A microdialysis study of striatal dopamine release in the circling rat, a genetic animal model with spontaneous lateralized rotational behavior

The Balance in the Head: How Developmental Factors Explain Relationships Between Brain Asymmetries and Mental Diseases

Cerebral lateralisation is a core organising principle of the brain that is characterised by a complex pattern of hemispheric specialisations and interhemispheric interactions. In various mental disorders, functional and/or structural hemispheric asymmetries are changed compared to healthy controls, and these alterations may contribute to the primary symptoms and cognitive impairments of a specific disorder. Since multiple genetic and epigenetic factors influence both the pathogenesis of mental illness and the development of brain asymmetries, it is likely that the neural developmental pathways overlap or are even causally intertwined, although the timing, magnitude, and direction of interactions may vary depending on the specific disorder. However, the underlying developmental steps and neuronal mechanisms are still unclear. In this review article, we briefly summarise what we know about structural, functional, and developmental relationships and outline hypothetical connections, which could be investigated in appropriate animal models. Altered cerebral asymmetries may causally contribute to the development of the structural and/or functional features of a disorder, as neural mechanisms that trigger neuropathogenesis are embedded in the asymmetrical organisation of the developing brain. Therefore, the occurrence and severity of impairments in neural processing and cognition probably cannot be understood independently of the development of the lateralised organisation of intra- and interhemispheric neuronal networks. Conversely, impaired cellular processes can also hinder favourable asymmetry development and lead to cognitive deficits in particular.

Benefits of a ketogenic diet on repetitive motor behavior in mice

Repetitive motor behaviors are repetitive and invariant movements with no apparent function, and are common in several neurological and neurodevelopmental disorders, including autism spectrum disorders (ASD). However, the neuropathology associated with the expression of these abnormal stereotypic movements is not well understood, and effective treatments are lacking. The ketogenic diet (KD) has been used for almost a century to treat intractable epilepsy and, more recently, disorders associated with inflexibility of behavioral routines. Here, we show a novel application for KD to reduce an abnormal repetitive circling behavior in a rodent model. We then explore potential mediation through the striatum, as dysregulation of cortico-basal ganglia circuitry has previously been implicated in repetitive motor behavior. In Experiments 1 and 2, adult FVB mice were assessed for levels of repetitive circling across a 3-week baseline period. Mice were then switched to KD and repetitive circling was assessed for an additional 3 weeks. In Experiment 1, time on KD was associated with reduced repetitive behavior. In Experiment 2, we replicated these benefits of KD and assessed dendritic spine density in the striatum as one potential mechanism for reducing repetitive behavior, which yielded no differences. In Experiment 3, adult female circling mice were given a single administration of a dopamine D2 receptor antagonist (L-741,646) that was associated with reduced repetitive behavior over time. Future research will explore the relationship between KD and dopamine within basal ganglia nuclei that may be influencing the benefits of KD on repetitive behavior.

Paradoxical Enhancement of Spatial Learning Induced by Right Hippocampal Lesion in Rats

The left–right hemispheric differences in some brain functions are well known in humans. Among them, savant syndrome has unique features, such as exceptional abilities in vision, memory, computation, and music, despite brain abnormalities. In cases of acquired savant and transient savant, brain damage or inhibition is often seen in the left hemisphere, suggesting a link between left hemispheric dysfunction and these talents. On the other hand, some functional left–right differences have been reported in rodent brains, and therefore, unilateral damage in rodents may also result in savant-like enhancements. In the present study, we examined the effects of hippocampal damage on spatial learning in rats with left, right, or bilateral hippocampal lesion. The results showed that learning performance was impaired in the bilateral lesion group, and there was no significant difference in the left lesion group, while performance was enhanced in the right lesion group. These results suggest that damage to the right hippocampus in rats may lead to savant-like enhancement in learning and memory. The construction of the savant model through these results will contribute to the neuroscientific elucidation of the paradoxical phenomenon observed in savants, that some abilities are enhanced despite their brain dysfunction.

Maternal immune activation leads to atypical turning asymmetry and reduced DRD2 mRNA expression in a rat model of schizophrenia

Atypical asymmetries have been reported in individuals diagnosed with schizophrenia, linking higher symptom severity to weaker lateralization. Furthermore, both lateralization and schizophrenia are influenced by the dopaminergic system. However, whether a direct link between the etiology of schizophrenia and atypical asymmetries exists is yet to be investigated. In this study, we examined whether maternal immune activation (MIA), a developmental animal model for schizophrenia and known to alter the dopaminergic system, induces atypical lateralization in adolescent and adult offspring. As the dopaminergic system is a key player in both, we analyzed neuronal dopamine D2 receptor (DRD2) mRNA expression. MIA was induced by injecting pregnant rats with 10 mg/kg polyinosinic:polycytidylic (PolyI:C) at gestational day 15. Controls were injected with 0.9 % NaCl. Offspring were tested at adolescence or early adulthood for asymmetry of turning behavior in the open field test. The total number of left and right turns per animal was assessed using DeepLabCut. Strength and preferred side of asymmetry were analyzed by calculating lateralization quotients. Additionally, DRD2 mRNA expression in the prefrontal cortex of offspring at both ages was analyzed using real-time PCR. MIA was associated with a rightward turning behavior in adolescents. In adults, MIA was associated with an absence of turning bias, indicating reduced asymmetry after MIA. The analysis of DRD2 mRNA expression revealed significantly lower mRNA levels after MIA compared to controls in adolescent, but not adult animals. Our results reinforce the association between atypical asymmetries, reduced DRD2 mRNA expression, and schizophrenia. However, more preclinical research is needed.

Paw preferences in mice and rats: Meta-analysis

Mice and rats are among the most common animal model species in both basic and clinical neuroscience. Despite their ubiquity as model species, many clinically relevant brain-behaviour relationships in rodents are not well understood. In particular, data on hemispheric asymmetries, an important organizational principle in the vertebrate brain, are conflicting as existing studies are often statistically underpowered due to small sample sizes. Paw preference is one of the most frequently investigated forms of hemispheric asymmetries on the behavioural level. Here, we used meta-analysis to statistically integrate findings on paw preferences in rats and mice. For both species, results indicate significant hemispheric asymmetries on the individual level. In mice, 81 % of animals showed a preference for either the left or the right paw, while 84 % of rats showed this preference. However, contrary to what has been reported in humans, population level asymmetries were not observed. These results are particularly significant as they point out that paying attention to potential individual hemispheric differences is important in both basic and clinical neuroscience.

Transportation in the Interstitial Space of the Brain Can Be Regulated by Neuronal Excitation

The transportation of substances in the interstitial space (ISS) is crucial for the maintenance of brain homeostasis, however its link to neuronal activity remains unclear. Here, we report a marked reduction in substance transportation in the ISS after neuronal excitation. Using a tracer-based method, water molecules in the interstitial fluid (ISF) could be specifically visualized in magnetic resonance (MR) imaging. We first observed the flow of ISF in the thalamus and caudate nucleus of a rat. The ISF flow was then modulated using a painful stimulation model. We demonstrated that the flow of ISF slowed significantly following neuronal activity in the thalamus. This reduction in ISF flow continued for hours and was not accompanied by slow diffusion into the ISS. This observation suggests that the transportation of substances into the ISS can be regulated with a selective external stimulation.

Ictal body turning in focal epilepsy

Despite the explanations of many lateralization findings, body turning in focal epilepsy has been rarely investigated. One of the aims of this study was to evaluate the role of ictal body turning in the lateralization of focal epilepsies. The records of 263 patients with focal epilepsy (temporal lobe epilepsy (TLE), n=178; extratemporal lobe epilepsy (ETLE), n=85) who underwent prolonged video-EEG monitoring during presurgical epilepsy evaluation were reviewed. Preoperative findings (TLE, n=16; ETLE, n=6) and postoperative outcomes (TLE, n=7) of patients with focal epilepsy with ictal body turning were assessed. For the evaluation of ictal body turning, two definitions were proposed. Nonversive body turning (NVBT) was used to denote at least a 90° nonforced (without tonic or clonic component) rotation of the upper (shoulder) and lower (hip) parts of the body around the body axis for a minimum of 3s. Versive body turning (VBT) was used to denote at least a 90° forced (with tonic or clonic component) rotation of the upper (shoulder) and lower (hip) parts of the body around the body axis for a minimum of 3s. Nonversive body turning was observed in 6% (n=11) of patients with TLE and 2% (n=2) of patients with ETLE. For VBT, these ratios were 5% (n=8) and 7% (n=6) for patients with TLE and ETLE, respectively. Nonversive body turning was frequently oriented to the same side as the epileptogenic zone (EZ) in TLE and ETLE seizures (76% and 80%, respectively). If the amount of NVBT was greater than 180°, then it was 80% to the same side in TLE seizures. Versive body turning was observed in 86% of the TLE seizures, and 55% of the ETLE seizures were found to be contralateral to the EZ. When present with head turning, NVBT ipsilateral to the EZ and VBT contralateral to the EZ were more valuable for lateralization. In TLE seizures, a significant correlation was found between the head turning and body turning onsets and durations. Our study demonstrated that ictal body turning is a rarely observed but reliable lateralization finding in TLE and ETLE seizures, which also probably has the same pathophysiological mechanism as head turning in TLE seizures.

Influence of anxiety in spatial memory impairments related to the loss of vestibular function in rat

It is now well established that vestibular information plays an important role in spatial memory processes. Although vestibular lesions induce anxiety in humans, this finding remains controversial in rodents. However, it is possible that anxiety-related behavior is associated with spatial memory impairments after vestibular lesions. We aimed to evaluate anxiety-like behavior and the effect of an anxiolytic treatment during a complex spatial memory task in a rat model of compensated bilateral vestibular lesions. Adult rats were divided into four groups, with or without vestibular lesions and, treated or untreated by diazepam. The vestibular lesion was performed by transtympanic injection of arsanilate and compared to transtympanic saline injection. Diazepam or saline was administered 1h before each test or learning session. Vestibular-lesioned rats exhibited anxiety-like behavior which was decreased with diazepam. Spatial memory performance was similar in control-treated and untreated groups, suggesting no effect on memory at the dose of diazepam used. Spatial memory performances were not modified by anxiolytic drug treatment in vestibular-lesioned rats compared to vestibular-lesioned rats without drug treatment. We conclude that bilateral vestibular lesions in rats induced anxiety-like behavior which was unrelated to spatial memory impairment and was probably specifically related to the loss of vestibular information.

Significance of F3/Contactin gene expression in cerebral cortex and nigrostriatal development

F3/Contactin is a neuronal surface glycoprotein, which plays a general role in neural development and, in particular, in neuronal and oligodendrocyte differentiation. In a previous study using the F3/EGFP transgenic mice, which express an EGFP reporter under control of the regulatory region from the mouse F3/Contactin gene, the activation of the F3/Contactin promoter was found to correlate with granule and Purkinje neuron differentiation in developing cerebellar cortex. Here we report that in developing cerebral cortex and basal ganglia the F3/Contactin gene is mostly activated during early commitment of neuronal precursors, thus indicating a region-specific profile of its developmental activation. We also report that, in the same structures of F3/EGFP mice, a downregulation of the endogenous F3/Contactin gene occurs, which correlates with upregulation of the dopaminergic phenotype and with locomotor pattern abnormalities. Therefore, F3/EGFP transgenic mice exhibit morphological and functional phenotypes recapitulating those arising from imbalance of the striatal dopaminergic pathway. As for the underlying mechanisms, we postulate that in F3/EGFP mice F3/Contactin downregulation results from the ability of transgene promoter sequences to interfere with the activation of the endogenous gene, thus realizing an F3/Contactin knockdown model, while dopaminergic upregulation is consistent with a general F3/Contactin inhibitory effect on the neuronal phenotype.

The D₂ dopamine receptor and locomotor hyperactivity following bilateral vestibular deafferentation in the rat

Rats and mice with bilateral vestibular loss exhibit dramatic locomotor hyperactivity and circling behaviours, which to date cannot be explained. Dysfunction of the striatal dopaminergic system is responsible for a number of known movement disorders and the D(2) dopamine receptor is known to be implicated. Therefore, it is possible that changes in striatal function are responsible for locomotor hyperactivity and circling following bilateral vestibular lesions. The aim of this study was to investigate the effects of the D(2) receptor antagonist, eticlopride (0.02, 0.04 and 0.06mg/kg; s.c.), on locomotor behaviour in rats at 5 months following bilateral vestibular deafferentation (BVD), using an open field maze. The levels of the D(2) receptor protein in the striatum were measured at 1 and 6 months post-BVD using western blotting. BVD rats exhibited locomotor hyperactivity and circling, which eticlopride did not eliminate. However, BVD rats did exhibit a decreased response to the inhibitory effect of eticlopride compared to sham controls at the 0.02 mg/kg dose. There were no changes in the amount of the D(2) receptor in the striatum at 1 or 6 months post-BVD; however, D(2) receptor levels were significantly higher on the right side than the left in both sham and BVD animals. These results suggest that locomotor hyperactivity and circling behaviours following BVD are not due simply to changes in D(2) receptor protein expression in the striatum and that other neurophysiological changes in the brain account for these behaviours following BVD.

Long-term deficits on a foraging task after bilateral vestibular deafferentation in rats

Animal studies have shown that bilateral vestibular deafferentation (BVD) causes deficits in spatial memory that may be related to electrophysiological and neurochemical changes in the hippocampus. Recently, human studies have also indicated that human patients can exhibit spatial memory impairment and hippocampal atrophy even 8-10 yr following BVD. Our previous studies have shown that rats with unilateral vestibular deafferentation (UVD) showed an impairment at 3 months after the surgery on a food foraging task that relies on hippocampal integration of egocentric cues, such as vestibular information; however, by 6 months postop, they showed a recovery of function. By contrast, the long-term effects of BVD on spatial navigation have never been well studied. In this study, we tested BVD or sham rats on a food foraging task at 5 months postop. Under light conditions, BVD rats were able to use visual cues to guide themselves home, but did so with a significantly longer homing time. However, in darkness, BVD rats were severely impaired in the foraging task, as indicated by a significantly longer homing distance and homing time, with more errors and larger heading angles when compared with sham rats. These results suggest that, unlike UVD, BVD causes long-term deficits in spatial navigation that are unlikely to recover, even with repeated T-maze training.

Stereotypic circling behavior in mice with vestibular dysfunction: asymmetrical effects of intrastriatal microinjection of a dopamine agonist

Bronx Waltzer (bv) mouse, which has been used as a model of hearing and vestibular dysfunction, shows remarkable repetitive circling behavior. This study investigated whether the behavior is caused by the asymmetry of striatal function by observing the behavior of the bv mice following microinjection of dopamine D1 agonist, A68930 into the striatum ipsilaterally and contralaterally to the preferred direction of rotation separately. High dose of the drug induced opposite effects on ipsilateral rotations by the side of injections with statistical significance (p = .0026). These results suggested that the stereotypic circling behavior involves striatum and is based on striatal asymmetry.

Comparative analysis of anxiety-like behaviors and sensorimotor functions in two rat mutants, ci2 and ci3, with lateralized rotational behavior

There is increasing evidence that developmental anomalies of cerebral asymmetry are involved in the etiology of psychiatric disorders, including schizophrenia, depression and anxiety. Thus, rodents with abnormal cerebral lateralization are interesting tools to study the association between such anomalies and behavioral dysfunction. The most studied indicator of cerebral asymmetry in the rat is that of circling or rotational behavior. We have recently described two rat mutants, ci2 and ci3, in which lateralized rotational behavior occurs either spontaneously or in response to external stimuli, such as new environment or handling. While cochlear and vestibular defects are found in ci2 rats, ci3 rats do not exhibit any inner ear abnormalities. The abnormal motor response to external stimuli raised the possibility that the circling rat mutants may be more likely to express anxiety-related behavior in tests of emotionality. In the present study, we characterized anxiety-related behaviors of ci2 and ci3 rats in the open field, elevated plus-maze and light/dark exploration test. Furthermore, sensorimotor functions of these rats were evaluated by the rotarod, accelerod and wire hang tests. Heterozygous (ci2/+) littermates or rats of the respective background strains (LEW, BH.7A) were used as controls. In contrast to our expectation, both mutants demonstrated less anxiety-related behavior than controls in tests of emotionality. Ci3 rats exhibited normal sensorimotor functions, whereas marked impairment was observed in ci2 rats, which is most likely a consequence of the vestibular dysfunction in these animals. The acoustic startle response (ASR) and prepulse inhibition of ASR did not differ between ci3 rats and controls. The reduced emotionality of the mutant rats indicated by the present experiments may not be specifically linked to anxiety per se, but is maybe more reflective of impulsivity or the inability to normally perceive or process potentially threatening situations. Based on previous findings of dysfunctions of the central dopamine system in ci2 and ci3 mutant rats, we assume that alterations in dopaminergic activity are involved in the maladaptive behavior observed in the present study.

Developmental regulation of the membrane properties of central vestibular neurons by sensory vestibular information in the mouse

The effect of the lack of vestibular input on the membrane properties of central vestibular neurons was studied by using a strain of transgenic, vestibular-deficient mutant KCNE1(-/-) mice where the hair cells of the inner ear degenerate just after birth. Despite the absence of sensory vestibular input, their central vestibular pathways are intact. Juvenile and adult homozygous mutant have a normal resting posture, but show a constant head bobbing behaviour and display the shaker/waltzer phenotype characterized by rapid bilateral circling during locomotion. In juvenile mice, the KCNE1 mutation was associated with a strong decrease in the expression of the calcium-binding proteins calbindin, calretinin and parvalbumin within the medial vestibular nucleus (MVN) and important modifications of the membrane properties of MVN neurons. In adult mice, however, there was almost no difference between the membrane properties of MVN neurons of homozygous and control or heterozygous mutant mice, which have normal inner ear hair cells and show no behavioural symptoms. The expression levels of calbindin and calretinin were lower in adult homozygous mutant animals, but the amount of calcium-binding proteins expressed in the MVN was much greater than in juvenile mice. These data demonstrate that suppression of sensory vestibular inputs during a 'sensitive period' around birth can generate the circling/waltzing behaviour, but that this behaviour is not due to persistent abnormalities of the membrane properties of central vestibular neurons. Altogether, maturation of the membrane properties of central vestibular neurons is delayed, but not impaired by the absence of sensory vestibular information.

Auditory and vestibular defects and behavioral alterations after neonatal administration of streptomycin to Lewis rats: Similarities and differences to the circling (ci2/ci2) Lewis rat mutant

The clinical usefulness of aminoglycoside antibiotics is limited by their ototoxicity. In rodents, damage to the inner ear is often associated with rotational behavior and locomotor hyperactivity reminiscent of such behaviors resulting from an imbalance of forebrain dopamine systems. Based on previous observations in the circling (ci2/ci2) Lewis (LEW) rat mutant, a spontaneous mutation leading to hair cell loss, deafness, impairment of vestibular functions, lateralized circling, hyperactivity and alterations in the nigrostriatal dopamine system, we have recently hypothesized that vestibular defects during postnatal development, independent of whether induced or inherited, lead to secondary changes in the dopaminergic system within the basal ganglia, which would be a likely explanation for the typical behavioral phenotype seen in such models. In the present study, we directly compared the phenotype induced by streptomycin in LEW rats with that of the ci2 LEW rat mutant. For this purpose, we treated neonatal LEW rats over 3 weeks by streptomycin, which induced bilateral degeneration of cochlear and vestibular hair cells. Following this treatment period, the behavioral syndrome of the streptomycin-treated animals, including the lateralized rotational behavior, was almost indistinguishable from that of ci2 mutant rats. However, in contrast to the ci2 mutant rat, all alterations, except the hearing loss, were only transient, disappearing between 7 and 24 weeks following treatment. In conclusion, in line with our hypothesis, vestibular defects induced in normal LEW rats led to the same phenotypic behavior as the inherited vestibular defect of ci2 mutant rats. However, with increasing time for recovery, adaptation to the vestibular impairment developed in streptomycin-treated rats, while all deficits persisted in the mutant animals. At least in part, the transient nature of the abnormal behaviors resulting from treatment with streptomycin could be explained by adaptation to the vestibular impairment by the use of visual cues, which is not possible in ci2 rats because of progressive retinal degeneration in these mutants. Although further experiments are needed to prove this hypothesis, the present study shows that direct comparisons between these two models serve to understand the mechanisms underlying the complex behavioral phenotype in rodents with vestibular defects and how these defects are compensated.

Striatal increase of extracellular dopamine levels during dystonic episodes in a genetic model of paroxysmal dyskinesia

In vivo microdialysis was used to examine the levels of dopamine, serotonin, and their metabolites dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in the striatum of dt(sz) mutant hamsters, an animal model of paroxysmal dyskinesia, in which stress can precipitate dystonic episodes. Measurements were made under three different conditions in each animal: (1) at baseline in the absence of abnormal involuntary movements, (2) during an episode of paroxysmal dystonia precipitated by handling, and (3) during the recovery (postdystonic) period. In comparison to nondystonic control hamsters, which were treated in the same manner as dystonic animals, no changes could be detected under basal conditions, although the levels of DOPAC and HVA tended to be higher in mutant hamsters. Significantly elevated striatal levels of dopamine and DOPAC became evident during the period of stress-induced dystonic attacks in mutant hamsters. During dystonic episodes, dopamine levels were approximately 6.5-fold higher (followed by a 2.5-fold increase of DOPAC) in dt(sz) hamsters than in normal controls. Before the disappearance of dystonia, the levels of dopamine returned to basal concentrations in mutant hamsters. Consistent with previous pharmacologic findings, paroxysmal dystonia in mutant hamsters is associated with temporary increases of extracellular dopamine levels in the striatum.

The circling behavior of the deafblind LEW-ci2 rat is linked to a segment of RNO10 containing Myo15 and Kcnj12

The LEW/Ztm-ci2 rat is an autosomal recessive mutant that displays circling behavior, deafness, progressive retinopathy, locomotor hyperactivity, ataxia, and opisthotonus. We performed a genome-wide scan of a (LEW/Ztm-ci2 x BN/Ztm) F1 x LEW/Ztm-ci2 backcross population with anonymous microsatellite markers to analyze the genetics of this mutant rat. This linkage analysis demonstrated a very strong association of RNO10 SSLP markers to the phenotype with a core region in the central part of the chromosome. The knowledge of genes mapping to this part of the rat genome and their linkage to SSLP markers is still poor. We developed SSLP markers closely linked to genes, which might be responsible for the mutant phenotype by using the growing amount of rat-specific DNA sequences available at World Wide Web databases. Application of this method facilitated the search for candidate genes for the phenotype of the LEW-ci2 rat. We were able to map Myo15 and its neighboring genes, Znf179 and Aldh3a1, to the region of interest and Myo1c to a more distal location on RNO10. Further rat BAC clones were used to create a physical map of the region of interest. This map revealed the position of further genes. Among those is Kcnj12. Owing to their localization on RNO10 and their involvement in a similar pathology in human and mouse, Myo15 and Kcnj12 can be regarded as candidate genes for the deafblind phenotype of the LEW-ci2 rat.

Urinary dopamine and turn bias in traumatized women with and without PTSD symptoms

Turning biases are known to occur in the direction of the brain hemisphere with decreased dopamine (DA). Although elevations in urinary DA have been shown in posttraumatic stress disorder (PTSD), evidence for dysregulation of dopaminergic activity in the brain is lacking. Turn bias and urinary DA levels were examined in mothers of childhood cancer survivors. As expected, cancer trauma mothers with PTSD symptoms (n=14) had higher urinary DA levels than trauma mothers without PTSD symptoms (n=7) and controls (n=8) (P=0.01). Groups were also significantly different in prevalence of left turn bias (P=0.03). All controls (100%) showed a left turn bias compared to 75 and 37.5% prevalence among trauma mothers with and without PTSD, respectively. Urinary DA levels and turn bias rates were not correlated. Results lend support for further exploration of DA in traumatized groups with and without PTSD.

Altered spontaneous discharge rate and pattern of basal ganglia output neurons in the circling (ci2) rat mutant

The circling rat is an autosomal recessive mutant (homozygous ci2/ci2) characterized by lateralized rotational behavior, locomotor hyperactivity, ataxia, stereotypic head movements, and deafness. Previous neurochemical investigations showed that ci2 rats of both genders have a lower tissue content of dopamine in the striatum ipsilateral to the preferred direction of circling. For further evaluation as to whether this striatal imbalance has functional consequences within basal ganglia structures, the spontaneous extracellular single unit activity of GABAergic neurons located in the striatum and, downstream to the dopaminergic nigrostriatal system, the substantia nigra pars reticulata (SNr) was recorded bilaterally in anesthetized ci2 rats. Heterozygous (ci2/+) littermates that display normal behavior, and rats from the background strain (LEW/Ztm) served as controls. No significant hemispheric imbalances in striatal discharge rate and firing pattern were evident in ci2 rats. Furthermore, there were no significant intergroup differences in striatal activity. However, the mean spontaneous discharge rate of SNr neurons was significantly increased in both brain sides, and there was a significant shift toward rhythmic burst-like firing in ci2 mutants. Again, no hemispheric differences were detected. The data substantiate previous findings of altered basal ganglia function in ci2 rats. The abnormal basal ganglia output activity, i.e. of the SNr, is likely to contribute to the complex behavioral disturbances seen in ci2 rats.

Ebselen blocks the quinolinic acid-induced production of thiobarbituric acid reactive species but does not prevent the behavioral alterations produced by intra-striatal quinolinic acid administration in the rat

Ebselen (EBS) is a seleno-organic compound with glutathione peroxidase-like activity which is neuroprotective in acute stroke ischemia. In this study, we investigated the effect of EBS on quinolinic acid (QA)-induced neurotoxicity. EBS inhibited QA-induced production of thiobarbituric acid reactive species (TBARS) by striatal homogenates in vitro with an IC(50) of 1.85 microM. Intra-striatal injection of QA (360 nmol) increased striatal content of TBARS and induced convulsions and contralateral rotational behavior. Intra-striatal pre-injection of EBS (10 nmol) 15 min before QA abolished QA-induced TBARS production but did not alter QA-induced behavioral effects. The present findings suggest that EBS acts on post-receptor events, neutralizing free radicals produced by overstimulation of N-methyl-D-aspartate receptors.

Spontaneous paroxysmal circling behavior in the ci2 rat mutant: epilepsy with rotational seizures or hyperkinetic movement disorder?

Circling, turning, rotating, spinning, wheeling, and cursive hyperkinesia are all synonymous terms used to describe the active movement of an animal in a circular direction. Circling behavior can be evoked by unilateral electrical and chemical stimulation or lesions of various brain sites, but can also occur after systemic drug administration or spontaneously in normal animals or mutant rodents. In humans, stereotypic body rotation can occur as a distinctive entity of generalized and focal epilepsy, and may be due to involvement of the striatum. We have previously described a Lewis rat mutant (ci2) with a behavioral phenotype characterized by lateralized circling, hyperactivity, opisthotonus, and ataxia. In these rats, circling occurs in phases or bursts either spontaneously or in response to stress. Neurochemical data indicate that the circling behavior of the ci2 mutants is related to an abnormal asymmetry in dopaminergic activity in the striatum. Because of the similarities to rotational epilepsy, we used video and electroencephalographic recordings to study whether the rotational behavior of the ci2 mutant rat is a result of a partial or generalized epilepsy. Epileptic WAG/Rij rats were used for comparison. Video monitoring of ci2 rats in the absence of any stress or disturbance showed that circling occurs in paroxysmal bursts during active wakefulness, but not during passive wakefulness or sleep. Circling was not preceded or followed by any convulsive motor seizures and was not associated with epileptiform abnormalities in the electroencephalogram, whereas WAG/Rij rats exhibited myoclonic seizures and epileptic spike-wave discharges during passive wakefulness and sleep. As a result of the association of circling with active wakefulness, ci2 rats exhibited many more rotations during the dark (active) phase compared with the light (rest) period. Increase in active wakefulness during the light phase by transfer of the rats to a new environment induced or intensified circling behavior. Most ci2 rats showed a consistent lateral preference during circling, but some rats changed their preference from one session to another. The data indicate that spontaneous paroxysmal circling behavior in the ci2 rat is not a consequence of epilepsy but reflects a hyperkinetic movement disorder with abnormal lateralization of brain function.

Auditory and vestibular defects in the circling (ci2) rat mutant

The circling rat is an autosomal recessive mutant (homozygous ci2/ci2) that displays lateralized circling behaviour, locomotor hyperactivity, ataxia and stereotypic head-movement. These abnormal behaviours occur in phases or bursts either spontaneously or in response to stress. Heterozygous (ci2/+) littermates display normal spontaneous behaviours. We have previously found that ci2/ci2 rats of both genders have a lower tissue content of dopamine in the striatum ipsilateral to the preferred direction of rotation, indicating that the rats turn away from the brain hemisphere with higher striatal dopaminergic activity. In view of the similarities of the motor syndrome of the ci2/ci2 mutant rat to that of mouse deafness mutants, the present study evaluated the hearing ability of the circling rat mutant by recording brainstem auditory-evoked potentials. To test for vestibular dysfunction, a swimming test was conducted. Histological methods were used to examine the cochlear and vestibular parts of the inner ear and the cochlear and vestibular brainstem nuclei for defects. The absence of auditory-evoked potentials demonstrated a complete hearing loss in the adult ci2/ci2 mutant rat, whereas heterozygous littermates exhibited auditory-evoked potentials with thresholds resembling those of other laboratory strains. Furthermore, the mutant rats were unable to swim. Histological analysis of the inner ear of adult mutants revealed virtually complete loss of the cochlear neuroepithelium, while no such hair cell degeneration was seen in the vestibular parts of the inner ear. However, part of the vestibular hair cells showed protrusions into the endolymphatic space, suggesting alterations in the cytoskeletal architecture. The histological findings in mutant circling rats strongly indicate that the hearing loss of the mutants is of the sensory neural type, the most prevalent type of hearing loss. In the cochlear nuclei of the brain stem of mutant rats, neurons exhibited an abnormal shape, reduced size and increased density compared to controls. In contrast, no abnormal neuronal morphology was seen in the vestibular nuclei, but a significantly reduced neuronal density was found in the medial vestibular nucleus. Abnormal vestibular function would be a likely explanation for the disturbed balance of mutant rats as exemplified by the ataxia and the inability to swim, whereas the previous data on these rats strongly indicate an involvement of the basal ganglia in the abnormal circling behaviour. The genetic defect in the mutant rats, thus, results in a clinical syndrome with features also seen in human genetic disorders with deafness and hyperkinesia, making the ci2/ci2 rat an excellent model for investigating both cochlear/vestibular dysfunction and hyperkinetic movement disorders.