Long-Lasting Enhancement of the Membrane-Associated Protein Kinase C Activity in the Hippocampal Kindled Rat

Abstract: We demonstrated that only membrane-associated protein kinase C (PKC) activity increased in the bilateral hippocampus (HIPP) up to 4 weeks and in the amyg-dala/pyriform cortex (AM/PC) at 4 weeks after the last kindled seizure. The enhancement of the membrane-associated PKC activity exceeds the increase in the protein concentration, which was observed in part. The overwhelming increase in the PKC activity should be of significance in the long-term maintenance of the kindling phenomenon.     

Effects of Intraamygdaloid Injection of Taurine and Valyltaurine on Amygdaloid Kindled Seizure in Rats

Abstract: Antiepileptic effects of intracerebral injections of taurine and valyltaurine were examined in amygdaloid kindled rats. The effects were assessed whether the animals can evoke generalized seizures by a 10,μA higher stimulation intensity than triggering thresholds. In all fully-kindled animals that have received intraamygdaloid injection of 500 nmol taurine, the kindled seizure was completely abolished. Such a significant seizure suppression (p < 0.05) was observed 12–24 h after the taurine injection. Valyltaurine (500 nmol) also suppressed the seizure in 60% of animals tested, but the effect was not statistically significant. The results indicate that taurine may effectively suppress epileptic seizures when it acts directly at the stimulation site amygdala.     

Anticonvulsive effect of dapsone (4,4′-diaminodiphenyl sulfone) on amygdala-kindled seizures in rats and cats

Dapsone (4,4′-diaminodiphenyl sulfone; DDS), an established anti-leprosy drug, showed anticonvulsive effects in the amygdaloid kindling model of epilepsy. Single doses of the drug in rats (6.25–12.5 mg/kg i.p.) suppressed the kindled seizures in a dose-dependent manner without overt behavioral toxicity. With repeated oral administration in cats, relatively higher initial doses (13–23 mg/kg) were required to obtain seizure suppression, and neurotoxic signs occurred within a few days with serum drug levels of approximately 20 μg/ml. Although dapsone showed anticonvulsive effects in both animal species, the effective serum levels overlapped the toxic levels reported in the clinical treatment of leprosy. In the majority of the cats, however, seizure suppression was maintained even after the discontinuation of dapsone with lower serum levels than those observed at the beginning of the seizure suppression. Therefore, dapsone would be useful as an antiepileptic drug only when long-term anticonvulsive efficacy is demonstrated using smaller doses comparable to those used in the treatment of leprosy.     

Hippocampal NPY gene transfer attenuates seizures without affecting epilepsy-induced impairment of LTP

Recently, hippocampal neuropeptide Y (NPY) gene therapy has been shown to effectively suppress both acute and chronic seizures in animal model of epilepsy, thus representing a promising novel antiepileptic treatment strategy, particularly for patients with intractable mesial temporal lobe epilepsy (TLE). However, our previous studies show that recombinant adeno-associated viral (rAAV)-NPY treatment in naive rats attenuates long-term potentiation (LTP) and transiently impairs hippocampal learning process, indicating that negative effect on memory function could be a potential side effect of NPY gene therapy.Here we report how rAAV vector-mediated overexpression of NPY in the hippocampus affects rapid kindling, and subsequently explore how synaptic plasticity and transmission is affected by kindling and NPY overexpression by field recordings in CA1 stratum radiatum of brain slices. In animals injected with rAAV-NPY, we show that rapid kindling-induced hippocampal seizures in vivo are effectively suppressed as compared to rAAV-empty injected (control) rats. Six to nine weeks later, basal synaptic transmission and short-term synaptic plasticity are unchanged after rapid kindling, while LTP is significantly attenuated in vitro. Importantly, transgene NPY overexpression has no effect on short-term synaptic plasticity, and does not further compromise LTP in kindled animals. These data suggest that epileptic seizure-induced impairment of memory function in the hippocampus may not be further affected by rAAV-NPY treatment, and may be considered less critical for clinical application in epilepsy patients already experiencing memory disturbances.     

Neonatal exposure to low-dose domoic acid lowers seizure threshold in adult rats

Exposing Sprague–Dawley rat pups to very low, sub-convulsant doses of domoic acid (DOM) during perinatal development has been previously shown to result in seizure-like activity in adulthood similar to partial complex epilepsy in humans, and to produce cellular and molecular changes in the dentate gyrus and area CA-3 of the hippocampus. To further these investigations we recorded electroencephalographical and behavioural activity in DOM and control rats following a normally sub-convulsant dose (25 mg/kg) of pentylenetetrazol. During this exposure, 50% of DOM-treated rats experienced a Stage V (tonic-clonic) seizure (X²₍₁₎=5.33, P=0.021), indicating a lowering of generalized seizure threshold in these animals. In a separate experiment we explored focal seizure (afterdischarge) threshold as well as seizure propagation rates in treated rats, using a 25 consecutive day standard amygdala kindling paradigm. We report that the afterdischarge threshold for DOM-treated rats was significantly lower than controls (F_(1,27)=7.117, P=0.013). No difference between groups was found in seizure progression as measured by afterdischarge duration, latency to first Stage V seizure, or latency to reach a fully kindled state (defined as five consecutive Stage V seizures). Timm staining to assess mossy fibre sprouting (MFS) in the hippocampus revealed a significant MFS increase relative to sham at the ventral level in both left and right inner molecular layer of the dentate gyrus for all DOM-treated animals, as well as in the dorsal stratum oriens of CA3 contralateral to electrode placement, and these increases were further enhanced by the kindling procedure. We conclude that perinatal exposure to subconvulsive doses of DOM results in permanent changes in neuronal excitability in the adult rat, as demonstrated by a lowering of both generalized seizure and focal afterdischarge threshold, and produces increased MFS following kindling.     

Evidence that limbic neural plasticity in the right hemisphere mediates partial kindling induced lasting increases in anxiety-like behavior: effects of low frequency stimulation (quenching?) on long term potentiation of amygdala efferents and behavior following kindling

Behavioral and physiological effects of partial kindling of the right ventral hippocampus by perforant path (PP) stimulation were investigated in the cat. Partial kindling produced lasting changes in affect (increased defensive response to rats) and predatory attack (decreased pawing and biting attack). Partial kindling also induced long term potentiation (LTP) of amygdala efferent transmission to ventromedial hypothalamus (VMH) and periaqueductal gray (PAG) in left and right hemispheres. LTP of field population spikes evoked in area CA3 by PP stimulation was also observed. LTP was detected using evoked potential methods. These findings parallel previous studies of left PP-CA3 partial kindling. Analysis of covariance removing effects of LTP from behavioral changes suggests that initiation of increased defensiveness at 2 days after completion of partial kindling depended on LTP of left and right amygdalo–VMH and right amygdalo–PAG transmission. From 6 days after kindling onward, increased defensiveness depended on LTP of right amygdalo–PAG transmission. Depotentiation of amygdala efferent LTP by bilateral low frequency amygdala stimulation (LFS) (900 pulses at 1 Hz, once daily for 7 days) selectively reduced LTP in right amygdala efferents. At the same time, defensive, but not predatory attack behavior, was returned to levels seen prior to partial kindling. Both depotentiation and reduction of defensiveness were transient. Defensiveness increased to post-kindling levels by 76 days after LFS. At the same time, LTP was restored in the right amygdalo–PAG pathway. In contrast LTP in the right amygdalo–VMH pathway remained depotentiated. Effects of LFS were not due to damage, as thresholds to evoke amygdala efferent response were unchanged. These findings suggest that lasting change in affect following partial hippocampal kindling depends on LTP of right amygdala efferent transmission to PAG. The findings parallel studies of non-convulsant pharmacological induction of lasting increases in defensiveness and amygdalo–PAG LTP with FG-7142. The parallel between the present findings and the FG-7142 experiments suggests that lasting changes in defensive response are dependent on LTP of right amygdala efferents to the PAG, however produced. The findings suggest further that the spectrum of behavioral changes produced by partial kindling are dependent on changes in a variety of neural circuits, and that amygdala efferent transmission changes are responsible for changes in defensive behavior, but not predatory attack behavior. Clinical implications are discussed.     

Chlorine conductance of the GABAA receptor of synaptoneurosomes from the brain cortex of WAG/Rij rats with absence epilepsy and wistar rats at an early period in the development of nonconvulsive or tonic-clonic kindling

We have studied muscimol-induced ³⁶Cl^? conductivity in synaptoneurosomes prepared from the frontal and somatosensory cortex of rats with three types of epileptic activity: tonic-clonic pentylenetetrazole kindling in Wistar rats, nonconvulsive absence pentylenetetrazole kindling in Wistar rats, and a genetic model of epilepsy in WAG/Rij rats. We used two concentrations of muscimol: 30 and 100 μM. The occurrence of kindling prior to tonic-clonic seizures in the Wistar rats was considerably decreased in the muscimol-induced ³⁶Cl^? conductivity as compared to the control. Development of nonconvulsive kindling considerably increased the ³⁶Cl^? conductance into the neocortical synaptoneurosomes. The control WAG/Rij rats demonstrated a significant increase in the ³⁶Cl^? conductance into neocortical synaptoneurosomes as compared to the control Wistar rats. The decrease in muscimol-induced ³⁶Cl^? conductivity after development of tonic-clonic kindling was in agreement with a large volume of literature data regarding the decrease in the activity of GABA_A receptor during tonic-clonic kindling. The high level of muscimol-induced ³⁶Cl^? conductivity in the neocortical synaptoneurosomes of the WAG/Rij rats supported the concept that absence epilepsy was induced by hyperpolarization. The high level of ³⁶Cl^? conductivity during nonconvulsive pentylenetetrazole-induced kindling suggested that the activity of the GABA_A receptor was similar in the genetic and drug-induced models of the absence epilepsy.