Lamina-specific changes in hippocampal GABAA/cBZR and mossy fibre sprouting during and following amygdala kindling in the rat

Alterations in hippocampal GABA_A/central benzodiazepine receptor (GABA_A/cBZR) expression and mossy fibre sprouting (MFS) may have aetiological significance in temporal lobe epileptogenesis. Their relationship with each other is also unknown. We utilised [³H]-flumazenil autoradiography to quantify changes in GABA_A/cBZR density and affinity in all hippocampal laminae, and Timm's staining for MFS at different stages of epileptogenesis in the amygdala kindling rat model (after 24 stimulations, 48 stimulations and two weeks post-kindling). During kindling, receptor density was significantly elevated within the dentate stratum moleculare and granulosum, but decreased within the stratum radiatum of CA3 and CA2. Two weeks post-kindling, receptor density remained upregulated in the dentate stratum moleculare and was also upregulated in CA3 stratum oriens and CA1 stratum moleculare. MFS was significantly increased in the dentate stratum moleculare at two weeks post-kindling, with a strong inverse correlation between MFS and GABA_A/cBZR density in this region. No changes in GABA_A/cBZR binding affinity were detected for any hippocampal subregion at any time point. Our results demonstrate that changes in hippocampal GABA_A/cBZR expression are lamina- and time-specific. Within the dentate gyrus, receptor density is upregulated throughout epileptogenesis, whilst within the hippocampus proper, receptor density is downregulated early in epileptogenesis but upregulated at the chronic phase. A novel association between MFS and GABA_A/cBZR density has been demonstrated by this study, which could represent an important compensatory or pathological mechanism associated with epileptogenesis.     

发作间痫样放电对大鼠情感行为及空间学习记忆的影响

目的　观察发作间痫样放电 (IED)对大鼠情感行为及空间学习和记忆的影响。方法　在大鼠海马快速电点燃后 13d ,反复惊厥阈下电刺激海马 ,并通过旷场活动性、拒俘反应性观察和Morris水迷宫训练 ,动态检测实验动物情感行为与空间学习和记忆能力改变。结果　电点燃后 14d ,IED可致实验动物旷场活动性明显减少 [正常对照 (17 3± 3 6 )分 ;IED动物 (4 6± 1 3)分 ,P <0 0 1],拒俘反应性显著增强 [正常对照 (1 4 9± 0 31)分 ;IED动物 (3 94± 0 81)分 ,P <0 0 1];大鼠Morris水迷宫训练潜伏期明显延长 [正常对照 (32± 7)s;IED动物 (4 7± 10 )s ,P <0 0 5 ],空间定向能力测试时在水迷宫的 4个象限中无目的漫游。结论　无明显惊厥行为的IED可引发或加重实验动物活动习性改变、警觉水平增高、惊恐行为、环境适应能力下降 ,及短暂空间学习和记忆能力受损。     

Ro 15-1788 suppresses the development of kindling through the benzodiazepine receptor

beta-Carboline (norharman) has been shown to produce kindled seizures when given systemically for long periods of time. The expression of the kindled seizure activity can be blocked by ligands of the benzodiazepine receptor suggesting the receptor as a site of vulnerability in the kindling mechanism. The present data show that Ro 15-1788, a receptor antagonist, suppresses the development of kindled seizures as demonstrated by the delayed appearance of each behavioral stage and the decreased severity of symptoms within each stage. Animals treated with Ro 15-1788 still expressed lower behavioral stages when Ro 15-1788 was eliminated from the trials indicating that this compound suppresses the very process of kindling itself and not just the expression of the kindled seizures. Ro 15-1788 given with norharman causes an increase in Bmax of [3H]flunitrazepam binding to the benzodiazepine receptor in cortex. It is not known if this increase is instrumental in lowering the kindling rate.     

Systemic Focal Epileptogenesis

Rats that receive radiation to 0.25 cc of one cerebral hemisphere are clinically and electroencephalographically normal until there is a breakdown of the blood-brain barrier (BBB) at 3 to 6 months postradiation. This BBB lesion can be detected by transient focal seizure activity produced by the BBB-excluded systemic convulsant bicuculline methiodide. In two rats the seizure activity induced by this one injection was self-sustaining. In seven of 15 other rats tested, the subsequent administration of repeated 2 mg/kg injections created a chronic focus that continued to spike with great frequency for 3 weeks or more without further administration of any convulsant. In three of eight other rats, implanted minipumps delivering 180 micrograms/h of bicuculline methiodide produced self-sustaining epileptic activity.     

Suppressive effects ofl-5-hydroxytryptophan in a feline model of photosensitive epilepsy

We recently demonstrated that long-lasting photosensitivity is acquired as a result of kindling of the lateral geniculate nucleus (LGN), and that the LGN-kindled cat pretreated withd,l-allylglycine represents a useful model of epilepsy for drug studies. The present experiments studied anticonvulsant effects of a serotonin precursor,l-5-hydroxytryptophan (5-HTP), on photosensitivity in the LGN-kindled cat underd,l-allylglycine and on LGN-kindled seizures. 5-HTP suppressed both myoclonic responses and paroxysmal EEG discharges induced by photic stimulation in a dose-related manner. Photically-induced seizures were completely blocked 1.5–2 h after injection of 20 mg/kg 5-HTP. 5-HTP was also effective in reducing the afterdischarge duration and behavioral seizure stage in LGN-kindled seizures; following 40 mg/kg administration, no electroclinical seizures were elicited in the LGN-kindled cats. Serotonergic mechanisms may play an important role in epileptic photosensitivity; the 5-HTP suppressive effect on photosensitivity is at least partly due to reduced neuronal activity at the level of the LGN via serotonergic inhibition.     

Intranasal delivery of a thyrotropin-releasing hormone analog attenuates seizures in the amygdala-kindled rat

PURPOSE: Thyrotropin-releasing hormone (TRH) is known to have anticonvulsant effects in several animal seizure models and is efficacious in treating patients with certain intractable epilepsies. However, the duration of TRH's action is limited due to low bioavailability and difficulty penetrating the blood-brain barrier (BBB). Since direct nose to brain delivery of therapeutic compounds may provide a means for overcoming these barriers, we utilized the kindling model of temporal lobe epilepsy to determine if intranasal administration of a TRH analog, 3-methyl-histidine TRH (3Me-H TRH), could significantly inhibit various seizure parameters. METHODS: Kindling was accomplished using a 1s train of 60 Hz biphasic square wave (200 microA peak to peak) administered daily to the basolateral amygdala until the animal was fully kindled. Afterdischarge duration (ADD) was assessed via electroencephalographs (EEGs) recorded bilaterally from bipolar electrodes in the basolateral amygdala and behavioral seizure severity (stage I-V) was simultaneously recorded digitally. Kindled subjects received 3Me-H TRH (10(-9), 10(-8), 10(-7) M) intranasally 60 and 30 min prior to amygdala stimulation. The ADD and seizure stage was compared to control kindled animals receiving physiological saline intranasally. RESULTS: Intranasal application of 3Me-H TRH resulted in a concentration-dependent reduction in total seizure ADD. Additionally, the analog had significant concentration-dependent effects on behavioral stages I through IV (partial) and stage V (generalized) seizures. However, 3Me-H TRH significantly reduced clonus duration only at the highest concentration. DISCUSSION: The results indicate that intranasal delivery of TRH/analogs may be a viable means to suppress temporal lobe seizures and perhaps other seizure disorders.     

Low-frequency stimulation of the hippocampal CA3 subfield is anti-epileptogenic and anti-ictogenic in rat amygdaloid kindling model of epilepsy

Neuromodulation with low-frequency stimulation (LFS), of brain structures other than epileptic foci, is effective in inhibiting seizures in animals and patients, whereas selection of targets for LFS requires further investigation. The hippocampal CA₃ subfield is a key site in the circuit of seizure generation and propagation. The present study aimed to illustrate the effects of LFS of the CA₃ region on seizure acquisition and generalization in the rat amygdaloid kindling model of epilepsy. We found that LFS (monophasic square-wave pulses, 1 Hz, 100 μA and 0.1 ms per pulse) of the CA₃ region significantly depressed the duration of epileptiform activity and seizure acquisition by retarding progression from focal to generalized seizures (GS). Moreover, GS duration was significantly shortened and its latency was significantly increased in the LFS group demonstrating an inhibition of the severity of GS and the spread of epileptiform activity. Furthermore, LFS prevented the decline of afterdischarge threshold (ADT) and elevated GS threshold indicating an inhibition of susceptibility to GS. These results suggest that LFS of the hippocampal CA₃ subfield is anti-epileptogenic and anti-ictogenic. Neuromodulation of CA₃ activity using LFS may be an alternative potential approach for temporal lobe epilepsy treatment.     

The Effects of Topiramate on Caspase-3 Expression in Hippocampus of Basolateral Amygdala (BLA) Electrical Kindled Epilepsy Rat

Caspase-3 expression was determined in the hippocampus of electrically kindled rats with and without topiramate treatment. Bipolar electrotrodes were implanted for chronic stimulation of the basolateral amygdala (BLA) to achieve a kindled state. Seizure and behavioral responses were observed, and video-electroencephalograms were recorded during and after kindling. After topiramate treatment (80 mg/kg, p.o.), the hippocampi were extracted and caspase-3 mRNA analyzed by semiquantitative RT-PCR. Caspase-3 immunoreactivity was determined with immunohistochemical staining. Topiramate treatment resulted in a significant decrease in the mean duration of seizures from 52 s in kindled rats to 13 s. The after-discharge duration was significantly decreased by 70% after topiramate treatment. Significant upregulations of both caspase-3 mRNA and caspase-3 immunoreactivity were observed in the kindled rats. These kindling-mediated increases in caspase-3 were prevented by topiramate treatment, and these levels were not different from those of sham-operated controls. In BLA-kindled rats, mRNA and immunoreactivity for caspase-3 were increased. Treatment with topiramate prevented the kindling-associated increases in caspase-3 as well as the increases in seizure duration and after-discharge duration. These data suggest that topiramate may have a neuroprotective role in addition to its action as an anticonvulsant.     

Behavioral depression induced by an amygdala seizure and the opioid fentanyl was mediated through the nucleus accumbens

Purpose:  To study the behavioral depression induced by a generalized limbic seizure and by an opioid. The hypothesis that an opioid fentanyl and an amygdala-evoked seizure induced behavioral depression through the nucleus accumbens was tested.
Methods:  The behavioral depression induced by an amygdala-kindled seizure was studied in fully kindled rats, with or without prior injection of fentanyl (0.05 mg/kg, s.c.). Local infusion of a nonspecific opioid antagonist, naloxone, or saline, was made bilaterally in the nucleus accumbens. The durations of loss of righting reflex (LORR), loss of tail-pinch response, and catalepsy were assessed.
Results:  Fentanyl induced an LORR following a generalized kindled seizure. The combination of fentanyl and a generalized seizure, as compared to fentanyl alone or a generalized seizure alone, resulted in a prolonged duration of LORR, catalepsy, and loss of tail pinch response. Infusion of naloxone as compared to saline in the nucleus accumbens reduced the duration of catalepsy and LORR induced by fentanyl, with or without a generalized seizure.
Conclusions:  Postictal depression that follows a generalized kindled seizure enhanced the behavioral effects of the opioid fentanyl. Network synaptic depression induced by the seizure acted synergistically with fentanyl to produce analgesia, catalepsy, and LORR, in part through the nucleus accumbens.     

Temporal profile of CRE DNA-binding activity in the rat hippocampus following a kindling stimulation

This study was designed to establish a role for cAMP-responsive element (CRE) binding protein (CREB) in signal transduction cascade in the hippocampus associated with kindling. Male Sprague–Dawley rats were kindled from the left amygdala until they exhibited Racine’s class 5 generalized seizures [Racine (1972). EMBO J. 11, 3337–3346] Nuclear proteins were extracted from dorsal hippocampi obtained from 0 to 24 h after final kindling stimulation. From these, we evaluated the temporal pattern of CRE DNA-binding activity by use of a gel mobility-shift assay with a ³²P-labeled CREB oligonucleotide probe. CRE-binding activity in the hippocampus was enhanced significantly at 2 h and returned to baseline level within 4 h after the stimulation. Our results suggest that CREB may be involved in the hippocampal signal transduction pathway of rats activated in response to a kindling stimulation to the amygdala. However, the transient elevation of CRE-binding activity following a seizure in a kindled animal also suggests that persistent activation of CREB may not be required for maintenance of the kindling phenomenon.