Ketamine blockade of spreading depression: rapid development of tolerance

Brain Research, 519 (1990) 351-354 Elsevier

351

BRES 24124

Ketamine blockade of spreading depression: rapid development of tolerance T. Amemori* and J. Bures Institute of Physiology, Czechoslovak Academy of Sciences, Prague (Czechoslovakia) (Accepted 27 February 1990)

Key words: Spreading depression; N-Methyl-D-aspartate receptor; Ketamine; Cerebral cortex; Caudate nucleus; Rat

Persistence of the ketamine-induced blockade of spreading depression (SD) was studied in 15 rats, anesthetized with 200 mg/kg ketamine followed at 50- to 60-min intervals by 3-5 injections of 100 mg/kg of the drug. Cortical or caudate SDs evoked 10 min after the first ketamine injection were blocked but the amplitude of SD waves elicited at regular 10-min intervals gradually increased while the blockade induced by subsequent ketamine injections weakened and became unrecognizable after the fifth injection. The result was not due to prolonged action of ketamine alone but rather to combined effect of ketamine and SD repetition. The development of tolerance is probably due to use-dependance of NMDA-gated channels which must be taken into account when assessing the therapeutic value of NMDA antagonists in treatment of brain ischemia. Leao's 15 spreading depression (SD) is a self-propagating neurohumoral reaction of large aggregates of CNS neurons mediated by release of K + ions and of other depolarizing substances from the depolarized nerve cells and b y their accumulation to an extracellular concentration inducing depolarization of the adjacent gray matter 4' 20. Experimental evidence suggests an important role of excitatory amino acids (EAA) in this process. Local application of N-methyl-D-aspartate (NMDA) 5 elicits SD at 200 times lower concentration than glutamate 22 in the mammalian neocortex. In the isolated turtle cerebellum N M D A , kainate and quisqualate elicit SD at 50, 200 and 2000 times lower concentrations than glutamate 14. While high SD eliciting potency does not guarantee that the particular substance attains effective intracerebral concentration during SD, participation of individual E A A receptor subtypes in the mechanism of SD can be more reliably inferred from experiments with E A A receptor antagonists. Cortical SD can be blocked by systemic application of the non-competitive N M D A antagonists ketamine 8'a°'ls, phencyclidine and MK 801 (ref. 18). The purpose of the present paper was to assess the effect of systemic application of ketamine on SD in the above brain regions of adult rats and to estimate the persistence of the block maintained by repeated applications of the drug. Three-month-old male hooded rats of the Long-Evans strain (n = 15) were obtained from the breeding colony

of the Institute. The animals were anesthetized with ketamine-hydrochloride (Narkamon, Spofa, 200 mg/kg) and fixed in the stereotaxic apparatus. The frontal or parietal cortex were exposed by circular trephine openings 4 mm in diameter. Glass capillary microelectrodes (tip diameter 2-4/~m) filled with physiological saline and connected to calomel halfcells were inserted with the microdrive of the stereotaxic instrument into frontoparietal cortex (1.0 mm deep) and into the head of the caudate nucleus (AP -2.0, L 2.0, V 4.0) according to the atlas by Fifkova and Marsala 7. A wick calomel cell electrode applied on the exposed neck muscles served as reference. The electrode leads were connected through high impedance input operational amplifiers to a polygraph. Spreading depression was elicited by microinjection of 0.5 to 1.0 pl of isotonic potassium acetate to a point about 1 mm more caudal in the caudate nucleus and 2-3 mm more caudal in the cerebral cortex. The injection was made with a glass micropipette connected with polyethylene tubing to a microinjector. In the first part of the study, rats (n = 8) were anesthetized with 200 mg/kg ketamine followed at 50- to 60-min intervals by 3-5 additional applications of 100 mg/kg ketamine. The first SD wave was elicited 10 min after the first ketamine injection and the K ÷ acetate injections were repeated at regular 10-min intervals throughout the 3-4 h of the experiment. In another group

* Visiting scientist from the Nihon University, Kanagawa, Japan, supported by UNESCO. Correspondence: J. Bures, Institute of Physiology,CzechoslovakAcademy of Sciences, Videnska 1083, 14220 Prague 4, Krc, Czechoslovakia.

0006-8993/90/$03.50 (~ 1990 Elsevier Science Publishers B.V. (Biomedical Division)

352

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of 7 rats, the first SD wave was only evoked after the third ketamine injection, i.e. 100 min after the onset of ketamine anesthesia. Further ketamine injections and SD-eliciting stimuli were applied as described above. SD blockade elicited in the cerebral cortex by a high dose of ketamine (200 mg/kg i.p.) is shown in Fig. 1. Whereas the first ketamine injection caused a prolonged SD block lasting 40-50 min, the block induced by the

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nucleus of 8 rats.

second ketamine injection was shorter and weaker and the third and fourth injections were practically ineffective. The results of similar experiments performed in 8 rats are summarized in Fig. 2 showing the average amplitudes of cortical and caudate SD at 10-min intervals after ketamine injections applied at 50- to 60-min intervals. Although the animals were maintained by repeated ketamine injections under deep anesthesia, the blocking effect gradually attenuated. One-way analysis of variance with repeated measures revealed significant effect of the ordinal number of ketamine application on the amplitude of SD waves elicited 10 min after each ketamine injection (F4,35 = 11.6, P < 0.01) in the cerebral cortex. Similar results were obtained in the caudate nucleus where the corresponding value was F4,35 = 3.82, P < 0.05. Newman-Keuls multiple comparisons indicated that the average slow potential amplitude 10 min after the first ketamine application was significantly lower than 10 min after any of the subsequent applications (P < 0.01). The average amplitude after the second and third injections was lower than after the fifth one (P < 0.05). Other differences were not statistically significant. In the caudate nucleus, the first, second and third ketamine injections were significantly more effective than the fifth injection (P < 0.05). Other differences were not statistically significant. Paired t-tests indicated that caudate SD amplitude was transiently decreased by the second, third, and fourth but not by the fifth ketamine injection. Amplitude of cortical SD was decreased by the second but not by the subsequent ketamine injections. In 7 rats the first 3 ketamine injections were applied at 40-min intervals but the first cortical and caudate SD waves were elicited only 20 min after the third ketamine injection. The results are summarized in Fig. 3 which shows that the initial reduction of slow potential amplitude after the third ketamine injection was similar as after the first injection of this drug (compare Fig. 2). The block rapidly subsided and the third SD wave elicited 120 min after the first ketamine injection displayed almost normal amplitude and duration. The fourth ketamine application did not cause any significant reduction of SD amplitude in the cortex and decreased the slow potential only by 25% in the caudate. Student's t-test showed that the tenth and first SD waves elicited after the same duration of ketamine anesthesia in Figs. 2 and 3, respectively, have significantly different amplitudes in the cortex (t = 7.2, P < 0.01) and in the caudate (t = 2.4, P < 0.05). On the other hand there was no significant difference between the effects of the fourth ketamine injection preceded by 12 (Fig. 2) or by 3 (Fig. 3) SD waves. The present study confirms ketamine blockade of cortical SD described in our earlier publications 8'1°, but

353

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specifies at the same time conditions under which the effect can be observed. The gradual decrease of the SD blocking effect of repeated ketamine dosages is consonant with the report by Albe-Fessard et al. z. The development of ketamine tolerance is probably related to use-dependence typical for the non-competitive NMDA antagonists. Phencyclidine- and ketamine-induced blockade of the NMDA receptor-mediated responses is increased by the presence of the agonist zl and also the recovery of these responses from the block is accelerated by repeated agonist applications 16. Similar use-dependence was demonstrated in radioligand binding experiments ~5 which show that the binding of the noncompetitive NMDA antagonist [3H]MK-801 to the mammalian CNS membranes is greatly enhanced by the presence of the NMDA receptor agonists. The present observations can be explained in the following way. The first SD wave elicited in a ketamine-anesthetized rat is markedly blocked because the ketamine effect is enhanced by glutamate, aspartate and other excitatory amino acids released during SD and by the marked depolarization accompanying SD. Subsequent reduction of the block is partly due to decreasing ketamine concentration and partly to release of excitatory amino acids during subsequent SD waves. The latter mechanism becomes more and more important and accounts for the impossibility to restore SD blockade by repeated ketamine injections. This explanation is corroborated by the

observation that ketamine alone does not lead to the development of tolerance which only appears after several SD waves have been elicited in a ketaminetreated animal. On the other hand tolerance is not produced by repeated SD waves preceding the ketamine application 8. Rapid adaptation to the blocking agent was also observed in the isolated turtle cerebellum by Lauritzen et al. 14. After several min superfusion with 100 /~M APV, SD was blocked but after another 12 min SD could be elicited by the stimulus of the same intensity. Similar decrease of block efficiency was also observed with prolonged kynurenic acid superfusion. To prevent development of tolerance, the turtle cerebellum had to be superfused with drug-free saline between tests. These results indicate that the gradual neutralization of the SD inhibitory effect is not limited to ketamine but is shared by other competitive selective and non-selective NMDA receptor antagonists. The mechanism of the above phenomenon remains obscure. The disappearance of ketamine blockade does not necessarily indicate that the NMDA receptor-gated channels are not more blocked by ketamine. SD is a complex process, the propagation of which can be maintained by transmitters affecting non-NMDA receptors and by potassium ions. Lauritzen et al. ~4 have recorded SD not only in the NMDA-rich granular layer of the turtle cerebellum but also in the molecular layer which contains kainate and quisqualate but not NMDA

354 receptors. It is possible that continued blockade of the

zation 9"1°'17"18. O n the other hand, it has been suggested

NMDA

that the protective effect of competitive and noncompetitive N M D A antagonists in models of focal brain ischemia 3'6A3'19'21 is due to inhibition of SD in the

receptor-gated

channels facilitates the

non-

N M D A mechanism of SD initiation and propagation. Further experiments are needed to decide between these possibilities. The impossibility to maintain SD blockade by repeated injections of ketamine must be taken into account when assessing the therapeutic value of this drug for treatment

' p e n u m b r a ' zone of low perfusion surrounding the ischemic core 2. This explanation is made unlikely by the present experiments which suggest that such protection

of anoxic brain damage. While the N M D A antagonists block SD, they do not delay onset of anoxic depolari-

must be sought in those posthypoxic effects of the N M D A receptor antagonists which are not influenced by the development of tolerance.

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12 Kemp, J.A., Foster, A.C. and Wong, E.H.E, Non-competitive antagonists of excitatory amino acid receptors, Trends Neurosci., 10 (1987) 294-298. 13 Kochar, A., Zivin, J., Lyden, P. and Mazzarella, V., Glutamate antagonist therapy reduces neurological deficit produced by focal central nervous system ischemia, Arch. Neurol., 45 (1988) 148-153. 14 Lauritzen, M., Rice, M.E., Okada, Y. and Nicholson, C., Quisqualate, kainate and NMDA can initiate spreading depression in the turtle cerebellum, Brain Research, 475 (1988) 317-327. 15 Leao, A.A.P., Spreading depression of activity in the cerebral cortex, J. Neurophysiol., 7 (1944) 359-390. 16 MacDonald, J.E, Schneiderman, J.H. and Miijkovic, Z., Excitatory amino acids and regenerative activity in cultured neurons. In R. Schwarcz and Y. Ben-Ari (Eds.), Advances in Experimental Biology and Medicine, Vol. 203: Excitatory Amino Acids and Epilepsy, Plenum, New York, 1986, pp. 425-437. 17 Magnusson, K., Gustafson, I., Westerberg, E. and Wieloch, T., Neurotransmitter modulation of neuronal damage following cerebral ischemia: effects on protein ubiquitation. In G. Somjen (Ed.), Mechanisms of Cerebral Hypoxia and Stroke, Plenum, New York, 1988, pp. 309-319. 18 Marrannes, R., De Prins, E., Willems, R. and Wauquier, A., NMDA antagonists inhibit cortical spreading depression but accelerate the onset of neuronal depolarization induced by asphyxia. In G. Somjen (Ed.), Mechanisms of Cerebral Hypoxia and Stroke, Plenum, New York, 1988, pp. 303-304. 19 Meldrum, B., Evans, M. and Swan, J., Excitatory amino acid neurotransmission and protection against ischaemic brain damage. In G. Somjen (Ed.), Mechanisms of Cerebral Hypoxia and Stroke, Plenum, New York, 1988, pp. 349-358. 20 Nicholson, C. and Kraig, R.P., The behavior of extracellular ions during spreading depression. In T. Zeuthen (Ed.), The Application of Ion-Selective Microelectrodes, Elsevier, Amsterdam, 1981, pp. 217-238. 21 Simon, R.P., Swan, J.H., Griffith, T. and Meldrum, B.S., Blockade of methyl-D-aspartate receptors may protect against ischemic damage in the brain, Science, 226 (1984) 850-852. 22 Van Harreveld, A., Components in brain extracts causing spreading depression of cerebral cortical activity and contraction of crustacean muscle, J. Neurochem., 3 (1959) 300-315.