Sleep deprivation increases thalamocortical excitability in the somatomotor pathway, especially during seizure-prone sleep or awakening states in feline seizure models

Sleep- and sleep deprivation-related changes of vertex auditory evoked potentials during the estrus cycle in female rats

The estrus cycle in female rodents has been shown to affect a variety of physiological functions. However, little is known about its presumably thorough effect on auditory processing during the sleep-wake cycle and sleep deprivation. Vertex auditory evoked potentials (vAEPs) were evoked by single click tone stimulation and recorded during different stages of the estrus cycle and sleep deprivation performed in metestrus and proestrus in female rats. vAEPs showed a strong sleep-dependency, with the largest amplitudes present during slow wave sleep while the smallest ones during wakefulness. Higher amplitudes and longer latencies were seen in the light phase during all vigilance stages. The largest amplitudes were found during proestrus (light phase) while the shortest latencies were seen during estrus (dark phase) compared to the 2nd day diestrus baseline. High-amplitude responses without latency changes were also seen during metestrus with increased homeostatic sleep drive. More intense and faster processing of auditory information during proestrus and estrus suggesting a more effective perception of relevant environmental cues presumably in preparation for sexual receptivity. A 4-h sleep deprivation resulted in more pronounced sleep recovery in metestrus compared to proestrus without difference in delta power replacement suggesting a better tolerance of sleep deprivation in proestrus. Sleep deprivation decreased neuronal excitability and responsiveness in a similar manner both during metestrus and proestrus, suggesting that the negative consequences of sleep deprivation on auditory processing may have a limited correlation with the estrus cycle stage.

Effect of Sleep on Epileptic Discharges in Patients with Idiopathic Generalized Epilepsy

Background. It is known that sleep and sleep deprivation affect the EEG findings, onset, frequency and semiology of the seizures. Generalized spike and wave discharges were found more common in drowsiness and sleep states, especially in childhood and juvenile absence epilepsy syndromes. Aim. In this study we aimed to show the effects of short sleep on the interictal and ictal discharges of the patients with genetic generalized epileptic seizures and to show the effects of treatment on the discharges during awake and sleep states. Method. 37 patients (29 females and 8 males) with a diagnosis of genetic generalized epilepsy syndrome were included. All the patients were investigated with video-EEG recording during awake, sleep and post sleep states. Epileptic discharges were counted manually. Discharge numbers and their relation with triggers were analyzed to see the difference between different vigilance states. Results. Number of ictal discharges is found to be increased after sleep. There was no difference in the control EEGs, which were taken under treatment. Conclusion. Sleep is a trigger of epileptic discharges in ictal nature, but an effective antiepileptic treatment prevents this effect.

Increased photosensitivity following short sleep in sleep deprived patients

INTRODUCTION

We aimed to determine the effect of short day-time sleep on photoparoxysmal epileptic activity in sleep-deprived patients.

METHODS

We retrospectively reviewed video-EEG recordings performed between 2003 and 2015. All recordings following at least four hours of sleep deprivation, including intermittent photic stimulation (IPS) both before and after sleep with any form of epileptiform activity were included. The study group was divided into four subgroups: (1) no photoparoxysmal response (PPR) group, with epileptiform activities other than PPRs; (2) increment group, with PPR duration increased by ≥200% after vs. before sleep; (3) no significant change group, with PPR duration increased between 50% and 200% after vs. before sleep; (4) decrement group, with PPR duration increased ≤50% after vs. before sleep.

RESULTS

A total number of 5805 EEG recordings from 459 patients was analyzed. Photosensitivity was present in 98 patients (21.4%). The PPRs after sleep were increased in 70% of the photosensitive patients, did not change in 23%, and were decreased in 7%. The increase in duration of PPRs was statistically significant (P<0.001). In our cohort, photosensitivity would have been detected in 67 patients if IPS was applied only before sleep and in 91 patients if IPS was applied only after awakening (P<0.05).

CONCLUSIONS

This study demonstrates that photosensitivity is enhanced after awakening from a short sleep following sleep deprivation. Thus, we recommend performing IPS after awakening to increase sensitivity to detect photoparoxysmal epileptiform discharges.

Sleep Deprivation and Recovery Sleep Prior to a Noxious Inflammatory Insult Influence Characteristics and Duration of Pain

STUDY OBJECTIVES

Insufficient sleep and chronic pain are public health epidemics. Sleep loss worsens pain and predicts the development of chronic pain. Whether previous, acute sleep loss and recovery sleep determine pain levels and duration remains poorly understood. This study tested whether acute sleep deprivation and recovery sleep prior to formalin injection alter post-injection pain levels and duration.

METHODS

Male Sprague-Dawley rats (n = 48) underwent sleep deprivation or ad libitum sleep for 9 hours. Thereafter, rats received a subcutaneous injection of formalin or saline into a hind paw. In the recovery sleep group, rats were allowed 24 h between sleep deprivation and the injection of formalin. Mechanical and thermal nociception were assessed using the von Frey test and Hargreaves' method. Nociceptive measures were performed at 1, 3, 7, 10, 14, 17 and 21 days post-injection.

RESULTS

Formalin caused bilateral mechanical hypersensitivity (allodynia) that persisted for up to 21 days post-injection. Sleep deprivation significantly enhanced bilateral allodynia. There was a synergistic interaction when sleep deprivation preceded a formalin injection. Rats allowed a recovery sleep period prior to formalin injection developed allodynia only in the injected limb, with higher mechanical thresholds (less allodynia) and a shorter recovery period. There were no persistent changes in thermal nociception.

CONCLUSION

The data suggest that acute sleep loss preceding an inflammatory insult enhances pain and can contribute to chronic pain. The results encourage studies in a model of surgical pain to test whether enhancing sleep reduces pain levels and duration.

Sleep affects cortical source modularity in temporal lobe epilepsy: A high-density EEG study

OBJECTIVE

Interictal epileptiform discharges (IEDs) constitute a perturbation of ongoing cerebral rhythms, usually more frequent during sleep. The aim of the study was to determine whether sleep influences the spread of IEDs over the scalp and whether their distribution depends on vigilance-related modifications in cortical interactions.

METHODS

Wake and sleep 256-channel electroencephalography (EEG) data were recorded in 12 subjects with right temporal lobe epilepsy (TLE) differentiated by whether they had mesial or neocortical TLE. Spikes were selected during wake and sleep. The averaged waking signal was subtracted from the sleep signal and projected on a bidimensional scalp map; sleep and wake spike distributions were compared by using a t-test. The superimposed signal of sleep and wake traces was obtained; the rising phase of the spike, the peak, and the deflections following the spike were identified, and their cortical generator was calculated using low-resolution brain electromagnetic tomography (LORETA) for each group.

RESULTS

A mean of 21 IEDs in wake and 39 in sleep per subject were selected. As compared to wake, a larger IED scalp projection was detected during sleep in both mesial and neocortical TLE (p<0.05). A series of EEG deflections followed the spike, the cortical sources of which displayed alternating activations of different cortical areas in wake, substituted by isolated, stationary activations in sleep in mesial TLE and a silencing in neocortical TLE.

CONCLUSION

During sleep, the IED scalp region increases, while cortical interaction decreases.

SIGNIFICANCE

The interaction of cortical modules in sleep and wake in TLE may influence the appearance of IEDs on scalp EEG; in addition, IEDs could be proxies for cerebral oscillation perturbation.

Are there really "epileptogenic" mechanisms or only corruptions of "normal" plasticity?

Plasticity in the nervous system, whether for establishing connections and networks during development, repairing networks after injury, or modifying connections based on experience, relies primarily on highly coordinated patterns of neural activity. Rhythmic, synchronized bursting of neuronal ensembles is a fundamental component of the activity-dependent plasticity responsible for the wiring and rewiring of neural circuits in the CNS. It is therefore not surprising that the architecture of the CNS supports the generation of highly synchronized bursts of neuronal activity in non-pathological conditions, even though the activity resembles the ictal and interictal events that are the hallmark symptoms of epilepsy. To prevent such natural epileptiform events from becoming pathological, multiple layers of homeostatic control operate on cellular and network levels. Many data on plastic changes that occur in different brain structures during the processes by which the epileptogenic aggregate is constituted have been accumulated but their role in counteracting or promoting such processes is still controversial. In this chapter we will review experimental and clinical evidence on the role of neural plasticity in the development of epilepsy. We will address questions such as: is epilepsy a progressive disorder? What do we know about mechanism(s) accounting for progression? Have we reliable biomarkers of epilepsy-related plastic processes? Do seizure-associated plastic changes protect against injury and aid in recovery? As a necessary premise we will consider the value of seizure-like activity in the context of normal neural development.

Neurochemical and electrophysiological changes induced by paradoxical sleep deprivation in rats

The present study aims to investigate the effects of paradoxical sleep deprivation (PSD) on the waking EEG and amino acid neurotransmitters in the hippocampus and cortex of rats. Animals were deprived of paradoxical sleep for 72h by using the multiple platform method. The EEG power spectral analysis was carried out to assess the brain's electrophysiological changes due to sleep deprivation. The concentrations of amino acid neurotransmitters were assessed in the hippocampus and cortex using HPLC. Control data showed slight differences from normal animals in the delta, theta and alpha waves while an increase in the beta wave was obtained. After 24h of PSD, delta relative power increased and the rest of EEG wave's power decreased with respect to control. After 48h and 72h the spectral power analysis showed non-significant changes to control. The amino acid neurotransmitter analysis revealed a significant increase in cortical glutamate, glycine and taurine levels while in the hippocampus, glutamate, aspartate, glutamine and glycine levels increased significantly. Both the waking EEG and neurotransmitter analyses suggest that PSD induced neurochemical and electrophysiological changes that may affect brain proper functionality.

Effects of sleep deprivation on cortical excitability in patients affected by juvenile myoclonic epilepsy: a combined transcranial magnetic stimulation and EEG study

OBJECTIVE

To investigate the effect of sleep deprivation on corticospinal excitability in patients affected by juvenile myoclonic epilepsy (JME) using different transcranial magnetic stimulation (TMS) parameters.

METHODS

Ten patients with JME and 10 normal subjects underwent partial sleep deprivation. Motor threshold (MT), motor evoked potential amplitude (MEP), and silent period (SP) were recorded from the thenar eminence (TE) muscles. Short latency intracortical inhibition (SICI) and short latency intracortical facilitation (SICF) were studied using paired magnetic stimulation. TMS was performed before and after sleep deprivation; EEG and TMS were performed simultaneously.

RESULTS

In patients with JME, sleep deprivation induced a significant decrease in SICI and an increase in SICF, which was associated with increased paroxysmal activity. A significant decrease in the MT was observed. No significant changes in any TMS parameters were noted in normal subjects after sleep deprivation. The F wave was unchanged by sleep deprivation in both control subjects and in patients with JME.

CONCLUSIONS

In patients with JME, sleep deprivation produces increases in corticospinal excitability in motor areas as measured by different TMS parameters.

Onchocerciasis-related epilepsy? Prospects at a time of uncertainty

Epilepsy and onchocerciasis (river blindness) constitute serious public health problems in several tropical countries. There are four main mechanisms that might explain a relationship between these two diseases: (i) the presence of Onchocerca volvulus in the central nervous system; (ii) the pathogenicity of various O. volvulus strains; (iii) immunological mechanisms involving cross-reactive immunization or cytokine production during infection; and (iv) the triggering role of insomnia due to itching.

Spike-and-wave discharges of absence seizures as a transformation of sleep spindles: the continuing development of a hypothesis

OBJECTIVES

This review aims to offer a critical account of recent scientific developments relevant to the hypothesis which Pierre Gloor proposed in the 1970s for the generation of spike and wave discharges (SWDs) of primary generalized absence seizures.

RESULTS

According to this hypothesis SWDs develop in the same circuits, which normally generate sleep spindles, by an initially cortical transformation of one every two or more spindle waves to a 'spike' component of SWDs, while the next one or more spindle waves are eliminated and replaced by a slow negative wave. This hypothesis was based on experiments in feline generalized penicillin epilepsy showing the possibility of transition from spindles to SWDs, when cortical neurons become hyper-responsive to thalamocortical volleys, which normally induce spindles, and thus engage feedback cortical inhibition, rebound excitation, recurrent intracortical dissemination of excitation during the 'spike' and strong excitation of thalamus for further augmentation of a brain wide synchronous oscillation. In the 1980s, electrophysiological studies in vitro and in vivo revealed the basic features of spindle rhythm generation by neurons in nucleus reticularis thalami and thalamocortical-corticothalamic oscillatory reverberations.

CONCLUSIONS

In the light of this knowledge, experimental studies in several genetic and pharmacological animal models of absence seizures, clinical observations and theoretical studies in computer models have considered, tested, modified and challenged this hypothesis. It may still be found useful in the era of dynamic digital EEG analysis of SWDs and its current sources.

Magnetic stimulation of the brain in generalized epilepsy: reversal of cortical hyperexcitability by anticonvulsants

Observations on experimental models suggest that diffuse cortical hyperexcitability is an important abnormality in the generalized epilepsies. We used the threshold for transcranial magnetic stimulation as an index of motor cortical excitability in 89 neurologically normal control subjects and 56 patients with idiopathic generalized epilepsy (20 untreated and 36 chronically treated with anticonvulsants). Magnetic stimulation was repeated in 10 patients after valproate monotherapy had been commenced and in 23 control subjects. The threshold intensity was significantly lower in the untreated patients (46 +/- 5% [mean +/- 95% confidence interval]) than in the control subjects (56 +/- 2%). Treated patients had significantly higher thresholds (64 +/- 4%) than did untreated patients and control subjects. A significant increase in threshold intensity (8 +/- 2%) occurred in patients retested after starting valproate; there was no significant change in retested control subjects (-1 +/- 2%). Threshold intensity was positively correlated with plasma valproate levels (rs = 0.37). The findings suggest that cortical excitability is increased in idiopathic generalized epilepsy and is reduced following anticonvulsant treatment. Transcranial magnetic stimulation is of use in examining the pathophysiology of generalized epilepsy. Furthermore, changes in threshold intensity in response to anticonvulsant treatment may prove useful in guiding therapy.

Effects of selective toxic lesions of cholinergic neurons of the laterodorsal tegmental nucleus on experimental seizures

This study determined the effects of bilateral discrete partial lesions of cholinergic neurons of the laterodorsal tegmental nucleus (LDTg) of the pontomesencephalic tegmentum on seizures induced by intravenous pentylenetetrazol (PTZ). Relatively selective lesions produced by bilateral 50 nl microinjections of 75 pmol of the cholinergic neurotoxin ethylcholine mustard aziridinium ion (AF64A) resulted in a significant reduction in the threshold of myoclonic and facial-forelimb clonic seizures but not tonic seizures when PTZ was infused 7 days later. This demonstrates that this cholinergic nucleus is a key site of subcortical seizure regulation. We propose that this control is mediated by ascending projections from the LDTg to the central medial intralaminar nucleus of the thalamus.

Anticonvulsant drugs selectively affect kindled and penicillin epilepsy, especially during seizure-prone sleep or awakening states in cats

Carbamazepine (CBZ) selectively suppressed kindled convulsions, whereas ethosuximide (ESM) suppressed spike-wave activity accompanying systemic penicillin epilepsy in cats. Evoked potential data indicated that CBZ acted at the thalamic level, whereas ESM acted at cortex. Reduction of seizures and thalamic or cortical excitability occurred throughout the sleep-wake cycle, but effects were most pronounced in seizure-prone sleep or awakening states. These findings extend previous work showing differential antiepileptic drug (AED) effects on temporal lobe and absence seizures. The results are also consistent with recent work suggesting that thalamocortical pathways provide a final common pathway for the manifestation of sleep and awakening epilepsy and also reflect a chronic, latent pathophysiology.

Temporal lobe and petit mal antiepileptics differentially affect ventral lateral thalamic and motor cortex excitability patterns

Evoked potential (EP) analysis of the somatomotor pathway in cats revealed that the temporal lobe anticonvulsant carbamazepine suppresses the thalamic relay, whereas the petit mal antiepileptic ethosuximide acts on the cortex. Moreover, a history of temporal lobe epilepsy (amygdala kindling) maximized thalamic response to carbamazepine, especially during sleep states vulnerable to generalized kindled seizures. Ethosuximide accentuated cortical response during sleep and awakening states vulnerable to generalized spike-wave complexes, regardless of a history of petit mal seizures (systemic penicillin epilepsy). The findings provide a neural basis for differential drug effects on generalized temporal lobe and petit mal epilepsy and further suggest that a chronic seizure disorder can create a predisposition for antiepileptic drug sensitivity.