Changing synaptic connections on cell bodies of growing identified spinal motoneurons of the eel, Anguilla

Human iPS Cell-Derived Neurons Uncover the Impact of Increased Ras Signaling in Costello Syndrome

Increasing evidence implicates abnormal Ras signaling as a major contributor in neurodevelopmental disorders, yet how such signaling causes cortical pathogenesis is unknown. We examined the consequences of aberrant Ras signaling in the developing mouse brain and uncovered several critical phenotypes, including increased production of cortical neurons and morphological deficits. To determine whether these phenotypes are recapitulated in humans, we generated induced pluripotent stem (iPS) cell lines from patients with Costello syndrome (CS), a developmental disorder caused by abnormal Ras signaling and characterized by neurodevelopmental abnormalities, such as cognitive impairment and autism. Directed differentiation toward a neuroectodermal fate revealed an extended progenitor phase and subsequent increased production of cortical neurons. Morphological analysis of mature neurons revealed significantly altered neurite length and soma size in CS patients. This study demonstrates the synergy between mouse and human models and validates the use of iPS cells as a platform to study the underlying cellular pathologies resulting from signaling deficits.

SIGNIFICANCE STATEMENT

Increasing evidence implicates Ras signaling dysfunction as a major contributor in psychiatric and neurodevelopmental disorders, such as cognitive impairment and autism, but the underlying cortical cellular pathogenesis remains unclear. This study is the first to reveal human neuronal pathogenesis resulting from abnormal Ras signaling and provides insights into how these phenotypic abnormalities likely contribute to neurodevelopmental disorders. We also demonstrate the synergy between mouse and human models, thereby validating the use of iPS cells as a platform to study underlying cellular pathologies resulting from signaling deficits. Recapitulating human cellular pathologies in vitro facilitates the future high throughput screening of potential therapeutic agents that may reverse phenotypic and behavioral deficits.

Mapping the spatio-temporal pattern of the mammalian target of rapamycin (mTOR) activation in temporal lobe epilepsy

Growing evidence from rodent models of temporal lobe epilepsy (TLE) indicates that dysregulation of the mammalian target of rapamycin (mTOR) pathway is involved in seizures and epileptogenesis. However, the role of the mTOR pathway in the epileptogenic process remains poorly understood. Here, we used an animal model of TLE and sclerotic hippocampus from patients with refractory TLE to determine whether cell-type specific activation of mTOR signaling occurs during each stage of epileptogenesis. In the TLE mouse model, we found that hyperactivation of the mTOR pathway is present in distinct hippocampal subfields at three different stages after kainate-induced seizures, and occurs in neurons of the granular and pyramidal cell layers, in reactive astrocytes, and in dispersed granule cells, respectively. In agreement with the findings in TLE mice, upregulated mTOR was observed in the sclerotic hippocampus of TLE patients. All sclerotic hippocampus (n = 13) exhibited widespread reactive astrocytes with overactivated mTOR, some of which invaded the dispersed granular layer. Moreover, two sclerotic hippocampus exhibited mTOR activation in some of the granule cells, which was accompanied by cell body hypertrophy. Taken together, our results indicate that mTOR activation is most prominent in reactive astrocytes in both an animal model of TLE and the sclerotic hippocampus from patients with drug resistant TLE.

Functional recovery and axonal growth following spinal cord transection is accelerated by sustained l-DOPA administration

The eel, Anguilla anguilla, as with other fish species, recovers well from spinal cord injury. We assessed the quality of locomotion of spinally transected eels from measurements made from video recordings of individuals swimming at different speeds in a water tunnel. Following transection of the spinal cord just caudal to the anus, the animals displayed higher tail beat frequencies and lower tail beat amplitudes than before surgery, owing to the loss of power in this region. Swimming performance then progressively recovered, appearing normal within 1 month of surgery. Eels with similar transections, but given regular, repeated intraperitoneal injections (50 mg/kg) of l-3,4-dihydroxyphenylalanine (L-DOPA) showed an equivalent pattern of decline and recovery that was 10-20 days shorter than that seen in non-treated fish. Axonal growth into the denervated cord, as determined from anterograde labelling experiments, was also more rapid in the drug-treated fish. L-DOPA treatment increased the activity of all fish for up to 18 h, and accelerated the spontaneous movements ('spinal swimming') made by the denervated, caudal portion of the animal that appeared following transection. We suggest that this enhancement of locomotion underlies the accelerated axonal growth and, hence, functional recovery.

Neuronal hypertrophy in the neocortex of patients with temporal lobe epilepsy

The underlying cause of neocortical involvement in temporal lobe epilepsy (TLE) remains a fundamental and unanswered question. Magnetic resonance imaging has shown a significant loss in temporal lobe volume, and it has been proposed that neocortical circuits are disturbed functionally because neurons are lost. The present study used design-based stereology to estimate the volume and cell number of Brodmann's area 38, a region commonly resected in anterior temporal lobectomy. Studies were conducted on the neocortex of patients with or without hippocampal sclerosis (HS). Results provide the surprising finding that TLE patients have significant atrophy of neocortical gray matter but no loss of neurons. Neurons are also significantly larger, dendritic trees appear sparser, and spine density is noticeably reduced in TLE specimens compared with controls. The increase in neuronal density we found in TLE patients is therefore attributable to large neurons occupying a much smaller volume than in normal brain. Neurons in the underlying white matter are also increased in size but, in contrast to other reports, are not significantly elevated in number or density. Neuronal hypertrophy affects HS and non-HS brains similarly. The reduction in neuropil and its associated elements therefore appears to be a primary feature of TLE, which is not secondary to cell loss. In both gray and white matter, neuronal hypertrophy means more perikaryal surface area is exposed for synaptic contacts and emerges as a hallmark of this disease.

The relationships of brain stem systems to their targets in the spinal cord of the eel, Anguilla anguilla

We have investigated the detail with which supraspinal neurons innervate different regions in the spinal cord. Horseradish peroxidase was applied at different levels of the cord: (1) to the cut surface; (2) injected iontophoretically into one side; or (3) into one of the motoneuron pools innervating different muscle compartments. In all cases, labeled neurons were found throughout the brain distributed over nuclear groups identified in previous fish studies. Some cells from all but one of the nuclei have axons that extend over the whole length of the cord and about 50% of all neurons project to post-anal levels. No topographical distribution relating somal position and target location was found. Sixty seven percent of the neurons send axons to the ipsilateral side of the cord, although most nuclear groups provide a bilateral projection. Nucleus ruber projects entirely contralaterally. The descending and magnocellular octavolateral nuclei, and the descending nucleus of the trigeminal nerve project entirely ipsilaterally. Neurons that project to the spinal motoneuron pools innervating the myotomal red- or white-muscle are distributed throughout the same brain stem nuclei, but the cell bodies of those neurons innervating white-muscle motoneurons are larger. Nineteen pairs of cells were found to be consistently identifiable and all project to all levels of the cord; they were only labeled from injections made into the white-muscle motoneuron pool.