Brain Research 880 (2000) 187–190
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Short communication
Does fucose or piracetam modify the effect of hypoxia
preconditioning against pentylenetetrazol-induced seizures?
*
Christine Rauca , Hannelore Jantze, Manfred Krug
Department of Pharmacology and Toxicology, Faculty of Medicine, Otto-von-Guericke University Magdeburg, Leipziger Str. 44, 39120 Magdeburg,
Germany
Accepted 25 July 2000
Abstract
To clarify the question whether the duration of hypoxia exposure has an influence on the point in time or the strength of hypoxic preconditioning, hypoxia exposure of rats lasting 1 and 8 h was tested regarding the modification of susceptibility to acute pentylenetetrazol-induced seizures. Following the short-lasting (1 h) hypoxia, the maximum level of preconditioning action was observed 7 days after hypoxia, whereas the longer-lasting hypoxia (8 h) produced the maximum level of protection 14 days after hypoxia. We investigated the influence of fucose and piracetam on the effect of hypoxia preconditioning by the application of the substances 20 min before the beginning of hypoxia exposure. Fucose did not modify the result of hypoxia preconditioning. But after the treatment with piracetam, the preconditioning effect was prevented following hypoxia lasting 1 and 8 h. We suggest that the radical scavenger properties of piracetam are responsible for the absence of protection against pentylenetetrazol-evoked seizures. 2000 Elsevier Science B.V. All rights reserved.
Keywords: Hypoxia preconditioning; Pentylenetetrazol; Seizure; Fucose; Piracetam
Moderate hypoxia reduces the susceptibility of mice to connection between the duration or strength of precondi-pentylenetetrazol (PTZ)-induced seizures [13] and protects tioning or the event producing ischemic tolerance and the rats against the neurotoxicity of kainic acid [4,11]. Inverse- consequence for hypoxic preconditioning or ischemic ly, it can be assumed that this phenomenon of ‘hypoxic tolerance, was not investigated. For this reason, our first preconditioning’ may be involved in the protection from question is whether the process of hypoxic preconditioning neuronal death following carotis artery ligation combined is dependent on the duration of hypoxia exposure. For this with hypoxia which is triggered by kainic acid- or flurothyl reason we exposed one group of rats to hypoxic conditions vapour-induced seizures [20]. However, it is becoming for 1 h and a second group for 8 h.
evident that the mammalian brain also possesses adaptive Another question is whether preconditioning may be processes that can confer tolerance to seizures or hypoxia / modified by treatment with nootropic drugs intervening in ischemia-induced neuronal damage which have not yet plastic-adaptive processes such as learning and memory or been clarified. During hypoxia or the ischemic period, or long-term-potentiation (LTP). In the present studies we both, an excessive glutamate release and an increased investigated fucose (FUC), a substance improving learning stimulation of different glutamatergic receptors and the and memory and LTP [7] and piracetam (PIR) facilitating subsequent enhanced formation of free radicals are pos- learning and memory [10] and influencing LTP in different sibly involved in the mediation of protection against the manner [16]. Both nootropic drugs were studied at doses
different noxes [21]. facilitating plastic adaptive processes.
The protective mechanisms are plastic-adaptive pro- The experiments were performed using 8-week-old male cesses of transient duration [13,14]. Whether there is a Wistar rats. The animals were kept under a lighting regime of light / dark 12:12 (light on at 6.00 a.m.), temperature 20628C, and air humidity 55–60%. They had free access
*Corresponding author. Tel.:149-391-671-5371; fax: 1
49-391-671-to food and water. For all procedures followed, ethical 5869.
E-mail address: christine.rauca@medizin.uni-magdeburg.de (C. Rauca). approval was obtained prior to the experiments according
188 C. Rauca et al. / Brain Research 880 (2000) 187 –190
to the requirements of the National Act on the use of Experimental Animals (Germany).
The following groups were prepared. Group 1: naive controls which were not treated; group 2: sham-exposed controls which were exposed to room air in the hypoxia chamber. Group 3: hypoxic animals which were exposed to 9% O and 91% N .2 2
A mixture of 9% O and 91% N streamed continuously2 2
through the chamber. Accurate mixing of O and N was2 2
achieved by controlling the air pump by an oxygen sensor (Oxopac RE, Draeger, Germany). Sham-exposed controls were exposed to the same chamber which was ventilated by room air. Every five rats were placed into the hypoxia chamber and exposed to the hypoxic conditions for 1 or 8 h.
Experiments to test the susceptibility to seizures induced by pentylenetetrazol (PTZ) were done 1, 4, 7, 14 or 21 days after hypoxia or sham exposure. Different groups were investigated at each time point. To estimate the influence of drug treatment on hypoxic preconditioning, the animals were injected with PTZ, 7 days following hypoxia lasting 1 h and 14 days following hypoxia lasting 8 h, respectively. The rats of all groups received an intraperitoneal application of 55 mg / kg PTZ dissolved in physiological saline solution. After administration of PTZ, the behavior of the animals was observed for a period of 20 min. The resultant seizures were classified as follows: Stage 0: no response. Stage 1: ear and facial twitching. Stage 2: convulsive waves though the body. Stage 3: myoclonic jerks, rearing. Stage 4: turn over onto side position. Stage 5: turn over onto back position, generalized tonic–clonic seizures. The experimenter was unaware of the pretreatment of the animals.
To test the influence of fucose (FUC) or piracetam (PIR) on hypoxia-induced changes in the susceptibility to
Fig. 1. The time course of the effect of hypoxic preconditioning (9% O ;2 seizures evoked by PTZ, both substances were
intraperito-91% N ) lasting 1 (upper part) or 8 h (lower part) estimated as2 neally injected at a dose of 100 mg / kg body weight 30
susceptibility to an acute application of 55 mg / kg pentylenetetrazol min before the start of hypoxia exposure. Saline controls (PTZ). The means6S.E.M. of 12 to 15 animals per group are shown;
received 10 ml NaCl / kg body weight. * P,0.05 statistically significant difference of seizure stages of
pre-conditioned rats (hypoxia) in comparison to naive (naive c.) and sham-Statistical differences were determined using
one-way-exposed (sham ex.) controls. Statistical significance was calculated using ANOVA followed by a modified LSD (Tukey) with a
one-way-ANOVA with Tukey’s multiple comparison test. significance level of 0.05 for post hoc comparisons. Data
are presented as mean6S.E.M. for each treatment group. As shown in Fig. 1, the hypoxia preconditioning lasting
C. Rauca et al. / Brain Research 880 (2000) 187 –190 189
hypoxia, the damaging processes are more continuously course of protection nor the strength of PTZ-induced and pronounced and so the protection can be established at seizures 7 or 14 days after hypoxia exposure.
a later point in time. The molecular action of FUC is different from that of
Fig. 2 demonstrates that the pretreatment of rats with PIR. FUC increases the fucosylation of brain glycopro-100 mg / kg fucose (FUC) was not able to modify the teins. The effect is thought to play a crucial role in the late susceptibility to PTZ independently of the duration of phase of LTP and influences memory trace processing hypoxia preconditioning. In contrast to this, the application [1,9]. In this connection, it was speculated that the late of 100 mg / kg piracetam (PIR) prevented significantly the phase of glycoprotein synthesis coincides with the modula-effects of preconditioning following hypoxia exposure tion of the cell–cell adhesion processes, reflecting the lasting 1 or 8 h, 7 or 14 days later. FUC injected 20 min section and stabilization of synapses which maintain an before the beginning of hypoxia influenced neither the time enduring representation of long-term memory [15,17]. From our data it may be concluded that increased fucosyla-tion and the resulting alterafucosyla-tion of synaptic connectivity have no importance for the induction of processes leading to a protection against PTZ seizures.
Different mechanisms were taken into consideration for the learning improvement by PIR. An involvement of glutamate receptors in the mediation of protection as was discussed for the implement of facilitating effects on learning and memory [22] can not explain this action. Hypoxia causes the formation of reactive oxygen species [14]. The generation of oxygen species has been usually considered a sign of oxidative stress that puts cells on the course to apoptotic cell death. Reactive oxygen species may initiate multiple signalling events such as the expres-sion of several genes that either protect against neurode-generation and seizures, respectively, or are involved in a cascade of events mediating cell injury [19].
The radical scavenger properties of PIR [12] may be a possible mechanism which inhibit the protective effect of hypoxia as described for the spin trap reagent N-t-butyl-a -phenylnitrone (PBN), too [14].
Acknowledgements
This study was supported by a grant of the Bundes-¨
ministerium fur Bildung und Forschung (FKZ:07 NBL 04 / 01 ZZ 9505).
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