Biomaterial Database

Spontaneous action potential activity and synaptic currents in the embryonic turtle cerebral cortex. 1991

M G Blanton, and A R Kriegstein

Department of Neurology and Neurological Sciences, Stanford University School of Medicine, California 94305.

We used loose-patch and whole-cell recording techniques to study the development of spontaneous action potential activity and spontaneous excitatory and inhibitory synaptic currents in embryonic neurons in the cerebral hemispheres of turtles. Sporadic action potential activity appeared early in development at stage 17, soon after morphologically identifiable pyramidal and nonpyramidal neurons were first observed in the cortex. As the cortical plate matured in midembryonic stages, action potential activity became more regular and fell into one of two distinct patterns, tonic and intermittent high-frequency firing. Spontaneous excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) appeared at developmental stages 18 and 20, respectively, after action potential activity was established. EPSCs and IPSCs exhibited characteristic ionic dependence and pharmacology throughout development. EPSCs reversed in direction at the equilibrium potential for cations and were sensitive to 6-cyano-7-nitroquinoxaline-2,3-dione, an antagonist of the non-NMDA type of glutamate receptor. IPSCs reversed at the equilibrium potential for chloride and were sensitive to bicuculline methiodide, a GABAA receptor antagonist. Spontaneous synaptic currents differed in their time course of development and in waveform parameters. Spontaneous synaptic currents differed in their time course of development and in waveform parameters. Spontaneous EPSCs appeared at stage 18 and increased progressively in frequency, from 0.2 +/- 0.1 Hz at stage 20 to 3.2 +/- 2.0 Hz at stage 26 (hatching), while spontaneous IPSCs appeared at stage 20 and surpassed EPSCs in frequency, increasing to 7.1 +/- 1.6 Hz at stage 26. EPSCs exhibited stable amplitudes during development, with a mean conductance of 126 +/- 20 pS at stage 26, while IPSCs increased in mean amplitude, from 180 +/- 12 pS at stage 18 to 260 +/- 44 pS at stage 26. The rise time to peak conductance of both types of synaptic currents increased with developmental time, for EPSCs increasing from 1.5 +/- 0.5 msec at stage 20 to 2.7 +/- 0.6 msec at stage 26 and for IPSCs increasing from 2.9 +/- 0.2 msec at stage 18 to 6.2 +/- 0.8 msec at stage 26. While the decay time constants increased for EPSCs, from 3.9 +/- 1.2 msec at stage 20 to 8.7 +/- 2.3 msec at stage 26, decay time constants for IPSCs showed a decreasing trend from 24.0 +/- 5.2 msec at stage 18 to 18.4 +/- 5.3 msec at stage 26. The excitatory and inhibitory synaptic currents were sensitive to the sodium channel blocker TTX and were thus dependent, in part, on spontaneous action potential activity.(ABSTRACT TRUNCATED AT 400 WORDS)

UI	MeSH Term	Description	Entries
D009433	Neural Inhibition	The function of opposing or restraining the excitation of neurons or their target excitable cells.	Inhibition, Neural
D002540	Cerebral Cortex	The thin layer of GRAY MATTER on the surface of the CEREBRAL HEMISPHERES that develops from the TELENCEPHALON and folds into gyri and sulci. It reaches its highest development in humans and is responsible for intellectual faculties and higher mental functions.	Allocortex,Archipallium,Cortex Cerebri,Cortical Plate,Paleocortex,Periallocortex,Allocortices,Archipalliums,Cerebral Cortices,Cortex Cerebrus,Cortex, Cerebral,Cortical Plates,Paleocortices,Periallocortices,Plate, Cortical
D004553	Electric Conductivity	The ability of a substrate to allow the passage of ELECTRONS.	Electrical Conductivity,Conductivity, Electric,Conductivity, Electrical
D005314	Embryonic and Fetal Development	Morphological and physiological development of EMBRYOS or FETUSES.	Embryo and Fetal Development,Prenatal Programming,Programming, Prenatal
D000200	Action Potentials	Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli.	Spike Potentials,Nerve Impulses,Action Potential,Impulse, Nerve,Impulses, Nerve,Nerve Impulse,Potential, Action,Potential, Spike,Potentials, Action,Potentials, Spike,Spike Potential
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D013569	Synapses	Specialized junctions at which a neuron communicates with a target cell. At classical synapses, a neuron's presynaptic terminal releases a chemical transmitter stored in synaptic vesicles which diffuses across a narrow synaptic cleft and activates receptors on the postsynaptic membrane of the target cell. The target may be a dendrite, cell body, or axon of another neuron, or a specialized region of a muscle or secretory cell. Neurons may also communicate via direct electrical coupling with ELECTRICAL SYNAPSES. Several other non-synaptic chemical or electric signal transmitting processes occur via extracellular mediated interactions.	Synapse
D014426	Turtles	Any reptile including tortoises, fresh water, and marine species of the order Testudines with a body encased in a bony or cartilaginous shell consisting of a top (carapace) and a bottom (plastron) derived from the ribs.	Sea Turtles,Terrapins,Tortoises,Sea Turtle,Terrapin,Tortoise,Turtle,Turtle, Sea,Turtles, Sea