Hippocampal α-adrenoceptors involve in the effect of histamine on spatial learning

Noradrenergic projections regulate the acquisition of classically conditioned eyelid responses in wild-type and are impaired in kreisler mice

During embryonic development, heterozygous mutant kreisler mice undergo ectopic expression of the Hoxa3 gene in the rostral hindbrain, affecting the opioid and noradrenergic systems. In this model, we have investigated behavioral and cognitive processes in their adulthood. We confirmed that pontine and locus coeruleus neuronal projections are impaired, by using startle and pain tests and by analyzing immunohistochemical localization of tyrosine hydroxylase. Our results showed that, even if kreisler mice are able to generate eyelid reflex responses, there are differences with wild-types in the first component of the response (R1), modulated by the noradrenergic system. The acquisition of conditioned motor responses is impaired in kreisler mice when using the trace but not the delay paradigm, suggesting a functional impairment in the hippocampus, subsequently confirmed by reduced quantification of alpha2a receptor mRNA expression in this area but not in the cerebellum. Moreover, we demonstrate the involvement of adrenergic projection in eyelid classical conditioning, as clonidine prevents the appearance of eyelid conditioned responses in wild-type mice. In addition, hippocampal motor learning ability was restored in kreisler mice by administration of adrenergic antagonist drugs, and a synergistic effect was observed following simultaneous administration of idazoxan and naloxone.

Cognitive and neuropsychiatric effects of noradrenergic treatment in Alzheimer's disease: systematic review and meta-analysis

BACKGROUND

Dysfunction of the locus coeruleus-noradrenergic system occurs early in Alzheimer's disease, contributing to cognitive and neuropsychiatric symptoms in some patients. This system offers a potential therapeutic target, although noradrenergic treatments are not currently used in clinical practice.

OBJECTIVE

To assess the efficacy of drugs with principally noradrenergic action in improving cognitive and neuropsychiatric symptoms in Alzheimer's disease.

METHODS

The MEDLINE, Embase and ClinicalTrials.gov databases were searched from 1980 to December 2021. We generated pooled estimates using random effects meta-analyses.

RESULTS

We included 19 randomised controlled trials (1811 patients), of which six were judged as 'good' quality, seven as 'fair' and six 'poor'. Meta-analysis of 10 of these studies (1300 patients) showed a significant small positive effect of noradrenergic drugs on global cognition, measured using the Mini-Mental State Examination or Alzheimer's Disease Assessment Scale-Cognitive Subscale (standardised mean difference (SMD): 0.14, 95% CI: 0.03 to 0.25, p=0.01; I2=0%). No significant effect was seen on measures of attention (SMD: 0.01, 95% CI: -0.17 to 0.19, p=0.91; I2=0). The apathy meta-analysis included eight trials (425 patients) and detected a large positive effect of noradrenergic drugs (SMD: 0.45, 95% CI: 0.16 to 0.73, p=0.002; I2=58%). This positive effect was still present following removal of outliers to account for heterogeneity across studies.

DISCUSSION

Repurposing of established noradrenergic drugs is most likely to offer effective treatment in Alzheimer's disease for general cognition and apathy. However, several factors should be considered before designing future clinical trials. These include targeting of appropriate patient subgroups and understanding the dose effects of individual drugs and their interactions with other treatments to minimise risks and maximise therapeutic effects.

PROSPERO REGISTERATION NUMBER

CRD42021277500.

Current Developments on the Role of α1-Adrenergic Receptors in Cognition, Cardioprotection, and Metabolism

The α₁-adrenergic receptors (ARs) are G-protein coupled receptors that bind the endogenous catecholamines, norepinephrine, and epinephrine. They play a key role in the regulation of the sympathetic nervous system along with β and α₂-AR family members. While all of the adrenergic receptors bind with similar affinity to the catecholamines, they can regulate different physiologies and pathophysiologies in the body because they couple to different G-proteins and signal transduction pathways, commonly in opposition to one another. While α₁-AR subtypes (α_1A, α_1B, α_1C) have long been known to be primary regulators of vascular smooth muscle contraction, blood pressure, and cardiac hypertrophy, their role in neurotransmission, improving cognition, protecting the heart during ischemia and failure, and regulating whole body and organ metabolism are not well known and are more recent developments. These advancements have been made possible through the development of transgenic and knockout mouse models and more selective ligands to advance their research. Here, we will review the recent literature to provide new insights into these physiological functions and possible use as a therapeutic target.

How do stupendous cannabinoids modulate memory processing via affecting neurotransmitter systems?

In the present study, we wanted to review the role of cannabinoids in learning and memory in animal models, with respect to their interaction effects with six principal neurotransmitters involved in learning and memory including dopamine, glutamate, GABA (γ-aminobutyric acid), serotonin, acetylcholine, and noradrenaline. Cannabinoids induce a wide-range of unpredictable effects on cognitive functions, while their mechanisms are not fully understood. Cannabinoids in different brain regions and in interaction with different neurotransmitters, show diverse responses. Previous findings have shown that cannabinoids agonists and antagonists induce various unpredictable effects such as similar effect, paradoxical effect, or dualistic effect. It should not be forgotten that brain neurotransmitter systems can also play unpredictable roles in mediating cognitive functions. Thus, we aimed to review and discuss the effect of cannabinoids in interaction with neurotransmitters on learning and memory. In addition, we mentioned to the type of interactions between cannabinoids and neurotransmitter systems. We suggested that investigating the type of interactions is a critical neuropharmacological issue that should be considered in future studies.

Alfa2-adrenoblockers attenuate the elevated plasma cholesterol, anxiety levels and restore impaired spatial memory of rats under the chronic noise exposure

Noise is considered one of the environmental hazards that negatively affect health. It can cause damage to the auditory, neurological, hormonal and cardiovascular systems, in addition to impairing psychological and cognitive functions. Considering the significance of vascular disturbances and oxidative stress in the development of the aforementioned negative effects, the purpose of our investigation was to study the level of high density lipoprotein-cholesterol (HDL-Cl), low density lipoprotein-cholesterol (LDL-Cl), and total cholesterol (TCl) in plasma, in addition to the behavioral characteristics of white rats, and the effects of the α₂-adrenoblockers beditin and mesedin to reveal their antiatherogenic effect during noise exposure. The "Open field" and "Y-maze" tests were used in order to evaluate the behavioral states of the rats. Investigations were carried out on albino rats divided into 4 groups. The 1^st group of rats served as a control. The 2^nd, 3^rd and 4^th groups were exposed to 91 dBA of noise; the duration of exposure was 8 h per day for 60 days. The 3^rd group was injected with beditin and the 4^th group with mesedin, both intraperitoneally and repeatedly. According to our results, the chronic exposure to high-volume noise leads to the increase of plasma TCl and LDL-Cl concentrations and the decrease of HDL-Cl levels, resulting in increase of the atherogenic coefficient, which is estimated to be one of the main cardiovascular disease risk factors. The "Open field" and "Y-maze" tests revealed that chronic noise exposure caused disturbances in the behavioral activity, a noise duration-dependent delay in movement and orientation, increased anxiety and deficit in the animals' spatial memory. The administration of α₂-adrenoblockers to the noise-exposed animals had a regulatoryeffects of varying intensities, depending on the medication used and the studied parameters under the conditions of chronic acoustic stress.

α1-Adrenergic Receptors in Neurotransmission, Synaptic Plasticity, and Cognition

α₁-adrenergic receptors are G-Protein Coupled Receptors that are involved in neurotransmission and regulate the sympathetic nervous system through binding and activating the neurotransmitter, norepinephrine, and the neurohormone, epinephrine. There are three α₁-adrenergic receptor subtypes (α_1A, α_1B, α_1D) that are known to play various roles in neurotransmission and cognition. They are related to two other adrenergic receptor families that also bind norepinephrine and epinephrine, the β- and α₂-, each with three subtypes (β₁, β₂, β₃, α_2A, α_2B, α_2C). Previous studies assessing the roles of α₁-adrenergic receptors in neurotransmission and cognition have been inconsistent. This was due to the use of poorly-selective ligands and many of these studies were published before the characterization of the cloned receptor subtypes and the subsequent development of animal models. With the availability of more-selective ligands and the development of animal models, a clearer picture of their role in cognition and neurotransmission can be assessed. In this review, we highlight the significant role that the α₁-adrenergic receptor plays in regulating synaptic efficacy, both short and long-term synaptic plasticity, and its regulation of different types of memory. We will also present evidence that the α₁-adrenergic receptors, and particularly the α_1A-adrenergic receptor subtype, are a potentially good target to treat a wide variety of neurological conditions with diminished cognition.

Adrenergic alpha-2 receptor antagonists cease augmented oxidation of plasma proteins and anxiety of rats caused by chronic noise exposure

BACKGROUND

Noise is one of the environmental factors, which is considered as a powerful stressor for the organism. Generally, the acoustic stress affects the behavior and physiological state of humans and animals.

AIMS

The goal of this study is to investigate the relationship between chronic noise exposure and the effects of adrenergic alpha-2 receptor antagonists, beditin and mesedin, on the anxiety and oxidation of plasma proteins and fibrinogen in rats.

METHODS

The experiments were carried out on non-linear albino male rats, divided into four groups (six animals in each): 1. Healthy controls 2. Exposed to noise of a level 91 dB(A), eight hours daily, during 7, 30 and 60 days; 3. Injected with 2 mg/kg of beditin (2-(2-amino-4-thiazolyl)-1,4-benzodioxane hydrochloride)); 4. Injected with 10 mg/kg mesedin (2-(2-methyl-amino-thiozolyl)-1,4-benzodioxane hydrochloride). For evaluating the cognitive impairment, the Any-maze test was applied. The level of carbonylation of proteins was assessed by reaction with 2,4-dinitrophenylhydrazine, spectrophotometrically.

RESULTS

Chronic noise decreased locomotor activity and increased anxiety and oxidation of plasma protein and fibrinogen. Intensity of these changes were dependent on the duration of noise exposure.

CONCLUSION

The Alpha 2 adrenoblockers alleviate oxidative modification of plasma proteins and reduce the cognitive impairment caused by chronic exposure to noise.

Combined network pharmacology and virtual reverse pharmacology approaches for identification of potential targets to treat vascular dementia

Dementia is a major cause of disability and dependency among older people. If the lives of people with dementia are to be improved, research and its translation into druggable target are crucial. Ancient systems of healthcare (Ayurveda, Siddha, Unani and Sowa-Rigpa) have been used from centuries for the treatment vascular diseases and dementia. This traditional knowledge can be transformed into novel targets through robust interplay of network pharmacology (NetP) with reverse pharmacology (RevP), without ignoring cutting edge biomedical data. This work demonstrates interaction between recent and traditional data, and aimed at selection of most promising targets for guiding wet lab validations. PROTEOME, DisGeNE, DISEASES and DrugBank databases were used for selection of genes associated with pathogenesis and treatment of vascular dementia (VaD). The selection of new potential drug targets was made by methods of NetP (DIAMOnD algorithm, enrichment analysis of KEGG pathways and biological processes of Gene Ontology) and manual expert analysis. The structures of 1976 phytomolecules from the 573 Indian medicinal plants traditionally used for the treatment of dementia and vascular diseases were used for computational estimation of their interactions with new predicted VaD-related drug targets by RevP approach based on PASS (Prediction of Activity Spectra for Substances) software. We found 147 known genes associated with vascular dementia based on the analysis of the databases with gene-disease associations. Six hundred novel targets were selected by NetP methods based on 147 gene associations. The analysis of the predicted interactions between 1976 phytomolecules and 600 NetP predicted targets leaded to the selection of 10 potential drug targets for the treatment of VaD. The translational value of these targets is discussed herewith. Twenty four drugs interacting with 10 selected targets were identified from DrugBank. These drugs have not been yet studied for the treatment of VaD and may be investigated in this field for their repositioning. The relation between inhibition of two selected targets (GSK-3, PTP1B) and the treatment of VaD was confirmed by the experimental studies on animals and reported separately in our recent publications.

Effects of glucocorticoid and noradrenergic activity on spatial learning and spatial memory in healthy young adults

BACKGROUND

Acute stress leads to a rapid release of noradrenaline and glucocorticoids, which in turn influence cognitive functions such as spatial learning and memory. However, few studies have investigated noradrenergic and glucocorticoid effects on spatial learning and memory in humans. Therefore, we examined the separate and combined effects of noradrenergic and glucocorticoid stimulation on spatial learning and memory.

METHODS

One hundred and four healthy men (mean age = 24.1 years ±SD 3.5) underwent the virtual Morris Water Maze (vMWM) task to test spatial learning and spatial memory retrieval after receiving either 10 mg hydrocortisone or 10 mg yohimbine (an alpha 2-adrenergic receptor antagonist that increases noradrenergic activity), 10 mg hydrocortisone and 10 mg yohimbine combined, or placebo. The vMWM task took place 90 min after yohimbine was administered and 75 min after hydrocortisone was administered. Placebo was given at the same times. Salivary cortisol and alpha amylase levels were measured to check pharmacological stimulation.

RESULTS

Hydrocortisone and yohimbine increased salivary cortisol and alpha amylase levels. Participants' task performance improved over time, suggesting successful spatial learning. However, separate and combined noradrenergic and glucocorticoid stimulation had no effect on spatial learning and spatial memory retrieval compared with placebo.

CONCLUSIONS

In healthy young men, hydrocortisone and/or yohimbine did not alter spatial learning or spatial memory retrieval. Importantly, pharmacological stimulation took place prior to learning. Further studies should examine the effects of glucocorticoid and noradrenergic stimulation during encoding, consolidation, and retrieval.

α1-Adrenoceptors in the hippocampal dentate gyrus involved in learning-dependent long-term potentiation during active-avoidance learning in rats

The hippocampus is the key structure for learning and memory in mammals and long-term potentiation (LTP) is an important cellular mechanism responsible for learning and memory. The influences of norepinephrine (NE) on the modulation of learning and memory, as well as LTP, through β-adrenoceptors are well documented, whereas the role of α1-adrenoceptors in learning-dependent LTP is not yet clear. In the present study, we measured extracellular concentrations of NE in the hippocampal dentate gyrus (DG) region using an in-vivo brain microdialysis and high-performance liquid chromatography techniques during the acquisition and extinction of active-avoidance behavior in freely moving conscious rats. Next, the effects of prazosin (an antagonist of α1-adrenoceptor) and phenylephrine (an agonist of the α1-adrenoceptor) on amplitudes of field excitatory postsynaptic potential were measured in the DG region during the active-avoidance behavior. Our results showed that the extracellular concentration of NE in the DG was significantly increased during the acquisition of active-avoidance behavior and gradually returned to the baseline level following extinction training. A local microinjection of prazosin into the DG significantly accelerated the acquisition of the active-avoidance behavior, whereas a local microinjection of phenylephrine retarded the acquisition of the active-avoidance behavior. Furthermore, in all groups, the changes in field excitatory postsynaptic potential amplitude were accompanied by corresponding changes in active-avoidance behavior. Our results suggest that NE activation of α1-adrenoceptors in the hippocampal DG inhibits active-avoidance learning by modulation of synaptic efficiency in rats.

Neuroprotective, Neurogenic, and Amyloid Beta Reducing Effect of a Novel Alpha 2-Adrenoblocker, Mesedin, on Astroglia and Neuronal Progenitors upon Hypoxia and Glutamate Exposure

Locus coeruleus-noradrenergic system dysfunction is known to contribute to the progression of Alzheimer’s disease (AD). Besides a variety of reports showing the involvement of norepinephrine and its receptor systems in cognition, amyloid β (Aβ) metabolism, neuroinflammation, and neurogenesis, little is known about the contribution of the specific receptors to these actions. Here, we investigated the neurogenic and neuroprotective properties of a new α2 adrenoblocker, mesedin, in astroglial primary cultures (APC) from C57BL/6 and 3×Tg-AD mice. Our results demonstrate that mesedin rescues neuronal precursors and young neurons, and reduces the lactate dehydrogenase (LDH) release from astroglia under hypoxic and normoxic conditions. Mesedin also increased choline acetyltransferase, postsynaptic density marker 95 (PSD95), and Aβ-degrading enzyme neprilysin in the wild type APC, while in the 3×Tg-AD APC exposed to glutamate, it decreased the intracellular content of Aβ and enhanced the survival of synaptophysin-positive astroglia and neurons. These effects in APC can at least partially be attributed to the mesedin’s ability of increasing the expression of Interleukine(IL)-10, which is a potent anti-inflammatory, neuroprotective neurogenic, and Aβ metabolism enhancing factor. In summary, our data identify the neurogenic, neuroprotective, and anti-amyloidogenic action of mesedin in APC. Further in vivo studies are needed to estimate the therapeutic value of mesedin for AD.

Harmaline-induced amnesia: Possible role of the amygdala dopaminergic system

In this study, we examined the effect of bilateral intra-basolateral amygdala (intra-BLA) microinjections of dopamine receptor agents on amnesia induced by a β-carboline alkaloid, harmaline in mice. We used a step-down method to assess memory and then, hole-board method to assess exploratory behaviors. The results showed that pre-training intra-BLA injections of dopamine D1 receptor antagonist and agonist (SCH23390 (0.5μg/mouse) and SKF38393 (0.5μg/mouse), respectively) impaired memory acquisition. In contrast, pre-training intra-BLA injections of dopamine D2 receptor antagonist and agonist (sulpiride and quinpirole, respectively) have no significant effect on memory acquisition. Pre-training intra-peritoneal (i.p.) injection of harmaline (1mg/kg) decreased memory acquisition. However, co-administration of SCH 23390 (0.01μg/mouse) with different doses of harmaline did not alter amnesia. Conversely, pre-training intra-BLA injection of SKF38393 (0.1μg/mouse), sulpiride (0.25μg/mouse) or quinpirole (0.1μg/mouse) reversed harmaline (1mg/kg, i.p.)-induced amnesia. Furthermore, all above doses of drugs had no effect on locomotor activity. In conclusion, the dopamine D1 and D2 receptors of the BLA may be involved in the impairment of memory acquisition induced by harmaline.

Noradrenergic dysfunction in Alzheimer's disease

The brain noradrenergic system supplies the neurotransmitter norepinephrine throughout the brain via widespread efferent projections, and plays a pivotal role in modulating cognitive activities in the cortex. Profound noradrenergic degeneration in Alzheimer's disease (AD) patients has been observed for decades, with recent research suggesting that the locus coeruleus (where noradrenergic neurons are mainly located) is a predominant site where AD-related pathology begins. Mounting evidence indicates that the loss of noradrenergic innervation greatly exacerbates AD pathogenesis and progression, although the precise roles of noradrenergic components in AD pathogenesis remain unclear. The aim of this review is to summarize current findings on noradrenergic dysfunction in AD, as well as to point out deficiencies in our knowledge where more research is needed.