Effect of noradrenalin and EGb 761 pretreatment on the ischemia-reperfusion injured spinal cord neurons in rabbits.

Short term sublethal ischemia or ischemic preconditioning gives protection to the neurons against subsequent lethal ischemic attack. This so-called ischemic tolerance can also be provided by certain drugs. We examined the effect of noradrenalin and EGb 761 on the spinal cord neurons injured by 30 min occlusion of abdominal aorta in rabbits. The animals survived 48 and 72 h. Degenerated neurons were visualized by Fluoro Jade B method, viable neurons were demonstrated immunohistochemically with NeuN and ubiquitin antibodies. The rabbits with noradrenalin administration 48 h before 30 min of ischemia and 48/72 h of reperfusion, showed significant increase of degenerated Fluoro Jade B labeled neurons. Animals of both groups were paraplegic. Rabbits pretreated 7 days with EGb 761 prior to 30 min of ischemia and with 48/72 h of reperfusion revealed significant decrease of Fluoro Jade B-positive neurons when compared with the groups with 30 min of ischemia followed by 48/72 h of reperfusion. In the NeuN sections, the number of viable neurons was moderately decreased. These animals showed no paraplegia. Ubiquitin aggregates occurred in the cytoplasm of degenerated neurons in the sections of rabbits preconditioned with noradrenalin 48 h prior to 30 min of ischemia and followed by 48 h of reperfusion while after 72 h of reperfusion, shrunk light shadows without ubiquitin reaction were visible. Our results indicate that EGb 761 could be involved in protection of spinal cord neurons against ischemic injury while effect of noradrenalin is not unambiguous.

Effect of antioxidant treatment in global ischemia and ischemic postconditioning in the rat hippocampus.

Ischemic postconditioning is a very effective way how to prevent delayed neuronal death. Effect of Ginkgo biloba extract (EGb 761; 40 mg/kg) posttreatment was studied on the rat model of transient forebrain ischemia and ischemia/postconditioning. Global ischemia was produced by four-vessel occlusion in Wistar male rats. Two experimental protocols were used: (a) 10 min of ischemia/7 days of reperfusion with or without EGb 761 treatment or (b) 10 min of ischemia/2 days of reperfusion/5 min of ischemia (postconditioning), following 5 days of reperfusion. EGb 761 was applied as follows: 30 min before 10 min of ischemia then 5 h, 1 and 2 days after 10 min of ischemia. Fluoro Jade B, marker for neuronal degeneration, was used for quantitative analysis of the most vulnerable hippocampal CA1 neurons. Cognitive and memory functions were tested by Morris water maze, as well. Administration of EGb 761 30 min before 10 min of ischemia or 5 h after ischemia has rather no protective effect on neuronal survival in CA1 region. Ten minutes of ischemia following ischemic postconditioning after 2 days of reperfusion trigger a significant neuroprotection of CA1 neurons, but it is abolished by EGb 761 posttreatment. Ischemia/postconditioning group showed a significant improvement of learning and memory on the seventh day of reperfusion. Protection of the most vulnerable CA1 neurons after ischemia/postconditioning is abolished by exogenous antioxidant treatment used in different time intervals after initial ischemia. Moreover, combination of EGb 761 administration with repeated stress (5 min ischemia used as postconditioning) causes cumulative injury of CA1 neurons.

Postconditioning and anticonditioning: possibilities to interfere to evoked apoptosis.

The aim of this study was to validate the ability of postconditioning, used 2 days after kainate intoxication, to protect selectively vulnerable hippocampal CA1 neurons against delayed neuronal death. Kainic acid (8 mg/kg, i.p.) was used to induce neurodegeneration of pyramidal CA1 neurons in rat hippocampus. Fluoro Jade B, the specific marker of neurodegeneration, and NeuN, a specific neuronal marker were used for visualization of changes 7 days after intoxication without and with delayed postconditioning (norepinephrine, 3.1 mumol/kg i.p., 2 days after kainate administration) and anticonditioning (Extract of Ginkgo biloba, 40 mg/kg p.o used simultaneously with kainate). Morris water maze was used on 6th and 7th day after kainate to test learning and memory capabilities of animals. Our results confirm that postconditioning if used at right time and with optimal intensity is able to prevent delayed neuronal death initiated not only by ischemia but kainate intoxication, too. The protective effect of repeated stress-postconditioning was suppressed if extract of Ginkgo biloba (EGb 761, 40 mg/kg p.o.) has been administered together with kainic acid. It seems that combination of lethal stress and antioxidant treatment blocks the activation of endogenous protecting mechanism known as ischemic tolerance, aggravates neurodegeneration and, after repeated stress is able to cause cumulative damage. This observation could be very valuable in situation when the aim of treatment is elimination of unwanted cell population from the organism.

Mapping of rat hippocampal neurons with NeuN after ischemia/reperfusion and Ginkgo biloba extract (EGb 761) pretreatment.

1. The neuroprotective effect of Ginkgo biloba extract (EGb 761) against transient forebrain ischemia following 7 days of reperfusion was studied in male Wistar rats after four-vessel occlusion for 20 min. 2. NeuN, a neuronal specific nuclear protein was used for immunohistochemical detection of surviving pyramidal neurons in the hippocampus, as well as counterstaining with hematoxylin in the same sections for detection of neurons that underwent delayed neuronal death and for glial nuclei staining. GFAP immunohistochemistry was used for detection of astrocytes in the studied area of CA1 region. 3. In the group of rats pretreated 7 days with Ginkgo biloba extract (EGb 761), following 20 min of ischemia and 7 days of reperfusion without EGb 761, increased number of NeuN immunoreactive cells were counted in the most vulnerable CA1 pyramidal layer of hippocampus. On the other hand, the group of rats with 7 days of EGb 761 pretreatment following 20 min of ischemia and 7 days of reperfusion with EGb 761 showed decreased number of surviving NeuN immunoreactive CA1 pyramidal cells in comparison with the first above-mentioned experimental group. 4. Increased number of reactive astrocytes immunolabeled for GFAP (Glial fibrilary acidic protein) was observed in both experimental groups in the stratum oriens and stratum lacunosum and moleculare. 5. Twenty minutes of ischemia is lethal for most population of CA1 pyramidal cell layer. Our results showed that prophylactic oral administration of Ginkgo biloba extract (EGb 761) in the dose 40 mg/kg/day during the 7 days protects the most vulnerable CA1 pyramidal cells against 20 min of ischemia.

Extract EGb 761 pretreatment limits ubiquitin positive aggregates in rabbit spinal cord neurons after ischemia-reperfusion.

1. Ubiquitin immunohistochemistry was used for investigation of time dependent changes of ubiquitin in the nerve cells reacting to ischemic/reperfusion damage. In the rabbit spinal cord ischemia model a period of 30 min ischemia followed by 24 and 72 h of reperfusion caused neuronal degeneration selectively in the ventral horn motor neurons as well as interneurons of the intermediate zone. 2. Ubiquitin aggregates were accumulated in the neurons of lamina IX and the neurons of intermediate zone destined to die 72 h after 30 min of the spinal cord ischemia. 3. The activation of ubiquitin hydrolytic system is related to a defective homeostasis and could trigger different degenerative processes. Having in mind this, we used EGb 761 to rescue the motor neurons and interneurons against ischemia/reperfusion damage. Our results show that after 30 min of ischemia and 24 or 72 h of reperfusion with EGb 761 pre-treatment for 7 days the vulnerable neurons in the intermediate zone and lamina IX exhibit marked elevation of ubiquitin-positive granules in the cytoplasm, dendrites and nuclei. Abnormal protein aggregates have not been observed in these cells. 4. The rabbits were completely paraplegic after 30 min of ischemia and 24 or 72 h of reperfusion. However, after 7 days EGb 761 pre-treatment, 30 min of ischemia and 24 or 72 h of reperfusion the animals did not show paraplegia. 5. Evaluated ubiquitin-positive neurons of the L(5)-L(6) segments showed significant decrease in number and significant increase of density after 30 min of ischemia followed by 24 h and mainly 72 h of reperfusion. Ubiquitin immunohistochemistry confirmed the protective effect of EGb 761 against ischemia/reperfusion damage in the rabbit spinal cord.

NADPH-diaphorase activity in the spinal cord after ischemic injury and the effects of pretreatment with Ginkgo biloba extract (EGb 761).

Histochemical analysis of NADPH-diaphorase (NADPH-d) activity was performed on segments of the lumbar spinal cord in rabbit after 7 days pretreatment with the Ginkgo biloba extract Tanakan, and 30 min of ischemia followed by 24 h of reperfusion. In sections of the L5 segment of the spinal cord of untreated controls, NADPH-d-positive neurons were identified in the dorsal horns, in the pericentral region and occasionally in the ventral horns. The rabbits were completely paraplegic after 30 min of ischemia and 24 h of reperfusion. High NADPH-d activity was found in the wall of blood vessels in sections of the L5 segment and the numbers of NADPH-d-positive neurons in all sites was moderately elevated. After 7 days of Tanakan pretreatment, 30 min of ischemia and 24 h of reperfusion, the animals did not show paraplegia. Only a light tremor of the hind limbs was observed. NADPH-d activity in blood vessels and neurons was similar to that in controls. In the dorsal horns, NADPH-d positivity in neurons and fibres was increased. Our results indicate that Tanakan can scavenge free radicals produced during ischemia/reperfusion and may reduce reperfusion damage.