Daniela Pechlivanova

Prophylactic treatment with melatonin after status epilepticus: Effects on epileptogenesis, neuronal damage, and behavioral changes in a kainate model of temporal lobe epilepsy

Melatonin is a potent antioxidant which showed anticonvulsant activities both in experimental and clinical studies. In the present study, we examined the effect of melatonin treatment (10mg/kg/day, diluted in drinking water, 8 weeks) during epileptogenesis on the consequences of a kainate (KA)-induced status epilepticus (SE) in rats. Melatonin increased the latency in the appearance of spontaneous recurrent seizures (SRSs) and decreased their frequency only during the treatment period. The behavioral alterations associated with hyperactivity, depression-like behavior during the light phase, and deficits in hippocampus-dependent working memory were positively affected by melatonin treatment in rats with epilepsy. Melatonin reduced the neuronal damage in the CA1 area of the hippocampus and piriform cortex and recovered the decrease of hippocampal serotonin (5-HT) level in rats with epilepsy. Taken together, long-term melatonin treatment after SE was unable to suppress the development of epileptogenesis. However, it showed a potential in reducing some of the deleterious alterations that develop during the chronic epileptic state in a diurnal phase-dependent mode.

Dose-dependent effects of caffeine on behavior and thermoregulation in a chronic unpredictable stress model of depression in rats.

The effects of the non-selective adenosine A(1)/A(2) receptor antagonist caffeine on behavior and thermoregulation in chronic unpredictable stress (CUS) model of depression was studied in Wistar rats. In the open field (OF) test, caffeine dose-dependently increased motor activity while decreased grooming and time spent in the corner. Five-week exposure to CUS procedure had the opposite effect in rats. Caffeine reversed CUS-induced effects on the above mentioned parameters. Caffeine (40 mg/kg) increased the motor activity in plus maze (PM) test while at doses of 20 and 40 mg/kg it decreased the number of entries in the open arms. Whereas CUS did not change the level of anxiety, caffeine (2, 20 and 40 mg/kg) administered after CUS diminished it by increasing the time in open arms. Caffeine dose-dependently decreased the immobility time while CUS had the opposite increasing effect in forced swimming test (FST). Caffeine at doses of 20 and 40 mg/kg reversed the effect of CUS on immobility in FST. Caffeine produced dose-dependent rice of body temperature in both non-treated and CUS-treated rats. The hyperthermic effect in normal rats pretreated with caffeine lasted about 90 min while in caffeine-pretreated rats exposed to CUS it lasted about 150 min. High dose of caffeine (100mg/kg) induced significant hypothermia between 90th and 150th minute in control rats and hyperthermia between 30th and 60th minute in CUS-treated rats. These results suggest a putative role of this methylxanthine in the adaptive responses to chronic unpredictable stress stimuli.

Effect of long-term caffeine administration on depressive-like behavior in rats exposed to chronic unpredictable stress.

Chronic unpredictable stress (CUS) was used to study the effects of a long-term treatment with either caffeine (8 mg/kg, orally) or desipramine (DMI) (10 mg/kg, intraperitoneally) in Wistar rats. The CUS procedure was applied for 6 weeks. Animals underwent a 2-week drug-free CUS procedure. Drugs were administered for 4 weeks alongside the stress and both drug and stress were continued throughout the behavioral testing period. CUS-exposed rats showed depressive-like behavior with reduced weight gain, reduced consumption of sucrose solution, increased immobility in the forced swimming test, and hypolocomotion in an open field. For the open field and elevated plus maze, calculation of an anxiety index confirmed that CUS increased anxiety, which was accompanied by an increase in the core temperature. DMI counteracted these physical and behavioral changes. Caffeine caused similar effects to DMI on weight gain, motor activity, anxiety level, and core temperature. In CUS-exposed rats, caffeine showed antidepressant and anxiolytic activity, accompanied by increased hippocampal dopamine and serotonin levels. However, no significant change in weight gain or core temperature was observed after caffeine treatment in CUS-exposed rats. These results suggest that, similar to the antidepressant DMI, long-term caffeine exposure exerts an antidepressant and anxiolytic effect in the CUS model. The involvement of the dopaminergic and serotonergic systems is discussed.

Diurnal variations in depression-like behavior of Wistar and spontaneously hypertensive rats in the kainate model of temporal lobe epilepsy

The purpose of this study was to explore whether the kainate (KA) model of temporal lobe epilepsy (TLE) can be used as a model of comorbid epilepsy and depression to study diurnal behavioral variations in rats. Development of chronic epilepsy was confirmed by the detection of spontaneous motor seizures (SMS) with video monitoring (24 hours/3-5 months after status epilepticus [SE]). KA-treated spontaneously hypertensive rats (SHRs) exhibited higher seizure frequency than Wistar rats during the light phase in the fourth and fifth months after SE. Although epileptic Wistar rats showed depression-like behavior and reduced anxiety mostly during the light phase, there were no diurnal variations in depression-like patterns in SHRs. Anxiety levels of control and epileptic SHRs were similar. Decreases in serotonin, tryptophan, and dopamine concentrations in the hippocampus were detected in epileptic Wistar rats compared with naive controls. However, monoamine levels of epileptic SHRs were close to those of their controls. Wistar rats and SHRs develop stable depression-like behavior during the chronic epileptic phase with strain-dependent diurnal differences.

Diurnal rhythms of spontaneous recurrent seizures and behavioral alterations of Wistar and spontaneously hypertensive rats in the kainate model of epilepsy

Attention deficit hyperactivity disorder (ADHD) can coexist with epilepsy. Spontaneously hypertensive rats (SHRs) are considered to model ADHD with overactivity, impulsiveness, deficient sustained attention, and alterations in circadian autonomic profiles. The present study explored spontaneous recurrent seizures (SRSs) and behavioral diurnal activity rhythms in normotensive Wistar rats and SHRs in the kainate model of epilepsy. Rats were video monitored (24 h/3 months) to detect SRSs. SHRs manifested a lower seizure frequency during the light phase in the 8th and 10th weeks and a lower frequency of SRSs during the night phase accompanied by attenuated responses in hyperexcitability tests. Both epileptic strains were hyperactive, with lower anxiety levels, and their diurnal rhythms were abolished. Epileptic Wistar rats and SHRs exhibited less exploration during the dark phase. This study suggests that SHRs may be useful in modeling some aspects (particularly hypertension-related diurnal rhythm disturbance) of behavior associated with epilepsy.

The effects of sarmesin, an Angiotensin II analogue on seizure susceptibility, memory retention and nociception

The present research studies the effects of sarmesin [Sar(1)Tyr(OMe)(4)] Angiotensin II (ANG II), an analogue of ANG II, on the seizure susceptibility, memory activity and nociception. It was found that this octapeptide, administered i.c.v., dose-dependently decreased the seizure intensity (pentylenetetrazol (PTZ) generalized seizure model and PTZ kindling) and augmented PTZ seizure threshold in mice. Sarmesin impaired the memory upon re-testing of rats 24 h later in the passive avoidance test. It decreased the pain threshold in a paw pressure nociceptive assay in rats. ANG II exerted pronociceptive effect as well. Taken together, these results reveal sarmesin as a behaviorally active peptide in the studied experimental animal models.

Treatment with melatonin after status epilepticus attenuates seizure activity and neuronal damage but does not prevent the disturbance in diurnal rhythms and behavioral alterations in spontaneously hypertensive rats in kainate model of temporal lobe epilepsy.

Melatonin is involved in the control of circadian and seasonal rhythmicity, possesses potent antioxidant activity, and exerts a neuroprotective and anticonvulsant effect. Spontaneously hypertensive rats (SHRs) are widely accepted as an experimental model of essential hypertension with hyperactivity, deficient sustained attention, and alterations in circadian autonomic profiles. The purpose of the present study was to determine whether melatonin treatment during epileptogenesis can prevent the deleterious consequences of status epilepticus (SE) in SHRs in the kainate (KA) model of temporal lobe of epilepsy (TLE). Spontaneous recurrent seizures (SRSs) were EEG- and video-recorded during and after the treatment protocol. Melatonin (10mg/kg diluted in drinking water, 8weeks) increased the seizure-latent period, decreased the frequency of SRSs, and attenuated the circadian rhythm of seizure activity in SHRs. However, melatonin was unable to affect the disturbed diurnal rhythms and behavioral changes associated with epilepsy, including the decreased anxiety level, depression, and impaired spatial memory. Melatonin reduced neuronal damage specifically in the CA1 area of the hippocampus and piriform cortex and decreased hippocampal serotonin (5-HT) levels both in control and epileptic SHRs. Although long-term melatonin treatment after SE shows a potential to attenuate seizure activity and neuronal loss, it is unable to restore epilepsy-associated behavioral abnormalities in SHRs.

Strain-dependent effects of long-term treatment with melatonin on kainic acid-induced status epilepticus, oxidative stress and the expression of heat shock proteins.

Oxidative stress is implicated in the pathogenesis of both hypertension and epileptogenesis, therefore it could be used as a tool for studying co-morbidity of hypertension and epilepsy. Clinical data suggest that melatonin is a potent antioxidant that is effective in the adjunctive therapy of hypertension and neurodegenerative diseases. The present study aimed to explore and compare the efficacy of chronic pretreatment with melatonin infused via subcutaneous osmotic mini-pumps for 14 days (10 mg/kg per day) on kainic acid (KA)-induced status epilepticus, oxidative stress and expression of heat shock protein (HSP) 72 in spontaneously hypertensive rats (SHRs) and normotensive Wistar rats. SHRs showed higher lipid peroxidation (LP) in the frontal cortex and hippocampus and decreased cytosolic superoxide dismutase (SOD/CuZn) production in the frontal cortex compared to Wistar rats. Status epilepticus (SE) induced by KA (12 mg/kg, i.p.) was accompanied by increased LP and expression of HSP 72 in the hippocampus of the two strains and increased SOD/CuZn production in the frontal cortex of SHRs. Melatonin failed to suppress seizure incidence and intensity though the latency for seizure onset was significantly increased in SHRs. Melatonin attenuated the KA-induced increase in the level of LP in the hippocampus both in SHRs and Wistar rats. However, an increased activity in SOD/CuZn and mitochondrial SOD Mn as well as reduced expression of HSP 72 in the hippocampus was observed only in Wistar rats pretreated with melatonin. Taken together, the observed strain differences in the efficacy of chronic melatonin exposure before SE suggest a lack of a direct link between the seizure activity and the markers of oxidative stress and neurotoxicity.

Antiepileptogenic and neuroprotective effects of losartan in kainate model of temporal lobe epilepsy

Recently, we have shown that the blockade of AT1 receptor might be useful as an adjuvant treatment strategy for the prevention of oxidative stress and neurotoxicity caused by status epilepticus (SE) in rats. The purpose of the present study was to further assess the efficacy of long-term treatment with losartan (10mg/kg), the selective AT1 receptor antagonist, during kainate (KA)-induced epileptogenesis in Wistar rats. Losartan treatment started after onset of SE and continued for 4weeks. The rats were video- and EEG-recorded for 3months. Locomotor activity, anxiety and depressive-like behavior were evaluated 9weeks after SE, when all rats had developed chronic epileptic state. Neuronal damage in hippocampus was analyzed by hematoxylin while serotonin (5-HT) levels in hippocampus by HPLC. AT1 receptor antagonism increased the latent seizure-free period and decreased the frequency of spontaneous motor seizures. Losartan positively affected epilepsy-provoked behavioral changes, including impulsivity, low anxiety level and depression in a phase-dependent manner and restored the changes in diurnal fluctuation of motor activity. Losartan exerted neuroprotection selectively in the CA1 area of the hippocampus in the KA-treated rats and lowered the 5-HT levels both in normal and abnormal conditions. Our findings suggest that the AT1 receptor antagonist exerts disease-modifying effects during KA-induced epileptogenesis and neuronal damage in CA1 hippocampal area, attenuated some of the behavioral changes and restored diurnal variability in locomotor activity.

Interaction of angiotensin II and adenosine A1 and A2A receptor ligands on the writhing test in mice

The effects of adenosine A1 and A2A receptor agonists and antagonists administered intraperitoneally (i.p.) and their interaction with angiotensin II (Ang II) administered intracerebroventricularly (i.c.v.) were studied in mice using the acetic acid-induced abdominal constriction test. Ang II (0.1 microg/mouse) induced antinociception in this model. The adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA; 0.05, 0.25 and 0.5 mg/kg) also showed a well-developed antinociceptive effect. Ang II (0.1 microg/mouse) administered 5 min before CPA (0.25 mg/kg) decreased the number of writhes, i.e., it enhanced the antinociceptive effect of CPA. Losartan, an AT1 receptor antagonist (25 microg/mouse i.c.v.), enhanced the antinociceptive effect of CPA, while the AT2 receptor antagonist 1-[-4-(dimethylamino)-3-methylphenylmethyl]-5-diphenylacetyl)-4,5,6,7-tetrahydro 1H-4-imidazol [4,5c]pyridine-6 carboxylic acid, ditrifluoroacetate, dihydrate (PD 123319; 10 microg/mouse) had less effect. 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.1 mg/kg), an adenosine A1 receptor antagonist, exhibited a pronociceptive effect and did not change the antinociceptive effect of Ang II. The adenosine A2A receptor agonist PD-125944 (DPMA; 0.1, 0.5 and 1 mg/kg) showed pronounced antinociceptive effect. Ang II (0.1 microg/mouse) did not significantly influence the antinociceptive effect of DPMA (0.1 mg/kg). The A2A receptor antagonist 3,7-dimethyl-1-propargilxanthine (DMPX; 0.1 mg/kg) had no effect on the number of writhes and did not influence the effect of Ang II. These data indicate that the antinociceptive effect of Ang II interacts with that produced by adenosine A1 receptor agonist.