Neuropathy in a rat model of mild diabetes induced by multiple low doses of streptozotocin: effects of the antioxidant stobadine in comparison with a high-dose alpha-lipoic acid treatment.

Hyperglycaemia-induced oxidative stress makes an important contribution to the aetiology of diabetic neuropathy. The aim of our study was to evaluate the effect of the antioxidant stobadine (STB) in comparison with a treatment by a high-dose of alpha-lipoic acid (ALA), on the neurological consequences of chronic hyperglycaemia in an animal model of diabetes in Wistar rats (16 weeks old), made diabetic by streptozotocin (STZ 3 x 20 mg i.v.). Neuropathy was evaluated electrophysiologically by measuring motor nerve conduction velocity (NCV) in the 4th and 8th week in vivo and motor NCV and resistance to ischaemic conduction failure (RICF) of the sciatic nerve in the 10th week of the experiment in vitro. The therapy with ALA (100 mg/kg i.p., 5 times a week) and STB (25 mg/kg i.p., 5 times a week) had a significant effect on NCV in vivo in the 8th week of the experiment and no effect in the 10th week in vitro. The RICF elevated in diabetic animals was significantly modified by ALA. The effect of the antioxidant STB on NCV was comparable with that of ALA, while RICF was affected only by ALA. We conclude that treatment with appropriate antioxidants might partially prevent nerve dysfunction in diabetic rats.

Effect of transient ischemia on long-term potentiation of synaptic transmission in rat hippocampal slices.

OBJECTIVES: Long-term potentiation (LTP) of neuronal activity in the hippocampus is thought to be a substrate for learning and memory. The influence of ischemia (IS) (hypoxia/hypoglycemia) on induction of LTP of synaptic transmission (ST) by high frequency stimulation (HFS) was investigated in rat hippocampal slices. METHODS: Neurons were stimulated via Schäffer collaterals and field excitatory postsynaptic potentials (fEPSP) were recorded extracellularly from the CA1 region. LTP was induced by one single train (100 Hz, 1s). RESULTS: In controls LTP of ST after HFS was 179.70+/-12.53%. Short IS of 2.5-4.5 min elicited a transient failure of ST, with return to former value followed by further increase of fEPSP amplitude to 142.28+/-16.24%, compared to amplitude before IS. HFS was elicited 40 min after exposure to IS and LTP was measured over further 40-60 min. LTP in slices exposed to 2.5-4.5-min IS was 139.94+/-14.01%. IS of 6-7.5 min elicited a prolonged failure of ST, with almost full recovery (96.69+/-14.42%). LTP was not activated 40 min after 6-7.5-min IS and the amplitude of fEPSP was even reduced to 80.14+/-19.19% compared to the former mean value of fEPSP 10 min before HFS. CONCLUSION: The results revealed that prolonged 6-7.5-min IS influenced induction of LTP of ST in the hippocampus and thus it could have deleterious effects on learning and memory. These findings may have clinical implications in stroke, brain ischemia, sleep apnoe and call for studying the effect of neuroprotectants on the induction of LTP in hippocampus exposed to oxidative stress.

Effect of the pyridoindole SMe1EC2 and compounds affecting A(1) and A(2A) adenosine receptors in rat hippocampus under ischemia in vitro.

The effect of the newly synthesized pyridoindole antioxidant SMe1EC2 (1 micromol/l) and drugs activating or inhibiting adenosine receptors was tested under ischemia. Synaptic transmission was recorded extracellularly before and under 6-min ischemia and 20-min reoxygenation in rat hippocampal slices in vitro. In untreated slices, ischemia elicited failure of synaptic transmission and excitability expressed by a population spike decay (t(0.5) = 1.7 +/- 0.1 min) and poor recovery of synaptic transmission at the end of reoxygenation, expressed as percentage of PoS amplitude of that at zero minute of ischemia (9.9 +/- 3.6%). The compound SMe1EC2 increased recovery of PoS amplitude in reoxygenation (31.2 +/- 7.0% of that at the beginning of ischemia) and decreased the number of irreversibly damaged slices in reoxygenation (64%) compared to untreated slices (80%). Co-administration of SMe1EC2 + SCH-58261 (1 micromol/l, A(2A) adenosine receptor antagonist) resulted in delayed synaptic transmission decay during 6-min ischemia (t(0.5) = 2.3 +/- 0.1 min), increased PoS amplitude recovery during reoxygenation (37.7 +/- 12.4% of that at zero minute of ischemia), and in a decreased number of slices with damaged synaptic transmission at the end of reoxygenation (54%), all data compared to untreated controls. Co-administration of pyridoindole with CGS 21680 (1 micromol/l, A(2A) adenosine receptor agonist) or with DPCPX (100 nmol/l, A(1) adenosine receptor antagonist) eliminated the described effect. Further studies are required to elucidate the putative influence of manipulation with adenosine receptors on the neuroprotective effect of SMe1EC2 under ischemia.

Content of protein carbonyl groups in gerbil brain after reversible bilateral carotid occlusion: effect of 2,3-dihydromelatonin.

OBJECTIVES: To investigate whether a new derivative of melatonin, (2,3-dihydromelatonin (DHM), prevented the oxidative stress induced by ischemia /reperfusion (I/R) in the gerbil brain. To specify the effect on endogenous antioxidant activity and protein modification in the brain cortex, we evaluated the contents of glutathione (total GSx=GSH+GSSG) and protein carbonyl groups (PCG). METHODS: Brain ischemia (I) was induced by (12 min) bilateral carotid occlusion (BCAO) in adult male gerbils (60-70 g b wt.) DHM (10 mg/kg) was administered i.p. 20 min before surgery, at the beginning of reperfusion (R), and then 2 and 6 hours later. Horizontal locomotor activity was recorded using the open-field test over the course of 24 hours. Contents of GSx and PCG were determined after 6h of reperfusion. Glutathione (GSx ) was determined spectrophotometrically using the microplate reader, lactate by the kit Randox, UK. The measurement of protein carbonyl (PCG) groups after their derivatization with 2,4-dinitrophenylhydrazine (DNPH) is the most widely used assessment of protein oxidation. The contents of PCG and malondialdehyde (MDA) were assayed spectrophotometrically. RESULTS: Evaluation of the data obtained from horizontal locomotor activity recorded over the course of 24 hours using the open-field test showed that hyperactivity induced by I/R was returned by DHM almost to its control value during the interval of up to 6 hours (from 18,000 to 5,000 cm distance traveled, p<0.05). I/R decreased the content of GSx by 27.2% (p<0.001). Administration of DHM resulted in maintaining the content of GSx at control values (p<0.05). DHM diminished the I/R-induced increase in PCG in the cortex by 34.2% (p<0.01). CONCLUSIONS: Our data indicate that the effect of DHM on the content of glutathione and protein carbonyl groups occurred during the first 6 hours of reperfusion. In this time interval both the content of GSx and protein carbonyl groups seem to be sensitive indicators of I/R-induced oxidative stress in the gerbil brain.