Electroencephalographic correlates of the sedative effects of dopamine agonists presumably acting on autoreceptors

L-DOPA increases slow-wave sleep duration and selectively modulates memory persistence in older adults

Introduction

Millions of people worldwide take medications such as L-DOPA that increase dopamine to treat Parkinson's disease. Yet, we do not fully understand how L-DOPA affects sleep and memory. Our earlier research in Parkinson's disease revealed that the timing of L-DOPA relative to sleep affects dopamine's impact on long-term memory. Dopamine projections between the midbrain and hippocampus potentially support memory processes during slow wave sleep. In this study, we aimed to test the hypothesis that L-DOPA enhances memory consolidation by modulating NREM sleep.

Methods

We conducted a double-blind, randomised, placebo-controlled crossover trial with healthy older adults (65-79 years, n = 35). Participants first learned a word list and were then administered long-acting L-DOPA (or placebo) before a full night of sleep. Before sleeping, a proportion of the words were re-exposed using a recognition test to strengthen memory. L-DOPA was active during sleep and the practice-recognition test, but not during initial learning.

Results

The single dose of L-DOPA increased total slow-wave sleep duration by approximately 11% compared to placebo, while also increasing spindle amplitudes around slow oscillation peaks and around 1-4 Hz NREM spectral power. However, behaviourally, L-DOPA worsened memory of words presented only once compared to re-exposed words. The coupling of spindles to slow oscillation peaks correlated with these differential effects on weaker and stronger memories. To gauge whether L-DOPA affects encoding or retrieval of information in addition to consolidation, we conducted a second experiment targeting L-DOPA only to initial encoding or retrieval and found no behavioural effects.

Discussion

Our results demonstrate that L-DOPA augments slow wave sleep in elderly, perhaps tuning coordinated network activity and impacting the selection of information for long-term storage. The pharmaceutical modification of slow-wave sleep and long-term memory may have clinical implications.

Clinical trial registration

Eudract number: 2015-002027-26; https://doi.org/10.1186/ISRCTN90897064, ISRCTN90897064.

Roles of adrenergic α1 and dopamine D1 and D2 receptors in the mediation of the desynchronization effects of modafinil in a mouse EEG synchronization model

BACKGROUND

Synchronized electroencephalogram (EEG) activity is observed in pathological stages of cognitive impairment and epilepsy. Modafinil, known to increase the release of catecholamines, is a potent wake-promoting agent, and has shown some abilities to desynchronize EEG,but its receptor mechanisms by which modafinil induces desynchoronization remain to be elucidated. Here we used a pharmacological EEG synchronization model to investigate the involvement of adrenergic α1 receptors (R, α1R) and dopamine (DA) D1 and D2 receptors (D1Rs and D2Rs) on modafinil-induced desynchronization in mice.

METHODOLOGY/PRINCIPAL FINDINGS

Mice were treated with cholinergic receptor antagonist scopolamine and monoamine depletor reserpine to produce experimental EEG synchronization characterized by continuous large-amplitude synchronized activity, with prominent increased delta and decreased theta, alpha, and beta power density. The results showed that modafinil produced an EEG desynchronization in the model. This was characterized by a general decrease in amplitude of all the frequency bands between 0 and 20 Hz, a prominent reduction in delta power density, and an increase in theta power density. Adrenergic α1R antagonist terazosin (1 mg/kg, i.p.) completely antagonized the EEG desynchronization effects of modafinil at 90 mg/kg. However, DA D1R and D2R blockers partially attenuated the effects of modafinil. The modafinil-induced decrease in the amplitudes of the delta, theta, alpha, and beta waves and in delta power density were completely abolished by pretreatment with a combination of the D1R antagonist SCH 23390 (30 µg/kg) and the D2R antagonist raclopride (2 mg/kg, i.p.).

CONCLUSIONS/SIGNIFICANCE

These results suggest that modafinil-mediated desynchronization may be attributed to the activation of adrenergic α1R, and dopaminergic D1R and D2R in a model of EEG synchronization.

To what extent do neurobiological sleep-waking processes support psychoanalysis?

Sigmund Freud's thesis was that there is a censorship during waking that prevents memory of events, drives, wishes, and feelings from entering the consciousness because they would induce anxiety due to their emotional or ethical unacceptability. During dreaming, because the efficiency of censorship is decreased, latent thought contents can, after dream-work involving condensation and displacement, enter the dreamer's consciousness under the figurative form of manifest content. The quasi-closed dogma of psychoanalytic theory as related to unconscious processes is beginning to find neurobiological confirmation during waking. Indeed, there are active processes that suppress (repress) unwanted memories from entering consciousness. In contrast, it is more difficult to find neurobiological evidence supporting an organized dream-work that would induce meaningful symbolic content, since dream mentation most often only shows psychotic-like activities.

The involvement of dopamine in the modulation of sleep and waking

Dopamine (DA)-containing neurons involved in the regulation of sleep and waking (W) arise in the ventral tegmental area (VTA) and the substantia nigra pars compacta (SNc). The VTA and SNc cells have efferent and afferent connections with the dorsal raphe nucleus (DRN), the pedunculopontine and laterodorsal tegmental nuclei (PPT/LDT), the locus coeruleus (LC), the lateral and posterior hypothalamus (LH), the basal forebrain (BFB), and the thalamus. Molecular cloning techniques have enabled the characterization of two distinct groups of DA receptors, D(1)-like and D(2)-like receptors. The D(1) subfamily includes the D(1) and D(5) receptors, whereas the D(2) subfamily comprises the D(2), D(3), and D(4) receptors. Systemic administration of a selective D(1) receptor agonist induces behavioral arousal, together with an increase of W and a reduction of slow wave sleep (SWS) and REM sleep (REMS). Systemic injection of a DA D(2) receptor agonist induces biphasic effects, such that low doses reduce W and increase SWS and REMS (predominant activation of the D(2) autoreceptor), whereas large doses induce the opposite effect (predominant facilitation of the D(2) postsynaptic receptor). Compounds with DA D(1) or D(2) receptor blocking properties augment non-REMS and reduce W. Preliminary findings tend to indicate that the administration of a DA D(3)-preferring agonist induces somnolence and sleep in laboratory animals and man. DA neurons in the VTA and the SNc do not change their mean firing rate across the sleep-wake cycle. It has been proposed that DA cells in the midbrain show a change in temporal pattern rather than firing rate during the sleep-wake cycle. The available evidence tends to indicate that during W there occurs an increase of burst firing activity of DA neurons, and an enhanced release of DA in the VTA, the nucleus accumbens (NAc), and a number of forebrain structures. A series of structures relevant for the regulation of the behavioral state, including the DRN, LDT/PPT, LC, and LH, could be partly responsible for the changes in the temporal pattern of activity of DA neurons.

Resting state oscillatory brain dynamics in Parkinson’s disease: An MEG study

OBJECTIVE

The pathophysiological mechanisms of cognitive dysfunction and dementia in Parkinson's disease (PD) are still poorly understood. Altered resting state oscillatory brain activity may reflect underlying neuropathological changes. The present study using magneto encephalography (MEG) was set up to study differences in the pattern of resting state oscillatory brain activity in groups of demented and non-demented PD patients and healthy, elderly controls.

METHODS

The pattern of MEG background oscillatory activity was studied in 13 demented PD patients, 13 non-demented PD patients and 13 healthy controls. Whole head MEG recordings were obtained in the morning in an eyes closed and an eyes open, resting state condition. Relative spectral power was calculated using Fast Fourier Transformation in delta, theta, alpha, beta and gamma frequency bands.

RESULTS

In the non-demented PD patients, relative theta power was diffusely increased and beta power concomitantly decreased relative to controls. gamma Power was decreased in central and parietal channels. In the demented PD patients, a diffuse increase in relative delta and to lesser extent theta power and a decrease in relative alpha, beta and to lesser extent gamma power were found in comparison to the non-demented PD group. In addition, reactivity to eye opening was much reduced in the demented PD group.

CONCLUSIONS

Parkinson's disease is characterized by a slowing of resting state brain activity involving theta, beta and gamma frequency bands. Dementia in PD is associated with a further slowing of resting state brain activity, additionally involving delta and alpha bands, as well as a reduction in reactivity to eye-opening.

SIGNIFICANCE

The differential patterns of slowing of resting state brain activity in demented and non-demented PD patients suggests that, in conjunction with a progression of the pathological changes already present in non-demented patients, additional mechanisms are involved in the development of dementia in PD.

Brain inhibitory mechanisms involved in basic and higher integrated sleep processes

Brain function is supported by central activating processes that are significant during waking, decrease during slow wave sleep following waking and increase again during paradoxical sleep during which brain activation is as high as, or higher than, during waking in nearly all structures. However, inhibitory mechanisms are crucial for sleep onset. They were first identified by behavioral, neuroanatomical and electrophysiological criteria, then by pharmacological and neurochemical ones. During slow wave sleep, they are supported by GABAergic mechanisms located at midbrain, mesopontine and pontine levels but are induced and sustained by forebrain and hindbrain influences. GABAergic processes are also responsible for paradoxical sleep occurrence, particularly by suppression of noradrenaline and serotonin (5-HT) inhibition of paradoxical sleep-generating structures. Hindbrain and forebrain modulate these structures situated at the mesopontine level. For sleep mentation, the noradrenergic and serotonergic silence is thought, today, to be directly, or indirectly, responsible for dopamine predominance and glutamate decrease in the nucleus accumbens, which could be the background of the well-known psychotic-like mental activity of dreaming.

Apomorphine delays simple reaction time in Parkinsonian patients

BACKGROUND

Parkinsonian patients have difficulty in the preparation and execution of movements, which translate into delayed performance of simple reaction time (SRT) paradigms.

OBJECTIVE

To examine short-term effects of an acute subcutaneous injection of the dopamine agonist apomorphine on the results of a SRT task.

METHODS

We studied a SRT paradigm in 26 non-fluctuating idiopathic Parkinsonian patients, before and 30, 60, 90 min after administration of apomorphine.

RESULTS

The reaction time (RT) was significantly delayed after apomorphine injection. We found no significant change in movement time (MT).

CONCLUSION

Delay of RT and the lack of response of MT to apomorphine administration may result from the sedative effects of apomorphine, overstimulation of postsynaptic dopaminergic receptors with subsequent inhibition of prefrontal cholinergic neurotransmission, and at least partial binding of apomorphine to presynaptic dopaminergic autoreceptors, which cause inhibition of locomotor activity. We suggest that future studies testing the capacity for reaction in Parkinsonian patients should consider the exact timing of the delivery of dopamine substituting drugs prior to the test.

The atypical antipsychotics risperidone, clozapine and olanzapine differ regarding their sedative potency in rats

The atypical antipsychotics risperidone, clozapine and olanzapine were studied for their ability to antagonise apomorphine-induced stereotypy and to affect electroencephalographic (EEG) activity in rats. The compounds antagonised apomorphine-induced stereotypy with ED(50)s of 0.15 mg/kg s.c. for risperidone, 0.42 mg/kg s.c. for olanzapine and 1.3 mg/kg s.c. for clozapine. At a dose close to that required for apomorphine antagonism (0.16 mg/kg s.c.), risperidone induced only minor changes in EEG power spectral activity. At a higher dosage (0.63 mg/kg s.c.) it increased the power density in the high frequency range (9.8-18.6 Hz), characteristic of a sedative-like effect. Olanzapine and clozapine caused a dose-dependent increase in power density in all frequency bands. These effects were already present at doses (0.04 and 0.16 mg/kg s.c., respectively) 10 times below those required for apomorphine antagonism. The effects increased dose-dependently and were pronounced at the doses required for apomorphine antagonism. These results in rats are in agreement with the clinical observation that risperidone has less propensity for inducing sedation at therapeutic dose levels than olanzapine and clozapine.

Purinergic modulation of neuronal activity in the mesolimbic dopaminergic system in vivo

ATP and its metabolite adenosine activate membrane receptors, termed P2 and P1, respectively. In the present study, the modulation of the mesolimbic neuronal circuit by ATPergic and adenosinergic mechanisms was investigated by microdialysis in the nucleus accumbens (NAc) and by telemetrically recorded EEG from both the NAc and the ventral tegmental area (VTA) of freely moving rats. The basal extracellular dopamine concentration was enhanced after accumbal perfusion with the ATP analog 2-methylthio ATP (2-MeSATP; 100 microM); by contrast, adenosine (100 microM) caused a reduction of extracellular dopamine. When given alone, the P2 receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; 20 microM) decreased the concentration of dopamine, whereas the P1 receptor antagonist 8-(p-sulfophenyl)theophylline (8-SPT; 100 microM) increased it. In the same animals, P2 receptor stimulation by 2-MeSATP caused neuronal activation, indicated by an elevation of the absolute power in the EEG of the NAc mainly by enhancement of the relative power in the alpha band (8-13 Hz) of the EEG spectrum. By contrast, adenosine led to a depression of the absolute power in the VTA accompanied by an elevation of the delta-band power (0.4-6 Hz) in the NAc corresponding to a slowing of neuronal activity. When given alone, PPADS reduced the absolute EEG power in the NAc accompanied by a decrease in the high-frequency power, but had no effects on the VTA. 8-SPT on its own enhanced the total power in both the NAc and the VTA, reflected by an enhancement in the slow and the high-frequency bands. Whereas the 8-SPT-evoked changes of EEG pattern as well as of dopamine concentration in the NAc were abolished by the co-application of PPADS, the 8-SPT-induced EEG changes in the VTA persisted under these conditions. In conclusion, the accumbal neuronal output, reflected by both dopamine release and neuronal electrical activity, is modulated in a functionally antagonistic manner by P2 and P1 receptor stimulation. It is suggested that an inhibitory GABAergic feedback projection to the VTA is stimulated by adenosine, either directly or indirectly via glutamate release.

Dopaminergic substitution in Parkinson's disease

Motor complications associated with long-term levodopa application, which follow the so-called honeymoon period of well-tolerated levodopa administration and are looked upon as one clinical marker for progression of Parkinson's disease (PD), initiated a long and controversial debate on the putative neurotoxicity of levodopa. Since dopamine agonists (DA) delay onset of motor complications, they support the neuroprotective treatment strategy in PD. Efficacy and tolerability of DA differs in particular due to their affinity to various dopamine receptor subtypes. The accumulating evidence for levodopa-associated homocysteinaemia, which represents a risk factor for increased incidence of vascular disease in PD, supports the strategy of initial DA application and the use of levodopa as an add-on compound in as low a dose as possible in young PD patients.

Electroencephalographic activation by tacrine, deprenyl, and quipazine: cholinergic vs. non-cholinergic contributions

Drugs that stimulate central cholinergic transmission can induce activated, high frequency electroencephalographic (EEG) activity in rats. Monoaminergic enhancement also produces EEG activation, either by a direct stimulation of monoaminergic transmission in cortex, or a transsynaptic excitation of cholinergic projection neurons receiving excitatory monoaminergic afferents. We examined the degree of cholinergic involvement in EEG activation produced by monoaminergic and cholinergic drugs in rats. All animals were pretreated with 10 mg/kg reserpine and either 1 or 5 mg/kg scopolamine to abolish EEG activation. The acetylcholinesterase inhibitor tacrine (5-20 mg/kg) restored EEG activation in the low dose scopolamine group, but was less effective against the high scopolamine dose. The monoamine oxidase inhibitor deprenyl and the serotonergic receptor agonist quipazine restored EEG activation, an effect that was largely unaffected by different scopolamine doses. These results confirm that tacrine produces EEG activation by means of cholinergic stimulation. In contrast, activation produced by deprenyl or quipazine does not appear to be mediated by a transsynaptic excitation of cholinergic neurons and likely depends on a direct enhancement of cortical monoaminergic neurotransmission.

Discharge profiles of ventral tegmental area GABA neurons during movement, anesthesia, and the sleep-wake cycle

Although mesolimbic dopamine (DA) transmission has been implicated in behavioral and cortical arousal, DA neurons in the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) are not significantly modulated by anesthetics or the sleep-wake cycle. However, VTA and SN non-DA neurons evince increased firing rates during active wakefulness (AW) and rapid eye movement (REM) sleep, relative to quiet wakefulness. Here we describe the effects of movement, select anesthetics, and the sleep-wake cycle on the activity of a homogeneous population of VTA GABA-containing neurons during normal sleep and after 24 hr sleep deprivation. In freely behaving rats, VTA GABA neurons were relatively fast firing (29 +/- 6 Hz during AW), nonbursting neurons that exhibited markedly increased activity during the onset of discrete movements. Adequate anesthesia produced by administration of chloral hydrate, ketamine, or halothane significantly reduced VTA GABA neuron firing rate and converted their activity into phasic 0.5-2.0 sec ON/OFF periods. VTA GABA neuron firing rate decreased 53% during slow-wave sleep (SWS) and increased 79% during REM, relative to AW; however, the discharging was not synchronous with electrocortical alpha wave activity during AW, delta wave activity during SWS, or gamma wave activity during REM. During deprived SWS, there was a direct correlation between increased VTA GABA neuron slowing and increased delta wave power. These findings indicate that the discharging of VTA GABA neurons correlates with psychomotor behavior and that these neurons may be an integral part of the extrathalamic cortical activating system.

Differential effects of dopaminergic drugs on anxiety and arousal in healthy volunteers with high and low anxiety

1. The appearance of frontal midline theta activity (Fm theta), the distinct EEG theta rhythm in the frontal midline area during performance of a mental task, indicates relief from anxiety in humans. 2. The authors examined the effects of bromocriptine and sulpiride on anxiety and arousal in 24 male university students with (Fm theta group, n = 12) and without (non-Fm theta group, n = 12) Fm theta. Subjects were given placebo, 2.5 mg bromocriptine and 100 mg sulpiride in a double-blind crossover design. 3. Blood samples were obtained, STAI scores were determined, and EEGs were recorded before and during the performance of an arithmetic addition task. The test was repeated twice: before and 1 hr after drug administration. 4. Bromocriptine reduced the HVA concentration in both groups; sulpiride caused an increase in both groups. In the Fm theta group, bromocriptine did not alter the appearance time of Fm theta, the state anxiety score or the task performance; sulpiride increased the Fm theta amount and reduced the state anxiety but did not affect the task performance. In the non-Fm theta group, bromocriptine increased the Fm theta duration and reduced the state anxiety score but did not influence the task performance, while sulpiride reduced Fm theta and increased the state anxiety but had no effect on the task performance. 5. These results suggest that the sensitivity of presynaptic D2 receptors is higher in high-anxiety subjects compared with low-anxiety subjects, and that anxiolytic effects in high-anxiety humans and those in low-anxiety humans may be caused by decreased and increased DA activity, respectively. In addition, the stimulation of DA function may cause anxiogenic effects in high-anxiety individuals.

Evidence for the occurrence of depressant EEG effects after stimulation of dopamine D3 receptors: a computerized study in rabbits

The putative dopamine D3 receptor agonist, (+/-) 7-OH-di-n-propylaminotetralin (+/- 7-OH-DPAT), induced depressant effects on rabbit EEG at the dose of 1 mg/kg i.v. Bromocriptine, a preferential dopamine D2 receptor agonist, induced EEG activation at the dose of 0.5 mg/kg i.v. Although the lack of very selective ligands makes it difficult to discriminate between D2- and D3- dependent effects, these findings suggest that -unlike D2 receptors-dopamine D3 receptors may mediate depressant effects on the electrocorticogram.

Local administration of dopaminergic drugs into the ventral tegmental area modulates cataplexy in the narcoleptic canine

Cataplexy in the narcoleptic canine may be modulated by systemic administration of monoaminergic compounds. In the present study, we have investigated the effects of monoaminergic drugs on cataplexy in narcoleptic canines when perfused locally via microdialysis probes in the amygdala, globus pallidus/putamen, basal forebrain, pontine reticular formation and ventral tegmental area of narcoleptic and control Doberman pinchers. Cataplexy was quantified using the Food-Elicited Cataplexy Test and analyzed by electroencephalogram, electroculogram and electromyogram. Local perfusion with the monoaminergic agonist quinpirole, 7-OH-DPAT and BHT-920, into the ventral tegmental area produced a dose-dependent increase in cataplexy without significantly reducing basal muscle tone. Perfusion with the antagonist raclopride in the same structure produced a moderate reduction in cataplexy. Local perfusion with quinpirole, 7-OH-DPAT and BHT-920 into the globus pallidus/putamen also produced an increase, while raclopride produced a decrease, in cataplexy in narcoleptic canines. In control animals, none of the above drugs produced cataplexy or muscle atonia when perfused into either the ventral tegmental area or the globus pallidus/putamen. Other monoaminergic drugs tested in these two brain areas; prazosin, yohimbine, amphetamine, SKF 38393 and SCH 23390 had no effects on cataplexy. Local perfusion with each of the above listed drugs had no effect on cataplexy in any of the other brain regions examined. These findings show that cataplexy may be regulated by D2/D3 dopaminergic receptors in the ventral tegmental area and perhaps the globus pallidus/ putamen. It is suggested that neurons in the mesolimbic dopamine system of narcoleptics are hypersensitive to dopaminergic autoreceptor agonists.

Some general anesthetics reduce serotonergic neocortical activation and enhance the action of serotonergic antagonists

In urethane-anesthetized rats, neocortical LVFA induced by 100 Hz electrical stimulation of the median raphe area or by tail pinching was completely eliminated by a combination of scopolamine (5 mg/kg, IP) and p-chlorophenylalanine (500 mg/kg/day x 3, IP), providing evidence that LVFA is dependent on cholinergic-muscarinic and serotonergic inputs to the neocortex in urethane-anesthetized as well as in freely moving rats. The serotonergic receptor antagonists ketanserin and methiothepin (1-10 mg/kg, IP) also produced a dose-dependent blockade of LVFA in urethane-anesthetized rats, and eliminated virtually all LVFA when combined with scopolamine. A combination of diethyl ether anesthesia and scopolamine completely eliminated all neocortical LVFA without additional antiserotonergic treatment, and a combination of chloral hydrate anesthesia and scopolamine similarly blocked all LVFA in about 50% of the rats tested. In the remaining chloral hydrate-anesthetized rats, the residual LVFA could be eliminated by the serotonergic antagonist ritanserin (10 mg/kg, IP). As shown previously, in nonanesthetized rats treated with scopolamine, LVFA can be maintained by a serotonergic input to the neocortex. The present data suggest that some general anesthetics reduce or completely abolish this serotonergic LVFA. Further, the serotonergic antagonists used here exert much stronger antiserotonergic effects in rats anesthetized with urethane or chloral hydrate than in freely moving rats. Therefore, studies of serotonergic transmission or antagonist action, especially in the neocortex, in anesthetized rats may not be applicable to the waking state.

Effects of morphine on EEG in rats and their possible relations to hypo- and hyperkinesia

It was previously shown in rats that administration of cocaine or d-amphetamine in moderate doses produced alterations in EEG characteristic for activation of D1 dopamine receptors, whereas large doses induced alterations resembling activation of D2 dopamine receptors. Since morphine, among other effects, enhances the dopaminergic transmission, it was investigated whether this effect might be apparent in the EEG which was recorded telemetrically in awake, not restrained rats. In a moderate dose (3 mg/kg IP), morphine produced a desynchronisation and a general decrease of power in all of the frequency bands except beta-2. This effect was antagonized by naloxone (0.5 mg/kg IP) but only in part by the blocker of D1 receptors SCH 23390 (0.2 mg/kg IP) and not by haloperidol in a dose which mainly blocks D2 receptors (0.1 mg/kg IP). The dose of morphine used (3 mg/kg IP) produced only slight signs of behavioural activation. The results suggest that the decrease in power observed after this dose of morphine was only in part due to an activation of dopaminergic mechanisms via D1 receptors and partly must be explained by other actions of morphine. A large dose of morphine (15 mg/kg IP) at the beginning produced catalepsy and muscular rigidity and subsequent behavioural activation; in the EEG during both behavioural phases a general increase in power in all of the frequency bands was observed which was most pronounced in the alpha-2 band (9.75-12.50 Hz).(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on electroencephalogram (EEG) in rats suggest that moderate doses of cocaine or d-amphetamine activate D1 rather than D2 receptors

The effects of cocaine and d-amphetamine, two psychomotor stimulant drugs with pronounced addictive properties, on the electroencephalogram (EEG) of rats were studied by telemetric recordings from the skull in non-anesthetized, freely moving rats. The electrocorticogram (ECoG) was recorded. Both cocaine (10 mg/kg IP) and d-amphetamine (0.4 mg/kg IP) produced a desynchronization, characterized by a general lowering in power in all of the frequency bands. These effects of both drugs were mimicked by the selective agonist at D1 receptors SK&F 38393 (3 mg/kg SC) and were reversed by the antagonist at D1 receptors SCH 23390 (0.2 mg/kg IP) but not influenced by haloperidol (0.1 mg/kg IP) in a dose which is likely to block D2 rather than D1 receptors. These doses of cocaine or d-amphetamine did not produce stereotyped behaviour and slight, if any, increases in locomotor activity only. Large doses of cocaine (30 mg/kg IP) or d-amphetamine (4 mg/kg IP) produced stereotyped behaviour and alterations in EEG which are, based on previous own studies, characteristic for additional stimulation of D2 receptors. This was manifest in a selective increase in power of the alpha-1 band. A similar effect was also produced by the agonist both at D1 and D2 receptors, apomorphine (0.5 mg/kg SC). These results suggest that moderate, but probably rewarding doses of cocaine or d-amphetamine mainly activate D1 dopamine receptors. This activation might be relevant for the rewarding properties of these drugs.

Alpha 2-adrenoceptors and vigilance in cats: antagonism of medetomidine sedation by atipamezole

In order to evaluate the effect of a specific alpha 2-adrenoceptor antagonist, atipamezole, on vigilance, adult cats with implanted electrodes for polygraphy were tested in a double-blind Latin square design. The standard clinical dose (0.1 mg/kg i.m.) of the specific alpha 2-adrenoceptor agonist, medetomidine, promptly induced stuporous sedation. Atipamezole, given 30 min later at 0.2, 0.4 or 0.8 mg/kg i.m., reversed the sedation within 3 min, resulting in complete awareness of the animal. After the small dose of atipamezole, arousal with some motor excitation continued for 6 h, whereas after the larger doses, the physiological sleep-wake cycle returned earlier. Used alone, the preferred dose, 0.4 mg/kg atipamezole i.m., allowed physiological sleep within 33 +/- 9 min, compared to 22 +/- 3 min after saline. Atipamezole thus proved to be a most effective antagonist to sedation with alpha 2-adrenoceptor agonist drugs, without disturbing excitatory effects. Specific alpha 2-adrenoceptor modulating drugs have evident clinical application, as antidotes to overdosage of alpha 2-adrenoceptor agonists, or to terminate their effect after surgical procedures.

Effects of stimulation of dopamine D1 receptors on the cortical EEG in rats: different influences by a blockade of D2 receptors and by an activation of putative dopamine autoreceptors

The effects of a stimulation of dopamine D1 receptors by using (+/-)SKF 38393 on the cortical EEG in rats which were chronically implanted with electrodes were studied. Administration of SKF 38393 (3 or 9 mg/kg, s.c.) produced alterations suggesting an arousal in the EEG: the power in all of the frequency bands decreased to a level of 70-80% of baseline activity, which effect was dose- and time-dependent. In behaviour, episodes of intensive grooming (face-washing) alternated with those of lack of spontaneous motility and occasionally chewing movements were noted. In contrast, apomorphine (0.5 mg/kg, s.c.) produced a selective increase in power in the alpha 1 band, accompanied by stereotyped sniffing and licking. The effects of SKF 38393 (9 mg/kg) were completely blocked by pretreatment with the selective antagonist at D1 dopamine receptors, SCH 23390 (0.2 mg/kg, i.p.). The application of haloperidol (0.1 mg/kg, i.p.), which is mainly a D2 blocker, failed to influence the alterations induced by SKF 38393 (9 kg/kg, s.c.). In a further experimental group, the effects produced by stimulation of D1 receptors (SKF 38393 9 mg/kg), followed by activation of putative dopamine autoreceptors by a small dose of apomorphine (0.05 mg.kg, s.c.) were studied: in this case, the effects of SKF 38393 were abolished and typical effects of small doses of apomorphine were manifest, such as hypokinesia and sedation, accompanied by large increases of power in all of the frequency bands, except beta 2. The results suggest that stimulation of D1 receptors produces some desynchronization in the EEG.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of quinpirole on the behaviour shown by mice in the light-dark box and during social interactions

Quinpirole (0.25, 0.5 and 1.0 mg/kg) was administered by intraperitoneal injection to pair-housed adult DBA/2 mice. Controls received injections of physiological saline. Effects on behaviour during 5 min social encounters with untreated partners were examined by ethological procedures, commencing at 30 min after injection. Behaviour was examined in an aversive and less aversive situation, an unfamiliar neutral cage and the home cage. Behavioural effects were then assessed in a two-compartment black and white test box. Quinpirole dose-dependently increased the frequency and duration of flight, including the specific element "retreat". At 0.5 mg/kg, the element, "freeze", was also increased during encounters in the neutral cage. Immobility (a flaccid sitting posture) and sniffing of the substrate were increased by quinpirole to a similar extent at all dose levels, while non-social activity and social investigation were reduced. The significance of the effects of quinpirole in the home cage and neutral cage were qualitatively similar; the only quantitative differences were a greater enhancement of the duration of immobility and the frequency of substrate sniffing in the home cage. In the light-dark box, quinpirole reduced the number of transitions between light and dark compartments and decreased line crossings and scans/unit time in the light compartment, although it increased the amount of time in the light compartment into which mice had been originally placed. The induction of immobility and decrease of several active behavioural responses may arise from a D2 autoreceptor inhibition of locomotor activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of stimulation of putative dopamine autoreceptors on electroencephalographic power spectrum in comparison with effects produced by blockade of postsynaptic dopamine receptors in rats

Alterations in cortical EEG activity in male rats produced by putative agonists at dopamine (DA) autoreceptors and by antagonists at postsynaptic DA receptors were compared in order to study, whether an impairment in dopaminergic neurotransmission via two different mechanisms might result in similar or different effects. Simultaneously to the EEG recordings, gross behaviour was observed. Putative agonists at DA autoreceptors (apomorphine 0.05 mg/kg, quinpirole 0.05 mg/kg, or talipexole 0.02 mg/kg s.c.) produced increases in the power in all of the frequency bands, except beta-2, with the most pronounced increase in the delta band. These EEG alterations were accompanied by hypokinesia, ptosis and yawning. In contrast, antagonists at DA receptors (haloperidol 0.1 mg/kg i.p., D2 blocker) or SCH 23390 (0.2 mg/kg i.p., D1 blocker) led to little increases in the delta band, but more pronounced increases in the alpha-2 band. Behavioural signs were hypokinesia, but little ptosis and yawning. The combination of both blockers produced, in addition, strong increases in the delta band and behavioural signs of ptosis and yawning. These results suggest that activation of putative dopamine autoreceptors produces EEG patterns and behavioural patterns different from those produced by blockade of either D1 or D2 postsynaptic dopamine receptors. In contrast, the effects following a stimulation of putative DA autoreceptors, which are expected to decrease the release of the agonist and its action at postsynaptic D1 and D2 receptors, were very similar to those found after a combined blockade of both types of postsynaptic dopamine receptors.

Determination of extracellular glutamate after local K+ stimulation in the striatum of non-anaesthetised rats after treatment with dopaminergic drugs ? studies using microdialysis

The present experiments were performed in order to investigate the effects of dopamine(DA)ergic drugs on the concentrations of extracellular glutamate (GLU) in the striatum of non-anaesthetised, freely moving rats by using microdialysis and to get further information about the interactions between glutamatergic and dopaminergic pathways. GLU was determined after pre-column derivatisation with o-phthaldialdehyde by HPLC and fluorescence detection. For increasing the fraction of extracellular GLU which is of neuronal origin, an enhanced release of this neurotransmitter was evoked by 100 mM K+ administered via the dialysis probe. This stimulation was applied twice in each experiment, at the second time after administration of a subcutaneously (s.c.) given DAergic drug. For basal conditions, a perfusion fluid containing 148.2 mM Na+, 4mM K+, 1.2 mM Ca2+ was used, for conditions of stimulation with 100 mM K+ the Na+ concentration was reduced correspondingly. Activation of the D1 receptor with the selective D1 sector agonist SKF 38393 ((+/-) 1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol) 15 mg/kg) failed to influence the stimulated release of GLU, and neither a combination of the selective D2 antagonist (-)sulpiride (150 mg/kg) with the mixed D1/D2 agonist apomorphine (1 mg/kg), nor a combination of sulpiride (150 mg/kg) with SKF 38393 (15 mg/kg) were effective. Also the two selective D2 agonists quinpirole (0.5 mg/kg) or talipexole (50 micrograms/kg) had no significant influence on the release of GLU. The results suggest that DA receptor agonists have less effect on the K(+)-stimulated GLU-release than might be expected from in vitro studies or behavioral experiments (Kornhuber and Kornhuber, 1986).