Maternal immune suppression during pregnancy does not prevent abnormal behavior in offspring

BACKGROUND

Offspring of hypertensive disorders of pregnancy are at an increased risk of developing neurodevelopmental and neurobehavioral disorders compared to offspring from non-affected pregnancies. Using rodent models of Preeclampsia (PreE; new onset of hypertension after 20 weeks gestation) and HELLP (hemolysis, elevated liver enzymes, and low platelets), we studied the behavioral outcome of their offspring in adolescence.

METHODS

A subset of dams received Orencia, a T-cell activation inhibitor, as T cells have been associated with the induction of hypertension and inflammation during pregnancy. We hypothesized that offspring from hypertensive dams would experience adverse behavioral outcomes in social, cognitive, locomotor, and anxiety tests, and offspring from dams treated with Orencia would demonstrate less adverse behaviors.

RESULTS

Male offspring of PreE + Orencia dams (p < 0.05) and female offspring from HELLP + Orencia dams (p < 0.05) spent more time playing compared to normal pregnant offspring. All offspring from hypertensive and Orencia-treated dams performed worse on the Barnes Maze test compared to normal pregnant. We also measured adult (postnatal day > 60) myelin basic protein (MBP) and NeuN expression in both the prefrontal cortex and hippocampus. In the hippocampus and prefrontal cortex, there was no difference in expression of either MBP or NeuN in all groups regardless of sex.

CONCLUSION

The results from this study suggest that offspring of hypertensive disorders of pregnancy have behavioral changes, specifically cognitive differences. This study has shown that there is a sex dependent difference in offspring neurobehavioral development, influenced in part by the type of hypertensive disorder of pregnancy, and alterations in the maternal immune system.

Pharmaco-EEG analysis of ligands varying in selectivity for α1 subunit-containing GABAA receptors during the active phase in rats

RATIONALE

Benzodiazepines are known to evoke changes in cortical electrophysiological activity that can be correlated with action at distinct γ-aminobutyric acid type A (GABAA) receptor subtypes.

OBJECTIVES

We used electroencephalography (EEG) paired with electromyography (EMG) to evaluate the role of α1 subunit-containing GABAA receptors (α1GABAARs) in benzodiazepine-induced sedation and changes in EEG band frequencies during the active phase of the light/dark cycle.

METHODS

Male Sprague-Dawley rats (N = 4/drug) were surgically instrumented with EEG/EMG electrodes. The rats were injected i.p. with zolpidem, an α1GABAAR-preferring compound, or L-838,417, which has selective efficacy for α2/3/5 subunit-containing GABAARs (i.e., α1GABAAR-sparing compound), in comparison with the non-selective benzodiazepine, triazolam.

RESULTS

All ligands evaluated induced changes in sleep-wake states during the active phase consistent with an increase in slow-wave sleep (SWS). The degree of SWS increase appeared to be related to the magnitude of delta power band changes induced by the ligands, with the strongest effects engendered by the α1GABAAR-preferring drug zolpidem and the weakest effects by the α1GABAAR-sparing compound, L-838,417. Consistent with other research, a selective increase in beta band power was observed with L-838,417, which may be associated with α2GABAAR-mediated anxiolysis.

CONCLUSIONS

Overall, these findings support the establishment of pharmaco-EEG "signatures" for identifying subtype-selective GABAA modulators in vivo.

Howard P. Roffwarg: sleep pioneer, legend, and ontogenetic hypothesis author

Narrated in this article are accounts of the many contributions Howard P. Roffwarg, MD, made to the field of sleep research and sleep medicine across his entire professional career as a student, a mentor, a leader in the Sleep Research Society, a sleep medicine clinician, and a scientist who performed experimental investigations in humans and animals. Dr Roffwarg was the originator of what is known as the "Ontogenetic Hypothesis" of sleep. His research over many years on physiology has contributed greatly to much of the experimental support substantiating a role for rapid eye-movement sleep (REMS) in the early development of the brain. Though much is still unknown, the Ontogenetic Hypothesis, still to this day, inspires many neuroscientists in their investigations. These studies have demonstrated roles for both REMS and NREMS in development as well as on brain function throughout his life span. Dr Howard P. Roffwarg, is one of the legends in the field of sleep research.

Evidence of Anxiety, Depression and Learning Impairments following Prenatal Hypertension

Background: Hypertensive disorders of pregnancy, such as Preeclampsia (PreE) and HELLP (hemolysis, elevated liver enzyme, low platelet) syndrome, affects approximately 5–10% of pregnancies and increases the risk of women developing disorders, such as anxiety or depression, in the postpartum period. Using preclinical rodent models, we set out to determine whether rats with a history of PreE or HELLP had evidence of anxiety, depression or cognitive impairment and whether immune suppression during pregnancy prevented these changes in mood and/or cognition. Methods: Timed-pregnant rats were infused with sFlt-1 and/or sEng to induce PreE or HELLP beginning on gestational day 12. After delivery, a battery of validated behavioral assays was used to assess post-partum depression, anxiety and learning. Results: There was no negative effect on maternal pup interaction due to PreE or HELLP; however, hypertensive dams spent more time immobile in the forced swim test (p < 0.0001). Hypertensive dams also spent less time in the open area of the open field (p = 0.001). There were no significant changes in recognition memory (p = 0.08); however, spatial learning was impaired in hypertensive dams (p = 0.003). Immobility time in the forced swim test was positively correlated with increased circulating S100B (p = 0.04), while increased time spent in the outer zones of the open field was negatively correlated with BDNF levels (p < 0.0001). Conclusion: The results from this study suggest that hypertensive pregnancy disorders are associated with depression, anxiety and learning impairments in the post-partum period.

Acid Sensing Ion Channel 2a Is Reduced in the Reduced Uterine Perfusion Pressure Mouse Model and Increases Seizure Susceptibility in Pregnant Mice

Eclampsia is diagnosed in pregnant women who develop novel seizures. Our laboratory showed that the reduced uterine perfusion pressure (RUPP) rat model of preeclampsia displays reduced latency to drug-induced seizures. While acid sensing ion channels (ASIC1a and 3) are important for reducing seizure longevity and severity, the role of ASIC2a in mediating seizure sensitivity in pregnancy has not been investigated. We hypothesized that 1) RUPP reduces hippocampal ASIC2a, and 2) pregnant mice with reduced ASIC2a (ASIC2a+/-) have increased seizure sensitivity. On gestational day 18.5, hippocampi from sham and RUPP C57BL/6 mice were harvested, and ASIC2a was assessed using Western blot. Pregnant wild-type and ASIC2a+/- mice received 40 mg/kg of pentylenetetrazol (i.p.) and were video recorded for 30 min. Behaviors were scored using a modified Racine scale (0-7: 0 = no seizure; 7 = respiratory arrest/death). Seizure severity was classified as mild (score = 1-3) or severe (score = 4-7). RUPP mice had reduced hippocampal and placental ASIC2a protein. ASIC2a+/- mice had reduced latency to seizures, increased seizure duration, increased severe seizure duration, and higher maximum seizure scores. Reduced hippocampal ASIC2a in RUPP mice and increased seizure activity in pregnant ASIC2a+/- mice support the hypothesis that reduced ASIC2a increases seizure sensitivity associated with the RUPP.

Aging exacerbates impairments of cerebral blood flow autoregulation and cognition in diabetic rats

Diabetes mellitus (DM) is a leading risk factor for aging-related dementia; however, the underlying mechanisms are not well understood. The present study, utilizing a non-obese T2DN diabetic model, demonstrates that the myogenic response of the middle cerebral artery (MCA) and parenchymal arteriole (PA) and autoregulation of cerebral blood flow (CBF) in the surface and deep cortex were impaired at both young and old ages. The impaired CBF autoregulation was more severe in old than young DM rats, and in the deep than the surface cortex. The myogenic tone of the MCA was enhanced at perfusion pressure in the range of 40-100 mmHg in young DM rats but was reduced at 140-180 mmHg in old DM rats. No change of the myogenic tone of the PA was observed in young DM rats, whereas it was significantly reduced at 30-60 mmHg in old DM rats. Old DM rats had enhanced blood-brain barrier (BBB) leakage and neurodegeneration, reduced vascular density, tight junction, and pericyte coverage on cerebral capillaries in the CA3 region in the hippocampus. Additionally, DM rats displayed impaired functional hyperemia and spatial learning and short- and long-term memory at both young and old ages. Old DM rats had impaired non-spatial short-term memory. These results revealed that impaired CBF autoregulation and enhanced BBB leakage plays an essential role in the pathogenesis of age- and diabetes-related dementia. These findings will lay the foundations for the discovery of anti-diabetic therapies targeting restoring CBF autoregulation to prevent the onset and progression of dementia in elderly DM.

Anxiety behavior and hypothalamic-pituitary-adrenal axis altered in a female rat model of vertical sleeve gastrectomy

Surgical weight loss results in a host of metabolic changes that culminate in net positive health benefit to the patients. However, the psychological impact of these surgeries has not been fully studied. On one hand, surgical weight loss has been reported to improve standard quality of life and resolution of symptoms of depression. But on the other hand, reports of self-harm and increased ER visits for self-harm suggest other psychological difficulties. Inability to handle anxiety following surgical weight loss has alarming potential ramifications for these gastric surgery patients. In the present study, we used models of diet-induced obesity and vertical sleeve gastrectomy (VSG) to ask whether anxiety behavior and hypothalamic-pituitary-adrenal (HPA) axis gene changes were affected by surgical weight loss under two diet regimens: i.e. low-fat diet (LFD) and high-fat diet (HFD). We show reduced exploratory behavior in the open field test but increased time in the open arms of the elevated plus maze. Furthermore, we show increased plasma levels of corticosterone in female VSG recipients in the estrus phase and increased levels of hypothalamic arginine-vasopressin (avp), pro-opiomelanocortin (pomc), and tyrosine hydroxylase (th). We report reduced dopamine receptor D1 (drd1) gene in prefrontal cortex (PFC) in VSG animals in comparison to Sham. Further we report diet-driven changes in stress-relevant gene targets in the hypothalamus (oxt, pomc, crhr1) and adrenal (nr3c1, nr3c2, mc2r). Taken together, these data suggest a significant impact of both surgical weight loss and diet on the HPA axis and further impact on behavior. Additional assessment is necessary to determine whether molecular and hormonal changes of surgical weight loss are the source of these findings.

Selective rapid eye movement sleep deprivation affects cell size and number in kitten locus coeruleus

Cells in the locus coeruleus (LC) constitute the sole source of norepinephrine (NE) in the brain and change their discharge rates according to vigilance state. In addition to its well established role in vigilance, NE affects synaptic plasticity in the postnatal critical period (CP) of development. One form of CP synaptic plasticity affected by NE results from monocular occlusion, which leads to physiological and cytoarchitectural alterations in central visual areas. Selective suppression of rapid eye movement sleep (REMS) in the CP kitten enhances the central effects of monocular occlusion. The mechanisms responsible for heightened cortical plasticity following REMS deprivation (REMSD) remain undetermined. One possible mediator of an increase in plasticity is continuous NE outflow, which presumably persists during extended periods of REMSD. Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the synthesis of NE and serves as a marker for NE-producing cells. We selectively suppressed REMS in kittens for 1 week during the CP. The number and size of LC cells expressing immunoreactivity to tyrosine hydroxylase (TH-ir) was assessed in age-matched REMS-deprived (RD)-, treatment–control (TXC)-, and home cage-reared (HCC) animals. Sleep amounts and slow wave activity (SWA) were also examined relative to baseline. Time spent in REMS during the study was lower in RD compared to TXC animals, and RD kittens increased SWA delta power in the latter half of the REMSD period. The estimated total number of TH-ir cells in LC was significantly lower in the RD than in the TXC kittens and numerically lower than in the HCC animals. The size of LC cells expressing TH-ir was greatest in the HCC group. HCC cells were significantly larger than TH-ir cells in the RD kittens. These data are consistent with presumed reduction in NE in forebrain areas, including visual cortex, caused by 1 week of REMSD.

Brain-derived neurotrophic factor (BDNF) reverses the effects of rapid eye movement sleep deprivation (REMSD) on developmentally regulated, long-term potentiation (LTP) in visual cortex slices

Work in this laboratory demonstrated a role for rapid eye movement sleep (REMS) in critical period (CP), postnatal days (P) 17-30, synaptic plasticity in visual cortex. Studies in adolescent rats showed that REMS deprivation (REMSD) reinitiates a developmentally regulated form of synaptic plasticity that otherwise is observed only in CP animals. Subsequent work added that REMSD affects inhibitory mechanisms that are thought to be involved in terminating the CP. Neurotrophins are implicated in the synaptic plasticity that underlies CP maturation and also final closure of the CP in visual cortex. Expression of brain-derived neurotrophic factor (BDNF) is dependent upon neuronal activity, and REMSD may block BDNF expression. We propose that REMS contributes to the maturation of visual cortex through regulation of BDNF expression and consequent, downstream increase in cortical inhibitory tone. In this study, osmotic minipumps delivered BDNF into visual cortex on one side of brain. The opposite hemisphere was not implanted and served as an internal control. We tested the hypothesis that BDNF is blocked by REMSD in late-adolescent rats and investigated whether replacing BDNF prevents induction of LTPWM-III by theta burst stimulation (TBS). We also assessed relative inhibitory tone in visual cortex with paired-pulse stimulation (PPS) in animals that were similarly REMSD- and BDNF-infused. After REMSD, both hemispheres were prepared in parallel for in vitro synaptic plasticity studies (LTPWM-III or PPS). In visual cortex of REMSD rats on the side receiving BDNF infusions (8 of 8 animals), TBS consistently failed to induce LTPWM-III. In contrast, LTPWM-III was obtained (5 of 5 animals) in the matched, non-infused hemisphere, as expected in rats of this age. REMSD animals that were unilaterally infused with saline produced LTPWM-III in both hemispheres. PPS studies in another group of REMSD animals that were unilaterally BDNF-infused displayed age-appropriate inhibition of the second response on the BDNF-infused side (5/5), whereas on the non-infused side facilitation was observed (3/3). Intracortical infusion of BDNF in REMSD adolescent rats appears to restore neurochemical processes necessary for termination of the CP for developmentally regulated synaptic plasticity in visual cortex. The results suggest that REMSD blocks BDNF expression and also maturation of inhibitory processes in adolescent visual cortex. These data support REMS' function in brain development.

Interleukin-10/Ceftriaxone prevents E. coli-induced delays in sensorimotor task learning and spatial memory in neonatal and adult Sprague-Dawley rats

Intrauterine infection during pregnancy is associated with early activation of the fetal immune system and poor neurodevelopmental outcomes. Immune activation can lead to alterations in sensorimotor skills, changes in learning and memory and neural plasticity. Both interleukin-10 (IL-10) and Ceftriaxone have been shown to decrease immune system activation and increase memory capacity, respectively. Using a rodent model of intrauterine infection, we examined sensorimotor development in pups, learning and memory, via the Morris water maze, and long-term potentiation in adult rats. Pregnant rats at gestational day 17 were inoculated with 1 x 10(5) colony forming units of Escherichia coli (E. coli) or saline. Animals in the treatment group received IL-10/Ceftriaxone for 3 days following E. coli administration. Intrauterine infection delayed surface righting, negative geotaxis, startle response and eye opening. Treatment with IL-10/Ceftriaxone reduced the delay in these tests. Intrauterine infection impaired performance in the probe trial in the Morris water maze (saline 25.13+/-1.01; E. coli 20.75+/-1.01; E. coli+IL-10/Ceftriaxone 20.2+/-1.62) and reduced the induction of long-term potentiation (saline 141.5+/-4.3; E. coli 128.7+/-3.9; E. coli+IL-10/Ceftriaxone 140.0+/-10). In summary, the results of this study indicate that E. coli induced intrauterine infection delays sensorimotor and learning and memory, while IL-10/Ceftriaxone rescues some of these behaviors. These delays were also accompanied by an increase in interleukin-1beta levels, which indicates immune activation. IL-10/Ceftriaxone prevents these delays as well as decreases E. coli-induced interleukin-1beta activation and may offer a window of time in which suitable treatment could be administered.

Rapid eye movement sleep deprivation decreases long-term potentiation stability and affects some glutamatergic signaling proteins during hippocampal development

Development of the mammalian CNS requires formation and stabilization of neuronal circuits and synaptic connections. Sensory stimulation provided by the environment orchestrates neuronal circuit formation in the waking state. Endogenous sources of activation are also implicated in these processes. Accordingly we hypothesized that sleep, especially rapid eye movement sleep (REMS), the stage characterized by high neuronal activity that is more prominent in development than adulthood, provides endogenous stimulation, which, like sensory input, helps to stabilize and refine neuronal circuits during CNS development. Young (Y: postnatal day (PN) 16) and adolescent (A: PN44) rats were rapid eye movement sleep-deprived (REMSD) by gentle cage-shaking for only 4 h on 3 consecutive days (total 12 h). The effect of REMS deprivation in Y and A rats was tested 3-7 days after the last deprivation session (Y, PN21-25; A, PN49-53) and was compared with younger (immature, I, PN9-12) untreated, age-matched, treated and normal control groups. REMS deprivation negatively affected the stability of long-term potentiation (LTP) in Y but not A animals. LTP instability in Y-REMSD animals was similar to the instability in even the more immature, untreated animals. Utilizing immunoblots, we identified changes in molecular components of glutamatergic synapses known to participate in mechanisms of synaptic refinement and plasticity. Overall, N-methyl-d-aspartate receptor subunit 2B (NR2B), N-methyl-d-aspartate receptor subunit 2A, AMPA receptor subunit 1 (GluR1), postsynaptic density protein 95 (PSD-95), and calcium/calmodulin kinase II tended to be lower in Y REMSD animals (NR2B, GluR1 and PSD-95 were significantly lower) compared with controls, an effect not present in the A animals. Taken together, these data indicate that early-life REMS deprivation reduces stability of hippocampal neuronal circuits, possibly by hindering expression of mature glutamatergic synaptic components. The findings support a role for REMS in the maturation of hippocampal neuronal circuits.

Effects of rapid eye movement sleep deprivation on hypocretin neurons in the hypothalamus of a rat model of depression

Hypocretin (Hcrt, also known as orexin) is a hypothalamic neuropeptide linked to narcolepsy, a disorder diagnosed by the appearance of rapid eye-movement sleep (REMS)-state characteristics during waking. Major targets of Hcrt-containing fibers include the locus coeruleus and the raphe nucleus, areas with important roles in regulation of mood and sleep. A relationship between REMS and mood is suggested by studies demonstrating that REMS-deprivation (REMSD) ameliorates depressive symptoms in humans. Additional support is found in animal studies where antidepressants and REMSD have similar effects on monoamiergic systems thought to be involved in major depression. Recently, we have reported that Wistar-Kyoto (WKY) rats, an animal model of depression, have reduced number and size of hypothalamic cells expressing Hcrt-immunoractivity compared to the parent, Wistar (WIS) strain, suggesting the possibility that the depressive-like attributes of the WKY rat may be determined by this relative reduction in Hcrt cells [Allard, J.S., Tizabi, Y., Shaffery, J.P., Trouth, C.O., Manaye, K., 2004. Stereological analysis of the hypothalamic hypocretin/orexin neurons in an animal model of depression. Neuropeptides 38, 311-315]. In this study, we sought to test the hypothesis that REMSD would result in a greater increase in the number and/or size of hypothalamic, Hcrt-immunoreactive (Hcrt-ir) neurons in WKY, compared to WIS rats. The effect of REMSD, using the multiple-small-platforms-over-water (SPRD) method, on size and number of Hcrt-ir cells were compared within and across strains of rats that experienced multiple-large-platforms-over-water (LPC) as well as to those in a normal, home-cage-control (CC) setting. In accord with previous findings, the number of Hcrt-ir cells was larger in all three WIS groups compared to the respective WKY groups. REMSD produced a 20% increase (p<0.02) in the number of hypothalamic Hcrt-ir neurons in WKY rats compared to cage control WKY (WKY-CC) animals. However, an unexpected higher increase in number of Hcrt-ir cells was also observed in the WKY-LPC group compared to both WKY-CC (31%, p<0.001) and WKY-SPRD (20%, p<0.002) rats. A similar, smaller, but non-significant, pattern of change was noted in WIS-LPC group. Overall the data indicate a differential response to environmental manipulations where WKY rats appear to be more reactive than WIS rats. Moreover, the findings do not support direct antidepressant-like activity for REMSD on hypothalamic Hcrt neurons in WKY rats.

Rapid eye movement sleep deprivation in post-critical period, adolescent rats alters the balance between inhibitory and excitatory mechanisms in visual cortex

Suppression of rapid eye movement sleep (REMS) in developing animals has both anatomical and physiological consequences. We have recently shown that initiating REMS deprivation (REMSD) prior to the end of the critical period in young rats delays termination of the critical period (CP) in visual cortex, and, consequently, the synaptic plasticity mechanisms that support a developmentally regulated form of long-term potentiation (LTP) are maintained in an immature state [J.P. Shaffery, C.M. Sinton, G. Bisset, H.P. Roffwarg, G.A. Marks, Rapid eye movement sleep deprivation modifies expression of long-term potentiation in visual cortex of immature rats, Neuroscience, 110 (2002) 431-443]. In CP animals, high-frequency, theta burst stimulation (TBS) directed at the white matter (WM) below visual cortex produces LTP in the post-synaptic cells in layer II/III (LTPWM-III). However, LTPWM-III can be induced in cortical tissue taken from REMS-deprived animals for up to a week beyond the usual end of the CP [J.P. Shaffery, C.M. Sinton, G. Bisset, H.P. Roffwarg, G.A. Marks, Rapid eye movement sleep deprivation modifies expression of long-term potentiation in visual cortex of immature rats, Neuroscience, 110 (2002) 431-443]. Further, in post-CP, adolescent animals (as late as postnatal day 60), REMSD appears to unmask synaptic plasticity mechanisms that allow for production of developmentally regulated LTPWM-III [J.P. Shaffery, J. Lopez, G. Bissette, H.P. Roffwarg, Rapid eye movement sleep deprivation revives a form of developmentally regulated synaptic plasticity in the visual cortex of post-critical period rats, Neurosci Lett., (2005), in press]. It has been proposed that REMSD's effects on production of LTPWM-III result from a reduction in efficiency of the inhibitory mechanisms thought to precipitate termination of the CP of brain development [J.P. Shaffery, J. Lopez, G. Bissette, H.P. Roffwarg, Rapid eye movement sleep deprivation revives a form of developmentally regulated synaptic plasticity in the visual cortex of post-critical period rats, Neurosci Lett., (2005), in press]. In this study we tested the hypothesis that low-frequency stimulation (LFS) of the fibers of the WM, which usually produces the related form of synaptic plasticity, long-term depression (LTD), will also reflect the reduction in inhibitory tone. We report here that LFS protocols, which in normally sleeping, adolescent rats usually produce either LTD or no change in response magnitude, in REMS-deprived, adolescent rats are more likely to produce LTP.

Rapid eye movement sleep deprivation revives a form of developmentally regulated synaptic plasticity in the visual cortex of post-critical period rats

The critical period for observing a developmentally regulated form of synaptic plasticity in the visual cortex of young rats normally ends at about postnatal day 30. This developmentally regulated form of in vitro long-term potentiation (LTP) can be reliably induced in layers II-III by aiming high frequency, theta burst stimulation (TBS) at the white matter situated directly below visual cortex (LTPWM-III). Previous work has demonstrated that suppression of sensory activation of visual cortex, achieved by rearing young rats in total darkness from birth, delays termination of the critical period for inducing LTPWM-III. Subsequent data also demonstrated that when rapid eye movement sleep (REMS) is suppressed, thereby reducing REMS cortical activation, just prior to the end of the critical period, termination of this developmental phase is delayed, and LTPWM-III can still be reliably produced in the usual post-critical period. Here, we report that for approximately 3 weeks immediately following the usual end of the critical period, suppression of REMS disrupts the maturational processes that close the critical period, and LTPWM-III is readily induced in brain slices taken from these somewhat older animals. Insofar as in vitro LTP is a model for the cellular and molecular changes that underlie developmental synaptic plasticity, these results suggest that mechanisms of synaptic plasticity, which participate in brain development and perhaps also in learning and memory processes, remain susceptible to the effects of REMS deprivation during the general period of adolescence in the rat.

Stereological analysis of the hypothalamic hypocretin/orexin neurons in an animal model of depression

Affective disorders often occur in combination with disrupted sleep-wake cycles and abnormal fluctuations in hypothalamic neurotransmitters. Hypocretin (orexin) is a hypothalamic neuropeptide linked to narcolepsy, a sleep-related disorder characterized by profound disturbances in the normal sleeping pattern and variable degrees of depression. Wistar-Kyoto (WKY) rats exhibit depressive characteristics and patterns of sleep disruption similar to that observed in depressed human patients. In this study we sought to determine whether the total number or the size of hypothalamic hypocretin neurons in WKY rats differ from their control, Wistar (WIS) rats. Immunocytochemical and stereological methods were applied to quantify hypocretin-1 containing neurons in the hypothalamus. The study revealed 18% fewer hypocretin-1 positive neurons as well as a 15% decrease in average neuronal soma size of hypocretin-1 producing cells in the hypothalamus of WKY rats compared to WIS rats. These findings support the view that reduced number or size of hypothalamic hypocretinergic neurons may underlie the disrupted sleep pattern associated with depressive characteristics in WKY rats.

Rapid eye-movement sleep deprivation does not 'rescue' developmentally regulated long-term potentiation in visual cortex of mature rats

The age at which it is possible to obtain a usually age-limited (developmental) form of long-term potentiation (LTP) in rat visual cortex slices can be extended by suppressing rapid eye movement (REM) sleep. In this study, we examined whether REM sleep deprivation can also 'rescue' this type of LTP in older rats. Rats, 42-59 days of age, were either REM sleep-deprived for 7-10 days (n=8), or not deprived of REM sleep (control group, n=8). Brain slices from visual cortex were tested for the developmental form- and a related, non-developmental form of LTP. Three of the eight REM sleep-deprived animals and four of the eight non-deprived animals met criteria for a valid attempt to induce the developmental form of LTP. Though the non-age-regulated form of LTP could be obtained in all seven of these animals, the developmental form could not be elicited in any, indicating that REM sleep deprivation does not uniformly affect all forms of LTP in adult rats. We conclude that extended periods of REM sleep deprivation do not facilitate induction of developmentally regulated LTP once the animal is beyond a certain age.

Enhancement of rapid eye movement sleep in the rat by actions at A1 and A2a adenosine receptor subtypes with a differential sensitivity to atropine

The adenosine agonist cyclohexaladenosine injected into the medial pontine reticular formation of the rat induces a long-lasting increase in rapid eye movement sleep. To investigate the adenosine receptor-subtype(s) mediating this effect, the dose-response relationships for increasing rapid eye movement sleep by two highly selective adenosine receptor agonists were compared. Rats were surgically prepared for chronic sleep recording and bilateral guide cannulae were aimed at medial sites in the caudal, oral pontine reticular formation. Injections were made unilaterally in 60 nl volumes within 1 h after lights-on. The adenosine agonists used were A1-selective cyclohexaladenosine (10(-6)-10(-4) M) and A2a-selective CGS 21680 (10(-7)-10(-3) M). Each animal also received a series of three, paired-consecutive injections of the muscarinic receptor antagonist atropine (4x10(-3) M) followed by the lowest effective dose of each agonist or saline as control. The A2a receptor agonist, CGS 21680, was one order of magnitude more potent than the A1 receptor agonist, cyclohexaladenosine, in inducing rapid eye movement sleep increases. Preinjection of atropine at a dose that did not itself affect rapid eye movement sleep resulted in antagonism of CGS 21680, but not cyclohexaladenosine-induced rapid eye movement sleep. The differential sensitivity of these ligands to antagonism by atropine supports the conclusion that both A1 and A2a adenosine receptor subtypes in the reticular formation subserve agonist-induced rapid eye movement sleep and that they do so by independent mechanisms. The A2a mechanism requires the cholinergic system and may act through the increased release of acetylcholine. The A1 mechanism operates at a different locus possibly through an inhibition of GABA neurotransmission.

Rapid eye movement sleep deprivation modifies expression of long-term potentiation in visual cortex of immature rats

During rapid eye movement (REM) sleep, activity of non-retinal origin is propagated into central visual-system pathways in a manner similar, in pattern and intensity, to central visual-system activity that is exogenously generated in waking. It has been hypothesized that REM sleep, which is more abundantly represented early in life than later, functions to provide adjunct 'afferent' input for shaping synaptic connectivity during brain maturation. Here we present data that support this proposal. Recent studies have described a developmentally regulated form of in vitro long-term potentiation (LTP) in the visual cortex that is experience- and age-dependent. In immature rats, suppression of retinal activation of the visual system by removal of visual experience (dark rearing) extends the age when the developmentally regulated form of LTP can be produced. This study tests whether suppression of REM-state activation of the visual system also lengthens the developmental period in which this specific form of LTP can be elicited. Young rats were deprived of REM sleep by the multiple-small-platforms-over-water method during the typically latest week for induction of such LTP in slices of visual cortex. After this week, we could still induce LTP in slices from nearly all the REM-sleep-deprived rats (8/9) but not from age-matched rats that had not lost REM sleep (0/5). The control rats had been housed on large platforms that allow the animals to obtain REM sleep. Only body weights and the concentration of thyrotrophin-releasing hormone in the hypothalamus distinguished home-caged, normal-sleeping controls from both groups of platform animals. On all measures, stress levels were not dissimilar in the two platforms groups. After 7 days of behavioral suppression of REM sleep in immature rats, and consequent reduction of the intense, extra-retinal activity endogenously generated during this sleep state, we found that the period was extended in which developmentally regulated synaptic plasticity (LTP) could be elicited in slices of visual neocortex. These studies support the role of REM sleep and its associated neuronal activity in brain maturation.

The effects of 1 week of REM sleep deprivation on parvalbumin and calbindin immunoreactive neurons in central visual pathways of kittens

Many maturational processes in the brain are at high levels prenatally as well as neonatally before eye-opening, when extrinsic sensory stimulation is limited. During these periods of rapid brain development, a large percentage of time is spent in rapid eye movement (REM) sleep, a state characterized by high levels of endogenously produced brain activity. The abundance of REM sleep in early life and its ensuing decline to lower levels in adulthood strongly suggest that REM sleep constitutes an integral part of the activity-dependent processes that enable normal physiological and structural brain development. We examined the effect of REM sleep deprivation during the critical period for visual development on the development of two calcium-binding proteins that are associated with developmental synaptic plasticity and are found in the lateral geniculate nucleus (LGN) and visual cortex. In this study, REM sleep deprivation was carried out utilizing a computer-controlled, cage-shaking apparatus that successfully suppressed REM sleep. Body weight data suggested that this method of REM sleep deprivation produced less stress than the classical multiple-platform-over-water method. In REM sleep-deprived animals with normal binocular vision, the number of parvalbumin-immunoreactive (PV) neurons in LGN was found to be lower compared with control animals but was not affected in visual cortex. The pattern of calbindin-immunoreactivity (CaB) was unchanged at either site after REM sleep deprivation. Parvalbumin-immunoreactivity develops later than calbindin-immunoreactivity in the LGN, and the REM sleep deprivation that we applied from postnatal day 42-49 delayed this essential step in the development of the kitten's visual system. These data suggest that in early postnatal brain development, REM sleep facilitates the usual time course of the expression of PV-immunoreactivity in LGN neurons.

Ponto-geniculo-occipital-wave suppression amplifies lateral geniculate nucleus cell-size changes in monocularly deprived kittens

We have previously shown that during the post-natal critical period of development of the cat visual system, 1 week of instrumental rapid eye movement (REM) sleep deprivation (IRSD) during 2 weeks of monocular deprivation (MD) results in significant amplification of the effects of solely the 2-week MD on cell-size in the binocular segment of the lateral geniculate nucleus (LGN) [36,40]. In this study, we examined whether elimination of ponto-geniculo-occipital (PGO)-wave phasic activity in the LGN during REM sleep (REMS), rather than suppression of all REMS state-related activity, would similarly yield enhanced plasticity effects on cell-size in LGN. PGO-activity was eliminated in LGN by bilateral pontomesencephalic lesions [8,32]. This method of removing phasic activation at the level of the LGN preserved sleep and wake proportions as well as the tonic activities (low voltage, fast frequency ECoG and low amplitude EMG) that characterize REM sleep. The lesions were performed in kittens on post-natal day 42, at the end of the first week of the 2-week period of MD, the same age when IRSD was started in the earlier study. LGN interlaminar cell-size disparity increased in the PGO-wave-suppressed animals as it had in behaviorally REM sleep-deprived animals. Smaller A1/A-interlaminar ratios reflect the increased disparity effect in both the REM sleep- and PGO-suppressed groups compared to animals subjected to MD-alone. With IRSD, the effect was achieved because the occluded eye-related, LGN A1-lamina cells tended to be smaller relative to their size after MD-alone, whereas after PGO-suppressing lesions, the A1-lamina cells retained their size and the non-occluded eye-related, A-lamina cells tended to be larger than after MD-alone. Despite this difference, for which several possible explanations are offered, these A1/A-interlaminar ratio data indicate that in conjunction either with suppression of the whole of the REMS state or selective removal of REM sleep phasic activity at the LGN, altered visual input evokes more LGN cell plasticity during the developmental period than it would otherwise. These data further support involvement of the REM sleep state in reducing susceptibility to plasticity changes and undesirable variability in the course of normative CNS growth and maturation.

Neuronal activity in the lateral geniculate nucleus associated with ponto-geniculo-occipital waves lacks lamina specificity

Ponto-geniculo-occipital (PGO) waves are spontaneously occurring field potentials recorded in the dorsal lateral geniculate nucleus (LGN) just prior to and during rapid eye movement (REM) sleep. Facilitated discharge rates of LGN neurons are associated with PGO waves. In kittens during the critical period of visual system development, both visual experience and PGO waves appear capable of influencing the course of development through activity-dependent mechanisms. Retinal innervation of LGN segregates into eye-specific laminae and is critical to supporting the role of binocular visual experience in development. We sought to determine whether neuronal activity associated with PGO waves also exhibits lamina specificity. PGO wave-related discharges were examined in LGN neurons identified as to lamina location in adult cats administered urethane anesthesia and the reserpine-like compound, RO4-1284. Spontaneous activity of LGN neurons was related to the occurrence of PGO-like waves in all cells studied. No factors could be found that differentiated lamina location and PGO wave-related discharges. We conclude that the PGO wave influence on neuronal activity in the visual system is fundamentally different from that derived from visual experience. The implications of this difference for the role of the two sources of activation in the control of neural activity in development are discussed.

REM sleep deprivation in monocularly occluded kittens reduces the size of cells in LGN monocular segment

STUDY OBJECTIVES

In this study, we test the hypothesis that when REM-state activation (which impinges upon all lateral geniculate nucleus laminae irrespective of stimulating eye) is deprived, the monocular segment (MS) that is cut off from visual input and also deprived of REM-state activation will exhibit smaller cells, owing to the loss of extrinsic as well as intrinsic activation.

DESIGN

We carried out a study comparing soma sizes in the MSs of kittens subjected to monocular deprivation (MD) + REM deprivation (RD) to two age-matched nonRD groups, MD ONLYs and MD MOMS (MD kittens living in their home cages).

MEASUREMENTS AND RESULTS

Perikaryal outlines of 100 cells in each of the bilateral MSs were measured. As predicted, mean cell size in the MS connected to the patched eye of MD + RD kittens, but in neither of the control groups, was significantly smaller than in the MS afferented by the nonpatched eye. One-way ANOVAs comparing MS cell-size means from the same sides across groups were also significant, but the two MSs showed different results on post hoc tests. The ordering of MS cell-size means correlated significantly with a measure that aggregates the sources of activation reaching a particular MS and their durations.

CONCLUSIONS

These results reveal that removal of REM-state activation during CNS development amplifies the plasticity processes generated when normal visual afferentation to central visual areas is interrupted. Our findings in the MS of the LGN indicate that during the usual operation of REM sleep, central visual-sensory sites receive intrinsic activation that, in the visual system, is additive and complementary to the stimulation obtained from extrinsic sources. In the course of early development, normative symmetrical activation of central visual areas during REM sleep may counterbalance plasticity changes caused either by absent or aberrant sensory stimulation.

Rapid eye movement sleep deprivation in kittens amplifies LGN cell-size disparity induced by monocular deprivation

The abundance of rapid eye movement (REM) sleep in the neonatal mammal and its subsequent decline in the course of development, as well as the dramatic and widespread enhancement of CNS activity during REM sleep, led us to propose that this state plays a functional role in the normative physiological and structural maturation of the brain [54]. When, after 1 week of monocular deprivation (MD), a second week of MD was coupled with behavioral deprivation of REM sleep, the structural alteration in the visual system provoked by MD alone (interlaminar relay cell-size disparity in the lateral geniculate nucleus (LGN) was amplified. With the addition of REM deprivation during MD, the LGN cells connected to the surgically patched eye, which are smaller than normal after MD, became even smaller, whereas the LGN cells receiving input from the seeing eye, which display compensatory hypertrophy after MD, grew even larger. We believe that the interlaminar disparity effect widened because during REM deprivation, the already vision-compromised LGN cells associated with the patched eye also lose the ascending brainstem activation reaching them during the REM state. Loss of the two main sources of 'afference' by these LGN cells permits their seeing-eye LGN counterparts to gain even greater advantage in the competition for synaptic connections in cortex, which is reflected in the relative soma sizes of the LGN relay cells. It is likely that the relatively abundant REM state in early maturation provides symmetric stimulation to all LGN relay cells, irrespective of eye of innervation. The symmetric activation propagated from brainstem to LGN acts to 'buffer' abnormal, asymmetric visual input and, thereby diminishes the extreme, asymmetric structural alteration that results from MD in the absence of REM sleep. We conclude that REM sleep-generated CNS discharge in development has the effect of 'protecting' the CNS against excessive plasticity changes. This is consistent with the possibility that REM sleep plays a role in the genetically programmed processes that direct normative brain development.

A preliminary study of sleep in the ferret, Mustela putorius furo: a carnivore with an extremely high proportion of REM sleep

Sleep and wakefulness were studied polygraphically in two adult male ferrets between the ages of 3 months and 2.5 years. Nine 24-hour recordings were obtained on different light/dark schedules, and one animal was also monitored for 3 days following administration of the serotonin synthesis inhibitor, parachlorophenylalanine. Stage scoring was accomplished utilizing criteria similar to those used in the cat. Certain modifications to the criteria were made to accommodate apparent differences in electrographic indicators of state. Mean daily percentages [+/- standard error of the mean (SEM)] for the major stages were: slow-wave sleep, 36.0 +/- 1.33; rapid eye movement (REM) sleep, 24.4 +/- 0.94; and wake, 39.4 +/- 1.17. Under laboratory conditions, ferrets spend over 60% of the time in sleep and 40.28% +/- 0.93% of total sleep time in REM sleep. The high amount of REM sleep is achieved by having a high number of REM sleep episodes rather than long REM periods. Sleep cycle length was computed in two ways: with long wake episodes removed, 16.7 +/- 0.4 minutes; and with all wake removed, 13.2 +/- 0.3 minutes. Sleep and waking indices in the ferret are compared to those in the cat and discussed with respect to predictions based on several constitutional variables. The high amount of REM sleep and the relative immaturity of the ferret at birth lends additional support for a functional role of REM sleep on ontogenetic development.

A functional role for REM sleep in brain maturation

The biological function of REM sleep is defined in terms of the functions of neural processes that selectively operate during the REM sleep state. The high amounts of REM sleep expressed by the young during a period of central nervous system plasticity suggest that one function of REM sleep is in development. The phenomenon of activity-dependent development has been clearly shown to be one mechanism by which early sensory experience can affect the course of neural development. Activity-dependent development may be a ubiquitous process in brain maturation by which activity in one brain region can influence the developmental course of other regions. We hypothesize an ontogenetic function of REM sleep; namely, the widespread control of neuronal activity exerted by specific REM sleep processes help to direct brain maturation through activity-dependent developmental mechanisms. Preliminary tests of the hypothesis have been conducted in the developing feline visual system, which has long been known to incorporate information derived from visual experience in establishing neuronal connectivity. We find that suppression of REM sleep processes by an instrumental REM deprivation procedure results in a significant enhancement of the effects of altered visual experience by monocular occlusion. Bilateral brainstem lesions that selectively block the occurrence of ponto-geniculo-occipital (PGO) waves are sufficient to produce similar results. These data indicate that the propagation of phasic influences during REM sleep interacts with other processes subserving neural development. This source of influence appears not to derive from the environment but rather stems from an intrinsic source of genetic origin. Examination of the neural activity associated with PGO waves in the lateral geniculate nucleus reveals a distribution of facilitatory influence markedly different from that induced by visual experience. We conclude that REM sleep directs the course of brain maturation in early life through the control of neural activity.