Neuroethological evaluation of audiogenic seizures and audiogenic-like seizures induced by microinjection of bicuculline into the inferior colliculus. I. Effects of midcollicular knife cuts

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.

Transcriptome of the Krushinsky-Molodkina Audiogenic Rat Strain and Identification of Possible Audiogenic Epilepsy-Associated Genes

Audiogenic epilepsy (AE), inherent to several rodent strains is widely studied as a model of generalized convulsive epilepsy. The molecular mechanisms that determine the manifestation of AE are not well understood. In the present work, we compared transcriptomes from the corpora quadrigemina in the midbrain zone, which are crucial for AE development, to identify genes associated with the AE phenotype. Three rat strains without sound exposure were compared: Krushinsky-Molodkina (KM) strain (100% AE-prone); Wistar outbred rat strain (non-AE prone) and “0” strain (partially AE-prone), selected from F2 KM × Wistar hybrids for their lack of AE. The findings showed that the KM strain gene expression profile exhibited a number of characteristics that differed from those of the Wistar and “0” strain profiles. In particular, the KM rats showed increased expression of a number of genes involved in the positive regulation of the MAPK signaling cascade and genes involved in the positive regulation of apoptotic processes. Another characteristic of the KM strain which differed from that of the Wistar and “0” rats was a multi-fold increase in the expression level of the Ttr gene and a significant decrease in the expression of the Msh3 gene. Decreased expression of a number of oxidative phosphorylation-related genes and a few other genes was also identified in the KM strain. Our data confirm the complex multigenic nature of AE inheritance in rodents. A comparison with data obtained from other independently selected AE-prone rodent strains suggests some common causes for the formation of the audiogenic phenotype.

Cannabinoids in Audiogenic Seizures: From Neuronal Networks to Future Perspectives for Epilepsy Treatment

Cannabinoids and Cannabis-derived compounds have been receiving especial attention in the epilepsy research scenario. Pharmacological modulation of endocannabinoid system's components, like cannabinoid type 1 receptors (CB1R) and their bindings, are associated with seizures in preclinical models. CB1R expression and functionality were altered in humans and preclinical models of seizures. Additionally, Cannabis-derived compounds, like cannabidiol (CBD), present anticonvulsant activity in humans and in a great variety of animal models. Audiogenic seizures (AS) are induced in genetically susceptible animals by high-intensity sound stimulation. Audiogenic strains, like the Genetically Epilepsy Prone Rats, Wistar Audiogenic Rats, and Krushinsky-Molodkina, are useful tools to study epilepsy. In audiogenic susceptible animals, acute acoustic stimulation induces brainstem-dependent wild running and tonic-clonic seizures. However, during the chronic protocol of AS, the audiogenic kindling (AuK), limbic and cortical structures are recruited, and the initially brainstem-dependent seizures give rise to limbic seizures. The present study reviewed the effects of pharmacological modulation of the endocannabinoid system in audiogenic seizure susceptibility and expression. The effects of Cannabis-derived compounds in audiogenic seizures were also reviewed, with especial attention to CBD. CB1R activation, as well Cannabis-derived compounds, induced anticonvulsant effects against audiogenic seizures, but the effects of cannabinoids modulation and Cannabis-derived compounds still need to be verified in chronic audiogenic seizures. The effects of cannabinoids and Cannabis-derived compounds should be further investigated not only in audiogenic seizures, but also in epilepsy related comorbidities present in audiogenic strains, like anxiety, and depression.

Evaluation of Maternal Reproductive Outcomes and Biochemical Analysis from Wistar Audiogenic Rats (WAR) and Repercussions in Their Offspring

The objective of the present study was to evaluate maternal reproductive performance, body weight, and frequency of external and internal anomalies of newborns of Wistar Audiogenic Rat (WAR) females as compared with Wistar rats. The adult WAR and Wistar rats were mated within their respective strains. After confirming the pregnancy, the body weights were weekly evaluated. On day 21 of pregnancy, the female rats were anesthetized and sacrificed to evaluate the maternal reproductive outcomes and biochemical profile, newborn weight, and external and internal anomalies. The WAR strain gained less weight during the pregnancy and presented hyperproteinemia, hypertriglyceridemia, and embryonic losses concerning Wistar rats, suggesting an inadequate intrauterine condition for embryonic development and fetal viability. WAR also presented a higher percentage of newborns classified as small for gestational age related to intrauterine growth restriction, which was confirmed by the lower number of ossification centers. There was a higher percentage of skeletal anomalies compared with fetuses of the Wistar dams, confirming their greater susceptibility during the formation and development of their skeletal system. Thus, the WAR presents physiological alterations compromising the viability of their embryos and fetuses, leading to impaired development of the newborns.

Maternal reproductive performance and fetal development of the Wistar Audiogenic Rat (WAR) strain

Wistar Audiogenic Rat (WAR) strain is an animal model for epilepsy studies, the chronic multifactorial disease that affects millions of people worldwide. The animals of this strain are genetically predisposed to sound-induced seizures, called audiogenic seizures, and have been used for many years in studies to understand the mechanisms involved in the epilepsies and their neuropsychiatric comorbidities, as well as the screening of potential anti-convulsant agents. Nevertheless, little is known about the reproductive characteristics of these animals. The main goal of this study was to characterize the female reproductive performance and the fetal growth of WARs in comparison to the Wistar rats, obtaining important information for physiology and behavioral studies, as well as for the preservation of the strain. The results indicated few differences between WAR and Wistar regarding the female reproductive performance. There was no significant difference in the number of pregnant females by mating, number of live births per female, number of cells per blastocyst, and several characteristics related to reproductive performance, such as pre- and post-implantation losses. However, significant differences were observed in birth weight and weight gain until weaning, with WAR animals presenting a body weight below Wistar at birth and reduced body weight gain during the lactation period. In addition, the WAR females showed lower body weight on the day 20 of pregnancy and a larger number of corpora lutea, when compared with those of Wistar animals. Thus, we conclude that although Wistar and WAR strains have few differences in their reproductive performance, which might impact future physiological life challenges or others experimentally induced procedures, it still is a very viable strain regarding reproduction. Abbreviations: CONCEA: National Council for the Control of Animal Experimentation; GEPR: genetically epilepsy-prone rats; WAR: Wistar Audiogenic Rat.

Intense olfactory stimulation blocks seizures in an experimental model of epilepsy

There are reports of patients whose epileptic seizures are prevented by means of olfactory stimulation. Similar findings were described in animal models of epilepsy, such as the electrical kindling of amygdala, where olfactory stimulation with toluene (TOL) suppressed seizures in most rats, even when the stimuli were 20% above the threshold to evoke seizures in already kindled animals. The Wistar Audiogenic Rat (WAR) strain is a model of tonic-clonic seizures induced by acute acoustic stimulation, although it also expresses limbic seizures when repeated acoustic stimulation occurs - a process known as audiogenic kindling (AK). The aim of this study was to evaluate whether or not the olfactory stimulation with TOL would interfere on the behavioral expression of brainstem (acute) and limbic (chronic) seizures in the WAR strain. For this, animals were exposed to TOL or saline (SAL) and subsequently exposed to acoustic stimulation in two conditions that generated: I) acute audiogenic seizures (only one acoustic stimulus, without previous seizure experience before of the odor test) and II) after AK (20 acoustic stimuli [2 daily] before of the protocol test). We observed a decrease in the seizure severity index of animals exposed only to TOL in both conditions, with TOL presented 20s before the acoustic stimulation in both protocols. These findings were confirmed by behavioral sequential analysis (neuroethology), which clearly indicated an exacerbation of clusters of specific behaviors such as exploration and grooming (self-cleaning), as well as significant decrease in the expression of brainstem and limbic seizures in response to TOL. Thus, these data demonstrate that TOL, a strong olfactory stimulus, has anticonvulsant properties, detected by the decrease of acute and AK seizures in WARs.

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".

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

The superior colliculus (SC), substantia nigra pars reticulata (SNPr), and striatum have been characterized as important structures involved in the modulation of seizure activity. In the current study, bicuculline (GABA(A) antagonist) and muscimol (GABA(A) agonist) were microinjected into the deep layers of either the anterior SC (aSC) or posterior SC (pSC) of genetically developed Wistar audiogenic rats. Behavior and EEG activity were studied simultaneously. Only muscimol microinjected into the pSC had behavioral and EEG anticonvulsant effects in Wistar audiogenic rats, eliciting EEG oscillation changes in both SNPr and pSC, primarily during tonic seizures. The SC of Wistar audiogenic rats thus comprises two functionally different subregions, pSC and aSC, defined by distinct behavioral and EEG features. The pSC has proconvulsant audiogenic seizure activity in Wistar audiogenic rats. Our data suggest that this phenomenon may be a consequence of the genetic selection of the Wistar audiogenic rat strain.

Role of the superior colliculus in the expression of acute and kindled audiogenic seizures in Wistar audiogenic rats

PURPOSE

The role of the superior colliculus (SC) in seizure expression is controversial and appears to be dependent upon the epilepsy model. This study shows the effect of disconnection between SC deep layers and adjacent tissues in the expression of acute and kindling seizures.

METHODS

Subcollicular transections, ablation of SC superficial and deep layers, and ablation of only the cerebral cortex were evaluated in the Wistar audiogenic rat (WAR) strain during acute and kindled audiogenic seizures. The audiogenic seizure kindling protocol started 4 days after surgeries, with two acoustic stimuli per day for 10 days. Acute audiogenic seizures were evaluated by a categorized seizure severity midbrain index (cSI) and kindled seizures by a severity limbic index (LI).

RESULTS

All subcollicular transections reaching the deep layers of the SC abolished audiogenic seizures or significantly decreased cSI. In the unlesioned kindled group, a reciprocal relationship between limbic and brainstem pattern of seizures was seen. The increased number of stimuli provoked an audiogenic kindling phenomenon. Ablation of the entire SC (ablation group) or of the cerebral cortex only (ctx-operated group) hampered the acquisition of limbic behaviors. There was no difference in cSI and LI between the ctx-operated and ablation groups, but there was a difference between ctx-operated and the unlesioned kindled group. There was also no difference in cSI between SC deep layer transection and ablation groups. Results of histologic analyses were similar for acute and kindled audiogenic seizure groups.

CONCLUSIONS

SC deep layers are involved in the expression of acute and kindled audiogenic seizure, and the cerebral cortex is essential for audiogenic kindling development.

EEG wavelet analyses of the striatum–substantia nigra pars reticulata–superior colliculus circuitry: Audiogenic seizures and anticonvulsant drug administration in Wistar audiogenic rats (War strain)

The importance of the substantia nigra pars reticulata (SNPr), striatum (STR) and superior colicullus (SC) in the blockade of experimental seizures is well known. But, in audiogenic seizures (brainstem tonic-clonic seizures), the anticonvulsant activity of these nuclei is still controversial. In the present study we aimed to analyze the STR-SNPr-CS circuitry in the audiogenic seizures of Wistar audiogenic rat (WAR). Behavioral and electroencephalographic (EEG) data were collected from WARs under no treatment or injection with systemic (phenobarbital) or intracerebral (intranigral) drugs (muscimol and phenobarbital). The main EEG frequency oscillation of STR, SNPr and SC seen before, during and after audiogenic seizures or during seizure protection, was determinated with wavelet spectral analyses. This method allows the association between behavior and EEG (video-EEG). Audiogenic seizures last only for half a minute in average, suggesting that the interruptions of seizures are probably not due to exhaustion. Systemic phenobarbital caused an acute and dose-dependent behavioral and EEGraphic anticonvulsant effect both in WARs. The dose of phenobarbital 15mg/kg protected animals almost completely, without side effects such as ataxia and sedation. In our data, this endogenous "natural" seizure blockade (or termination) seems to be similar to the "forced" seizure abolition, like the one caused by a systemic non-ataxic phenobarbital dose, because in both cases an intense decrease in the EEG main frequency oscillation can be seen in SNPr and SC. Intranigral phenobarbital or muscimol did not protect animals, and actually induced an increase in the main EEG frequency oscillation in SC. The main finding of the present study is that, in contrast to what is well believed about the incapacity to control audiogenic seizures by the striato-nigro-tectal circuitry, we collected here evidences that these nuclei are involved in the ability to block these seizures. However, the striato-nigro-tectal circuitry in WARs, a genetically developed strain, seems to have different functional mechanisms when compared with normal rats.

Neuroethological study of status epilepticus induced by systemic pilocarpine in Wistar audiogenic rats (WAR strain)

The administration of pilocarpine (PILO) is widely recognized as resulting in an experimental model of temporal lobe epilepsy; it is characterized by induction of status epilepticus (SE) and spontaneous recurrent seizures after a latent period. We provide in this work a neuroethological description of the SE induced by PILO. Behavioral evaluations were made in Wistar Audiogenic Rats (WARs) and Wistar resistant (R) animals. The experimental group (R) and WARs were pretreated with methyl scopolamine (1mg/kg ip) and injected with PILO (R animals, 340-380 mg/kg ip; WARs, 240-280 mg/kg ip). Among R animals, 36% developed SE, and among WARs, 53%. The control group (R animals and WARs) was injected only with methyl scopolamine plus saline. The ETHOMATIC method was used for evaluation of seizures. Sequences included in the analysis were chosen using (1) fixed observation windows and (2) behavioral triggers. The R group showed that the threshold for seizure is variable, so seizure onset and behavioral evolution were better described using behavioral triggers than fixed observation windows. The observation windows selected in similar duration intervals do not characterize the seizures. Sequential analysis in the WAR group showed high mortality after SE and greater susceptibility to PILO, compared with R animals. We conclude that with neuroethological tools it is possible to better map the sequence and evolution of SE induced by PILO compared to only using behavioral and arbitrary seizure severity scales. This sequence is faster and stronger in severity when WARs are compared with R animals. Although the WARs underwent an evolution of SE in some way equivalent to that of R animals, some rats presented tonic-clonic convulsions after PILO injection, very similar to acute audiogenic seizures, a brainstem-dependent model. The current data also point to the PILO-plus-WAR combination as a suitable protocol to study the genetic-epilepsy connection in experimental temporal lobe epilepsy.

Behavioral effects of bicuculline microinjection in the dorsal versus ventral hippocampal formation of rats, and control of seizures by nigral muscimol

This work aims to describe behavioral/electroencephalographic (EEG) seizures induced by bicuculline microinjection intracerebroventricularly (ICV) and in the dorsal hippocampal formation (DHF) or ventral hippocampal formation/amygdala area (VHF-AMY). We also test if GABAergic manipulation in the substantia nigra pars reticulata (SNPR) is capable of controlling those seizures. ICV injection of bicuculline induced a progressive sequence of convulsive responses, jumps and escapes from the open-field. This effect was partially reached by bicuculline injection in the DHF or VHF-AMY injection. Also: muscimol injection, but not GABA uptake blockers (nipecotic acid or a spider venom neurotoxin FrPbA2), into the SNPR abolished seizures induced by bicuculline injection in the DHF. It was concluded that different neuronal circuitry in the hippocampal formation are modulated, at least partially by nigral GABAergic mechanisms.

Role of the superior colliculus and the intercollicular nucleus in the brainstem seizure circuitry of the genetically epilepsy-prone rat

PURPOSE

The neuronal network responsible for the convulsive behavior associated with sound-induced seizures in genetically epilepsy-prone rats (GEPRs) is believed to include the inferior colliculus and other brainstem structures such as the deep layers of the superior colliculus (DLSC), periaqueductal gray, and pontine reticular formation. However, previous studies also suggested that the DLSC and the nearby intercollicular nucleus (ICN) are part of a midbrain anticonvulsant zone capable of suppressing tonic convulsions when activated with bicuculline. Our aim in this study was to investigate the role of the superior colliculus (SC) and the ICN in generalized tonic-clonic seizures (GTCSs).

METHODS

Bilateral lesions of the SC and the ICN as well as bicuculline infusions into the ICN were used to assess the role of this dorsal midbrain region in brainstem seizures induced by sound stimulation in GEPR-9s and GEPR-3s.

RESULTS

Lesions of the SC markedly attenuated audiogenic seizure (AGS) severity by abolishing all behavioral components except the wild running. Lesions of the ICN significantly reduced seizure severity in GEPR-9s, but were somewhat less effective than SC lesions. Bicuculline infusion into the deep layers of the SC and/or the ICN produced audiogenic-like seizures in GEPR-9s.

CONCLUSIONS

These findings support the hypothesis that the SC and ICN are important components of the brainstem seizure network, but suggest they are not necessary for the wild-running component of the seizure. The results further indicate that stimulation of the tectum facilitates GTCSs. Thus these findings suggest that the dorsal midbrain, when stimulated, is proconvulsant rather than anticonvulsant regarding brainstem seizures in GEPRs.

A critical review on the participation of inferior colliculus in acoustic-motor and acoustic-limbic networks involved in the expression of acute and kindled audiogenic seizures

The main goal of this article is to review the key role that the inferior colliculus plays in the expression of acoustic-motor and acoustic-limbic integration involved, respectively, in acute and chronic audiogenic seizures. In order to put this in context, we will review the behavioral characterization of acute and chronic audiogenic seizures, neuroanatomical substrates, neurochemistry, neuropharmacology, electrophysiology, as well as the cellular and molecular mechanisms involved in their expression. Secondly, we will also correlate our results, collected from audiogenic seizures susceptible rats, before and after the genetic selection of our own audiogenic susceptible strain, and from those sensitized by lesions or drug microinjections, with those pertinent from the international literature. In brief, genetic or sensitized animals express acute audiogenic seizures as a wild running behavior preceding the onset of tonic-clonic seizures. The latter can have several presentations including opistotonus and fore- and hindlimb tonic hyperextensions, followed by clonic convulsions of fore- and hindlimbs. Chronic (kindled) audiogenic seizures change this behavioral expression, with similar patterns such as those present in temporal lobe epileptic seizures, intermingled with the original audiogenic seizure pattern, which is known to be dependent on brainstem networks.

Neurons in the deep layers of superior colliculus are a requisite component of the neuronal network for seizures during ethanol withdrawal

Ethanol withdrawal (ETX) in ethanol-dependent animals and humans often results in seizure susceptibility. The deep layers of superior colliculus (DLSC) are proposed to be involved in the neuronal networks of several types of seizures. In rodents, ETX results in susceptibility to audiogenic seizures (AGS), and the DLSC are implicated as a critical component of the seizure network in a genetic form of AGS. Ethanol inhibits NMDA receptors, and the binding at these receptors is increased during ETX in certain brain regions. Therefore, the effect of focal microinjection into DLSC of a competitive NMDA receptor antagonist, DL-2-amino-7-phosphonoheptanoic acid (AP7) on ETX seizures was examined. AP7 (2 and 5 nmol/side) microinjected bilaterally into DLSC suppressed AGS, supporting a critical role of the DLSC in the AGS network during ETX. DLSC neuronal firing changes in behaving rats were subsequently examined, using chronically implanted microwire electrodes. Acoustically-evoked DLSC firing was significantly suppressed during ethanol intoxication and during ETX. However, DLSC neurons began firing tonically 1-2 s before the onset of the wild running behavior of AGS. Acoustically-evoked DLSC firing was suppressed during post-ictal depression with recovery beginning as the righting reflex returned. These data support a requisite role of the DLSC in AGS during ETX. These neuronal firing changes suggest an important role of DLSC neurons in generation of the wild running phase of AGS during ETX, which may be a general pathophysiological mechanism and a critical event in the initiation of wild running, since a similar pattern was seen previously in a genetic form of AGS.

Developmental and genetic audiogenic seizure models: behavior and biological substrates

Audiogenic seizure (AGS) models of developmental or genetic origin manifest characteristic indices of generalized seizures such as clonus or tonus in rodents. Studies of seizure-resistant strains in which AGS is induced by intense sound exposure during postnatal development provide models in which other neural abnormalities are not introduced along with AGS susceptibility. A critical feature of all AGS models is the reduction of neural activity in the auditory pathways from deafness during development. The initiation and propagation of AGS activity relies upon hyperexcitability in the auditory system, particularly the inferior colliculus (IC) where bilateral lesions abolish AGS. GABAergic and glutaminergic mechanisms play crucial roles in AGS, as in temporal lobe models of epilepsy, and participate in AGS modulatory and efferent systems including the superior colliculus, substantia nigra, basal ganglia and structures of the reticular formation. Catecholamine and indolamine systems also influence AGS severity. AGS models are useful for elucidating the underlying mechanisms for formation and expression of generalized epileptic behaviors, and evaluating the efficacy of modern treatment strategies such as anticonvulsant medication and neural grafting.

Neuroethological analysis of the effects of spider venom from Scaptocosa raptoria (Lycosidae: Araneae) microinjected in the lateral ventricle of Wistar rats

The inhibition of excitatory mechanisms by components of low molecular weight, isolated from spiders and solitary wasps, such as, the acyl-polyamines, has demonstrated, on the one hand, neuroprotection potential, and on the other hand, it is well known that some arthropod venom components have convulsant activity. While many sophisticated experiments are conducted to determine the mechanisms and effects of arthropod venoms, relatively little attention has been paid to the behavioral changes that occur in mammals after being administered given doses of them. The precise detection of these behavioral changes can be used as a sensitive indicator of central nervous system dysfunction. This study investigated the behavioral effects of crude venom from the spider Scaptocosa raptoria after intracerebroventricular injection in male Wistar rats. The venom induced behavioral changes quantified using a neuroethological method, which allows the evaluation of the following parameters: frequency, duration, and strength of statistical association (chi-square) between pairs of behaviors. The rats exhibited a period of freezing, which was always followed by procursive-type seizures (running, gyrating, atonic falling, and jumping).

Seizures induced by penicillin microinjections in the mesencephalic tegmentum

The location and extension of a convulsive area in the brain stem in cats was determined through penicillin microinjections (0.5-1.0 microl) of a concentrated sodium penicillin solution (500 IU/microl), stereotactically oriented to multiple structures, in fully awake animals, partially restrained through a rod fixation system that avoided pain, allowed the observation of clinical seizures and simultaneous recording of EEG, EMG and multiple unit activity (MUA) from the injected site and the motor cortex (Cx). Clinical and EEG seizure patterns in relation to the injected sites and penicillin doses were studied in another group of animals using doses from 12.5 IU/0.1 microl to 125 IU/1.0 microl. The time relationship between muscular clonus, EEG spikes and MUA at the injected site and Cx were analyzed. The only area in which penicillin induced seizures was the mesencephalic tegmentum (MT). The amount of penicillin but not the stereotactic coordinates determined the seizure type. MT EEG and MUA paroxysms anticipated clinical seizure and Cx EEG spikes. When Cx EEG appeared, they were accompanied by an increase in MUA beginning in the Cx and EMG, followed by significant increase in MT MUA. The sequence of events suggest that MT seizure activity propagates via alternative pathways not involving direct reticulospinal or pyramidal tract pathways.

Morphological deficits in noradrenergic neurons in GEPR-9s stem from abnormalities in both the locus coeruleus and its target tissues

The epileptic condition of the genetically epilepsy-prone rat (GEPR) appears to be caused partially by deficiencies in the locus coeruleus (LC) innervation of the superior colliculus (SC). Previous studies provide quantitative documentation of noradrenergic morphological deficits in the moderately epileptic GEPR-3. The present findings extend these studies by applying cell culture methodology to assessments of the severely epileptic GEPR-9. Our data show that total neurite length, the number of neurite branch points per cell, the cross-sectional area of cell bodies, and the cell perimeter are deficient in noradrenergic neurons in LC + SC cocultures derived exclusively from GEPR-9s compared to analogous cocultures obtained solely from nonepileptic control rats. Partial restoration of LC neuron morphology toward normal occurs when the GEPR-9 SC component of the coculture is replaced with nonepileptic control SC. Finally, when the GEPR-9 SC is cocultured with the control LC, a partial morphological deficit occurs in the otherwise normal noradrenergic neurons. However, the magnitude of this deficit is less than that observed in noradrenergic neurons of the GEPR-9 LC cocultured with the control SC. These data support the hypothesis that the developmental deficiencies of noradrenergic neurons of the GEPR-9 are derived from two sources, the LC and its target tissue, in this case, the SC. Also, intrinsic abnormalities of the LC appear to make a more pronounced contribution to the noradrenergic deficits than do those which reside in the SC.

Prepulse inhibition following lesions of the inferior colliculus: prepulse intensity functions

The magnitude of the acoustic startle response can be reduced by a relatively weak sound presented immediately before the startle-eliciting sound; this phenomenon has been termed prepulse inhibition (PPI). Previous studies reported that PPI was present in the decerebrate rat, indicating that the primary neural pathways mediating PPI are located in the brainstem. The present study investigated the effects of focal excitotoxic lesions of the inferior colliculus (IC) on acoustic PPI in rats. In the first part, startle magnitudes were measured in six normal rats as the interstimulus interval (ISI) between the prepulse and startle-eliciting sounds varied between 10 and 100 ms. Prepulse-inhibited startle changed in an ISI-dependent manner with the most effective ISI at 50 ms. In the second part, 21 rats were assigned to three groups: normal unoperated, cortical lesion, and IC lesion. With the ISI fixed at 50 ms, as the prepulse sound level increased from 29 to 49 dB SPL, startle responses decreased quickly in both normal and cortical lesion rats. However, rats with unilateral IC lesions made with ibotenic acid had significantly lower PPI but did not display any increase in startle magnitude. These data suggest that the IC is an important structure in the neural circuit mediating acoustic PPI.

Magnesium deficiency-dependent audiogenic seizures (MDDASs) in adult mice: a nutritional model for discriminatory screening of anticonvulsant drugs and original assessment of neuroprotection properties

A great many animal models for audiogenic seizures have been described. The extent to which these models may provide insight into neuroscience fields such as abnormal locomotor behavior (wild running), seizures and anticonvulsants, and neuroinsults and neuroprotectors is examined here by our study of magnesium deficiency-dependent audiogenic seizures (MDDASs) in adult mice. MDDASs were induced in all of the eight tested adult murine strains and are presented as a sequence of four successive components (latency, wild running, convulsion, and recovery phase periods). Compared with several classic seizure tests, the nutritional MDDAS model responded to low doses of prototype antiepileptic drugs (AEDs), including phenytoin (PHT), carbamazepine (CBZ), phenobarbital (PB), valproic acid (VPA), ethosuximide (ESM), and diazepam (DZP). Modulation by AEDs of the four components of MDDAS indicated that this seizure test was discriminatory, distinguishing between phenytoinergic (PHT, CBZ), GABAergic (PB, VPA, DZP), and ethosuximide (ESM) compounds. Suitability of the MDDAS test for evaluation of neuroprotective compounds was also examined: it showed partial (melatonin) and complete (WEB2170, an anti-PAF agent) reduction of recovery phase by non-anticonvulsant doses of test compounds. These neuroprotective responses were compared with neuroprotective potentials determined in a model of neonatal cerebral injury induced by focal injection of ibotenate (a glutamate analog). WEB2170 and melatonin reduced the size of lesions in white matter, but only WEB2170 protected cortical plate against ibotenate-induced lesions. In addition to the original neuroprotective behavior of WEB2170, studies on the neuroprotectors also supported GABAergic anticonvulsant activity of melatonin in the MDDAS test.

Neuroethological and morphological (Neo-Timm staining) correlates of limbic recruitment during the development of audiogenic kindling in seizure susceptible Wistar rats

Acute audiogenic seizures are a model of generalized tonic-clonic seizures, induced by high intensity acoustic stimulation in genetically susceptible rodents. The neural substrate are sensory motor brainstem nuclei. Recruitment of forebrain structures takes places upon repetition of acoustically evoked seizures. The term audiogenic kindling means forebrain kindling evoked by repeated brainstem seizures and has been described in several strains of genetically epilepsy-prone rats. Thus, the present work was conducted in order to test the hypothesis that audiogenic kindling recruits the forebrain, which may be behaviorally evaluated and associated with morphological changes as well. The behavioral sequences observed during the development of audiogenic kindling were assessed by neuroethological methods (cluster analysis), with the ETHOMATIC program. Seizure severity indexes (brainstem and limbic seizures) and latencies of wild running and tonic-clonic seizures were measured to quantify seizure evolution. Densitometric analysis of Neo-Timm staining was used for assessing morphological changes associated with audiogenic kindling. In group I, II resistant (R) and 16 susceptible (S) animals were stimulated (120 dB) 21 times, and allowed a 10 day recovery period prior to retesting. In group II, 22 R and 20 S were stimulated 60 times, and allowed a 2 month recovery period prior to retesting. Repetition of the acoustic stimulation in group I and group II susceptible animals led to a progressive and statistically significant attenuation of the behaviors associated with brainstem seizures and a concomitant increased expression of the behaviors associated with limbic seizures. After either a 10 day (group I) or 2 month (group II) recovery period, acoustic stimulation preferentially evoked brainstem-associated behaviors and seizures rather than limbic ones in the audiogenic susceptible animals, although in some animals overlapped brainstem and limbic seizures were detected. Latencies for the wild running and tonic seizures after acoustic stimulation significantly increased during audiogenic kindling for both group I and group II susceptible animals. The quantitative ethological evaluation in both group I and group II, illustrated by flowcharts, showed the evolution of the kindling installation by the presence of limbic seizure clusters, competing in time with the original tonic-clonic clusters. Expression of limbic seizures by group I animals, after acoustic stimulation, was not associated with changes in the mossy fiber Neo-Timm staining pattern of these animals. In group II however, Neo-Timm staining revealed mossy fiber sprouting in the ventral hippocampus (but not in the dorsal), and a significant change in the optical density of amygdaloid nuclei and perirhinal cortex in susceptible animals as compared to resistant ones. In conclusion, audiogenic kindling effectively recruits forebrain structures, responsible for the appearance of limbic seizures. It is possible that the paradigm used in group I was subthreshold for the development of clear-cut synaptic reorganization in the hippocampal mossy fiber system, since the behavioral patterns reverted ten days after the last seizure induction. In group II, however, an increased number of evoked seizures and a more prolonged time after the last chronic seizure showed structural re-arrangements in amygdala, perirhinal cortex and hippocampus, associated with permanence in terms of behavioral data (lack of regression of limbic seizures to control values).

The role of the inferior colliculus in a genetic model of audiogenic seizures

Previous studies have shown the functional importance of the inferior colliculus (IC) for the propagation and initiation of audiogenic seizures in several models of epilepsy in rats. A review of the cell types and cytoarchitecture of the IC, including its three major subdivisions, is presented. Significant increases in GABA levels and the number of GABAergic neurons are found in the central nucleus of the IC (ICCN) of genetically epilepsy-prone rats (GEPR-9s) as compared to Sprague-Dawley rats that do not display audiogenic seizures. Two independent anatomical methods were used to determine the number of GABAergic neurons, immunocytochemistry and in situ hybridization. In both types of preparation, the labeled cells in the ICCN appeared to be of different sizes but the number of small cells with diameters less than 15 microns showed the greatest increase. Nissl-stained sections showed that the total number of neurons in the ICCN was increased in GEPR-9s and indicated that the increase in GABAergic neurons was not due to a change in the phenotype of collicular neurons from non-GABAergic to GABAergic. The number of small neurons in Nissl-stained sections of the ICCN was shown to correlate with seizure severity in the offspring of crosses made between Sprague-Dawley rats and GEPR-9s. Furthermore, the GEPR-3s that display moderate seizures showed a significant increase in the number of small neurons in the ICCN, and the magnitude of this increase was predicted from this correlation. Finally, the use of knife cuts through the midbrain indicated that the ICCN sends an important projection to the external nucleus and that this projection plays a vital role in the propagation of seizure activity from the site of seizure initiation in the ICCN. It remains to be resolved how the increase in small GABAergic neurons in the ICCN is responsible for the known pharmacological defects observed at GABAergic synapses.

NMDA-dependent audiogenic seizures are differentially regulated by inferior colliculus subnuclei

Wistar rats were classified as susceptible (S) and resistant (R) to audiogenic seizures (AS) by evaluation of their response to high intensity sound stimulation (110.3 dB). R rats usually do not respond with any convulsive behavior to sound stimulation, whereas S animals develop a complex wild running sequence plus tonic-clonic seizure patterns after sound stimulation. Thus, R rats were injected with phosphate buffer (PB; 0.2 microliter) or N-methyl-D-aspartate (NMDA) in three different doses (2.0 micrograms, 2.5 micrograms and 3.0 micrograms/0.2 microliter) into central ventral or cortical dorsal inferior colliculus (IC) nuclei. Dose-response curves were evaluated by means of an ethological method in which behavioral sequences typical of S and R animals were quantitated. Animals displayed more severe spontaneous audiogenic-like seizures with the dose of 2.5 micrograms/0.2 microliter NMDA, which were potentiated by the acoustic stimulus. Significant differences were apparent between central and cortical nuclei and more severe seizures were observed in IC cortical microinjected animals. These audiogenic seizures were blocked with microinjections of 2-amino-7-phosphono-heptanoate (AP7) applied just before 2.5 micrograms NMDA microinjections into central or cortical nuclei. In S rats, AP7 totally blocked AS when microinjected into the central IC and partially, but significantly, blocked AS when applied into the cortical IC nucleus. In the last case, wild running was still present in 100% of the animals after AP7 treatment. These data may suggest an NMDA-dependent differential participation of IC subnuclei in the development of AS.

A microdialysis study of amino acid concentrations in the extracellular fluid of the substantia nigra of freely behaving GEPR-9s: relationship to seizure predisposition

Substantia nigra (SN) is known to play an important role in seizure generalization. Both excitatory and inhibitory neurotransmitters can modulate this role of SN. Previous studies have shown that GABA as well as aspartate and glutamate participate in seizure regulation through this site. Evidence for such a role comes from studies on the genetically epilepsy-prone rat (GEPR) and other seizure models. In the GEPR, bilateral microinjections of NMDA receptor antagonists in SN block or reduce seizure severity. In order to further evaluate which neurotransmitters are specifically involved at the SN level of seizure regulation in the GEPR, we undertook a microdialysis study of K+ stimulated release of amino acids in the SN of GEPR-9s- and non-epileptic controls. A 1 mm loop-type microdialysis probe was inserted through pre-implanted guides into the SN of awake and freely moving rats (seven GEPR-9s and four non-epileptic controls), and used to perfuse a 100 mM K+ (high K+) solution for 2 h. Four 30 microliters samples were collected prior to high K+ stimulation (basal release), during high K+ perfusion, and after high K+ infusion. After precolumn derivatization with phenylisothiocyanate, levels of aspartic (ASP) and glutamic (GLU) acids, glycine (GLY), taurine (TAU) and GABA were measured by reversed phase high performance liquid chromatography. Two hours after the initiation of high K+ infusion, the increases relative to basal were, for non-epileptic controls, 35%, 74%, 68%, 847% and 283% respectively for ASP, GLU, GLY, TAU and GABA. Corresponding increases for GEPR-9s were 14%, 10%, 41%, 505% and 123% respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Midbrain substrates of audiogenic seizures in rats

Audiogenic seizures (AS) are a rodent model of generalized tonic-clonic seizures, induced in susceptible (S) animals by high intensity (110 dB) acoustic stimulation. Resistant (R) animals do not respond to the sound with any seizure-related behavior, but they display facial automatisms and grooming clusters. Genetic selection and neuroethology are the basic tools used in our laboratory to perform behavioral analysis of AS S and R animals. Based upon selective lesion and microinjection (GABA, clobazam, NMDA) studies of substantia nigra (SN), inferior colliculus (IC), superior colliculus (SC), and on specific knife cuts at midcollicular levels, we have suggested differential roles for these substrates in the origin and spreading of AS. The IC central nucleus is suggested to be the most critical area involved in the afferent pathway whose activation is necessary for AS origin. IC cortical nuclei seem to be the most important structures involved in the transduction of sensory to motor activity. SC, SN and other reticular subnuclei are suggested to be modulators or components of the efferent pathway. Although the midbrain is considered to be the only network necessary for acute AS origin, both emotion-linked acoustic memories and plastic changes linked to audiogenic kindling involve midbrain-forebrain connections. This paper reviews the behavioral manifestations of acute and chronic AS, our contribution to the knowledge of some AS neurobiological midbrain substrates and the suggested implications of midbrain-forebrain interactions typical of AS kindling.