Angelman syndrome (AS) is a neurodevelopmental disorder arising from loss-of-function mutations in the maternally inherited copy of theUBE3Agene, and is characterized by an absence of speech, ...excessive laughter, cognitive delay, motor deficits, and seizures. Despite the fact that the symptoms of AS occur in early childhood, behavioral characterization of AS mouse models has focused primarily on adult phenotypes. In this report we describe juvenile behaviors in AS mice that are strain-independent and clinically relevant. We find that young AS mice, compared with their wild-type littermates, produce an increased number of ultrasonic vocalizations. In addition, young AS mice have defects in motor coordination, as well as abnormal brain activity that results in an enhanced seizure-like response to an audiogenic challenge. The enhanced seizure-like activity, but not the increased ultrasonic vocalizations or motor deficits, is rescued in juvenile AS mice by genetically reducing the expression level of the activity-regulated cytoskeleton-associated protein,Arc.These findings suggest that therapeutic interventions that reduce the level ofArcexpression have the potential to reverse the seizures associated with AS. In addition, the identification of aberrant behaviors in young AS mice may provide clues regarding the neural circuit defects that occur in AS and ultimately allow new approaches for treating this disorder.
GLT-1 (EAAT2; slcla2) is the major glutamate transporter in the brain, and is predominantly expressed in astrocytes, but at lower levels also in excitatory terminals. We generated a conditional GLT-1 ...knock-out mouse to uncover cell-type-specific functional roles of GLT-1. Inactivation of the GLT-1 gene was achieved in either neurons or astrocytes by expression of synapsin-Cre or inducible human GFAP-CreERT2. Elimination of GLT -1 from astrocytes resulted in loss of ~ 80% of GLT -1 protein and of glutamate uptake activity that could be solubilized and reconstituted in liposomes. This loss was accompanied by excess mortality, lower body weight, and seizures suggesting that astrocytic GLT-1 is of major importance. However, there was only a small (15%) reduction that did not reach significance of glutamate uptake into crude forebrain synaptosomes. In contrast, when GLT-1 was deleted in neurons, both the GLT-1 protein and glutamate uptake activity that could be solubilized and reconstituted in liposomes were virtually unaffected. These mice showed normal survival, weight gain, and no seizures. However, the synaptosomal glutamate uptake capacity (V sub(max)) was reduced significantly (40%). In conclusion, astrocytic GLT-1 performs critical functions required for normal weight gain, resistance to epilepsy, and survival. However, the contribution of astrocytic GLT-1 to glutamate uptake into synaptosomes is less than expected, and the contribution of neuronal GLT -1 to synaptosomal glutamate uptake is greater than expected based on their relative protein expression. These results have important implications for the interpretation of the many previous studies assessing glutamate uptake capacity by measuring synaptosomal uptake.
Transcranial direct current stimulation (tDCS) is a noninvasive neuromodulation technique where weak direct current is administered through electrodes placed on the subject's head. Transcranial ...magnetic stimulation (TMS) is a noninvasive method for focal brain stimulation where small intracranial currents are induced by a pulsed magnetic field. TMS can be applied simultaneously with tDCS to probe brain excitability or to effect synergistic neuromodulation. Delivering TMS simultaneously with tDCS can induce electric current pulses in the tDCS electrodes even when the tDCS device is turned off or is set to 0 mA output, as long as the electrodes are connected to the tDCS current source. The output impedance of commercial tDCS devices is in the range of 2-5 kΩ which can allow substantial currents to be induced by TMS. In a rat TMS-tDCS setup, the induced currents are comparable to the tDCS current magnitude. To mitigate the induced currents, the area of the loop formed by the tDCS electrode leads should be minimized and the impedance of the tDCS circuit at TMS pulses frequencies (1-10 kHz) should be maximized.
Diffuse Optical Imaging (DOI) is a non-invasive neuroimaging technique which measures the changes in oxy- and deoxy-hemoglobin concentrations at a high temporal resolution based on the principle of ...Near-Infrared Spectroscopy. DOI was combined with repetitive Transcranial Magnetic Stimulation (rTMS) to assess the neuronal changes induced in the cortical regions, which are directly under rTMS and the connected areas, by applying 1Hz rTMS to the left hemisphere of the motor cortex followed by the stimulation to the prefrontal cortex for two visits. The DOI signals were simultaneously acquired from both ipsilateral and contralateral brain regions before, during, and after rTMS. We observed that there was no significant difference in the temporal responses between visit 1 and visit 2. Stimulation of both the cortices resulted in a significant decrease in oxy-hemoglobin concentration in both the ipsilateral and contralateral sides, which showed high temporal consistency. Also functional connectivity between the stimulated site (at the selected seed region) and the contralateral regions was investigated by performing a correlation analysis of the DOI time series using seed-region correlation mapping. The correlation maps exhibited a remarkable degree of temporal synchronization between the two hemispheres in both motor and prefrontal cortex, confirming that rTMS generated strong inter-hemispheric effects during and after rTMS. In another clinical study, DOI and Electromyography (EMG) were employed together to assess the cortical activity and reorganization in children affected with Cerebral Palsy (CP), a motor impairment. The results showed that the functional connectivity patterns along with EMG responses for a finger-tapping protocol differentiate the brain activity in healthy and CP children. Finally in a pilot study, the feasibility of a simultaneous functional MRI (fMRI) and DOI approach was tested to validate the DOI results with fMRI yielding high consistency between the two.
