Neurotransmitter Receptors In Brain Research Articles

MRNA Expression of Dopamine Receptors in Peripheral Blood Lymphocytes of Social Networking Sites (SNS) Addicts: A Case-Control Study

Background: The increasing importance of and reliance on social networking sites (SNS) has led people to frequent usage and addiction. The dopaminergic system plays a crucial role in the addiction process. Additionally, research suggests that the level of expression of brain neurotransmitter receptors may be reflected in peripheral blood lymphocytes. Objectives: This study aimed to investigate the expression of dopamine receptors in peripheral blood lymphocytes (PBL) among SNS addicts and their relatives. Patients and Methods: The mRNA expression of dopamine D3, D4, and D5 receptors in peripheral blood lymphocytes was assessed using real-time PCR in SNS addicts (n = 10) and their first-degree relatives (n = 10) compared with normal subjects (n = 10). Results: The findings revealed a significant decrease in D5 and D4 receptor mRNA expression in the PBL of SNS addicts compared to the control group (P < 0.05). In contrast, D3 receptor mRNA levels showed no significant change (P > 0.05). First-degree relatives of SNS addicts also exhibited a significant decrease in D5 receptor mRNA levels compared to the control group (P < 0.05), but unlike SNS addicts, D4 receptor levels did not show any significant decrease. D3 levels also remained unchanged (P > 0.05). Conclusions: Based on the results of this study, considering the genetic factors that strongly influence social network addiction, necessary measures should be implemented to prevent this type of addiction in families and institutions such as schools and universities.

Whole exome/genome sequencing in cyclic vomiting syndrome reveals multiple candidate genes, suggesting a model of elevated intracellular cations and mitochondrial dysfunction.

To utilize whole exome or genome sequencing and the scientific literature for identifying candidate genes for cyclic vomiting syndrome (CVS), an idiopathic migraine variant with paroxysmal nausea and vomiting. A retrospective chart review of 80 unrelated participants, ascertained by a quaternary care CVS specialist, was conducted. Genes associated with paroxysmal symptoms were identified querying the literature for genes associated with dominant cases of intermittent vomiting or both discomfort and disability; among which the raw genetic sequence was reviewed. "Qualifying" variants were defined as coding, rare, and conserved. Additionally, "Key Qualifying" variants were Pathogenic/Likely Pathogenic, or "Clinical" based upon the presence of a corresponding diagnosis. Candidate association to CVS was based on a point system. Thirty-five paroxysmal genes were identified per the literature review. Among these, 12 genes were scored as "Highly likely" (SCN4A, CACNA1A, CACNA1S, RYR2, TRAP1, MEFV) or "Likely" (SCN9A, TNFRSF1A, POLG, SCN10A, POGZ, TRPA1) CVS related. Nine additional genes (OTC, ATP1A3, ATP1A2, GFAP, SLC2A1, TUBB3, PPM1D, CHAMP1, HMBS) had sufficient evidence in the literature but not from our study participants. Candidate status for mitochondrial DNA was confirmed by the literature and our study data. Among the above-listed 22 CVS candidate genes, a Key Qualifying variant was identified in 31/80 (34%), and any Qualifying variant was present in 61/80 (76%) of participants. These findings were highly statistically significant (p < 0.0001, p = 0.004, respectively) compared to an alternative hypothesis/control group regarding brain neurotransmitter receptor genes. Additional, post-analyses, less-intensive review of all genes (exome) outside our paroxysmal genes identified 13 additional genes as "Possibly" CVS related. All 22 CVS candidate genes are associated with either cation transport or energy metabolism (14 directly, 8 indirectly). Our findings suggest a cellular model in which aberrant ion gradients lead to mitochondrial dysfunction, or vice versa, in a pathogenic vicious cycle of cellular hyperexcitability. Among the non-paroxysmal genes identified, 5 are known causes of peripheral neuropathy. Our model is consistent with multiple current hypotheses of CVS.

Review: A history and perspective of mitochondria in the context of anoxia tolerance.

Symbiosis is found throughout nature, but perhaps nowhere is it more fundamental than mitochondria in all eukaryotes. Since mitochondria were discovered and mechanisms of oxygen reduction characterized, an understanding gradually emerged that these organelles were involved not just in the combustion of oxygen, but also in the sensing of oxygen. While multiple hypotheses exist to explain the mitochondrial involvement in oxygen sensing, key elements are developing that include potassium channels and reactive oxygen species. To understand how mitochondria contribute to oxygen sensing, it is informative to study a model system which is naturally adapted to survive extended periods without oxygen. Amongst air-breathing vertebrates, the most highly adapted are western painted turtles (Chrysemys picta bellii), which overwinter in ice-covered and anoxic water bodies. Through research of this animal, it was postulated that metabolic rate depression is key to anoxic survival and that mitochondrial regulation is a key aspect. When faced with anoxia, excitatory neurotransmitter receptors in turtle brain are inhibited through mitochondrial calcium release, termed "channel arrest". Simultaneously, inhibitory GABAergic signalling contributes to the "synaptic arrest" of excitatory action potential firing through a pathway dependent on mitochondrial depression of ROS generation. While many pathways are implicated in mitochondrial oxygen sensing in turtles, such as those of adenosine, ATP turnover, and gaseous transmitters, an apparent point of intersection is the mitochondria. In this review we will explore how an organelle that was critical for organismal complexity in an oxygenated world has also become a potentially important oxygen sensor.

Relaxation Effects of Essential Oils Are Explained by Their Interactions with Human Brain Neurotransmitter Receptors and Electroencephalography Rhythms.

Inhaled essential oils (EOs) are bioavailable to the brain and are consistently reported to promote relaxation effects. Their mechanisms of action are however not well understood. The aim of this investigation was to assess the neuroactivity of EOs based on their (i) binding interactions to neurotransmitter receptors and (ii) bioelectrical activities in the brain as measured by electroencephalography (EEG). These EO properties were compared to those of reference pharmaceutical compounds with effects also measured by EEG. Relative receptor binding efficacies of 10 reference compounds, 180 EOs, and 9 EO extracts with 7 different neurotransmitter receptors were calculated using in silico molecular docking procedures. Changes in brain EEG rhythms, as standardized changes in absolute power, were determined for the reference compounds and selected EOs and compared to receptor binding efficacy results. The reference compounds had diverse receptor binding patterns, with EEG responses dominated by EEG-delta wave frequencies. In contrast, the receptor binding pattern of the EOs was remarkably consistent and replicated a subclinical affinity pattern corresponding to the inhibitory glycine-α-GLRA3 and dopamine-D2 receptors, producing responses dominated by EEG-alpha wave frequencies. The results support the hypothesis that EOs stimulate neuroactivity by modulating patterns of neurotransmission affecting alpha wave EEG responses.

The Effect of Membrane Polyunsaturated Fatty Acids on Receptor Partitioning to Ordered Domains

Numerous G protein-coupled receptors (GPCRs) contain cholesterol binding sites, and are therefore assumed to partition into cholesterol-rich ordered membrane domains to function properly. Neurotransmitter receptors - many of which are GPCRs and located mainly in the nervous system - are responsible for regulating our behavior and mood, and their compromised signaling often results in neurodegenerative diseases. Interestingly, many such diseases are associated with a decrease in polyunsaturated fatty acid (PUFA) levels in the brain.The PUFAs, usually paired with a saturated lipid tail in hybrid lipids, are known to favorably interact with receptors. This might - in addition to modulating the activation of individual receptors - also affect larger scale GPCR organization, including their partitioning between ordered and disordered membrane domains. However, such effects are very tedious to be studied experimentally, and therefore the determinants of membrane protein partitioning remain currently elusive.Here, using multi-scale computer simulations and free energy calculations, we show that the association of the adenosine A2A receptor, a prototypical GPCR, with the PUFA tail of a hybrid lipid drastically affects its partitioning. The strong PUFA-receptor interaction results in the formation of a well defined lipid corona, whose outer shell is consists of the saturated tails of a hybrid lipid. This cushion softens the membrane perturbation caused by the rough receptor surface and hence makes it more compatible with ordered membrane domains. Interestingly, this favorable solvation by PUFAs seems to be characteristic only for membrane proteins consisting of helical bundles.Our results reveal an unexpected connection between PUFAs and disease: A decrease in the brain PUFA levels might affect GPCR partitioning, thereby compromising their function and perhaps eventually leading to disease. This finding, together with our previous study revealing the role of PUFAs on GPCR oligomerization, highlights the complex interplay of brain membrane lipid composition and neurotransmitter receptor function.

The Effects of Kainic Acid-Induced Seizure on Gene Expression of Brain Neurotransmitter Receptors in Mice Using RT2 PCR Array.

Introduction:Kainic acid (KA) induces neuropathological changes in specific regions of the mouse hippocampus comparable to changes seen in patients with chronic temporal lobe epilepsy (TLE). According to different studies, the expression of a number of genes are altered in the adult rat hippocampus after status epilepticus (SE) induced by KA. This study aimed to quantitatively evaluate changes in the gene expression of brain neurotransmitter receptors one week after administration of kainic acid in the mouse hippocampus.Methods:We used 12 BALB/c mice in this study and randomly divided them into 2 groups. To both groups, saline (IP) was administered for 7 days, and on the last day, KA (10 mg/kg, IP) was injected 30 minutes after administration of saline. Subsequently, behavioural changes were observed in mice. Then, in one group (1 day group), 2 hours and in another group (7 days group), 7 days after KA administration, the hippocampus tissue of mice was removed and used for gene expression analyses. Total brain RNA was isolated and reversely transcribed. We performed qPCR using RT2 Profiler TMPCR Array Mouse Neurotransmitter Receptors and Regulators (QIAGEN) containing primers for 84 genes. In this regard, we selected 50 related genes for KA model.Results:Our results showed significant changes in the gene expression of GABAA subunits receptors, including α1-α3, α5, α6, β2, β3, γ1, ρ, and rho1-2 on day 7 compared with the day 1.Conclusion:Expression of both inhibitory and excitatory receptors changed after one week. Further studies are needed to find more molecular changes in the gene expression of brain neurotransmitter receptors and regulators over longer periods of time in KA models using RT2 PCR array.

Effect of Gestational Exposure of Cypermethrin on Postnatal Development of Brain Cytochrome P450 2D1 and 3A1 and Neurotransmitter Receptors.

Oral administration of low doses (1.25, 2.5, or 5 mg/kg) of cypermethrin to pregnant Wistar rats from gestation days 5 to 21 led to dose-dependent differences in the induction of cytochrome P450 2D1 (CYP2D1) and 3A1 messenger RNA (mRNA) and protein in brain regions isolated from the offsprings postnatally at 3 weeks that persisted up to adulthood (12 weeks). Similar alterations were observed in the expression of GABAergic, muscarinic, dopaminergic, and serotonergic neurotransmitter receptors in brain regions of rat offsprings. Rechallenge of the prenatally exposed offsprings at adulthood (12 weeks old) with cypermethrin (p.o., 10 mg/kg for 6 days) led to a greater magnitude of alterations in the expression of CYPs, neurotransmitter receptors, and neurotransmitter receptor binding in the brain regions when compared to the control offsprings treated at adulthood with cypermethrin or prenatally exposed offsprings. A greater magnitude of decrease was also observed in the spontaneous locomotor activity (SLA) in prenatally exposed offsprings rechallenged with cypermethrin. The present data indicating similarities in the alterations in the expression of CYPs (2D1 and 3A1) and neurotransmitter receptors in brain has led us to suggest that endogenous function regulating CYPs is possibly associated with neurotransmission processes. A greater magnitude of alterations in CYP2D1, 3A1, neurotransmitter receptors, and SLA in rechallenged animals has further provided evidence that alterations in CYPs are possibly linked with neurotransmission processes.

The effects of scopolamine and the nootropic drug phenotropil on rat brain neurotransmitter receptors during testing of the conditioned passive avoidance task

We studied the effects of administration of the new nootropic drug phenotropil (N-carbamoylmethyl-4-phenyl-2-pyrrolidone) at a dose of 100 mg/kg on the quantitative characteristics of dopamine (DA), serotonin (5-HT), glutamate (NMDA), GABA-A (BDZ), and acetylcholine (nACh) receptors in rats using the conditioned passive avoidance task (PAT) under normal conditions and during scopolamine-induced amnesia ex vivo. We found that the cholinolytic drug scopolamine induced a substantial increase in the density (Bmax) of n-choline receptors in the cortex (by 99% as compared to the control) and NMDA receptors in the hippocampus (by 93%). A single administration of phenotropil (100mg/kg, intraperitoneally) abolished the effect of scopolamine and decreased the number of nACh and NMDA receptors by 46% and 14%, respectively. Phenotropil also abolished the effect of scopolamine on the benzodiazepine receptors and dopamine D1 receptors. Scopolamine decreased the density of D1 receptors by 20% and BDZ receptors by 17%, whereas phenotropil increased the density of receptors by 16% and 25%, respectively. Phenotropil considerably increased the density of dopamine D2 and D3 receptors by 29% and 62%, respectively. Scopolamine also increased the density of D3 receptors by 44% as compared to the control. We did not find any changes in the binding characteristics of 5-HT2 receptors during scopolamine-induced amnesia or during phenotropil treatment. These results demonstrate the role of these receptors in the development of scopolamine-induced amnesia and in neurochemical mechanisms of the anti-amnestic effects of phenotropil.

Late-onset seizures associated with quetiapine poisoning

Quetiapine, a second-generation antipsychotic, acts at multiple brain neurotransmitter receptors and has the potential for serious complications. Although seizures have been described in the literature, delayed seizure onset has not been reported. We report the first case of delayed seizures after a significant quetiapine overdose. A 27-year-old female presented to the emergency department following an overdose of approximately 30 g of quetiapine. Twenty-four hours after arrival, the patient had 2 seizures. The patient was then intubated and remained in the ICU for four days. EEG was negative for epileptiform activity. The serum quetiapine levels (MedTox, St. Paul, MN) were 8.67 mg/L on hospital day one and 3.28 mg/L on hospital day three. Quetiapine poisoning, with serum levels, associated with seizures has been reported in one prior case. Our case report represents late-onset seizures with serum levels above therapeutic range (>1 mg/L). The serum concentrations of quetiapine in this case were consistent with those in postmortem case reports.

Brain neurotransmitter receptor-binding characteristics in rats after oral administration of haloperidol, risperidone and olanzapine

The present study was conducted to characterize the binding of neurotransmitter receptors (dopamine D 2, serotonin 5-HT 2, histamine H 1, adrenaline α 1 and muscarine M l receptors) in the rat's brain after the oral administration of haloperidol, risperidone, and olanzapine. Haloperidol at 1 and 3 mg/kg displayed significant activity to bind the D 2 receptor (increase in the Kd value for [ 3H]raclopride binding) in the corpus striatum with little change in the activity toward the 5-HT 2 receptor (binding parameters for [ 3H]ketanserin). In contrast, risperidone (0.1–3 mg/kg) showed roughly 30 times more affinity for the 5-HT 2 receptor than D 2 receptor. Also, olanzapine (1–10 mg/kg) was most active toward the H 1 receptor in the cerebral cortex, corpus striatum, and hippocampus, was less active in binding 5-HT 2 and D 2 receptors, and showed the least affinity for α 1 and M 1 receptors. In conclusion, haloperidol and risperidone administered orally selectively bind D 2 and 5-HT 2 receptors, respectively, in the rat brain, while olanzapine binds H 1, 5-HT 2, and D 2 receptors more than α 1 and M 1 receptors.

Subdivisions of human parietal area 5 revealed by quantitative receptor autoradiography: a parietal region between motor, somatosensory, and cingulate cortical areas

Brodmann's area (BA) 5 of the human superior parietal cortex occupies a central anatomical position between the primary motor (BA 4), somatosensory (area 3b and BA 2), cingulate (area 23c), and superior parietal association cortex (BA 7). We studied the regional and laminar distributions of the binding sites of 12 different neurotransmitter receptors (glutamatergic: AMPA, kainate, NMDA; GABAergic: GABA A, GABA B; cholinergic: muscarinic M2, nicotinic; adrenergic: α 1, α 2; serotoninergic: 5-HT 1A, 5-HT 2; dopaminergic: D1) in human postmortem brains by means of quantitative receptor autoradiography, since the structural and functional aspects of human BA 5 are widely unknown, and previous observations have demonstrated characteristic differences in receptor distribution between motor and somatosensory areas. Binding site densities were measured in the cytoarchitectonically defined BA 5 and surrounding regions. Similarities and differences of receptor distribution between cortical areas were studied by cluster analysis of mean binding site densities averaged over all cortical layers, univariate and multivariate statistics, and by density profiles representing laminar receptor distribution patterns. Based on regional heterogeneities of binding site densities and of the cytoarchitecture within BA 5, we suggest a subdivision into three subareas: medial area 5M, lateral area 5L, and area 5Ci in the region around the cingulate sulcus. BA 5 is therefore a heterogeneous cortical region, comprising three subareas showing receptor expression patterns similar to the adjoining higher order somatosensory, multimodal parietal, or cingulate regions. These findings suggest that human BA 5 constitutes a higher order cortical area, clearly distinct from the primary somatosensory and motor cortex.

Neuroendocrine pharmacology of stress

Exposure to hostile conditions initiates responses organized to enhance the probability of survival. These coordinated responses, known as stress responses, are composed of alterations in behavior, autonomic function and the secretion of multiple hormones. The activation of the renin–angiotensin system and the hypothalamic–pituitary–adrenocortical axis plays a pivotal role in the stress response. Neuroendocrine components activated by stressors include the increased secretion of epinephrine and norepinephrine from the sympathetic nervous system and adrenal medulla, the release of corticotropin-releasing factor (CRF) and vasopressin from parvicellular neurons into the portal circulation, and seconds later, the secretion of pituitary adrenocorticotropin (ACTH), leading to secretion of glucocorticoids by the adrenal gland. Corticotropin-releasing factor coordinates the endocrine, autonomic, behavioral and immune responses to stress and also acts as a neurotransmitter or neuromodulator in the amygdala, dorsal raphe nucleus, hippocampus and locus coeruleus, to integrate brain multi-system responses to stress. This review discussed the role of classical mediators of the stress response, such as corticotropin-releasing factor, vasopressin, serotonin (5-hydroxytryptamine or 5-HT) and catecholamines. Also discussed are the roles of other neuropeptides/neuromodulators involved in the stress response that have previously received little attention, such as substance P, vasoactive intestinal polypeptide, neuropeptide Y and cholecystokinin. Anxiolytic drugs of the benzodiazepine class and other drugs that affect catecholamine, GABA A, histamine and serotonin receptors have been used to attenuate the neuroendocrine response to stressors. The neuroendocrine information for these drugs is still incomplete; however, they are a new class of potential antidepressant and anxiolytic drugs that offer new therapeutic approaches to treating anxiety disorders. The studies described in this review suggest that multiple brain mechanisms are responsible for the regulation of each hormone and that not all hormones are regulated by the same neural circuits. In particular, the renin–angiotensin system seems to be regulated by different brain mechanisms than the hypothalamic–pituitary–adrenal system. This could be an important survival mechanism to ensure that dysfunction of one neurotransmitter system will not endanger the appropriate secretion of hormones during exposure to adverse conditions. The measurement of several hormones to examine the mechanisms underlying the stress response and the effects of drugs and lesions on these responses can provide insight into the nature and location of brain circuits and neurotransmitter receptors involved in anxiety and stress.

Regulation of GRK 2 and 6, β-arrestin-2 and associated proteins in the prefrontal cortex of drug-free and antidepressant drug-treated subjects with major depression

G protein-coupled receptor kinases (GRKs) and β-arrestin-2 play a crucial role in the regulation of neurotransmitter receptors in brain. In this study, GRK 2, GRK 6, β-arrestin-2 and associated proteins (Gβ proteins and protein phosphatase (PP)-2A) were quantitated in parallel (immunodensity with specific antibodies) in brains of depressed subjects (drug-free and antidepressant-treated) to investigate the effect of major depression and antidepressant drugs on these receptor regulatory proteins. Specimens of the prefrontal cortex (Brodmann’s area 9) were collected from 19 suicide and non-suicide depressed subjects and 13 control subjects. In drug-free ( n=9), but not in antidepressant-treated ( n=10), depressed subjects an increase in the density of membrane-associated GRK 2 (30%, n=9, P=0.005) was found compared with that in sex-, age-, and PMD-matched controls. Comparison between drug-free and antidepressant-treated depressed subjects showed that GRK 2 was reduced in membrane (39%, n=10, P=0.008) and cytosolic (44%, n=10, P=0.09) preparations after antidepressant drug treatment. In contrast, membrane-associated GRK 6 (drug-free and antidepressant-treated depressed subjects) was found unchanged when compared with that in matched controls. Similarly, the densities of β-arrestin-2, PP-2A, and Gβ proteins were not significantly different from those in matched controls. There was a positive correlation between the immunodensities of GRK 2 and β-arrestin-2 in membrane preparations ( r=0.48, n=19, P=0.04), suggesting that both proteins are regulated in a coordinated manner in brains of depressed subjects. The results of this study indicate that major depression is associated with upregulation of brain GRK 2, but not GRK 6, and that antidepressant drug treatment appears to induce downregulation of GRK 2 protein.

G protein-coupled receptor kinases, β-arrestin-2 and associated regulatory proteins in the human brain: postmortem changes, effect of age and subcellular distribution

G protein-coupled receptor kinases (GRKs) and β-arrestin-2 play a crucial role in the regulation of neurotransmitter receptors in brain. In this study, GRK2, GRK6, β-arrestin-2 and associated regulatory proteins (Gβ proteins and protein phosphatase (PP)-2A) were quantitated in human brains (immunodensity with specific antibodies) to assess for postmortem changes (pattern of protein degradation) and to investigate the effect of aging on these regulatory proteins as well as their subcellular distribution (cytosol and membrane fractions). In brain (prefrontal cortex, total homogenate) of healthy subjects ( n=14) the immunodensities of GRK2 ( r=−0.76), GRK6 ( r=−0.64), β-arrestin-2 ( r=−0.57), Gβ proteins ( r=−0.59) and neurofilament (NF)-L ( r=−0.64), but not PP-2A, declined markedly with the length of postmortem delay (PMD, 3–81 h). With these linear decay models, the average decreases per 12 h of PMD (from 12 to 72 h) were 7–11% for the various proteins. The immunodensities of GRK2 ( r=−0.71), GRK6 ( r=−0.61), and β-arrestin-2 ( r=−0.54) in human brain ( n=12) also declined with aging (16 to 87 years) and the average decreases per decade (from 20 to 80 years) were 3–5%. In contrast, the immunodensities of PP-2A, Gβ and NF-L in brain did not correlate significantly with the age of the subject at death (16–87 years). The immunodensities of GRK2/6 and β-arrestin-2 showed marked individual variations and were strongly reduced after several freeze/thaw cycles. In the prefrontal cortex the subcellular distribution (cytosol/membrane) of the two GRKs differed markedly (GRK2: 60%/40%; GRK6: 5%/95%), and that of β-arrestin-2 was as expected for a soluble protein (60%/40%). In brains of healthy subjects, the immunodensities of cytosolic GRK2 and β-arrestin-2 correlated, respectively, with those of membrane-associated GRK2 ( r=0.67, P=0.049, n=9) and membrane-associated β-arrestin-2 ( r=0.77, P=0.01, n=9). The results of this study emphasize the importance of examining relevant variables (PMD, age) and potential artifacts (individual variation, freeze–thawing effect) when designing signal transduction studies in neuropsychiatric disorders using the postmortem human brain.

The N-Methyl-[formula omitted]-aspartate Neurotransmitter Receptor Is a Mammalian Brain Target for the Dinoflagellate Pfiesteria piscicida Toxin

Blooms of Pfiesteria piscicida, a dinoflagellate in eastern U.S. coastal rivers, are believed to secrete toxins that kill fish and produce short-term memory loss in humans. Only one or two of Pfiesteria's multiple stages secrete the toxin, and only under certain environmental conditions. Thus, neither the presence of Pfiesteria nor fish kill alone can be indicative of toxin presence. The objective of this study was to identify the mammalian molecular brain target for the toxin that is associated with decrements in memory. Seven rat brain neurotransmitter receptors were selected to study because of their reported roles in cognitive function: receptors for nicotine, muscarine, AMPA/kainate, N-methyl-d-aspartate (NMDA), γ-aminobutyric acid, and dopamine 1 and 2. The effects of 17 environmental and laboratory samples on radioactive ligand binding to these receptors were studied. Of the seven receptors, binding only to the NMDA receptor was inhibited by only the two Pfiesteria-containing waters (identified by PCR) that also killed fish, and not by any of the other 15 samples tested. It is suggested that inhibition of NMDA-receptor binding is the cause of memory loss in exposed humans. Thus, it could be a useful biomarker for the toxin's presence in rivers for decisions on closures and for identification of the fractions containing the toxin during its purification. Knowledge of the toxin's molecular target, and how it affects its function, also leads to suggestions for therapeutics to use in animal models.

Effect of estradiol and tamoxifen on brain membranes: investigation by infrared and fluorescence spectroscopy

Nongenomic effects of steroids on rat brain neurotransmitter transporters and receptors have been reported in several laboratories. In the present study, we have investigated possible membrane effects of 17α- and 17β-estradiol, as well as tamoxifen, by studying their interactions with synthetic phospholipid membranes using Fourier transform infrared spectroscopy. We have also used the fluidity of rat striatal and frontal cortex membranes, as determined by fluorescence depolarization of the probe 1,6-diphenyl-1,3,5-hexatriene (DPH), to probe the effects of these drugs on membranes. Our results show that tamoxifen induces conformational disorder along the acyl chains of deuterated dimirystoylphosphatidylcholine and decreases the gel to liquid-crystalline phase transition temperature by approximately 10°C. Similar effects, although less pronounced, were observed with 17β-estradiol, whereas 17α-estradiol had no significant effect. The DPH fluorescence anisotropy of striatum and frontal cortex membranes was decreased in vitro with 17β-estradiol or tamoxifen and also with 17α-estradiol, but to a lesser extent. These results suggest a stereospecific estradiol effect on membranes and that the effects of these compounds are not related to their activity on estrogen receptors. These observations support a different mechanism of action of steroids that could be implicated in their neuroprotective activity.

Altered brain neurotransmitter receptors in transgenic mice expressing a portion of an abnormal human huntington disease gene.

Loss of neurotransmitter receptors, especially glutamate and dopamine receptors, is one of the pathologic hallmarks of brains of patients with Huntington disease (HD). Transgenic mice that express exon 1 of an abnormal human HD gene (line R6/2) develop neurologic symptoms at 9-11 weeks of age through an unknown mechanism. Analysis of glutamate receptors (GluRs) in symptomatic 12-week-old R6/2 mice revealed decreases compared with age-matched littermate controls in the type 1 metabotropic GluR (mGluR1), mGluR2, mGluR3, but not the mGluR5 subtype of G protein-linked mGluR, as determined by [3H]glutamate receptor binding, protein immunoblotting, and in situ hybridization. Ionotropic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and kainate receptors were also decreased, while N-methyl-D-aspartic acid receptors were not different compared with controls. Other neurotransmitter receptors known to be affected in HD were also decreased in R6/2 mice, including dopamine and muscarinic cholinergic, but not gamma-aminobutyric acid receptors. D1-like and D2-like dopamine receptor binding was drastically reduced to one-third of control in the brains of 8- and 12-week-old R6/2 mice. In situ hybridization indicated that mGluR and D1 dopamine receptor mRNA were altered as early as 4 weeks of age, long prior to the onset of clinical symptoms. Thus, altered expression of neurotransmitter receptors precedes clinical symptoms in R6/2 mice and may contribute to subsequent pathology.

Localization of a novel human RNA-editing deaminase (hRED2 or ADARB2) to chromosome 10p15.

RNA-editing deaminase 2 (RED2; ADARB2) is a newly identified potential double-stranded RNA adenosine deaminase. It is the third member of this family, which includes DRADA and RED1. Genes of this family are candidates for involvement in neurological diseases such as epilepsy, because of their expression patterns and described functions. All three described genes are well expressed in brain, and DRADA and RED1 have been shown to play a role in the editing of mRNAs coding for glutamate receptor subunits in vitro, thereby changing the properties of these channels, which are the main excitatory neurotransmitter receptors in brain. Here we report the mapping of the human RED2 (hRED2; ADARB2) gene. Using the sequence of rat RED2, we identified a homologous human expressed sequence tag, and subsequently designed primers in the 3' untranslated region of the hRED2 transcript to perform polymerase chain reaction amplification on two somatic cell hybrid mapping panels. This allowed us to localize hRED2 on chromosome 10p15; until now, no genetic diseases have been mapped in this region or in the syntenic mouse chromosomal region that may involve RED2.

Molecular biology of the GABA(A) receptor: functional domains implicated by mutational analysis.

GABA(A) receptors are the major inhibitory neurotransmitter receptors in mammalian brain. They belong to a family of ligand-gated ion channels that also includes the nicotinic acetylcholine receptors, glycine receptors and 5HT(3) receptors. Each receptor in the family is believed to be a pentamer of homologous subunits that assemble to form a central transmembrane ion pore which, in the case of the GABA(A) receptor, is anion-selective. For almost twenty years, there has been tremendous interest in the structure and function of GABA(A) receptors, not only because of their importance in regulating brain excitability but also because these proteins are the specific targets for a wide variety of therapeutic agents including the anxiolytic benzodiazepines and barbiturates. Molecular cloning has revealed that GABA(A) receptors are heterogeneous, being formed by combinations of different isoforms of several subunit classes (alpha, beta, gamma, delta). The physiological and pharmacological properties of individual GABAA receptor subtypes appear to depend on their precise subunit complement. In this review, we focus on the application of modern techniques in molecular biology, particularly mutational analysis, to identify structural domains of these receptors that are important for ligand recognition and receptor function.

Neurobiology of Rett syndrome.

From a neurobiologic perspective, Rett syndrome appears to disrupt the growth of axonodendritic connections among neurons. The cell packing density within the grey matter is increased but the total number of neurons is relatively normal, except for selected neuronal populations such as the nucleus basalis of Meynert (NBM) and the substantia nigra. Neurochemical assays of postmortem brain from patients with Rett syndrome patients demonstrate reductions in choline acetyltransferase (ChAT), the acetylcholine synthetic enzyme localized in NBM nerve terminals. In an animal model, early postnatal injury to the cholinergic pathways projected from the NBM causes permanent disruption of developing cholinergic neurons and a behavioral disorder on maze testing. The results suggest a mechanism by which early deficits in cholinergic and dopamine neurons projecting to the cerebral cortex from the brainstem and basal forebrain could disrupt axonodendritic development in the cerebral cortex. Studies in our laboratory are examining the mechanisms for these effects as well as the distribution and densities of neurotransmitter receptors in postmortem brains from Rett patients.