Abnormalities in Cortical GABAergic Interneurons of the Primary Motor Cortex Caused by Lis1 (Pafah1b1) Mutation Produce a Non-drastic Functional Phenotype.

LIS1 (PAFAH1B1) plays a major role in the developing cerebral cortex, and haploinsufficient mutations cause human lissencephaly type 1. We have studied morphological and functional properties of the cerebral cortex of mutant mice harboring a deletion in the first exon of the mouse Lis1 (Pafah1b1) gene, which encodes for the LisH domain. The Lis1/sLis1 animals had an overall unaltered cortical structure but showed an abnormal distribution of cortical GABAergic interneurons (those expressing calbindin, calretinin, or parvalbumin), which mainly accumulated in the deep neocortical layers. Interestingly, the study of the oscillatory activity revealed an apparent inability of the cortical circuits to produce correct activity patterns. Moreover, the fast spiking (FS) inhibitory GABAergic interneurons exhibited several abnormalities regarding the size of the action potentials, the threshold for spike firing, the time course of the action potential after-hyperpolarization (AHP), the firing frequency, and the frequency and peak amplitude of spontaneous excitatory postsynaptic currents (sEPSC's). These morphological and functional alterations in the cortical inhibitory system characterize the Lis1/sLis1 mouse as a model of mild lissencephaly, showing a phenotype less drastic than the typical phenotype attributed to classical lissencephaly. Therefore, the results described in the present manuscript corroborate the idea that mutations in some regions of the Lis1 gene can produce phenotypes more similar to those typically described in schizophrenic and autistic patients and animal models.

Intraventricular injections of mesenchymal stem cells activate endogenous functional remyelination in a chronic demyelinating murine model.

Current treatments for demyelinating diseases are generally only capable of ameliorating the symptoms, with little to no effect in decreasing myelin loss nor promoting functional recovery. Mesenchymal stem cells (MSCs) have been shown by many researchers to be a potential therapeutic tool in treating various neurodegenerative diseases, including demyelinating disorders. However, in the majority of the cases, the effect was only observed locally, in the area surrounding the graft. Thus, in order to achieve general remyelination in various brain structures simultaneously, bone marrow-derived MSCs were transplanted into the lateral ventricles (LVs) of the cuprizone murine model. In this manner, the cells may secrete soluble factors into the cerebrospinal fluid (CSF) and boost the endogenous oligodendrogenic potential of the subventricular zone (SVZ). As a result, oligodendrocyte progenitor cells (OPCs) were recruited within the corpus callosum (CC) over time, correlating with an increased myelin content. Electrophysiological studies, together with electron microscopy (EM) analysis, indicated that the newly formed myelin correctly enveloped the demyelinated axons and increased signal transduction through the CC. Moreover, increased neural stem progenitor cell (NSPC) proliferation was observed in the SVZ, possibly due to the tropic factors released by the MSCs. In conclusion, the findings of this study revealed that intraventricular injections of MSCs is a feasible method to elicit a paracrine effect in the oligodendrogenic niche of the SVZ, which is prone to respond to the factors secreted into the CSF and therefore promoting oligodendrogenesis and functional remyelination.

Mesenchymal stromal-cell transplants induce oligodendrocyte progenitor migration and remyelination in a chronic demyelination model.

Demyelinating disorders such as leukodystrophies and multiple sclerosis are neurodegenerative diseases characterized by the progressive loss of myelin that may lead toward a chronic demyelination of the brain's white matter, impairing normal axonal conduction velocity and ultimately causing neurodegeneration. Current treatments modifying the pathological mechanisms are capable of ameliorating the disease; however, frequently, these therapies are not sufficient to repress the progressive demyelination into a chronic condition and permanent loss of function. To this end, we analyzed the effect that bone marrow-derived mesenchymal stromal cell (BM-MSC) grafts exert in a chronically demyelinated mouse brain. As a result, oligodendrocyte progenitors were recruited surrounding the graft due to the expression of various trophic signals by the grafted MSCs. Although there was no significant reaction in the non-grafted side, in the grafted regions oligodendrocyte progenitors were detected. These progenitors were derived from the nearby tissue as well as from the neurogenic niches, including the subependymal zone and dentate gyrus. Once near the graft site, the cells matured to myelinating oligodendrocytes. Finally, electrophysiological studies demonstrated that axonal conduction velocity was significantly increased in the grafted side of the fimbria. In conclusion, we demonstrate here that in chronic demyelinated white matter, BM-MSC transplantation activates oligodendrocyte progenitors and induces remyelination in the tissue surrounding the stem cell graft.

A study of F-waves in patients with unilateral lumbosacral radiculopathy.

BACKGROUND AND PURPOSE: The F wave, a late response of low amplitude, is widely used in the study of peripheral nerve lesions, and its persistence and latencies are the main parameters that are usually considered. The analysis of repeater F-waves, which are commonly observed in association with focal or generalized motor neuropathy, is not always performed as a standard electrodiagnostic protocol. METHODS: We recorded and quantified the F waves from 13 healthy subjects and 22 patients with unilateral lumbosacral radiculopathy (ULSR) affecting the L5 or S1 roots. RESULTS: We found differences between the injured and normal sides of patients with ULSR in several F-wave parameters. Taking into consideration the normalized and pooled values of tibial and peroneal nerves in the injured side of patients with ULSR, the minimum and mean latencies were higher (1.05 and 1.04 with respect to 1.00; P < 0.01), the relative amplitude of the F waves was higher (1.95 with respect to 1.00; P < 0.001), and the percentage of repeater F-waves was also higher (4.19 with respect to 1.00; P < 0.001). This latter parameter was the most sensitive to detect lateral differences as indicated by the percentage of change and its high z score. CONCLUSIONS: Our results show that the use of F-waves may improve the electrodiagnosis of the ULSR if the number of repeater waves is evaluated given the clear and consistent increase of this variable in patients with lumbosacral root injury.

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.

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 microM 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 microM) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 20 microM); 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.

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).

A comparison of electrophysiological tests for the early diagnosis of diabetic neuropathy.

Clinical criteria and several electrophysiological parameters for detecting nerve damage were compared in 99 patients with diabetes mellitus type 1 and type 2. Abnormal results were found in sural/radial amplitude ratio (51%), minimal F-wave latency of the tibial nerve (36.4%), sensory conduction velocity of the sural nerve (29.8%), and sural sensory nerve action potential amplitude (29.3%) when pooling data from all patients and comparing them to age- and height-matched normal control subjects. Analysis of all the parameters revealed large differences between the diabetes mellitus type 1 and type 2 groups, suggesting that the type of diabetes must be taken into account when comparing the sensitivity of nerve conduction tests. In diabetes mellitus type 1, the sural/radial ratio had the clearest correlation with course of illness and was the first parameter to show a significant reduction. We conclude that the simple ratio between sural and radial amplitudes is a very sensitive parameter and abnormalities in this ratio provide the means for earliest detection of neuropathy in diabetes mellitus type 1.

Calcium-activated chloride current in normal mouse sympathetic ganglion cells.

1. In rat sympathetic ganglion cells, axotomy induces the appearance of a depolarizing after-potential (ADP) produced by a calcium-activated chloride current. Here we report that this current is also present in normal sympathetic neurones from the mouse. 2. In an in vitro preparation of the superior cervical ganglion, an ADP was observed after spike firing in 50% of the cells studied with single-electrode current- and voltage-clamp techniques. 3. When the cells were voltage clamped at -50 mV in the presence of tetrodotoxin (TTX) and tetraethylammonium chloride (TEA), depolarizing jumps evoked inward calcium currents which were contaminated by outward chloride currents, followed by slowly decaying inward chloride tail currents. 4. The ADP and the inward tail currents disappeared when calcium was removed from the extracellular solution or when cadmium was added. 5. The reversal potential for the inward tail current was approximately -24 mV and was displaced in agreement with the Nernst equation for chloride when the extracellular NaCl was replaced by sucrose or sodium isethionate. The chloride channel blocker anthracene-9-carboxylic acid (9AC) inhibited both the ADP and the tail current. 6. Using intracellular injection of neurobiotin, we found that cells with shorter dendrites had larger ADPs. In axotomized ganglia practically all cells showed very pronounced ADPs. 7. We conclude that normal mouse sympathetic ganglion cells have a calcium-activated chloride current that generates an ADP. The channels responsible for this current are probably located in the dendrites.

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 single-electrode 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 morphological and physiological differences from the rest of the pyramidal neurons studied. This group of neurons had shorter and less complex apical dendritic arbors, fired action potentials of lower amplitude and longer duration, and were the only type of pyramidal neurons able to generate bursts of action potentials. In addition, the inhibitory synaptic potentials elicited by stimulation of layer I were more powerful in this group of neurons. This research provides new evidence for the presence of the LTCC in subsets of cortical pyramidal neurons, which have specific and well defined morphological and physiological properties.

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.