Role of brain alpha 1B-adrenoceptors in modafinil-induced behavioral activity

Evidence of roles of central alpha1-adrenoceptors and epinephrine in orexin A-induced hyperactivity in mice

Previous studies have shown that central alpha1-adrenoceptor activity is necessary, acutely, for gross behavioral activity in response to novel surroundings and various psychostimulants. The present experiment tested whether it is also necessary for the hyperactivity produced by the peptide, orexin A, which is present in several central monoaminergic nuclei. Mice, pretreated intraventricularly with the alpha1-antagonist, terazosin, or the alpha2-antagonist, atipamezole, were given orexin A, intraventricularly (i.v.t.), and videotaped for gross movement and locomotion in the home cage between 30 and 60 min post-infusion. The alpha1-antagonist was found to produce a significant dose-dependent decrease of orexin A-induced activity, which was first seen at the 3 nmol dose and was near total at 30 nmol. The alpha2-antagonist, at 10 nmol, had no effect on the orexin A response. Pharmacological inhibition of the synthesis of epinephrine, a potential neurotransmitter at central motoric alpha1-adrenoceptors, with 2,3-dichloro-alpha-methylbenzylamine also significantly attenuated orexin A-induced hyperactivity. It is concluded that central alpha1-adrenoceptor activity, presumably caused by epinephrine release, is necessary for the gross behavioral activation produced by orexin A.

Modafinil enhances the increase of extracellular serotonin levels induced by the antidepressant drugs fluoxetine and imipramine: a dual probe microdialysis study in awake rat

In view of a postulated role of the vigilance-promoting drug modafinil in depression, the interaction of modafinil and two classical antidepressant drugs, fluoxetine and imipramine, were studied in 5-HT levels in the dorsal raphe-cortical system using dual-probe microdialysis. Fluoxetine (1-10 mg/kg) dose-dependently increased dorsal raphe-cortical 5-HT levels. Modafinil at a very low dose (3 mg/kg), by itself ineffective, enhanced the fluoxetine (5 mg/kg)-induced increases of 5-HT levels in both brain areas. A synergistic interaction was observed in the prefrontal cortex with fluoxetine (1 mg/kg) in terms of 5-HT release, but not in the dorsal raphe. Imipramine (1.3 mg/kg) increased 5-HT levels in the dorsal raphe, but not in the prefrontal cortex, while the higher doses (10.9-21.8 mg/kg) caused substantial increases in both brain areas. Modafinil (3 mg/kg), injected before imipramine (1.3 mg/kg), which by itself was ineffective on cortical 5-HT levels, increased cortical 5-HT levels. On other hand, modafinil failed to affect the high-dose imipramine (10.9 mg/kg)-induced increase of 5-HT levels in the prefrontal cortex and the imipramine (1.3; 10.9 mg/kg)-induced increase of 5-HT levels in the dorsal raphe nucleus. These results demonstrate that modafinil in low doses enhances the acute effects of fluoxetine and imipramine on 5-HT levels in the dorsal raphe nucleus (fluoxetine only) and especially in the prefrontal cortex of the awake rat. These findings suggest a therapeutic potential of low doses of modafinil in the treatment of depression when combined with low doses of classical antidepressants, especially by increasing 5-HT transmission in cortical regions.

Emerging drugs for narcolepsy

Narcolepsy is characterised by excessive daytime sleepiness, usually associated with cataplexy, hypnagogic hallucinations, sleep paralysis and fragmented nocturnal sleep. Although uncommon, it results in significant disability. Most cases occur sporadically, but genetic factors probably form a susceptibility background on which unknown environmental triggers act. The hypocretin system is strongly implicated in the development of narcolepsy. Cerebrospinal fluid levels of hypocretin-1 are significantly reduced in narcoleptic subjects with cataplexy. Despite the advances in our understanding of narcolepsy, current therapy is primarily symptomatic. Stimulants (standard and novel) combat excessive daytime sleepiness. Antidepressants (tricyclics, dual-action or selective serotonin re-uptake inhibitors) and sodium oxybate are anticataplexy agents. Hypnagogic hallucinations and sleep paralysis respond to antidepressants. Sodium oxybate consolidates sleep. Novel and experimental treatments include histamine antagonists, hypocretin agonists, slow-wave sleep enhancers, intravenous gamma-globulin, tramadol and corticosteroids.

Gross mapping of α1-adrenoceptors that regulate behavioral activation in the mouse brain

Brain alpha1-adrenoceptors that participate in behavioral activation were mapped in the mouse brain by determining where microinjection of the alpha1-antagonist, terazosin, inhibited behavioral activity in a novel cage test. A total of 5 out of 23 tested regions were shown to be involved including the dorsal pons/locus coeruleus region (DP/LC), the dorsal raphe/periaqueductal gray area (DR/PAG), the vermis cerebellum (CER), the nucleus accumbens (ACC) and the medial preoptic area (MPOA). Injection in the 4th ventricle was also effective perhaps by acting on several of these regions simultaneously. A partial inhibition was obtained from the motor cortex. Coinjection of the alpha1/2-agonist, 6-fluoronorepinephrine (6FNE) but not the alpha2-agonist, dexmedetomidine (DMT) reversed the behavioral inhibition in all regions. It is hypothesized that brain motoric alpha1-receptors elicit behavioral activation by coordinately exciting several monoaminergic, motor and motivational systems.

Immobility from administration of the alpha1-adrenergic antagonist, terazosin, in the IVth ventricle in rats

Brain alpha1-adrenoceptors have been shown to be essential for motor activity and movement in mice using intraventricular injection of alpha1-antagonists. To facilitate subsequent neuroanatomical mapping of these receptors, the present study was undertaken to replicate these effects in the rat. Rats were administered the alpha1-antagonist, terazosin, in the absence and presence of the alpha1-agonist, phenylephrine, in the IVth ventricle and were tested for their motor activity responses to an environmental change. Terazosin was found to produce a dose-dependent, virtually complete cessation of behavioral activity that was reversed by coinfusion of phenylephrine. The results could not be explained by sedation. It is concluded that central alpha1-adrenoceptors are essential for behavioral activation in rats as in mice.

Temporal pattern of hippocampal high-frequency oscillations during sleep after stimulant-evoked waking

Hippocampal ripple oscillations (140-200 Hz) are believed to be critically involved in the consolidation of memory traces during slow-wave sleep (SWS). We investigated the temporal pattern of ripple occurrence in relation to sleep phases following different types of waking. Amphetamine, the atypical wakening drug modafinil or non-pharmacological sleep deprivation lead to an increased ripple occurrence ("rebound") during the subsequent SWS episode. Waking of the same duration evoked by amphetamine or sleep deprivation led to a ripple rebound of similar extent (approximately 200%). The mean intraripple frequency was also elevated by up to 20 Hz during SWS following all treatments. Ripple amplitude was significantly increased only in experiments with amphetamine. Ripple occurrence but not intraripple frequency clearly correlated with the antecedent waking duration independent of treatment. Recovery of ripple occurrence and frequency to the pretreatment level during SWS depended on SWS duration. At the end of the recovery period paradoxical sleep (PS) acted like waking, elevating ripple occurrence during subsequent SWS episodes. On the other hand, PS decreased ripple occurrence if recovery from the rebound was not yet complete. Thus occurrence and structure of ripple oscillations are regulated by the timing and duration of previous SWS, PS and waking episodes.

Emerging evidence for a central epinephrine-innervated alpha 1-adrenergic system that regulates behavioral activation and is impaired in depression

Currently, most basic and clinical research on depression is focused on either central serotonergic, noradrenergic, or dopaminergic neurotransmission as affected by various etiological and predisposing factors. Recent evidence suggests that there is another system that consists of a subset of brain alpha(1B)-adrenoceptors innervated primarily by brain epinephrine (EPI) that potentially modulates the above three monoamine systems in parallel and plays a critical role in depression. The present review covers the evidence for this system and includes findings that brain alpha(1)-adrenoceptors are instrumental in behavioral activation, are located near the major monoamine cell groups or target areas, receive EPI as their neurotransmitter, are impaired or inhibited in depressed patients or after stress in animal models, and are restored by a number of antidepressants. This "EPI-alpha(1) system" may therefore represent a new target system for this disorder.

Role of epinephrine stimulation of CNS alpha1-adrenoceptors in motor activity in mice

The role of brain epinephrine (EPI) in the regulation of motor activity and movement in mice was examined. Blockade of EPI synthesis with i.p. 2,3-dichloro-alpha-methylbenzylamine (DCMB) or LY134046 was found to produce marked behavioral inactivity which could be significantly reversed by intraventricular injection of EPI and by three other alpha(1)-adrenoceptor agonists, norepinephrine (NE), 6-fluoronorepinephrine (6FNE), and phenylephrine (PE), as well as by serotonin (5HT). EPI had the largest effect of these agonists and also was the only one that reversed nondrug-induced inactivity of mice in their home cages during the light phase. The effects of EPI were blocked by coinfusion of an alpha(1)-adrenoceptor antagonist (terazosin) but not of an alpha(2)-(atipamezole) or beta(1) (betaxolol)-blocker. The rank order of maximal behavioral responses to EPI, 6FNE, and PE in DCMB-treated mice was the same as the rank order of their maximal stimulation of hydrolysis of phosphatidylinositol at cloned alpha(1B)-adrenoceptors in cell culture. On the basis of the above findings and of the central distributions of adrenergic neurons and alpha(1)-adrenoceptors, the existence of a central EPI-innervated alpha(1)-adrenergic receptor system is postulated which serves to coexcite or enhance signaling in several monoaminergic brain regions involved in movement and motor activity.