Variations in genes regulating neuronal migration predict reduced prefrontal cognition in schizophrenia and bipolar subjects from mediterranean Spain: A preliminary study

Both neural development and prefrontal cortex function are known to be abnormal in schizophrenia and bipolar disorder. In order to test the hypothesis that these features may be related with genes that regulate neuronal migration, we analyzed two genomic regions: the lissencephaly critical region (chromosome 17p) encompassing the LIS1 gene and which is involved in human lissencephaly; and the genes related to the platelet-activating-factor, functionally related to LIS1, in 52 schizophrenic patients, 36 bipolar I patients and 65 normal control subjects. In addition, all patients and the 25 control subjects completed a neuropsychological battery. Thirteen (14.8%) patients showed genetic variations in either two markers related with lissencephaly or in the platelet-activating-factor receptor gene. These patients performed significantly worse in the Wisconsin Card Sorting Test–Perseverative Errors in comparison with patients with no lissencephaly critical region/platelet-activating-factor receptor variations. The presence of lissencephaly critical region/platelet-activating-factor receptor variations was parametrically related to perseverative errors, and this accounted for 17% of the variance (P=0.0001). Finally, logistic regression showed that poor Wisconsin Card Sorting Test–Perseverative Errors performance was the only predictor of belonging to the positive lissencephaly critical region/platelet-activating-factor receptor group. These preliminary findings suggest that the variations in genes involved in neuronal migration predict the severity of the prefrontal cognitive deficits in both disorders.This study was supported by the following: Lilly, S.A. (Spain), the Stanley Medical Research Institute (Bethesda, MD, USA), European Union grants U.E. QLG2-CT-1999-00793; UE QLRT-1999-31556; UE QLRT-1999-31625; QLRT-2000-02310; Spanish grants DIGESIC-MEC BFI2002-02979/BFU2005-09085 to S.M.; BFI2002-03467 to E.G.-B. and FIS-MSC (PI051293) and GV2005-303 to R.T.-S.Peer reviewe

Evidence for association between structural variants in lissencephaly-related genes and executive deficits in schizophrenia or bipolar patients from a Spanish isolate population

There is evidence for an association between structural variants in genes for lissencephaly, which are involved in neuronal migration, and prefrontal cognitive deficits in schizophrenia and bipolar patients. On the basis of these intriguing findings, we analyzed 16 markers located in the lissencephaly critical region (LCR in chromosome 17p13.3) in 124 schizophrenic, 56 bipolar, and 141 healthy individuals. All recruits were from a Spanish population isolate of Basque origin that is characterized by low genetic heterogeneity. In addition, we examined whether structural genomic variations in the LCR were associated with executive cognition. Twenty-three patients (12.8%), but none of the controls, showed structural variants (deletions and insertions) in either of two markers related with lissencephaly (D17S1566 on tumor suppressor gene TP53: tumor protein p53 and D17S22 on SMG6 gene: Smg-6 homolog, nonsense mediated mRNA decay factor- Caenorhabditis elegans). These patients performed significantly worse in the Wisconsin Card Sorting Test-Categories in comparison with patients without such variations in lissencephaly-related genes. The presence of structural variants was related to completed categories, and accounted for 10.7% of the variance (P= 0.001). Finally, logistic regression showed that poor Wisconsin Card Sorting Test-Categories performance was the only predictor of belonging to the positive LCR variations group. These new findings provide further evidence for the association between some lissencephaly-related genes and both schizophrenia and bipolar disorder, and influence on frontal executive functioning. © 2008 Wolters Kluwer Health|Lippincott Williams & Wilkins.FIS-MSC PI051293, AstraZeneca, Spanish Ministry of Health, Instituto de Salud Carlos III, Ciber en Salud Mental (CIBER-SAM) GV2005-303.Peer Reviewe

Subthreshold inward membrane currents in guinea-pig frontal cortex neurons

Current-clamp and single-electrode voltage-clamp recordings were used to study the inward currents activated in the subthreshold membrane potential range of cortical pyramidal neurons. The experiments were done on slices from guinea-pig frontal cortex and all recordings were obtained at a distance of 600-900 microm from the pial surface. In current-clamp recordings and from membrane potentials hyperpolarized to about -70 mV, the depolarization leading to spike firing was partially blocked by 1 microM tetrodotoxin, but not by calcium-free extracellular solution. The calcium-free solution only affected this depolarization when the membrane potential was held at a level more negative than -75 mV. Under voltage-clamp, an inward current was recorded between the resting membrane potential and the level of spike firing. This current was activated at about -60 mV and part of it was blocked by 1 microM tetrodotoxin; the remaining current was blocked by calcium-free extracellular solution. In five neurons both components were recorded and isolated in the same cell. The tetrodotoxin-sensitive component activated at close to -60 mV, was similar to the persistent sodium current (I(Na-p)). The Ca2+-sensitive component activated at close to -60 or -65 mV, was less voltage-dependent than I(Na-p). This component was similar to the low threshold calcium current (I(T)). These results suggest that the subthreshold depolarization which led to spike firing was dependent on I(Na-p) and I(T), I(Na-p) being the most important factor up to resting membrane potentials of -70 or -75 mV. A physiological role of this finding is revealed by the action of dopamine, which (at 10 microM) prevented the firing of action potentials from -60 mV, but not from -80 mV due to the inhibition of I(Na-p) and the lack of effect on I(T).This work was supported by Grant PM95-0107 from the DGICYT (Spain).Peer reviewe

Intra- and Interhemispheric Propagation of Electrophysiological Synchronous Activity and Its Modulation by Serotonin in the Cingulate Cortex of Juvenile Mice.

Disinhibition of the cortex (e.g., by GABA -receptor blockade) generates synchronous and oscillatory electrophysiological activity that propagates along the cortex. We have studied, in brain slices of the cingulate cortex of mice (postnatal age 14-20 days), the propagation along layer 2/3 as well as the interhemispheric propagation through the corpus callosum of synchronous discharges recorded extracellularly and evoked in the presence of 10 μM bicuculline by electrical stimulation of layer 1. The latency of the responses obtained at the same distance from the stimulus electrode was longer in anterior cingulate cortex (ACC: 39.53 ± 2.83 ms, n = 7) than in retrosplenial cortex slices (RSC: 21.99 ± 2.75 ms, n = 5; p<0.05), which is equivalent to a lower propagation velocity in the dorso-ventral direction in ACC than in RSC slices (43.0 mm/s vs 72.9 mm/s). We studied the modulation of this propagation by serotonin. Serotonin significantly increased the latency of the intracortical synchronous discharges (18.9% in the ipsilateral hemisphere and 40.2% in the contralateral hemisphere), and also increased the interhemispheric propagation time by 86.4%. These actions of serotonin were mimicked by the activation of either 5-HT1B or 5-HT2A receptors, but not by the activation of the 5-HT1A subtype. These findings provide further knowledge about the propagation of synchronic electrical activity in the cerebral cortex, including its modulation by serotonin, and suggest the presence of deep differences between the ACC and RSC in the structure of the local cortical microcircuits underlying the propagation of synchronous discharges

Compartmental structure of the otic placode: junctional permeability and clonal restriction

The work was supported by a grant from the DGICYT PB96/0087 and Junta de Castilla y León. Esther Vázquez is recipient of a DGICYT fellowship.Peer Reviewe

The effects of dopamine on the subthreshold electrophysiological responses of rat prefrontal cortex neurons in vitro

The rat prefrontal cortex is densely innervated by dopaminergic fibres originating in the mesencephalic ventral tegmental area, and dopamine application in vivo has an inhibitory effect. We have studied the effects of dopamine on the persistent sodium current that is present in prefrontal cortex neurons and on the subthreshold electrophysiological responses generated by that current: a slow depolarization and a fast oscillatory activity. Experiments were made in coronal slices of rat frontal cortex (300-400 microns thickness) and intracellular recordings from regularly spiking cells were obtained with 3 M potassium acetate-filled glass microelectrodes (80-150 M omega). Dopamine was applied dissolved in the extracellular medium and, in current-clamp recordings, reversibly inhibited the slow subthreshold depolarization. Dopamine was ineffective when applied after tetrodotoxin (1 microM) had blocked the action potentials. This inhibition was dose-dependent in the range of 0.1-10 microM). Dopamine, applied at 10 microM, decreased the steady-state firing frequency and also inhibited the subthreshold fast oscillatory activity. The currents activated in the subthreshold range were recorded with the single-electrode voltage-clamp technique and a clear persistent, tetrodotoxin-sensitive component was isolated. This component was inhibited by 50% in a reversible way by 20 microM dopamine. These results show that dopamine increases the threshold for spike firing and suggest a mechanism for the inhibitory action of this neurotransmitter in the prefrontal cortex.Peer reviewe

Laminar localization, morphology, and physiological properties of pyramidal neurons that have the low-threshold calcium current in the guinea-pig medial frontal cortex

One of the several types of ionic currents present in central neurons is the low-threshold, or T-type calcium current (LTCC). This current is responsible for the firing of low-threshold calcium spikes (LTS) and participates in the generation of rhythmic activity and bursts of action potentials in several brain nuclei. We have studied the distribution and properties of pyramidal neurons recorded from the guinea-pig medial frontal cortex that have this calcium current. Pyramidal neurons were recorded in an in vitro slice preparation using either current clamp or singleelectrode voltage-clamp recording. Pyramidal neurons that generated LTS or had the LTCC were found only between 500 mm from the pial surface and the white matter (approximately layers V/VI) and were absent in more superficial layers. All pyramidal neurons that fired LTS or had the LTCC were characterized as regular spiking and had some important morphologica

Participation of low-threshold calcium spikes in excitatory synaptic transmission in guinea pig medial frontal cortex

We studied the activation of low-threshold calcium spikes (LTS) by excitatory postsynaptic potentials in pyramidal neurons from guinea pig medial frontal cortex with intracellular recording. We used extracellular bicuculline and phaclofen and intracellular QX-314 to block inhibitory synaptic potentials and sodium currents. Postsynaptic potentials were evoked by stimulation of layer I. We found that large (> 10–15 mV) excitatory synaptic potentials evoked from membrane potentials more negative than −75 mV were able to trigger LTS. The activation of LTS resulted in an increase of the rising slope or amplitude of the synaptic potentials depending on the size of the excitatory postsynaptic potential (EPSP). We used 100 μm NiCl2 to confirm the presence of LTS as part of the EPSPs. The N-methyl-d-aspartate (NMDA) and non-NMDA components of the excitatory synaptic potentials were isolated using (±)2-amino-5-phosphonovaleric acid (APV; 50 μm) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 20 μm); both components could, independently, trigger an LTS. With recordings made with K+ acetate-filled electrodes, we show that the activation of LTS was critical to allow excitatory synaptic potentials to reach the threshold of action potential firing; also, this amplification of synaptic responses produced the firing of more than a single action potential by the postsynaptic cell. These results demonstrate that in cortical pyramidal neurons the activation of low-threshold calcium spikes results in the amplification of synaptic responses.This work was supported by grant PM95-0107 from the DGICYT (Spain).Peer reviewe

Inhibition by 5-HT of the synaptic responses evoked by callosal fibers on cortical neurons in the mouse

We have studied the modulation by 5-HT of the synaptic excitatory responses evoked by callosal fibers on cortical pyramidal neurons. We have used a mouse brain slice preparation that preserves the callosal fibers and allows their selective activation. EPSCs evoked by callosal stimulation (ccEPSCs) were recorded with patch electrodes from pyramidal neurons identified visually. We observed that 5-HT (10-40 mu M) inhibited the ccEPSCs peak amplitude in 64% of the neurons; 5-HT had no effect in the remaining neurons. 5-HT also increased the frequency and amplitude of spontaneous EPSCs. This inhibition was accompanied with an increase in the coefficient of variation of the fluctuations of the ccEPSCs amplitude and with an increase in the ratio of the amplitudes of paired ccEPSCs. Agonists of 5-HT receptor subtypes 5-HT1A (8-OH-DPAT) and 5-HT2A (DOI) mimicked the effect of 5-HT; also, the effect of 8-OH-DPAT and DOI was blocked in the presence of specific blockers of 5-HT1A (WAY 100135) and 5-HT2A (MDL 11,939) receptors. Application of 5-HT did not change the amplitude of currents evoked by direct application of glutamate to neurons in which 5-HT decreased the amplitude of ccEPSC. The effects of 5-HT on ccEPSCs and on the synaptic currents evoked by intracortical stimulation were not correlated; this suggests that the effect of 5-HT was specific to particular synaptic inputs to a neuron. These results demonstrate the presynaptic modulation of the callosal synaptic responses by 5-HT and the implication of 5-HT1A and 5-HT2A receptors in this effect.This study was supported by grants AP 090/08 and PROMETEO (Generalitat Valenciana), grant PI052561 (Instituto de Salud Carlos III), grant from the Fundación Navarro-Trípodi, and Grupo Consolider (Spanish Ministry of Education and Science Grant CONSOLIDER-INGENIO 2010 CSD2007-00023).Peer Reviewe

Inhibition by 5-HT of the synaptic responses evoked by callosal fibers on cortical neurons in the mouse

We have studied the modulation by 5-HT of the synaptic excitatory responses evoked by callosal fibers on cortical pyramidal neurons. We have used a mouse brain slice preparation that preserves the callosal fibers and allows their selective activation. EPSCs evoked by callosal stimulation (ccEPSCs) were recorded with patch electrodes from pyramidal neurons identified visually. We observed that 5-HT (10-40 mu M) inhibited the ccEPSCs peak amplitude in 64% of the neurons; 5-HT had no effect in the remaining neurons. 5-HT also increased the frequency and amplitude of spontaneous EPSCs. This inhibition was accompanied with an increase in the coefficient of variation of the fluctuations of the ccEPSCs amplitude and with an increase in the ratio of the amplitudes of paired ccEPSCs. Agonists of 5-HT receptor subtypes 5-HT1A (8-OH-DPAT) and 5-HT2A (DOI) mimicked the effect of 5-HT; also, the effect of 8-OH-DPAT and DOI was blocked in the presence of specific blockers of 5-HT1A (WAY 100135) and 5-HT2A (MDL 11,939) receptors. Application of 5-HT did not change the amplitude of currents evoked by direct application of glutamate to neurons in which 5-HT decreased the amplitude of ccEPSC. The effects of 5-HT on ccEPSCs and on the synaptic currents evoked by intracortical stimulation were not correlated; this suggests that the effect of 5-HT was specific to particular synaptic inputs to a neuron. These results demonstrate the presynaptic modulation of the callosal synaptic responses by 5-HT and the implication of 5-HT1A and 5-HT2A receptors in this effect.This study was supported by grants AP 090/08 and PROMETEO (Generalitat Valenciana), grant PI052561 (Instituto de Salud Carlos III), grant from the Fundación Navarro-Trípodi, and Grupo Consolider (Spanish Ministry of Education and Science Grant CONSOLIDER-INGENIO 2010 CSD2007-00023).Peer Reviewe