Spreading Depression: Imaging and Blockade in the Rat Neocortical Brain Slice

Abstract

. Spreading depression: imaging and blockade in the rat neocortical brain slice. J Neurophysiol 88: 2713-2725, 2002; 10.1152/jn.00321.2002. Spreading depression (SD) is a profound but transient depolarization of neurons and glia that migrates across the cortical and subcortical gray at 2-5 mm/min. Under normoxic conditions, SD occurs during migraine aura where it precedes migraine pain but does not damage tissue. During stroke and head trauma, however, SD can arise repeatedly near the site of injury and may promote neuronal damage. We developed a superfused brain slice preparation that can repeatedly support robust SD during imaging and electrophysiological recording to test drugs that may block SD. Submerged rat neocortical slices were briefly exposed to artificial cerebrospinal fluid (ACSF) with KCl elevated to 26 mM. SD was evoked within 2 min, recorded in layers II/III both as a negative DC shift and as a propagating front of elevated light transmittance (LT) representing transient cell swelling in all cortical layers. An SD episode was initiated focally and could be repeatedly evoked and imaged with no damage to slices. As reported in vivo, pretreatment with one of several N-methyl-D-aspartate (NMDA) receptor antagonists blocked SD, but a non-NMDA glutamate receptor antagonist (CNQX) had no effect. NMDA receptor (NMDAR) activation does not initiate SD nor are NMDAR antagonists tolerated therapeutically so we searched for more efficacious drugs to block SD generation. Pretreatment with the sigma-one receptor ( 1 R) agonists dextromethorphan (10 -100 M), carbetapentane (100 M), or 4-IBP (30 M) blocked SD, even when KCl exposure was extended beyond 5 min. The block was independent of NMDA receptor antagonism. Two 1 R antagonists [(ϩ)-3PPP and BD-1063] removed this block but had no effect upon SD alone. Remarkably, the 1 R agonists also substantially reduced general cell swelling evoked by bath application of 26 mM KCl. More potent 1 R ligands that are therapeutically tolerated could prove useful in reducing SD associated with migraine and be of potential use in stroke or head trauma.

Critical role of calcitonin gene-related peptide receptors in cortical spreading depression

“…In line with previous in vitro (10,22,32) and in vivo (14) studies, we found that activation of the NMDA glutamate receptor is required for CSD, as demonstrated by the inhibition of CSD by the NMDA receptor antagonist L-APV. Conversely, CSD is not affected by blockade of the AMPA glutamate receptor.…”

“…Clinical studies using neurophysiological approaches and imaging techniques have established a link between migraine aura and CSD. Auras most often anticipate headache onset, and experimental data indicate that CSD activates the trigeminovascular system, possibly provoking headache (5,10,12).…”

“…IOS are produced by changes in light transmittance from cortical slices (10). Optical imaging of IOS maps the brain by measuring intrinsic activity-related changes in tissue reflectance.…”

“…1A). Reproducible CSD episodes were induced by repetitively elevating the extracellular K + concentration through 2-to 3-min bath applications of 26 mM KCl solution (9,10). These transient increases in K + concentration induced increases in IOS that began within cortical layers II and III, expanded radially, and then propagated along all cortical layers (Fig.…”

“…The pivotal event in the generation and propagation of CSD is a marked decrease in neuronal membrane resistance associated with massive increases in extracellular K + and neurotransmitters, as well as increases in intracellular Na + and Ca 2+ (7)(8)(9). Genetic and environmental factors modulate individual susceptibility by lowering the CSD threshold, and cortical excitation can cause sufficient elevation in extracellular K + and glutamate to initiate CSD (5,7,8,(10)(11)(12)(13)(14). Conversely, the CSD threshold also may be increased by factors that reduce the susceptibility to migraine, such as postmenopausal age and male gonadal hormones (15,16).…”