Débora Cristina Hipólide

Sleep deprivation induced by the modified multiple platform technique: quantification of sleep loss and recovery.

Vigilance status was continually monitored in socially stable groups of rats exposed to the modified multiple platform (MMP) technique for sleep deprivation. For comparison, sleep parameters were also monitored in socially isolated rats deprived of sleep by the single platform (SP) method. In all cases, sleep was continuously recorded during baseline, during 96 h of sleep deprivation and during 4 days of recovery. Both multiple- and single-platform techniques completely abolished paradoxical sleep (PS) during the deprivation period, but also resulted in significant decreases in slow wave sleep (SWS) (-31% and -37%, respectively). Unexpectedly, animals on large platforms, which are normally intended as controls, also showed significant reductions in PS and SWS, and these effects were more pronounced in rats deprived in groups than in animals deprived in isolation. Another control preparation, rats placed on wire-mesh grids in the deprivation tank, also showed PS reduction (-39%) but no loss of SWS during the 4 test days. Paradoxical sleep rebound was observed in the first 24 h in all groups, except for grid controls. Overall, no significant differences were found between single- and multiple-platform procedures during the 4 days of deprivation. However, sleep rebound was more pronounced in MMP-deprived rats than in SP-deprived rats. Sleep loss in both control groups may reflect residual effect of stress that remain in the platform technique. These findings indicate that the MMP technique is effective in inducing PS deprivation (PSD). However, the fact that SWS is also affected may have implications for conclusions on paradoxical sleep function based upon paradoxical sleep deprivation.

Increased ACTH and corticosterone secretion induced by different methods of paradoxical sleep deprivation.

The methods used to induce paradoxical sleep (PS) deprivation are believed to be stressful. In the present study, two methods were compared in regard to their ability to activate the hypothalamic‐pituitary‐adrenal (HPA) axis. Animals were placed on multiple large (MLP) or small (MSP) platforms or on single large (SLP) or small (SSP) platforms and blood sampled at the end of a 4‐day period of PS deprivation (experiment 1) or on Days 1 (short‐term) and 4 (long‐term) of PS deprivation (experiment 2). ACTH and corticosterone (CORT) levels were determined by RIA. The results of experiment 1 showed that all experimental animals presented increased ACTH response, compared to controls. CORT levels, however, were only elevated in MSP animals, suggesting increased adrenal sensitivity. Experiment 2 showed that ACTH levels of MSP animals were higher than MLP and SSP animals, and that animals placed on the multiple platform tanks showed the highest ACTH levels on Day 4 of manipulation. CORT levels were elevated in the animals kept over small platforms, and these levels where higher on Day 1 than basal and further elevated on Day 4 of PS deprivation. These results indicate that the multiple platform technique induces a distinct activation of the HPA axis, and that PS deprivation may act as an additional stressor.

Deep Brain Stimulation Reverses Anhedonic-Like Behavior in a Chronic Model of Depression: Role of Serotonin and Brain Derived Neurotrophic Factor

BACKGROUND Deep brain stimulation (DBS) is being investigated as a treatment for major depression, but its mechanisms of action are still unknown. We have studied the effects of ventromedial prefrontal cortex (vmPFC) stimulation in a chronic model of depression and assessed the involvement of the serotonergic system and brain derived neurotrophic factor (BDNF) in a DBS response. METHODS Rats were subjected to chronic unpredictable mild stress during 4 weeks. Decline in preference for sucrose solutions over water, an index suggested to reflect anhedonic-like behavior, was monitored on a weekly basis. The outcome of chronic vmPFC stimulation alone (8 hours/day for 2 weeks) or combined with serotonin-depleting lesions was characterized. BDNF levels were measured in the hippocampus. RESULTS Stress induced a significant decrease in sucrose preference as well as hippocampal BDNF levels as compared with those recorded in control subjects. vmPFC stimulation completely reversed this behavioral deficit and partially increased BDNF levels. In contrast, DBS did not improve stress-induced anhedonic-like behavior in animals bearing serotonin-depleting raphe lesions with associated normal hippocampal BDNF levels. CONCLUSIONS vmPFC stimulation was effective in a chronic model of depression. Our results suggest that the integrity of the serotonergic system is important for the anti-anhedonic-like effects of DBS but question a direct role of hippocampal BDNF.

Pain hypersensitivity induced by paradoxical sleep deprivation is not due to altered binding to brain μ-opioid receptors

Previous studies have established a relationship between sleep disruption and pain, and it has been suggested that hyperalgesia induced by paradoxical sleep deprivation (PSD) could be due to a reduction of opioidergic neurotransmission in the brain. In the present study rats deprived of sleep for 96 h as well as rats allowed to recover for 24h after PSD and normal controls received vehicle or morphine (2.5, 5 and 10 mg/kg, i.p.) and were tested on a hot plate 1h later. Quantitative receptor autoradiography was used to map alterations in binding to brain mu-opioid receptors in separate groups. Results demonstrated that PSD induced a significant reduction in thermal pain threshold, as measured by paw withdrawal latencies. This effect did not return to baseline control values after 24h of sleep recovery. The usual analgesic effect of morphine was observed in the control group but not in PSD or rebound groups except at the highest dose (10 mg/kg). Binding of [3H]DAMGO to mu sites did not differ significantly among the three groups in any of the 33 brain regions examined. These results do not exclude the participation of the opioid system in PSD-induced pain hypersensitivity since sleep-deprived rats were clearly resistant to morphine. However, the fact no changes were seen in [3H]DAMGO binding indicates that mechanisms other than altered mu-opioid binding must be sought to explain the phenomenon.

Sensitization to ethanol's stimulant effect is associated with region-specific increases in brain D2 receptor binding

Abstract  Rationale: Stimulation of locomotor activity by low doses of ethanol (EtOH) and the potentiation of this response after repeated administration (sensitization) have been related to EtOH’s rewarding and addictive properties and to altered dopaminergic activity in brain. In mice, behavioral sensitization to EtOH occurs only in a subset of treated animals, and this provides an opportunity for distinguishing general drug effects from sensitization-specific brain effects. Objectives: In view of evidence suggesting a role for dopamine D2 receptors in EtOH preference and abuse liability, the present study addressed the hypothesis that D2 binding would be altered in specific brain regions in mice showing differential sensitization responses to chronic EtOH administration. Methods: Male albino Swiss mice received 2.4 g/kg EtOH i.p. daily for 21 days and were then separated into sensitized or non-sensitized subgroups on the basis of weekly locomotor activity tests. Results: Autoradiographic analyses of [3H]raclopride binding to D2 sites revealed significant increases in the anterior caudate-putamen of mice in the EtOH-sensitized group when compared with either saline controls (+40%, P<0.00009) or to mice in the EtOH non-sensitized group (+32%; P<0.0003). Smaller increases were seen in the ventrolateral caudate-putamen of sensitized animals (+18% vs control, P<0.02; and 12% vs non-sensitized mice, P<0.07). No differences were found in other brain regions, including the nucleus accumbens, olfactory bulb and substantia nigra. Conclusions: The observed increases in D2-receptor binding in circumscribed targets of nigrostriatal projections may reflect either a pre-existing condition in sensitization-prone animals or a selective vulnerability of D2 receptors to chronic EtOH in these animals. In either case, it may be a marker for differential susceptibility to EtOH sensitization.

Resistance to ethanol sensitization is associated with increased NMDA receptor binding in specific brain areas.

Co-administration of N-methyl-D-aspartate (NMDA) receptor antagonists is known to block the development of behavioral sensitization to ethanol and other psychostimulants. Since ethanol sensitization in mice does not occur uniformly in all treated animals, the present study examined the possibility that NMDA receptor binding would be selectively altered in mice susceptible to ethanol sensitization. Mice received 2.4 g/kg ethanol or saline i.p. daily for 21 days and were sacrificed 24 h later. No differences in [3H]dizocilpine ([3H](+)MK-801) binding were found between sensitized and vehicle-treated mice in any of the brain regions analyzed. However, ethanol-treated mice that did not develop sensitization showed significantly higher binding in the nucleus accumbens core (+32% and +40% compared to controls and ethanol-sensitized mice, respectively; P<0.04) and the prefrontal cortex (+15% and +22%; P<0.02). In a separate experiment, sensitization resistant mice challenged with 0.25 mg/kg (+)MK 801 showed significantly less motor activation than saline-treated or ethanol-sensitized mice. These results point to a clear association between elevated NMDA receptor binding in specific brain regions and resistance to ethanol sensitization.

Distinct effects of sleep deprivation on binding to norepinephrine and serotonin transporters in rat brain

There is evidence to suggest that the antidepressant activity of sleep deprivation may be due to an enhancement of serotonergic and/or noradrenergic neurotransmission in brain. In the present study we examined the possibility that such changes may occur at the level of the norepinephrine (NET) and serotonin (SERT) and transporters. Rats were deprived of sleep for 96 h using the modified multiple platform method and then sacrificed for autoradiographic assessments of NET and SERT binding throughout the brain. [3H]Nisoxetine binding to the NE transporter was generally decreased in 44 of 45 areas examined, with significant reductions occurring in the anterior cingulate cortex (-16%), endopiriform n. (-18%), anterior olfactory n. (-19%), glomerular layer of olfactory bulb (-18%), ventral pallidum (-14%), medial preoptic area (-16%), retrochiasmatic/arcuate hypothalamus (-18%), anteromedial thalamic n. (-15%), and rostral raphe (-17%). In contrast, SERT binding measured with [11C]DASB showed no clear directional trends in 61 brain areas examined, but was significantly reduced in subdivisions of the anterior olfactory nucleus (-22%) and substantia nigra (-18%). Thus, sleep deprivation induced widespread decreases in NET binding, and fewer and well-localized decreases in SERT binding. Significant down-regulation in one brain region, the anterior olfactory nucleus, was observed in the case of both transporters. These results suggest that mechanisms involved in the antidepressant action of sleep deprivation may involve generalized NET down-regulation as well as decreased SERT binding in specific areas. Insofar as these changes may be associated with increased levels of serotonin (5-HT) and norepinephrine (NE) in the synapse, they suggest that sleep deprivation may share some basic mechanisms of action with several current antidepressant medications.

Absence of oxidative stress following paradoxical sleep deprivation in rats

Paradoxical sleep deprivation was performed on rats using platform technique to investigate the oxidative process associated with it. Levels of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), total glutathione (GSH) and malondialdehyde production were measured in brain of rats under control conditions (C) and those on single large platforms (SLP), multiple large platforms (MLP), single small platforms (SSP) and multiple small platforms (MSP) groups. SOD, CAT and GPx brain activity and malondialdehyde production were not modified by any of the procedures. Brain GSH, however, was significantly reduced in both SSP and SLP groups. These results suggest that paradoxical sleep deprivation per se is not associated with oxidative damage. The observed alterations could be attributed to factors such as immobilization and social isolation present in the single platform techniques.

Hemiparkinsonian rats rotate toward the side with the weaker dopaminergic neurotransmission

Rats with unilateral lesion of the substantia nigra pars compacta (SNpc) have been used as a model of Parkinsons disease. Depending on the lesion protocol and on the drug challenge, these rats rotate in opposite directions. The aim of the present study was to propose a model to explain how critical factors determine the direction of these turns. Unilateral lesion of the SNpc was induced with 6-hydroxydopamine (6-OHDA) or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Separate analysis showed that neither the type of neurotoxin nor the site of lesion along the nigrostriatal pathway was able to predict the direction of the turns these rats made after they were challenged with apomorphine. However, the combination of these two factors determined the magnitude of the lesion estimated by tyrosine-hydroxylase immunohistochemistry and HPLC-ED measurement of striatal dopamine. Very small lesions did not cause turns, medium-size lesions caused ipsiversive turns, and large lesions caused contraversive turns. Large-size SNpc lesions resulted in an increased binding of [(3)H]raclopride to D2 receptors, while medium-size lesions reduced the binding of [(3)H]SCH-23390 D1 receptors in the ipsilateral striatum. These results are coherent with the model proposing that after challenged with a dopamine receptor agonist, unilaterally SNpc-lesioned rats rotate toward the side with the weaker activation of dopamine receptors. This activation is weaker on the lesioned side in animals with small SNpc lesions due to the loss of dopamine, but stronger in animals with large lesions due to dopamine receptor supersensitivity.

Ethanol-induced behavioral sensitization is associated with dopamine receptor changes in the mouse olfactory tubercle.

Accumulating evidence points to the mesolimbic and the nigrostriatal dopamine systems as critical to behavioral sensitization induced by several drugs of abuse. In the present study, we analyzed D1 and D2 binding to brain regions related to these dopaminergic systems during the expression of ethanol-induced behavioral sensitization. The first experiment was performed to demonstrate the effectiveness of the ethanol treatment schedule and challenge used to induce the expression of the behavioral sensitization phenomenon. The second experiment was conducted to study D1 and D2 alterations in several brain regions during the expression of this phenomenon. Mice were ip treated with ethanol or saline for 21 consecutive days and 24 h after the last injection they received an ethanol or a saline challenge injection. Five minutes later, the animals were observed in an open-field for locomotion quantification or were sacrificed and their brains were submitted to autoradiographic binding analyses. No differences among the groups were found for D1 binding levels in all the brain regions analyzed. However, ethanol-sensitized mice showed reduced levels of D2 binding in the olfactory tubercle when compared to the other groups. Our data suggest that D2 receptor changes in the olfactory tubercle seem to play an important role in the expression of ethanol-induced behavioral sensitization.