Biomedical subjects

P Pokk

Publications and source records attributed to P Pokk.

14 recordsLinked to original sources

PubMed2001

Small platform stress increases exploratory activity of mice in staircase test.

Small platform (SP) stress was induced by placing mice on small platforms (3.5 cm diameter) surrounded by water for 24 h. This model contains several factors of stress like rapid eye movement (REM) sleep deprivation, isolation, immobilization and falling into the water. The staircase test consisted of placing a mouse in an enclosed staircase with 5 steps and recording (1) the number of steps and (2) rearings made during 3 min. SP stress increased the exploratory activity of mice in the staircase test as evidenced by an increase in the number of steps and rearings made In control mice diazepam (0.25 and 0.5 mg/kg) induced an anxiolytic effect in the staircase test as evidenced by a decrease in the number of rearings without changes in the number of steps. In SP stressed mice the anxiolytic effect of diazepam was not seen and the sedative effect as evidenced by a decrease in the number of steps was more pronounced. Buspirone at a dose of 1.0 mg/kg did not have effect on the behaviour of control or SP stressed mice in the staircase test. To study possible diurnal variations the staircase test was carried out at 3 different times of a day (08:00, 14:00, 20:00) with control and SP stressed mice. The exploratory activity of control mice in the staircase test gradually increased from 08:00 to 20:00 as evidenced by an increased number of steps and rearings made. SP stress increased the exploratory activity of mice irrespective of the time of testing. In conclusion, on the basis of these data the authors can propose that SP stress increases the exploratory activity of mice in the staircase test and induces a hyposensitivity of mice to the anxiolytic effect of diazepam. The effect of SP stress on the behaviour of mice in the staircase test is not caused by the disruptance of diurnal rhythms.

Animals↗

PubMed2001

The effects of flumazenil, Ro 154513 and beta-CCM on the behaviour of control and stressed mice in the staircase test.

The effects of flumazenil, Ro 154513 and beta-CCM in the staircase test were studied in control and small platform (SP) stressed mice. SP stress was induced by placing mice on small platforms (3.5 cm in diameter) surrounded by water for 24 h. This model contains several factors of stress, such as rapid eye movement sleep deprivation, isolation, immobilization and falling into the water. The staircase test consisted of placing a mouse in an enclosed staircase with five steps and recording: (i) the number of rearings and (ii) steps made during 3 min. SP stress increased the exploratory activity of mice in the staircase test as demonstrated by an increase in the number of rearings and steps made. In control mice flumazenil (2.0 and 10.0 mg/kg), Ro 15-4513 (1.0 and 3.0 mg/kg) and beta-CCM (1.0 and 2.0 mg/kg) exerted an anxiogenic effect that was demonstrated by an increase in the number of rearings without significant changes in the number of steps. Similar to control mice, flumazenil induced an anxiogenic effect in SP stressed mice as demonstrated by an increase in the number of rearings. However, the sedative effect of flumazenil as demonstrated by a decrease in the number of steps made was more pronounced in SP stressed mice. In the SP stressed mice, the anxiogenic effect of Ro 15-4513 and beta-CCM was masked by their strong sedative effect and a decrease in both measures of exploratory activity (number of rearings and number of steps). These data suggest that SP stress induces hypersensitivity to the sedative effect of flumazenil, Ro 15-4513 and beta-CCM in the staircase test.

Animals↗

PubMed2000

Neuroprotective action of group I metabotropic glutamate receptor agonists against oxygen-glucose deprivation-induced neuronal death.

The metabotropic glutamate receptor (mGluR) non-selective agonist (1S,3R)-1-aminocycloheptane-trans-1,3-dicarboxylic acid [(1S, 3R)ACPD] and group I selective receptor agonist 3, 5-dihydrophenylglycine (DHPG) effectively attenuated oxygen-glucose deprivation (OGD)-induced death of the cultured cerebellar granule cells. Furthermore, (1S,3R)ACPD (100 microM) reduced the number of apoptotic cells. Antiapoptotic action of (1S,3R)ACPD was prevented by the group I selective antagonist (RS)-1-aminoindan-1, 5-dicarboxylic acid (AIDA, 100 microM) and protein kinase C (PKC) inhibitor bisindolylmaleimide (BMI, 1 microM).

Animals↗

PubMed2000

The effect of baclofen on the locomotor activity of control and small-platform-stressed mice.

The effect of baclofen on the locomotor activity of control and small-platform-stressed mice was studied. In the small platform technique, mice are forced to stay on small platforms (d= 3.5 cm) surrounded by water for 24 h. Small platform stress increased the locomotor activity of mice in the actometer. Baclofen administered at doses of 0.25, 0.5 and 1.0 mg kg(-1)(i.p.) had no effect on the locomotor activity of control mice. In small-platform-stressed mice, the locomotor depressant effect of baclofen was pronounced, being statistically significant at a dose of 1.0 mg kg(-1). These data suggest that small platform stress induces hypersensitivity of mice to the motor depressant effect of baclofen. On the basis of these data it could be proposed that small platform stress induces changes in the function of GABA(B)receptors and that GABA(B)receptors participate in the behavioural changes caused by small platform stress.

Animals↗

PubMed2000

The influence of the nitric oxide synthase inhibitor L-NOARG on the effects of ethanol in rats after acute ethanol administration.

The aim of this work was to study the effects of the nitric oxide synthase inhibitor N(G)-nitro-L-arginine (L-NOARG) on the sedative and toxic effects of ethanol in rats. Ethanol at a dose of 3 g/kg, intraperitoneally induced sleep in rats (sleep time: 111.2+/-10.3 min.). Administration of the nitric oxide synthase inhibitor L-NOARG (20 and 40 mg/kg, intraperitoneally) 30 min. before ethanol significantly increased the duration of ethanol-induced sleep. L-NOARG at doses of 20 and 40 mg/kg reduced the exploratory activity of rats in the open-field test and significantly enhanced the sedative effect of ethanol in this test. It is possible that this effect is not caused by the interaction of ethanol with nitric oxide pathways but by synergistic CNS depression caused by ethanol and L-NOARG. L-NOARG (20 and 40 mg/kg) had no effect on ethanol concentrations in blood after acute ethanol administration (2 and 3 g/kg). Moreover, the combined administration of ethanol (2 g/kg) and L-NOARG (20 and 40 mg/kg) caused a decrease in the body weight of animals, observed for 14 days. Also, livers of these rats were studied for necrosis and connective tissue reaction. In histological studies L-NOARG at a dose of 40 mg/kg had no effect on hepatic necrosis caused by the acute administration of ethanol but strengthened connective tissue reaction. L-NOARG is widely used in pharmacological studies, including those concerning the effects of ethanol. However, on the basis of our data the possibility of toxic interactions with ethanol should be considered.

Animals↗

PubMed1998

Small platform stress attenuates the anxiogenic effect of diazepam withdrawal in the plus-maze test.

The effect of stress on the behavioural changes caused by diazepam withdrawal was studied in mice. Diazepam (2.5 mg/kg) or vehicle was injected intraperitoneally twice a day for 2 weeks. When the last vehicle or diazepam injection had been administered to the mice, 12 h later, the mice were subjected to small platform stress exposure or left in their home cages. Small platform stress was induced by placing mice on small platforms (3.5 cm diameter) surrounded by water for 24 h. This experimental model contains several factors of stress like rapid eye movement (REM) sleep deprivation, isolation, immobilization and falling into the water. The plus-maze test was carried out with stressed mice as well as with mice not subjected to stress. Small platform stress induced an anxiolytic effect and diazepam withdrawal--an anxiogenic effect in the plus-maze test. Small platform stress also attenuated the anxiogenic effect of diazepam withdrawal. On the basis of this data it was proposed that small platform stress counteracts the anxiogenic effect of diazepam withdrawal in the plus-maze test. It was also proposed that the effect of stress on the signs of benzodiazepine withdrawal depends on the characteristics and duration of stress.

Animals↗

PubMed1998

The effects of buspirone on the behaviour of control and stressed mice.

The effects of buspirone on the locomotor activity and behaviour in the plus-maze and hole-board tests were studied in control and small platform stressed mice. Small platform stress for 24 hours increased the locomotor activity of mice and induced anxiolytic-like effect in the plus-maze and hole-board tests. Administration of buspirone either did not affect (2.0 and 4.0 mg/kg) or inhibited (8.0 mg/kg) locomotions in control animals. The inhibition of locomotor activity by buspirone was greater in small platform stressed mice. In control mice buspirone in doses 2.0 and 4.0 mg/kg exerted anxiolytic effect in the plus-maze and hole board test that was reflected by an increase in the percentage of entries onto and the percentage of time spent on the open arms of the plus-maze and increased number of head-dippings in the hole-board test. In contrast, in small platform stressed mice, buspirone did not induce anxiolytic action in the plus-maze and hole-board tests at any dose tested. In doses 2.0 and 4.0 mg/kg buspirone produced a sedative effect that was reflected by a decrease in the total number of entries made onto the open and into the closed arms of the plus-maze and a decrease in the number of head-dippings and rearings in the hole-board test. These data suggest that small platform stress induces a sensitization of mice to the motor depressant effect of buspirone. At the same time small platform stress induces hyposensitivity to the anxiolytic effect of buspirone. It is proposed that these changes might be due to alterations in the serotonergic transmission or to changes in the release of corticosterone.

Animals↗

PubMed1997

The effects of flumazenil, Ro 15-4513 and beta-CCM on the behaviour of control and stressed mice in the plus-maze test.

The effects of the benzodiazepine receptor antagonist flumazenil (Ro 15-1799), the benzodiazepine receptor partial inverse agonist Ro 15-4513 and the benzodiazepine receptor inverse agonist beta-CCM on the behaviour of control and small platform stressed mice studied. Small platform stress was induced by placing the animals on small platforms (d = 3.5 cm) surrounded by water for 24 hours. This technique involves several factors of stress such as rapid eye movement sleep-deprivation, isolation, immobilization, falling into the water and soaking. In the plus-maze test small platform stress induced changes indicating anxiolytic action-an increase of the percentage of entries made onto and the percentage of time spent on the open arms. In control mice flumazenil (2.0 and 10.0 mg/kg), Ro 15-4513 (0.5; 1.0; 2.5; 5.0 and 10.0 mg/kg), and beta-CCM (1.0 and 2.0 mg/kg) exerted dose-dependent anxiogenic effect. The small platform stress induced an enhancement of the anxiogenic effect of flumazenil, but not that of Ro 15-4513 and beta-CCM. The selective enhancement of flumazenil's action may be explained with the mode of action of flumazenil. It is proposed that small platform stress causes changes in the concentration of the endogenous benzodiazepine receptor ligand with stress protective activity and flumazenil acts by blocking the effects of this endogenous ligand.

Animals↗

PubMed1996

Ro 15-4513 potentiates, instead of antagonizes, ethanol-induced sleep in mice exposed to small platform stress.

The effects of ethanol and the benzodiazepine receptor ligand ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo-[1,5a] [1,4] benzodiazepine-3-carboxylate (Ro 15-4513), were examined in NMRI mice exposed to small platform stress. This model contains several factors of stress, like rapid eye movement (REM) sleep deprivation, isolation, immobilization, falling into water and soaking. In control mice, ethanol exerted an anxiolytic effect in the plus-maze, but did not further enhance the anxiolytic-like effects induced by small platform stress. Ro 15-4513 antagonized ethanol-induced sleep in control animals, but enhanced the hypnotic and lethal actions of ethanol in small platform stressed mice. Small platform stress did not alter the characteristics (KD and Bmax) of [3H]Ro 15-4513 binding to cerebellar membranes. Muscimol-stimulated 36Cl- uptake into brain microsacs was significantly reduced in cortex from small platform stressed animals. Ethanol had no effect on 36Cl- uptake into brain microsacs from cortex or cerebellum. It is proposed that small platform stress alters the activity of the gamma-aminobutyric acid (GABA)A receptor-chloride ionophore complex, causing changes in the interaction between ethanol and Ro 15-4513.

Animals↗

PubMed1996

Is upregulation of benzodiazepine receptors a compensatory reaction to reduced GABAergic tone in the brain of stressed mice?

Effects of various forms of stress on the GABAA receptor-chloride ionophore complex in the brain of NMRI mice were investigated. Male albino mice were subjected to stress by placing them on small platforms (SP; 3.5 cm diameter) surrounded by water for 24 h. This experimental model contains several stress factors like rapid eye movement (REM) sleep deprivation, isolation, immobilization, falling into water and soaking. As additional stress control groups we used animals subjected to isolation, large platform (9.0 cm diameter) and repeated swimming stress. SP stress induced an increase in the number of cortical benzodiazepine (BDZ) receptors and a reduction in the GABA-stimulated 36Cl-uptake by brain microsacs, whereas none of these changes could be observed in animals exposed to isolation, swimming or large platform stresses. Furthermore, the amount of GABA-induced stimulation of [3H]flunitrazepam binding was reduced in cortical brain membranes of SP-stressed animals, an effect due to fact that these animals displayed an increase in the basal [3H]flunitrazepam binding, whereas the absolute level of maximally enhanced BDZ binding in the presence of GABA did not differ from those found in controls. Neither basal [3H]muscimol binding or thiopentone sodium-induced stimulation of [3H]flunitrazepam binding were changed in any group of stressed mice. It is proposed that the observed upregulation in the number (Bmax) of cortical BDZ receptors in SP-stressed mice may represent a compensatory response to a stress-induced attenuation of GABAergic neurotransmission.

Animals↗

PubMed1995

The effects of drugs acting at GABA-benzodiazepine-barbiturate receptor complex on the behaviour of sleep-deprived mice.

The effects of the benzodiazepine receptor agonist diazepam, the benzodiazepine receptor antagonist flumazenil and the benzodiazepine receptor inverse agonist ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo-[1,5-a][1-4] benzodiazepine-3-carboxylate (RO 15-4513) on the locomotor activity and the behaviour of animals in the plus-maze test were studied in sleep-deprived mice. The effects of convulsants acting at GABA-benzodiazepine-barbiturate receptor complex-bicuculline, picrotoxin and pentylenetetrazole, were also studied. Sleep deprivation of mice for 24 hr using the platform technique caused behavioural excitation that was reflected by an increase in the locomotor activity. Administration of diazepam (0.5 and 2.0 mg/kg), flumazenil (5.0 and 10.0 mg/kg) and RO 15-4513 (1.0, 2.0 and 3.0 mg/kg) either did not affect (in low doses) or inhibited (in high doses) locomotions of control animals. The inhibition of locomotor activity by these drugs was greater in sleep-deprived animals. In the plus-maze test, diazepam in a dose of 2.5 mg/kg had an anxiolytic effect in control mice that was reflected by an increase in the percentage of entries onto and the percentage of time spent on the open arms of the plus-maze. In contrast, in sleep-deprived animals, diazepam did not induce anxiolytic action at any dose tested. In the highest dose (2.5 mg/kg) diazepam produced a sedative effect that was reflected by a decrease in the total number of entries made onto the open and into the closed arms of the plus-maze.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMedDate not supplied

The effects of the nitric oxide synthase inhibitor 7-nitroindazole on ethanol pharmacokinetics in rats after acute and chronic ethanol administration.

The aim of this work was to study the effects of the nitric oxide synthase (NOS) inhibitors 7-nitroindazole (7-NI) and NG-nitro-L-arginine (L-NOARG) on the effects and pharmacokinetics of ethanol in rats. Ethanol at a dose of 4 g/kg, i.p. induced sleep in rats (sleep time: 117.2+/-30.7 min). Administration of the NOS inhibitors 7-NI (20 mg/kg, i.p.) and L-NOARG (20 mg/kg, i.p.) 30 min before ethanol significantly increased the duration of ethanol-induced sleep. L-NOARG also significantly increased the toxicity of ethanol as evidenced by increased post-experimental lethality. Ethanol at a dose of 2 g/kg (i.p.) did not induce sleep in vehicle-treated rats; however, the combined administration of ethanol (2 g/kg) and 7-NI at doses of 40, 80, and 120 mg/kg caused sleep, for 49.4+/-3.7, 204.0+/-13.3, and 447.5+/-62.8 min, respectively. L-NOARG (20 mg/kg) had no effect on ethanol concentrations in blood after acute ethanol administration (4 g/kg). 7-NI in lower doses (20 and 40 mg/kg) had no effect and in higher doses (80 and 120 mg/kg) significantly slowed ethanol clearance during the 12 h after ethanol administration. The effect of 7-NI (20 mg/kg) on ethanol pharmacokinetics after chronic ethanol administration (inhalation for 18 days) was also studied. The administration of 7-NI immediately after the end of ethanol exposure had a pronounced effect on ethanol pharmacokinetics; in 7-NI-treated rats the fall in ethanol concentrations was significantly slower as compared with vehicle-treated rats. In 7-NI-treated rats, blood-ethanol levels were higher at 3, 6, 9, and 12 h after the end of ethanol exposure.

Animals↗

PubMedDate not supplied

The effects of the nitric oxide synthase inhibitor 7-nitroindazole on the behaviour of mice after chronic ethanol administration.

The effects of the nitric oxide synthase (NOS) inhibitor 7-nitroindazole (7-NI) on the behaviour of mice after chronic and acute ethanol administration were studied. Male albino mice received ethanol by inhalation for 25 days. The plus-maze and staircase tests were carried out with control, ethanol-intoxicated and ethanol-withdrawn mice (7.5 h after the end of ethanol administration). The administration of NOS inhibitor 7-NI [20.0 mg/kg, intraperitoneally (i.p.)] 60 min or 7.5 h before the plus-maze test induced an anxiolytic effect in control mice. Chronic ethanol administration induced an anxiolytic, and ethanol withdrawal an anxiogenic, effect in mice. The administration of 7-NI (20.0 mg/kg, i.p.) caused behavioural depression in ethanol-intoxicated mice, but had no effect on the behaviour of ethanol-withdrawn mice. 7-NI had no effect on the behaviour of control mice in the staircase test. Chronic ethanol administration increased, and ethanol withdrawal decreased, the locomotor activity of mice in the staircase test. Likewise, in the plus-maze test, administration of 7-NI caused behavioural depression in ethanol-intoxicated mice, but had no effect on the behaviour of ethanol-withdrawn mice. In additional experiments, vehicle or 7-NI (20.0-120.0 mg/kg, i.p.) were administered 30 min before ethanol (3.0 g/kg, i.p.). 7-NI dose-dependently increased the duration of ethanol-induced sleep and inhibited ethanol clearance. On the basis of these data we can propose that the NO system has no major role in behavioural changes caused by ethanol withdrawal. At the same time NOS inhibitors can cause synergistic CNS depression with ethanol.

Animals↗

PubMedDate not supplied

Small platform stress increases.

Small platform stress was induced in male BALB/c mice by placing them on small platforms (d = 3.5 cm) surrounded by water for 24 or 72 h. This experimental model contains several factors of stress, like rapid eye movement (REM) sleep deprivation, isolation, immobilization and falling into the water. After 24 h small platform stress exposure latency to sleep was measured after the administration of the benzodiazepine receptor agonist diazepam (1.0 and 2.5 mg/kg, i.p.) and the benzodiazepine receptor inverse agonist Ro 15-4513 (1.0 mg/kg, i.p.). As could be expected, diazepam significantly shortened the latency to sleep. Surprisingly the administration of Ro 15-4513 also shortened the latency to sleep. In addition [3H]Ro 15-4513 binding was measured in the cerebellum of control and small platform stressed mice. Small platform stress for 24 h did not alter the maximal number of [3H]Ro 15-4513 binding sites (Bmax) and decreased their affinity (K(D)). Small platform stress for 72 h significantly increased the number of [3H]Ro 15-4513 binding sites and decreased their affinity. These effects were due to changes in diazepam-sensitive binding. In conclusion, it could be supposed that exposure of mice to small platform stress causes changes in the function of the [3H]Ro 15-4513 binding sites, probably a shift of binding sites toward agonist conformation, that leads to changes in the effects of Ro 15-4513.

Affinity Labels↗