Differential audiogenic seizure sensitization by selective unilateral substantia nigra lesions in resistant Wistar rats

Optogenetic stimulation of the superior colliculus suppresses genetic absence seizures

While anti-seizure medications are effective for many patients, nearly one-third of individuals have seizures that are refractory to pharmacotherapy. Prior studies using evoked preclinical seizure models have shown that pharmacological activation or excitatory optogenetic stimulation of the deep and intermediate layers of the superior colliculus (DLSC) display multi-potent anti-seizure effects. Here we monitored and modulated DLSC activity to suppress spontaneous seizures in the WAG/Rij genetic model of absence epilepsy. Female and male WAG/Rij adult rats were employed as study subjects. For electrophysiology studies, we recorded single unit activity from microwire arrays placed within the DLSC. For optogenetic experiments, animals were injected with virus coding for channelrhodopsin-2 or a control vector, and we compared the efficacy of continuous neuromodulation to that of closed-loop neuromodulation paradigms. For each, we compared three stimulation frequencies on a within-subject basis (5, 20, 100 Hz). For closed-loop stimulation, we detected seizures in real time based on the EEG power within the characteristic frequency band of spike-and-wave discharges (SWDs). We quantified the number and duration of each SWD during each 2 h-observation period. Following completion of the experiment, virus expression and fibre-optic placement was confirmed. We found that single-unit activity within the DLSC decreased seconds prior to SWD onset and increased during and after seizures. Nearly 40% of neurons displayed suppression of firing in response to the start of SWDs. Continuous optogenetic stimulation of the DLSC (at each of the three frequencies) resulted in a significant reduction of SWDs in males and was without effect in females. In contrast, closed-loop neuromodulation was effective in both females and males at all three frequencies. These data demonstrate that activity within the DLSC is suppressed prior to SWD onset, increases at SWD onset, and that excitatory optogenetic stimulation of the DLSC exerts anti-seizure effects against absence seizures. The striking difference between open- and closed-loop neuromodulation approaches underscores the importance of the stimulation paradigm in determining therapeutic effects.

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.

Descending projections from the substantia nigra pars reticulata differentially control seizures

Three decades of studies have shown that inhibition of the substantia nigra pars reticulata (SNpr) attenuates seizures, yet the circuits mediating this effect remain obscure. SNpr projects to the deep and intermediate layers of the superior colliculus (DLSC) and the pedunculopontine nucleus (PPN), but the contributions of these projections are unknown. To address this gap, we optogenetically silenced cell bodies within SNpr, nigrotectal terminals within DLSC, and nigrotegmental terminals within PPN. Inhibition of cell bodies in SNpr suppressed generalized seizures evoked by pentylenetetrazole (PTZ), partial seizures evoked from the forebrain, absence seizures evoked by gamma-butyrolactone (GBL), and audiogenic seizures in genetically epilepsy-prone rats. Strikingly, these effects were fully recapitulated by silencing nigrotectal projections. By contrast, silencing nigrotegmental terminals reduced only absence seizures and exacerbated seizures evoked by PTZ. These data underscore the broad-spectrum anticonvulsant efficacy of this circuit, and demonstrate that specific efferent projection pathways differentially control different seizure types.

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.

Wistar audiogenic rats display abnormal behavioral traits associated with artificial selection for seizure susceptibility

Accumulating evidence from different animal models has contributed to the understanding of the bidirectional comorbidity associations between the epileptic condition and behavioral abnormalities. A strain of animals inbred to enhance seizure predisposition to high-intensity sound stimulation, the Wistar audiogenic rat (WAR), underwent several behavioral tests: forced swim test (FST), open-field test (OFT), sucrose preference test (SPT), elevated plus maze (EPM), social preference (SP), marble burying test (MBT), inhibitory avoidance (IAT), and two-way active avoidance (TWAA). The choice of tests aimed to investigate the correlation between underlying circuits believed to be participating in both WAR's innate susceptibility to sound-triggered seizures and the neurobiological substrates associated with test performance. Comparing WAR with its Wistar counterpart (i.e., resistant to audiogenic seizures) showed that WARs present behavioral despair traits (e.g., increased FST immobility) but no evidence of anhedonic behavior (e.g., increased sucrose consumption in SPT) or social impairment (e.g., no difference regarding juvenile exploration in SP). In addition, tests suggested that WARs are unable to properly evaluate degrees of aversiveness (e.g., performance on OFT, EPM, MBT, IAT, and TWAA). The particularities of the WAR model opens new venues to further untangle the neurobiology underlying the co-morbidity of behavioral disorders and epilepsy. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

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.

Study of spontaneous recurrent seizures and morphological alterations after status epilepticus induced by intrahippocampal injection of pilocarpine

Epileptic seizures are clinical manifestations of neuronal discharges characterized by hyperexcitability and/or hypersynchrony in the cortex and other subcortical regions. The pilocarpine (PILO) model of epilepsy mimics temporal lobe epilepsy (TLE) in humans. In the present study, we used a more selective approach: microinjection of PILO into the hilus of the dentate gyrus (H-PILO). Our main goal was to evaluate the behavioral and morphological alterations present in this model of TLE. Seventy-six percent of all animals receiving H-PILO injections had continuous seizures called status epilepticus (SE). A typical pattern of evolution of limbic seizures during the SE with a latency of 29.3 ± 16.3 minutes was observed using an analysis of behavioral sequences. During the subsequent 30 days, 71% of all animals exhibited spontaneous recurrent seizures (SRSs) during a daily 8-hour videotaping session. These SRSs had a very conspicuous and characteristic pattern detected by behavioral sequences or neuroethiological analysis. Only the animals that had SE showed positive Neo-Timm staining in the inner molecular layer of the dentate gyrus (sprouting) and reduced cell density in Ammon's horn pyramidal cell subfield CA1. However, no correlation between the intensity of sprouting and the mean number and total number of SRSs was found. Additionally, using Fluoro-Jade staining, we observed neurodegeneration in the hilus and pyramidal cell subfields CA3 and CA1 24 hours after SE. These data indicate that H-PILO is a reliable, selective, efficient, low-mortality model that mimics the acute and chronic behavioral and morphological aspects of TLE.

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.

Is dystonic posturing during temporal lobe epileptic seizures the expression of an endogenous anticonvulsant system?

In temporal lobe epilepsy (TLE) seizures, tonic or clonic motor behaviors (TCB) are commonly associated with automatisms, versions, and vocalizations, and frequently occur during secondary generalization. Dystonias are a common finding and appear to be associated with automatisms and head deviation, but have never been directly linked to generalized tonic or clonic behaviors. The objective of the present study was to assess whether dystonias and TCB are coupled in the same seizure or are associated in an antagonistic and exclusive pattern. Ninety-one seizures in 55 patients with TLE due to mesial temporal sclerosis were analyzed. Only patients with postsurgical seizure outcome of Engel class I or II were included. Presence or absence of dystonia and secondary generalization was recorded. Occurrence of dystonia and occurrence of bilateral tonic or clonic behaviors were negatively correlated. Dystonia and TCB may be implicated in exclusive, non-coincidental, or even antagonistic effects or phenomena in TLE seizures. A neural network related to the expression of one behavioral response (e.g., basal ganglia activation and dystonia) might theoretically "displace" brain activation or disrupt the synchronism of another network implicated in pathological circuit reverberation and seizure expression. The involvement of basal ganglia in the blockade of convulsive seizures has long been observed in animal models. The question is: Do dystonia and underlying basal ganglia activation represent an attempt of the brain to block imminent secondary generalization?

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.

Neocortical injuries at different developmental stages determine different susceptibility to seizures induced in adulthood

Gliosis, axonal sprouting and remodelling of nerve connections in the injured brain have been regarded as epileptogenic processes dependent on the age when the injury was inflicted. The present study examines whether brains injured at different developmental stages may acquire different susceptibility to experimental status epilepticus induced in adulthood. In 6- and 30-day-old Wistar rats (P6s and P30s, respectively), a mechanical injury was performed in the left cerebral hemisphere. On postnatal day 60, all the animals and controls received single injections of kainic acid to evoke status epilepticus. During a 6-h period following the injection, the animals were observed continuously and motor symptoms of seizure activity were recorded and rated. P6s showed significantly lower intensity of kainic acid-induced epileptic symptoms and significantly longer survival than controls or P30s. In P30s, no significant change was detected. The data provide evidence that the developmental stage when the brain is injured determines epileptogenecity of the lesion. However, a considerable discrepancy between these data and those obtained previously following pilocarpine administration in the same experimental models of brain injury shows that each of the two models of epilepsy may display different aspects of the same age-dependent process triggered by the brain injury.

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.

Effect of lactation on the expression of audiogenic seizures: association with plasma prolactin profiles

Female Wistar rats and Wistar audiogenic rats (WARs) were used to investigate the potential roles of prolactin (PRL) and progesterone in the modulation of seizure expression. Animals were screened for seizure severity in both groups. All WARs at least displayed tonic-clonic convulsions followed by clonic spasms (TC) whereas none of the Wistar rats displayed seizures (Resistant). After seizures the plasma level of PRL in nulliparous female WARs increased about 8-fold compared to their basal levels and to the levels of Resistant animals. This value was still significantly higher than basal levels 15 min later. Lactation produced a decrease in the TC proportion in seizures in WARs both with and without pups. Two sub-populations of animals could be characterized: one that had TC suppressed (low seizure severity; LSS) and one that did not (high seizure severity; HSS). In animals of the LSS subgroup, either with or without pups, seizure severity decreased gradually and lowest values were seen on the 30th day after delivery. The temporal profile of plasma PRL during a 90-min period of suckling without sound stimulation showed significantly higher levels for LSS, the HSS levels being similar to those of the Resistant group. A progressive decrease in the group means for progesterone plasma concentration between the 9th and 29th days of lactation was detected in Resistant rats (P<0.05) but not in WARs. No significant differences between groups were revealed by comparison of the overall means. Taken together these data confirm the presence of a clear-cut post-ictal PRL peak after TC with a decrease in seizure severity in female WARs with and without pups. An eventual long-term role of PRL in modulating seizure activity might be related to the multifactorial physiological conditions of both pregnancy and lactation.

Long-term changes in susceptibility to pilocarpine-induced status epilepticus following neocortical injuries in the rat at different developmental stages

In the brain, injury-induced gliosis and axonal sprouting have been regarded as age-dependent repairing processes with, unfortunately, epileptogenic effects. The present study examines whether brains injured at different developmental stages become more or less susceptible to experimentally-induced status epilepticus. In 6- and 30-day-old Wistar rats (P6s and P30s, respectively), a mechanical injury was performed in the cortex of the left cerebral hemisphere. On postnatal day 60, all the animals and naïve controls received single intraperitoneally pilocarpine injections to evoke status epilepticus. During a 6-h period following the injection, the animals were observed continuously and motor manifestations of seizure activity were recorded and rated. Seven days after pilocarpine injection, the animals were perfused and their body and brain weights recorded. When compared to controls, P6s showed neither significant variations in their epileptic behavior nor in brain and body weights. In relation to controls and to P6s, P30s presented an extremely high mortality, a significant loss of body weight and much longer-lasting seizures of much higher intensity. The data provide evidence that the long-term variations in susceptibility to experimentally-induced status epilepticus are determined by differences in the brain response to injury at different stages of postnatal development.

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.

Rapid lesioning of large numbers of identified vertebrate neurons: applications in zebrafish

Establishing a causal role between the activity of specific individual nerve cells and the behaviors they produce (or the neural computations they execute) is made difficult in vertebrate animals because of the large numbers of neurons involved. Traditional techniques for establishing causal roles, such as tract cutting and electrolytic lesions, are limited because they produce damage that affects a variety of different cell types, invariably intermingled, and often of uncertain identity. We propose here an alternative lesioning technique in which large numbers of neurons are lesioned, but the lesioned neurons are specifically identified by fluorescent labeling. We use the locomotor control system of the larval zebrafish to illustrate this approach. In this example, the technique involves injection of fluorescent dextrans into far-rostral spinal cord to label descending nerve fibers. Such injections appear to interrupt the descending nerve fibers, and therefore their accompanying locomotor control signals. This protocol is shown to produce significant behavioral deficits. Because the CNS of the larval zebrafish is transparent, the entire population of lesioned cells can be imaged in vivo and reconstructed using confocal microscopy. This large-scale lesioning technique is important, even in this relatively 'simple' vertebrate animal, because the ablation of smaller numbers of neurons, using more precise laser-ablation techniques, often fails to produce observable behavioral deficits. While this technique is most readily applied in simpler and transparent vertebrate animals, the approach is general in nature and might, in principle, be applied to any vertebrate nerve tract.

Behavioral effects of intra-nigral microinjections of manganese chloride: interaction with nitric oxide

1. Microinjection of manganese chloride (MnCl2) into the rat substantia nigra pars compacta (SNc) induces a neurodegenerative process manifested by apomorphine-induced rotational behavior. Manganese intoxication produces a parkinsonism-like phenotype in humans. 2. In addition to motor control the substantia nigra has also been proposed to be related to epilepsy and emotional behavior. 3. Although nitric oxide (NO) participation in neurodegenerative processes is still questioned, neurons stained for NAPDH-diaphorase, a marker of NO-producing cells, are spared in several experimental neuronal lesions. Additionally, NO has also been suggested to participate in motor control. 4. The objective of this study was to analyze the effects of MnCl2-induced nigral degeneration in audiogenic seizure susceptibility, anxiety and motor activity. We also analyzed if NO synthesis inhibition (N(G)-nitro-L-arginine 25 mg/Kg twice a day for 4 days) modifies MnCl2-induced neurodegenerative process. 5. MnCl2 (50 microg) microinjection into the SNc caused a statistical significant higher number of apomorphine (0.75 mg/kg s.c.)-induced rotations. No sensitization to audiogenic seizure was found but the lesion induced an increase of open arm exploration in the elevated plus maze, suggesting an anxiolytic effect. 6. The MnCl2-nigral lesion was accompanied by an increased number of NADPH-d positive neurons in the ipsilateral SNc and striatum (both sides). NO synthesis inhibition potentiated the MnCl2-nigral lesion and reversed the NADPH-d cell number increase. 7. The present results show that MnCl2-nigral lesion can influence emotional behavior and suggest that NO may modify the progression of manganese-induced degenerative process.

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.

Current controversies and future directions in basal ganglia research. Integrating basic neuroscience and clinical investigation

This article discusses current controversies and future directions in basal ganglia research, detailing behavioral aspects, anatomic models, neurochemistry, pharmacology, and diagnostic methods as well as surgical techniques. A neuroethologic perspective is highlighted. Furthermore, the relevant literature pertaining to contemporary molecular approaches such as brain microinjections of embryonic or genetically modified cells, for therapeutic purposes and the use of transgenic and knockout animals.

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).