Gloria Arankowsky-Sandoval

Caffeine and muscarinic antagonists act in synergy to inhibit haloperidol-induced catalepsy

The possible synergism between caffeine and muscarinic antagonists to inhibit haloperidol-induced catalepsy was investigated with the bar test in rats. Pretreatment with low doses of caffeine (1-3 mg/kg), a non-selective adenosine antagonist, dose dependently reduced the intensity and increased the onset latency of catalepsy induced by haloperidol (0.5-2 mg/kg). Similar effects were produced by the muscarinic antagonists atropine (4.1 mg/kg), and trihexyphenidyl (THP, 0.01-3 mg/kg). THP inhibited catalepsy intensity with an ED(50) of 0.38 mg/kg, and increased its onset latency with an ED(50) of 0.52 mg/kg. The anticataleptic effect of anticholinergics was potentiated when a low dose of caffeine (1 mg/kg) was applied simultaneously. In the presence of caffeine, THP inhibited catalepsy intensity with an ED(50) of 0.19 mg/kg, and prolonged the latency with an ED(50) of 0.30 mg/kg. The synergism was more evident when THP was administered at subthreshold doses that were unable to modify haloperidol-induced catalepsy when applied alone, but produced a clear inhibition of catalepsy when injected with caffeine. To assess whether repeated administration of caffeine could induce tolerance to the synergism with THP, a group of rats was pretreated with three daily doses of caffeine (1 mg/kg) for seven days, and the catalepsy test was performed on the eighth day. In these animals, caffeine was still able to enhance the anticataleptic actions of THP, suggesting that repeated administration of 1 mg/kg caffeine does not induce tolerance to the synergism with anticholinergics. These results indicate that low doses of caffeine enhance the anticataleptic actions of muscarinic antagonists, and leave open the possibility of using caffeine as adjunctive therapy to reduce the doses and the adverse effects of anticholinergics in Parkinsons disease.

Basic Sleep Mechanisms: An Integrative Review

Regulation of the sleep-waking cycle is complex and involves diverse brain circuits and molecules. On one hand, an interplay among many neuroanatomical and neurochemical systems including acetylcholine, dopamine, noradrenaline, serotonin, histamine, and hypocretin has been shown to control the waking state. On the other hand the sleep-onset is governed by the activity of sleep-promoting neurons placed in the anterior hypothalamus that utilize GABA to inhibit wake-promoting regions. Moreover, brainstem regions inhibited during wakefulness (W) and slow wave sleeps (SWS) become active during rapid eye movement (REM) sleep. Further complexity has been introduced by the recognition of sleep-promoting molecules that accumulate in the brain in prolonged W as well as the physiological role of gene expression during sleep. The sleep-wake cycle is currently undergoing intense research with many new findings leading to new paradigms concerning sleep regulation, brain organization and sleep function. This review provides a broader understanding of our present knowledge in the field of sleep research.

Biochemical modulation of the sleep-wake cycle: endogenous sleep-inducing factors.

Regulation of the sleep–wake cycle involves diverse brain circuits and molecules. Further complexity has been introduced by the recognition of sleep‐promoting factors that accumulate in the brain naturally or during prolonged waking. The variety of sleep‐inducing molecules includes peptides, cytokines, and lipids. With regard to the lipids, current evidence indicates the existence of endogenous lipids, called endocannabinoids, that mimic the pharmacological actions of the psychoactive ingredient of marijuana and that are likely to be essential factors in sleep promotion. This Mini‐Review presents current knowledge concerning the role of endogenous compounds with sleep‐promoting properties.

The Emerging Role of the Endocannabinoid System in the Sleep-Wake Cycle Modulation

The endocannabinoid system comprises amides, esters and ethers of long chain polyunsaturated fatty acids. Narachidonoylethanolamide (anandamide; ANA) and 2-arachidonoylglycerol (2-AG) are endogenous cannabinoids (endocannabinoids) ligands for the cannabinoid family of G-protein-coupled receptors named CB1 and CB2. Endocannabinoids are released upon demand from lipid precursors in a receptor-dependent manner and behave as retrograde signaling messengers, as well as modulators of postsynaptic transmission, interacting with other neurotransmitters systems. The two principal enzymes that are responsible for the metabolism of ANA and 2-AG are fatty acid amide hydrolase and monoacylglycerol lipase, respectively. Pharmacological experiments have shown that the administration of endocannabinoids induce cannabimimetic effects, including sleep promotion. This review will focus on some of the current evidence of the pharmacological potential of the endocannabinoid system on sleep modulation.

Intrahypothalamic injection of cannabidiol increases the extracellular levels of adenosine in nucleus accumbens in rats.

Cannabidiol (CBD) is a constituent of Cannabis sativa that promotes wakefulness as well as enhances endogenous levels of wake-related neurotransmitters, including dopamine. However, at this date, the effects of CBD on the sleep-inducing molecules, such as adenosine (AD), are unknown. Here, we report that intrahypothalamic injection of CBD (10μg/1μL) increases the extracellular levels of AD collected from nucleus accumbens. Furthermore, the pharmacodynamic of this drug shows that effects on the contents of AD last 2h post-injection. These preliminary findings suggest that CBD promotes the endogenous accumulation of AD.

Quinolinic acid lesions of the pedunculopontine nucleus impair sleep architecture, but not locomotion, exploration, emotionality or working memory in the rat

Anatomical and functional studies have shown that the NADPH-diaphorase-positive cholinergic neurons of the pedunculopontine nucleus (PPN) send projections to several areas in the brain. The purpose of this work was to investigate whether bilateral lesions with quinolinic acid, a neurotoxin with greater selectivity for NADPH-diaphorase-positive neurons, aimed at the compact portion of the PPN would affect the performance of adaptive behaviors, such as sleep, locomotion, and spontaneous alternation. Lesioned animals were divided in a low lesion group (LL, <50% neuron loss) and a high lesion group (HL, ≥50% neuron loss). The LL animals did not show any significant changes in sleep patterns, as compared to controls. In contrast, the HL group showed a significant increase in the number of REM sleep periods, and a reduction of REM sleep average duration, but did not differ in the total time spent in REM sleep. HL animals also showed an increase in the number of SWS periods, though wakefulness parameters did not show significant alterations. The duration and number of both REM and SWS sleep episodes were significantly correlated with the number of NADPH-diaphorase-positive neurons in the PPN. The short-term habituation pattern of locomotion, the vertical exploratory activity, as well as the thigmotaxis (an index of emotionality), displayed by LL and HL rats in a novel environment were similar to those of control animals. Likewise, there were no significant differences in spontaneous alternation among the groups. Our results indicate that quinolinic acid lesions of NADPH-diaphorase-positive cholinergic neurons localized in the posterior region of the PPN disrupt normal sleep structure, while motor activity and spontaneous alternation remain unaffected.

Treatment with subthreshold doses of caffeine plus trihexyphenidyl fully restores locomotion and exploratory activity in reserpinized rats

Trihexyphenidyl (THP) is a drug commonly used to reduce parkinsonian symptoms. An important side effect of this agent is memory impairment. Since caffeine enhances the potency of THP to inhibit haloperidol-induced catalepsy, caffeine may be used as an adjuvant of lower doses of THP, in order to improve its antiparkinsonian effects without causing memory disruption. To further assess the synergism between caffeine and THP, both drugs were tested in reserpinized rats, another preclinical model of Parkinsons disease. Four groups of rats (n = 7) were treated with reserpine (5 mg/kg, i.p.). A control group (n = 7) was treated only with the vehicle for reserpine (dimethylsulphoxide). The spontaneous locomotor behavior was tested 24 h later in a box with infrared sensors, 30 min after receiving one of the following treatments: distilled water (1 ml/kg), caffeine (1 mg/kg), THP (0.1 mg/kg) or caffeine plus THP. The levels of horizontal locomotion (14 +/- 5%) and vertical exploration (15 +/- 10%) were significantly lower in reserpinized rats treated with distilled water, compared with the mean activity values (100%) recorded in animals pretreated only with the vehicle for reserpine. The reserpine-induced hypokinesia was neither reversed by caffeine alone nor by THP alone. However, the combination of caffeine plus THP restored locomotion (141 +/- 19%) and vertical exploration (82 +/- 17%) to levels not significantly different to those of non-reserpinized rats. Moreover, the time-course of locomotion and exploration displayed the characteristic habituation over time, in which short-term memory processes are involved. Also, the thigmotaxis index indicated that the combined treatment did not induce anxiety-like behavior. Hence, these results support the proposal that low, subthreshold doses of caffeine plus THP have the potential to alleviate the motor disabilities in parkinsonian patients, with a low risk of causing anxiety or memory impairment.

Circling behavior induced by microinjection of serotonin reuptake inhibitors in the substantia nigra

The nigrostriatal dopaminergic neurons of the substantia nigra pars compacta (SNc) and the nondopaminergic neurons of the substantia nigra pars reticulata (SNr) receive a dense synaptic input from the serotonergic neurons of the raphe nuclei. To assess whether serotonin [5-hydroxytryptamine (5-HT)] spontaneously released at the substantia nigra could modulate motor activity, the 5-HT reuptake inhibitors (SRIs), duloxetine (6-12 nmol) and clomipramine (12 nmol), were unilaterally microinjected either into the SNc or the SNr of freely moving rats, and the circling behavior was counted with an automated rotometer. In the SNc, the main effect of the SRIs was a contraversive circling behavior that was not observed when applied at distances > or = 0.2 mm above the SNc. The circling induced by clomipramine was blocked by microinjection of haloperidol (53 nmol) into the ipsilateral neostriatum, suggesting that the circling elicited by microinjection of the SRIs into the SNc depends on an intact striatal dopaminergic transmission. Microinjection of 5-HT (21 nmol) only produced a significant contraversive circling response when it was coinjected with the SRIs. Pretreatment with methysergide (1 mg/kg ip), a nonselective 5-HT(2) antagonist, did not block the circling elicited by microinjection of clomipramine into the SNc, either alone or in combination with 5-HT. However, microinjection of the 5-HT(2) antagonist mianserin (2 nmol) into the SNc partially inhibited the circling induced by duloxetine (6 nmol), alone or coinjected with 5-HT. Since current theories of circling behavior hypothesize that the animal turns away from the cerebral hemisphere where dopamine neurotransmission predominates, these results suggest that the contraversive circling induced by the unilateral microinjection of SRIs into the SNc could be mediated by a 5-HT-induced increase of firing frequency of nigrostriatal dopaminergic neurons. When applied into the SNr, clomipramine and duloxetine also elicited a contraversive circling behavior and enhanced the circling induced by 5-HT. Systemic methysergide (1 mg/kg i.p.), but not intranigral mianserin (2 nmol), blocked the circling elicited by microinjection of clomipramine into the SNr, either alone or in combination with 5-HT. These results suggest that 5-HT(2)-like receptors are involved in the contraversive circling induced by enhancement of serotonergic transmission in the SNr.

Synergism of theophylline and anticholinergics to inhibit haloperidol-induced catalepsy: A potential treatment for extrapyramidal syndromes

Extrapyramidal syndromes (EPS) impose a heavy burden on patients receiving antipsychotic therapy. Anticholinergics are the drugs of choice for preventing EPS, but they also produce many adverse reactions. Using the EPS model of haloperidol-induced catalepsy we evaluated the potential therapeutic value of a mixture of low doses of the non-selective adenosine antagonist theophylline (0.93 and 1.86 mg/kg), and the muscarinic antagonists benztropine (0.134 and 0.268 mg/kg) and ethopropazine (0.116 and 0.232 mg/kg). In rats pretreated with vehicle (distilled water), the cumulative catalepsy time over 5 h was 4199±228 s, and the mean latency was 67.5±7.8 min. Applied separately, neither of the drugs at the doses used caused significant changes of catalepsy intensity vs. control rats. However, the combination of the larger doses of theophylline and benztropine caused a significant reduction of catalepsy intensity (-41±10%) compared with the effects of the vehicle, vs. the lower dose of benztropine, and vs. both doses of theophylline alone. The mixture of the larger doses of theophylline and benztropine also delayed catalepsy onset (156±21 min) as compared with the lower doses of these same drugs applied alone. In the case of theophylline plus ethopropazine, only the association of the larger doses showed a non-significant tendency to inhibit catalepsy (-21±8%) and to prolong its latency (108±13 min). Further, neither catalepsy intensity nor its latency was affected by a combination of the selective A(1)R antagonist DPCPX (1 mg/kg), with the larger doses of both anticholinergics. In contrast, the anticholinergics showed synergism with a subthreshold dose of the selective A(2A)R antagonist ZM 241395 (0.5 mg/kg), causing a significant reduction of catalepsy intensity (ethopropazine, -27±5%; benztropine, -35±9%) and prolonging its latency (ethopropazine, 65±9 min; benztropine, 78±11 min), compared with the effect of their respective vehicle (DMSO plus mineral oil: catalepsy time, 5100±196 s; latency, 17.5±2.5 min). These findings suggest that neuroleptic-induced EPS could be effectively controlled by a combination of lower doses of theophylline and anticholinergics, with the advantage of maximizing their efficacy and minimizing their adverse reactions.

Sleep and neurochemical modulation by the nuclear peroxisome proliferator-activated receptor α (PPAR-α) in rat.

The peroxisome proliferator-activated receptor alpha (PPARα) is a nuclear protein that plays an essential role in diverse neurobiological processes. However, the role of PPARα on the sleep modulation is unknown. Here, rats treated with an intrahypothalamic injection of Wy14643 (10μg/1μL; PPARα agonist) enhanced wakefulness and decreased slow wave sleep and rapid eye movement sleep whereas MK-886 (10μg/1μL; PPARα antagonist) promoted opposite effects. Moreover, Wy14643 increased dopamine, norepinephrine, serotonin, and adenosine contents collected from nucleus accumbens. The levels of these neurochemicals were diminished after MK-886 treatment. The current findings suggest that PPARα may participate in the sleep and neurochemical modulation.