Marko Zivin

Alterations in cytochrome c oxidase activity and energy metabolites in response to kainic acid-induced status epilepticus.

The effects of kainic acid (KA)-induced limbic seizures have been investigated on cytochrome c oxidase (COx) activity, COx subunit IV mRNA abundance, ATP and phosphocreatine (PCr) levels in amygdala, hippocampus and frontal cortex of rat brain. Rats were killed either 1 h, three days or seven days after the onset of status epilepticus (SE) by CO2 and decapitation for the assay of COx activity and by head-focused microwave for the determination of ATP and PCr. Within 1 h COx activity and COx subunit IV mRNA increased in all brain areas tested between 120% and 130% of control activity, followed by a significant reduction from control, in amygdala and hippocampus on day three and seven, respectively. In amygdala, ATP and PCr levels were reduced to 44% and 49% of control 1 h after seizures. No significant recovery was seen on day three or seven. Pretreatment of rats with the spin trapping agent N-tert-butyl-alpha-phenylnitrone (PBN, 200 mg kg(-1), i.p.) 30 min before KA administration had no effect on SE, but protected COx activity and attenuated changes in energy metabolites. Pretreatment for three days with the endogenous antioxidant vitamin E (Vit-E, 100 mg/kg, i.p.) had an even greater protective effect than PBN. Both pretreatment regimens attenuated KA-induced neurodegenerative changes, as assessed by histology and prevention of the decrease of COx subunit IV mRNA and COx activity in hippocampus and amygdala, otherwise seen following KA-treatment alone. These findings suggest a close relationship between SE-induced neuronal injury and deficits in energy metabolism due to mitochondrial dysfunction.

Seizure-induced changes in energy metabolites and effects of N-tert-butyl-α-phenylnitrone (PNB) and vitamin E in rats

Abstract Impaired energy metabolism may play a critical role in the neuronal injury caused by kainic acid (KA) induced status epilepticus (SE). Following an acute dose of KA (15 mg/kg, sc) rats developed SE within 1 h. Rats were sacrificed 1 or 72 h after the onset of SE using a head focused microwave technique and the brain regions (pyriform cortex, amygdala, and hippocampus) were assayed for energy metabolites: ATP, ADP, AMP, phosphocreatine (PCr) and creatine (Cr) using reversed-phase HPLC (RP-HPLC). Control values were significantly higher in cortex (23-32%) than in other brain regions. Within 1 h, SE caused a marked decline in ATP (44-56%), PCr (49-64%), total adenine nucleotides (TAN, 45-50%) and total creatine compounds (TCC, 32-51%). Within three days, the hippocampus showed the greatest recovery, as the reduced values returned to normal. Pretreatment of rats with an antioxidant (PBN, 200 mg/kg, ip, 30 min prior to KA; or vitamin E (Vit-E), 100 mg/kg, ip/day for 3 days), which did not prevent seizure activity, attenuated depletion of high-energy phosphates caused by KA. These findings suggest that the depletion of energy metabolites caused by KA-induced seizures may be linked to oxidative stress mediated toxicity.

Nitrone spin trapping compound N-tert-butyl-α-phenylnitrone prevents seizures induced by anticholinesterases

The neuroprotection afforded by spin trapping agents such as N-tert-butyl-alpha-phenylnitrone (PBN) has lent support to the hypothesis that increased production of reactive oxygen species (ROS) is a major contributing factor to excitotoxicity, aging and cognitive decline. Little is known, however, about the pharmacological properties of PBN. We have compared the acute effects of PBN on the development of seizures induced by the irreversible acetylcholinesterase (AChE) inhibitor diisopropylphosphorofluoridate (DFP), the reversible AChE inhibitor physostigmine (PHY), the muscarinic cholinergic receptor agonist pilocarpine (PIL) and the glutamatergic receptor agonist kainic acid (KA). Rats were sacrificed 90 min after the injection of seizure-inducing agents. In situ hybridization was used to detect the induction of immediate early gene (IEG) c-fos and c-jun mRNAs and the levels of AChE mRNA. The activity of AChE was visualized by AChE staining and quantified using an in vitro AChE assay. The seizures correlated with the induction of IEG mRNAs with all agents used. The pre-treatment with 150 mg/kg of PBN prevented DFP- and PHY-induced seizures and the related expression of IEG mRNAs, but had no effect on PIL- or KA-induced seizures and associated IEG mRNAs changes. PBN prevented seizures and significantly protected AChE activity against DFP inhibition when given before, but not when given after DFP. This study shows that PBN specifically protects against anticholinesterase-induced seizures by reversible protection of AChE activity and not by the blockade of muscarinic or glutamate receptors, reactivation of AChE or scavenging of ROS. The anticholinesterase properties should be considered when using PBN in studies of cholinergic dysfunction.

5HT-1A receptors and anxiety-like behaviours: studies in rats with constitutionally upregulated/downregulated serotonin transporter.

Altered activity of brain serotonergic (5HT) system has been implicated in a wide range of behaviours and behavioural disorders, including anxiety. Functioning of 5HT-1A receptor has been suggested as a modulator of emotional balance in both, normal and pathological forms of anxiety. Here, we studied serotonergic modulation of anxiety-like behaviour using a genetic rat model with constitutional differences in 5HT homeostasis, named Wistar-Zagreb 5HT (WZ-5HT) rats. The model, consisting of high-5HT and low-5HT sublines, was developed by selective breeding of animals for extreme activities of peripheral (platelet) 5HT transporter, but selection process had affected also central 5HT homeostasis, as evidenced from neurochemical and behavioural studies. Anxiety-like behaviour in WZ-5HT rats was evaluated by two commonly used paradigms: open field and elevated-plus maze. The involvement of 5HT-1A receptors in behavioural response was assessed by measuring mRNA expression in cell bodies (raphe nuclei) and projection regions (frontal cortex, hippocampus) by use of RT-PCR and in situ hybridization, and by measuring functionality of cortical 5HT-1A receptors by use of [(3)H]8-OH-DPAT radioligand binding. Animals from the high-5HT subline exhibit increased anxiety-like behaviour and decreased exploratory activity when exposed to novel environment. No measurable differences in constitutional (baseline) functionality or expression of 5HT-1A receptors between sublines were found. The results support contribution of increased serotonergic functioning to the anxiety-like behaviour. They also validate the high-5HT subline of WZ-5HT rats as a potential model to study mechanisms of anxiety, especially of its nonpathological form, while the low-5HT subline may be useful to model sensation seeking phenotype.

Changes in Cholinergic but Not in GABAergic Markers in Amygdala, Piriform Cortex, and Nucleus Basalis of the Rat Brain Following Systemic Administration of Kainic Acid

Abstract: Three days after systemic administration of kainic acid (15 mg/kg, s.c), selected cholinergic markers (choline acetyltransferase, acetylcholinesterase, muscarinic acetylcholine receptor, and high‐affinity choline uptake) and GABAergic parameters [benzodiazepine and γ‐aminobutyric acid (GABA) receptors] were studied in the frontal and piriform cortex, dorsal hippocampus, amygdaloid complex, and nucleus basalis. Kainic acid treatment resulted in a significant reduction of choline acetyltransferase activity in the piriform cortex (by 20%), amygdala (by 19%), and nucleus basalis (by 31%) in comparison with vehicle‐injected control rats. A lower activity of acetylcholinesterase was also determined in the piriform cortex following parenteral kainic acid administration. [3H]Quinuclidinyl benzilate binding to muscarinic acetylcholine receptors was significantly decreased in the piriform cortex (by 33%), amygdala (by 39%), and nucleus basalis (by 33%) in the group treated with kainic acid, whereas such binding in the hippocampus and frontal cortex was not affected by kainic acid. Sodium‐dependent high‐affinity choline uptake into cholinergic nerve terminals was decreased in the piriform cortex (by 25%) and amygdala (by 24%) after kainic acid treatment. In contrast, [3H]flunitrazepam binding to benzodiazepine receptors and [3H]muscimol binding to GABA receptors were not affected 3 days after parenteral kainic acid application in any of the brain regions studied. The data indicate that kainic acid‐induced limbic seizures result in a loss of cholinergic cells in the nucleus basalis that is paralleled by degeneration of cholinergic fibers and choli‐noceptive structures in the piriform cortex and amygdala, a finding emphasizing the important role of cholinergic mechanisms in generating and/or maintaining seizure activity.

Synaptotagmins in Neurodegeneration

Synaptotagmins (Syts) are transmembrane proteins involved in the regulation of membrane trafficking. Here, we summarize literature data that provide growing evidence that several Syts are involved in the pathophysiological mechanisms of temporal lobe epilepsy and Parkinsons disease, as well as few reports related to brain ischemia and Alzheimers disease (AD). We also report new data from our laboratories, showing changes of the expression of several Syts in Tg2576 mouse model of AD that may be related to neuroinflammation surrounding the β‐amyloid plaques. Furthermore, we demonstrate N‐methyl‐D‐aspartate receptor‐mediated upregulation of Syt 4 mRNA in a model of excitotoxic striatal lesion induced by unilateral striatal injection of quinolinic acid, associating the upregulation of Syt 4 with mechanisms of excitotoxicity. We propose that phamacological manipulation of Syt expression in animal models of neurodegeneration should be further explored, as it may help to clarify the role of individual Syt isoforms in the regulation of membrane trafficking in neurodegeneration. Anat Rec, 292:1849–1862, 2009.

Dopaminergic regulation of synaptotagmin I and IV mRNAs in hemiparkinsonian rats.

Synaptotagmins (Syts) I and IV are synaptic proteins involved in the regulation of neurosecretion. Dopaminergic drugs have been shown to modulate their expression. Here we investigate whether dopaminergic regulation of syt I and syt IV expression could play a role in the hypersensitive striatum of rats with unilateral lesions of dopaminergic nigrostriatal neurons with 6-hydroxydopamine. We show that chronic dopaminergic denervation resulted in a small down-regulation of striatal syt I mRNA, whereas acute treatment with SKF-82958, a dopamine D1 receptor agonist, induced a massive syt IV mRNA up-regulation in the striatum on the lesioned side. We conclude that chronic lack of dopamine and treatment with dopamine D1 receptor agonists alter the synaptic plasticity in dopamine depleted basal ganglia.

Upregulation of synaptotagmin IV protein in kainate-induced seizures

Synaptotagmin IV is a product of immediate early-response gene. It is involved in the regulated neurosecretion in the brain. Its putative role, however, in vesicular transport and localization in secretor y vesicles is still a matter of debate. Here we followed the spatiotemporal pattern of synaptotagmin IV protein upregulation in the hippocampus, caudate putamen, nucleus accumbens, nucleus amygdalae, piriform and entorhinal cortices of rats with kainate-induced seizures. We found that upregulation pattern paralleled the direction of depolarization through the hippocampus and also reflecting seizure activity spreading to other brain regions. We speculate that synaptotagmin IV may have a role in the vesicular transport of the upregulated peptides and proteins involved in the plasticity and/or neurodegeneration provoked by the kainate.

N-tert-butyl-alpha-phenylnitrone, a free radical scavenger with anticholinesterase activity does not improve the cognitive performance of scopolamine-challenged rats.

Reversible inhibitors of acetylcholinesterase improve spatial learning and memory in animal models of cognitive impairment. Here we investigate if the beneficial effects of free radical scavenger N‐tert‐butyl‐alpha‐phenylnitrone (PBN) on cognitive performance could be explained by its recently discovered anticholinesterase activity. Morris water maze experiment was performed to examine the effect of PBN on the impairment of spatial learning and memory induced by the antagonist of cholinergic muscarinic transmission scopolamine. In situ hybridization histochemistry experiment was performed to study its effects on the induction of immediate early gene expression (c‐fos, c‐jun) by dopamine D1 receptor agonist SKF‐82958 and on the augmentation of the SKF‐82958‐induced expression of these genes by scopolamine. In both experiments, the effects of PBN were compared to the effects of reversible anticholinesterase physostigmine. We found that physostigmine but not PBN significantly reversed the cognitive impairment in scopolamine‐challenged rats, prevented the induction of c‐fos and c‐jun mRNAs by SKF‐82958 and attenuated the augmentation of the SKF‐82958‐induced expression of these genes by scopolamine. The present experiments did not reveal a significant in vivo anticholinesterase activity of PBN.

Effect of apomorphine on striatal synaptotagmin 7 mRNA levels in reserpinized rats.

Synaptotagmin 7 (Syt 7) is a Ca2+ sensor implicated in the regulation of membrane fusion in vesicular transport, but its precise role in neurons is still a matter of controversy. Dopaminergic drugs have been shown to modulate its expression in the striatum. Here we investigate whether dopamine receptor agonist-up-regulation of Syt 7 mRNA is specifically involved in the pathophysiological adaptations of hypersensitive striatum by analyzing other dopaminergic neurons containing brain regions. We treated rats with systemic reserpine injections that rapidly depletes dopamine throughout the brain, but leaves dopaminergic neurons spared from destruction. We analyzed the effects of apomorphine, a D1 and D2 receptor agonist on Syt 7 mRNA expression in caudate putamen, nucleus accumbens, cingulate cortex, substantia nigra compacta, ventral tegmental area and hippocampus. The treatment with reserpine resulted in akinesia, catalepsy and rigidity and up-regulation of proenkephalin and down-regulation of preprotachykinin mRNA in caudate putamen, indicating a severe depletion. By acute treatment with apomorphine proenkephalin mRNA was down-regulated and preprotachykinin mRNA up-regulated in the caudate putamen of reserpinized rats. Apomorphine increased Syt 7 mRNA levels only in striatum (caudate putamen and nucleus accumbens) of reserpinized rats, while in other brain regions it did not have such effect. The reserpinization and/or apomorphine treatment had no effect on Syt 1 mRNA expression in caudate putamen. It may be concluded, that in the striatum depleted of biogene amines, such as occurs after reserpine treatment, the up-regulation of Syt 7 could play a specific role as part of hypersensitive response to dopaminergic agonists.