Behavioral and EEG effects of GABAergic manipulation of the nigrotectal pathway in the Wistar audiogenic rat strain

Behavior and electrophysiological effects on striatum-nigra circuit after high frequency stimulation. Relevance to Parkinson and epilepsy

The phenomenon of plasticity in the striatum, and its relation with the striatum-nigra neuronal circuit has clinical and neurophysiological relevance to Parkinson and epilepsy. High frequency stimulation (HFS) can induce neural plasticity. Furthermore, it is possible to induce plasticity in the dorsal striatum and this can be modulated by substantia nigra activity. But it has not been shown yet what would be the effects in the striatum-nigra circuit after plasticity induction in striatum with HSF. Literature also misses a detailed description of the way back loop of the circuit: the striatal firing rate after substantia nigrás inhibition. We here conducted: First Experiment, application of HFS in dorsomedial striatum and measure of spontaneous and longlasting behavior expression in the open field three days later; Second, application of single pulses on dorsomedial striatum and measure of the evoked potentials in substantia nigra before and after HFS; Third Experiment: inhibition of substantia nigra and recording of the firing rate of dorsomedial striatum. HFS in dorsomedial striatum caused increased locomotion behaviors, but not classical stereotypy. However, rats had either an increase or decrease in substantia nigrás evoked potentials. Also, substantia nigrás inhibition caused an increase in dorsomedial striatum firing rate. Present data are suggestive of a potential application of HFS in striatum, as an attempt to modulate behavior rigidity and hypokinesia of diseases involving the basal ganglia, especially Parkinson´s Disease.

Parvalbumin Role in Epilepsy and Psychiatric Comorbidities: From Mechanism to Intervention

Parvalbumin is a calcium-binding protein present in inhibitory interneurons that play an essential role in regulating many physiological processes, such as intracellular signaling and synaptic transmission. Changes in parvalbumin expression are deeply related to epilepsy, which is considered one of the most disabling neuropathologies. Epilepsy is a complex multi-factor group of disorders characterized by periods of hypersynchronous activity and hyperexcitability within brain networks. In this scenario, inhibitory neurotransmission dysfunction in modulating excitatory transmission related to the loss of subsets of parvalbumin-expressing inhibitory interneuron may have a prominent role in disrupted excitability. Some studies also reported that parvalbumin-positive interneurons altered function might contribute to psychiatric comorbidities associated with epilepsy, such as depression, anxiety, and psychosis. Understanding the epileptogenic process and comorbidities associated with epilepsy have significantly advanced through preclinical and clinical investigation. In this review, evidence from parvalbumin altered function in epilepsy and associated psychiatric comorbidities were explored with a translational perspective. Some advances in potential therapeutic interventions are highlighted, from current antiepileptic and neuroprotective drugs to cutting edge modulation of parvalbumin subpopulations using optogenetics, designer receptors exclusively activated by designer drugs (DREADD) techniques, transcranial magnetic stimulation, genome engineering, and cell grafting. Creating new perspectives on mechanisms and therapeutic strategies is valuable for understanding the pathophysiology of epilepsy and its psychiatric comorbidities and improving efficiency in clinical intervention.

Divergent brain changes in two audiogenic rat strains: A voxel-based morphometry and diffusion tensor imaging comparison of the genetically epilepsy prone rat (GEPR-3) and the Wistar Audiogenic Rat (WAR)

Acoustically evoked seizures (e.g., audiogenic seizures or AGS) are common in models of inherited epilepsy and occur in a variety of species including rat, mouse, and hamster. Two models that have been particularly well studied are the genetically epilepsy prone rat (GEPR-3) and the Wistar Audiogenic Rat (WAR) strains. Acute and repeated AGS, as well as comorbid conditions, displays a close phenotypic overlap in these models. Whether these similarities arise from convergent or divergent structural changes in the brain remains unknown. Here, we examined the brain structure of Sprague Dawley (SD) and Wistar (WIS) rats, and quantified changes in the GEPR-3 and WAR, respectively. Brains from adult, male rats of each strain (n=8-10 per group) were collected, fixed, and embedded in agar and imaged using a 7 tesla Bruker MRI. Post-acquisition analysis included voxel-based morphometry (VBM), diffusion tensor imaging (DTI), and manual volumetric tracing. In the VBM analysis, GEPR-3 displayed volumetric changes in brainstem structures known to be engaged by AGS (e.g., superior and inferior colliculus, periaqueductal grey) and in forebrain structures (e.g., striatum, septum, nucleus accumbens). WAR displayed volumetric changes in superior colliculus, and a broader set of limbic regions (e.g., hippocampus, amygdala/piriform cortex). The only area of significant overlap in the two strains was the midline cerebellum: both GEPR-3 and WAR showed decreased volume compared to their control strains. In the DTI analysis, GEPR-3 displayed decreased fractional anisotropy (FA) in the corpus callosum, posterior commissure and commissure of the inferior colliculus (IC). WAR displayed increased FA only in the commissure of IC. These data provide a biological basis for further comparative and mechanistic studies in the GEPR-3 and WAR models, as well as provide additional insight into commonalities in the pathways underlying AGS susceptibility and behavioral comorbidity.

The Wistar Audiogenic Rat (WAR) strain and its contributions to epileptology and related comorbidities: History and perspectives

In the context of modeling epilepsy and neuropsychiatric comorbidities, we review the Wistar Audiogenic Rat (WAR), first introduced to the neuroscience international community more than 25years ago. The WAR strain is a genetically selected reflex model susceptible to audiogenic seizures (AS), acutely mimicking brainstem-dependent tonic-clonic seizures and chronically (by audiogenic kindling), temporal lobe epilepsy (TLE). Seminal neuroethological, electrophysiological, cellular, and molecular protocols support the WAR strain as a suitable and reliable animal model to study the complexity and emergent functions typical of epileptogenic networks. Furthermore, since epilepsy comorbidities have emerged as a hot topic in epilepsy research, we discuss the use of WARs in fields such as neuropsychiatry, memory and learning, neuroplasticity, neuroendocrinology, and cardio-respiratory autonomic regulation. Last, but not least, we propose that this strain be used in "omics" studies, as well as with the most advanced molecular and computational modeling techniques. Collectively, pioneering and recent findings reinforce the complexity associated with WAR alterations, consequent to the combination of their genetically-dependent background and seizure profile. To add to previous studies, we are currently developing more powerful behavioral, EEG, and molecular methods, combined with computational neuroscience/network modeling tools, to further increase the WAR strain's contributions to contemporary neuroscience in addition to increasing knowledge in a wide array of neuropsychiatric and other comorbidities, given shared neural networks. During the many years that the WAR strain has been studied, a constantly expanding network of multidisciplinary collaborators has generated a growing research and knowledge network. Our current and major wish is to make the WARs available internationally to share our knowledge and to facilitate the planning and execution of multi-institutional projects, eagerly needed to contribute to paradigm shifts in epileptology. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

Optogenetic activation of superior colliculus neurons suppresses seizures originating in diverse brain networks

Because sites of seizure origin may be unknown or multifocal, identifying targets from which activation can suppress seizures originating in diverse networks is essential. We evaluated the ability of optogenetic activation of the deep/intermediate layers of the superior colliculus (DLSC) to fill this role. Optogenetic activation of DLSC suppressed behavioral and electrographic seizures in the pentylenetetrazole (forebrain+brainstem seizures) and Area Tempestas (forebrain/complex partial seizures) models; this effect was specific to activation of DLSC, and not neighboring structures. DLSC activation likewise attenuated seizures evoked by gamma butyrolactone (thalamocortical/absence seizures), or acoustic stimulation of genetically epilepsy prone rates (brainstem seizures). Anticonvulsant effects were seen with stimulation frequencies as low as 5 Hz. Unlike previous applications of optogenetics for the control of seizures, activation of DLSC exerted broad-spectrum anticonvulsant actions, attenuating seizures originating in diverse and distal brain networks. These data indicate that DLSC is a promising target for optogenetic control of epilepsy.

Looking for complexity in quantitative semiology of frontal and temporal lobe seizures using neuroethology and graph theory

Epileptic syndromes and seizures are the expression of complex brain systems. Because no analysis of complexity has been applied to epileptic seizure semiology, our goal was to apply neuroethology and graph analysis to the study of the complexity of behavioral manifestations of epileptic seizures in human frontal lobe epilepsy (FLE) and temporal lobe epilepsy (TLE). We analyzed the video recordings of 120 seizures of 18 patients with FLE and 28 seizures of 28 patients with TLE. All patients were seizure-free >1 year after surgery (Engel Class I). All patients' behavioral sequences were analyzed by means of a glossary containing all behaviors and analyzed for neuroethology (Ethomatic software). The same series were used for graph analysis (CYTOSCAPE). Behaviors, displayed as nodes, were connected by edges to other nodes according to their temporal sequence of appearance. Using neuroethology analysis, we confirmed data in the literature such as in FLE: brief/frequent seizures, complex motor behaviors, head and eye version, unilateral/bilateral tonic posturing, speech arrest, vocalization, and rapid postictal recovery and in the case of TLE: presence of epigastric aura, lateralized dystonias, impairment of consciousness/speech during ictal and postictal periods, and development of secondary generalization. Using graph analysis metrics of FLE and TLE confirmed data from flowcharts. However, because of the algorithms we used, they highlighted more powerfully the connectivity and complex associations among behaviors in a quite selective manner, depending on the origin of the seizures. The algorithms we used are commonly employed to track brain connectivity from EEG and MRI sources, which makes our study very promising for future studies of complexity in this field.

Neuroanatomical and neuropharmacological approaches to postictal antinociception-related prosencephalic neurons: the role of muscarinic and nicotinic cholinergic receptors

Several studies have suggested the involvement of the hippocampus in the elaboration of epilepsy. There is evidence that suggests the hippocampus plays an important role in the affective and motivational components of nociceptive perception. However, the exact nature of this involvement remains unclear. Therefore, the aim of this study was to determine the role of muscarinic and nicotinic cholinergic receptors in the dorsal hippocampus (dH) in the organization of postictal analgesia. In a neuroanatomical study, afferent connections were found from the somatosensory cortex, the medial septal area, the lateral septal area, the diagonal band of Broca, and the dentate gyrus to the dH; all these areas have been suggested to modulate convulsive activity. Outputs to the dH were also identified from the linear raphe nucleus, the median raphe nucleus (MdRN), the dorsal raphe nucleus, and the locus coeruleus. All these structures comprise the endogenous pain modulatory system and may be involved either in postictal pronociception or antinociception that is commonly reported by epileptic patients. dH-pretreatment with cobalt chloride (1.0 mmol/L CoCl2/0.2 μL) to transiently inhibit local synapses decreased postictal analgesia 10 min after the end of seizures. Pretreatment of the dH with either atropine or mecamylamine (1.0 μg/0.2 μL) attenuated the postictal antinociception 30 min after seizures, while the higher dose (5.0 μg/0.2 μL) decreased postictal analgesia immediately after the end of seizures. These findings suggest that the dH exerts a critical role in the organization of postictal analgesia and that muscarinic and nicotinic cholinergic receptor-mediated mechanisms in the dH are involved in the elaboration of antinociceptive processes induced by generalized tonic-clonic seizures.

The epilepsies: complex challenges needing complex solutions

It is widely accepted that epilepsies are complex syndromes due to their multi-factorial origins and manifestations. Different mathematical and computational descriptions use appropriate methods to address nonlinear relationships, chaotic behaviors and emergent properties. These theoretical approaches can be divided into two major categories: descriptive, such as flowcharts, graphs and other statistical analyses, and explicative, which include both realistic and abstract models. Although these modeling tools have brought great advances, a common framework to guide their design, implementation and evaluation, with the goal of future integration, is still needed. In the current review, we discuss two examples of complexity analysis that can be performed with epilepsy data: behavioral sequences of temporal lobe seizures and alterations in an experimental cellular model. We also highlight the importance of the creation of model repositories for the epileptology field and encourage the development of mathematical descriptions of complex systems, together with more accurate simulation techniques.

Behavioral and EEG effects of GABAergic manipulation of the nigro-tectal pathway in the Wistar audiogenic rat (WAR) strain II: an EEG wavelet analysis and retrograde neuronal tracer approach

The role of the substantia nigra pars reticulata (SNPr) and superior colliculus (SC) network in rat strains susceptible to audiogenic seizures still remain underexplored in epileptology. In a previous study from our laboratory, the GABAergic drugs bicuculline (BIC) and muscimol (MUS) were microinjected into the deep layers of either the anterior SC (aSC) or the posterior SC (pSC) in animals of the Wistar audiogenic rat (WAR) strain submitted to acoustic stimulation, in which simultaneous electroencephalographic (EEG) recording of the aSC, pSC, SNPr and striatum was performed. Only MUS microinjected into the pSC blocked audiogenic seizures. In the present study, we expanded upon these previous results using the retrograde tracer Fluorogold (FG) microinjected into the aSC and pSC in conjunction with quantitative EEG analysis (wavelet transform), in the search for mechanisms associated with the susceptibility of this inbred strain to acoustic stimulation. Our hypothesis was that the WAR strain would have different connectivity between specific subareas of the superior colliculus and the SNPr when compared with resistant Wistar animals and that these connections would lead to altered behavior of this network during audiogenic seizures. Wavelet analysis showed that the only treatment with an anticonvulsant effect was MUS microinjected into the pSC region, and this treatment induced a sustained oscillation in the theta band only in the SNPr and in the pSC. These data suggest that in WAR animals, there are at least two subcortical loops and that the one involved in audiogenic seizure susceptibility appears to be the pSC-SNPr circuit. We also found that WARs presented an increase in the number of FG+ projections from the posterior SNPr to both the aSC and pSC (primarily to the pSC), with both acting as proconvulsant nuclei when compared with Wistar rats. We concluded that these two different subcortical loops within the basal ganglia are probably a consequence of the WAR genetic background.