The effects of REM sleep-inhibiting drugs in neonatal rats: evidence for a distinction between neonatal active sleep and REM sleep

No phylogeny without ontogeny: a comparative and developmental search for the sources of sleep-like neural and behavioral rhythms

A comprehensive review is presented of reported aspects and putative mechanisms of sleep-like motility rhythms throughout the animal kingdom. It is proposed that 'rapid eye movement (REM) sleep' be regarded as a special case of a distinct but much broader category of behavior, 'rapid body movement (RBM) sleep', defined by intrinsically-generated and apparently non-purposive movements. Such a classification completes a 2 × 2 matrix defined by the axes sleep versus waking and active versus quiet. Although 'paradoxical' arousal of forebrain electrical activity is restricted to warm-blooded vertebrates, we urge that juvenile or even infantile stages of development be investigated in cold-blooded animals, in view of the many reports of REM-like spontaneous motility (RBMs) in a wide range of species during sleep. The neurophysiological bases for motorically active sleep at the brainstem level and for slow-wave sleep in the forebrain appear to be remarkably similar, and to be subserved in both cases by a primitive diffuse mode of neuronal organization. Thus, the spontaneous synchronous burst discharges which are characteristics of the sleeping brain can be readily simulated even by highly unstructured neural network models. Neuromotor discharges during active sleep appear to reflect a hierarchy of simple relaxation oscillation mechanisms, spanning a wide range of spike-dependent relaxation times, whereas the periodic alternation of active and quiet sleep states more likely results from the entrainment of intrinsic cellular rhythms and/or from activity-dependent homeostatic changes in network excitability.

Effects of oxcarbazepine on monoamines content in hippocampus and head and body shakes and sleep patterns in kainic acid-treated rats

The aim of this work was to analyze the effect of oxcarbazepine (OXC) on sleep patterns, "head and body shakes" and monoamine neurotransmitters level in a model of kainic-induced seizures. Adult Wistar rats were administered kainic acid (KA), OXC or OXC + KA. A polysomnographic study showed that KA induced animals to stay awake for the whole initial 10 h. OXC administration 30 min prior to KA diminished the effect of KA on the sleep parameters. As a measure of the effects of the drug treatments on behavior, head and body shakes were visually recorded for 4 h after administration of KA, OXC + KA or saline. The presence of OXC diminished the shakes frequency. 4 h after drug application, the hippocampus was dissected out, and the content of monoamines was analyzed. The presence of OXC still more increased serotonin, 5-hidroxyindole acetic acid, dopamine, and homovanilic acid, induced by KA.

A selective serotonin reuptake inhibitor reduces REM sleep in the homing pigeon

Avian and mammalian 'rapid eye movement' sleep (REM sleep) resemble each other in several aspects. However, the question of whether REM sleep has a shared evolutionary ancestry in birds and mammals has yet to be thoroughly explored. The brain regions and neurotransmitter systems involved in the generation of mammalian REM sleep are phylogenetically ancient, and are also found in extant birds and reptiles. Several pharmacological experiments in birds indicate that similar neural substrates are involved in the regulation of avian and mammalian sleep. However, because the drugs used in these studies generally resulted in non-specific sleep loss, the neurochemical regulation of avian REM sleep in particular remains uncertain. The selective serotonin reuptake inhibitor (SSRI) zimelidine is known to reduce REM sleep in mammals. If avian REM sleep is similarly regulated by serotonin, it would be expected that an acute dose of a SSRI should also reduce avian REM sleep. To investigate a putative role of serotonin in the regulation of avian REM sleep, changes in sleep electroencephalogram (EEG) and behavior were recorded in five pigeons (Columba livia) after the administration of an acute dose of zimelidine. Our results demonstrate that the effects of zimelidine on avian REM sleep are comparable to those observed in mammals, indicating that serotonin may serve a similar function in the control of avian and mammalian REM sleep.

Postnatal development of cholinergic neurons in the mesopontine tegmentum revealed by histochemistry

Cholinergic neurons in the laterodorsal tegmental nucleus (LDT) and pedunculopontine tegmental nucleus (PPT) play a role in the regulation of several kinds of behavior. Some of them, such as locomotion, motor inhibition or sleep, show dramatic changes at a certain period of postnatal development. To understand the neural substrate for the development of these physiological functions, we studied the development of cholinergic neurons in the LDT and PPT of postnatal and adult rats using histochemical staining of NADPH-diaphorase (NADPH-d) and immunohistochemical staining of choline acetyltransferase (ChAT) and the vesicular acetylcholine transporter (VAChT). At postnatal day 1 (P1), ChAT- and VAChT-stained cells localized more dorsally than those of NADPH-d-stained cells, and at P7 their distributions became similar to those of NADPH-d-stained cells. The number of NADPH-d-stained cells increased rapidly after birth, reaching the adult level by P7. In contrast, the number of ChAT- and VAChT-stained cells and the intensity of their staining decreased from P1 to P3 and then increased through P21. The volume of the LDT increased during the second postnatal week. These findings indicate that cholinergic neurons in the LDT develop their cholinergic properties during the second postnatal week and mature functionally thereafter. We discuss these results in light of the several physiological functions regulated by the cholinergic neurons in the mesopontine tegmentum.

The ontogeny of mammalian sleep: a response to Frank and Heller (2003)

In a recent review, Frank and Heller (2003) provided support for their 'presleep theory' of sleep development. According to this theory, rapid eye movement (REM) and non-rapid eye movement (Non-REM) sleep in rats emerge from a common 'dissociated' state only when the neocortical EEG differentiates at 12 days of age (P12). Among the assumptions and inferences associated with this theory is that sleep before EEG differentiation is only 'sleep-like' and can only be characterized using behavioral measures; that the neural mechanisms governing presleep are distinct from those governing REM and Non-REM sleep; and that the presleep theory is the only theory that can account for developmental periods when REM and Non-REM sleep components appear to overlap. Evidence from our laboratory and others, however, refutes or casts doubt on these and other assertions. For example, infant sleep in rats is not 'sleep-like' in that it satisfies nearly every criterion used to characterize sleep across species. In addition, beginning as early as P2 in rats, myoclonic twitching occurs only against a background of muscle atonia, indicating that infant sleep is not dissociated and that electrographic measures are available for sleep characterization. Finally, improved techniques are leading to new insights concerning the neural substrates of sleep during early infancy. Thus, while many important developmental questions remain, the presleep theory, at least in its present form, does not accurately reflect the phenomenology of infant sleep.

The adenosine kinase inhibitor ABT-702 augments EEG slow waves in rats

ABT-702 is a novel and selective non-nucleoside adenosine kinase (AK) inhibitor that produces increases in endogenous extracellular adenosine. Adenosine (ADO) is thought to be an important neuromodulator of sleep, therefore, the effects of ABT-702 and AK inhibition were examined on rat EEG and sleep, and compared to ADO receptor agonists to further evaluate the role of ADO receptor activation on sleep related EEG patterns. ABT-702 (10.0-30.0 micromol/kg, i.p.) increased the amplitude of the 1-4 Hz band (Fast Fourier Transform (FFT) analysis, p<0.05), which is indicative of augmented sleep-related slow waves. Theophylline (5.0 micromol/kg, i.p.), a centrally active, non-selective adenosine receptor antagonist, attenuated the effects of ABT-702 (20.0 micromol/kg, i.p.) on EEG, whereas 8-(p-sulfophenyl)-theophylline (8-PST, 150.0 micromol/kg, i.p.), a peripherally active antagonist, did not, indicating that the EEG effects of ABT-702 are mediated by a central ADO receptor mechanism. The selective A(1) agonist N6-cyclopentyladenosine (CPA, 30.0 micromol/kg, i.p.) also increased the amplitude of 1-4 Hz band, but was not as efficacious as ABT-702. In contrast, the A(2A) agonist CGS-21680 (1.0-10.0 micromol/kg, i.p.) and the non-selective agonist, N(6)-ethylcarboximidoadenosine (NECA, 0.03-0.1 micromol/kg, ip.), lowered 1-4 Hz amplitude for 2 h after injection. Finally, ABT-702 (10.0 micromol/kg, i.p.) was found to significantly increase slow wave sleep and decrease REM sleep in rats implanted with both EEG and EMG electrodes for evaluation of sleep. These studies demonstrate that increased extracellular adenosine through AK inhibition can elicit modulatory effects on EEG slow waves via an interaction with central ADO receptor subtypes.

Failure of ethanol and acetaldehyde to alter in vivo norepinephrine release in the striatum and hippocampus of rats

The effect of ethanol (EtOH) and acetaldehyde (AcH) on norepinephrine (NE) release was examined in the striatum and hippocampus of freely moving rats by means of in vivo microdialysis coupled with high-performance liquid chromatography and an electrochemical detector. Rats were treated intraperitoneally with EtOH (1 g/kg) or cyanamide (CY, 50 mg/kg, a potent aldehyde dehydrogenase inhibitor) plus EtOH (1 g/kg). No significant difference in NE levels in the dialysates was observed in the striatum and hippocampus in either the EtOH or CY+EtOH groups. NE levels in the hippocampal dialysates were about fivefolds higher than those in the striatum. The concentration of EtOH and AcH in the striatal dialysate reached a peak at 30 min after EtOH dosing and then gradually decreased in the CY+EtOH group. In the EtOH group the striatal concentration of EtOH also reached a peak at 30 min after EtOH dosing, and then gradually decreased while AcH was not detected. The present study suggests that there is no in vivo effect of brain EtOH or AcH on NE release in the striatum and hippocampus of awake rats.

REM sleep effects as a biomarker for the effects of antidepressants in healthy volunteers

The potential use of rapid eye movement (REM) sleep effects as a biomarker for the therapeutic effects of antidepressants in healthy volunteers is reviewed. A literature search was performed to select studies investigating the effects of antidepressants on REM sleep. To assess the specificity of REM sleep effects as a biomarker, the effects of other central nervous system drugs on REM sleep were also investigated. A significant REM sleep reduction was shown for 16 of 21 investigated antidepressants after single-dose (mean reduction 34.1%) and for 11/13 drugs after multiple-dose administration (mean reduction 29.2%). The median increase in REM latency was approximatety 60% after single- or multiple-dose administration. REM sleep effects were linearly normalized to therapeutic doses, by dividing the REM sleep effect by the investigated dose and multiplying by the therapeutic dose. Normalized REM sleep effects were highly variable (range -27.0% to 81.8% for REM sleep; range -17.0% to 266.3% for REM latency) and demonstrated no relationship with relevant pharmacological properties of the investigated drugs. No quantifiable dose-response relationship could be constructed after single and multiple dose administration. REM sleep effects were not specific for antidepressants. Benzodiazepines, for example, caused an average dose normalized REM sleep reduction of 8.7% and a median 8.6% increase of REM latency. This review demonstrates that although REM sleep effects occur with most of the antidepressants, it is by itself of limited value as a biomarker for antidepressant action. The specificity for antidepressants is limited, and it does not show a quantitative dose-response relationship to antidepressant agents. This is at least partly due to the complex relationships between drug pharmacokinetics and the variable time course of REM and other sleep stages throughout the night. Models that take these complex relationships into account may provide more comprehensive and quantifiable results.

The ontogeny of mammalian sleep: a reappraisal of alternative hypotheses

Newborn mammals spend as much as 90% or more of their time in a sleep state characterized by frequent twitches, rapid eye movements (REMs), and irregular respiratory cycles. These motor and respiratory patterns resemble the phasic motor/respiratory components of adult REM sleep, and as a consequence, this sleep state is traditionally viewed as an immature form of REM sleep. An alternative view is that a significant portion of what has been called REM sleep in these species is a form of spontaneous activity typical of the immature nervous system. In this review, we compare and contrast these two opposing views about the ontogenetic origins of REM sleep, and review the evidence most often cited to support the idea that REM sleep is present in newborn altricial mammals. Critical review of this evidence indicates that REM sleep may not be present at birth in these species; rather, it appears that all mammals early in development exhibit spontaneous, dissociated activity that progressively becomes organized into the distinct states of REM and non-rapid eye movement sleep.

The interaction between sleep and thermoregulation in adults and neonates

The interaction between sleep and thermoregulation leads to different thermoregulatory responses depending on the sleep stage and alterations in sleep when in a cool or warm environment. In the human adult, differences in thermoregulatory efficiency during rapid eye movement (REM) sleep and slow wave sleep (SWS) are less pronounced compared to other mammals: although thermoregulatory processes persist in REM sleep, they are less efficient than during SWS. Cold and warm loads disturb the efficiency and structure of sleep. The duration of REM sleep and (to a lesser extent) of SWS decreases. In contrast, pre-sleep warm loads enhance SWS and improve sleep continuity. This procedure may promote and maintain sleep in depressed patients, whose sleep and body temperature rhythms are modified. In contrast to adults, homeothermic processes in neonates are maintained or even enhanced during active sleep (AS) when compared to quiet sleep (QS). Sleeping in a cool environment increases the duration of AS at the expense of QS. As a result, the thermoregulatory function overcomes the need to conserve energy that would otherwise lead to increased QS. An interaction between sleep, respiration, and thermoregulation may be involved in Sudden Infant Death Syndrome: an alteration in the thermal balance may perhaps induce respiration instability, especially during AS.

5-HT(2A/2C) receptor-mediated hypopnea in the newborn rat: relationship to Fos immunoreactivity

Previous data derived from anesthetized, decerebrate, or in vitro preparations suggested that 5-HT(2) receptor activation might be responsible for respiratory dysfunction. Such a mechanism has not yet been documented in the intact animal, but might be of clinical relevance to the apneic spells of the premature infant. In the present investigation on conscious newborn rats we analyzed the respiratory response to the activation of 5-HT(2A/2C) receptors by the agonist 1-(2.5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), and we delineated central structures possibly involved in this response, using Fos expression as a marker of neuronal activation. We demonstrated that intraperitoneal injection of 5 mg/kg DOI produced a long-lasting decrease in respiratory frequency and tidal volume, which could be blocked by the antagonist ritanserin. Fos immunohistochemistry suggested that the rostral ventrolateral medulla and the lateral paragigantocellular nucleus might have a key role in the respiratory response to 5-HT(2) receptor activation. In addition, double immunostaining for Fos and tyrosine hydroxylase suggested that the contribution of catecholaminergic neurons to this response might be modest and indirect.

Postnatal development of choline acetyltransferase activity in the rat laterodorsal tegmental nucleus

Cholinergic neurons in the laterodorsal tegmental nucleus (LDT) have important roles in the regulation of sleep or waking in adult animals. In neonatal animals, sleep is largely occupied by paradoxical sleep. To investigate the relation between the cholinergic neurons in the LDT and the development of neonatal sleep, we dissected the LDT of rat by micropunch method at postnatal day 1--45 and measured the activity of choline acetyltransferase (ChAT). Either specific or total activity of ChAT was weak in the first week, increased strikingly in the second week and then moderately thereafter. The time course of the increase in ChAT activity correlates well to that of the decrease in the amount of paradoxical sleep or body twitches after birth.

Mesopontine contribution to the expression of active 'twitch' sleep in decerebrate week-old rats

Myoclonic twitching is a ubiquitous feature of infant behavior that has been used as an index of active sleep. Although the active sleep of infants differs in some ways from the REM sleep of adults, their marked similarities have led many to view them them as homologous behavioral states. Recently, however, this view has been challenged. One avenue for resolving this issue entails examination of the neural substrates of active sleep. If the neural substrates of active sleep were found to be similar to those of REM sleep, then this would support the view that the two states are homologous. Therefore, in the present study, decerebrations were performed in the pons and midbrain to determine whether the mesopontine region is important for the expression of active sleep in infants, just as it is for the expression of REM sleep in adults. It was found that, in comparison to controls, caudal pontine decerebrations reduced myoclonic twitching by 76%, rostral pontine decerebrations reduced twitching by 40%, and midbrain transections had no significant effect on twitching. Moreover, analysis of the temporal organization of twitching indicated that pontine decerebrations predominantly affected high-frequency twitching while leaving unaffected the low-frequency twitching that is thought to be contributed by local spinal circuits at this age. These results indicate that the mesopontine region plays a central role in the expression of active sleep in infant rats.

Determination of norepinephrine in microdialysis samples by microbore column liquid chromatography with fluorescence detection following derivatization with benzylamine

A microbore column liquid chromatographic method is described for the determination of norepinephrine (NE) in microdialysis samples from rat brain. The method is based on precolumn derivatization of NE with benzylamine in the presence of potassium hexacyanoferrate(III) resulting in a highly fluorescent and stable benzoxazole derivative. Typically, a 10-microl sample was mixed with 10 microl derivatization reagent containing 0.45 M Caps buffer (pH 12.0), 0.2 M benzylamine, 10 mM potassium hexacyanoferrate(III), and N,N-dimethylformamide (1:1:1:15, v/v). The derivatization was carried out at 50 degrees C for 20 min. Under these conditions only NE and epinephrine produced high fluorescence yields at excitation and emission wavelengths of 345 and 480 nm, respectively, while fluorescence of other catechols and 5-hydroxyindoles was quenched by 10-100 times. The NE derivative was separated on a reversed-phase column (100 x 1.0 mm i.d., packed with C18 silica, 5 microm) within 10 min with no late eluting peaks. The mobile phase consisted of 40 mM Britton-Robinson buffer (pH 7.5) containing 1 mM didodecyldimethylammonium bromide and acetonitrile (34%, v/v), the flow rate was 40 microl/min. The limit of detection (signal-to-noise ratio of 3) for NE was 90 amol in 10 microl sample injected. Microdialysis samples were collected in 5-min intervals from the probes implanted in the hippocampus, frontal cortex, or hypothalamus of awake rats. The basal extracellular NE levels in the respective areas were 4.7 +/- 0.9, 1.8 +/- 0.3, and 0.8 +/- 0.2 fmol/10 microl (mean +/- SE, n = 7). Perfusion with a Ringer solution containing 100 mM K+ increased hippocampal NE levels by 700%, while NE uptake inhibitors maprotiline and amitriptyline administered orally or subcutaneously increased extracellular NE in the frontal cortex by about 300%. On the other hand, reserpine (5 mg/kg) reduced cortical NE levels by 40% 3 h after the administration. This new fluorescence derivatization method provides better selectivity, sensitivity, and speed for NE determination than the electrochemical detection since no late-eluting compounds such as dopamine, serotonin, and their metabolites are detectable in the chromatograms of the microdialysis samples.

Effects of sleep deprivation in neonatal rats

This investigation represents the first systematic study of sleep homeostasis in developing mammals that spans the preweaning and postweaning periods. Neonatal rats from 12 to 24 days of postnatal life (P12-P24) were anesthetized with Metofane (methoxyflurane) and implanted with miniaturized electroencephalographic (EEG) and electromyographic electrodes. After 48 h of recovery, neonatal rats were sleep deprived for 3 h by either gentle handling or forced locomotion. We find that 3-h sleep deprivation produces dramatically different compensatory responses at different stages of postnatal development. In striking contrast to adult rats, sleep deprivation does not increase slow-wave sleep EEG delta (0.5-4.0 Hz) activity in rats younger than P24. However, P12-P20 rats do show evidence of sleep regulation because they show compensatory increases in sleep time and sleep continuity during recovery. In P12 rats, approximately 90% of total slow wave sleep time lost during the sleep-deprivation period was recovered during subsequent sleep. A similar recovery of active sleep time was observed in P20-P24 rats. These findings suggest not only that sleep is regulated in neonatal rats but that the accumulation and/or discharge of sleep need changes dramatically between the third and fourth postnatal weeks.