Synaptic potential

They act as analgesics by inhibiting release of nociceptive neurotransmitters from primary afferent terminals as well as by depressing post-synaptic potentials on second order neurons. Opioid receptors are also present on some nociceptors and their expression and peripheral transport is increased upon peripheral inflammation. Peripheral opioid analgesia has been established in animal models. Although clinical studies have yielded mixed results so far, this field holds great promise. Despite side effects, such as euphoria, dysphoria, sedation, respiratory depression and obstipation and tolerance and dependence phenomena which arise upon... 

The spontaneous electrical activity of the brain can be measured by electroencephalography (EEG), a technique that has been widely employed to study neurotoxic effects of chemicals both in humans and in experimental animals. EEG waves represent summated synaptic potentials generated by the pyramidal cells of the cerebral cortex (Misra 1992). These potentials are the responses of cortical cells to rhythmical changes arising from thalamic nuclei. The signals recorded can be separated into frequency bands—faster waves exceeding 13 Hz, and slower ones below 4 Hz. 

Figure 2.12 From voltage-clamp to current-clamp micro-electrode recordings of synaptic current (/, lower trace) and synaptic potential with superimposed action potential (V, upper trace) from a neuron in an isolated rat superior cervical sympathetic ganglion following a single stimulus (S) applied to the preganglionic nerve trunk. The interval between the stimulus and the postsynaptic response includes the conduction time along the unmyelinated axons of the preganglionic nerve trunk. (SJ Marsh and DA Brown, unpublished)...

Cole, AE and Nicoll, RA (1984) Characterization of a slow cholinergic post synaptic potential recorded in vitro from rat hippocampal pyramidal cells. J. Physiol. 352 173-188. 

Thompson, SM and Gahwiler, BH (1992) Effects of the GABA uptake inhibitor tiagabine on inhibitory synaptic potentials in rat hippocampal slice cultures. J. Neurophysiol. 67 1698-1701. 

It appears that the voltage waves recorded in the EEG represent the summation of synaptic potentials in the apical dendrites of pyramidal cells in the cortex. These cells generate sufficient extracellular current for it to reach, and be recorded from, the cranium and scalp. Although these waves originate from the cortex rather than the SCN, the distinctive REM and non-REM phases of sleep still remain after destruction of the SCN but they then occur randomly over the 24-h cycle. This is a further indication that the SCN is at least partly responsible for setting the overall circadian rhythm of the sleep cycle. 

The ion-channel blocking mechanism has been widely tested and found to be important in both pharmacology and physiology. Examples are the block of nerve and cardiac sodium channels by local anesthetics, or block of NMDA receptor channels by Mg2+ and the anesthetic ketamine. The channel-block mechanism was first used quantitatively to describe block of the squid axon K+ current by tetraethylammonium (TEA) ions. The effects of channel blockers on synaptic potentials and synaptic currents were investigated, particularly at the neuromuscular junction, and the development of the single-channel recording technique allowed channel blockages to be observed directly for the first time. 

Skrede, K. K. and Malthe-Sorenssen, D. Increased resting and evoked release of transmitter following repetitive electrical tetanization in hippocampus a biochemical correlate to long-lasting synaptic potentiation. Brain Res. 208 436—441,1981. 

Hirst You can easily see spontaneous synaptic potentials if you make long recordings from a non-pressurized arteriole. The clamps are big enough to see this property in situ. I have never seen a STOC in an arteriole or a piece of longitudinal muscle of the intestine unless I have applied a non-physiological stimulant. 

In electrophysiological studies aimed at elucidating the mechanism of action of kappa agonists, U-50488 has been shown to depress excitatory post-synaptic potentials in a rat locus coeruleus preparation, which indicates that it acts presynaptically to inhibit transmitter release [38]. Also, in spinal cord slice preparations from the 9-16-day-old rat, U-69593 (9) produced a naloxone-reversible depression of spontaneous and electrically evoked activity in dorsal horn neurones [39],... 

Frazier CJ, Buhler AV, Weiner JL, Dunwiddie TV (1998) Synaptic potentials mediated by a-bungarotoxin-sensitive nicotinic receptors in rat hippocampal interneurons. J Neurosci 18 8228-8235... 

Brown T, Chapman PF, Kairiss EW, Keenan CL (1988) Long-term synaptic potentiation. Science 242 724-728... 

Campeau S, Miserendino MJD, Davis M (1992) Intra-amygdala infusion of the N-methyl-D-asparate receptor antagonist AP5 blocks acquisition but not expression of fear-potentiated startle to an auditory conditioned stimulus. Behav Neurosci 106 569-574 Caton P, Tousman SA, Quock RM (1994) Involvement of nitric oxide in nitrous oxide anxiolysis in the elevated plus-maze. Pharmacol Biochem Behav 48 689-692 Chapman P, Kairiss EW, Keenan CL, Brown TH (1990) Long-term synaptic potentiation in the amygdala. Synapse 6 271-278... 

Read HL, Kiraly M, Dun NJ Serotonin differentially affects synaptic potentials evoked in the rat cerebral cortical slice. EurJ Pharmacol 183 1383P, 1990 Reading PJ Frontal lobe dysfunction in schizophrenia and Parkinson s disease—a meeting point for neurology, psychology and psychiatry discussion paper. J R Soc Med 84 349-353, 1991... 

The first systematic analysis of synaptic potentials in the CNS was in the early 1950s by Eccles and associates, who recorded intracellularly from spinal motor neurons. When a microelectrode enters a cell, there is a sudden change in the potential recorded by the electrode, which is typically about -70 mV (Figure 21-3). This is the resting membrane potential of the neuron. Two types of pathways—excitatory and inhibitory—impinge on the motor neuron. 

Effects of ethanol and crocin on non-NMDA receptor-mediated synaptic potentials in hippocampal slices... 

The synapic potential mediated by non-NMDA receptors was recorded in normal ACSF. When ethanol (10-50 mM) was added to the perfusing medium, no significant change in non-NMDA receptor-mediated synaptic potential was observed. However, the addition of ethanol at a higher concentration (100 mM) induced a small reduction in non-NMDA receptor-mediated synaptic potential (Fig.(5)A). The reduction in non-NMDA response rapidly occurred after the addition of 100 mM ethanol and reached a steady state within 10 min. After washing out the ethanol, the response gradually returned to the normal level. When 10 pM crocin was added 10 min prior to the ethanol, the non-NMDA response was similarly reduced in the presence of 100 mM ethanol (Fig.(5)B). Crocin (10 pM) did not significantly affect the inhibitory effect of 100 mM ethanol on non-NMDA response (Fig.(5)C) [22],... 

NMDA receptor-mediated synaptic potential evoked in normal ACSF in rat hippocampal slices. 

An alternative to the idea that synaptic potentiation and depression provide the chemical basis for learning is molecular coding. Thus, it was reported... 

Jacobson KA, Hoffmann C, Cattabeni F, Abbracchio MP (1999) Adenosine-induced cell death evidence for receptor-mediated signalling. Apoptosis 4(3) 197—211 Kafka SH, Corbett R (1996) Selective adenosine A2A receptor/dopamine D2 receptor interactions in animal models of schizophrenia. Eur J Pharmacol 295(2-3) 147-154 Latini S, Bordoni F, Corradetti R, Pepeu G, Pedata F (1998) Temporal correlation between adenosine outflow and synaptic potential inhibition in rat hippocampal slices during ischemia-like conditions. Brain Res., 794, (2) 325-328. 

Excitatory synaptic potentials and spike generation. The figure shows a resting membrane potential of-70 mV in a postsynaptic cell. Stimulation of an excitatory pathway (E) generates transient depolarization. Increasing the stimulus strength (second E) increases the size of the depolarization, so that the threshold for spike generation is reached. 

Kammermeier PJ, Ikeda SR (1999) Expression of RGS2 alters the coupling of metabotropic glutamate receptor la to M-type K+ and N-type Ca2+ channels. Neuron 22 819-29 Kaneko M, Takahashi T (2004) Presynaptic mechanism underlying cAMP-dependent synaptic potentiation. J Neurosci 24 5202-8... 

Bobker DH, Williams JT (1989) Serotonin agonists inhibit synaptic potentials in the rat locus ceruleus in vitro via 5-hydroxytryptamineiA and 5-hydroxytryptamineiB receptors. J Pharmacol Exp Ther 250 37-43... 

Endocannabinoids have also been suggested to participate in long-term synaptic potentiation (LTP), a widely recognized model of synaptic changes underlying learning and memory (Malenka and Bear 2004). Prior to discovery of the CB1 receptor, one study indicated that A9-THC alters hippocampal LTP (Nowicky et al. 1987). Activation of CB1 receptors by 2-AG was shown to prevent LTP induction at Schaffer collateral-CAl pyramidal cell synapses in hippocampus (Stella et al. 

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