Effects of metabolic alterations on dopamine release in an in vitro model of neostriatal ischaemia

doi:10.1016/S0361-9230(99)00016-7

Brain Research Bulletin

Volume 48, Issue 4, 1 March 1999, Pages 395-399

https://doi.org/10.1016/S0361-9230(99)00016-7 Get rights and content

Abstract

Release of neurotransmitters, including dopamine (DA), plays a central role in neuronal death during cerebral ischaemia. We investigated the effects of changes in energy demand and supply on DA release in cerebral ischaemia in vitro. Rat striatal slices were superfused (400 ml/h) with an artificial cerebrospinal fluid at 34°C, unless otherwise stated. Ischaemia were mimicked by removal of O₂ and reduction in glucose concentration from 4 to 2 mM. DA release was monitored by voltammetry. The profile of ischaemia-induced DA release was temperature-dependent. Hypothermia (to 24°C) delayed, slowed, and reduced ischaemia-induced DA release relative to 34°C. Pretreatment of the slices for 3 h with creatine (25 mM) delayed and slowed ischaemia-induced DA release. Conversely, blockade of Na⁺/K⁺ ATPase with ouabain induced an anoxic depolarisation and rapid DA release similar to ischaemia. In summary, the onset of DA release in this model is controlled by the balance between energy supply and utilisation. Strategies that increase availability of energy substrates for the membrane sodium pump (i.e., pre-incubation with creatine) or decrease their utilisation (hypothermia) slow and delay DA release. Hypothermia may owe part of its neuroprotective effect to a delay and slowing of ischaemia-induced release of DA and/or other neurotransmitters.

Introduction

Although the sequence of metabolic events in ischaemia is not firmly established, certain steps are clear. Initially, there is a period of relative ionic normality in which the principal changes are a modest increase in extracellular potassium (K⁺) and intracellular calcium (Ca²⁺) [16]. During this period, tissue adenosine triphosphate (ATP) levels fall until a critical threshold is reached at which the membrane sodium (Na⁺) pump (Na⁺,K⁺ ATPase) fails. At this point there is a sudden influx of Na⁺ ions into the cell, anoxic depolarisation [2] and transmitter release [31] occurs and irreversible neuronal damage is initiated.

Although the majority of ischaemia research has rightly been conducted in vivo, imposition of a sustained period of oxygen and glucose deprivation to brain slices has been shown to mimic many of the events associated with in vivo ischaemia. Several years of experience have now accumulated in which the validity of brain slices for “in vitro ischaemia” has been clearly demonstrated 8, 10, 12.

In many respects, brain slices are particularly suitable for investigating phenomena that cannot readily be studied in vivo, such as metabolic or osmotic interventions. Furthermore, the brain slice is divorced from its blood supply and thus actions on cerebral metabolism may be explicitly assessed without potentially confounding actions on the cerebral vasculature.

In the present study we investigated the effects of modulation of energy supply and demand on the dynamics of dopamine (DA) release in striatal brain slices subjected to periods of combined hypoxia and hypoglycaemia.

Section snippets

Materials and methods

Since the procedure used in the present work comprises both hypoxia and hypoglycaemia, we have used the terms ischaemia and ischaemic throughout this paper to describe the insult used. Ischaemia-induced DA release was measured by voltammetry in rat neostriatal slices according to the method previously described [28]. Brief details are given below.

Results

Imposition of a period of ischaemia (hypoxia/hypoglycaemia) to striatal slices at 34°C resulted in a consistent pattern of DA release in untreated control tissue. After an initial period of quiescence lasting 2–3 min, there was a sudden explosive release of DA rapidly reaching a peak extracellular DA concentration of 50–100 μM within 20 s before falling slowly back towards baseline over a period of several minutes.

This profile of ischaemia-induced DA release, whilst constant in control slices,

Discussion

The neuroprotective effects of profound hypothermia have been known for more than 40 years [22]. Moderate hypothermia is neuroprotective when applied during the ischaemic insult 4, 6, 9, 11, 21. However, the mechanisms underlying hypothermic neuroprotection remain unclear.

One possibility is that hypothermia inhibits the release of neurotoxic neurotransmitters. For instance, intracerebral microdialysis studies have shown that moderate hypothermia markedly attenuates ischaemia-induced release of

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Research ArticlesEffects of metabolic alterations on dopamine release in an in vitro model of neostriatal ischaemia

Abstract

Introduction

Section snippets

Materials and methods

Results

Discussion

Trends Neurosci.

Neurosci. Lett.

J. Neurosci. Meth.

Trends Neurosci.

J. Neurosci. Meth.

Carbon fibre microelectrodes

J. Neurosci. Meth.

Studies on anoxic depolarisation

Intraischemic hypothermia decreases the release of glutamate in the cores of permanent focal cerebral infarcts

Neurosurgery

Neuroprotective effect of hypothermia in cortical cultures exposed to oxygen-glucose deprivation or excitatory amino acids

J. Neurochem.

Hypothermia but not N-methyl-D-aspartate antagonist, MK 801, attenuates neuronal damage in gerbils subjected to transient global ischemia

J. Neurosci.

Small differences in intraischemic brain temperature critically determine the extent of ischemic neuronal injury

J. Cereb. Blood Flow Metab.

Effect of mild hypothermia on ischemia induced release of neurotransmitters and free fatty acids in rat brain

Stroke

On the mechanisms underlying hypoxia-induced membrane depolarisation in striatal neurons

Brain

Hypothermia prevents the ischemia induced translocation and inhibition of protein kinase C in the rat striatum

J. Neurochem.

The rat hippocampal slice preparation as an in vitro model of ischemia

Stroke

Effects of graded hypothermia on outcome from brain ischemia

Neurol. Res.

Research Articles
Effects of metabolic alterations on dopamine release in an in vitro model of neostriatal ischaemia