Release from brain slices

In a more intact in vitro preparation, i.e. the hippocampal brain slice, there is a large body of data showing that the release of Asp upon membrane depolarization is Ca +-dependent (Nadler etal., 1976, 1990 Burke andNadler, 1988 Szerb, 1988 Martinet ah, 1991 Roisinetal., 1991 Fleck et ah, 1993 Zhou et al., 1995). In addition, there is evidence for a Ca +-dependent release of Asp in cerebellar slices (Flint et al., 1981 Toggenburger et al., 1983 Sekiguchi et ah, 1986 Vollenweider et al., 1990 Maura et al., 1991), striatal slices (Reubi et al., 1980 Umeda and Sumi, 1989 Kimura et al., 1995) and spinal cord slices (Kangrga and Randic, 1990). 

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Fig. 9. Norepinephrine and dopamine release from brain slices (slices of rat nucleus accumbens). (A) Dopamine standard (10 pmol injected onto column—volume 100 pi) (B) norepinephrine standard (10 pmol injected onto column—volume 100 pi) (C) supernatant obtained after incubation of one sliced nucleus accumbens in Krebs buffer containing pargyline (10 M) at 37°C for 10 min, followed by centrifugation (Bennett et ai, 1981fl). The supernatant is deproteinized by addition of 20 pi 0.1 M perchloric acid per 2 ml supernatant and then centrifuged, and 100 pi is injected onto the column. Note the small norepinephrine and large dopamine peaks (D) same as C, except the nucleus accumbens (the other accumbens from the same animal as in G) was incubated in the presence of d-amphetamine (10 M). Note the increased norepinephrine and dopamine peaks. Chromatographic conditions column, cation-exchange Nucleosil (10 p) 30 cm X 2.1 mm mobile phase, 0.05 M acetate/citrate, pH 4.8 flow rate, 1.2 ml/min electrode potential, +0.65 V sensitivity, 2 nA/V full scale deflection volume injected, 100 pi.

Traditional methods for measuring amine release from brain slices in vitro under either static or superfusion incubation conditions have relied on prelabeling the amine pool with tritiated amine. The sensitivity of LC-... 

Plotsky, P. M., Wightman, R. M., Chey, W., and Adams, R. N., 1977, Liquid chromatographic analysis of endogenous catecholamines released from brain slices. Science 197 904-906. 

Katz, R. 1., and Kopin, 1. J. (1969) Effect of D-LSD and related compounds on release of norepinephrine-3H and serotonin-3H evoked from brain slices by electrical stimulation. Pharmacol. Res. Commun., 1 54-62. 

Russell V, de Villiers A, Sagvolden T, et al Differences between electrically, Ritalin-, and D-amphetamine-stimulated release of pH]dopamine from brain slices suggest impaired vesicular storage of dopamine in an animal model of attention-deficit hyperactivity disorder. Behav Brain Res 94 163-171, 1998... 

Orrego F, Jankelevich ), Ceruti L, and Ferrara E. (1974) Differential effects of electrical stimulation on release of H-noradrenaline and " C-a-aminoisobutyrate from brain slices Nature (Lond ) 251, 55-57... 

By Imposing even less stringent demands on the physiological nature of the neuronally mediated release, both NE and 5-HT have been shown to be releasable from isolated spinal cords or from brain slices by electrical stimulation. Release has also been studied by indirect methods in vivo by analyzing amine levels and related substrates after more or less physiologic electrical stimulation of the cell body regions ... 

Because of their strategic localization, astrocytes play a crucial role in maintaining the extracellular ionic homeostasis, provide energetic metabolites to neurons and remove excess of neurotransmitter in schedule with synaptic activity. In addition, the strategic location of astrocytes allows them to carefully monitor and control the level of synaptic activity. Indeed, number of papers during the last 15 years have shown that cultured astrocytes can respond to a variety of neurotransmitters with a variety of different patterns of intracellular calcium increases (Verkhratsky et al. 1998). Later on, studies performed in intact tissue preparations (acute brain slices) further established that the plasma membrane receptors can sense external inputs (such as the spillover of neurotransmitters during intense synaptic activity) and transduce them as intracellular calcium elevations, mostly via release of calcium from internal stores (Dani et al. 1992 Murphy et al. 1993 Porter and McCarthy... 

There is also the interesting possibility that presynaptie inhibition of this form, with or without potential changes, need not be restricted to the effect of the NT on the terminal from which it is released. Numerous studies in which brain slices have been loaded with a labelled NT and its release evoked by high K+ or direct stimulation show... 

Figure 1.9 Comparison of the effects of an endogenously released and exogenously applied neurotransmitter on neuronal activity (identity of action). Recordings are made either of neuronal firing (extracellularly, A) or of membrane potential (intracellularly, B). The proposed transmitter is applied by iontophoresis, although in a brain slice preparation it can be added to the bathing medium. In this instance the applied neurotransmitter produces an inhibition, like that of nerve stimulation, as monitored by both recordings and both are affected similarly by the antagonist. The applied neurotransmitter thus behaves like and is probably identical to that released from the nerve...

Murugaiah, KD and O Donnell, JM (1995) Facilitation of noradrenaline release from rat brain slices by beta-adrenoceptors. Naunyn-Schmiedebergs Arch. Pharmacol. 351 483--490. 

ATP certainly fulfils the criteria for a NT. It is mostly synthesised by mitochondrial oxidative phosphorylation using glucose taken up by the nerve terminal. Much of that ATP is, of course, required to help maintain Na+/K+ ATPase activity and the resting membrane potential as well as a Ca +ATPase, protein kinases and the vesicular binding and release of various NTs. But that leaves some for release as a NT. This has been shown in many peripheral tissues and organs with sympathetic and parasympathetic innervation as well as in brain slices, synaptosomes and from in vivo studies with microdialysis and the cortical cup. There is also evidence that in sympathetically innervated tissue some extracellular ATP originates from the activated postsynaptic cell. While most of the released ATP comes from vesicles containing other NTs, some... 

Attention has been given to the possibility that some of the above motor effects may arise from a metabolite of levodopa. The prime suspect is OMD which has a half-life of some 20 hours and reaches plasma concentrations three- to fourfold those of dopa. Suggestions that it may compete with dopa for entry across the blood-brain barrier or act as a partial agonist (effective antagonist) have not been substantiated experimentally although it does reduce DA release from rat striatal slices. Also if free radical production through deamination of DA is neurotoxic (see below) then this would be increased by levodopa. 

Johnson, M.P. Hoffman, A.J. and Nichols, D.E. Effects of the enantiomers of MDA, MDMA and related analogs on [ H] serotonin and [ Hjdopamine release from superfused rat brain slices. Eur J Pharmacol 132 269-276, 1986. 

In addition to its relatively high affinity at postsynaptic 5-HT receptors, MDMA exhibited high affinity for 5-HT uptake sites and has been shown to increase the release of [ H]5-HT and block [ H]5-HT uptake in vitro. These data suggest that some of the actions of MDMA may be mediated at presynaptic binding sites. With respect to [ H]5-HT release, MDMA has been reported to increase the release of [ H]5-HT from brain synaptosomes (Nichols et al. 1982) and hippocampal slices (Johnson et al. 1986). With respect to uptake blockade, MDMA has been reported to competitively inhibit H-5-HT uptake in vitro (Shulgin 1986). Furthermore, the neurotoxic effects of in vivo administration of MDMA on serotonin terminals can be blocked by concomitant administration of the 5-HT uptake blocker citalo-pram (Battaglia et al. 1988b Schmidt and Taylor 1987). Additional evidence in support of the hypothesis that MDMA produces some of its... 

Gifford AN, Tang Y, Gatley SJ, Volkow ND, Lan R, Makriyannis A. Effect of the cannabinoid receptor SPECT agent, AM 281, on hippocampal acetylcholine release from rat brain slices. Neurosci Lett 1997 238 84-86. 

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