Biomedical subjects

M Radulovacki

Publications and source records attributed to M Radulovacki.

At least 19 recordsLinked to original sources

PubMed1991

The effect of soluflazine on adenosine receptors in the rat brain.

Soluflazine, a potent adenosine transport inhibitor, was intracerebroventricularly administered to rats via ALZET mini osmotic pumps (4nmole, 0.5 L/hr) for 14 days and the effect on adenosine receptors was determined in specific brain areas. Soluflazine decreased adenosine A1 radioligand binding in the hippocampus as measured by [3H]R-PIA, and lowered adenosine A2 binding sites in the striatum, as estimated by the "NECA minus R-PIA" assay. Previous work from our lab has shown the ability of diazepam and triazolam to decrease adenosine binding in the same brain areas. The data show that a specific adenosine transport inhibitor produces the same effect on adenosine receptors as benzodiazepines, and suggest a role for adenosine in the CNS effects of benzodiazepines.

Adenosine↗

PubMed1991

The effect of soluflazine on sleep in rats.

Soluflazine, a specific adenosine transport inhibitor, was intracerebroventricularly administered to rats in a dose range of 10, 25, and 50 nmoles. At a dose of 50 nmoles, soluflazine decreased waking and increased sleep during the first hour of EEG recording. Our previous work has shown that chronic intracerebroventricular administration of soluflazine to rats decreased radioligand binding to adenosine A1 and A2 receptors in specific brain regions. The present data show that administration of an adenosine transport inhibitor to rats produces a transient hypnotic effect presumably through increases in synaptic adenosine levels.

Animals↗

PubMed1991

Role of adenosine in sleep and temperature regulation in the preoptic area of rats.

We have examined the effects on sleep and brain temperature of bilateral microinjections of adenosine and adenosine analogs to the preoptic area (PO) of rats. Administration of adenosine (12.5 nmoles), a nonselective adenosine A1/A2 receptor agonist NECA (N-ethyl-carboxamido-adenosine, 1.0 nmole), and the selective adenosine A1 receptor agonist CPA (cyclopentyladenosine, 0.25, 0.5 nmoles) increased total sleep primarily through an enhancement in deep slow-wave sleep (SWS2), while adenosine also increased REM sleep. Administration of 12.5 nmoles adenosine and 0.25 nmoles CPA did not affect brain temperature, while 1.0 nmole NECA and 0.5 nmoles CPA caused a transient and prolonged hypothermia, respectively. Administration of the selective adenosine A2 receptor agonist CV-1808 (2-phenylaminoadenosine, 5, 10 nmoles) had no effect on sleep or brain temperature. The present results demonstrate a site for the central hypnotic action of adenosine, and a functional role for adenosine A1 receptors in the hypothalamus.

Adenosine↗

PubMed1991

Radioligand binding to adenosine receptors and adenosine uptake sites in different brain regions of normal and narcoleptic dogs.

The present study compares the characteristics of radioligand binding to adenosine receptors and adenosine uptake sites in 100- and 50-day-old normal and narcoleptic dogs. Binding to A1 receptors was quantified using a selective A1 agonist ([3H]N6-[(R)-1-methyl-2-phenylethyl] adenosine, [3H]R-PIA) and an antagonist ([3H]dipropyl-8-cyclopentyl-xanthine, [3H]CPX). Differences in the binding of [3H]R-PIA and that of [3H]5'-ethylcarboxamide adenosine ([3H]NECA), which binds to both A1 and A2 receptors with similar affinities, were used to quantify A2 receptors. Nucleoside transport sites were labeled with [3H]nitrobenzylthioinosine ([3H]NBTI), a potent inhibitor of nucleoside transport systems. The present study offered no evidence that either adenosine A1 receptors and adenosine uptake sites in the frontal cortex or adenosine A2 receptors in the putamen were altered in narcoleptic dogs. However, we found that adenosine A1 receptors in the dog exist in different affinity states and that the affinity state in which the receptor is found depends on the brain region examined. A characterization of these low- and high-affinity sites was performed and results indicated that these sites cannot be explained by a single interaction of the A1 receptor with a single G-protein population.

Adenosine↗

PubMed1991

Chronic Ro 15-1788 treatment increases REM sleep in rats.

Administration of Ro 15-1788, a benzodiazepine antagonist (3.6 mg/kg/day in drinking water for 14 days), increased total sleep and rapid eye movement (REM) sleep in rats. Standard six-hour EEG recording periods were obtained on day 0, 1, 3, 7, 10, 14, as well as 24 and 72 hours following withdrawal. Enhanced REM sleep reached significance on day 7 of continuous drug treatment and remained significantly increased on day 10 and 14, as well as at 24 and 72 hours following drug withdrawal. The present data show that chronic administration of Ro 15-1788 increases total sleep time due to increases in REM sleep. The actions of Ro 15-1788 presumably occur through either adenosinergic or cholinergic mechanisms.

Analysis of Variance↗

PubMed1990

A comparison of the effects of caffeine, 8-cyclopentyltheophylline, and alloxazine on sleep in rats. Possible roles of central nervous system adenosine receptors.

The dose-response effects of administration of 8-cyclopentyltheophylline (CPT) (10, 20, and 40 mg/kg intraperitoneally [IP]) and alloxazine (ALX) (12.5, 25, and 50 mg/kg, IP) on sleep and wakefulness in rats were examined and compared to those of caffeine (12.5 mg/kg IP). Both CPT and ALX injected individually produced sleep suppression qualitatively similar to that produced by caffeine, but of a lower magnitude. However, when 20 mg/kg CPT and 50 mg/kg ALX were injected together, their sleep suppressant effect was of the same magnitude as that of 12.5 mg/kg caffeine. These results support the hypothesized involvement of adenosine receptor blockade in the effects of caffeine on sleep in rats. They further suggest that A1 adenosine receptor blockade may be more important than A2 receptor blockade, since behavioral effects of the selective in vitro A1 antagonist CPT were generally similar to those of nonselective in vitro adenosine receptor antagonists caffeine and ALX.

Animals↗

PubMed1989

Effects of prolonged administration of triazolam on adenosine A1 and A2 receptors in the brain of rats.

Continuous subcutaneous administration of triazolam, a benzodiazepine with short plasma half-life, for 10 days either decreased (31%, 2 mg/day) or increased (15%, 0.5 mg/day) radioligand binding to adenosine A2 receptors in the rat striatum. In a similar manner, we have shown previously that diazepam (5-10 mg/day), a benzodiazepine with a long plasma half-life attenuated radioligand binding to adenosine A2 receptors in the rat striatum by 45-25%.

Animals↗

PubMed1988

Dose-response effects of 8-cyclopropyltheophylline on sleep and wakefulness in rats.

The dose-response effects of the substituted xanthine 8-cyclopropyltheophylline (CPRT) on sleep and wakefulness (W) after intraperitoneal administration to rats were examined by means of simultaneous electroencephalographic (EEG) and electromyographic (EMG) recordings. Doses of 20 and 40 mg/kg CPRT increased W and decreased slow wave sleep (SWS) in rats, indicating CNS stimulant effects. The greatest CNS stimulation was produced by the lowest (20 mg/kg) dose of CPRT examined, which also increased the latency to SWS. In addition, the 20 mg/kg dose of CPRT also significantly decreased the amount of total sleep (TS), as compared to the vehicle group, during all time periods examined. In contrast, the 80 mg/kg dose of CPRT decreased W and increased both SWS and TS. However, this apparent hypnotic effect of the 80 mg/kg CPRT may be due to toxicity, since 80% of rats treated with this dose of the drug died within 48 h of injection.

Animals↗

PubMed1988

Desensitization of adenosine A2 receptors in the striatum of the rat following chronic treatment with diazepam.

Following prolonged treatment (7 days) with diazepam (10 mg/kg/day, using ALZET mini-osmotic pumps) in rats, the function of adenosine receptors was assessed in specific structures of the brain, using both agonist ligand binding and adenylate cyclase assays. Binding to A1 receptors was quantified using [3H]N6-[(R)-1-methyl-2-phenylethyl] adenosine, a selective ligand at A1 receptors. Differences in the binding of this ligand and that of [3H]5'-N-ethylcarboxamide adenosine, which binds to both A1 and A2 subtypes of receptors with similar affinities, were used to quantify A2 receptors. Treatment with diazepam failed to alter the binding of [3H]N6-[(R)-1-methyl-2-phenylethyl] adenosine in all areas of the brain studied. However, the binding of A2 receptors and A2 receptor-mediated stimulation of adenylate-cyclase were significantly attenuated in striatal membranes from diazepam-treated rats. Thus, the present study indicated that functional adenosine A2 receptors were desensitized after prolonged treatment with diazepam, since decreased agonist binding to A2 receptors paralleled an attenuation in the stimulation by adenosine of the activity of adenylate cyclase, an effect mediated by the A2 receptor. These results further indicate that the changes in adenosine A2 receptors correlated with significant short-lasting alterations in the sleep-wake cycle during the withdrawal of diazepam. The alterations in sleep-wakefulness did not correlate with the effect of diazepam on benzodiazepine receptors since no changes were observed in the binding of benzodiazepine receptors.

Adenylyl Cyclases↗

PubMed1988

An inexpensive sleep-wake state analyzer for the rat.

Manual classification of sleep stages is a tedious and time consuming task. We describe an inexpensive system for sleep-wake state classification for as many as eight rats at a time. It is based on determining threshold values for each parameter of each rat, then finding the natural transitions from one sleep state to another and finally classifying these states utilizing the cortical EEG and EMG signals.

Animals↗

PubMed1988

Chronic administration of diazepam downregulates adenosine receptors in the rat brain.

Following chronic administration (10 or 20 days) of diazepam (5 mg/kg/day, subcutaneous pellets) or RO 15-1788 (5 mg/kg/day, intraperitoneally), adenosine and benzodiazepine receptors in different rat brain areas were assessed by radioligand binding studies using [3H]R-PIA for A1 receptors, [3H]NECA and [3H]R-PIA for A2 receptors and [3H]FNZ for benzodiazepine receptors. Chronic administration of diazepam for 10, but not for 20 days, decreased A2 receptors in the striatum by 46% (p less than 0.05) and A1 receptors in the hippocampus by 13% (p less than 0.05). Administration of diazepam for 10 days and 20 days failed to alter [3H]FNZ binding in all brain areas studied. However, 20 days of diazepam administration decreased the magnitude of GABA enhancement of [3H]FNZ binding in the cortex by 25% (p less than 0.05). In contrast, chronic administration of RO 15-1788 failed to alter [3H]R-PIA, [3H]NECA and [3H]FNZ binding in all brain areas. These results suggest that adenosine receptors may play a role in the CNS actions of benzodiazepines.

Animals↗

PubMed1988

Effects of chronic administration of caffeine on adenosine A1 and A2 receptors in rat brain.

Chronic administration of caffeine (75 mg/kg/day) to rats for 12 days increased [3H]R-PIA binding in the cerebral cortex and cerebellum and [3H]NECA binding to high affinity receptor sites in the striatum. The results indicate that both adenosine A1 and A2 receptor subtypes possess mechanisms of adaptation to chronic caffeine treatment. In addition, adenosine A1 receptor binding shows heterogenous neuroanatomical pattern indicating that the A1 response to caffeine treatment presents regional variation in the rat brain.

Adenosine↗

PubMed1988

Low-frequency oscillations of cortical oxidative metabolism in waking and sleep.

To study the changes in cortical oxidative metabolism and blood volume during behavioral state transitions, we employed reflectance spectrophotometry of the cortical cytochrome c oxidase (cyt aa3) redox state and blood volume in unanesthetized cats implanted with bilateral cortical windows and EEG electrodes. Continuous oscillations in the redox state and blood volume (approximately 9/min) were observed during waking and sleep. These primarily metabolic oscillations of relatively high amplitude were usually synchronous in homotopic cortical areas, and persisted during barbiturate-induced electrocortical silence. Their mean amplitude and frequency did not vary across different behavioral/EEG states, although the mean levels of cyt aa3 oxidation and blood volume during rapid eye movement (REM) sleep significantly exceeded those during waking and slow-wave sleep. These data suggest the existence of a spontaneously oscillating metabolic phenomenon in cortex that is not directly related to neuroelectric activity. A superimposed increase in cortical oxidative metabolism and blood volume occurs during REM sleep. Experimental data concerning cerebral metabolism and blood flow that are obtained by clinical methods that employ relatively long sample acquisition times should therefore be interpreted with caution.

Animals↗

PubMed1988

Desensitization of adenosine and dopamine receptors in rat brain after treatment with adenosine analogs.

Maximally tolerated doses of N6-[(R)-1-methyl-2-phenylethyl] adenosine (0.50 nmol/hr/2 wk), 5'-N-ethylcarboxamide adenosine (NECA, 0.04 nmol/hr/2 wk) or deoxycoformycin (5 nmol/hr/1 wk) were administered i.c.v. to rats using mini-osmotic pumps. Adenosine receptor function was subsequently assayed using both ligand binding and adenylate cyclase assays. Binding to A1 receptors was quantitated using [3H]N6-[(R)-1-methyl-2-phenylethyl]adenosine, a selective agonist ligand at A1 receptors. Differences in the binding of this ligand and that of [3H]NECA, which binds to A1 and A2 receptors with similar affinities, were used to quantitate A2 receptors. None of the treatments affected A1 receptor function as assessed by both ligand binding and adenylate cyclase assays. A2 receptor binding and A2 receptor-mediated stimulation of adenylate cyclase were blunted in striatal membranes from NECA- and deoxycoformycin-treated rats but unaffected in striatal membranes from N6-[(R]-1-methyl-2-phenylethyl]adenosine-treated rats. All three pretreatments attenuated D1 dopamine receptor-mediated stimulation of adenylate cyclase in striatal membranes. These results suggest that 1) the A2 adenosine receptor system is susceptible to desensitization and 2) different mechanisms are involved in the NECA- and deoxycoformycin-induced desensitization of A2 adenosine receptor and D1 dopamine receptor systems. It is suggested that the D1 dopamine receptor desensitization is, in fact, due to the tonic stimulation of adenosine A1 receptors.

Adenosine↗

PubMed1987

A simplified method for monitoring the cytochrome aa3 redox state in bilateral cortical areas of unanesthetized cats.

We describe a versatile optical system that enables the simultaneous monitoring of the redox state of cytochrome c oxidase (cytochrome aa3) in two homologous cortical areas under chronically implanted windows in cats. A single light source, broad bandpass primary filters, light-conducting rods, and narrow-bandpass interference detecting filters are employed. We observed reproducible responses of the cytochrome redox state and blood volume to carotid occlusion and terminal anoxia during anesthesia, and to graded doses of pentobarbital in awake animals.

Animals↗

PubMed1987

The dose-response effects of caffeine on sleep in rats.

Caffeine at doses of 0.125, 1.25, 12.5 and 25 mg/kg was administered to rats and the subsequent effects on the sleep-wake cycle were measured. The 12.5 and 25 mg/kg doses of caffeine increased wakefulness, and decreased slow wave sleep-1 (SWS1), SWS2, rapid eye movement (REM) sleep and total sleep time (P less than or equal to 0.05). The 0.125 and 1.25 mg/kg doses of caffeine increased SWS1 at the expense of SWS2 (P less than or equal to 0.05), and did not affect total sleep time in any time period measured. Adenosine or adenosine agonists have been shown to increase SWS2 at the expense of waking or SWS1 with an increase in total sleep time. The effects of caffeine on sleep reported in this study suggest that caffeine administration not only antagonizes the effects of adenosine at the receptor level, but also at the behavioral level.

Animals↗

PubMed1987

REM sleep deprivation up-regulates adenosine A1 receptors.

Adenosine receptor binding was determined in the brains of rats deprived of rapid eye movement (REM) sleep for 48 and 96 h using [3H]L-phenylisopropyladenosine. Adenosine A1 receptors (Bmax) were significantly increased in the cortex and corpus striatum, and this increase was sleep-specific. Endogenous adenosine was assayed in microwave-fixed brain tissue and no significant changes were found in REM-deprived rats.

Adenosine↗

PubMed1985

Prenatal exposure to diazepam results in enduring reductions in brain receptors and deep slow wave sleep.

After prenatal exposure to diazepam (Valium), mature rats at 4 months of age displayed slow wave sleep (SWS) electroencephalographic patterns indicating impaired synchronization and SWS mechanisms. These animals spent a much greater portion of their SWS in the lighter SWS I, as compared to the control group which showed a predominance of the deeper SWS II. At one year of age, the diazepam-exposed rats had much fewer diazepam-specific binding sites in the thalamus than the vehicle-exposed controls. These results provide first evidence for a physiological role for benzodiazepine receptors by showing that prenatal exposure to diazepam has an enduring and detrimental effect on their ontogenesis and sleep mechanisms.

Animals↗