Long-lasting increase in protein kinase C activity in the hippocampus of amygdala-kindled rat.

Previous studies have demonstrated that membrane-associated protein kinase C (PKC) activities in the right and left hippocampus of rats kindled from the left hippocampus increased significantly at 4 weeks [9] and 4 months [22] after the last seizure compared with those in matched control rats. In this study, we investigated the effect of kindling from the left amygdala on PKC activities in the amygdala/pyriform cortex and hippocampus at long seizure-free intervals (4 and 16 weeks) from the last amygdala-kindled seizure. Membrane-associated PKC activity of the kindled group increased significantly only in the left hippocampus compared with the left side control (the left hippocampus of rats subjected to a sham operation) at 4 weeks (by 34%, P < 0.03) and 16 weeks (by 24%, P < 0.05) after the last seizure. There was no significant alteration in the membrane-associated PKC activity of the kindled group in the right hippocampus or amygdala/pyriform cortex in any seizure-free interval after the last amygdala seizure. Cytosolic PKC activity did not differ between the kindled and control groups in any brain region examined in any seizure-free interval. At 16 weeks after the last seizure, the PKC activity in the P1 fraction of the kindled group increased significantly only in the left hippocampus (by 49%, P < 0.005), but not in the right hippocampus. Neither PKC activity in the P2 fraction nor that in the cytosolic fraction was altered in the kindled group after this seizure-free interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Enduring increase in membrane-associated protein kinase C activity in the hippocampal-kindled rat.

In a previous study we demonstrated that the membrane-associated protein kinase C (PKC) activity in the amygdala/pyriform cortex (AM/PC) and both the right and left hippocampus (HIPP) of rats kindled from the left HIPP increased significantly 4 weeks after the occurrence of the last seizure compared with control rats. In this study, we carried out further investigations into the enduring effect of HIPP-kindling on membrane-associated PKC activity, the protein concentrations and brain wet tissue weights of the AM/PC and right (contralateral) and left (ipsilateral) HIPP 15-16 weeks after the last generalized kindled seizure had occurred. In addition, we determined the membrane-associated PKC activity one week after the occurrence of the last partial (stage 1-3) seizure. Fifteen to sixteen weeks after the final kindled full seizure, the membrane-associated PKC activity which was expressed as mol/min per mg protein increased significantly in the AM/PC (by 62%, P < 0.02) and left HIPP (by 33%, P < 0.03) compared with control rats, whereas the cytosolic PKC activities did not differ in any brain region examined. The wet tissue weight increased significantly (by 10%, P < 0.04) in the left HIPP only. Furthermore, when it was expressed as pmol/min per mg wet tissue weight, the membrane-associated PKC activity increased significantly in the AM/PC (by 47%, P < 0.02), right HIPP (by 27%, P < 0.05) and left HIPP (by 35%, P < 0.03) compared with the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Ionotropic excitatory amino acid receptors in discrete brain regions of kindled rats.

A study was performed to examine the specific binding of excitatory amino acid (EAA) receptor subtypes in 5 brain regions of rats kindled from the amygdala or hippocampus, using extensively washed and Triton X-100-treated membranes. Seven days after the last amygdala kindled seizure, [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10- imine maleate ([3H]MK-801) binding, which labels N-methyl-D-aspartate (NMDA)-sensitive receptor-linked cation channels, decreased significantly only in the amygdala of kindled rats compared to that of controls under equilibrium assay conditions. There was no significant change in [3H]MK-801 binding in the amygdala or hippocampus 7 days after the last hippocampal kindled seizure, or 28 days after the last amygdala kindled seizure. Nor was there a significant change in NMDA-sensitive [3H]glutamate, strychnine-insensitive [3H]glycine, [3H]spermidine, [3H]kainate or [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA) binding in any brain region 7 days after the last amygdala kindled seizure, or in the hippocampus 28 days after the last amygdala kindled seizure. These results indicate that [3H]MK-801 binding sites labeling NMDA-sensitive receptor-linked cation channels in the amygdala undergo downregulation only transiently, but that none of the subcomponents of the NMDA receptor macromolecular complex exhibit enduring changes at steady state following the completion of amygdala kindling.

Long-lasting enhancement of metabotropic excitatory amino acid receptor-mediated polyphosphoinositide hydrolysis in the amygdala/pyriform cortex of deep prepiriform cortical kindled rats.

We have previously demonstrated that ibotenate (IBO)-stimulated polyphosphoinositide (PPI) hydrolysis is increased for a long period in the amygdala/pyriform cortex (AM/PC) of amygdala (AM)- and hippocampal (HIPP)-kindled rats. This finding indicates that enhanced function of the PPI-coupled excitatory amino acid (EAA) receptor may be associated with the long-lasting seizure susceptibility of kindling. The present study further examined PPI hydrolysis induced by trans-ACPD, a selective agonist of the metabotropic EAA receptor, as well as by IBO in brain slices of rats kindled from the deep prepiriform cortex (DPC). IBO-stimulated accumulation of [3H]inositol monophosphate ([3H]InsP) was significantly increased in the AM/PC by 162 (P less than 0.0001), 130 (P less than 0.005) and 81% (P less than 0.03) at 24 h, 7 days and 28 days, respectively, after the last kindled seizure, whereas it was increased significantly only at 24 h after the last seizure in the HIPP and did not change at any time in the limbic forebrain (LFB). The IBO-stimulated accumulation of [3H]InsP was significantly increased by 55% (P less than 0.01) in the AM/PC of partially kindled rats reaching an average stage of 3.7, but not in the AM/PC of those remaining at stage 1, 7 days after the last kindled seizure. Trans-ACPD-stimulated PPI hydrolysis was significantly increased in the AM/PC of DPC-kindled rats by 65 (P less than 0.05) and 45% (P less than 0.005) at 7 and 28 days, respectively, after the last kindled seizure. Cis-ACPD-stimulated PPI hydrolysis was also significantly increased in the AM/PC of DPC-kindled rats by 45 (P less than 0.03) and 30% (P less than 0.04) at 7 and 28 days, respectively, after the last seizure. There was no increase in trans-ACPD- or cis-ACPD-stimulated PPI hydrolysis in the HIPP or LFB. These results further confirm our previous studies showing that the metabotropic EAA receptor-stimulated PPI hydrolysis exhibited a long-lasting increase in the AM/PC irrespective of the primary stimulation site for kindling.

Long-lasting enhancement of the membrane-associated protein kinase C activity in the hippocampal kindled rat.

We demonstrated that only membrane-associated protein kinase C (PKC) activity increased in the bilateral hippocampus (HIPP) up to 4 weeks and in the amygdala/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.

Long-lasting change in the membrane-associated protein kinase C activity in the hippocampal kindled rat.

The effect of hippocampal kindling on protein kinase C (PKC) activity and protein concentration was investigated in rat amygdala/pyriform cortex (AM/PC) and right (contralateral) and left (ipsilateral) hippocampus (HIPP). There was no difference in cytosolic PKC activity between control and kindled groups in any part of the brain. The membrane-associated PKC activity was altered as follows. One week after the last seizure, it was significantly increased in both right (by 26%, P less than 0.05) and left HIPP (by 30%, P less than 0.02). Four weeks after the last seizure, it was significantly increased in the AM/PC (by 14%, P less than 0.02), right HIPP (by 37%, P less than 0.01) and left HIPP (by 24%, P less than 0.05). The protein concentrations in the crude cytosolic extracts prior to elution of PKC through DE-52 columns were significantly increased in the AM/PC (by 11%, P less than 0.05) and right HIPP (by 18%, P less than 0.02) 4 weeks after the last seizure. In the membrane extracts, there was a significant increase by 23% (P less than 0.02) in the left HIPP 1 week after the last seizure. In the fraction co-eluted with PKC, a significant increase in protein concentration of the cytosolic preparation was confirmed in the AM/PC (by 12%, P less than 0.05) as well as in the left HIPP (by 15%, P less than 0.05) 4 and 1 weeks respectively after the last seizure.(ABSTRACT TRUNCATED AT 250 WORDS)