Antagonists of group I metabotropic glutamate receptors and cortical afterdischarges in immature rats

Metabotropic Glutamate Receptors and Interacting Proteins in Epileptogenesis

Neurotransmitter and receptor systems are involved in different neurological and neuropsychological disorders such as Parkinson's disease, depression, Alzheimer’s disease and epilepsy. Recent advances in studies of signal transduction pathways or interacting proteins of neurotransmitter receptor systems suggest that different receptor systems may share the common signal transduction pathways or interacting proteins which may be better therapeutic targets for development of drugs to effectively control brain diseases. In this paper, we reviewed metabotropic glutamate receptors (mGluRs) and their related signal transduction pathways or interacting proteins in status epilepticus and temporal lobe epilepsy, and proposed some novel therapeutical drug targets for controlling epilepsy and epileptogenesis.

Anticonvulsant and behavioral effects of muscimol in immature rats

Potentiation of GABAergic inhibition is a mechanism of action of many antiepileptic drugs. The potential use of an agonist of GABAA receptors, muscimol, as an antiepileptic drug was studied in immature rats by assessing anticonvulsant activity and side effects on motor activities. Anticonvulsant action was tested in two models of seizures (pentetrazol-induced convulsions and cortical epileptic afterdischarges). Off target effect on motor performance was assessed in a battery of tests and in the open field in three age groups (12-, 18- and 25-day-old rats). Muscimol was administered in doses from 0.1 to 1mg/kg i.p. Only the 1 mg/kg dose exhibited marked anticonvulsant effect against pentetrazol-induced convulsions in 12- and 18-day-old rats, proconvulsant effect was observed in the second model in 18- and 25-day-old rats as prolongation of afterdischarges. Even the 0.5 mg/kg dose suppressed spontaneous locomotion and heavily compromised motor performance. The effect on motor activity was marked in the youngest group and decreased with age. Due to the low anticonvulsant potency and serious side effects, systemic administration of a competitive agonist of GABAA receptors in immature animals is not a promising strategy for new anticonvulsants.

A1 not A2A adenosine receptors play a role in cortical epileptic afterdischarges in immature rats

Endo- as well as exogenous adenosine exhibits anticonvulsant action. Participation of individual types of adenosine receptors was studied in present experiments in immature rats. Cortical epileptic afterdischarges were used as a model in rat pups 12, 18 and 25 days old. CCPA, an agonist of A1 adenosine receptors, decreased markedly duration of afterdischarges whereas DPCPX, an antagonist of A1 receptors, exhibited strong proconvulsant action. Action of either drug was best expressed in 12-day-old rats and it decreased with age. Drugs influencing A2A adenosine receptors (agonist CGS21680 and antagonist ZM241385) did not exhibit systematic effects in our model. Motor phenomena accompanying cortical stimulation or epileptic afterdischarge were never influenced by any of the four drugs studied. A1 adenosine receptors are important in the model of cortical seizures, especially in the youngest group studied.

In vivo imaging of mGluR5 changes during epileptogenesis using [11C]ABP688 PET in pilocarpine-induced epilepsy rat model

Introduction

Metabotropic glutamate receptor 5 (mGluR5) that regulates glutamatergic neurotransmission contributes to pathophysiology of epilepsy. In this study, we monitored the changes of mGluR5 in vivo using [¹¹C]ABP688 PET during the epileptogenesis in a pilocarpine-induced epilepsy rat model.

Methods

In vivo mGluR5 images were acquired using [¹¹C]ABP688 microPET/CT in pilocarpine-induced chronic epilepsy rat models and controls. We also acquired microPET/CT at acute, subacute as well as chronic periods after status epilepticus. Non-displaceable binding potential (BP_ND) of [¹¹C]ABP688 was calculated using simplified reference tissue model in a voxel-based manner. mGluR5 BP_ND of the rat brains of epilepsy models and controls were compared.

Results

Status epilepticus developed after pilocarpine administration and was followed by recurrent spontaneous seizures for more than 3 weeks. In chronic epilepsy rat model, BP_ND in hippocampus and amygdala was reduced on a voxel-based analysis. Temporal changes of mGluR5 BP_ND was also found. In acute period after status epilepticus, mGluR5 BP_ND was reduced in the whole brain. BP_ND of caudate-putamen was restored in subacute period, while BP_ND of the rest of the brain was still lower. In chronic period, global BP_ND was normalized except in hippocampus and amygdala.

Conclusions

In vivo imaging of mGluR5 using [¹¹C]ABP688 microPET/CT could successfully reveal the regional changes of mGluR5 binding potential of the rat brain in a pilocarpine-induced epilepsy model. The temporal and spatial changes in mGluR5 availability suggest [¹¹C]ABP688 PET imaging in epilepsy provide abnormal glutamatergic network during epileptogenesis.

Effects of mGluR5 and mGluR1 antagonists on anxiety-like behavior and learning in developing rats

Antagonists of group I metabotropic receptors exhibit anxiolytic action in adult rats. In immature animals we demonstrated anticonvulsant action of MPEP and AIDA, antagonists of group 5 and group 1, respectively. However, there are no developmental data on anxiolytic-like and learning actions of both compounds. This study investigated whether the anticonvulsant dose range of MPEP and AIDA affects anxiety-like behavior and learning ability in immature rats. Animals at 12, 18 and 25 postnatal (P) days received MPEP in doses of 10, 20 or 40 mg/kg i.p., AIDA in doses of 10 or 20 mg/kg i.p. In P18 and P25 rats anxiety-like behavior and locomotor activity were tested in the light-dark box and open-field test at 15 (1st session) and 60 (2nd session) minutes after drug administration. Learning ability of P12, P18, and P25 animals was examined in the homing response test 15 min after drug administration. Both antagonists exhibited anxiolytic-like action in the 1st session, effects in the 2nd session were less marked. In the open-field test both antagonists increased locomotion only in P18 animals. Age-dependent changes were found in the homing response test, the return latency being longer only in P12 animals. While MPEP in doses of 20- and 40-mg/kg in P12 and 40-mg/kg in P18 rats prolonged the homing response, AIDA did not affect the homing behavior. Both MPEP and AIDA exert anxiolytic-like effect also in immature rats. Except for the youngest animals no changes in learning ability in the homing response test were found.