Differential contribution of cholecystokinin receptors to stress-induced modulation of seizure and nociception thresholds in mice

Impact of Stress on Epilepsy: Focus on Neuroinflammation-A Mini Review

Epilepsy, one of the most common neurological disorders worldwide, is characterized by recurrent seizures and subsequent brain damage. Despite strong evidence supporting a deleterious impact on seizure occurrence and outcome severity, stress is an overlooked component in people with epilepsy. With regard to stressor duration and timing, acute stress can be protective in epileptogenesis, while chronic stress often promotes seizure occurrence in epilepsy patients. Preclinical research suggests that chronic stress promotes neuroinflammation and leads to a depressive state. Depression is the most common psychiatric comorbidity in people with epilepsy, resulting in a poor quality of life. Here, we summarize studies investigating acute and chronic stress as a seizure trigger and an important factor that worsens epilepsy outcomes and psychiatric comorbidities. Mechanistic insight into the impact of stress on epilepsy may create a window of opportunity for future interventions targeting neuroinflammation-related disorders.

Transcranial direct current stimulation (tDCS) affects neuroinflammation parameters and behavioral seizure activity in pentylenetetrazole-induced kindling in rats

Despite the introduction of new antiepileptic drugs, about 30 % of patients with epilepsy are refractory to drug therapy. Thus, the search for non-pharmacological interventions such as transcranial direct current stimulation (tDCS) may be an alternative, either alone or in combination with low doses of anticonvulsants. This study evaluated the effect of anodal (a-tDCS) and cathodal tDCS (c-tDCS) on seizure behavior and neuroinflammation parameters. Rats were submitted to the kindling model induced by pentylenetetrazole (PTZ) using diazepam (DZP) as anticonvulsant standard. tDCS groups were submitted to 10 sessions of a-tDCS or c-tDCS or SHAM-tDCS. Every 3 days they received saline (SAL), low dose of DZP (alone or in combination with tDCS) or effective dose of DZP 30 min before administration of PTZ, totaling 16 days of protocol. Neither a-tDCS nor c-tDCS reduced the occurrence of clonic forelimb seizures (convulsive motor seizures - stage 3 by the adapted Racine scale we based on). Associated with DZP, c-tDCS (c-tDCS/DZP0.15) increased the latency to first clonic forelimb seizure on the 10th and 16th days. Hippocampal IL-1β levels were reduced by c-tDCS and c-tDCS/DZP0.15. In contrast, these treatments induced an increase in cortical IL-1β levels. Hippocampal TNF-α levels were not altered by c-tDCS or a-tDCS, but c-tDCS and c-tDCS/DZP0.15 increased those levels in cerebral cortex. Cortical NGF levels were increased by c-tDCS and c-tDCS/DZP0.15. a-tDCS/DZP0.15 reduced hippocampal BDNF levels and c-tDCS/DZP0.15 increased these levels in cerebral cortex. In conclusion, c-tDCS alone or in combination with a low dose of DZP showed to affect neuroinflammation, improving central neurotrophin levels and decreasing hippocampal IL-1β levels after PTZ-induced kindling without statistically significant effect on seizure behavior.

Acute foot-shock stress decreased seizure susceptibility against pentylenetetrazole-induced seizures in mice: Interaction between endogenous opioids and cannabinoids

BACKGROUND

Stressful conditions affect the brain's neurotransmission and neural pathways that are involved in seizure susceptibility. Stress alters the intensity and/or frequency of seizures. Although evidence indicates that chronic stress exerts proconvulsant effects and acute stress has anticonvulsant properties, the underlying mechanisms which mediate these effects are not well understood. In the present study, we assessed the role of endogenous opioids, endocannabinoids, as well as functional interaction between opioid and cannabinoid systems in the anticonvulsant effects of acute foot-shock stress (FSS) against pentylenetetrazole (PTZ)-induced seizures in mice.

METHODS

Prolonged intermittent FSS was chosen as an acute stress model. Seizure threshold was determined after 30 min of stress induction in male Naval Medical Research Institute (NMRI) mice (20-30 g). Opioid and cannabinoid receptor antagonists were administered before animal placement in the FSS apparatus.

RESULTS

Acute FSS significantly decreased seizure susceptibility in animals. The administration of the cannabinoid receptor 1 (CB₁) antagonist, AM251, completely blocked the anticonvulsant effect of acute FSS at the doses of 1 pg/kg-100 μg/kg but not at 1 fg/kg. Pretreatment with the nonspecific opioid receptor antagonist, naltrexone (NTX), significantly inhibited the anticonvulsant effects of acute FSS at 1 and 2 mg/kg but not at 0.3 mg/kg. However, coadministration of the subeffective doses of AM251 (1 fg/kg) and NTX (0.3 mg/kg) reversed the anticonvulsant effects of acute FSS.

CONCLUSIONS

Opioid and cannabinoid systems are involved in the anticonvulsant effects of acute FSS, and these neurotransmission systems interact functionally in response to acute FSS.

Improving effect of mild foot electrical stimulation on pentylenetetrazole-induced impairment of learning and memory

Epilepsy is a common neurological disorder that affects learning and memory. Recently it has been shown that mild foot electrical stimulation (MFES) can increase learning and memory in normal rats. Pentylenetetrazole (PTZ) kindling is a model of human epilepsy. As with human epilepsy, PTZ kindling impairs learning and memory in rats. The purpose of this study was to investigate the effect MFES on kindling-induced learning and memory deficits in rats. Forty-nine male Wistar rats weighting 200 to 250 g were divided into the following seven groups: PTZ only, phenytoin only, MFES only, PTZ plus phenytoin, PTZ plus MFES, phenytoin plus MFES, and saline (control), with the treatments administered for 26 days. Forty-eight hours after the last injection, the animals performed the Morris water maze (MWM) task, and spatial learning and memory were measured. The results indicated that although chronic administration of phenytoin inhibited the development of PTZ kindling, it did not exert a protective effect against kindling-induced spatial learning and memory impairment in rats. On the other hand, pretreatment of PTZ-kindled animals with MFES significantly improved spatial working and reference memory. The results point to potential novel beneficial effects of MFES on learning and memory impairment induced by PTZ kindling in rats.

Effect of PaCO2 and PaO2 on lidocaine and articaine toxicity

Alterations in arterial PaCO₂ can influence local anesthetic toxicity. The objective of this study was to evaluate the effect of stress-induced changes in PaCO₂ and PaO₂ on the seizure threshold of lidocaine and articaine. Lidocaine (2% with 1 : 100,000 epinephrine) or articaine (4% with 1 : 100,000 epinephrine) was administered intravenously under rest or stress conditions to 36 rats separated into 4 groups. Propranolol and prazosin were administered preoperatively to minimize cardiovascular effects of epinephrine. Mean arterial pressure (MAP), heart rate (HR), and arterial pH, PaCO₂, and PaO₂ were measured. Results showed no differences in MAP, HR, or pH. Stress significantly increased the latency period for the first tonic-clonic seizure induced by a toxic dose of both lidocaine and articaine (P < .05). Seizures were brought on more rapidly by articaine. No significant difference between toxic doses of lidocaine and articaine was noted. Stress raised the seizure threshold dose for both drugs and significantly (P < .01) increased arterial PaO₂ from 94.0 ± 1.90 mm Hg to 113.0 ± 2.20 mm Hg, and reduced PaCO₂ from 36.0 ± 0.77 mm Hg to 27.0 ± 0.98 mm Hg. In conclusion, reduction in PaCO₂ and/or increase in PaO₂ raised the seizure threshold of lidocaine and articaine. This study also confirmed that lidocaine and articaine have equipotent central nervous system toxicity.

Cholecystokinin-8 sulfate modulates the anticonvulsant efficacy of vigabatrin in an experimental model of partial complex epilepsy in the rat

PURPOSE

We evaluated the possible additive effect induced by the administration of the anticonvulsant vigabatrin (VGB) and cholecystokinin-8 sulfate (CCK-8S) on an experimental model of partial complex seizures (maximal dentate gyrus activation, MDA). Moreover, the functional involvement of gamma-aminobutyric acid (GABA) neurotransmission was tested by iontophoretically administering bicuculline (GABA receptor antagonist) in the dentate gyrus.

METHODS

Urethane anesthetized rats were pretreated with VGB (50, 100 or 200 mg/kg, i.p.) or CCK-8S (8 nmol/kg, i.p.) alone or coadministered with VGB (50 mg/kg, i.p.). Dentate gyrus epileptic activity was obtained through the repetitive electrical stimulation of the angular bundle. MDA latency, duration, and poststimulus afterdischarge (AD) duration were evaluated. The extracellular activity of some dentate neurons was recorded before and during bicuculline iontophoresis.

RESULTS

Only the higher dose of VGB reduced the mean duration of dentate MDA and AD. CCK-8S significantly decreased the number of animals exhibiting MDA responses, characterized by increased latency and shorter duration. The coadministration of CCK-8S and VGB (50 mg/kg) significantly increased the anticonvulsant effects, either reducing the number of responding animals or decreasing both MDA and AD durations. During bicuculline iontophoresis, all the modifications induced on the MDA-related activity of dentate neurons by the pretreatments (VGB and/or CCK-8S) were abolished.

DISCUSSION

The results indicate that CCK-8S significantly enhances the VGB-induced anticonvulsant effect in the MDA model of partial epilepsy, probably through an increase of GABA cerebral levels. Such increased anticonvulsant effect becomes evident by using VGB at a lower dose.

Sedative and anticonvulsant effects of zolpidem in adult and aged mice

To evaluate the possible age-related differences in the behavioral effects of zolpidem, a widely used hypnotic, we compared the effects of zolpidem on the locomotor activity and on the seizure threshold for pentylenetetrazole (PTZ) and picrotoxin (given by i.v. infusion) between adult (3 months) and aged (13 months) mice. Zolpidem (10 mg/kg) produced similar enhancements of the seizure threshold in adult and aged mice. The drug was more potent against PTZ- than against picrotoxin-induced seizures. Diazepam (1 mg/kg), which was taken for comparison, had a weaker effect on picrotoxin-induced tonic seizures in aged than in adult mice. Sedative effect of zolpidem (10 mg/kg), as assessed by its effect on the locomotor activity, was very strong in both groups of mice. The results suggest that sedative and antiseizure effects of zolpidem are not changed in aged mice.

Ang II and Ang III modulate PTZ seizure threshold in non-stressed and stressed mice: possible involvement of noradrenergic mechanism

The present study evaluated the effects of Angiotensin (Ang) Ang II and Ang III on pentylenetrazol (PTZ) seizure threshold in non-stressed and stressed mice as well as the possible participation of noradrenergic (NA) mechanism in their effects. While intracerebroventricular (i.c.v.) administered Ang II and Ang III increased the PTZ threshold for myoclonic twitch (MTW), generalized clonus (GNCL) and tonic hindlimb extension (THE) in non-stressed mice, they attenuated the anticonvulsant effects of acute restraint stress. The selective AT(1) receptor antagonist losartan rather than the selective AT(2) receptor antagonist PD 123319 antagonized the effects of Ang II in both non-stressed and stressed animals. Losartan also reversed the effects of Ang III on the thresholds for MTW and GNCL in stressed mice. Concurrent administration of desipramine (NA-uptake inhibitor) and either Ang II or Ang III produced a greater effect on MTW and GNCL in non-stressed mice. However, desipramine reversed the peptide-induced attenuation on PTZ seizure threshold in stressed mice. Prazosin (alpha(1)-adrenoreceptor (AR) antagonist) blocked the effects of Ang II on PTZ seizure threshold for the three convulsive phases in both non-stressed and stressed mice. Prazosin potentiated the anti-seizure effect of Ang III against MTW, GNCL, and THE in non-stressed mice while it reversed the seizure threshold-decreasing effect of this heptapeptide on MTW and GNCL in stressed mice. Yohimbine (alpha(2)-AR antagonist) blocked only the effects exerted by Ang II on the PTZ seizure threshold in non-stressed mice. Our findings suggest that the responses of Ang II and Ang III on PTZ seizure threshold can be mediated by AT(1) receptors in non-stressed and even more in stressed mice. We also hypothesize that the NA-dependent mechanism plays a major role in the effects of Ang peptides in both non-stressed and stressed mice.

Mediation of cognitive function by high fat diet following stress and inflammation

In addition to commonly advertised hazards of obesity contributed by excess dietary fat, evidence of alterations in brain chemistry and structure are well documented. This brief review examines the role of nutrients, minerals and certain lipids, primarily the essential fatty acids (FA), that are beneficial to the maintenance of good health and that may offer therapeutic options by dietary supplementation. The review also considers the damaging effects of stress, especially in pre-existing conditions of obesity and diabetes, as studied in both animals and humans. The main focus of this brief review is to examine the effects of a high fat diet on stress and the immune system with particular emphasis on brain and cognitive function.

Effect of acute versus chronic theophylline administration on acute restraint stress-induced increase of pentylenetetrazol seizure threshold in mice

Various stressful paradigms were found to induce anticonvulsant effects in different seizure models. Methylxanthines, such as theophylline might contribute to the reduction of restraint-induced stress. Therefore, in this study the influence of acute restraint stress on pentylenetetrazol (PTZ) seizure thresholds as well as the effect of acute and chronic theophylline pretreatment on stress-induced modulation of the seizure threshold were assessed in mice. The onset of the three consecutive seizure phases: myoclonic twitch (MTW), generalized clonus (GNCL) and tonic hind limb extension (THE) was delayed after exposure to a 2 h restraint stress by 34%, 23% and 24%, respectively. In nonstressed mice, acute theophylline injection (100 mg/kg, i.p.) decreased the threshold only for THE. However, in stressed animals, the pretreatment with the methylxanthine significantly enhanced the dose of the convulsant producing the same seizure phase. In nonstressed mice, long-term theophylline treatment (50 mg/kg, twice daily for 14 days) increased PTZ threshold for all three seizure phases. In contrast, in chronically treated with theophylline mice exposed to restraint stress, significant decrease in the PTZ threshold for all seizure phases compared to control stressed animals have been observed. These results suggest that, depending on the treatment regimen (acute versus chronic), theophylline specifically and differentially modulates the anticonvulsant effect of restraint stress in mice.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.