Lack of resveratrol neuroprotection in developing rats treated with kainic acid.

In adult rats, trans-resveratrol attenuates kainic acid (KA)-induced convulsions and the associated hippocampal neurotoxicity. Increased neuronal survival was correlated with reduced lipid peroxidation. Since free radical generation after KA is age dependent and does not correlate with the onset of seizure-induced injury, the present study investigated whether daily trans-resveratrol treatment in development could protect the juvenile hippocampus from seizures and onset of damage at postnatal (P) day 21. Rat pups were treated with daily injections of trans-resveratrol under three dosage regimens (1-15 mg/kg and 20-50mg/kg). Weight, electroencephalography (EEG), histology, and N-methyl-d-aspartate (NMDA) receptor expression were determined. Malondialdehyde (MDA) concentration was assessed from separate animals. trans-Resveratrol did not interfere with growth or attenuate KA-induced EEG seizures. However, modest protection was afforded in the CA1, the subregion most sensitive to injury at this age. The CA3 and entorhinal amygdala cortex (AMG/EC) were not spared. Changes in NR1 subunit or NR1 C2 splice variant expression were also not prevented. Baseline MDA concentrations of hippocampal subfields were low at P14, P21, and P60 and high in aged adults. Glutamate (100 µM) to stimulate peroxidation products was significant at young ages but was much greater at older ages. After KA, elevated MDA levels were observed at 24h but only in adult preparations. Thus, while antioxidant therapy with trans-resveratrol may be considered as an adjunctive therapy to hinder epileptic activity and neurodegeneration at adult ages, it had only modest effects at young ages when production of free radicals within limbic structures is limited in this experimental model of seizures.

Inverse relationship of cannabimimetic (R+)WIN 55, 212 on behavior and seizure threshold during the juvenile period.

Cannabinoids have anti-convulsant effects in both in vivo and in vitro models of status epilepticus. Since the development of spontaneous seizures and neuronal vulnerability are age-dependent, we hypothesized that the anti-convulsant effects of cannabimimetics are also age-dependent. We administered a single injection of varied doses of (R+)WIN 55,212 (0.5, 1, 5 mg/kg) to postnatal (P) day 20 rats 90 min prior to induction of kainate (KA)-induced status epilepticus. The highest dose of (R+)WIN 55,212 (5 mg/kg) resulted in rapid onset of behavioral stupor, loss of balance, stiffening and immobility while standing on hind legs or laying flat in prone position; lower doses had minimal or no behavioral effect. After KA administration, seizure scores and electroencephalography (EEG) recordings were inversely related to (R+)WIN 55,212 dosage whereby higher doses were associated with high seizures scores and synchronous epileptiform activity and low doses with low seizure scores and diminished spiking in the EEG. Immunohistochemistry revealed a dose-dependent reduction in CB1 receptor expression with increasing concentrations of (R+)WIN 55,212 in presence or absence of KA seizures. Nissl and NeuN staining showed hippocampal injury was attenuated only when seizures were mild following low doses of WIN 55,212 (0.5, 1 mg/kg), consistent with the level of CB1 expression. Since low doses abolished seizures without psychotropic side-effects further study may facilitate a groundbreaking cannabamimetic therapeutic strategy to treat early-life seizures. Higher doses had adverse effects on behavior and failed to prevent seizures and protect CA1 neurons possibly due to inactivation or loss of CB1 receptors.

Glutamatergic and morphological alterations associated with early life seizure-induced preconditioning in young rats.

Postnatal day (P)20 rats are sensitive to CA1 injury following a single injection of kainic acid (KA) but are resistant to this injury when animals have a history of two neonatal seizures. We hypothesized that the two earlier seizures led to neuroprotection by a preconditioning mechanism. Therefore, morphology, [Ca(2+)](i) and NMDA subunit proteins of the hippocampus were examined after KA was administered once (1 × KA, on P6, P9, P13 or P20), twice (2 × KA, on P6 and P9) or three times (3 × KA, on P6, P9, P13 or P20). After 1 × KA on P20, the Golgi method revealed marked decreases in spine densities and aborization of CA1 and CA3 apical dendrites. After 3 × KA, morphological alterations were attenuated in CA1 neurons and were similar to pruning observed after 1 × KA on P6 or 2 × KA. After 1 × KA at P13, baseline [Ca(2+)](i) was elevated within pyramidal and dentate granule cells. N-methyl-D-aspartate (NMDA) responses were simultaneously enhanced. After 3 × KA, Ca(2+) elevations were attenuated. Immunohistochemistry revealed selective depletion of the NR2A/B subunit modulator in the same areas. NR1 subunit expression was downregulated in the subiculum and increased in the CA3, causing a significant shift in the NR1:NR2A/B ratio throughout the hippocampus. After 1 × KA or 3 × KA at P20, reduced expression was only observed in areas of cell injury. Results indicate that different changes in morphology and excitatory responses occur depending upon when seizures begin. Partial pruning and persistent shift in the NR1:NR2A/B ratio among excitatory synapses of the hippocampus early in life may produce epileptic tolerance and protect against subsequent insults.