Biomaterial Database

Posttetanic potentiation of group Ia EPSPs: possible mechanisms for differential distribution among medial gastrocnemius motoneurons. 1983

A Lev-Tov, and M J Pinter, and R E Burke

We have reinvestigated the phenomenon of posttetanic potentiation (PTP) of group Ia monosynaptic excitatory postsynaptic potentials (EPSPs) in medial gastrocnemius (MG) alpha-motoneurons of pentobarbital-anesthetized cats. The results generally confirm earlier reports by Lüscher and colleagues (43, 44) of a negative correlation between the maximum percentage potentiation of Ia EPSP amplitude (Pmax) and 1) the mean amplitude of the pretetanic control EPSP in the same cell and 2) the input resistance of the postsynaptic motoneuron. These negative correlations, which we will refer to as "differential distribution of PTP" within the MG motor pool, were less strong in the present work than reported by Lüscher et al. (43, 44). We also found a relatively strong negative correlation between posttetanic EPSP depression, assessed by the amplitude of the first posttetanic EPSP, and the level of Pmax subsequently attained. We found no evidence that posttetanic depression is caused by failure of presynaptic action potentials. We investigated a second type of depression, referred to as "specific" synaptic depression, in which the second EPSP of paired responses (interval 250 ms) is, on average, smaller in peak amplitude than the first EPSP. This phenomenon appears to reflect decreases in the probability of transmitter release from previously activated synapses. Specific synaptic depression was consistently increased when paired responses were conditioned by a high-frequency tetanus. This is most easily explained by postulating that PTP results, at least in part, from an increase in the statistical probability of transmitter liberation from group Ia synapses that are activated (i.e., presumably invaded by action potentials) both before and after afferent tetanization. On the basis of the present results and other available evidence, we conclude that the differential distribution of PTP can be explained by two main factors: 1) the nonlinear relation between conductance and voltage changes inherent in all chemical synapses and 2) systematic variations in the properties of group Ia synapses that innervated different motoneurons, which remain to be clarified.

UI	MeSH Term	Description	Entries
D008564	Membrane Potentials	The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization).	Resting Potentials,Transmembrane Potentials,Delta Psi,Resting Membrane Potential,Transmembrane Electrical Potential Difference,Transmembrane Potential Difference,Difference, Transmembrane Potential,Differences, Transmembrane Potential,Membrane Potential,Membrane Potential, Resting,Membrane Potentials, Resting,Potential Difference, Transmembrane,Potential Differences, Transmembrane,Potential, Membrane,Potential, Resting,Potential, Transmembrane,Potentials, Membrane,Potentials, Resting,Potentials, Transmembrane,Resting Membrane Potentials,Resting Potential,Transmembrane Potential,Transmembrane Potential Differences
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
D009435	Synaptic Transmission	The communication from a NEURON to a target (neuron, muscle, or secretory cell) across a SYNAPSE. In chemical synaptic transmission, the presynaptic neuron releases a NEUROTRANSMITTER that diffuses across the synaptic cleft and binds to specific synaptic receptors, activating them. The activated receptors modulate specific ion channels and/or second-messenger systems in the postsynaptic cell. In electrical synaptic transmission, electrical signals are communicated as an ionic current flow across ELECTRICAL SYNAPSES.	Neural Transmission,Neurotransmission,Transmission, Neural,Transmission, Synaptic
D009475	Neurons, Afferent	Neurons which conduct NERVE IMPULSES to the CENTRAL NERVOUS SYSTEM.	Afferent Neurons,Afferent Neuron,Neuron, Afferent
D011930	Reaction Time	The time from the onset of a stimulus until a response is observed.	Response Latency,Response Speed,Response Time,Latency, Response,Reaction Times,Response Latencies,Response Times,Speed, Response,Speeds, Response
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
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