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M Margulis

Publications and source records attributed to M Margulis.

7 recordsLinked to original sources
PubMed1999

Functional synapses are formed between human NTera2 (NT2N, hNT) neurons grown on astrocytes.

The formation of functional synapses is a late milestone of neuronal differentiation. The establishment of functional synapses can be used to assess neuronal characteristics of different cell lines. In the present study, we examined the in vitro conditions that influence the ability of human neurons derived from the NT2 cell line (NT2N neurons) to establish synapses. The morphologic, immunologic, and electrophysiologic characteristics of these synapses was examined. In the absence of astrocytes, NT2N neurons rarely formed synapses and their action potentials were weak and uncommon. In contrast, when plated on primary astrocytes, NT2N neurons were able to form both glutamatergic excitatory (71%) and GABAergic inhibitory (29%) functional synapses whose properties (kinetics, ion selectivity, pharmacology, and ultrastructure) were similar to those of synapses of neurons in primary cultures. In addition, coculture of NT2N neurons with astrocytes modified the morphology of the neurons and extended their in vitro viability to more than 1 year. Because astrocyte-conditioned medium did not produce these effects, we infer that direct contact between NT2N neurons and astrocytes is required. These results suggest that NT2N neurons are similar to primary neurons in their synaptogenesis and their requirement for glial support for optimal survival and maturation. This system provides a model for further investigations into the neurobiology of synapses formed by human neurons.

2-Amino-5-phosphonovalerate↗
PubMed1998

Temporal integration can readily switch between sublinear and supralinear summation.

Temporal summation at dendrites of cultured rat hippocampal neurons was examined as a function of the interval separating two dendritic inputs. A novel method that relies on single-mode optical fibers to achieve rapid photorelease of glutamate was developed. Dendritic excitation achieved with this approach resembles that associated with miniature excitatory postsynaptic currents (mEPSCs), but the strengths, sites, and timing of the inputs can be precisely controlled. Dendritic summation deviated markedly from behavior predicted by passive cable theory. Subthreshold temporal summation varied as a triphasic function of the interpulse interval. As the interpulse interval decreased, local dendritic Na+ conductances were recruited to generate a marked transition from sublinear to supralinear summation. These results suggest that active dendritic conductances acting in concert with passive cable properties may serve to boost coincident synaptic inputs and attenuate noncoincident inputs.

Animals↗
PubMed1997

N-Nmoc-L-glutamate, a new caged glutamate with high chemical stability and low pre-photolysis activity.

We report the synthesis, the physicochemical characterization, and biological evaluation of a new caged glutamate, N-(o-nitromandelyl)oxycarbonyl-L-glutamic acid (Nmoc-Glu), that liberates free glutamate on photolysis. The low affinity of certain glutamate receptors and their rapid entry into desensitization have effectively prevented the creation of an ideal caged glutamate. In the absence of an ideal compound, Nmoc-Glu was designed to resist spontaneous hydrolysis while maintaining reasonable photorelease yield and kinetics. Chemical and physiological analyses reveal that Nmoc-Glu, indeed, has exceptionally low residual activity and high chemical stability. The quantum yield of Nmoc-Glu is 0.11. Photolytic uncaging and release of free glutamate occur in two steps, consisting of an initial light-induced cleavage that proceeds on the sub-millisecond time scale, and a subsequent light-independent, pH-dependent decarboxylation step that proceeds on the millisecond time scale. The low residual activity and high chemical stability of Nmoc-Glu are important advantages in applications where pre-photolysis Glu receptor activation and desensitization must be minimized.

Animals↗
PubMed1994

Saturation of postsynaptic glutamate receptors after quantal release of transmitter.

Miniature excitatory postsynaptic currents (mEPSCs) were elicited from small numbers of release sites after brief microperfusion of Ba2+ and K+ onto proximal dendritic processes of hippocampal neurons in culture. Temporal summation of closely timed mEPSCs deviated significantly from linearity. The number of instances of closely timed mEPSCs that were also closely matched in terms of peak amplitudes was significantly greater than that expected by chance. Amplitude pairing became statistically more significant after prolongation of mEPSC duration and inhibition of glutamate receptor desensitization with cyclothiazide. These results are best explained by postsynaptic receptors that approach saturation after quantal release of transmitter.

Animals↗