Arnold Kriegstein, M.D., Ph.D.

Our laboratory works on basic mechanisms underlying neocortical development. In particular, we are interested in the roles of amino acid transmitters and their receptors during very early stages of corticogenesis. Techniques in use in the lab include patch clamp electrophysiology in brain slices, molecular analysis of gene expression using single cell RT-PCR, immunocytochemistry, and slice culture. Results of recent experiments are summarized below.

We found that receptors for the principal excitatory and inhibitory amino acids in adult brain, GABA and glutamate, are present and functional on cortical neuroepithelial cells. To answer the question of what these receptors may be doing, we developed an in vitro assay of DNA synthesis. We discovered that receptor activation with either GABA or glutamate led to significant inhibition of DNA synthesis and that receptor blockade accelerated the rate of DNA synthesis. There may thus be transmitter-mediated feedback regulation from cortical neurons on the production of new neurons in the VZ.

We also discovered that neuronal precursor cells in the embryonic ventricular zone (VZ) are coupled together by gap junction channels into discrete radial columns throughout the period of neurogenesis. More recently we observed spontaneous increases in [Ca2+]_I restricted to clustered precursor cells, confirming that these clusters are functional compartments during early cortical development. We found that cell clusters are dynamic, with cells uncoupling during M phase and re-coupling at G1 or S phase, and demonstrated that coupling was necessary for VZ cells to progress through the cell cycle. We also discovered that most cell clusters include one radial glial cell. Coupling of VZ cell clusters to radial glial cells suggests the possibility that cells maintain an association with specific radial glia during migration and that descendents of cells coupled together in the VZ may ultimately form individual cortical columns.

We found that glycine receptors are functionally expressed by migrating and differentiating cortical neurons. Dose-response data show that cortical glycine receptors have a low affinity for agonist, suggesting that taurine, which is present in very high concentrations in developing neocortex, is the more likely endogenous ligand than glycine, which is present in very low concentrations. Consistent with this hypothesis, we found that glycine receptors are activated by release of endogenous taurine. These data demonstrate the existence of a previously unknown amino acid transmitter signaling system in the developing mammalian neocortex and provide an explanation for the cortical migration defects observed in taurine-deprived newborn kittens.

N-methyl-D-aspartate (NMDA) receptors play important roles in learning and memory and in sculpting neural connections during development. Following the period of peak cortical plasticity, NMDA receptor-mediated excitatory postsynaptic currents (NMDAR-EPSCs) decrease in duration. Using single-cell PCR methods we found that the developmental decrease in NMDAR-EPSC duration is due to a switch in receptor subunit expression, thus providing a molecular basis for the developmental changes in excitatory postsynaptic currents.

Selected Publications:

• Lo Turco, J.J. and Kriegstein, A.R. Clusters of coupled neuroblasts in embryonic neocortex. Science. 252: 563-566 (1991).

• LoTurco, J.J., Owens, D.F., Heath, M. J. S., Davis, M. B. E., and Kriegstein, A.R. GABA and glutamate depolarize cortical progenitor cells and inhibit DNA synthesis. Neuron 15: 1287-1298 (1995).

• Owens, D.F., Boyce, L.H., Davis, M.B.E., and Kriegstein, A.R. Excitatory GABA responses in embryonic and neonatal cortical slices demonstrated by gramicidin perforated-patch recordings and calcium imaging. Journal of Neuroscience. 16: 6414-6423 (1996).

• Flint, A.C., Maisch, U.S., Weishaupt, J., Monyer, H., and Kriegstein, A.R. NR2A subunit expression shortens NMDA receptor synaptic currents in developing neocortex. Journal of Neuroscience 17(7): 2469-2476 (1997).

• Bittman, K., Owens, D.F., Kriegstein, A.R., and LoTurco, J.J.: Cell coupling and uncoupling in the ventricular zone of developing neocortex. Journal of Neuroscience 17(18): 7037-44 (1997).

• Flint, A.C., Liu, X., and Kriegstein, A.R. Nonsynaptic activation of glycine receptors by taurine during neocortical development. Neuron. 20: 43-53 (1998).

• Owens, D.F., and Kriegstein, A.R. Patterns of intracellular calcium fluctuation in precursor cells of the neocortical ventricular zone. Journal of Neuroscience 18(14): 5374-88 (1998).