The regional and cellular distribution of GABAA receptor subunits in the human amygdala.

GABAergic neurotransmission in the amygdala plays a crucial role in mediating emotional learning, fear, and memory. In this study, expression of five major GABAA receptor subunits (α1, α2, α3, ß2,3, and γ2) was investigated in the normal human amygdala using immunohistochemistry. At the regional level, the amygdala contains a highly heterogeneous distribution of all the subunits investigated. The most intense staining for α1, α2, ß2,3, and γ2 subunits was present in the lateral nucleus (LA), and α3 in the intercalated nuclei (ICM). Six distinct cell populations that express GABAA receptor subunits were identified throughout the amygdala: type 1 aspiny cells in the basolateral nuclear group (BLNG) and superficial cortical-like nuclear region (SCLR) express α1, ß2,3, and γ2; type 2 larger aspiny cells in the paralaminar nucleus (PL) express α1, ß2,3, and γ2; type 3 aspiny cells in the BLNG express α1, ß2,3, and γ2 as well as calcium-binding proteins including parvalbumin (PV), calbindin (CB), and calretinin (CR); type 4 pyramidal cells in the BLNG and SCLR express α2, α3, ß2,3, and γ2 subunits at high levels on proximal specialised spines; type 5 cells in the central nucleus (CE) express α2, α3, and ß2,3; type 6 cells are found closely packed in the intercalated cell masses (ICM) and express α3 and ß2,3. The α1 subunit rarely co-labelled with α2 and α3 in the same cell population, while the α2 and α3 were often expressed within the same type 4 or 5 cell though not at always at the same puncta. The predominant GABAA receptor subunit combinations expressed in the human amygdala are the α1ß2,3γ2 and α2ß2,3γ2. Cells classified as interneuron types (types 1-3) contained GAD and principally expressed α1ß2,3γ2. The major projection neurons of the BLNG (type 4) are non-GABAergic and mainly express α2ß2,3γ2. The α3 subunit was found intracellularly in type 5 cells and decorating the surface of type 6 cells but rarely co-labelled with the subunits investigated. The results reveal a complex and heterogeneous distribution of GABAA receptor subtypes throughout the amygdala as well as on a variety of cell types through which inhibitory processing is carried out to maintain emotional responses, and control anxiety and fear responses in the brain.

mGluR1α expression in the hippocampus, subiculum, entorhinal cortex and superior temporal gyrus in Alzheimer's disease.

Glutamate is the main excitatory neurotransmitter in the central nervous system, responsible for a plethora of cellular processes including memory formation and higher cerebral function and has been implicated in various neurological disease states. Alzheimer's disease (AD) is the leading neurodegenerative disorder worldwide and is characterized by significant cell loss and glutamatergic dysfunction. While there has been a focus on ionotropic glutamatergic receptors few studies have attempted to elucidate the pathological changes of metabotropic glutamate receptors (mGluRs) in AD. mGluRs are G-protein coupled receptors which have a wide-ranging functionality, including the regulation of neuronal injury and survival. In particular, the group I mGluRs (mGluR1 and mGluR5) are associated with ionotropic receptor activation and upregulation with resultant glutamate release in normal neuronal functioning. The mGluR subtype 1 splice variant a (mGluR1α) is the longest variant of the mGluR1 receptor, is localized to dendritic processes and is mainly plasma membrane-bound. Activation of mGluR1a has been shown to result in increased constitutive activity of ionotropic receptors, although its role in neurodegenerative and other neurological diseases is controversial, with some animal studies demonstrating potential neuroprotective properties in excito- and neurotoxic environments. In this study, the expression of mGluR1a within normal and AD human hippocampal tissue was quantified using immunohistochemistry. We found a significantly reduced expression of mGluR1α within the stratum pyramidale and radiatum of the CA1subregion, subiculum, and entorhinal cortex. This downregulation could result in potential dysregulation of the glutamatergic system with consequences on AD progression by promoting excitotoxicity, but alternatively may also be a neuroprotective mechanism to prevent mGluR1α associated excitotoxic effects. In summary, more research is required to understand the role and possible consequences of mGluR1α downregulation in the human AD hippocampus, subiculum and entorhinal cortex and its potential as a therapeutic target.

Variable colocalisation of GABAA receptor subunits and glycine receptors on neurons in the human hypoglossal nucleus.

The hypoglossal nucleus, the nucleus of the twelfth cranial nerve, is located dorsally in the midline of the medulla oblongata. The hypoglossal nucleus contains lower motor neurons which innervate the tongue muscles that control tongue movements involved in speech production, swallowing, mastication and associated respiratory movements. GABAA and glycine receptors are heteropentameric ionotropic receptors that facilitate fast-response, inhibitory neurotransmission in the mammalian brain and spinal cord. We investigated the immunohistochemical distribution of the GABAA receptor α1, α2, ß2,3 subunits and glycine receptors as well as their relationship to the vesicular GABA transporter (VGAT) in the human hypoglossal nucleus at the light and confocal laser scanning microscope levels. The results showed that all of the GABAA receptor subunits as well as glycine receptor display punctate labelling indicative of synapses on the soma and dendritic membranes of large neurons within the hypoglossal nucleus. On average, approximately 50% of glycine receptors were co localised with GABAA receptor α1 subunits. Also on average GABAA α2 and ß2,3 subunits were colocalised with approximately 30% of glycine receptor subunits. VGAT positive terminals were associated with both GABAA and glycine receptor types. Both glycinergic and GABAergic positive puncta were found adjacent to VGAT terminal-like staining. These results suggest that inhibition of human hypoglossal motor neurons occurs not only through complex interaction of separated GABAAR and glycine receptor regions, but also through synapses containing both inhibitory receptor types co-existing at the same synaptic sites.

The immunohistochemical distribution of the GABAA receptor α1, α2, α3, ß2/3 and γ2 subunits in the human thalamus.

The GABAA receptor is the most abundant inhibitory receptor in the human brain and is assembled from a variety of different subunit subtypes which determines their pharmacology and physiology. To determine which GABAA receptor subunit proteins are found in the human thalamus we investigated the distribution of five major GABAA receptor subunits α1, α2, α3, ß2,3 and γ2 using immunohistochemical techniques. The α1-, ß2,3- and γ2- subunits which combine to form a benzodiazepine sensitive GABAA receptor showed the most intense levels of staining and were the most common subunits found throughout the human thalamus especially in the ventral and posterior nuclear groups. The next most intense staining was for the α3-subunit followed by the α2-subunit. The intralaminar nuclear group, the mediodorsal nucleus and the thalamic reticular nucleus contained α1-, ß2,3- and γ2- subunits staining as well as the highest levels of the α2- and α3- subunits. The sensory dorsal lateral geniculate nucleus contained very high levels of α1- and ß2,3- and γ2-subunits. The highest densities of GABAA receptors found throughout the thalamus which contained the subunits α1, ß2,3, and γ2 included nuclei which are especially involved in the control or the modulation of the cortico-basal ganglia-thalamo-cortical motor circuits and are thus important in disorders such as Huntington's disease where the GABAergic projections of the basal ganglia are compromised. In addition the majority of receptors in the thalamic reticular nucleus contain α3 and γ2 subunits whilst the intralaminar nuclei contain high levels of α2 and α3 subunits.

The diversity of GABA(A) receptor subunit distribution in the normal and Huntington's disease human brain.

GABA(A) receptors are assembled into pentameric receptor complexes from a total of 19 different subunits derived from a variety of different subunit classes (α1-6, ß1-3, γ1-3, δ, ɛ, θ, and π) which surround a central chloride ion channel. GABA(A) receptor complexes are distributed heterogeneously throughout the brain and spinal cord and are activated by the extensive GABAergic inhibitory system. In this chapter, we describe the heterogeneous distribution of six of the most widely distributed subunits (α1, α2, α3, ß2,3, and γ2) throughout the human basal ganglia. This review describes the studies we have carried out on the normal and Huntington's disease human basal ganglia using autoradiographic labeling and immunohistochemistry in the human basal ganglia. GABA(A) receptors are known to react to changing conditions in the brain in neurological disorders, especially in Huntington's disease and display a high degree of plasticity which is thought to compensate for loss of function caused by disease. In Huntington's disease, the variable loss of GABAergic medium spiny striatopallidal projection neurons is associated with a loss of GABA(A) receptor subunits in the striosome and/or the matrix compartments of the striatum. By contrast in the globus pallidus, a loss of the GABAergic striatal projection neurons results in a dramatic upregulation of subunits on the large postsynaptic pallidal neurons; this is thought to be a compensatory plastic mechanism resulting from the loss of striatal GABAergic input. Most interestingly, our studies have revealed that the subventricular zone overlying the caudate nucleus contains a variety of proliferating progenitor stem cells that possess a heterogeneity of GABA(A) receptor subunits which may play a role in human brain repair mechanisms.

Differential Changes in Postsynaptic Density Proteins in Postmortem Huntington's Disease and Parkinson's Disease Human Brains.

NMDA and AMPA-type glutamate receptors and their bound membrane-associated guanylate kinases (MAGUKs) are critical for synapse development and plasticity. We hypothesised that these proteins may play a role in the changes in synapse function that occur in Huntington's disease (HD) and Parkinson's disease (PD). We performed immunohistochemical analysis of human postmortem brain tissue to examine changes in the expression of SAP97, PSD-95, GluA2 and GluN1 in human control, and HD- and PD-affected hippocampus and striatum. Significant increases in SAP97 and PSD-95 were observed in the HD and PD hippocampus, and PSD95 was downregulated in HD striatum. We observed a significant increase in GluN1 in the HD hippocampus and a decrease in GluA2 in HD and PD striatum. Parallel immunohistochemistry experiments in the YAC128 mouse model of HD showed no change in the expression levels of these synaptic proteins. Our human data show that major but different changes occur in glutamatergic proteins in HD versus PD human brains. Moreover, the changes in human HD brains differ from those occurring in the YAC128 HD mouse model, suggesting that unique changes occur at a subcellular level in the HD human hippocampus.

Neurogenesis and progenitor cell distribution in the subgranular zone and subventricular zone of the adult sheep brain.

Progenitor cell proliferation is ubiquitous in the subventricular zone (SVZ) and subgranular zone (SGZ) of adult mammalian brains, however, the abundance and distribution of proliferation are surprisingly heterogeneous between species. In rodents, proliferation is high in both the SVZ and SGZ, while in humans proliferation is prominent in the SVZ but limited in the SGZ. To accurately study proliferation and how it changes in human disease, we should focus on animals in which the patterns of proliferation are consistent with the human brain. In this study, we characterized the neurogenic niches of the adult sheep, an animal model with a longer lifespan than rodents and a highly gyrencephalic brain, using 5-bromo-2'-deoxyuridine (BrdU) as a mitotic marker and neuronal nuclear antigen to identify neuronal lineage cells. Our study demonstrates that the sheep SVZ is organized into the same distinct layers that are comparable to what has been described in humans. The rate of maturation of new neurons was slower in sheep than in previous reports in rodents, with only 20% of BrdU-positive cells showing neuronal phenotype after 4 months survival following BrdU administration. Most importantly, as in the human, there was much greater proliferation in the sheep SVZ than in the SGZ. These results suggest that the sheep is a better basis for comparisons with human SVZ and SGZ neurogenesis than rodents.

Changes in brainstem serotonergic and dopaminergic cell populations in experimental and clinical Huntington's disease.

The predominant motor symptom in Huntington's disease (HD) is chorea. The patho-anatomical basis for the chorea is not well known, but a link with the dopaminergic system has been suggested by post-mortem and clinical studies. Our previous work revealed an increased number of dopamine-containing cells in the substantia nigra and ventral tegmental area in a transgenic rat model of HD (tgHD). Since there were no changes in the total number of cells in those regions, we hypothesized that changes in cell phenotype were taking place. Here, we tested this hypothesis by studying the dorsal raphe nucleus (DRN), which houses dopaminergic and non-dopaminergic (mainly serotonergic) neurons in tgHD rat tissue and postmortem HD human tissue. We found an increased number of dopamine and reduced number of serotonin-containing cells in the DRN of tgHD rats. Similar findings in postmortem HD brain tissue indicate that these changes also occur in patients. Further investigations in the tgHD animal tissue revealed the presence of dopaminergic cell bodies in the B6 raphe region, while in control animals exclusively serotonin-containing cells were found. These data suggest the existence of phenotype changes in monoaminergic neurons in the DRN in HD and shed new light on the neurobiology of clinical neurological symptoms such as chorea and mood changes.

No change in progenitor cell proliferation in the hippocampus in Huntington's disease.

Increases in cell proliferation in the hippocampus have been robustly demonstrated in animal models of neurodegenerative diseases like Huntington's disease (HD). However, in the subventricular zone, animal models of HD have demonstrated no change in cell proliferation compared to wild types, while in humans there is a distinct increase in cell proliferation in HD cases. Interestingly, there have been no reports on cell proliferation in the human subgranular zone (SGZ) of the hippocampus in HD, despite numerous transgenic mouse models of HD showing decreased proliferation in the SGZ. Furthermore, HD can be divided into those with mainly mood and mainly motor symptomatology. We hypothesized that HD cases with mainly mood symptomatology would show a greater change in hippocampal proliferation, which has previously been implicated in mood disorders such as depression. Therefore, in the current study we examined and compared proliferation in the SGZ in normal vs. HD, HD mood, and HD motor affected cases. However, our results revealed no significant differences in SGZ proliferation between normal and HD cases, and no differences when divided into groups based on mood and motor symptomatology. Our results were confirmed using a range of cell-cycle protein markers and, overall, were comparable with previous studies of the human hippocampus, where very little proliferation was detected in the adult SGZ. These results demonstrate that in humans the SGZ is far less proliferative than the SVZ, and suggests that hippocampal plasticity in humans does not primarily involve cell proliferation.

Allelic imbalance of tissue-type plasminogen activator (t-PA) gene expression in human brain tissue.

We have identified a single-nucleotide polymorphism (SNP) in the t-PA enhancer (-7351C>T), which is associated with endothelial t-PA release in vivo. In vitro studies demonstrated that this SNP is functional at the level of transcription. In the brain, t-PA has been implicated in both physiologic and pathophysiologic processes. The aim of the present study was to examine the effect of the t-PA -7351C>T SNP on t-PA gene expression in human brain tissue. Allelic mRNA expression was measured in heterozygous post-mortem brain tissues using quantitative TaqMan genotyping assay. Protein-DNA interactions were assessed using electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP). Significantly higher levels of t-PA mRNA were generated from chromosomes that harboured the wild-type -7351C allele, as compared to those generated from the mutant T allele (for the hippocampus, C to T allelic ratio of ~1.3, p=0.010, n=12; and for the cortex, C to T allelic ratio of ~1.2, p=0.017, n=12). EMSA showed reduced neuronal and astrocytic nuclear protein binding affinity to the T allele, and identified Sp1 and Sp3 as the major transcription factors that bound to the -7351 site. ChIP analyses confirmed that Sp1 recognises this site in intact cells. In conclusion, the t-PA -7351C>T SNP affects t-PA gene expression in human brain tissue. This finding might have clinical implications for neurological conditions associated with enhanced t-PA levels, such as in the acute phase of cerebral ischaemia, and also for stroke recovery.

Behavioural and molecular consequences of chronic cannabinoid treatment in Huntington's disease transgenic mice.

Early loss of CB1 receptors is a hallmark of human Huntington's disease. Data from rodent studies suggest that preservation and activation of CB1 receptors may be protective against disease progression. R6/1 transgenic mice are considered to be a model of early pathogenic changes in Huntington's disease. We have shown previously that levels of CB1 in R6/1 mice prior to the onset of motor symptoms (12 weeks of age) remain high enough to justify commencement of cannabinoid drug treatment. Eight weeks of daily treatment with the cannabinoid agonists HU210 (0.01 mg/kg) and Delta(9)-tetrahydrocannabinol (THC, 10.00 mg/kg), or the inhibitor of endocannabinoid metabolism URB597 (0.30 mg/kg), did not alter the progressive deterioration of performance observed in motor behavioural testing. HU210-treated R6/1 mice experienced a significant increase in seizure events suggesting that this therapy may lower the seizure threshold and cautioning against highly efficacious agonists as potential therapy in this disease. Molecular characterisation of brains at the end of the study showed that there were no significant effects of HU210 or THC treatment on the ligand binding of cannabinoid CB1, dopamine D1, D2, serotonin 5HT2A or GABA(A) receptors, nor CB1 or fatty acid amide hydrolase (FAAH) mRNA expression in R6/1 mice. Intriguingly, a significant increase in the number of ubiquitinated aggregates was observed in the striatum with HU210 treatment, indicating an influence of CB1 on the disease process. Chronic URB597 treatment preserved CB1 receptors in the R6/1 striatum, suggesting that the manipulation of endocannabinoid levels warrants further exploration.

Characterization of the netrin/RGMa receptor neogenin in neurogenic regions of the mouse and human adult forebrain.

In the adult rodent forebrain, astrocyte-like neural stem cells reside within the subventricular zone (SVZ) and give rise to progenitors and neuroblasts, which then undergo chain migration along the rostral migratory stream (RMS) to the olfactory bulb, where they mature into fully functional interneurons. Neurogenesis also occurs in the adult human SVZ, where neural precursors similar to the rodent astrocyte-like stem cell and neuroblast have been identified. A migratory pathway equivalent to the rodent RMS has also recently been described for the human forebrain. In the embryo, the guidance receptor neogenin and its ligands netrin-1 and RGMa regulate important neurogenic processes, including differentiation and migration. We show in this study that neogenin is expressed on neural stem cells (B cells), progenitor cells (C cells), and neuroblasts (A cells) in the adult mouse SVZ and RMS. We also show that netrin-1 and RGMa are ideally placed within the neurogenic niche to activate neogenin function. Moreover, we find that neogenin and RGMa are also present in the neurogenic regions of the human adult forebrain. We show that neogenin is localized to cells displaying stem cell (B cell)-like characteristics within the adult human SVZ and RMS and that RGMa is expressed by the same or a closely apposed cell population. This study supports the hypothesis that, as in the embryo, neogenin regulates fundamental signalling pathways important for neurogenesis in the adult mouse and human forebrain.

Differential localization of gamma-aminobutyric acid type A and glycine receptor subunits and gephyrin in the human pons, medulla oblongata and uppermost cervical segment of the spinal cord: an immunohistochemical study.

Gephyrin is a multifunctional protein responsible for the clustering of glycine receptors (GlyR) and gamma-aminobutyric acid type A receptors (GABA(A)R). GlyR and GABA(A)R are heteropentameric chloride ion channels that facilitate fast-response, inhibitory neurotransmission in the mammalian brain and spinal cord. We investigated the immunohistochemical distribution of gephyrin and the major GABA(A)R and GlyR subunits in the human light microscopically in the rostral and caudal one-thirds of the pons, in the middle and caudal one-thirds of the medulla oblongata, and in the first cervical segment of the spinal cord. The results demonstrate a widespread pattern of immunoreactivity for GlyR and GABA(A)R subunits throughout these regions, including the spinal trigeminal nucleus, abducens nucleus, facial nucleus, pontine reticular formation, dorsal motor nucleus of the vagus nerve, hypoglossal nucleus, lateral cuneate nucleus, and nucleus of the solitary tract. The GABA(A)R alpha(1) and GlyR alpha(1) and beta subunits show high levels of immunoreactivity in these nuclei. The GABA(A)R subunits alpha(2), alpha(3), beta(2,3), and gamma(2) present weaker levels of immunoreactivity. Exceptions are intense levels of GABA(A)R alpha(2) subunit immunoreactivity in the inferior olivary complex and high levels of GABA(A)R alpha(3) subunit immunoreactivity in the locus coeruleus and raphe nuclei. Gephyrin immunoreactivity is highest in the first segment of the cervical spinal cord and hypoglossal nucleus. Our results suggest that a variety of different inhibitory receptor subtypes is responsible for inhibitory functions in the human brainstem and cervical spinal cord and that gephyrin functions as a clustering molecule for major subtypes of these inhibitory neurotransmitter receptors.

Immunohistochemical localisation of the creatine transporter in the rat brain.

Creatine (Cr) is required to maintain ATP levels in the brain. The transport of Cr across the blood-brain barrier and into neurones requires a specific creatine transporter (CRT). Mutations in the CRT gene (SLC6A8) result in a novel form of X-linked mental retardation, characterised by developmental delays, seizures and a complete absence of Cr from the brain. To identify cell types and regions that depend on Cr for energy metabolism we have determined the regional and cellular localisation of CRT protein in the rat brain using immunohistochemical techniques with a highly specific, affinity-purified, CRT antibody. The results show high levels of CRT localisation is associated with specific brain regions and certain cell types. The CRT is predominantly found in neurones. CRT immunoreactivity is particularly abundant in the olfactory bulb, granule cells of the dentate gyrus of the hippocampus, pyramidal neurones of the cerebral cortex, Purkinje cells of the cerebellum, motor and sensory cranial nerve nuclei in the brainstem and the dorsal and ventral horns of the spinal cord. Low levels of CRT were seen in the basal ganglia and white matter. Overall, CRT was found to show high intensities of labelling in the major motor and sensory regions of the forebrain, brainstem and spinal cord and forebrain regions associated with learning, memory and limbic functions. It is hypothesised that regions with high CRT expression are likely to have high metabolic ATP requirements and that areas with low CRT levels are those regions which are particularly vulnerable in neurodegenerative diseases.

Cannabinoid (CB(1)), GABA(A) and GABA(B) receptor subunit changes in the globus pallidus in Huntington's disease.

Huntington's disease (HD) is a disease of the basal ganglia which results in a major loss of the striatal GABAergic medium spiny neurons containing enkephalin and substance P. These neurons project principally to the globus pallidus (GP) and substantia nigra pars reticulata (SNr). Both GABA(A) and GABA(B) receptors are localised postsynaptically on neurons in the GP and SNr, and cannabinoid (CB(1)) receptors are localised presynaptically on the axon terminals of the medium spiny projection neurons in the GP and SNr. The aims of this project were to investigate the changes in the distribution of CB(1), GABA(A), and GABA(B) receptor subunits, as well as enkephalin and substance P in the GP in the HD brain compared to the normal brain. The results of this study have shown firstly, that in the HD brain there is a dramatic loss of enkephalin and CB(1) receptor immunoreactivity (IR) in the external segment of the globus pallidus (GPe) and a major loss of substance P and CB(1) receptor-IR from the internal segment of the globus pallidus (GPi). Secondly, the degeneration of these striatal efferent neurons results in the upregulation of the various subunits of both GABA(A) (alpha(1), beta(2,3) and gamma(2)) and GABA(B) (R(1)) receptors in the GP in HD. Detailed double labelling confocal microscopy studies show that in HD the increased GABA(A) and GABA(B) receptor-IR is distributed not just in punctate "synaptic" regions, but throughout all dendritic and somal membranes of pallidal neurons. These results provide the first comprehensive description of the changes of CB(1), GABA(A) and GABA(B) receptor subunits in the HD basal ganglia. The upregulation of both GABA(A) and GABA(B) receptors may serve to increase the sensitivity of pallidal neurons to the decreased levels of GABA that occurs in the GP in HD. The loss of CB(1) receptors in HD is also thought to be a compensatory mechanism due to evidence that endocannabinoids modulate the reuptake of GABA in the GP. These findings show the high degree of plasticity of CB(1), GABA(A) and GABA(B) receptors and provide a better understanding of the GABAergic modulation of basal ganglia neurons in the normal and diseased human brain.

Altered CB1 receptor and endocannabinoid levels precede motor symptom onset in a transgenic mouse model of Huntington's disease.

Huntington's disease (HD) is an inherited neurodegenerative disease characterised by cell dysfunction and death in the basal ganglia and cortex. Currently there are no effective pharmacological treatments available. Loss of cannabinoid CB1 receptor ligand binding in key brain regions is detected early in HD in human postmortem tissue [Glass M, Dragunow M, Faull RL (2000) The pattern of neurodegeneration in Huntington's disease: a comparative study of cannabinoid, dopamine, adenosine and GABA(A) receptor alterations in the human basal ganglia in Huntington's disease. Neuroscience 97:505-519]. In HD transgenic mice environmental enrichment upregulates the CB1 receptors and slows disease progression [Glass M, van Dellen A, Blakemore C, Hannan AJ, Faull RL (2004) Delayed onset of Huntington's disease in mice in an enriched environment correlates with delayed loss of cannabinoid CB1 receptors. Neuroscience 123:207-212]. These findings, combined with data from lesion studies have led to the suggestion that activation of cannabinoid receptors may be protective. However, studies suggest that CB1 mRNA may be decreased early in the disease progression in HD mice, making this a poor drug target. We have therefore performed a detailed analysis of CB1 receptor ligand binding, protein, gene expression and levels of endocannabinoids just prior to motor symptom onset (12 weeks of age) in R6/1 transgenic mice. We demonstrate that R6/1 mice exhibit a 27% decrease in CB1 mRNA in the striatum compared to wild type (WT). Total protein levels, determined by immunohistochemistry, are not significantly different to WT in the striatum or globus pallidus, but are significantly decreased by 19% in the substantia nigra. CB1 receptor ligand binding demonstrates significant but small decreases (<20%) in all basal ganglia regions evaluated. The levels of the endocannabinoid 2-arachidonoyl glycerol are significantly increased in the cortex (147%) while anandamide is significantly decreased in the hippocampus to 67% of WT. Decreases are also apparent in the ligand binding of neuronal D1 and D2 dopamine receptors co-located with CB1, while there is no change in GABA(A) receptor ligand binding. These results suggest that in this R6/1 mouse colony at 12 weeks there are only very small changes in CB1 protein and receptors and thus this would be an appropriate time point to evaluate therapeutic interventions.

The histamine H4 receptor is functionally expressed on neurons in the mammalian CNS.

BACKGROUND AND PURPOSE: The histamine H4 receptor is the most recently identified of the G protein-coupled histamine receptor family and binds several neuroactive drugs, including amitriptyline and clozapine. So far, H4 receptors have been found only on haematopoietic cells, highlighting its importance in inflammatory conditions. Here we investigated the possibility that H4 receptors may be expressed in both the human and mouse CNS. METHODS: Immunological and pharmacological studies were performed using a novel anti-H4 receptor antibody in both human and mouse brains, and electrophysiological techniques in the mouse brain respectively. Pharmacological tools, selective for the H4 receptor and patch clamp electrophysiology, were utilized to confirm functional properties of the H4 receptor in layer IV of the mouse somatosensory cortex. RESULTS: Histamine H4 receptors were prominently expressed in distinct deep laminae, particularly layer VI, in the human cortex, and mouse thalamus, hippocampal CA4 stratum lucidum and layer IV of the cerebral cortex. In layer IV of the mouse somatosensory cortex, the H4 receptor agonist 4-methyl histamine (20 micromol x L(-1)) directly hyperpolarized neurons, an effect that was blocked by the selective H4 receptor antagonist JNJ 10191584, and promoted outwardly rectifying currents in these cells. Monosynaptic thalamocortical CNQX-sensitive excitatory postsynaptic potentials were not altered by 4-methyl histamine (20 micromol x L(-1)) suggesting that H4 receptors did not act as hetero-receptors on thalamocortical glutamatergic terminals. CONCLUSIONS AND IMPLICATIONS: This is the first demonstration that histamine H4 receptors are functionally expressed on neurons, which has major implications for the therapeutic potential of these receptors in neurology and psychiatry.

The localization of inhibitory neurotransmitter receptors on dopaminergic neurons of the human substantia nigra.

The substantia nigra pars compacta (SNc) is comprised mainly of dopaminergic pigmented neurons arranged in groups, with a small population of nonpigmented neurons scattered among these groups. These different types of neurons possess GABAA, GABAB, and glycine receptors. The SNc-pigmented dopaminergic neurons have postsynaptic GABAA receptors (GABAAR) with a subunit configuration containing alpha3 and gamma2 subunits, with a small population of pigmented neurons containing alpha1 beta2,3 gamma2 subunits. GABAB receptors comprised of R1 and R2 subunits and glycine receptors are also localized on pigmented neurons. In contrast, nonpigmented (mainly parvalbumin positive neurons) located in the SNc are morphologically and neurochemically similar to substantia nigra pars reticulata (SNr) neurons by showing immunoreactivity for parvalbumin and GABAARs containing immunoreactivity for alpha1, alpha3, beta2,3, and gamma2 subunits as well as GABAB R1 and R2 subunits and glycine receptors. Thus, these two neuronal types of the SNc, either pigmented dopaminergic neurons or nonpigmented parvalbumin positive neurons, have similar GABAB and glycine receptor combinations, but differ mainly in the subunit composition of the GABAARs located on their membranes. The different types of GABAARs suggest that GABAergic inputs to these neuronal types operate through GABAARs with different pharmacological and physiological profiles, whereas GABABR and glycine receptors of these cell types are likely to have similar properties.

Doublecortin expression in the normal and epileptic adult human brain.

Mesial temporal lobe epilepsy (MTLE) is a neurological disorder associated with spontaneous recurrent complex partial seizures and hippocampal sclerosis. Although increased hippocampal neurogenesis has been reported in animal models of MTLE, increased neurogenesis has not been reported in the hippocampus of adult human MTLE cases. Here we showed that cells expressing doublecortin (Dcx), a microtubule-associated protein expressed in migrating neuroblasts, were present in the hippocampus and temporal cortex of the normal and MTLE adult human brain. In particular, increased numbers of Dcx-positive cells were observed in the epileptic compared with the normal temporal cortex. Importantly, 56% of Dcx-expressing cells in the epileptic temporal cortex coexpressed both the proliferative cell marker, proliferating cell nuclear antigen and early neuronal marker, TuJ1, suggesting that they may be newly generated neurons. A subpopulation of Dcx-positive cells in the epileptic temporal cortex also coexpressed the mature neuronal marker, NeuN, suggesting that epilepsy may promote the generation of new neurons in the temporal cortex. This study has identified, for the first time, a novel population of Dcx-positive cells in the adult human temporal cortex that can be upregulated by epilepsy and thus, raises the possibility that these cells may have functional significance in the pathophysiology of epilepsy.

The collection and processing of human brain tissue for research.

To further understand the neuroanatomy, neurochemistry and neuropathology of the normal and diseased human brain, it is essential to have access to human brain tissue where the biological and chemical nature of the tissue is optimally preserved. We have established a human brain bank where brain tissue is optimally processed and stored in order to provide a resource to facilitate neuroscience research of the human brain in health and disease. A donor programme has been established in consultation with the community to provide for the post-mortem donation of brain tissue to the brain bank. We are using this resource of human brain tissue to further investigate the basis of normal neuronal functioning in the human brain as well as the mechanisms of neuronal dysfunction and degeneration in neurodegenerative diseases. We have established a protocol for the preservation of post-mortem adult human brain tissue firstly by snap-freezing unfixed brain tissue and secondly by chemical fixation and then storage of this tissue at -80 degrees C in a human brain bank. Several research techniques such as receptor autoradiography, DNA and RNA analysis, are carried out on the unfixed tissue and immunohistochemical and histological analysis is carried out on the fixed human tissue. Comparison of tissue from normal control cases and from cases with neurodegenerative disorders is carried out in order to document the changes that occur in the brain in these disorders and to further investigate the underlying pathogenesis of these devastating neurological diseases.