Impaired fast-spiking, suppressed cortical inhibition and increased susceptibility to seizures in mice lacking Kv3.2 K+ channel proteins

Voltage-gated K+ channels of the Kv3 subfamily have unusual electrophysiological properties, including activation at very depolarized voltages (positive to −10 mV) and very fast deactivation rates, suggesting special roles in neuronal excitability. In the brain, Kv3 channels are prominently expressed in select neuronal populations, which include fast-spiking (FS) GABAergic interneurons of the neocortex, hippocampus, and caudate, as well as other high-frequency firing neurons. Although evidence points to a key role in high-frequency firing, a definitive understanding of the function of these channels has been hampered by a lack of selective pharmacological tools. We therefore generated mouse lines in which one of the Kv3 genes, Kv3.2, was disrupted by gene-targeting methods. Whole-cell electrophysiological recording showed that the ability to fire spikes at high frequencies was impaired in immunocytochemically identified FS interneurons of deep cortical layers (5-6) in which Kv3.2 proteins are normally prominent. No such impairment was found for FS neurons of superficial layers (2-4) in which Kv3.2 proteins are normally only weakly expressed. These data directly support the hypothesis that Kv3 channels are necessary for high-frequency firing. Moreover, we found that Kv3.2 −/− mice showed specific alterations in their cortical EEG patterns and an increased susceptibility to epileptic seizures consistent with an impairment of cortical inhibitory mechanisms. This implies that, rather than producing hyperexcitability of the inhibitory interneurons, Kv3.2 channel elimination suppresses their activity. These data suggest that normal cortical operations depend on the ability of inhibitory interneurons to generate high-frequency firing.

K(+) channel expression distinguishes subpopulations of parvalbumin- and somatostatin-containing neocortical interneurons

Kv3.1 and Kv3.2 K+ channel proteins form similar voltage-gated K+ channels with unusual properties, including fast activation at voltages positive to −10 mV and very fast deactivation rates. These properties are thought to facilitate sustained high-frequency firing. Kv3.1 subunits are specifically found in fast-spiking, parvalbumin (PV)-containing cortical interneurons, and recent studies have provided support for a crucial role in the generation of the fast-spiking phenotype. Kv3.2 mRNAs are also found in a small subset of neocortical neurons, although the distribution of these neurons is different. We raised antibodies directed against Kv3.2 proteins and used dual-labeling methods to identify the neocortical neurons expressing Kv3.2 proteins and to determine their subcellular localization. Kv3.2 proteins are prominently expressed in patches in somatic and proximal dendritic membrane as well as in axons and presynaptic terminals of GABAergic interneurons. Kv3.2 subunits are found in all PV-containing neurons in deep cortical layers where they probably form heteromultimeric channels with Kv3.1 subunits. In contrast, in superficial layer PV-positive neurons Kv3.2 immunoreactivity is low, but Kv3.1 is still prominently expressed. Because Kv3.1 and Kv3.2 channels are differentially modulated by protein kinases, these results raise the possibility that the fast-spiking properties of superficial- and deep-layer PV neurons are differentially regulated by neuromodulators. Interestingly, Kv3.2 but not Kv3.1 proteins are also prominent in a subset of seemingly non-fast-spiking, somatostatin- and calbindin-containing interneurons, suggesting that the Kv3.1–Kv3.2 current type can have functions other than facilitating high-frequency firing.

Calbindin D-28K and parvalbumin immunoreactivity in the frontal cortex in patients with frontal lobe dementia of non-Alzheimer type associated with amyotrophic lateral sclerosis

The morphology and distribution of local-circuit neurons (interneurons) were examined, by calbindin D-28k and parvalbumin immunocytochemistry, in the frontal cortex (area 8) in two patients with frontal lobe dementia of non-Alzheimer type associated with classical amyotrophic lateral sclerosis (ALS), and in seven normal cases. The density of calbindin D-28k immunoreactive cells was dramatically reduced in ALS patients, but the density of parvalbumin-immunoreactive neurons was preserved. Decreased density of calbindin D-28k-immunoreactive neurons, which are mainly located in the upper cortical layers, may interfere with the normal processing of cortico-cortical connections, whereas integrity of parvalbumin-immunoreactive cells may be associated with the preservation of the major inhibitory intracortical circuits in patients with frontal lobe dementia.

Cortistain is expressed in a distinct subset of cortical interneurons

Cortistatin is a presumptive neuropeptide that shares 11 of its 14 amino acids with somatostatin. In contrast to somatostatin, administration of cortistatin into the rat brain ventricles specifically enhances slow wave sleep, apparently by antagonizing the effects of acetylcholine on cortical excitability. Here we show that preprocortistatin mRNA is expressed in a subset of GABAergic cells in the cortex and hippocampus that partially overlap with those containing somatostatin. A significant percentage of cortistatin-positive neurons is also positive for parvalbumin. In contrast, no colocalization was found between cortistatin and calretinin, cholecystokinin, or vasoactive intestinal peptide. During development there is a transient increase in cortistatin-expressing cells in the second postnatal week in all cortical areas and in the dentate gyrus. A transient expression of preprocortistatin mRNA in the hilar region at P16 is paralleled by electrophysiological changes in dentate granule cells. Together, these observations suggest mechanisms by which cortistatin may regulate cortical activity.

ADHD candidate gene (DRD4 exon III) affects inhibitory control in a healthy sample.

Background Dopamine is believed to be a key neurotransmitter in the development of attention-deficit/ hyperactivity disorder (ADHD). Several recent studies point to an association of the dopamine D4 receptor (DRD4) gene and this condition. More specifically, the 7 repeat variant of a variable number of tandem repeats (VNTR) polymorphism in exon III of this gene is suggested to bear a higher risk for ADHD. In the present study, we investigated the role of this polymorphism in the modulation of neurophysiological correlates of response inhibition (Go/Nogo task) in a healthy, high-functioning sample. Results Homozygous 7 repeat carriers showed a tendency for more accurate behavior in the Go/Nogo task compared to homozygous 4 repeat carriers. Moreover, 7 repeat carriers presented an increased nogo-related theta band response together with a reduced go-related beta decrease. Conclusions These data point to improved cognitive functions and prefrontal control in the 7 repeat carriers, probably due to the D4 receptor's modulatory role in prefrontal areas. The results are discussed with respect to previous behavioral data on this polymorphism and animal studies on the impact of the D4 receptor on cognitive functions.

Synthesis of a tetrahydroimidazo-[2',1':2,3]thiazolo[5,4-c]pyridine derivative with Met inhibitory activity

A straightforward synthesis of the Met antagonist JLK1360 involving an alkylationcyclocondensation process using aminothiazole 1 and nitrophenacyl bromide 2, reduction of the nitro group, and coupling of the resulting tetracyclic aniline 5 with an appropriate N-acyl alanine derivative, is reported.

Synthesis of a tetrahydroimidazo-[2',1':2,3]thiazolo[5,4-c]pyridine derivative with Met inhibitory activity

A straightforward synthesis of the Met antagonist JLK1360 involving an alkylationcyclocondensation process using aminothiazole 1 and nitrophenacyl bromide 2, reduction of the nitro group, and coupling of the resulting tetracyclic aniline 5 with an appropriate N-acyl alanine derivative, is reported.

In vivo co-ordinated interactions between inhibitory systems to control glutamate mediated hippocampal excitability.

We present an overview of the long-term adaptation of hippocampal neurotransmission to cholinergic and GABAergic deafferentation caused by excitotoxic lesion of the medial septum. Two months after septal microinjection of 2.7 nmol a -amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), a 220% increase of GABA A receptor labelling in the hippo- campal CA3 and the hilus was shown, and also changes in hippocampal neurotransmission characterised by in vivo microdialysis and HPLC. Basal amino acid and purine extra- cellular levels were studied in control and lesioned rats. In vivo effects of 100 m M KCl perfusion and adenosine A 1 receptor blockade with 1,3-dipropyl- 8-cyclopentylxanthine (DPCPX) on their release were also investigated. In lesioned animals GABA, glutamate and glutamine basal levels were decreased and taurine, adenosine and uric acid levels increased. A similar response to KCl infusion occurred in both groups except for GABA and glutamate, which release decreased in lesioned rats. Only in lesioned rats, DPCPX increased GABA basal level and KCl-induced glutamate release, and decreased glutamate turnover. Our results evidence that an excitotoxic septal lesion leads to increased hippocampal GABA A receptors and decreased glutamate neurotransmis- sion. In this situation, a co-ordinated response of hippocampal retaliatory systems takes place to control neuron excitability.

Déficits y sesgos neurocognitivos y afectivos en la toma de decisiones de jugadores patológios y otros trastornos

Los déficits y sesgos tanto cognitivos como afectivos han sido fuente creciente de interés en el ámbito de la Neurociéncia de los Trastornos Mentales. En este proyecto, que se inicia en 2004 y finaliza a finales de 2008, se han estudiado los siguientes Trastornos Mentales: Juego Patológico (JP), Trastornos de la Conducta Alimentaria (TCA) y Trastornos Depresivos. En esta memoria nos centraremos en resumir parte de los resultados obtenidos en un estudio sobre JP y toma de decisiones (articulo en revisión y pendiente de aceptación) y otro de funcionamiento ejecutivo en JP y Bulimia Nerviosa (BN) (artículo en prensa). Resumiento el primer estudio los JP (N=32) muestran un proceso de toma de decisiones sesgado por la búsqueda de recompensa en forma de elevada toma de riesgos en comparación con Controles Sanos (CS). También se observan déficits en flexibilidad cognitiva pero no en control inhibitorio entre JP y CS. Los resultados descartan miopía conductual para lo toma de decisiones en JP, pero apuntan a un sesgo cognitivo-afectivo, en el que el control de los impulsos jugaría un papel relevante, en forma de ilusión de control, para los procesos de toma de decisiones con recompensa inmediata pero con castigo diferido, medidos por una prueba de toma de decisiones (IGT ABCD). En el segundo estudio, basándose en las vulnerabilidadades compartidas descritas entre JP y BN se comparó el funcionamiento ejecutivo de mujeres con JP y BN. Tras la administración del WCST y Stroop y ajustando el análisis por edad y educación, las JP mostraron mayor afectación, en concreto mayor porcentaje de errores perservaritvos, menor nivel de respuestas conceptuales y mayor número de ensayos administrados, mientras que el grupo de BN mostró mayor porcentaje de errores no persevarativos. Ambas, mujeres JP y BN mostraron disfunción ejecutiva en relación a los CS pero con diferentes correlatos específcos.

Selección de péptidos sintéticos del Virus de la Hepatitis G (GBV-C/HGV) inhibidores del Péptido de Fusión HIV-I

El GB virus C (GBV-C) o virus de l'hepatitis G (HGV) es un virus format per una única cadena de RNA que pertany a la familia Flaviviridae. En els últims anys, s'han publicat nombrosos treballs en els quals s'associa la coinfecció del GBV-C i del virus de la immunodeficiència humana (VIH) amb una menor progressió de l'esmentada malaltia així com amb una major supervivència dels pacients una vegada que la SIDA s'ha desenvolupat. El mecanisme pel qual el virus GBV-C/HGV exerceix un “efecte protector” en els pacients amb VIH encara no està descrit. L’estudi de la interacció entre els virus GBVC/HGV i VIH podria donar lloc al desenvolupament de nous agents terapèutics per al tractament de la SIDA.Treballs recents mostren com la capacitat inhibitòria del virus del GBV-C/HGV és deguda a la seva glicoproteina estructural E2. S’ha vist que aquesta proteina seria capaç d’inhibir la primera fase de replicació de VIH, així com la unió i la fusió amb les membranes cel•lulars. Sobre la base d’aquests estudis, l’objectiu d’aquest treball ha estat seleccionar inhibidors del pèptid de fusió del VIH utilitzant pèptids sintètics de la proteina E2 del GBV-C/HGV. El treball realitzat ha consistit en estudiar, utilitzant assajos biofísics de leakage i de lipid mixing, la capacitat dels pèptids de la proteina estructural del virus del GBV-C/HGV per inhibir la interacció i el procés de desestabilització de membranes induïdes pel pèptid de fusió de la glicoproteina de l’embolcall, GP41, del VIH. Aquests assajos, com es descriu en treballs anteriors, han resultat útils per a la selecció i la identificació de compostos amb activitat específica anti-GP41. Es pot afirmar que efectivament els pèptids seleccionats de la proteina E2 del virus del GBV-C/HGV inhibeixen l’activitat del pèptid de fusió del VIH probablement com a consequència d’un canvi conformacional en aquest darrer.

Analysis of nonlinear noisy integrate & fire neuron models: blow-up and steady states

Nonlinear Noisy Leaky Integrate and Fire (NNLIF) models for neurons networks can be written as Fokker-Planck-Kolmogorov equations on the probability density of neurons, the main parameters in the model being the connectivity of the network and the noise. We analyse several aspects of the NNLIF model: the number of steady states, a priori estimates, blow-up issues and convergence toward equilibrium in the linear case. In particular, for excitatory networks, blow-up always occurs for initial data concentrated close to the firing potential. These results show how critical is the balance between noise and excitatory/inhibitory interactions to the connectivity parameter.

Funcions de les molècules associades a la mielina i la proteïna priònica cel•lular (PrPc) en neurodegeneració (Malaltia d’Alzheimer) i neuroinflamació (Esclerosi Múltiple)

Les proteïnes associades a la mielina (MAIS), Nogo-A, MAG i OMgp, són molècules que presenten una capacitat inhibitòria molt important per el recreixement axonal i la neuroreparació després de lesió. No obstant des de fa anys les seves funcions han estat ampliades i s’han involucrat en diferents processos degeneratius del sistema nerviós o en processos neuroinflamatoris del sistema nerviós central i el perifèric com ara l'Escleresi Múltiple (MS). La base neurobiològica d’indicadors moleculars que són responsables del dany axonal en MS segueixen sense estar plenament descrits. Recentment s’ha publicat que el mecanisme de senyalització Nogo-A pot regir els primers canvis de la desmielinització immunomediada del sistema nerviós central en el model animal de MS, l’encefalomielitis autoimmune experimental (EAE). De la mateixa forma la proteïna priònica cel•lular és una proteïna que s’ha associat majoritàriament a malalties espongiformes, però que recentment s’ha vinculat (no sense controvèrsia) amb la seva possible relació amb la Malaltia d'Alzheimer (AD), ja que seria capaç de reclutar els oligòmers d’Aβ (ADDLs), els quals correlacionen millor amb el grau de demència, i amb els que interacciona directament, actuant així com un possible mediador de la fosforilació de tau en la malaltia. No obstant, les funcions de les MAIS i de la PrPc en aquests models de la malaltia no estan clarament definits i, per altra banda, es desconeixen els mecanismes de senyalització implicats, no descartant de forma clara el component neural i l’immune.