Biomaterial Database

An in vivo pharmacological study of single group Ia fibre contacts with motoneurones in the cat spinal cord. 1994

B Walmsley, and P S Bolton

Neuroscience Group, University of Newcastle, Callaghan, NSW, Australia.

1. Direct experimental evidence was obtained on the spatial distribution of active synaptic contacts from single Ia muscle afferents on the dendrites of lumbosacral motoneurones in anaesthetized cats. 2. An extracellular micropipette was used to pressure eject the AMPA/kainate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline (NBQX) in close proximity to the intracellular recording site, in order to create an extracellular concentration gradient of the antagonist. The effect of antagonist ejection on the time course and amplitude of excitatory postsynaptic potentials (EPSPs) evoked in motoneurones by impulses in single group Ia fibres was examined. 3. Pressure ejection of NBQX resulted in a complete block of the monosynaptic group Ia EPSP in two cells, and a significant reduction to 23-57% of control EPSP peak amplitudes in a further six cells (mean, 27%; n = 8). These effects were not associated with changes in membrane potential or membrane time constant. 4. The reduction in amplitude of these single group Ia fibre EPSPs following ejection of NBQX was usually accompanied by a pronounced slowing in the time course of the EPSPs. On average, the EPSP rise times and half-widths were increased by 269 and 37%, respectively. This is most probably due to a considerable spatial spread of the synaptic contacts along the dendrites of motoneurones, with the most proximal synaptic contacts (producing the briefest synaptic potentials) subjected to a greater reduction in amplitude due to a higher local antagonist concentration. 5. An equivalent dendritic cable model of the motoneurone was used to interpret the observed changes in the time course of single fibre EPSPs. The time course of control single fibre EPSPs examined in the present study could be well matched using the cable model and assuming a single location for synaptic input. The observation of a slowed EPSP time course following antagonist ejection indicated that this assumption was not correct and that there was in fact considerable spatial spread in the synaptic contacts arising from these single afferent fibres. These results provide direct evidence that spatial spread of synaptic input may not be detected using the time course of a synaptic potential in conjunction with a neuronal cable model of the postsynaptic cell.

UI	MeSH Term	Description	Entries
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
D009434	Neural Pathways	Neural tracts connecting one part of the nervous system with another.	Neural Interconnections,Interconnection, Neural,Interconnections, Neural,Neural Interconnection,Neural Pathway,Pathway, Neural,Pathways, Neural
D011810	Quinoxalines		Quinoxaline
D002415	Cats	The domestic cat, Felis catus, of the carnivore family FELIDAE, comprising over 30 different breeds. The domestic cat is descended primarily from the wild cat of Africa and extreme southwestern Asia. Though probably present in towns in Palestine as long ago as 7000 years, actual domestication occurred in Egypt about 4000 years ago. (From Walker's Mammals of the World, 6th ed, p801)	Felis catus,Felis domesticus,Domestic Cats,Felis domestica,Felis sylvestris catus,Cat,Cat, Domestic,Cats, Domestic,Domestic Cat
D003712	Dendrites	Extensions of the nerve cell body. They are short and branched and receive stimuli from other NEURONS.	Dendrite
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
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
D013997	Time Factors	Elements of limited time intervals, contributing to particular results or situations.	Time Series,Factor, Time,Time Factor