Postsynaptic potential

An inhibitory postsynaptic potential is a local hypetpo-larizing potential at a postsynaptic membrane, which is elicited by the release of an inhibitory neurotransmitter via an inhibitory postsynaptic current. 

The AMPA receptors for glutamate, the nicotinic acetylcholine receptor and the 5-HT3-receptor for serotonin are cation channels (Table 1). When they open, the major consequence is a sudden entry of Na+, depolarization and an excitatory postsynaptic potential (EPSP Fig. 1). 

The GABAA-receptor and the glycine receptor are Cl-channels (Table 1). When they open at a resting membrane potential of about -60 mV, the consequence is an entry of Cl-, hyperpolarization and an inhibitory postsynaptic potential (DPSP Fig. 1). 

An inhibitory input increases the influx of Cl to make the inside of the neuron more negative. This hyperpolarisation, the inhibitory postsynaptic potential (IPSP), takes the membrane potential further away from threshold and firing. It is the mirror-image of the EPSP and will reduce the chance of an EPSP reaching threshold voltage. 

Such clear postsynaptic potentials can be recorded intracellularly with microelectrodes in large quiescent neurons after appropriate activation but may be somewhat artificial. In practice a neuron receives a large number of excitatory and inhibitory inputs and its bombardment by mixed inputs means that its potential is continuously changing and may only move towards the threshold for depolarisation if inhibition fails or is overcome by a sudden increase in excitatory input. 

Figure 1.4 Ionic basis for excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). Resting membrane potential ( — 70 mV) is maintained by Na+ influx and K+ efflux. Varying degrees of depolarisation, shown by different sized EPSPs (a and b), are caused by increasing influx of Na. When the membrane potential moves towards threshold potential (60-65 mV) an action potential is initiated (c). The IPSPs (a b ) are produced by an influx of Cl. Coincidence of an EPSP (b) and IPSP (a ) reduces the size of the EPSP (d)...

Figure 11.5 Chloride distribution and the GABAa response. The change in membrane voltage (Fm) that results from an increase in chloride conductance following activation of GABAa receptors is determined by the resting membrane potential and the chloride equilibrium potential (Fci)- (a) Immature neurons accumulate CF via NKCC, while mature neurons possess a Cl -extruding transporter (KCC2). (b) In immature neurons GABAa receptor activation leads to CF exit and membrane depolarisation while in mature neurons the principal response is CF entry and h5q)erpolarisation. This is the classic inhibitory postsynaptic potential (IPSP)...

Figure 5.2 Temporal summation. Multiple excitatory postsynaptic potentials (EPSPs) produced by a single presynaptic neuron in close sequence may add together to depolarize the postsynaptic neuron to threshold and generate an action potential.

Figure 5.3 Spatial summation. Multiple excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs) produced by many presynaptic neurons simultaneously may add together to alter the membrane potential of the postsynaptic neuron. Sufficient excitatory input (A and B) will depolarize the membrane to threshold and generate an action potential. The simultaneous arrival of excitatory and inhibitory inputs (A and C) may cancel each other out so that the membrane potential does not change.

Imon, H., Ito, K., Dauphin, L. McCarley, R. W. (1996). Electrical stimulation of the cholinergic laterodorsal tegmental nucleus elicits scopolamine-sensitive excitatory postsynaptic potentials in medial pontine reticular formation neurons. Neuroscience 74, 393-401. 

Chase, M. H., Soja, P. J. Morales, F. R. (1989). Evidence that glycine mediates the postsynaptic potentials that inhibit lumbar motoneurons during the atonia of... 

FIGURE 6-1 Path of excitation in a simplified spinal reflex that mediates withdrawal of the leg from a painful stimulus. In each of the three neurons and in the muscle cell, excitation starts with a localized slow potential and is propagated via an action potential (a.p.). Slow potentials are generator potential (g.p.) at the skin receptor the excitatory postsynaptic potentials (e.p.s.p.) in the interneuron and the motoneuron and end-plate potential (e.p.p.) at the neuromuscular junction. Each neuron makes additional connections to other pathways that are not shown. 

Both NMDA and AMPA receptor components of excitatory postsynaptic potentials (EPSPs) are produced by the brief (1 ms) appearance of free transmitter in the synaptic cleft (Fig 15-10A). Synaptically released glutamate thus... 

EPSP excitatory postsynaptic potential HIF hypoxia-inducible factor... 

Excitatory postsynaptic potentials (EPSPs), spikes from, 172... 

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