Effects of clomethiazole on spreading depression in the rat hippocampal slice

Cortical spreading depression-induced preconditioning in mouse neocortex is lamina specific

Cortical spreading depression (CSD) is able to confer neuroprotection when delivered at least 1 day in advance of an ischemic event. However, its ability to confer neuroprotection in a more immediate time frame has not previously been investigated. Here we have used mouse neocortical brain slices to study the effects of repeated episodes of CSD in layer V and layer II/III pyramidal neurons. In layer V, CSD evoked at 15-min intervals caused successively smaller membrane depolarizations and increases in intracellular calcium compared with the response to the first CSD. With an inter-CSD interval of 30 min this preconditioning effect was much less marked, indicating that preconditioning lasts between 15 and 30 min. A single episode of CSD also provided a degree of protection in oxygen-glucose deprivation (OGD) by significantly lengthening the time a cell could withstand OGD before anoxic depolarization occurred. In layer II/III pyramidal neurons no preconditioning by CSD on subsequent episodes of CSD was observed, demonstrating that the response of pyramidal neurons to repeated CSD is lamina specific. The A1 receptor antagonist 8-cyclopentyl theophylline (8-CPT) reduced the layer V preconditioning in a concentration-related manner. Inhibition of extracellular formation of adenosine by blocking ecto-5'-nucleotidase with α,β-methyleneadenosine 5'-diphosphate prevented preconditioning in most but not all cells. Block of equilibrative nucleoside transporters 1 and 2 with dipyramidole alone or in combination with 6-[(4-nitrobenzyl)thio]-9-β-d-ribofuranosylpurine also prevented preconditioning in some but not all cells. These data provide evidence that rapid preconditioning of one CSD by another is primarily mediated by adenosine.

The effect of estrogen and progesterone on spreading depression in rat neocortical tissues

Although gender differences in the incidence of migraine with aura appear to be related to high circulating levels of ovarian hormones, the underlying mechanisms are not yet fully understood. Several studies have suggested a major role for spreading depression (SD) in the pathogenesis and symptomatology of migraine with aura. To investigate a possible role of SD in the association of high female hormones and attacks of migraine with aura, the effects of beta-estradiol and progesterone on SD were studied in rat neocortical tissues. Application of both hormones enhanced the repetition rate as well as the amplitude of SD in neocortical slices treated with hypotonic artificial cerebrospinal fluid. beta-Estradiol and progesterone also dose dependently increased the amplitude of SD induced by KCl microinjection. Both hormones exhibited a pronounced, persisting, and significant enhancement of long-term potentiation of the field excitatory postsynaptic potential in the neocortical tissues. The changes in SD characteristics in the presence of estrogen and progesterone may responsible for increased migraine with aura attacks associated by high female hormones. These hormones may exert their effects on SD via facilitation of synaptic transmission.

Brief, repeated, oxygen-glucose deprivation episodes protect neurotransmission from a longer ischemic episode in the in vitro hippocampus: role of adenosine receptors

1. Ischemic preconditioning in the brain consists of reducing the sensitivity of neuronal tissue to further, more severe, ischemic insults. We recorded field epsps (fepsps) extracellularly from hippocampal slices to develop a model of in vitro ischemic preconditioning and to evaluate the role of A1, A2A and A3 adenosine receptors in this phenomenon. 2. The application of an ischemic insult, obtained by glucose and oxygen deprivation for 7 min, produced an irreversible depression of synaptic transmission. Ischemic preconditioning was induced by four ischemic insults (2 min each) separated by 13 min of normoxic conditions. After 30 min, an ischemic insult of 7 min was applied. This protocol substantially protected the tissue from the irreversible depression of synaptic activity. 3. The selective adenosine A1 receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 100 nm), completely prevented the protective effect of preconditioning. The selective adenosine A2A receptor antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM 241385, 100 nm) did not modify the magnitude of fepsp recovery compared to control slices. The selective A3 adenosine receptor antagonists, 3-propyl-6-ethyl-5[ethyl(thio)carbonyl]-2-phenyl-4-propyl-3-pyridinecarboxylate (MRS 1523, 100 nm) significantly improved the recovery of fepsps after 7 min of ischemia. 4. Our results show that in vitro ischemic preconditioning allows CA1 hippocampal neurons to become resistant to prolonged exposure to ischemia. Adenosine, by stimulating A1 receptors, plays a crucial role in eliciting the cell mechanisms underlying preconditioning; A2A receptors are not involved in this phenomenon, whereas A3 receptor activation is harmful to ischemic preconditioning.

Adenosine-mediated synaptic depression and EPSP/spike dissociation following high potassium-induced depolarization in rat hippocampal slices

Simultaneous recordings of orthodromic PS, fEPSP and antidromic PS revealed EPSP/spike (E-S) dissociation, indicating a conversion of input/output relations from early and brief excitability to a late and prolonged depression during the recovery from depolarization induced by high levels of potassium. E-S potentiation was partially attenuated by pre-treating the slices with BAPTA-AM and lidocaine and totally eliminated by a submaximal concentration of muscimol. The time lag for recovery was decreased by the GABA(A) antagonist and completely eliminated by the A(1) antagonist. From these observations, we conclude that Ca(2+) dependent inhibitory suppression is the main cause of a brief period of E-S potentiation, and accumulation of adenosine is the mechanism responsible for prolonged depression of synaptic transmission