Brain Research 888 2001 212–220 www.elsevier.com locate bres
Research report
Long-term reduction of benzodiazepine receptor density in the rat cerebellum by acute seizures and kindling and its recovery 6 months
later by a pentylenetetrazole challenge
a , a
b b
b
A.S. Bazyan , V.V. Zhulin , M.N. Karpova , N.Y. Klishina , R.N. Glebov
a
Institute of Higher Nervous Activity and Neurophysiology , Russian Academy of Sciences, Butlerov St. 5A, GSP-7, Moscow 117865, Russia
b
Institute of General Pathology and Pathophysiology , Russian Academy of Medical Sciences, Moscow, Russia
Accepted 26 September 2000
Abstract
Seizures induced by an acute pentylenetetrazole 50 mg kg injection were accompanied by a long-term at 1–48 h, but not on day 7
3
decrease in the density B of [ H]-diazepam binding to benzodiazepine receptors in rat cerebellar cortex with no change in affinity
max
K . Kindling for 24 days by daily administrations of pentylenetetrazole 20 mg kg led to the same decrease in benzodiazepine receptor
d
density at 1–48 h, but not on day 7 as that observed after a single dose of pentylenetetrazole 50 mg kg. This suggests a common mechanism for both acute and kindling-induced seizures, dependent on the long-term receptor changes. The increased susceptibility to
seizures persisted for 6 months after the termination of kindling, with BDZ receptor density in cerebellar cortex reduced almost by half. In
3
age-matched controls, an acute dose of PTZ 30 mg kg induced seizures and decrease in both B and K of [ H]-diazepam binding. In
max d
kindled rats, at 6 months post-kindling, the same dose of PTZ 30 mg kg restored the benzodiazepine receptor density to the level found 6 months before, at the time of termination of kindling. Also, the severity of seizures was enhanced in the kindled rats. The results are
discussed in terms of a balance of inhibitory and excitatory processes, in which the reduced BDZ receptor density at 6 months post-kindling may represent a compensatory reaction to outbalance some alterations in excitatory systems that have been reported to be
induced by kindling.
2001 Elsevier Science B.V. All rights reserved.
Keywords : Kindling; Cerebellum; Pentylenetetrazole; Benzodiazepine; GABA
36 2
1. Introduction BDZ receptors and GABA-stimulated
Cl influx into
cortical membrane preparations [29,40,49–52,55]. BDZ It is known that GABA , benzodiazepine BDZ, pic-
agonists manifest a marked anticonvulsive effect on
A 2
rotoxin-barbiturate PCT-BB receptors and Cl channels
clonic–tonic seizures in PTZ-kindled rats, with a marked are assembled in a single supramolecular complex. Both
dose-effect dependence [3,5,13,34,53,54]. BDZ and PCT-BB receptors act as allosteric sites for the
Chronic subthreshold stimulation of some brain struc- GABA receptor and vice versa. Pentylenetetrazole PTZ
tures, or chronic subconvulsive doses of convulsants result
A
interacts with the PCT-BB receptor of the GABA BDZ in kindling which is maintained for a long time
A
PCT-BB receptor complex, inhibiting the GABA and
[18,29,42,67]. It is known that electrical kindling develops
A 2
BDZ receptors, closing the Cl channels and provoking
with the active involvement of long-term potentiation- seizures
in convulsive
doses [5,11,12,25,35,41,46,47,
induced NMDA receptors [10,26,37,38,48,61]. While the 50,55,65,69].
long-term suppression of the GABA BDZ PCT-BB re-
A
In subconvulsive doses, chronic administration of PTZ ceptor activity by kindling has been described in a number
induces kindling phenomena and modifies the GABA of studies, little is known about the initial long-term
A
BDZ PCT-BB receptor complex, suppressing GABA , responses. Is the long-term response attributable to kindl-
A
ing development, or initial attribute of GABA BDZ
A
PCT-BB receptors complex, as for NMDA receptors?
Corresponding author. Tel.: 17-95-334-7789; fax: 17-95-338-8500. E-mail address
: bazyanmail.ru A.S. Bazyan.
Similarly, little is known of the GABA BDZ PCT-BB
A
0006-8993 01 – see front matter
2001 Elsevier Science B.V. All rights reserved. P I I : S 0 0 0 6 - 8 9 9 3 0 0 0 3 0 4 5 - 6
A .S. Bazyan et al. Brain Research 888 2001 212 –220
213
mechanisms in kindling seizures retrieval after very long 2.2.1. Three to four-months-old rats
times of acute administration of subconvulsive doses of The first series comprised the rats, in which a convulsive
convulsants. dose of PTZ 50 mg kg resulted in seizure scores of 4–5
3
Previously, we have found [29] that changes in [ H]- points. They were decapitated 60 min 30 min after the
diazepam binding are maximal in the cerebellar cortex, termination of seizures or 48 h later and on day 7 after the
rather than in the neocortex, of the kindled rats. It has been injection n536, including control rats.
shown that 81 of the total BDZ receptors in cerebellar The second series comprised the rats, in which a
cortex contain high-affinity sites for PTZ [6]. In the subconvulsive dose of PTZ 20 mg kg elicited kindled
forebrain, only 34 of the total BDZ receptor population seizures scoring 4–5 points, followed by decapitation 60
bear high-affinity sites for PTZ. At the same time, the min 30 min after the termination of seizures or 48 h later
cerebellar cortex actualizes movement control. The cere- and on day 7 after the last injection n548, including
bellar cortex exerts its influence by inhibiting and dis- control rats.
inhibiting motor control action, in the premotor networks The third series comprised the rats endogenously sensi-
of the brainstem, sensomotor cortex, and spinal cord [19– tive and insensitive to the convulsant. One group of
22,24]. On the other hand, the cerebellum and its associ- animals n525 was treated with 25 mg kg PTZ and the
ated brainstem circuitry does appear to be essential neces- second group with 30 mg kg n525. Then, the rats were
sary and sufficient for learning and memory of the selected according to their sensitivity: the first subgroup
conditioned response [32,33,62–64,68]. This indicates that n56 with seizures 2 points provoked by 25 mg kg
long-term reactions are inherent to the neurons of cere- PTZ; and the second subgroup n56 with no seizures
bellum; for instance, in long-term depression [23]. provoked by 30 mg kg PTZ. Both groups were decapitated
The goal of the present investigation was to study on day 7 after the injection.
3
long-term characteristics of [ H]-diazepam binding in cerebellar cortex after an acute injection of PTZ in
2.2.2. After 6 months about 10-months-old rats convulsive doses, after kindling development; peculiarities
For the period of 6 months both the control and kindled
3
of the retrieval of kindled seizures and of [ H]-diazepam rats were kept in the breeding facility. Their weights at the
binding 6 months after the termination of kindling, follow- second stage of experiments reached 360–450 g.
ing a challenge with a subconvulsive dose of PTZ. At the second stage, the persistence of kindling was
studied. Two control groups and two groups of kindled rats were treated with 20 and 30 mg kg PTZ n525 in each
2. Materials and methods control and kindled group.
