Understanding the Global Problem of Drug Addiction is a Challenge for IDARS Scientists

IDARS is an acronym for the International Drug Abuse Research Society. Apart from our scientific and educational purposes, we communicate information to the general and scientific community about substance abuse and addiction science and treatment potential. Members of IDARS are research scientists and clinicians from around the world, with scheduled meetings across the globe. IDARS is developing a vibrant and exciting international mechanism not only for scientific interactions in the domain of addiction between countries but also ultimately as a resource for informing public policy across nations. Nonetheless, a lot more research needs to be done to better understand the neurobiological basis of drug addiction - A challenge for IDARS scientists.

Identifying changes in the synaptic proteome of cirrhotic alcoholic superior frontal gyrus

Hepatic complications are a common side-effect of alcoholism. Without the detoxification capabilities of the liver, alcohol misuse induces changes in gene and protein expression throughout the body. A global proteomics approach was used to identify these protein changes in the brain. We utilised human autopsy tissue from the superior frontal gyrus (SFG) of six cirrhotic alcoholics, six alcoholics without comorbid disease, and six non-alcoholic non-cirrhotic controls. Synaptic proteins were isolated and used in two-dimensional differential in-gel electrophoresis coupled with mass spectrometry. Many expression differences were confined to one or other alcoholic sub-group. Cirrhotic alcoholics showed 99 differences in protein expression levels from controls, of which half also differed from non-comorbid alcoholics. This may reflect differences in disease severity between the sub-groups of alcoholics, or differences in patterns of harmful drinking. Alternatively, the protein profiles may result from differences between cirrhotic and non-comorbid alcoholics in subjects’ responses to alcohol misuse. Ten proteins were identified in at least two spots on the 2D gel; they were involved in basal energy metabolism, synaptic vesicle recycling, and chaperoning. These post-translationally modified isoforms were differentially regulated in cirrhotic alcoholics, indicating a level of epigenetic control not previously observed in this disorder.

Transmitter amino acid neurochemistry in chronic alcoholism with and without cirrhosis of the liver

Neurotransmitter receptor studies are beginning to be applied more widely to human brain tissue obtained at autopsy. By taking tissue from well-documented cases which have been extensively characterized on histological and morphometric criteria, it is becoming possible to make clinicopathological correlations in studies of the effects of chronic alcohol abuse. Recent findings of alterations in the nature and amounts of amino acid neurotransmitter receptors in alcoholism are summarized, with special emphasis on the effects of chronic severe liver disease. There are selective changes in receptors in the superior frontal cortex of alcoholics. There is a marked increase in the density of the GABA binding site, and a lesser change in the density of the 'central-type' benzodiazepine site, on the GABAA-benzodiazepine receptor complex. In contrast, glutamate receptors may be much less affected. Together with morphological and cognitive studies, the results suggest that the superior frontal cortex is preferentially damaged in chronic alcoholism. An increase in 'central-type' benzodiazepine sites in both superior frontal cortex and motor cortex in cirrhotic alcoholics may reflect a more global brain damage, as observed in morphological studies. However, it should be noted the changes in [3H]GABA/muscimol binding were less pronounced in cirrhotic alcoholics than in non-cirrhotic alcoholics.

NMDA receptor subunit-dependent modulation by conantokin-G and Ala(7)-conantokin-G

The modulation of recombinant NMDA receptors by conantokin-G (con-G) and Ala7-conantokin-G (Ala7-Con-G) was investigated in Xenopus oocytes injected with capped RNA coding for NR1 splice variants and NR2 subunits using the two-electrode voltage clamp technique. Glutamate exhibited a marginally higher apparent affinity for NR2A-containing receptors than NR2B-containing receptors, regardless of the NR1 subunit present. Conantokins were bath applied to give cumulative concentration responses in the presence of 3 and 30 mum glutamate. Both contantokins exhibited biphasic concentration-response relationships at NR2A-containing NMDA receptors, producing potentiation at low conantokin concentrations and inhibition at high concentrations. These effects were stronger with glutamate concentrations near its EC50, and less marked at saturating concentrations. In contrast, the conantokin concentration-response relation was monophasic and inhibitory at NR2B-containing receptors. We conclude that the combinations of subunits that comprise the NMDA receptor complex influence conantokin and glutamate affinities and the nature of the responses to conantokins.

The effects of alanine-substituted conantokin-G and ifenprodil on the human spermine-activated N-methyl-D-aspartate receptor

We evaluated the effects of Ala-7-conantokin-G (Con-G(A7)) and ifenprodil on the modulation by spermine of [(3)H]MK801 binding to human cortical membranes. Human cortical tissue was obtained at autopsy and stored at -80 degrees C until assay. Both Con-G(A7) and ifenprodil inhibited [(3)H]MK801 binding, but spermine affected these inhibitions differently. Con-G(A7) IC(50) changed little with spermine concentration, indicative of a non-competitive interaction, whereas the rightward shift in ifenprodil IC(50) with increasing spermine concentration suggested partial competition. When the two agents were tested against the biphasic activation of [(3)H]MK801 binding by spermine, they again differed in their effects. In the activation phase Con-G(A7) was a non-competitive inhibitor of spermine activation, and may even enhance the spermine EC(50), while the ifenprodil data indicated a partially competitive interaction. Both agents were non-competitive in the inhibitory phase. Overall, the data suggest that Con-G(A7) and ifenprodil interact differently with the polyamine modulation of the glutamate-N-methyl-D-aspartate receptor.

Association studies of neurotransmitter gene polymorphisms in alcoholic Caucasians

Ethanol enhances mesolimbic/cortical dopamine activity in reward and reinforcement circuits. We investigated the hypothesis that risk for alcoholism may be mediated by genes for neurotransmitters associated with the dopamine reward system as well as genes for enzymes involved in ethanol metabolism. DNA was extracted from brain tissue collected at autopsy from pathologically characterized alcoholics and controls. PCR-based assays showed that alcoholism was associated with polymorphisms of the dopamine D2 receptor (DRD2) TaqI B (P = .029) and the GABAA-beta2 subunit C1412T (P = .012) genes, but not with the glutamate receptor subunit gene NMDAR2B (366C/G), the serotonin transporter gene (5HTTL-PR), the dopamine transporter gene DAT1(SLC6A3), the dopamine D2 receptor gene DRD2 TaqI A, or the GABAA alpha1(A15G), alpha6(T1519C), and gamma2(G3145A) subunit genes. The glial glutamate transporter gene EAAT2 polymorphism G603A was associated with alcoholic cirrhosis (P = .048). The genotype for the most active alcohol dehydrogenase enzyme ADH1C was associated with a lower risk of alcoholism (P = .026) and was less prevalent in alcoholics with DRD2TaqIA2/A2 (P = .047), GABAA-beta2 1412C/C (P = .01), or EAAT2 603G/A (P = .022) genotypes. Combined DRD2TaqI A or B with GABAA-beta2 or EAAT2 G603A genotypes may have a concerted influence in the predisposition to alcoholism.

Increased TUNEL positive cells in human alcoholic brains

Alcohol-sensitive neuronal cell loss, which has been reported in the superior frontal cortex and hippocampus, may underlie the pathogenesis of subsequent cognitive deficits. In the present study, we have used the TUNEL labeling to detect the DNA damage in human alcoholic brains. Seven out of eleven alcoholics exhibited TUNEL-positive cells in both superior frontal cortex and hippocampus, which were co-localized with GFAP immunoreactivity. In contrast, almost no positive cells were detected in the non-alcoholic controls. None of the TUNEL-positive cells showed any typical morphological features of apoptosis or necrosis. TUNEL-positive cells observed in the present study may indicate DNA damage induced by ethanol-related overproduction of reactive oxygen species.

Synaptic vesicle transport and synaptic membrane transporter sites in excitatory amino acid nerve terminals in Alzheimer disease

The apparent l-[3H]glutamate uptake rate (v') was measured in synaptic vesicles isolated from cerebral cortex synaptosomes prepared from autopsied Alzheimer and non-Alzheimer dementia cases, and age-matched controls. The initial synaptosome preparations exhibited similar densities of d-[3H]aspartate membrane binding sites (BMAX values) in the three groups. In control brain the temporal cortex d-[3H]aspartate BMAX was 132% of that in motor cortex, parallel with the l-[3H]glutamate v' values (temporal=139% of motor; NS). Unlike d-[3H]aspartate BMAX values, l-[3H]glutamate v' values were markedly and selectively lower in Alzheimer brain preparations than in controls, particularly in temporal cortex. The difference could not be attributed to differential effects of autopsy interval or age at death. Non-Alzheimer dementia cases resembled controls. The selective loss of vesicular glutamate transport is consistent with a dysfunction in the recycling of transmitter glutamate.

GABA(A) receptor alpha-subunit proteins in human chronic alcoholics

Antibodies were raised against specific peptides from N-terminal regions of the alpha1 and alpha3 isoforms of the GABA(A) receptor, and used to assess the relative expression of these proteins in the superior frontal and primary motor cortices of 10 control, nine uncomplicated alcoholic and six cirrhotic alcoholic cases were matched for age and post-mortem delay. The regression of expression on post-mortem delay was not statistically significant for either isoform in either region. In both cortical areas, the regression of alpha1 expression on age differed significantly between alcoholic cases, which showed a decrease, and normal controls, which did not. Age had no effect on alpha3 expression. The alpha1 and alpha3 isoforms were found to be expressed differentially across cortical regions and showed a tendency to be expressed differentially across case groups. In cirrhotic alcoholics, alpha1 expression was greater in superior frontal than in motor cortex, whereas this regional difference was not significant in controls or uncomplicated alcoholics. In uncomplicated alcoholics, alpha3 expression was significantly lower in superior frontal than in motor cortex. Expression of alpha1 was significantly different from that of alpha3 in the superior frontal cortex of alcoholics, but not in controls. In motor cortex, there were no significant differences in expression between the isoforms in any case group.

Glutamate(NMDA) receptor NR1 subunit mRNA expression in Alzheimer's disease

We analyzed the expression profile of two NMDAR1 mRNA isoform subsets, NR1(0XX) and NR1(1XX), in discrete regions of human cerebral cortex. The subsets are characterized by the absence or presence of a 21-amino acid N-terminal cassette. Reverse transcription polymerase chain reaction for NR1 isoforms was performed on total RNA preparations from spared and susceptible regions from 10 pathologically confirmed Alzheimer's disease (AD) cases and 10 matched controls. Primers spanning the splice insert yielded two bands, 342 bp (NR1(0XX)) and 405 bp (NR1(1XX)), on agarose gel electrophoresis. The bands were visualized with ethidium and quantified by densitometry. NR1(1XX) transcript expression was calculated as a proportion of the NR1(1XX) + NR1(0XX) total. Values were significantly lower in AD cases than in controls in mid-cingulate cortex, p < 0.01, superior temporal cortex, p < 0.01 and hippocampus, p approximately 0.05. Cortical proportionate NR1(1XX) transcript expression was invariant over the range of ages and areas of controls tested, at approximately 50%. This was also true for AD motor and occipital cortex. Proportionate NR1(1XX) expression in AD cingulate and temporal cortex was lower at younger ages and increased with age: this regression was significantly different from that in the homotropic areas of controls. Variations in NR1 N-terminal cassette expression may underlie the local vulnerability to excitotoxic damage of some areas in the AD brain. Alternatively, changes in NR1 mRNA expression may arise as a consequence of the AD disease process.

Molecular cloning and characterization of hNP22: a gene up-regulated in human alcoholic brain

An improved differential display technique was used to search for changes in gene expression in the superior frontal cortex of alcoholics. A cDNA fragment was retrieved and cloned. Further sequence of the cDNA was determined from 5' RACE and screening of a human brain cDNA library. The gene was named hNP22 (human neuronal protein 22). The deduced protein sequence of hNP22 has an estimated molecular mass of 22.4 kDa with a putative calcium-binding site, and phosphorylation sites for casein kinase II and protein kinase C. The deduced amino acid sequence of hNP22 shares homology (from 67% to 42%) with four other proteins, SM22alpha, calponin, myophilin and mp20. Sequence homology suggests a potential interaction of hNP22 with cytoskeletal elements. hNP22 mRNA was expressed in various brain regions but in alcoholics, greater mRNA expression occurred in the superior frontal cortex, but not in the primary motor cortex or cerebellum. The results suggest that hNP22 may have a role in alcohol-related adaptations and may mediate regulatory signal transduction pathways in neurones.

Application of DNA microarrays to study human alcoholism

An emerging idea is that long-term alcohol abuse results in changes in gene expression in the brain and that these changes are responsible at least partly for alcohol tolerance, dependence and neurotoxicity. The overall goal of our research is to identify genes which are differentially expressed in the brains of well-characterized human alcoholics as compared with non-alcoholics. This should identify as-yet-unknown alcohol-responsive genes, and may well confirm changes in the expression of genes which have been delineated in animal models of alcohol abuse. Cases were carefully selected and samples pooled on the basis of relevant criteria; differential expression was monitored by microarray hybridization. The inherent diversity of human alcoholics can be exploited to identify genes associated with specific pathological processes, as well as to assess the effects of concomitant disease, severity of brain damage, drinking behavior, and factors such as gender and smoking history. Initial results show selective changes in gene expression in alcoholics; of particular importance is a coordinated reduction in genes coding for myelin components.

Gene expression in human alcoholism: microarray analysis of frontal cortex

BACKGROUND

Changes in brain gene expression are thought to be responsible for the tolerance, dependence, and neurotoxicity produced by chronic alcohol abuse, but there has been no large scale study of gene expression in human alcoholism.

METHODS

RNA was extracted from postmortem samples of superior frontal cortex of alcoholics and nonalcoholics. Relative levels of RNA were determined by array techniques. We used both cDNA and oligonucleotide microarrays to provide coverage of a large number of genes and to allow cross-validation for those genes represented on both types of arrays.

RESULTS

Expression levels were determined for over 4000 genes and 163 of these were found to differ by 40% or more between alcoholics and nonalcoholics. Analysis of these changes revealed a selective reprogramming of gene expression in this brain region, particularly for myelin-related genes which were down-regulated in the alcoholic samples. In addition, cell cycle genes and several neuronal genes were changed in expression.

CONCLUSIONS

These gene expression changes suggest a mechanism for the loss of cerebral white matter in alcoholics as well as alterations that may lead to the neurotoxic actions of ethanol.

Localisation of GABA(A) receptor subunits in the CNS using RT-PCR

This paper presents an RT-PCR in situ histochemistry (RT-ISH) method for the detection and localisation of isoforms of the GABA(A) receptor in formalin-fixed, paraffin-embedded brain sections. RT-ISH was performed using PCR conditions already established in our laboratory for the amplification of the alpha(1-3) and beta(1-3) subunits of the GABA(A) receptor [2,5]. Initial experiments determined whether mRNA isolated from such sections was suitable for use in RT-PCR. Transcripts encoding both the alpha- and beta-subunits of the GABA(A) receptor were successfully amplified. RT-ISH, a one-step RT-PCR method, was used to amplify the transcripts and digoxigenin-labeled nucleotides were directly incorporated into the amplified products during cycling. RT-PCR products were detected using anti-digoxigenin antibody conjugated to alkaline-phosphatase and signal was visualised using light microscopy. This protocol may be used to study the expression of GABA(A) receptor isoforms in vivo and examine alterations in receptor composition during development and disease states.

Glutamate-mediated transmission, alcohol, and alcoholism

Glutamate-mediated neurotransmission may be involved in the range of adaptive changes in brain which occur after ethanol administration in laboratory animals, and in chronic alcoholism in human cases. Excitatory amino acid transmission is modulated by a complex system of receptors and other effectors, the efficacy of which can be profoundly affected by altered gene or protein expression. Local variations in receptor composition may underlie intrinsic regional variations in susceptibility to pathological change. Equally, ethanol use and abuse may bring about alterations in receptor subunit expression as the essence of the adaptive response. Such considerations may underlie the regional localization characteristic of the pathogenesis of alcoholic brain damage, or they may form part of the homeostatic change that constitutes the neural substrate for alcohol dependence.

Expression and distribution of GABAA receptor subtypes in human alcoholic cerebral cortex

Long-term alcohol abuse is known to target specific areas of the brain such as the superior frontal cortex (SFC), resulting in neuronal cell loss. Abnormal transmission of the inhibitory neurotransmitter GABA may contribute to this damage. Previous work in our laboratory has found differential expression and distribution of certain a subunit genes of the GABAA receptor in the SFC of human alcoholic brain, suggesting that differences in GABAA receptor subunit expression could give rise to the locally altered GABAA pharmacology which is associated with alcohol abuse. A competitive RT-PCR assay has been developed to study the expression of the GABAA receptor beta-subunit genes beta1, beta2, and beta3. A single set of primers homologous to all three beta isoform sequences has been shown to amplify each of the beta isoforms from mRNA isolated from human brain tissue obtained at autopsy. An internal standard has been designed which is identical to the target except for a 61-bp deletion and a unique restriction enzyme (RE) site. This is co-amplified with the target sequences to allow amplification efficiency to be assessed and thus enable the quantitation of gene expression. A range of GABAA receptor ligands were used to look at differential distribution of receptor subtypes in the cortical laminae by autoradiography. Differences in distribution of the ligands were demonstrated, consistent with a hypothesis of alcohol-induced variations in the expression of receptor subunits.

The modulatory effect of spermine on the glutamate-NMDA receptor is regionally variable in normal human adult cerebral cortex

The MK-801, glutamate and polyamine binding sites on the N-methyl-D-aspartate class of glutamate receptors labelled with [3H]MK-801 were characterized in four cortical areas (sensorimotor, superior temporal, mid-frontal and occipital) from seven human adult control cases. Age, post-mortem delay, tissue storage time and sex had no significant effects on any of the parameters measured. Dissociation constants (K(D) values) for MK-801 showed similar mean values in the four cortical areas, whereas receptor densities (B(max) values) showed significant differences between sensorimotor or occipital and superior temporal or mid-frontal cortex. There were marked regional differences in the profiles of the spermine- and glutamate-incremented enhancement of specific [3H]MK-801 binding. The EC(50) for the glutamate enhancement was significantly higher in the occipital than in the mid-frontal and sensorimotor cortex, whereas maximal glutamate-enhanced binding values did not differ. The maximal enhancement of [3H]MK-801 binding by spermine and glutamate varied between the cases, ranging from zero to 40.4+/-9.3 fmol x mg protein(-1) for spermine, and from 85+/-5 to 111+/-10 fmol x mg protein(-1) for glutamate. Maximal spermine enhancement of [3H]MK-801 binding was significantly more variable in superior temporal or mid-frontal than in sensorimotor or occipital cortex. The results suggest that N-methyl-D-aspartate receptor sites, especially the polyamine site, are heterogeneous in human cerebral cortex, and show a high degree of regional and individual variability.

Increased expression of mitochondrial genes in human alcoholic brain revealed by differential display

Polymerase chain reaction (PCR)-based differential display was used to screen for alterations in gene expression in the mesolimbic system of the human alcoholic brain. Total RNA was extracted from the nucleus accumbens of five alcoholic and five control brains. A selected subpopulation of mRNA was reverse-transcribed to cDNA and amplified by PCR. A differentially expressed cDNA fragment was recovered, cloned, and sequenced. Full sequence analysis of this 467 bp fragment revealed 98.2% homology with the human mitochondrial 12S rRNA gene. Dot-blot analysis showed increased expression of this gene in nucleus accumbens and hippocampus, but not in the superior frontal cortex, primary motor cortex, caudate, and pallidus/putamen in a total of eight human alcoholic brains, compared with seven control brains. A similar increased expression was observed by dot-blot analysis, using RNA from the cerebral cortex of rats chronically treated with alcohol vapor. Hybridization of a 16S rRNA oligonucleotide probe indicated that the expression of both rRNAs genes was significantly increased in nucleus accumbens. These results indicate that chronic alcohol consumption induces alteration in expression of mitochondrial genes in selected brain regions. The altered gene expression may reflect mitochondrial dysfunction in the alcohol-affected brain.

Structure-activity studies of conantokins as human N-methyl-D-aspartate receptor modulators

The activities of conantokin-G (con-G), conantokin-T (con-T), and several novel analogues have been studied using polyamine enhancement of [3H]MK-801 binding to human glutamate-N-methyl-D-aspartate (NMDA) receptors, and their structures have been examined using CD and 1H NMR spectroscopy. The potencies of con-G[A7], con-G, and con-T as noncompetitive inhibitors of spermine-enhanced [3H]MK-801 binding to NMDA receptor obtained from human brain tissue are similar to those obtained using rat brain tissue. The secondary structure and activity of con-G are found to be highly sensitive to amino acid substitution and modification. NMR chemical shift data indicate that con-G, con-G[D8, D17], and con-G[A7] have similar conformations in the presence of Ca2+. This consists of a helix for residues 2-16, which is kinked in the vicinity of Gla10. This is confirmed by 3D structure calculations on con-G[A7]. Restraining this helix in a linear form (i.e., con-G[A7,E10-K13]) results in a minor reduction in potency. Incorporation of a 7-10 salt-bridge replacement (con-G[K7-E10]) prevents helix formation in aqueous solution and produces a peptide with low potency. Peptides with the Leu5-Tyr5 substitution also have low potencies (con-G[Y5,A7] and con-G[Y5,K7]) indicating that Leu5 in con-G is important for full antagonist behavior. We have also shown that the Gla-Ala7 substitution increases potency, whereas the Gla-Lys7 substitution has no effect. Con-G and con-G[K7] both exhibit selectivity between NMDA subtypes from mid-frontal and superior temporal gyri, but not between sensorimotor and mid-frontal gyri. Asn8 and/or Asn17 appear to be important for the ability of con-G to function as an inhibitor of polyamine-stimulated [3H]MK-801 binding, but not in maintaining secondary structure. The presence of Ca2+ does not increase the potencies of con-G and con-T for NMDA receptors but does stabilize the helical structures of con-G, con-G[D8,D17], and, to a lesser extent, con-G[A7]. The NMR data support the existence of at least two independent Ca2+-chelating sites in con-G, one involving Gla7 and possibly Gla3 and the other likely to involve Gla10 and/or Gla14.

Association of missense and 5'-splice-site mutations in tau with the inherited dementia FTDP-17

Thirteen families have been described with an autosomal dominantly inherited dementia named frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), historically termed Pick's disease. Most FTDP-17 cases show neuronal and/or glial inclusions that stain positively with antibodies raised against the microtubule-associated protein Tau, although the Tau pathology varies considerably in both its quantity (or severity) and characteristics. Previous studies have mapped the FTDP-17 locus to a 2-centimorgan region on chromosome 17q21.11; the tau gene also lies within this region. We have now sequenced tau in FTDP-17 families and identified three missense mutations (G272V, P301L and R406W) and three mutations in the 5' splice site of exon 10. The splice-site mutations all destabilize a potential stem-loop structure which is probably involved in regulating the alternative splicing of exon10. This causes more frequent usage of the 5' splice site and an increased proportion of tau transcripts that include exon 10. The increase in exon 10+ messenger RNA will increase the proportion of Tau containing four microtubule-binding repeats, which is consistent with the neuropathology described in several families with FTDP-17.

Cell death mediated by amino acid transmitter receptors in human alcoholic brain damage: conflicts in the evidence

Human alcoholics have reduced neuronal counts in certain brain regions, such as superior frontal cortex (SFC), where the form and quantity of synaptic gamma-aminobutyric acid type A (GABAA) receptor sites are atypical. We measured the expression of GABAA receptor isoform mRNA and protein, since GABAA receptor pharmacology is strongly influenced by its subunit composition. Cortex samples were obtained at autopsy; whole-tissue extracts were assayed for mRNA by quantitative reverse transcriptase polymerase chain reaction (RT-PCR), while synaptic membranes were studied for both GABAA receptor pharmacology and subunit protein levels by Western blots with isoform-specific antibodies. Although alpha 1 and alpha 3 mRNA species were strongly expressed in alcoholics irrespective of cirrhosis than in controls, alpha 1 protein differed little between case groups, and alpha 3 protein showed some complex variations. Differences in GABAA pharmacology conformed more closely with differences in protein levels than with altered mRNA expression.

Regional development of glutamate-N-methyl-D-aspartate receptor sites in asphyxiated newborn infants

The N-methyl-D-aspartate (NMDA) subclass of glutamate receptors was examined in newborn infants dying between 25 weeks' gestation and term, either from acute cerebral hypoxia, or from other noncerebral conditions incompatible with life. Frontal, occipital, temporal, and motor cortex tissue samples were obtained at autopsy (post mortem delay: median, 45.9 hr; range, 24-96 hr) and frozen for subsequent [3H]MK801 homogenate binding assays. Whereas no significant variation was observed in ligand affinity (KD), in all cases receptor density (BMAX) increased with gestational age, in occipital cortex (27 weeks, BMAX = 222 +/- 44 fmol x mg protein(-1); 39 weeks, 439 +/- 42 fmol x mg protein[-1]), but not in motor or temporal cortex. The gestational-age increase also occurred in control frontal cortex (27 weeks, 284 +/- 80; 39 weeks, 567 +/- 40 fmol x mg protein[-1]), but was significantly less marked in frontal cortex in hypoxia cases (27 weeks, 226 +/- 90; 39 weeks, 326 +/- 47 fmol x mg protein[-1]). In all cortical areas except temporal, the maximal response to glutamate did not vary across case groups. Hypoxia cases showed an increased response to glutamate enhancement selectively in temporal cortex. Binding site density did not correlate with degree of hypoxia as assessed pathologically, suggesting that receptor differences preceded the hypoxic episode. Regional differences in glutamate-NMDA receptor sites may underlie increased vulnerability to hypoxia at birth.

Expression of GABA(A) receptor isoform genes in the cerebral cortex of cirrhotic and alcoholic cases assessed by S1 nuclease protection assays

Pathogenic processes underlying the localized reduction in neuronal number in cerebral cortex in human alcoholics have been reported to be associated with selective variations in the parameters of GABA(A) receptor site binding. Since the properties of the receptor complex depend on its isoform composition, we studied how the expression of GABA(A) receptor subunit isoform genes varied with alcoholism. Cerebral cortex tissue was obtained at autopsy from chronic human alcoholics (average ethanol intake > 80 g/day for most of their adult lives; n = 17) and matched controls (< 20 g/day ethanol; n = 15). Eight of the alcoholics and five of the controls had pathologically confirmed cirrhosis of the liver. Expression of alpha1, alpha2, alpha3, alpha5, beta1, beta3, and gamma2 GABA(A) mRNA was assessed by S1 nuclease protection assays. After phosphorimager quantitation and normalization to GAPDH mRNA and 18S rRNA, none of the mRNA species showed significantly different expression in uncomplicated alcoholics. Analysis of differences in the patterns of expression of the various subunits showed the alpha1 signal was strongest in combined cirrhotic motor cortex while the alpha3 and beta3 values were greatest in combined cirrhotic frontal cortex. It appears that only major differences in mRNA expression may be detected by this technique in human brain.

A method for the quantitation of the alpha 1, alpha 2, and alpha 3 isoforms of the GABAA receptor in human brain using competitive PCR

The GABAA receptor is the site of action of the inhibitory neurotransmitter GABA, as well as a number of pharmacologically important drugs such as benzodiazepines, barbiturates, and ethanol. The GABAA receptor is a pentameric complex composed of distinct polypeptides, which have been divided into five subunit classes on the basis of sequence homology. To date, 17 isoforms of the receptor have been identified and cloned in mammalian brain, and designated alpha 1-6, beta 1-4, gamma 1-4, delta and rho 1-2. In addition, several isoforms exist in alternatively spliced forms (for review see ref.). Studies on recombinant receptors have revealed that receptors constituted from different isoforms exhibit distinct pharmacological properties. For example, the alpha subunit class appears to be responsible for GABA enhancement of benzodiazepine binding. GABAA receptor function is modulated by benzodiazepine agonists such as flunitrazepam and diazepam, barbiturates, anaesthetics, neurosteroids, and ethanol. Chronic treatment of animals with many of these compounds can bring about profound changes in receptor expression and pharmacology. The RT/PCR assay described here was developed to quantify the alpha 1, alpha 2 and alpha 3 isoforms in the same assay. The amount of each isoform was quantified on the basis of a standard curve generated under identical PCR conditions to the target sequences. In this way it is possible to quantify multiple samples in each RT/PCR assay, thereby reducing inter-assay variability. The assay can be applied to quantify the expression of these isoforms in response to acute and chronic drug administration, or in particular disease states. Altered expression may reflect a corresponding change in protein synthesis, or an alteration of the subtype composition of GABAA receptor.

Zolpidem binding sites on the GABA(A) receptor in brain from human cirrhotic and non-cirrhotic alcoholics

The displacement of [3H]flunitrazepam by unlabelled flunitrazepam or zolpidem was used to assess the affinity and density of sub-types of GABA(A) receptors in the superior frontal and primary motor cortices of ten alcoholic, seven alcoholic-cirrhotic and ten matched control cases. The binding was best fitted by a model with a single site for flunitrazepam, but two sites for zolpidem. Neither the patients' age nor the post-mortem interval were significantly correlated with the affinity or density of any of the binding sites. The affinity of all ligands did not differ either between cortical regions or across case groups. Hence, the density of each binding site was analyzed at constant affinity. The densities of flunitrazepam and high-affinity zolpidem binding sites were invariant across cortical regions and case groups. Low-affinity zolpidem binding sites were significantly more dense in the frontal than in the motor cortex of alcoholic cases irrespective of cirrhosis, whereas this regional difference was not significant in control cases.

Expression of the alpha 1, alpha 2 and alpha 3 isoforms of the GABAA receptor in human alcoholic brain

The expression of the alpha 1, alpha 2 and alpha 3 isoforms of the GABAA receptor was studied in the superior frontal and motor cortices of 10 control, 10 uncomplicated alcoholic and 7 cirrhotic alcoholic cases matched for age and post-mortem delay. The assay was based on competitive RT/PCR using a single set of primers specific to the alpha class of isoform mRNA species, and was normalized against a synthetic cRNA internal standard. The assay was shown to be quantitative for all three isoform mRNA species. Neither the patient's age nor the post-mortem interval significantly affected the expression of any isoform in either cortical area. The profile of expression was shown to be significantly different between the case groups, particularly because alpha 1 expression was raised in both groups of alcoholics of controls. The two groups of alcoholics could be differentiated on the basis of regional variations in alpha 1 expression. In frontal cortex, alpha 1 mRNA expression was significantly increased when uncomplicated alcoholics were compared with control cases whereas alcoholic-cirrhotic cases were not significantly different from either controls or uncomplicated alcoholic cases. In the motor cortex, alpha 1 expression was elevated only when alcoholic-cirrhotic cases were compared with control cases. There was no significant difference between case groups or areas for any other isoform.

Alcohol, alcoholic brain damage, and GABAA receptor isoform gene expression

Selective variations in cerebral GABAA receptor pharmacology and function are observed in experimental animals subjected to a number of alcohol-treatment and -withdrawal paradigms, and where human alcoholics with and without a range of concomitant diseases are compared with non-alcoholic cases. Recombination studies have shown that variations in GABAA receptor pharmacology and function can result from altering its subunit isoform composition. This commentary examines the rôle of subunit isoform expression in the response to long-term alcohol administration in animals, and in the pathogenesis of alcoholism-related brain damage in human cases.

The neurochemical pathology of thiamine deficiency: GABAA and glutamateNMDA receptor binding sites in a goat model

Synaptic plasma membranes were prepared from four cerebrocortical areas from six male Angora goats made chronically thiamine deficient (TD) by the administration of AmproliumTM (600-900 mg/kg daily for 38-44 d). Four male controls were matched for age (27-30 mo). Four different radioligands were used to characterise GABAA and Glu-RNMDA receptor binding sites. There were marked, localised and contrasting changes in motor cortex, with an increase in GABAA and a decrease in Glu-RNMDA binding site densities. Less clearcut changes of a similar nature were seen in visual cortex. There was no variation in the parameters of GABA-activated [3H]diazepam binding between cortical areas in control goats, but there was a reduction in the maximal response to GABA in all areas in TD goats. There were regional variations in glutamate-activated [3H]MK-801 binding in control goat brain, and a non-selectively reduced maximal response in TD. Alterations in these indices of GABA- and glutamate-mediated neurotransmission may underlie the neurological signs of acute thiamine deficiency in these animals.

Receptor binding sites and uptake activities mediating GABA neurotransmission in chronic alcoholics with Wernicke encephalopathy

Superior frontal cortex (SFC) and primary motor cortex tissue was obtained at autopsy from thirteen severe chronic alcoholics with neuropathologically confirmed Wernicke Encephalopathy (WE) and 22 controls. Cases with both WE and cirrhosis showed markedly fewer neurones in SFC than did WE cases without cirrhosis. The extent of the apparent neuronal loss corresponded to an increase in post-synaptic GABAA receptor sites, as assessed by the binding of [3H]muscimol to synaptic membranes. Increased [3H]muscimol binding was not accompanied by an increase in 'central-type' benzodiazepine binding sites: as assessed by [3H]flunitrazepam binding, these sites were apparently unaltered, while as assessed by [3H]diazepam binding, they were decreased. The affinities of the two benzodiazepine ligands varied differently with disease. These discrepancies between [3H]flunitrazepam and [3H]diazepam binding could not be accounted for, either by the presence of a second, diazepam-preferring, 'central-type' benzodiazepine binding site, or by loss of 'peripheral-type' sites. The changes in the post-synaptic GABAA-benzodiazepine receptor sites did not reflect any regional, disease-related deficit of afferent GABAergic terminals, as assessed by synaptosomal high-affinity [3H]GABA uptake. On a number of indices, it appears most likely that the data reflect both a loss of receptor sites, and a change in the population of receptor sub-types.

Developmental rearrangements of cortical glutamate-NMDA receptor binding sites in late human gestation

NMDA-preferring glutamate receptor biding sites were characterized using the site-selective ligand [3H]MK801, in synaptic membranes prepared from cerebral cortex tissue obtained postmortem from human infants who had died with minimal neurological and neuropathological impairment between 22 and 42 weeks' gestation. It proved necessary to modify the assay protocol used with adult tissue before reliable data could be obtained. In the four cortical region studied (prefrontal, motor, occipital, temporal), [3H]MK801 bound to a single class of sites which showed significant variations in affinity only in motor cortex. The density of [3H]MK801 binding sites (calculated at constant affinity) showed marked increases in all cortical regions over this period. The extent to which glutamate could enhance [3H]MK801 binding became significantly lower in prefrontal and motor cortex as gestation progressed, so that at term, little activation was apparent. In occipital and temporal cortex, this parameter was low throughout late gestation. The evidence suggests that Glutamate-NMDA binding sites may undergo structural rearrangements which alter their ability to interact with ligands during the later stages of human gestation, and that such changes are regionally variable.

The nature of d,l-fenfluramine-induced 5-HT reuptake transporter loss in rats

The administration of the anorexigenic drug d,l-fenfluramine (Ponderax) to laboratory animals results in a dose-dependent reduction in presynaptically located serotonergic reuptake transporter protein. This long-term effect may represent an altered mechanism of synthesis of the transporter (downregulation). Alternatively, fenfluramine may destroy the serotonergic terminals on which 5-HT transporters are located. To distinguish between these two alternatives, we applied an assay of neurotransmitter-specific nerve endings (alpha) to brain tissue from two animal models of reduced 5-HT transporter density. In Model 1, serotonergic nerve terminals were destroyed (rats received 5,7-dihydroxytryptamine [5,7-DHT] intracisternally); in Model 2, there was a loss of 5-HT transporter per se on otherwise intact serotonergic nerve terminals. The manner in which alpha declined as transporter density was decreased (reducing Vmax values) in animal Models 1 and 2 was found to be significantly different. In rats treated with fenfluramine, the association between 5-HT transporter density and alpha was the same as in the neurotoxic model.

Variant forms of neuronal glutamate transporter sites in Alzheimer's disease cerebral cortex

The displacement of Na(+)-dependent D-[3H]-aspartate binding by unlabeled D-aspartate or the inhibitors DL-threo-beta-hydroxyaspartate, L-cysteate, L-glutamate, dihydrokainate, DL-alpha-aminoadipate, alpha-methyl-DL-glutamate, and 1-aminocyclobutane-cis-1,3-dicarboxylate was used to characterize the high-affinity glutamate/aspartate uptake site in human cerebral cortex. Synaptosomal membranes were prepared from tissue obtained at autopsy from nondemented control, Alzheimer's disease (AD), and diffuse Lewy body disease (DLBD) cases. Areas that are damaged in AD (midtemporal, frontal, caudal cingulate, and hippocampal cortices) were compared with those that are spared (occipital and motor cortices). Profiles of the affinities (Ka values) of the ligands showed that areas spared from damage in AD cases differed significantly from equivalent areas in control (p < 0.001) and DLBD (p < 0.001) cases and also from areas susceptible to damage in the same AD cases (p < 0.001). Areas susceptible to damage in AD showed comparable profiles across the three case groups (p = 0.980). The glutamate/aspartate uptake site may be regionally variant in AD cases, and this may underlie local excitotoxicity. D-[3H]Aspartate binding site density was significantly lower in both dementia groups (control vs. AD, p < 0.001; control vs. DLBD, p = 0.009; but AD vs. DLBD, p = 0.528); within-group differences were not significant (control, p = 0.874; AD, p = 0.285; DLBD, p = 0.741).

Benzodiazepine binding sites in alcoholic cirrhotics: evidence for gender differences

Synaptic plasma membranes were prepared from superior frontal gyrus and motor cortex obtained at autopsy from 17 chronic alcoholics not differentiated on thiamine status, of whom 8 had pathologically confirmed cirrhosis of the liver, and 10 controls. Three of the cirrhotic alcoholic cases were female, as was one control. Cases were closely matched for age at death and post-mortem delay. The affinity of "central-type" benzodiazepine sites for [3H]diazepam tended to be lower in both brain regions of both groups of alcoholics of cf controls, but the reverse was true for [3H]flunitrazepam, especially in cirrhotic cases. [3H]Diazepam affinity was invariant across all males and the female control, but lower in the female cirrhotic alcoholics. Affinity for [3H]flunitrazepam tended to be the reverse of that for [3H]diazepam. [3H]Diazepam Bmax was markedly lower in female cirrhotic alcoholics, especially in superior frontal gyrus, whereas this region showed a much higher Bmax in the female control case. A small regional difference in [3H]flunitrazepam Bmax was the reverse of that for [3H]diazepam Bmax and was seen in all groups. GABA-mediated neurotransmission may be selectively altered in a pathologically abnormal region of cerebral cortex in cirrhotic alcoholics, and the sexes may show differing susceptibilities to change.

[3H]MK-801 binding asymmetry in the IMHV region of dark-reared chicks is reversed by imprinting

Glutamate NMDA-type receptor binding in the intermediate medial hyperstriatum ventrale (IMHV) of dark-hatched chicks is lateralized. This lateralization was found to be markedly influenced by imprinting. In dark-reared chicks the binding of the selective ligand [3H]MK-801 was two-fold higher in the right IMHV than in the left IMHV. In contrast, imprinted chicks have significantly higher levels of [3H]MK-801 binding in the left IMHV region than in the right IMHV. Imprinting results in 2a learning-related increase in NMDA-type receptor binding levels in the left IMHV, whereas [3H]MK-801 binding levels in the right IMHV remain unchanged by imprinting. Thus, the plasticity present in the NMDA-type receptor system and associated with imprinting appears to occur in the left hemisphere only.

Excitotoxic mechanisms in the pathogenesis of dementia

Alzheimer disease and related dementias, in common with most major neurological diseases, are characterized by localized brain damage. An abundance of senile plaques and neurofibrillary tangles in certain brain areas is pathognomic of the disease: of the two, the density of tangles may correlate more closely with disease severity ante mortem. Clinical manifestation of the disease also results from a locally severe loss of neurones. This might be caused by over-stimulation by excitant amino acid transmitters such as glutamate, which would promote cell death. Mechanisms which might give rise to the localization of Alzheimer pathogenesis include hypersensitivity to damage because a cell carries a particular sub-set of post-synaptic receptors; local variations in the efficiency of excitatory amino acid transport; and, possibly, local exacerbation of toxicity by substances such as beta-amyloid. Elucidation of such mechanisms could lead to new pharmacotherapies of dementia.

Pharmacology of morphine and morphine-3-glucuronide at opioid, excitatory amino acid, GABA and glycine binding sites

Morphine in high doses and its major metabolite, morphine-3-glucuronide, cause CNS excitation following intrathecal and intracerebroventricular administration by an unknown mechanism. This study investigated whether morphine and morphine-3-glucuronide interact at major excitatory (glutamate), major inhibitory (GABA or glycine), or opioid binding sites. Homogenate binding assays were performed using specific radioligands. At opioid receptors, morphine-3-glucuronide and morphine caused an equipotent sodium shift, consistent with morphine-3-glucuronide behaving as an agonist. This suggests that morphine-3-glucuronide-mediated excitation is not caused by an interaction at opioid receptors. Morphine-3-glucuronide and morphine caused a weak inhibition of the binding of 3H-MK801 (non-competitive antagonist) and 125I-ifenprodil (polyamine site antagonist), but at unphysiologically high concentrations. This suggests that CNS excitation would not result from an interaction of morphine-3-glucuronide and high-dose morphine with these sites on the NMDA receptor. Morphine-3-glucuronide and morphine inhibited the binding of 3H-muscimol (GABA receptor agonist). 3H-diazepam and 3H-flunitrazepam (benzodiazepine agonists) binding very weakly, suggesting the excitatory effects of morphine-3-glucuronide and high-dose morphine are not elicited through GABAA receptors. Morphine-3-glucuronide and high-dose morphine did not prevent re-uptake of glutamate into presynaptic nerve terminals. In addition, morphine-3-glucuronide and morphine did not inhibit the binding of 3H-strychnine (glycine receptor antagonist) to synaptic membranes prepared from bovine spinal cord. It is concluded that excitation caused by high-dose morphine and morphine-3-glucuronide is not mediated by an interaction with postsynaptic amino acid receptors.

Characterization of non-conventional opioid binding sites in rat and human lung

Indirect evidence suggests that nebulized morphine relieves dyspnoea and bronchoconstriction via opioid receptors within the lung. This study used equilibrium binding studies to characterize opioid binding sites in lung membrane preparations. [3H]Morphine and [3H]naloxone were incubated separately with homogenates of Wistar rat brain and lung, and human lung. Binding affinities for both morphine and naloxone in rat and human lung were two orders of magnitude lower than those in brain. However, opioid binding site densities in lung were up to 100 times greater than that in brain. The addition of Na+ or GTP to lung homogenate preparations caused atypical effects on opioid binding. Na+ (50 mM) decreased the specific binding of [3H]naloxone 50% viz-à-vis a 20% increase in binding in the brain. GTP (100 microM) caused a 200% increase in the apparent capacity of morphine binding in the lung compared with a marked decrease in binding in the brain.

Brain extracts containing a Huntington disease antigen inhibit [3H]kainate binding and block synaptosomal amino acid transport

Fractions isolated from mammalian brain which had previously been shown to inhibit the rate of migration of peripheral blood leukocytes taken from Huntington disease cases, and also to inhibit [3H]kainic acid binding, were characterized further. By use of repeated ultrafiltration onto a 1000D MW cutoff filter, and by the isolation and extensive washing of an enriched ammonium sulfate fraction, their activity was shown not to be due to the presence of endogenous glutamate, and to be relatively selective for brain glutamate receptor binding sites. Inhibitory activity at [3H]GABA, 5-[3H]hydroxytryptamine 5HT1 and dopamine D1 or D2 binding sites was much weaker or absent. Factor extracts were also shown to act as non-competitive inhibitors of synaptosomal amino acid transport: increasing concentrations of the factor had no significant effect on the KM for the uptake of either [3H]glutamate or [3H]GABA, but at a final concentration of 66 micrograms protein x ml-1 had reduced the VMAX for [3H]glutamate uptake to approximately 20% of control, and the VMAX for [3H]GABA uptake to approximately 40% of control. This may enhance the factor's potential excitotoxicity.

The regeneration of d,l-fenfluramine-destroyed serotonergic nerve terminals

The regeneration of serotonergic nerve terminals subsequent to their destruction by high-dose fenfluramine administration was examined. Treating rats with fenfluramine (80 mg/kg over 2 days) destroyed 80% of serotonergic nerve terminals, indicated by reduced maximal [3H]paroxetine binding to 5-hydroxytryptamine (5-HT) uptake sites on synaptic membranes (Bmax) and maximal [14C]5-HT uptake rate into synaptosomes (Vmax). 25 weeks later, these indices of serotonergic nerve terminals had returned to 72% of control. Maximal synaptosomal loading (alpha) with [14C]5-HT also recovered (to 79% of control), reflecting an increased number of serotonergic synaptosomes. This suggests that the rebound in 5-HT uptake site density found after fenfluramine illustrates the regeneration of 5-HT-containing nerve endings.

New evidence for a loss of serotonergic nerve terminals in rats treated with d,l-fenfluramine

Fenfluramine has been classified as a neurotoxin because animals treated with this anorectic lose 5-HT uptake sites located on serotonergic nerve terminals. However, there are two possible bases for this finding: either uptake sites are lost because the terminals themselves have been destroyed (neurotoxicity); or uptake sites are lost from otherwise intact terminals. To distinguish between these possibilities, we established an animal model in which male Wistar rats were injected (intraperitoneally) with an irreversible 5-HT uptake site antagonist (EEDQ). Since their 5-HT sites were inhibited (blocked) non-competitively, by this agent, such animals had effectively lost 5-HT uptake sites from intact serotonergic terminals. Synaptosomes prepared from such animals showed the predicted reduction in the Bmax of [3H]paroxetine binding to the 5-HT uptake site, and a reduction in the Vmax of [14C]5-HT uptake. However, they showed no significant reduction in maximal [14C]5-HT loading (alpha) compared with synaptosome from sham-injected controls. In contrast, fenfluramine-treated animals showed reduced [3H]paroxetine binding, reduced maximal [14C]5-HT uptake and significantly (P < 0.02) reduced synaptosomal [14C]5-HT loading. Therefore, the results suggest that fenfluramine does indeed cause the destruction of serotonergic nerve terminals.

Amino acid neurotransmitter receptor changes in cerebral cortex in alcoholism: effect of cirrhosis of the liver

Gamma-aminobutyric acidA/benzodiazepine receptor binding sites and the N-methyl-D-aspartate subclass of glutamate receptor sites were assessed in synaptic plasma membrane homogenates of cerebral cortex tissue obtained at autopsy from cirrhotic and noncirrhotic alcoholic patients and matched control subjects. The alcoholic patients consumed an average of greater than 80 g of ethanol/day, the control subjects less than 20 g/day. Postmortem delays up to approximately 100 h caused no significant loss of any of the binding sites; the patient and subject groups were closely matched for age. The affinities (KD) of the receptor sites did not differ between the patient and subject groups, nor between cortical regions. Using three different radioligands ([3H]muscimol, [3H]flunitrazepam, and [3H]diazepam), the gamma-aminobutyric acidA/benzodiazepine receptor complex was found to have greater density (Bmax) in superior frontal gyrus in alcoholic patients (which selectively shows morphological change in alcoholic patients), but was unchanged in motor cortex. Alcoholic patients with cirrhosis had much less pronounced changes. The density of the N-methyl-D-aspartate subclass of glutamate receptors, assessed with [3H]MK-801, did not vary across patient and subject groups.

Glutamate and gamma-aminobutyric acid neurotransmitter systems in the acute phase of maple syrup urine disease and citrullinemia encephalopathies in newborn calves

Cerebral cortex tissue was obtained at autopsy from neonatal Poll Hereford calves with clinically confirmed maple syrup urine disease (MSUD), neonatal Holstein-Friesian calves with clinically confirmed citrullinemia, and matched controls. From this, synaptosomes were prepared for studies of neurotransmitter amino acid uptake and stimulus-induced release, and synaptic plasma membranes were obtained for studies of associated postsynaptic receptor binding sites. As well as having abnormal brain tissue concentrations of the pathognomic plasma amino acids (markedly increased levels of the branched-chain compounds valine, isoleucine, and leucine in MSUD; marked elevation of citrulline levels in citrullinemia), both groups of diseased animals showed reduced brain tissue concentrations of each of the transmitter amino acids glutamate, aspartate, and gamma-aminobutyric acid (GABA). Nontransmitter amino acids were generally unaffected in either disease. Citrullinemic calves showed a marked increase in brain glutamine concentration; in calves with MSUD, the glutamine concentration was raised, but to a much lesser extent. The Na(+)-dependent synaptosomal uptake of both glutamate and GABA was markedly reduced (to less than 50% of control values in both cases) in citrullinemic calves but was unaltered in calves with MSUD. Whereas synaptosomes from normal calves showed the expected stimulus-coupled release of transmitter amino acids, especially glutamate and aspartate, and no response to stimulus of nontransmitter amino acids, there was no increased release of transmitter amino acids in response to depolarization in synaptosomes from citrullinemic calves.(ABSTRACT TRUNCATED AT 250 WORDS)

[3H]MK-801 binding in immature and mature chicken forebrain

Previous studies have shown that the rate of calcium uptake stimulated by N-methyl-D-aspartate (NMDA) increased during the maturation phase of synapse development in chicken forebrain. To investigate whether this change in function is due to a change in the properties of NMDA receptor associated ion channels, we measured the binding of [3H]MK-801 (a ligand which binds to the NMDA receptor associated ion channel) to membranes from immature and mature chicken brain. The binding properties of MK-801 in chicken brain were similar to those in mammalian brain. There was no significant difference in any of the binding parameters measured at the two ages, i.e. KD, Bmax and optimal glutamate concentration for and maximal enhancement by glutamate of MK-801 binding. These results suggest that there is no change in the NMDA operated ion-channels during maturation. Thus the maturational change in NMDA receptor function could be due to: a change in the agonist portion of the NMDA receptor, a change in the regulation of the receptor/ionophore complex, perhaps by the postsynaptic density whose structure and composition changes during the same period, or a change in the number of voltage-sensitive calcium channels recruited as a result of NMDA receptor activation.

The interaction of a Huntington disease factor with receptors for the neurotoxin kainic acid

A factor from mammalian and human brain, which inhibits the rate of migration of leukocytes obtained from sufferers from Huntington disease (Walls and Ruwoldt, 1984), inhibited the specific binding of the neurotoxin [3H]kainic acid to rat brain synaptic membranes. The factor was present in sucrose-particulate but not in soluble fractions from rat sub-cortical tissue, and was destroyed by tryptic digestion. Whereas an ammonium sulfate fraction of direct saline extracts of brain (Walls and Ruwoldt, 1984) gave poor chromatography on HPLC, prior separation of a sucrose-particulate fraction resulted in much improved chromatography. There was a good concordance between leukocyte migration inhibitory activity and [3H]kainic acid binding inhibitory activity. The factor may be an endogenous modulator of the kainic acid subset of receptors for the excitatory neurotransmitter glutamic acid.