Olga Vajnerová

Spatial navigation testing discriminates two types of amnestic mild cognitive impairment

The hippocampus is essential for consolidation of declarative information and spatial navigation. Alzheimers disease (AD) diagnosis tends to be preceded by a long prodromal period and mild cognitive impairment (MCI). Our goal was to test whether amnestic MCI comprises two different subgroups, with hippocampal and non-hippocampal memory impairment, that vary with respect to spatial navigation ability. A total of 52 patients were classified into two subgroups: non-amnestic MCI (naMCI) (n=10) and amnestic MCI (aMCI) (n=42). The aMCI subgroup was further stratified into memory impairment of hippocampal type-hippocampal aMCI (HaMCI) (n=10) (potential preclinical AD) and isolated retrieval impairment-non-hippocampal (NHaMCI) (n=32). Results were compared to control (n=28) and AD (n=21) groups. We used the Hidden Goal Task, a human analogue of the Morris Water Maze, to examine spatial navigation either dependent (egocentric) or independent of individuals position (allocentric). Overall, the HaMCI group performed poorer on spatial navigation than the NHaMCI group, especially in the latter trials when the HaMCI group exhibited limited capacity to learn and the NHaMCI group exhibited a learning effect. Finally, the HaMCI group performed almost identically as the AD group. Spatial navigation deficit is particularly pronounced in individuals with hippocampus-related memory impairment and may signal preclinical AD.

Prevention of Mast Cell Degranulation by Disodium Cromoglycate Attenuates the Development of Hypoxic Pulmonary Hypertension in Rats Exposed to Chronic Hypoxia

Background: Chronic hypoxia induces lung vascular remodeling, which results in pulmonary hypertension. Vascular remodeling is associated with collagenolysis and activation of matrix metalloproteinases (MMPs). One of the possible sources of MMPs in hypoxic lung are mast cells. Objective: The role of lung mast cell collagenolytic activity in hypoxic pulmonary hypertension was tested by the inhibitor of mast cell degranulation disodium cromoglycate (DSCG). Methods: Rats were treated with DSCG in an early or later phase of isobaric hypoxia. Control groups were exposed to hypoxia only or to normoxia. Lung hemodynamics, muscularization and collagen metabolism in the walls of peripheral pulmonary vessels in the lungs were measured. Results: DSCG applied at an early phase of exposure to hypoxia reduced the development of pulmonary hypertension, inhibited muscularization in peripheral pulmonary arteries and decreased the amount of collagen cleavage fragments in prealveolar vessels. Conclusions: Mast cell degranulation plays a role in the initiation of hypoxic pulmonary vascular remodeling.

Functional ablation of deep cerebellar nuclei temporarily impairs learned coordination of forepaw and tongue movements

The role of the cerebellum in complex skilled movements was assessed by the use of functional ablation technique. Rats were trained to synchronize tongue and forepaw movements in a drinking box equipped with a retractable spout which was automatically withdrawn after every lick but could be returned by pressing and releasing a lever placed 4 cm below the spout. The animals learned to perform short presses synchronized with the lick cycle in such a way as to allow continuous drinking. The contribution of the neocerebellum to these lick-associated instrumental movements was estimated by intracranial injection of 2 ng of tetrodotoxin into the dentate and lateral part of interposed nuclei. Bilateral blockade of the mainly neocerebellar output interfered with learned synchronization of licking and bar pressing, but did not suppress licking from a stationary spout and only decreased the licking frequency by 10%. It is concluded that the tongue-forepaw synchronization is disrupted by elimination of the neocerebellar output but for a much shorter time (< 9 h) than the tetrodotoxin-induced inactivation of the lateral part of the caudate nucleus (72 h) reported earlier. The results confirm participation of cerebellar hemispheres in learned tongue-forepaw synchronization, but indicate at the same time that elimination of this link can be easily compensated.

Prevention of Mast Cell Degranulation by Disodium Cromoglycate Delayed the Regression of Hypoxic Pulmonary Hypertension in Rats

Background: Pulmonary vascular remodeling induced by chronic hypoxia regresses after return to normoxia. This regression is associated with an increased amount of collagenase in pulmonary mast cells and increased collagenolytic and elastolytic activity in the lung tissue. Objective: The role of lung mast cells during recovery from chronic hypoxia was tested by the inhibition of their degranulation by disodium cromoglycate (DSCG). Methods: Male Wistar rats (n = 46) were exposed to isobaric hypoxia (3 weeks, FiO2 0.1). Thirteen of them were tested immediately at the end of exposure, 17 were treated with DSCG during the first 4 days of recovery and tested on the 5th or 14th day of recovery, 16 untreated animals were measured at the same time intervals. These groups were compared with 12 animals kept in normoxia. The rats were anesthetized (Thiopental) and their pulmonary arterial blood pressure (PAP), cardiac output and heart weight were tested, as well as the collagen composition of the walls of the peripheral pulmonary arteries. Results: DSCG applied during the first 4 days of recovery from chronic hypoxia blocked the decrease in PAP during the early phase of recovery and had no influence on PAP at a later phase. DSCG administration prevents collagen splitting in peripheral pulmonary vessels at the early phase of recovery. PAP and right ventricle hypertrophy were normalized after 14 days of return to normoxia. Conclusions: Mast cell degranulation plays a role in the regression of pulmonary hypertension during the early phase of recovery from chronic hypoxia.

Intracranial Pressure and Experimental Model of Diffuse Brain Injury in Rats

OBJECTIVE In this study, we present a simple closed head injury model as a two-stage experiment. The height of the weight drop enables gradation of head trauma severity. METHODS The head injury device consists of three parts and there are three adjustable parameters-weight (100-600 g), height of fall (5-100 cm) and elasticity of the springs. Thirty male Wistar rats underwent monitoring of intracranial pressure with and without induction of the head injury. RESULTS The weight drop from 45 to 100 cm led to immediate seizure activity and early death of the experimental animals. Severe head injury was induced from 40 cm weight drop. There was 50% mortality and all surviving rats had behavioral deterioration. Intracranial pressure was 9.3 +/- 3.76 mmHg. Moderate head injury was induced from 35 cm, mortality decreased to 20-40%, only half of the animals showed behavioral pathology and intracranial pressure was 7.6 +/- 3.54 mmHg. Weight drop from 30 cm caused mild head injury without mortality and neurological deterioration. Intracranial pressure was slightly higher compared to sham group- 5.5 +/- 0.74 mmHg and 2.9 +/- 0.81 mmHg respectively. CONCLUSION This model is an eligible tool to create graded brain injury with stepwise intracranial pressure elevation.

The effect of direct administration of drugs into the licking generator in rats.

Spontaneous licking of thirsty rats was investigated under the effect of GYKI (an AMPA/kainate receptor antagonist) and of 2-amino-5-phosphonopentanoic acid (AP5, an NMDA receptor antagonist) applied intracranially into the central rhythm generator of licking. Adult Long Evans male rats were stereotaxically implanted with guiding cannulae aimed at the oral part of nucleus reticularis gigantocellularis (NRG). After a recovery (1 week at least), animals after 24 h water deprivation were trained to drink in an experimental box. Then 1 microl of GYKI (1 mM solution) or 1 microl of AP5 (20 mM solution) was administrated by microinjection through the guiding cannula directly into the target structure. Lick-lick interval (LLI) was recorded by an electrical lick sensor and analysed with a laboratory computer Pentium. Localisation of the administration was checked by a routine histological method. GYKI administration significantly prolonged the LLI i.e. slowed down licking frequency. The effect was immediate and began to dwindle in the period between 10 min to 2 h. Licking frequency under the influence of AP5 was faster (shorter LLI). This effect culminated after 30 min and almost disappeared after 2 h. Both our findings are in a good accordance with those of Grillners group that NMDA receptors are important for slow swimming movements while non-NMDA receptors are responsible for fast ones.

Pregestational diabetes increases fetoplacental vascular resistance in rats

INTRODUCTION Diabetes is a well-known risk factor in pregnancy. Because maternal diabetes involves oxidative stress that is also induced by chronic hypoxia and can alter vascular function, we sought to determine the effects of chronic maternal hyperglycemia on the fetoplacental vasculature in rats and to compare it with the effects of chronic hypoxia. METHODS Diabetes was induced in female rats by a streptozotocin injection at a neonatal age. When these animals reached adulthood, their hyperglycemia was confirmed and they were inseminated. Half of them were exposed to hypoxia (10% O2) for the last week before the delivery. One day before the expected date of delivery, one of their placentae was isolated and perfused. RESULTS Fetoplacental vascular resistance was increased equally by experimental diabetes, chronic hypoxia, and their combination. Fetoplacental perfusion pressure-flow analysis suggested increased resistance in the small vessels in chronic hypoxia and in larger vessels in diabetes. Fetal plasma nitrotyrosine levels, measured as a marker of peroxynitrite (reaction product of superoxide and nitric oxide), mirrored the differences in fetoplacental resistance, suggesting a causative role. Fetoplacental vasoconstrictor reactivity to acute hypoxic stimuli was reduced similarly in all groups. Fasudil, a strong vasodilator agent, reduced fetoplacental vascular resistance similarly in all groups, suggesting that for the observed differences among the groups, the changes in vascular morphology were more important than variances in vascular tone. DISCUSSION Maternal diabetes increases fetoplacental vascular resistance to a similar extent as chronic hypoxia. These stimuli are not additive. Changes in vascular tone are not responsible for these effects.

Chronic hypoxia increases fetoplacental vascular resistance in rat placenta perfused with blood.

BACKGROUND Chronic hypoxia elevates vascular resistance on the fetal side of the placenta. However, when a low-viscosity perfusate is used, the increase in resistance caused by chronic hypoxia is relatively small (12 mmHg). In the present study, we tested the hypothesis that perfusion with more viscous fluid (blood) will reveal more substantial effect of chronic hypoxia. METHODS Using an isolated, dually perfused rat placenta perfused at a constant flow rate with homologous blood, perfusion pressure on the fetal side was measured. Then, the relationship between perfusion pressure and flow (P/Q) was determined. RESULTS Fetoplacental vascular resistance was increased by chronic hypoxia (10 % O2) during the last third of gestation. This was observed when the placentas were perfused with a low viscosity Krebs solution and more enhanced when perfused with blood. Nevertheless, we found no clear advantage for using blood instead of Krebs solution to study the effects of hypoxia on the fetoplacental vasculature. The elevation of fetoplacental vascular resistance caused by chronic hypoxia was at least partly resistant to acute reoxygenation. CONCLUSION Using blood for the perfusion of the isolated rat placenta does not confer any clear methodological advantage over using Krebs solution (Tab. 2, Fig. 2, Ref. 21).