Biomaterial Database

Non-linear summation of excitatory synaptic inputs to small neurones: a case study in spinal motoneurones of the young Xenopus tadpole. 1998

E Wolf, and F Y Zhao, and A Roberts

School of Biological Sciences, University of Bristol, Bristol BS8 1UG, UK.

1. We examined the steady-state summation of postsynaptic potentials (PSPs) in small, electrotonically compact neurones with short dendrites, using a one-compartment electrical equivalent model of the passive membrane with conductances to represent chemical synapses and electrotonic junctional connections to neighbouring neurones. 2. Our model shows that PSP summation is non-linear and for small depolarizations is mainly determined by the increase in total neurone conductance due to the opening of synaptic channels. At bigger depolarizations the change in synaptic driving force becomes an equally important cause of non-linearity. 3. Non-linear summation of AMPA-mediated PSPs was measured experimentally when two monosynaptic pathways to motoneurones were stimulated. The conductances underlying these PSPs were calculated relative to the resting neurone conductance using our model. These conductance ratios were hardly affected by the size of electrotonic coupling conductances. The non-linearity in PSP summation could be predicted by the model provided that the depolarizations remained negative to potentials at which voltage-dependent channels open. 4. The model was used to estimate the relative contributions of glutamatergic, cholinergic and electrotonic excitation to EPSPs measured in Xenopus tadpole spinal motoneurones during swimming. Estimates of synaptic conductances and electrotonic coupling to other motoneurones suggest that ligand-gated conductance mediated by glutamate may be twice that due to acetylcholine. 5. We conclude that in small electrotonically compact motoneurones of the Xenopus tadpole, our simple model can predict the non-linearity in PSP summation and may allow the conductances of different synaptic inputs to be compared. Furthermore, excitatory synaptic conductances can increase the resting neurone conductance significantly and limit depolarization. Our general model may also be applicable to other small neurones.

UI	MeSH Term	Description	Entries
D007814	Larva	Wormlike or grublike stage, following the egg in the life cycle of insects, worms, and other metamorphosing animals.	Maggots,Tadpoles,Larvae,Maggot,Tadpole
D008959	Models, Neurological	Theoretical representations that simulate the behavior or activity of the neurological system, processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment.	Neurologic Models,Model, Neurological,Neurologic Model,Neurological Model,Neurological Models,Model, Neurologic,Models, Neurologic
D009046	Motor Neurons	Neurons which activate MUSCLE CELLS.	Neurons, Motor,Alpha Motorneurons,Motoneurons,Motor Neurons, Alpha,Neurons, Alpha Motor,Alpha Motor Neuron,Alpha Motor Neurons,Alpha Motorneuron,Motoneuron,Motor Neuron,Motor Neuron, Alpha,Motorneuron, Alpha,Motorneurons, Alpha,Neuron, Alpha Motor,Neuron, Motor
D002451	Cell Compartmentation	A partitioning within cells due to the selectively permeable membranes which enclose each of the separate parts, e.g., mitochondria, lysosomes, etc.	Cell Compartmentations,Compartmentation, Cell,Compartmentations, Cell
D004553	Electric Conductivity	The ability of a substrate to allow the passage of ELECTRONS.	Electrical Conductivity,Conductivity, Electric,Conductivity, Electrical
D004594	Electrophysiology	The study of the generation and behavior of electrical charges in living organisms particularly the nervous system and the effects of electricity on living organisms.
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
D013116	Spinal Cord	A cylindrical column of tissue that lies within the vertebral canal. It is composed of WHITE MATTER and GRAY MATTER.	Coccygeal Cord,Conus Medullaris,Conus Terminalis,Lumbar Cord,Medulla Spinalis,Myelon,Sacral Cord,Thoracic Cord,Coccygeal Cords,Conus Medullari,Conus Terminali,Cord, Coccygeal,Cord, Lumbar,Cord, Sacral,Cord, Spinal,Cord, Thoracic,Cords, Coccygeal,Cords, Lumbar,Cords, Sacral,Cords, Spinal,Cords, Thoracic,Lumbar Cords,Medulla Spinali,Medullari, Conus,Medullaris, Conus,Myelons,Sacral Cords,Spinal Cords,Spinali, Medulla,Spinalis, Medulla,Terminali, Conus,Terminalis, Conus,Thoracic Cords
D013550	Swimming	An activity in which the body is propelled through water by specific movement of the arms and/or the legs. Swimming as propulsion through water by the movement of limbs, tail, or fins of animals is often studied as a form of PHYSICAL EXERTION or endurance.
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