Pathogenesis and pharmacology of epilepsy in the lithium-pilocarpine model.

To try to identify the critical structures during epileptogenesis, we used the lithium-pilocarpine model that reproduces most clinical and neuropathological features of temporal lobe epilepsy (TLE). We used imaging techniques as well as a disease modifying approach and pharmacological strategy. With [14C]-2-deoxyglucose autoradiography, we assessed changes in cerebral glucose utilization. T2-weighted magnetic resonance imaging (MRI, 4.7 T) allowed follow-up of structures involved in epileptogenesis. A potential disease-modifying effect was studied using preconditioning with brief seizures (amygdala kindling, maximal electroshocks) and pharmacological strategies including vigabatrin (250 mg/kg), caffeine (0.3 g/L in drinking water), topiramate (10-60 mg/kg), pregabalin (50 mg/kg followed by 10 mg/kg), or RWJ-333369 (10-120 mg/kg). In adult and PN21 rats that became epileptic, entorhinal, and piriform cortices were the initial structures exhibiting significant signal changes on MRI scans, from 6 h after status epilepticus (SE) onset, reflecting neuronal death. In PN21 rats that did not become epileptic, no signal occurred in parahippocampal cortices. In hippocampus, MRI signal change appeared 36-48 h after SE, and progressively worsened to sclerosis. During the latent and chronic phases, the metabolic level in the hilus of adult and PN21 epileptic rats was normal although neuronal loss reached 60-75%. Protection limited to CA1 and/or CA3 (caffeine, topiramate, vigabatrin, amygdala kindling) did not affect the latency to spontaneous seizures. Protection limited to the entorhinal and piriform cortices (pregabalin) delayed epileptogenesis. The combined protection of Ammon's horn and parahippocampal cortices (RWJ-333369) prolonged the latency before the onset of seizures in a dose-dependent manner or, in some cases, prevented the epilepsy. The entorhinal and piriform cortices are critically involved in the early phase of the epileptogenesis while the hilus may initiate and/or maintain epileptic seizures. Pharmacological protection of the basal cortices is necessary for a beneficial disease-modifying effect but this must be combined with protection of the hippocampus to prevent epileptogenesis in this model of TLE.

Acute and chronic changes in glycogen phosphorylase in hippocampus and entorhinal cortex after status epilepticus in the adult male rat.

Glial cells provide energy substrates to neurons, in part from glycogen metabolism, which is influenced by glycogen phosphorylase (GP). To gain insight into the potential subfield and laminar-specific expression of GP, histochemistry can be used to evaluate active GP (GPa) or totalGP (GPa + GPb). Using this approach, we tested the hypothesis that changes in GP would occur under pathological conditions that are associated with increased energy demand, i.e. severe seizures (status epilepticus or 'status'). We also hypothesized that GP histochemistry would provide insight into changes in the days and weeks after status, particularly in the hippocampus and entorhinal cortex, where there are robust changes in structure and function. One hour after the onset of pilocarpine-induced status, GPa staining was reduced in most regions of the hippocampus and entorhinal cortex relative to saline-injected controls. One week after status, there was increased GPa and totalGP, especially in the inner molecular layer, where synaptic reorganization of granule cell mossy fibre axons occurs (mossy fibre sprouting). In addition, patches of dense GP reactivity were evident in many areas. One month after status, levels of GPa and totalGP remained elevated in some areas, suggesting an ongoing role of GP or other aspects of glycogen metabolism, possibly due to the evolution of intermittent, recurrent seizures at approximately 3-4 weeks after status. Taken together, the results suggest that GP is dynamically regulated during and after status in the adult rat, and may have an important role in the pilocarpine model of epilepsy.

Pentylenetetrazol-induced status epilepticus up-regulates the expression of glucose transporter mRNAs but not proteins in the immature rat brain.

Prolonged pentylenetetrazol (PTZ)-induced seizures increase cerebral energy demands in a region-specific manner. During PTZ seizures, cerebral glucose utilization increases over control levels in all brain regions at 10 days while 21-day-old rats exhibit increases, decreases or no change. To explore the effects of such acute changes in metabolic demand on the expression of glucose transporter proteins mediating glucose delivery to brain, we studied the consequences of PTZ seizures on GLUT1 and GLUT3 mRNAs and proteins between 1 and 72 h after seizure induction. At both ages, seizures induced a rapid up-regulation of GLUT1 and GLUT3 mRNAs which was prominent at 1 and 4 h, and was greater at 10 than at 21 days. By 24 h and 72 h, the levels of the mRNAs of the two transporter returned to control levels or were slightly down-regulated. The levels of GLUT1 and GLUT3 proteins were not affected by the seizures and only scattered decreases in GLUT3 protein were recorded, mainly in midbrain-brainstem areas. These data show that acute pentylenetetrazol seizures induce a rapid up-regulation of the GLUT1 and GLUT3 mRNAs, but do not result in measurable increases in protein levels, suggesting translational regulation.

Seizure susceptibility in intact and ovariectomized female rats treated with the convulsant pilocarpine.

Despite numerous neuroendocrinological studies of seizures, the influence of estrogen and progesterone on seizures and epilepsy remains unclear. This may be due to the fact that previous studies have not systematically compared distinct endocrine conditions and included all relevant controls. The goal of the present study was to conduct such a study using pilocarpine as chemoconvulsant. Thus, age and weight-matched, intact or ovariectomized rats were tested to determine incidence of status epilepticus and to study events leading to status. Intact female rats were sampled at each cycle stage (proestrus, estrus, metestrus, or diestrus 2). Convulsant was administered at the same time of day, 10:00-10:30 a.m. Statistical analysis showed that there was a significantly lower incidence of status on the morning of estrus, but differences were attenuated in older animals. Ovariectomized rats were distinct in their rapid progression to status. These results show that the incidence of status in female rats following pilocarpine injection, and the progression to pilocarpine-induced status, are influenced by reproductive state as well as age. The hormonal milieu present specifically on the morning of estrus appears to decrease susceptibility to pilocarpine-induced status, particularly at young ages. In contrast, the chronic absence of reproductive steroids that characterizes the ovariectomized rat leads to a more rapid progression to status. This dissociation between incidence vs. progression provides new insight into the influence of estrogen and progesterone on seizures.

Long-term pregabalin treatment protects basal cortices and delays the occurrence of spontaneous seizures in the lithium-pilocarpine model in the rat.

PURPOSE: To determine whether a pharmacologic treatment could delay or prevent the epileptogenesis induced by status epilepticus (SE) through the protection of some brain areas, we studied the effects of the long-term exposure to pregabalin (PGB) on neuronal damage and epileptogenesis induced by lithium-pilocarpine SE. METHODS: SE was induced in adult and 21-day-old (P21) rats. At 20 min after pilocarpine, rats received 50 mg/kg PGB (pilo-preg) or saline (pilo-saline). PGB treatment was given daily at the dose of 50 mg/kg for 7 days after SE and at 10 mg/kg from day 8 until killing. Neuronal damage was assessed in hippocampus and piriform and entorhinal cortices in brain sections stained with thionine and obtained from adult and P21 animals killed 6 days after SE. The number of glial fibrillary acidic protein (GFAP)-reactive astrocytes was tested by immunohistochemistry in sections adjacent to those used for cell counting. The latency to spontaneous seizures was controlled by visual observation and EEG recording. RESULTS: PGB induced neuroprotection in layer II of piriform cortex and layers III-IV of ventral entorhinal cortex of adult rats, whereas no hippocampal region was protected. In P21 rats, damage was limited to the hilus and similar in pilo-preg and pilo-saline animals. The number of GFAP-positive astrocytes was higher in pilocarpine- than in saline-treated rats. It was decreased in pilo-preg compared with pilo-saline rats in layer II of the piriform cortex. Adult pilo-preg rats became epileptic after a longer latency (39 days) than did pilo-saline rats (22 days). CONCLUSIONS: These data underline the antiepileptogenic consequences of long-term PGB treatment, possibly mediated by the protection of piriform and entorhinal cortices in the lithium-pilocarpine model of epilepsy.

Prolonged low-dose caffeine exposure protects against hippocampal damage but not against the occurrence of epilepsy in the lithium-pilocarpine model in the rat.

PURPOSE: Acute caffeine exposure has proconvulsant effects and worsens epileptic and ischemic neuronal damage. Surprisingly, prolonged caffeine exposure decreases the susceptibility to seizures and the extent of ischemic damage. We explored whether the exposure to a low long-term dose of caffeine could protect the brain from neuronal damage and epileptogenesis in the lithium-pilocarpine model of temporal lobe epilepsy. METHODS: Rats received either plain tap water or water containing caffeine (0.3 g/L) for 15 days before the induction of status epilepticus (SE) by lithium-pilocarpine and for 7 days after SE. The extent of neuronal damage was assessed in the hippocampus and piriform and entorhinal cortices in brain sections stained with thionine and obtained from animals killed 7 days after SE. The latency to spontaneous recurrent seizures was controlled by video monitoring. RESULTS: Caffeine treatment induced a marked, almost total neuroprotection in CA1 and a very limited protection in the hilus of the dentate gyrus, whereas damage in layers III-IV of the piriform cortex was slightly worsened by the treatment. All rats, whether they received caffeine or plain tap water, became epileptic after the same latency (17-19 days). CONCLUSIONS: Thus these data extend the neuroprotective effects of low long-term caffeine exposure to epileptic damage and confirm that the sole protection of the Ammon's horn has no influence on the genesis of spontaneous recurrent seizures in this model.

Effects of topiramate in two models of genetically determined generalized epilepsy, the GAERS and the Audiogenic Wistar AS.

PURPOSE: The antiepileptic effects of topiramate (TPM) were assessed in two models of genetically determined generalized epilepsy. The model of nonconvulsive epilepsy used was a model of absence seizures, the GAERS (Genetic Absence Epilepsy Rat from Strasbourg); and the model of convulsive seizures was an audiogenic rat model, the Wistar Audiogenic Sensitive (AS) rat. METHODS: GAERS were equipped with four cortical electrodes over the frontoparietal cortex, and the duration of spike-and-wave discharges (SWDs) on the EEG was recorded for periods of 20 to 120 or 300 min. In Wistar AS, the occurrence of, latency to, and duration of one or two wild running episodes and tonic seizures were recorded. RESULTS: In the 16 GAERS studied, TPM (10, 30, and 60 mg/kg) dose-dependently reduced the expression of SWD that almost totally disappeared at the two highest doses between 40 and 120 min. SWD duration returned to control levels by 180 and 280 min after the injection of 30 and 60 mg/kg TPM, respectively. In Wistar AS, 10 mg/kg TPM induced the occurrence of a second running episode not present in control rats, indicative of a decrease in sensitivity of the rats to the stimulus and increased by 330% the latency to the tonic seizure that still occurred in the eight rats studied. At 30 and 60 mg/kg, the latency to wild running increased by 140%; the second running episode was suppressed in six and seven rats, respectively, whereas the tonic seizure occurred only in one of the eight rats studied at these two doses. CONCLUSIONS: These results support the broad spectrum of antiepileptic activity of TPM, confirming its efficacy in primary generalized seizures of both tonic-clonic and of the absence type.