REM sleep suppression by monoamine reuptake blockade: development of tolerance with repeated drug administration

Noradrenaline from Locus Coeruleus Neurons Acts on Pedunculo-Pontine Neurons to Prevent REM Sleep and Induces Its Loss-Associated Effects in Rats

Normally, rapid eye movement sleep (REMS) does not appear during waking or non-REMS. Isolated, independent studies showed that elevated noradrenaline (NA) levels inhibit REMS and induce REMS loss-associated cytomolecular, cytomorphological, psychosomatic changes and associated symptoms. However, the source of NA and its target in the brain for REMS regulation and function in health and diseases remained to be confirmed in vivo. Using tyrosine hydroxylase (TH)-siRNA and virus-coated TH-shRNA in normal freely moving rats, we downregulated NA synthesis in locus coeruleus (LC) REM-OFF neurons in vivo. These TH-downregulated rats showed increased REMS, which was prevented by infusing NA into the pedunculo-pontine tegmentum (PPT), the site of REM-ON neurons, normal REMS returned after recovery. Moreover, unlike normal or control-siRNA- or shRNA-injected rats, upon REMS deprivation (REMSD) TH-downregulated rat brains did not show elevated Na-K ATPase (molecular changes) expression and activity. To the best of our knowledge, these are the first in vivo findings in an animal model confirming that NA from the LC REM-OFF neurons (1) acts on the PPT REM-ON neurons to prevent appearance of REMS, and (2) are responsible for inducing REMSD-associated molecular changes and symptoms. These observations clearly show neuro-physio-chemical mechanism of why normally REMS does not appear during waking. Also, that LC neurons are the primary source of NA, which in turn causes some, if not many, REMSD-associated symptoms and behavioral changes. The findings are proof-of-principle for the first time and hold potential to be exploited for confirmation toward treating REMS disorder and amelioration of REMS loss-associated symptoms in patients.

Depression impairs learning, whereas the selective serotonin reuptake inhibitor, paroxetine, impairs generalization in patients with major depressive disorder

To better understand how medication status and task demands affect cognition in major depressive disorder (MDD), we evaluated medication-naïve patients with MDD, medicated patients with MDD receiving the selective serotonin reuptake inhibitors (SSRI) paroxetine, and healthy controls. All three groups were administered a computer-based cognitive task with two phases, an initial phase in which a sequence is learned through reward-based feedback (which our prior studies suggest is striatal-dependent), followed by a generalization phase that involves a change in the context where learned rules are to be applied (which our prior studies suggest is hippocampal-region dependent). Medication-naïve MDD patients were slow to learn the initial sequence but were normal on subsequent generalization of that learning. In contrast, medicated patients learned the initial sequence normally, but were impaired at the generalization phase. We argue that these data suggest (i) an MDD-related impairment in striatal-dependent sequence learning which can be remediated by SSRIs and (ii) an SSRI-induced impairment in hippocampal-dependent generalization of past learning to novel contexts, not otherwise seen in the medication-naïve MDD group. Thus, SSRIs might have a beneficial effect on striatal function required for sequence learning, but a detrimental effect on the hippocampus and other medial temporal lobe structures is critical for generalization.

Behavior-dependent modulation of hippocampal EEG activity by the selective norepinephrine reuptake inhibitor reboxetine in rats

Both active wakefulness and rapid eye movement sleep (REM) give rise to rhythmic synchronized hippocampal field oscillations, known as theta activity. Antidepressant drugs, including norepinephrine re-uptake inhibitors are proven to diminish REM sleep, and REM sleep-related hippocampal theta oscillation. Since reboxetine, a highly selective norepinephrine re-uptake inhibitor has been shown to block REM sleep, but induce or facilitate hippocampal theta activity in anesthetized rats, the current study investigated the effects of reboxetine on stage- and behavior dependent theta activity. Polysomnographic recordings, which included hippocampal field potentials at the hippocampal fissure, were carried out in rats for 8 h during the light phase of the circadian cycle. Theta rhythm was analyzed during three different behavioral conditions: REM sleep, during motor activity in a familiar environment, and during exploration in a novel environment. We found that, compared with REM sleep, theta power was relatively low during periods of active wakefulness when the animal was in the familiar home cage, but considerably increased during exploration in a novel environment. Reboxetine suppressed sleep and thus abolished REM sleep-related hippocampal theta rhythm, attenuated theta in the familiar environment, and significantly enhanced theta oscillations associated with exploratory behavior. Our findings demonstrate a state- and behavior-dependent modulation of hippocampal theta activity by reboxetine, providing further evidence for a prominent role of norepinephrine in arousal and focused or selective attention.

Role of noradrenergic and GABA-ergic inputs in pedunculopontine tegmentum for regulation of rapid eye movement sleep in rats

Rapid eye movement (REM) sleep disturbance is associated with several psycho-behavioral disorders, hence, it is important to understand its neural mechanism of regulation. Although it was known that the noradrenergic (NA-ergic) neurons from locus coeruleus (LC) project to the pedunculopontine tegmentum (PPT), the role of noradrenaline (NA) alone and in association with GABA, an inhibitory neurotransmitter, in PPT for REM sleep regulation was not known and was investigated in this study in freely moving normally behaving rats. Rats were surgically prepared for electrophysiological sleep-wake recording and simultaneous bilateral microinjections into PPT. 200nl of prazosin (alpha1-antagonist) or clonidine (alpha2-agonist) or propranolol (beta-antagonist) or combination of picrotoxin (GABA-A antagonist) and clonidine or vehicle (control) was microinjected bilaterally into PPT using a remote-controlled pump and the effects on REM sleep compared. Prazosin, clonidine and propranolol increased the total time spent in REM sleep whereas co-injection of picrotoxin and clonidine did not affect REM sleep. The results suggest that NA in PPT tonically inhibits REM sleep, possibly by acting on the cholinergic REM-ON neurons, while GABA inhibits the release of NA for REM sleep regulation. A model of neural connections explaining such regulation has been presented.

Role of alpha and beta adrenoceptors in locus coeruleus stimulation-induced reduction in rapid eye movement sleep in freely moving rats

Based on the results of independent studies the involvement of norepinephrine in REM sleep regulation was known. Isolated studies showed that the effect could be mediated through either one or more subtypes of adrenoceptors. Earlier we have reported that REM-OFF neurons continue firing during REM sleep deprivation and mild but continuous stimulation of locus coeruleus (LC) or picrotoxin injection into the LC, that did not allow the REM-OFF neurons in the LC to stop firing, reduced REM sleep. However, the mechanism of action and type of adrenoreceptors involved in REM sleep regulation were unknown. The possible mechanism of action has been investigated in this study. It was proposed that if LC stimulation-induced decrease in REM sleep was due to norepinephrine, adrenergic antagonist must prevent the effect. Therefore, in this study, the effects of alpha1, alpha2 and beta-antagonists, viz. prazosin, yohimbine and propranolol, respectively, and alpha2 agonist, clonidine, on LC stimulation-induced reduction in REM sleep were investigated. The results showed that stimulation of LC inhibited REM sleep by reducing the frequency of generation of REM sleep, although the duration per episode remained unaffected. This decrease in the frequency of REM sleep was blocked by beta-antagonist propranolol while the duration of REM sleep per episode was blocked by alpha1-antagonist, prazosin. Also, a critical level of norepinephrine in the system was required for the generation of REM sleep, however, a higher level may be inhibitory. Based on the results of this study and our earlier studies, an interaction between neurons, containing different neurotransmitters and their subtypes of receptors for LC-mediated regulation of REM sleep has been proposed.

Treatment of insomnia in patients with mood disorders

Mood disorders and chronic insomnia share complex theoretical and clinical relationships. This article reviews the subjective symptoms and polysomnographic findings of subjects with mood and insomnia syndromes. The polysomnographic findings reviewed include macro-architectural and micro-architectural data. Various treatments of patients with insomnia and mood disorders will be presented, including both behavioral and pharmacological interventions.

Fluoxetine decreases brain temperature and REM sleep in Syrian hamsters

The antidepressant drug, fluoxetine (FLX), a selective serotonin reuptake inhibitor, was administered to Syrian hamsters, and its acute and chronic effects on EEG sleep and hypothalamic temperature were recorded. Acute fluoxetine treatment at doses of 5, 10, 20 and 40 mg/kg decreased REM sleep and hypothalamic temperature in a dose-dependent manner. It increased NREM sleep, and, at doses of 20 and 40 mg/kg, it increased wakefulness. At 40 mg/kg, it decreased motor activity. During chronic treatment, tolerance developed to FLX's REM sleep-inhibiting effects, but tolerance did not develop to FLX's hypothalamic temperature-decreasing effects. Chronic FLX treatment produced circadian phase-dependent decreases in temperature beyond those that were observed during acute treatment. The apparent dissociation during chronic treatment between FLX's temperature-lowering effects and its REM-decreasing effects might be related to long-term changes in 5HT receptor function or FLX pharmacokinetics.

Mapping of serotonin transporter messenger RNA-containing nerve cell populations in the cat brainstem

The anatomical distribution of nerve cells populations expressing serotonin transporter messenger RNA was investigated in the cat brain by means of in situ hybridization histochemistry. Formalin fixed coronal sections were hybridized with [35S]dATP 3' end-labeled oligoprobes complementary to three nucleotide sequences taken from the human and serotonin transporter. A strong hybridization signal was found in nerve cells populations exclusively localized within the brainstem. These positive cells mainly resided in the nuclei of the raphe, especially in the nuclei of the raphe dorsalis and raphe centralis superior. A small number of labeled cells was also observed in various areas including the dorsal part of the interpeduncular nucleus, in the midbrain, and the region ventrolateral to the inferior olive, the ventral midline and around the central canal, in the medulla oblongata. Overall, these data agree with the notion that in the cat, as previously suggested in the human and in the rat brain, the serotonin membrane transporter messenger RNA is predominantly expressed in areas known to contain serotonergic cell bodies.

REM sleep inhibition by desipramine: evidence for an alpha-1 adrenergic mechanism

The acute administration of drugs that block norepinephrine (NE) reuptake suppresses rapid eye movement (REM) sleep in cats and other mammals. The mechanism is presumed to involve NE acting on cells in a pontine REM sleep-generator region. Postsynaptic noradrenergic receptor mechanisms have not been identified. In the present experiments, we tested the ability of the alpha-1 antagonist prazosin and the beta antagonist propranolol to reverse the REM sleep suppression produced by the NE reuptake blocker desipramine (DMI) in the cat. DMI reduced the number of REM sleep episodes, the REM percentage (REM sleep time/total sleep time), and the average REM sleep episode duration. The co-administration of prazosin, but not propranolol, increased the REM percentage and the average REM sleep episode duration toward the placebo level. The co-administration of the peripherally-acting, anti-hypertensive agent hydralazine did not reverse the DMI-induced REM sleep suppression. While the identity of the brain region(s) involved in mediating the alpha-1 noradrenergic suppression of REM sleep by DMI remains unclear, there is reason to consider forebrain structures including the amygdala as well as the pontine areas that generally have been implicated in REM sleep control.

The influence of ipsapirone, a 5-HT1A agonist, on sleep patterns of healthy subjects

Ipsapirone is a new pyrimidinylpiperazine ligand specific for 5-HT1A receptors, with potential therapeutic use in affective disorders. Because 5-HT is involved in the regulation of sleep, we investigated the effect of ipsapirone hydrochloride on sleep patterns in 18 normal, healthy subjects of both sexes. Compared to placebo, ipsapirone 5 mg administered by mouth three times daily for 14 days decreased rapid eye movement (REM) sleep duration and, by the tenth day of treatment, began to reduce slow wave sleep (SWS) duration. The decrease in REM sleep occurred in the first 3 h of sleep. The latency to REM sleep was increased from the first night following ipsapirone administration, remained increased throughout the 14 days of administration, and fell to equal latency on placebo immediately administration ended. Subjective assessments of sleep revealed no differences between ipsapirone and placebo. Our experiments confirm a role of 5-HT1A receptors in sleep. The effects of ipsapirone on the sleep patterns of patients with affective disorders still need to be determined.

Canine cataplexy is preferentially controlled by adrenergic mechanisms: evidence using monoamine selective uptake inhibitors and release enhancers

Narcolepsy is currently treated with anti-depressants to control REM-related symptoms such as cataplexy and with amphetamine-like stimulants for the management of sleepiness. Both stimulant and antidepressant drugs presynaptically enhance monoaminergic transmission but both classes of compounds lack pharmacological specificity. In order to determine which monoamine is selectively involved in the therapeutic effect of these compounds, we examined the effects of selective monoamine uptake inhibitors and release enhancers on cataplexy using a canine model of the human disorder. A total of 14 compounds acting on the adrenergic (desipramine, nisoxetine, nortriptyline, tomoxetine, viloxazine), serotoninergic (fenfluramine, fluoxetine, indalpine, paroxetine, zimelidine) and dopaminergic (amfonelic acid, amineptine, bupropion, GBR 12909) systems were tested. Some additional compounds interesting clinically but with less pharmacological selectivity, i.e., cocaine, dextroamphetamine, methylphenidate, nomifensine and pemoline, were also included in the study. All compounds affecting noradrenergic transmission completely suppressed canine cataplexy at low doses in all dogs tested, whereas compounds which predominantly modified serotoninergic and dopaminergic transmission were either inactive or partially active at high doses. Our results demonstrate the preferential involvement of adrenergic systems in the control of cataplexy and, presumably, REM sleep atonia. Our findings also demonstrate that canine narcolepsy is a useful tool in assessing the pharmacological specificity of antidepressant drugs.