Changes in sleep-wakefulness after 6-hydroxydopamine lesion of the preoptic area

The 6-Hydroxydopamine model of parkinson’s disease

The neurotoxin 6-hydroxydopamine (6-OHDA) continues to constitute a valuable topical tool used chiefly in modeling Parkinson's disease in the rat. The classical method of intracerebral infusion of 6-OHDA involving a massive destruction of nigrostriatal dopaminergic neurons, is largely used to investigate motor and biochemical dysfunctions in Parkinson's disease. Subsequently, more subtle models of partial dopaminergic degeneration have been developed with the aim of revealing finer motor deficits. The present review will examine the main features of 6-OHDA models, namely the mechanisms of neurotoxin-induced neurodegeneration as well as several behavioural deficits and motor dysfunctions, including the priming model, modeled by this means. An overview of the most recent morphological and biochemical findings obtained with the 6-OHDA model will also be provided, particular attention being focused on the newly investigated intracellular mechanisms at the striatal level (e.g., A(2A) and NMDA receptors, PKA, CaMKII, ERK kinases, as well as immediate early genes, GAD67 and peptides). Thanks to studies performed in the 6-OHDA model, all these mechanisms have now been hypothesised to represent the site of pathological dysfunction at cellular level in Parkinson's disease.

Alpha-1 adrenergic receptors in the medial preoptic area are involved in the induction of sleep

This paper reviews the recent studies that led to the conclusion that the noradrenergic neurons projecting to the medial preoptic area (mPOA) are hypnogenic and that they mediate this action through alpha(1) adrenergic receptors. Microinjection of noradrenaline (NA) into the mPOA induced arousal. Studies using alpha(2) adrenergic drugs showed that the arousal induced by intrapreoptic injection of NA was due to its action on presynaptic alpha(2) adrenergic receptors. A combination of lesion and chemical stimulation techniques demonstrated that when NA acted on the postsynaptic alpha(1 )receptors in the mPOA, it induced sleep. Intrapreoptic injection of alpha(1) agonist, methoxamine could induce sleep, when the hypothermia, which was simultaneously produced, was behaviorally compensated for by the animal. Increased arousal produced by the destruction of noradrenergic fibers in the mPOA further confirmed the hypnogenic role of these fibers.

Sleep induction and temperature lowering by medial preoptic α1 adrenergic receptors

Changes in sleep-wakefulness (S-W) and body temperature (T(b)) on administration of alpha(1) agonist (methoxamine) and antagonist (prazosin) into the medial preoptic area (mPOA) were studied in rats. Presynaptic catecholaminergic terminals of the mPOA were destroyed by injecting 6-hydroxydopamine at the ventral noradrenergic bundle (VNA), before administration of the drugs. Microinjection of 0.05 microg methoxamine induced sleep, though 0.1 microg prazosin produced no change in S-W. On the other hand, in normal rats, the same dose of methoxamine produced no change, while prazosin produced arousal. Denervation hypersensitivity may be responsible for the appearance of hypnogenic response on methoxamine administration, in the VNA-lesioned rats. The VNA-lesioned animals (before administration of any drug) had higher pre-injection values of wake period than the normal rats. A reduction in the tonic activity of noradrenergic fibers to the mPOA, and resulting reduced activity of alpha(1) receptors, may be responsible for increased wake period in the VNA-lesioned rats. The action of prazosin was probably abolished in the absence of tonic activity of alpha(1) receptor in the VNA-lesioned rats. Reduction and increase in T(b) produced by methoxamine and prazosin, respectively, confirm the involvement of alpha(1) receptors in the thermal changes. Methoxamine was less effective, than in normal rats, in reducing T(b). So, the possibility of involvement of presynaptic receptors in the thermal response is suggested. The results suggest the involvement of separate sets of alpha(1) receptors (and neurons) in hypnogenesis and in lowering T(b). As sleep is associated with fall in T(b), the alpha(1) adrenergic receptors may be involved in interlinking sleep regulation and thermoregulation.

Tonic activity of alpha1 adrenergic receptors of the medial preoptic area contributes towards increased sleep in rats

Several studies have suggested that noradrenergic afferents to the medial preoptic area might be involved in hypnogenesis and in lowering the body temperature, and that the alpha1 adrenergic receptors might be mediating these responses. This study was undertaken to find out the changes in sleep-wakefulness and body temperature in rats, when these adrenergic receptors of the medial preoptic area are blocked by alpha1 selective antagonist, prazosin. Adult male Wistar rats were chronically implanted with electrooculogram, electroencephalogram and electromyogram electrodes for sleep-wakefulness assessment, and a bilateral guide cannula for microinjection of prazosin at the medial preoptic area. A radio-transmitter was implanted in the abdomen for telemetric measurement of body temperature in four groups of rats. Sleep-wakefulness was also assessed telemetrically in four other groups of rats. Sleep-wakefulness recordings from these rats were done in a specialized chamber, where they could move about freely and select the ambient temperature which they prefer. Prazosin induced a dose dependent increase in wake period and in body temperature, when microinjected into the medial preoptic area. Results suggest that preoptic alpha1 adrenergic receptors mediate hypnogenic and hypothermic responses. It is proposed that the noradrenergic afferents to the medial preoptic area, by tonic activation of alpha1 adrenergic receptors, contribute towards increase in sleep especially during the daytime.

Acute administration of the novel serotonin and noradrenaline reuptake inhibitor, S33005, markedly modifies sleep-wake cycle architecture in the rat

RATIONALE

The interrelationship between depressive states and sleep-wake cycle architecture is characterised by a decreased latency to the first paradoxical sleep (PS) episode, together with an enhancement of PS during the first part of the night. Conversely, slow-wave sleep (SWS) is decreased and intermittent awakenings increased. Notably, antidepressant treatment is generally associated with a diminution of PS.

OBJECTIVES

In light of these observations, we examined the influence of acute administration of the novel mixed serotonin-noradrenaline reuptake blocker, (-)1-(1-dimethylaminomethyl 5-methoxybenzocyclobutan-1-yl)-cyclohexanol HCl (S33005), upon sleep-wake architecture in rats.

METHODS

Animals were injected with vehicle or incremental doses of S33005 at the onset of either the dark or light periods. Digitised polygraphic recordings were performed, and changes evoked by S33005 were determined over 24-h recording periods, i.e., number and duration of sleep-wake episodes, latencies to PS and SWS, power band spectra of the electroencephalogram (EEG) and circadian changes.

RESULTS

At 0.04 mg/kg, S33005 was inactive, whereas at 0.63 mg/kg, it modestly increased PS latencies and diminished PS duration during the light period. At 10 mg/kg, S33005 reduced markedly PS duration for about 4-h when injected prior to both light and dark periods. Latency to PS was prolonged, and the circadian acrophase was delayed. These effects are in keeping with previous studies of monoamine reuptake inhibitors, but, notably, SWS duration was increased when S33005 was injected at the onset of the light phase (+4%). These changes occurred without marked modifications in circadian rhythmicity or EEG spectral band power. Finally, even at the highest dose of S33005, only a limited rebound of SWS (+5%) and PS (+10%) was apparent. Amongst antidepressant to date examined, this is an original profile of influence upon sleep patterns.

CONCLUSIONS

These results demonstrate a pattern of influence of S33005 upon sleep-wake architecture in rats which is globally consistent with antidepressant properties, but with a distinctive enhancement of restorative slow-wave sleep.

Changes in thermal preference, sleep–wakefulness, body temperature and locomotor activity of rats during continuous recording for 24 hours

This study was aimed at correlating diurnal changes in thermal preference of rats with their body temperature (Tb), sleep-wakefulness (S-W) and locomotor activity (LMA). Electroencephalogram (EEG), electromyogram (EMG), electrooculogram (EOG) and Tb were recorded by telemetry, while an activity monitor measured LMA and thermal preference. A special environmental chamber, which was designed and fabricated, enabled for the first time, simultaneous measurement of thermal preference, along with S-W and Tb. S-W, thermal preference and LMA were recorded continuously in six adult male Wistar rats, for 24 h, for 3 days, and Tb with thermal preference and LMA were recorded for another 3 days. LMA and Tb were higher at night than during day. The rats slept less during the night time. Increased frequency of sleep episodes contributed towards increased sleep during day time. They preferred an ambient temperature (Tamb) of 24 degrees C at night and 27 degrees C during the day. Though the preference for higher Tamb during day time coincided with increased sleep, the rats did not move over to higher Tamb prior to the onset of sleep episodes. Though the diurnal alterations in sleep, Tb and LMA were similar to those reports from animals kept in constant Tamb, the day-night variation of paradoxical sleep (PS) was exaggerated when the rats selected their own preferred Tamb.

Ozone exposure alters 5-hydroxy-indole-acetic acid contents in dialysates from dorsal raphe and medial preoptic area in freely moving rats. Relationships with simultaneous sleep disturbances

Ozone (O3) has been reported to affect sleep patterns and also striatal and mesencephalic contents of 5-hydroxy-indole-acetic acid (5-HIAA) in rats. The aim of this work was to elucidate the effects of O3 exposure in rats upon extracellular 5-HIAA levels in the dorsal raphe (DR) and the hypothalamic medial preoptic area (MPO), two structures involved in sleep-wake homeostasis. Exposure to O3 followed a bell-shaped diurnal pattern, similar to that observed in cities with high air pollution levels. The highest O3 concentration employed was 0.5 ppm. Simultaneous polygraphic records were performed to evaluate the concomitant effects of this exposure model on sleep patterns. Results showed that extracellular 5-HIAA levels increased by 28% in the DR (P=0.0213) while paradoxical sleep (PS) decreased by 56% (P=0.0000) during the light O3 exposure phase. A decrease of 32% in 5-HIAA levels in the MPO (P=0.0450), and of 22% in slow wave sleep (SWS) (P=0.0002) and an increase of 21% in wakefulness (P=0.0430) during the dark post-exposure (Dpost) phase were also observed. We propose that the decrease in PS is the behavioral expression of disruptions of serotonergic DR modulation and, that post-exposure effects observed in the MPO can be explained on the basis of the hypothalamic role in the sleep-wake cycle.

Role of noradrenergic fibers of the preoptic area in regulating sleep

The preoptic area (POA) has noradrenergic (NE) terminals, and this area controls sleep apart from body temperature and reproduction. The destruction of catecholaminergic (CA) terminals in the POA produced a decrease in sleep in rats. This effect was shown to be due to the destruction of NE and not dopaminergic terminals. The rats, which were hyperthermic after the destruction of CA fibers in the POA, preferred a lower ambient temperature. Though they were unable to have normal amount of sleep after lesion, it did not affect their behavioral thermoregulation. Acute total sleep deprivation for 48 h led to a significant decrease in noradrenaline, increase in the level of metabolites of monoamines, and an enhancement in the number of dendritic spines at the medial preoptic area (mPOA). Enhanced sleep pressure during sleep deprivation could have led to a higher release of noradrenaline, and an increase in dendritic spines in the mPOA. Arousal was produced by application of noradrenaline at the mPOA, whereas the alpha antagonists produced sleep in free-moving rats. This was in contrast to the increased wakefulness produced by the destruction of NE terminals. As wakefulness and sleep, respectively, were induced on local application of alpha-2 antagonist and agonists, it was suspected that the noradrenaline and alpha antagonists might have acted on the alpha-2 receptors, which are predominantly present on the pre-synaptic terminals. Sleep produced by noradrenaline, which was locally applied at the mPOA, after destroying the NE terminals, further confirmed this possibility. Hypothermia and sexual arousal produced by application of alpha- and beta-adrenergic agonists at the mPOA would have contributed towards the wakefulness induced by these drugs in normal rats. Thus, the available evidence shows that the NE fibers in the POA are involved in the induction of sleep.

Orexin A (hypocretin-1) application at the medial preoptic area potentiates male sexual behavior in rats

The medial preoptic area plays an important role in the regulation of male sexual behavior in rats, and this area receives orexinergic inputs. The role of orexinergic inputs in the medial preoptic area in sexual behavior has not been studied, though they have been shown to play a role in some other physiological functions. In this study, the changes in male sexual behavior in rats were studied after local injection of orexin A (Hypocretin-1) at the medial preoptic area. The results of the study showed that orexin A application at the medial preoptic area increased sexual arousal as well as the copulatory performance. Sexual arousal is one of the physiological stimuli, which influences wakefulness. It is possible that the earlier reports showing increased wakefulness, on application of orexin A at the medial preoptic area/basal forebrain, has a contribution from sexual arousal.