (3-5 months), aged (25-27 months) unimpaired (AU) and aged impaired (AI) rats. Working-memory performances of AU and AI rats were close to normal (though young and aged rats differed in exploration strategies). All aged rats showed impaired procedural-memory. Electrically evoked release of tritium was assessed in striatal slices (preloaded with [(3)H]choline) in the presence of oxotremorine, physostigmine, atropine+physostigmine, quinpirole, nomifensine or sulpiride. Aged rats exhibited reduced accumulation of [(3)H]choline (-30%) and weaker transmitter release. Drug effects (highest concentration) were reductions of release by 44% (oxotremorine), 72% (physostigmine), 84% (quinpirole) and 65% (nomifensine) regardless of age. Sulpiride and atropine+physostigmine facilitated the release more efficiently in young rats versus aged rats. The sulpiride-induced facilitation was weaker in AI rats versus AU rats; it significantly correlated with reference-memory performance. The results confirm age-related alterations of cholinergic and dopaminergic striatal functions, and point to the possibility that alterations in the D(2)-mediated dopaminergic regulation of these functions contribute to age-related reference-memory deficits.

Presynaptic modulation of 5-HT release in the rat septal region

5-HT released from serotonergic axon terminals in the septal nuclei modulates the activity of septal output neurons (e.g. septohippocampal cholinergic neurons) bearing somatodendritic 5-HT receptors. Therefore, we studied the mechanisms involved in the presynaptic modulation of 5-HT release in the lateral (LS) and medial septum (MS), and the diagonal band of Broca (DB). HPLC analysis showed that tissue concentrations of noradrenaline, dopamine and 5-HT were highest in DB (DB>MS>LS). Slices prepared from LS, MS and DB regions were preincubated with [(3)H]5-HT, superfused in the presence of 6-nitro-2-(1-piperazinyl)-quinoline (6-nitroquipazine) and electrically stimulated up to three times (first electrical stimulation period (S(1)), S(2), S(3); 360 pulses, 3 Hz, 2 ms, 26-28 mA). In all septal regions the Ca(2+)-dependent and tetrodotoxin-sensitive electrically-evoked overflow of [(3)H] was inhibited by the 5-HT(1B) agonist CP-93,129 and the alpha(2)-adrenoceptor agonist 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline tartrate (UK-14,304). Also the mu- and kappa-opioid receptor agonists (d-Ala(2), N-Me-Phe(4), glycinol(5))-enkephalin (DAMGO) and [trans-(1S,2S(-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]-benzenacetamide hydro-chloride] (U-50,488H), respectively, acted inhibitory (although less potently), whereas the delta-opioid receptor agonist (d-Pen(2), d-Pen(5))-enkephalin (DPDPE), the dopamine D(2) receptor agonist quinpirole and the adenosine A(1) receptor agonist N(6)-cyclopentyladenosine were all ineffective; the GABA(B) receptor agonist baclofen had weak effects. All inhibitory effects of the agonists were antagonized by the corresponding antagonists (3-[3-(dimethylamino)propyl]-4-hydroxy-N-[4-(4-pyridinyl)phenyl]benzamide dihydrochloride (GR-55,562), idazoxan, naloxone, nor-binaltorphimine), which also significantly enhanced the evoked release of 5-HT at S(1). It is concluded that 5-HT release in septal nuclei of the rat is modulated by presynaptic 5-HT(1B) autoreceptors, as well as by alpha(2)-, mu- and kappa-opioid heteroreceptors. All of these receptors seem to be under a tonic inhibitory influence of the corresponding endogenous agonists and show qualitatively comparable modulatory properties along the dorso-ventral distribution of the 5-HT terminals.

Sex differences in the effect of acute tryptophan depletion on declarative episodic memory: A pooled analysis of nine studies

Acute tryptophan depletion (ATD) studies have shown that serotonin plays a role in learning and memory processes. In this study, we performed a pooled analysis of nine ATD studies in order to examine the nature of the memory-impairing effects of ATD and mediating factors, such as gender, age and vulnerability for disease in which disturbed serotonin was hypothesized to play a role. All studies that were used in this pooled analysis assessed declarative episodic memory using a verbal learning task paradigm. Immediate recall, delayed recall, and delayed recognition scores were examined. A total of 211 participants were included in the analysis. The analysis revealed that ATD impaired not only delayed recall, but also immediate recall. The ATD-induced impairments were larger in females than in males. Furthermore, ATD did not interact with any other serotonergic vulnerability and age. This suggests that the only factor that actually has the properties of a serotonergic vulnerability factor for declarative memory performance is female gender. The findings provide further support for a critical role of serotonin in declarative episodic memory.

Nerve Growth Factor Differentially Affects Spatial and Recognition Memory in Aged Rats

In rats, object discrimination depends on the integrity of the cholinergic system, thus it could be expected that nerve growth factor (NGF) can improve the behavior in aged subjects. The interactive effect of age and cholinergic improvement was assessed behaviorally in young and aged rats. Animals were injected by infusion of NGF into the lateral ventricles and they were tested in two behavioral tasks: an object-location and an object-recognition task. Spatial and recognition memory were assessed in an open field containing five different objects. Rats were submitted to six consecutive sessions. Both age-groups showed comparable habituation of exploratory response in Session 1-4. Discrimination index (DI) was calculated to assess responses to spatial change in Session 5 and object change in Session 6. Control young and aged rats were able to discriminate between familiar and novel object, however DI was lower in aged rats. Treatment with NGF induced decline of object discrimination in both age-groups. Different results were obtained in spatial displacement test. NGF was able to improve spatial memory in aged rats, but had no effect in young controls. These data confer on NGF potential role in improving spatial but not episodic memory in aged rats.

Neuroprotective effects of behavioural training and nicotine on age-related deficits in spatial learning

Studies in humans and animals show a clear decline in spatial memory with age and several approaches have been adopted to alleviate this impairment. The purpose of our review is to assess the studies that have suggested the possible neuroprotective actions of behavioural training and nicotine-applied both independently and in conjunction-on age-related deficits in spatial learning. Both spatial pretraining and nonspatial experiences influence an animal's performance in spatial tasks. In aged rats, the experience of training in the water maze task increases the number of newly generated neurons in the hippocampus. The neuroprotective effects of nicotine have been demonstrated in both in-vitro and in-vivo models, although the molecular mechanisms underlying these actions are not yet fully understood. It had been concluded in different studies that nicotine can improve, impair or have no effect on performance in the water maze. Neurobiological data also suggest an interaction between nicotine and prior experience in complex tasks, although few studies have raised the question of whether nicotine treatment and training in spatial tasks may contribute in an interactive manner to alleviate spatial cognition impairment associated with the ageing process. Different findings suggest that past experience could be a confounding variable in longitudinal studies that aim to evaluate the neuroprotective effects of nicotine on age-related deficits in spatial learning.

Age-related alterations of GABAergic input to CA1 pyramidal neurons and its control by nicotinic acetylcholine receptors in rat hippocampus

The aim of this study was to determine whether age-associated alterations in the GABAergic input to pyramidal neurons in the hippocampus are due to a dysfunction of GABAergic interneurons, and/or a decrease in their cholinergic control via nicotinic receptors (nAChRs). Electrophysiological recordings were obtained from pyramidal cells in the CA1 area of hippocampal slices from young (3-4 months old) and aged (25-30 months old) Sprague-Dawley rats. Synaptic GABA(A) receptor-mediated inhibitory postsynaptic currents and inhibitory postsynaptic potentials induced by stimulation of the stratum oriens were significantly smaller in aged rats. The frequency (but not amplitude) of spontaneous and miniature GABA inhibitory postsynaptic currents (IPSCs) was reduced in aged rats, suggesting a presynaptic alteration. Tetanic stimulation of cholinergic afferents to release endogenous acetylcholine, or an exogenous application of the nAChR agonist cytisine, increased the frequency of spontaneous IPSCs in young rats; however these effects were not evident in aged rats, indicating that the nicotinic control of GABA release is lowered during aging. None of these age-related alterations were reversed by a chronic treatment with donepezil, a cholinesterase inhibitor. Immunofluorescent labeling of GABA interneurons with somatostatin (SOM), parvalbumin (PV) or calbindin (CB), together with the vesicular acetylcholine transporter VAChT, revealed a selective loss of subpopulations of SOM and CB positive interneurons. This loss was associated with a general decrease in density of the cholinergic network in aged rats. Thus, the lower GABAergic inhibition observed in the aged rat hippocampus is due to a selective loss/dysfunction of subpopulations of GABAergic interneurons, associated with a widespread cholinergic deficit.

Presynaptic serotonergic modulation of 5-HT and acetylcholine release in the hippocampus and the cortex of 5-HT1B-receptor knockout mice

Lesioning of serotonergic afferents increases hippocampal ACh release and attenuates memory deficits produced by cholinergic lesions. Improved memory performance described in 5-HT1B-knockout (KO) mice might thus be due to a weaker 5-HT1B-mediated inhibitory influence of 5-HT on hippocampal ACh release. The selective delay-dependent impairment of working memory observed in these KO mice suggests, however, that cortical regions also participate in task performance, possibly via indirect influences of 5-HT on ACh release. To provide neuropharmacological support for these hypotheses we measured evoked ACh and 5-HT release in hippocampal and cortical slices of wild-type (WT) and 5-HT1B KO mice. Superfused slices (preincubated with [3H]choline or [3H]5-HT) were electrically stimulated in the absence or presence of 5-HT1B receptor ligands. In hippocampus and cortex, 5-HT1B agonists decreased and antagonists increased 5-HT release in WT, but not in 5-HT1B KO mice. In 5-HT1B KO mice, 5-HT release was enhanced in both structures, while ACh release (in nCi) was reduced. ACh release was inhibited by 5-HT1B agonists in hippocampal (not cortical) slices of WT but not of 5-HT1B KO mice. Our data (i) confirm the absence of autoinhibition of 5-HT release in 5-HT1B-KO mice, (ii) demonstrate a reduced release of ACh, and the absence of 5-HT1B-receptor-mediated inhibition of ACh release, in the hippocampus and cortex of 5-HT1B-KO mice, and (iii) are compatible with an indirect role of cortical ACh in the working memory impairment observed in these KO mice.

Effect of LTP-reinforcing paradigms on neurotransmitter release in the dentate gyrus of young and aged rats

Long-term potentiation (LTP) is considered a cellular correlate of memory processing. A short-lasting early-LTP can be prolonged into a late-L TP (>4h) by stimulation of the basolateral amygdala (BLA) or motivational behavioral stimuli in young, but not in aged, cognitively impaired rats. We measured the changes in transmitter release-induced by BLA or behavioral reinforcement-in young and aged cognitively impaired rats, after implanting a microdialysis cannula at the dentate gyrus. Samples were taken under baseline conditions and during stimulation of BLA. Rats were water deprived and tested again next day, taking samples after allowing access to water. Higher concentrations of choline, HIAA, aspartate, glutamate, and glycine were found in baseline samples from young animals compared to aged. In young animals, BLA stimulation increased the levels of ACh and reduced norepinephrine and serotonine, while behavioral reinforcement reduced the levels of glutamate and glycine. These effects were absent among aged rats, suggesting that this reduced neurochemical response might be linked to the impaired LTP-reinforcement reported previously.

The protective role of dl-α-lipoic acid in biogenic amines catabolism triggered by Aβ amyloid vaccination in mice

The major pathological consequence of Alzheimer disease (AD) is accumulation of beta-amyloid (Abeta) peptide fibrillar plaque in the brain and subsequent inflammatory reaction associated with the surrounding cells due to the presence of these aggregates. Inflammation is the major complication associated with Abeta peptide vaccination. Abeta peptide activated T-helper cells are shown to enhance the existing-inflammatory conditions in the brain and other organs of AD patients. Hence systematic studies on potential approaches that will prevent inflammation during the vaccination are highly desired. DL-alpha-lipoic acid (LA), an antioxidant with known function as cofactor in mitochondrial dehydrogenase reactions, will be a good candidate to annul the oxidative damage due to vaccination triggered inflammation. For the first time, levels of principal neurotransmitters and their major metabolites in hippocampus and neocortex regions of brain are quantified to find out the level of inflammation. We have used high performance liquid chromatography with electro chemical detection (HPLC-EC) for monitoring neurotransmitter levels. We have shown a significant (p<0.05) reduction of 5-hydroxytryptamine (5-HT), dopamine (DA) and norepinephrine (NE) in the systemic inflammation induced (SI), vaccinated (VA) and inflammation induced vaccinated (IV) mice. Nevertheless their metabolites such as 5-hydroxyindole acetic acid (5-HIAA) and homovanillic acid (HVA) are significantly (p<0.05) increased when compared with control. Interestingly, antioxidant LA treated mice with systemic inflammation (IL), vaccinated (VL) and inflammation induced vaccinated (IVL) mice exhibited enhanced level of 5-HT, DA and NE and the concentration of 5-HIAA and HVA gradually returned to normal. These results suggest a possible new way for monitoring and modifying the inflammation and thereby preventing Abeta vaccination mediated tissue damage.

Cognitive deficits in aged rats correlate with levels of L-arginine, not with nNOS expression or 3,4-DAP-evoked transmitter release in the frontoparietal cortex

Aging is associated with altered neurotransmitter function in the brain. In this study, we measured release parameters for acetylcholine (ACh), norepinephrine and serotonin in the frontoparietal cortex of young and aged rats. We also determined cortical amino acid concentrations and nitric oxide (NO) synthase function. Prior to sacrifice, the rats had been tested for Morris water-maze performance. In aged, compared with young rats, we observed a reduction in both uptake of choline and acetylcholine release. Serotonin release and L-arginine concentrations (a precursor of NO) showed an aging-related increase; however, L-citrulline/L-arginine ratios were decreased in aged rats. Moreover, while most age-related changes in transmitter release or neurochemical markers were not related to the learning performance, L-arginine concentrations were positively correlated to cognitive deficits. NO synthase concentrations were not affected by aging. It is suggested that events related to L-arginine-to-L-citrulline/NO metabolism in the frontoparietal cortex may take part in age-related cognitive deficits.

Behavioral Effects of Basal Forebrain Cholinergic Lesions in Young Adult and Aging Rats

The interactive effects of age and cholinergic damage were assessed behaviorally in young and middle-aged rats. Rats were lesioned at either 3 or 17 months of age by injection of 192 IgG-saporin immunotoxin into the medial septum and the nucleus basalis magnocellularis, and they were then tested on a range of behavioral tasks: a nonmatching-to-position task in a T-maze, an object-recognition task, an object-location task, and an open-field activity test. Depending on the task used, only an age or a lesion effect was observed, but there was no Age X Lesion interaction. Middle-aged and young rats responded to the cholinergic lesions in the same manner. These results show that in the middle-aged rats in which cholinergic transmission was affected, additional injury to the system was not always accompanied by major cognitive dysfunctions.

3,4-DAP-evoked transmitter release in hippocampal slices of aged rats with impaired memory

Based on a slice superfusion technique, this study investigated the release of acetylcholine, noradrenaline and serotonin in the hippocampus of aged rats (25-27 months) showing no or severe deficits in a spatial reference-memory task (water maze). Young adults (3-5 months) were used as controls. 3,4-diaminopyridine (3,4-DAP), a potassium channel antagonist which increases neuronal excitability, was used to evoke the overflow of the three neurotransmitters. The release of [3H]noradrenaline induced by stimulation of presynaptic nicotinic receptors was also assessed. The experiment compared the accumulation and 3,4-DAP-evoked (or nicotine-evoked) overflow of [3H] in hippocampal slices preincubated with [3H]choline, [3H]noradrenaline, or [3H]serotonin. In aged rats, only the accumulation of [3H]serotonin was reduced significantly (-17%). In percent of tissue-[3H], the 3,4-DAP-evoked overflow of [3H]serotonin was increased (+28%), and that of [3H]acetylcholine was reduced (-23%) in the aged rats. The nicotine-evoked overflow of [3H]noradrenaline was not altered in aged rats. There was a significant correlation of water-maze performance (distance to platform) and evoked overflow of [3H]serotonin. It is concluded that hippocampal cholinergic functions are more altered by aging than noradrenergic or serotonergic ones. Excessive excitability of serotonergic terminals, perhaps in addition to cholinergic dysfunction, might be a crucial factor accounting for age-related cognitive deficits in the present population of rats.

Presynaptic regulation of neurotransmitter release in the cortex of aged rats with differential memory impairments

Cluster analysis of water-maze reference-memory performances of 25-27-month-old (compared to 3-5-month-old) rats distinguished subpopulations of young adult rats (YOUNG), aged rats with no significant impairment (AU), aged rats with moderate impairment (AMI), and aged rats with severe impairment (ASI). In the frontoparietal cortex, we subsequently assessed the electrically evoked release of tritium in slices preloaded with [3H]choline, [3H]noradrenaline (NA), or [3H]serotonin (5-HT) and the effects of an agonist (oxotremorine, UK 14,304, and CP 93,129) of the respective autoreceptors. Cholinergic and monoaminergic markers were measured in homogenates. Overall, aged rats exhibited reduced accumulation of [3H]choline (-25%) and weaker evoked transmitter release (in % of accumulated tritium: -44%, -20%, and -34%, for [3H]acetylcholine, [3H]NA, and [3H]5-HT, respectively). In all rats, the inhibitory effects of the autoreceptor agonists on the evoked release of [3H] were comparable. Acetylcholinesterase (AChE), not choline acetyltransferase (ChAT), activity was reduced. The results suggest age-related modifications in the cholinergic, noradrenergic, and serotonergic innervation of the frontoparietal cortex, alterations of evoked transmitter release, but no interference with presynaptic autoinhibition of the release. Neither of these alterations seemed to account for the cognitive impairment assessed.

Does the release of acetylcholine in septal slices originate from intrinsic cholinergic neurons bearing p75ntr receptors? a study using 192 IgG-saporin lesions in rats

In previous studies electrically-evoked release of acetylcholine in septal slices was demonstrated. The present experiment aimed at verifying if this release involved intrinsic neurons bearing p75(NTR) receptors. Long-Evans rats sustained injections of 192 IgG-saporin into the medial septum/diagonal band of Broca (0.8 microg). Sham-operated rats served as controls. Two to 3.5 weeks later, the electrically-evoked release of acetylcholine ([(3)H]ACh) was measured in slices from the lateral septum (LS), medial septum (MS) and diagonal band of Broca (DBB). Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity, and monoamine concentrations were measured in the septum, cortex and hippocampus. The lesion extent was also assessed by ChAT immunostaining in a separate series of rats. In the septum, the number of ChAT-positive neurons was depleted dramatically (>90% at the level of the injection site). In the hippocampus, the lesions reduced ChAT and AChE activity by 91% and 84%, respectively. In the cortex, this reduction was weaker (-55% and -47%). In the septal region, the reduction was either weak or not significant. The evoked release of acetylcholine in septal slices was not reduced, except in the slices from the LS (-64%). The effects of physostigmine and atropine confirmed the presence of autoreceptors. Our data exclude that a major part of the acetylcholine released by MS and DBB slices derived from intrinsic neurons bearing p75(NTR) receptors. In the LS, part of the released acetylcholine might be from projections of such neurons located in the LS, MS and/or DBB. These data also suggest that the MS and the DBB may be the target of extrinsic cholinergic innervation that does not bear p75(NTR) receptors.