Biomaterial Database

Quantal analysis of transmitter release at an inhibitory synapse in the central nervous system of the leech. 1978

J Nicholls, and B G Wallace

The quantal nature of transmitter release has been analysed at central inhibitory synapses in the leech nervous system between an interneurone (HN) and a motoneurone (HE) that regulate the heartbeat. 1. Ganglia were bathed in leech Ringer fluid containing 20 mM-Mg and 1.8 mM-Ca and the membrane of the presynaptic HN interneurone was hyperpolarized by current injection. Under these conditions successive inhibitory potentials in the HE motoneurone, evoked by impulses in the HN interneurone, showed striking fluctuations in amplitude. 2. Assuming a Poisson distribution of the i.p.s.p.s and estimating the number of failures from the amplitude histograms of the observed responses, the mean size of the quantal unit was estimated as 0.25 +/- 0.015 mV (S.E. of mean, n = 26). When m, the mean number of quanta released per trial, was varied by changing the membrane potential of the presynaptic HN cell (Nicholls & Wallace, 1978), the experimentally observed amplitude distributions could be predicted by the Poisson theory. 3. An independent estimate of the unit size was obtained by noise analysis. A long subthreshold depolarizing pulse applied to the presynaptic HN interneurone evoked a sustained hyperpolarization of the HE motoneurone, apparently caused by an increase in the rate of on-going release of quanta by the HN cell terminals. From the mean change in membrane potential and the increase in variance, the size of the unit was calculated as 0.21 +/- 0.039 mV (S.E. of mean, n = 11). For ten pairs of cells an estimate of unit amplitude was made both from the Poisson analysis and the analysis of variance, again with good agreement. For these cells the estimated unit sizes were 0.24 +/- 0.023 mV (S.E. of mean, n = 10) from the failures and 0.21 +/- 0.043 m V (S.E. of mean, n = 10) from the noise. 4. A similar analysis was made of the inhibitory synaptic potentials evoked in one HN interneurone by stimulation of its contralateral homologue. Transmission again appeared to be qualtal; the mean unit amplitude from Poisson analysis was 0.31 +/- 0.022 mV (S.E. of mean, n = 19) and from the noise 0.29 +/- 0.027 mV (S.E. of mean, n = 3). 5. We conclude that transmitter is released from the terminals of the HN interneurone in quantal units that evoke miniature i.p.s.p.s of about 0.25 mV in the post-synaptic cells. Furthermore, modulation of transmission proudced by variation in the presynaptic resting potential and during presynaptic inhibition results from changes in the mean number of quanta released by each impulse.

UI	MeSH Term	Description	Entries
D007395	Interneurons	Most generally any NEURONS which are not motor or sensory. Interneurons may also refer to neurons whose AXONS remain within a particular brain region in contrast to projection neurons, which have axons projecting to other brain regions.	Intercalated Neurons,Intercalated Neuron,Interneuron,Neuron, Intercalated,Neurons, Intercalated
D007865	Leeches	Annelids of the class Hirudinea. Some species, the bloodsuckers, may become temporarily parasitic upon animals, including man. Medicinal leeches (HIRUDO MEDICINALIS) have been used therapeutically for drawing blood since ancient times.	Hirudinea,Hirudineas,Leeche
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
D009433	Neural Inhibition	The function of opposing or restraining the excitation of neurons or their target excitable cells.	Inhibition, Neural
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
D006321	Heart	The hollow, muscular organ that maintains the circulation of the blood.	Hearts
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