Larry E. Becker

Activation of PI3-kinase is required for AMPA receptor insertion during LTP of mEPSCs in cultured hippocampal neurons.

Hippocampal CA1 homosynaptic long-term potentiation (LTP) is expressed specifically at activated synapses. Increased insertion of postsynaptic alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid receptors (AMPARs) appears to be crucial for CA1 LTP. However, the mechanism underlying AMPAR insertion during LTP remains largely unknown. We now report that phosphatidylinositol 3-kinase (PI3K) is complexed with AMPARs at synapses and activated by selective stimulation of synaptic N-methyl-D-aspartate (NMDA) receptors. Activation of the AMPAR-associated PI3K is required for the increased cell surface expression of AMPARs and LTP. Thus, our results strongly suggest that the AMPAR-PI3K complex may constitute a critical molecular signal responsible for AMPAR insertion at activated CA1 synapses during LTP, and consequently, this lipid kinase may serve to determine the polarity of NMDA receptor-dependent synaptic plasticity.

Clinical presentation of mitochondrial respiratory chain defects in NADH-coenzyme Q reductase and cytochrome oxidase: Clues to pathogenesis of Leigh disease*

Measurement of pyruvate and lactate produced from glucose by confluent skin fibroblast cultures from 95 patients with lactic acidemia revealed 10 in whom the lactate/pyruvate ratio (L/P) was increased (L/P = 57 to 232) compared with that observed in control cell lines (L/P = 18 to 35). Mitochondria prepared from these cells revealed two types of respiratory chain defect. In four patients the deficient activity was present in NADH-coenzyme Q reductase (14% to 21% of controls), and in six the deficiency was in cytochrome c oxidase (21% to 28% of controls). The four patients with NADH-coQ reductase deficiency presented early with lactic acidosis, respiratory failure, anorexia, and hypotonia; all four died within 7 months. The group with cytochrome oxidase deficiency had a somewhat later (18 months to 2 years of age) presentation with milder lactic acidemia, but also with hypotonia and anorexia. They had delayed development, beginning to walk and talk at 18 to 24 months, and then slowly regressed. Although an investigation of central nervous system disorders in this latter group has not been possible, the clinical progression fits into the broad category of Leigh disease. We conclude that in these two groups respiratory chain defects can be detected and localized by the use of skin fibroblast cultures.

Abnormal electric membrane properties of Down's syndrome DRG neurons in cell culture.

Cell cultures were prepared from normal and Downs syndrome dorsal root ganglia (DRG). Both pre- and postnatal specimens were utilized; 8 normal and 4 Downs. Cultures were maintained in medium with normal (4 mM) and elevated (20 mM) potassium (K) since the latter was found to enhance neuron survival. After various period of incubation, cultures were transferred to normal K medium and their electrical membrane properties (EMP) determined using intracellular recording techniques. An analysis of variance was performed with 5 covariates: developmental stage, culture duration, K concentration, type of action potential, and neuronal surface area. This analysis indicated that the Downs neurons had abnormal EMP, the most affected being the after hyperpolarization (-41%), membrane time constant (+30%), threshold rheobasic depolarization (-22%), rate of falling phase of action potential (-20%), specific membrane resistance (+18%) and absolute refractory period (+12%). All differences were also observed when samples of normal and Downs neurons were matched for the 5 covariates mentioned above, take separately. If the abnormal EMP observed in the present study for Downs DRG neurons in culture occurred for CNS neurons in situ they would disrupt the normal function of the nervous system and could therefore constitute the neurobiological basis of the mental retardation observed in Downs syndrome.

Synaptic development in the human fetus: A morphometric analysis of normal and Down's syndrome neocortex

Postmortem tissue was obtained from six normal and four Downs syndrome brains ranging in age from 12 to 40 weeks postconception. Tissue was processed for electron microscopy using routine osmium and EPTA staining procedures, and to examine synaptic development, photomicrographs were systematically taken throughout the molecular layer of the sensorimotor neocortex. The number of EPTA-stained synapses were consistently greater than the number of osmium-stained synaptic contacts. A progressive increase in synaptic density throughout the range of ages examined was observed for both normal and Downs syndrome tissue. There was also an increase with developmental age in apparent measures of synaptic maturity, e.g., an increased ratio of mature to primitive contacts and asymmetrical to symmetrical contacts. In normal tissue, pre- and postsynaptic membrane lengths were observed to increase with the ages studied, whereas synaptic membrane widths appeared to attain mature values by 29 weeks postconception. Cleft width remained fairly constant to 28 weeks postconception. Although direct statistical comparisons could not be made, in Downs tissue synaptic parameter development was generally less consistent and the parameters appeared to be reduced during the later stages of development studied.

Experience with pineal region tumours in childhood

Sixty-one children with pineal region tumours were managed at the Hospital for Sick Children during the period 1950-1982. Histologic verification of these tumours was possible in forty-six children. Although germ cell tumours were the commonest form, germinomas only made up one third of the pineal region tumours. Since 1967, an aggressive approach has been adopted in the management of pineal region tumours at the Hospital for Sick Children with thirty-four patients having direct surgery on their pineal region mass out of a total of forty-one patients with such tumours. The operative mortality for pineal tumour surgery has steadily fallen so that the operative mortality between 1975 and 1982 was 4.3% and there have been no operative deaths since 1977 among the thirteen patients with pineal region tumours who have been operatively treated. Pineal tumours are operable lesions which should be removed if they are benign. Histologic confirmation should be obtained if they are malignant in order to provide for rational management of these lesions.

Electric membrane properties of human DRG neurons in cell culture and the effect of high K medium

Cell cultures were prepared from human fetal and newborn dorsal root ganglia (DRG) and maintained in culture medium with normal (4 mM) and elevated (20 mM) potassium (K). Both types of cultures were transferred to 4 mM K, and the electrical membrane properties of the DRG neurons characterized by an extensive investigation of resting membrane potential, specific membrane resistance (Rm) and capacitance, time constant (tau), rheobasic current, and various aspects of the action potential, including overshoot, duration (DT), afterhyperpolarization and absolute refractory period (ARP). No previous quantitative determinations of these membrane properties for human neurons could be found. However, our values were in good agreement with those reported for the DRG neurons of other mammalian species both in vitro and in situ. Significant correlations occurred between membrane properties and the developmental age of each specimen used for culturing. However, the data must be interpreted cautiously due to the limited number of specimens used (4) and the possibility of differential responses of the specimens to the experimental situation. Precultivation in high K medium had profound effects on both passive and active membrane properties: the primary effect being to reduce Rm, and as a result tau, DT, and ARP were also reduced. These observations add further support to the hypothesis that high K in vitro can substitute to some extent for trophic factors normally present in situ.

Extraneural metastases of a cerebral astrocytoma.

Extraneural spread of a cerebral glioma has been described infrequently. The present case provides an example of this unique mode of metastasis.