Cholinergic stimulation of the nucleus basalis of Meynert and reticular thalamic nucleus affects spike-and-wave discharges in WAG/Rij rats

The role of the nucleus basalis of Meynert in neuromodulation therapy: a systematic review from the perspective of neural network oscillations

As a crucial component of the cerebral cholinergic system and the Papez circuit in the basal forebrain, dysfunction of the nucleus basalis of Meynert (NBM) is associated with various neurodegenerative disorders. However, no drugs, including existing cholinesterase inhibitors, have been shown to reverse this dysfunction. Due to advancements in neuromodulation technology, researchers are exploring the use of deep brain stimulation (DBS) therapy targeting the NBM (NBM-DBS) to treat mental and neurological disorders as well as the related mechanisms. Herein, we provided an update on the research progress on cognition-related neural network oscillations and complex anatomical and projective relationships between the NBM and other cognitive structures and circuits. Furthermore, we reviewed previous animal studies of NBM lesions, NBM-DBS models, and clinical case studies to summarize the important functions of the NBM in neuromodulation. In addition to elucidating the mechanism of the NBM neural network, future research should focus on to other types of neurons in the NBM, despite the fact that cholinergic neurons are still the key target for cell type-specific activation by DBS.

State-dependent modulation of low-threshold-current-regulated dendritic Ca2+ response in thalamic reticular neurons with extracellular electric fields

Deep brain stimulation (DBS) in thalamic reticular nucleus (TRN) neuron provides a novel treatment for drug-resistant epilepsy via the induced electrical field (EFs). However, the mechanisms underlying EF effects remain unclear. This paper investigated how EFs regulate low-threshold dendritic Ca2+ (dCa) response and thus contribute to the input-output relationship of TRN cell. Our results showed that EFs modulate firing modes differently in a neuronal state-dependent manner. At the depolarized state, EFs only regulate the spike timing of a somatic stimulus-evoked single action potential (AP) with less contribution in the regulation of dCa response but could induce the transition between a dendritic stimulus-evoked single AP and a tonic burst of APs via the moderate regulation of dCa response. At the hyperpolarized state, EFs have significant effects on the dCa response, which modulate the large dCa response-dependent burst discharge and even cause a transition from this type of burst discharge to a single AP with less dCa response. Moreover, EF effects on stimulation threshold of somatic spiking prominently depend on EF-regulated dCa responses and the onset time differences between the stimulus and EF give rise to the distinct effect in the EF regulation of dCa responses. Finally, the larger neuronal axial resistance tends to result in the dendritic stimulus-evoked dCa response independent of somatic state. Interestingly, in this case, the EF application could reproduce the similar somatic state-dependent dCa response to dendritic stimulus which occurs in the case of lower axial resistance. These results suggest that the influence of EF on neuronal activities depends on neuronal intrinsic properties, which provides insight into understanding how DBS in TRN neuron modulates epilepsy from the point of view of biophysics.

Nicotinic receptor abnormalities as a biomarker in idiopathic generalized epilepsy

PURPOSE

Mutations of cholinergic neuronal nicotinic receptors have been identified in the autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE), associated with changes on PET images using [¹⁸F]-F-85380-A (F-A-85380), an α4β2 nicotinic receptor ligand. The aim of the present study was to evaluate potential changes in nicotinic receptor availability in other types of epilepsy.

METHODS

We included 34 male participants, 12 patients with idiopathic generalized epilepsy (IGE), 10 with non-lesional diurnal focal epilepsy, and 12 age-matched healthy controls. All patients underwent PET/CT using F-A-85380 and [¹⁸F]-fluorodeoxyglucose (FDG), 3D T1 MRI and diffusion tensor imaging (DTI). F-A-85380 and FDG images were compared with the control group using a voxel-wise (SPM12) and a volumes of interest (VOI) analysis.

RESULTS

In the group of patients with IGE, the voxel-wise and VOI analyses showed a significant increase of F-A-85380 ratio index of binding potential (BP_RI, corresponding to the receptor availability) in the anterior cingulate cortex (ACC), without structural changes on MRI. At an individual level, F-A-85380 BP_RI increase in the ACC could distinguish IGE patients from controls and from patients with focal epilepsy with good accuracy.

CONCLUSIONS

We observed focal changes of density/availability of nicotinic receptors in IGE, namely an increase in the ACC. These data suggest that the modulation of α4β2 nicotinic receptors plays a role not only in ADNFLE, but also in other genetic epileptic syndromes such as IGE and could serve as a biomarker of epilepsy syndromes with a genetic background.

Pharmacokinetic/pharmacodynamic considerations for epilepsy - depression comorbidities

INTRODUCTION

Epilepsy may be frequently associated with psychiatric disorders and its co-existence with depression usually results in the reduced quality of life of patients with epilepsy. Also, the efficacy of antiepileptic treatment in depressed patients with epilepsy may be significantly reduced.

AREAS COVERED

Results of experimental studies indicate that antidepressants co-administered with antiepileptic drugs may either increase their anticonvulsant activity, remain neutral or decrease the protective action of antiepileptic drugs in models of seizures. Apart from purely pharmacodynamic interactions, pharmacokinetic mechanisms have been proven to contribute to the final outcome. We report on clinical data regarding the pharmacokinetic interactions of enzyme-inducing antiepileptic drugs with various antidepressants, whose plasma concentration may be significantly reduced. On the other hand, antidepressants (especially selective serotonin reuptake inhibitors) may influence the metabolism of antiepileptics, in many cases resulting in the elevation of plasma concentration of antiepileptic drugs.

EXPERT OPINION

The preclinical data may provide valuable clues on how to combine these two groups of drugs - antidepressant drugs neutral or potentiating the anticonvulsant action of antiepileptics are recommended in this regard. Avoidance of antidepressants clearly decreasing the convulsive threshold or decreasing the anticonvulsant efficacy of antiepileptic drugs (f.e. bupropion or mianserin) in patients with epilepsy is recommended.

Unilateral and Bilateral Cortical Resection: Effects on Spike-Wave Discharges in a Genetic Absence Epilepsy Model

Research Question

Recent discoveries have challenged the traditional view that the thalamus is the primary source driving spike-and-wave discharges (SWDs). At odds, SWDs in genetic absence models have a cortical focal origin in the deep layers of the perioral region of the somatosensory cortex. The present study examines the effect of unilateral and bilateral surgical resection of the assumed focal cortical region on the occurrence of SWDs in anesthetized WAG/Rij rats, a well described and validated genetic absence model.

Methods

Male WAG/Rij rats were used: 9 in the resected and 6 in the control group. EEG recordings were made before and after craniectomy, after unilateral and after bilateral removal of the focal region.

Results

SWDs decreased after unilateral cortical resection, while SWDs were no longer noticed after bilateral resection. This was also the case when the resected areas were restricted to layers I-IV with layers V and VI intact.

Conclusions

These results suggest that SWDs are completely abolished after bilateral removal of the focal region, most likely by interference with an intracortical columnar circuit. The evidence suggests that absence epilepsy is a network type of epilepsy since interference with only the local cortical network abolishes all seizures.

The use of automated system for EEG analysis and feedback cerebral stimulation to stop epileptiform activity in WAG/Rij rats

Original software program is described, which revealed EEG activity characteristic of the onset of epileptic seizure and turned on electrical stimulation of the nucleus basalis of Meynert in WAG/Rij rats with congenital absence epilepsy. The program reliably detected the onset of seizure and automatically stopped it with a high-frequency train of electrical impulses (100-150 Hz). Thus, a feedback system of deep brain stimulation has been developed to stop early manifestations of absence epileptiform seizures. The study can be a base to develop an implanted apparatus to automatically analyze EEG and stimulate the brain to stop the epileptic seizures.

Termination of ongoing spike-wave discharges investigated by cortico-thalamic network analyses

PURPOSE

While decades of research were devoted to study generation mechanisms of spontaneous spike and wave discharges (SWD), little attention has been paid to network mechanisms associated with the spontaneous termination of SWD. In the current study coupling-dynamics at the onset and termination of SWD were studied in an extended part of the cortico-thalamo-cortical system of freely moving, genetic absence epileptic WAG/Rij rats.

METHODS

Local-field potential recordings of 16 male WAG/Rij rats, equipped with multiple electrodes targeting layer 4 to 6 of the somatosensory-cortex (ctx4, ctx5, ctx6), rostral and caudal reticular thalamic nucleus (rRTN & cRTN), ventral postero medial (VPM), anterior- (ATN) and posterior (Po) thalamic nucleus, were obtained. Six seconds lasting pre-SWD->SWD, SWD->post SWD and control periods were analyzed with time-frequency methods, and between-region interactions were quantified with frequency-resolved Granger Causality (GC) analysis.

RESULTS

Most channel pairs showed increases in GC lasting from onset to offset of the SWD. While for most thalamo-thalamic pairs a dominant coupling direction was found during the complete SWD, most cortico-thalamic pairs only showed a dominant directional drive (always from cortex to thalamus) during the first 500ms of SWD. Channel pair ctx4-rRTN showed a longer lasting dominant cortical drive, which stopped 1.5sec prior to SWD offset. This early decrease in directional coupling was followed by an increase in directional coupling from cRTN to rRTN 1sec prior to SWD offset. For channel pairs ctx5-Po and ctx6-Po the heightened cortex->thalamus coupling remained until 1.5sec following SWD offset, while the thalamus->cortex coupling for these pairs stopped at SWD offset.

CONCLUSION

The high directional coupling from somatosensory cortex to the thalamus at SWD onset is in good agreement with the idea of a cortical epileptic focus that initiates and entrains other brain structures into seizure activity. The decrease of cortex to rRTN coupling as well as the increased coupling from cRTN to rRTN preceding SWD termination demonstrates that SWD termination is a gradual process that involves both cortico-thalamic as well as intrathalamic processes. The rostral RTN seems to be an important resonator for SWD and relevant for maintenance, while the cRTN might inhibit this oscillation. The somatosensory cortex seems to attempt to reinitiate SWD following its offset via its strong coupling to the posterior thalamus.

Anti-epileptogenic effect of high-frequency stimulation in the thalamic reticular nucleus on PTZ-induced seizures

BACKGROUND

Deep brain stimulation, specifically high-frequency stimulation (HFS), is an alternative and promising treatment for intractable epilepsies; however, the optimal targets are still unknown. The thalamic reticular nucleus (TRN) occupies a key position in the modulation of the cortico-thalamic and thalamo-cortical pathways.

OBJECTIVE

We determined the efficacy of HFS in the TRN against tonic-clonic generalized seizures (TCGS) and status epilepticus (SE), which were induced by scheduled pentylenetetrazole (PTZ) injections.

METHODS

Male Wistar rats were stereotactically implanted and assigned to three experimental groups: Control group, which received only PTZ injections; HFS-TRN group, which received HFS in the left TRN prior to PTZ injections; and HFS-Adj group, which received HFS in the left adjacent nuclei prior to PTZ injections.

RESULTS

The HFS-TRN group reported a significant increase in the latency for development of TCGS and SE compared with the HFS-Adj and Control groups (P < 0.009). The number of PTZ-doses required for SE was also significantly increased (P < 0.001). Spectral analysis revealed a significant decrease in the frequency band from 0.5 Hz to 4.5 Hz of the left motor cortex in the HFS-TRN and HFS-Adj groups, compared to the Control group. Conversely, HFS-TRN provoked a significant increase in all frequency bands in the TRN. EEG asynchrony was observed during spike-wave discharges by HFS-TRN.

CONCLUSION

These data indicate that HFS-TRN has an anti-epileptogenic effect and is able to modify seizure synchrony and interrupt abnormal EEG recruitment of thalamo-cortical and, indirectly, cortico-thalamic pathways.

Rhythm and blues: animal models of epilepsy and depression comorbidity

Clinical evidence shows a strong, bidirectional comorbidity between depression and epilepsy that is associated with decreased quality of life and responsivity to pharmacotherapies. At present, the neurobiological underpinnings of this comorbidity remain hazy. To complicate matters, anticonvulsant drugs can cause mood disturbances, while antidepressant drugs can lower seizure threshold, making it difficult to treat patients suffering from both depression and epilepsy. Animal models have been created to untangle the mechanisms behind the relationship between these disorders and to serve as screening tools for new therapies targeted to treat both simultaneously. These animal models are based on chemical interventions (e.g. pentylenetetrazol, kainic acid, pilocarpine), electrical stimulations (e.g. kindling, electroshock), and genetic/selective breeding paradigms (e.g. genetically epilepsy-prone rats (GEPRs), genetic absence epilepsy rat from Strasbourg (GAERS), WAG/Rij rats, swim lo-active rats (SwLo)). Studies on these animal models point to some potential mechanisms that could explain epilepsy and depression comorbidity, such as various components of the dopaminergic, noradrenergic, serotonergic, and GABAergic systems, as well as key brain regions, like the amygdala and hippocampus. These models have also been used to screen possible therapies. The purpose of the present review is to highlight the importance of animal models in research on comorbid epilepsy and depression and to explore the contributions of these models to our understanding of the mechanisms and potential treatments for these disorders.

Vagus nerve stimulation modulates cortical synchrony and excitability through the activation of muscarinic receptors

Vagus nerve stimulation (VNS) is an FDA approved treatment for drug-resistant epilepsy and depression. Recently, we demonstrated the capacity for repeatedly pairing sensory input with brief pulses of VNS to induce input specific reorganization in rat auditory cortex. This was subsequently used to reverse the pathological neural and perceptual correlates of hearing loss induced tinnitus. Despite its therapeutic potential, VNS mechanisms of action remain speculative. In this study, we report the acute effects of VNS on intra-cortical synchrony, excitability, and sensory processing in anesthetized rat auditory cortex. VNS significantly increased and decorrelated spontaneous multi-unit activity, and suppressed entrainment to repetitive noise burst stimulation at 6-8 Hz but not after application of the muscarinic antagonist scopolamine. Collectively, these experiments demonstrate the capacity for VNS to acutely influence cortical synchrony and excitability and strengthen the hypothesis that acetylcholine and muscarinic receptors are involved in VNS mechanisms of action. These results are discussed with respect to their possible implications for sensory processing, neural plasticity, and epilepsy.