Preventive action of Ginkgo biloba in stress- and corticosterone-induced impairment of spatial memory in rats

In this study, we tested preventive effects of a natural medicine the extract of Ginkgo biloba (EGB 761) on post-stress cognitive dysfunction. Exposure to chronic restraint stress in rats and psychosocial stress in humans has been shown to alter cognitive functions such as learning and memory and have been linked to the pathophysiology of mood and anxiety disorders.Our findings indicate that chronic restraint stress impaired egocentric spatial memory as observed in the eight-arm radial maze but it did not alter the allocentric spatial memory in the Morris water maze. In control rats EGB 761 (100 mg/kg, orally) improved spatial memory in these two tests. Also, EGB 761 normalized cognitive deficits seen in rats chronically stressed or treated with an ‘equivalent’ dose of exogenous corticosterone (5 mg/kg, subcutaneously).We conclude that, in rats, repeated administration of EGB 761 prevents stress- and corticosterone-induced impairments of spatial memory.     

Proliferating activity, DNA ploidy changes of lung cancer cells before and after chemotherapy

To assess proliferating activity, DNA ploidy changes of lung cancer cells before and after chemotherapy, we performed a flow cytometry analysis (FC) using fresh bronchoscopy specimens from 38 patients with lung cancer. Among 33 males and 5 females, squamous cell carcinoma (NSLC) was recognized in 12 males, 15 males had small cell lung cancer (SCLC) and 6 males had lung cancer with no histological type (LC) defined. Three women had SCLC, 1 had NSCLC and one had LC. Control consisted of 11 COPD patients. The percentage of diploid cells was significantly lower and cells with hypoploid cells were significantly higher in study group before treatment. High percentage of G2M cells characterised NSCLC and LC groups, whether high number of S phase cells characterised NSCLC and SCLC group before treatment. The treatment lowered percentage of G2M cells in NSCLC and CA group, whether diploid, hypoploid and S phase cells did not differ than those from before treatment.     

The participation of sialic acids in microglia-neuron interactions

Since it is known that sialic acid participates in neuronal plasticity, it is resonable to investigate its role in microglia-neuron interactions. In this study, we tested the effects of enzymatic removal of sialic acid on neurite and cell body density in microglia-neuron co-cultures. Additionaly, we analyzed the expression of Siglec-F protein, putative receptor for sialic acids, in microglial cells as well as its affinity to neurons. The results showed that removal of sialic acids affects neuronal integrity and changes microglial morphology. In presence of microglial cells, endoneuraminidase and α-neuraminidase significantly reduced neurite density (p<0.05). Endoneuraminidase (p<0.05) and α-neuraminidase (p>0.05) decreased the number of neuronal cell bodies in comparison to control co-cultures. Neuraminidases-treated neurons showed reduced binding of Siglec-F protein, which we found in microglial cells. Our results suggest that interactions between sialic acids and Siglec receptors may protect neuronal integrity during neurodegenerative processes.     

Involvement of D1 dopamine receptors in the cognitive effects of angiotensin IV and des-Phe6 angiotensin IV

An important role for angiotensin IV (Ang IV) in the processes of learning and memory has now been well established. We have previously found that intracerebroventricular (ICV) administration of Ang IV as well as des-Phe6-Ang IV enhances learning of conditioned avoidance responses (CARs), facilitates recall of a passive avoidance (PA) task, and improves object recognition (OR) in rats. Since the dopaminergic system is crucial for the cognitive processes, in this study our aim was to determine the dopaminergic D1 mediation of these effects using SCH 23390 as a selective D1 receptor antagonist. Male Wistar rats (180-200 g), pretreated with SCH 23390 (R-[+]-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine) 0.05 mg/kg intraperitoneally (IP), were given Ang IV or des-Phe6-Ang IV (1 nmol ICV) 1 h later and then tested in the above cognitive paradigms, as well as in the open field and an elevated 'plus' maze to control for the unspecific, respectively, motor and emotional, effects of our treatments. Both, Ang IV and des-Phe6-Ang IV effectively enhanced learning of CARs (P < 0.05), recall of PA (P < 0.001), and improved OR (P < 0.001). Pretreatment with SCH 23390 abolished the cognitive effects of both peptides. SCH 23390, Ang IV, and des-Phe6-Ang IV, given at the same doses and routes as in the cognitive tests, did not significantly influence crossings, rearings and bar approaches in the open field, nor the parameters measured in the elevated 'plus' maze, thus making a major contribution of the unspecific effects of our treatments to the results of the memory tests improbable. In conclusion, these results indicate that the functional dopaminergic D1 receptors are necessary for the Ang IV and des-Phe6-Ang IV cognitive effects to occur.     

Effect of angiotensin II and saralasin on motor activity and the passive avoidance behavior of rats

One nmole of angiotensin II (ANG II) or saralasin, given intracerebroventricularly, failed to alter the motor activity of rats in open field. A combined injection of both peptides caused a significant decrease of the number of crossings and rearings. In the electromagnetic motimeter horizontal activity of animals was changed by neither of the peptides while the vertical activity was increased by ANG II. Again, a combined injection of saralasin and ANG II inhibited both horizontal and vertical activity. Stereotypies evoked by both apomorphine (2 mg/kg) and amphetamine (6.5 mg/kg), given intraperitoneally, were markedly intensified by ANG II and saralasin. A five-fold increase of the re-entry latencies in the passive avoidance situation was observed after pre-test administration of ANG II or saralasin but not the two in combination. These results suggest that ANG II and saralasin may improve processes related to learning and memory through an unspecific mechanism involving central dopamine systems.     

Angiotensin II--derived peptides devoid of phenylalanine in position 8 have full psychotropic activity of the parent hormone.

In this work we compared in rats the influence of heptapeptide 1-7-angiotensin II, hexapeptide 2-7-angiotensin II, pentapeptide 3-7-angiotensin II and angiotensin II on motility, stereotypy, learning of conditioned avoidance responses and recall of passive avoidance behaviour allowing to avoid aversive stimulation. The 4 peptides administered 15 min before the experiment, tended to increase the number of crossings, rearings and bar approaches in open field, significantly accelerated acquisition of conditioned avoidance responses and improved recall of the passive avoidance. All the peptides applied immediately before the experiment intensified stereotypy evoked by apomorphine in the dose 1 mg/kg and amphetamine in the dose 6.5 mg/kg given intraperitoneally. These results show full psychotropic activity of the examined fragments of angiotensin II, comparable with the activity of the parent octapeptide. Our previous hypothesis that the Val-Tyr-Ile-His-Pro fragment of angiotensin II is responsible for the psychotropic activity evoked by angiotensins in rats is thus confirmed.     

Effects of angiotensin II and its receptor antagonists on motor activity and anxiety in rats.

The neuropeptide angiotensin II (Ang II) has been recently found to be involved in cognitive processes. Both AT1 and AT2 angiotensin receptors seem to mediate this action. However, unspecific behavioural effects of the peptide, particularly motor and emotional, appear to influence the interpretation of cognition-oriented tests and contribute to considerable differences in opinions of various authors on the subject. In this study, aimed specifically at the assessment of these effects, we found small and insignificant changes in motor performance measured in open field after intracebroventricular injections of Ang II and its receptor subtype-specific antagonists; losartan (AT1) and PD 123319 (AT2). However, Ang II was found to increase substantially anxiety measured in elevated 'plus' maze and impair motor coordination measured in 'chimney test'. Interestingly, both antagonists abolished Ang II generated anxiety and only losartan counteracted impaired motor coordination caused by the peptide. The AT2 receptor antagonist PD 123319 impairing motor coordination on its own, nonetheless partly diminished that caused by Ang II. Therefore it appears safe to conclude that mood but not motor effects of AT1 and AT2 receptor affecting drugs may significantly bias interpretation of the cognition-oriented tests on these drugs.     

The significance of Na+ ions in angiotensin II stimulation of acquisition of active avoidance in rats

Angiotensin II (1 microgram) dissolved in water and given intracerebroventricularly on day 1, 15 min before the first learning session, enhanced rate of learning of active avoidance in rats over the next 7 days. However, the peptide, dissolved in 0.25 M NaCl, and given at the same dose and route, stimulated learning significantly more than that dissolved in water. A possible involvement of Na+ ions in facilitating learning action of A II is discussed.