Role of the corpus callosum in expression of behavioral asymmetries induced by a unilateral dopamine lesion of the substantia nigra in the rat

The cross-hemispheric nigrostriatal pathway prevents the expression of levodopa-induced dyskinesias

Parkinson's disease (PD) is a neurodegenerative movement disorder that is routinely treated with levodopa. Unfortunately, long-term dopamine replacement therapy using levodopa leads to levodopa-induced dyskinesias (LID), a significant and disabling side-effect. Clinical findings indicate that LID typically only occurs following the progression of PD motor symptoms from the unilateral (Hoehn and Yahr (HY) Stage I) to the bilateral stage (HY Stage II). This suggests the presence of some compensatory interhemispheric mechanisms that delay the occurrence of LID. We therefore investigated the role of interhemispheric connections of the nigrostriatal pathway on LID expression in a rat model of PD. The striatum of one hemisphere of rats was first injected with a retrograde tracer to label the ipsi- and cross-hemispheric nigrostriatal pathways. Rats were then split into groups and unilaterally lesioned in the striatum or medial forebrain bundle of the tracer-injected hemisphere to induce varying levels of hemiparkinsonism. Finally, rats were treated with levodopa and tested for the expression of LID. Distinct subsets emerged from rats that underwent the same lesioning paradigm based on LID. Strikingly, non-dyskinetic rats had significant sparing of their cross-hemispheric nigrostriatal pathway projecting from the unlesioned hemisphere. In contrast, dyskinetic rats only had a small proportion of this cross-hemispheric nigrostriatal pathway survive lesioning. Crucially, both non-dyskinetic and dyskinetic rats had nearly identical levels of ipsi-hemispheric nigrostriatal pathway survival and parkinsonian motor deficits. Our data suggest that the survival of the cross-hemispheric nigrostriatal pathway plays a crucial role in preventing the expression of LID and represents a potentially novel target to halt the progression of this devastating side-effect of a common anti-PD therapeutic.

Novel Neuromodulation Techniques to Assess Interhemispheric Communication in Neural Injury and Neurodegenerative Diseases

Interhemispheric interaction has a major role in various neurobehavioral functions. Its disruption is a major contributor to the pathological changes in the setting of brain injury such as traumatic brain injury, peripheral nerve injury, and stroke, as well as neurodegenerative diseases. Because interhemispheric interaction has a crucial role in functional consequence in these neuropathological states, a review of noninvasive and state-of-the-art molecular based neuromodulation methods that focus on or have the potential to elucidate interhemispheric interaction have been performed. This yielded approximately 170 relevant articles on human subjects or animal models. There has been a recent surge of reports on noninvasive methods such as transcranial magnetic stimulation and transcranial direct current stimulation. Since these are noninvasive techniques with little to no side effects, their widespread use in clinical studies can be easily justified. The overview of novel neuromodulation methods and how they can be applied to study the role of interhemispheric communication in neural injury and neurodegenerative disease is provided. Additionally, the potential of each method in therapeutic use as well as investigating the pathophysiology of interhemispheric interaction in neurodegenerative diseases and brain injury is discussed. New technologies such as transcranial magnetic stimulation or transcranial direct current stimulation could have a great impact in understanding interhemispheric pathophysiology associated with acquired injury and neurodegenerative diseases, as well as designing improved rehabilitation therapies. Also, advances in molecular based neuromodulation techniques such as optogenetics and other chemical, thermal, and magnetic based methods provide new capabilities to stimulate or inhibit a specific brain location and a specific neuronal population.

The interhemispheric connections of the striatum: Implications for Parkinson's disease and drug-induced dyskinesias

Parkinson's disease (PD) is characterized by loss of nigrostriatal neurons and depletion of dopamine. This pathological feature leads to alterations to basal ganglia circuitry and subsequent motor disability. Pharmacological dopamine replacement therapy with medications such as levodopa ameliorates the symptoms of PD but can lead to motor complications known as drug-induced dyskinesias. We have recently shown that clinically hemiparkinsonian rhesus monkeys do not develop levodopa-induced dyskinesias despite chronic intermittent exposure and significant unilateral loss of nigrostriatal neurons and dopamine. It is currently unclear what mechanisms prevent the onset of dyskinesias in these animals. Based on our study and results from previous lesioning studies in both the rat and monkey models of PD, we hypothesize that one potential mechanism that may prevent the genesis of dyskinesias in these animals is interhemispheric neuromodulation. Two potential interhemispheric connections that may modulate dyskinesias are the interhemispheric nigrostriatal and corticostriatal pathways. Few investigators have examined the interhemispheric nigrostriatal and corticostriatal connections and the functional role they may play in drug-induced dyskinesias in PD. Therefore, in the following review, we assess the neuroanatomical, electrophysiological and behavioral properties of these interhemispheric connections. Future studies evaluating these interhemispheric striatal pathways and the pathophysiological changes that occur to these pathways in the dyskinetic state are warranted to further develop treatments that prevent or mitigate drug-induced dyskinesias in PD.

Behavioral effects of corpus callosum transection and environmental enrichment in adult rats

A common assumption about the corpus callosum transection (CCX) is that it only affects behaviors heavily relying on interhemispheric communication. However, cerebral laterality is ubiquitous across motor and perceptual, cognitive and emotional domains, and the corpus callosum is important for its establishment. Several recent studies showed that the partial denervation of the sensorimotor isocortex through CCX derepressed neural growth processes that were sensitive to motor demand (experience-dependent neural plasticity). We investigated whether the facilitatory effects of CCX on cortical neural plasticity, shaped by differential housing, extended beyond the motor domain. Adult rats were housed in enriched (EE), standard (SE) or impoverished environments (IE) for 10 weeks, that is, 2 weeks before they underwent CCX or sham surgery, and, then, 8 weeks throughout the experiments. After they recovered from surgery, the behavioral performance of rats was tested using open-field, spontaneous alternation in the T-maze, paw preference, Morris water maze, and tone fear conditioning. The results indicated that the effects of CCX and housing on open-field behavior were independent, with CCX increasing the time spent in the center of the field at the beginning of the observation (i.e., emotionality), and EE and IE increasing rearing (emotionality) and reducing teeth-chattering (habituation), respectively. CCX reduced the frequency of spontaneous alternation, denoting spatial working memory deficits, while housing did not influence this performance. Neither CCX, nor housing significantly affected paw preference lateralization, although CCX was associated with a leftward bias in paw preference. In the Morris water maze, housing had effects on spatial acquisition, while CCX reduced activity, without interfering with spatial memory. CCX did not influence tone fear conditioning, but context fear conditioning seemed to benefit from EE. We conclude that CCX in adult rats has subtle, but specific behavioral effects pertaining to emotionality, spatial working memory, and, possibly, aversively motivated exploration, and these effects are either independent or only peripherally interact with the effects of housing.

Effects of callosal agenesis on rotational side preference of BALB/cCF mice in the free swimming test

In order to test the hypothesis that the ontogenetic development of the corpus callosum is related to the establishment of behavioral laterality, the rotatory behavior in the free swimming test was studied in male mice of the BALB/cCF strain, in which approximately 20% of the animals present total or partial callosal agenesis. All animals were submitted to three sessions of the free-swimming rotatory test in three different sessions (diameter of the recipient = 21 cm; session duration = 5 min; inter-test interval = 48 h). The number and direction of the 30 and 360 degrees turns were recorded. Animals were classified as side-consistent turners (to the right or to the left) when they did not change their preferred side of rotation in all three sessions and in both turning units. In general our results suggested that acallosal animals present more pronounced laterality than normal ones. In the acallosal group, the percentage of consistent turners was significantly higher than that of non-consistent turners. The percentage of animals that presented strong turning preferences in the acallosal group was higher than in the normal group. In first session, the acallosal group presented a higher average number of turns to preferred side than the normal group. Taken together, our results constitute an endorsement to the hypothesis that the normal development of the corpus callosum is related to the establishment of cerebral laterality.

Contralateral rotatory bias in the free-swimming test after unilateral hemispherectomy in adult Swiss mice

In the free-swimming rotatory test mice spend most of the time swimming close to the wall of the container attempting to escape from an aversive test situation. The attraction to the wall may suggest that turning behavior in the free-swimming test reflects the existence of intrinsic sensory asymmetries, which determine preferential attention adhesion to one side. In order to test this hypothesis, we investigated the rotatory swimming behavior of mice submitted to a unilateral hemispherectomy at adulthood, a condition of extreme sensory asymmetry. Fifteen days after surgery procedures, each mouse was tested for 5 min on 3 different days. We found that the hemispherectomized mice had a significant strong bias to turn in the direction contralateral to their lesion. These data could be explained considering that, in attempting to escape from the test situation, animals bring the recipient wall into their intact sensory field and, as a consequence, set the direction of locomotion. Thus, the free-swimming test may be useful to investigate sensory asymmetries during an aversive test situation.

Unilateral dopamine depletion paradoxically enhances amphetamine-induced Fos expression in basal ganglia output structures

The ability of amphetamine to induce expression of the immediate early gene protein, Fos, was examined by immunocytochemistry in animals with unilateral 6-hydroxydopamine lesions of the nigrostriatal bundle. Amphetamine induced Fos expression in the globus pallidus (GP) on the intact side of the brain, but this response was greatly attenuated on the dopamine-depleted side. In contrast, amphetamine induced little Fos expression in the entopeduncular nucleus (EPN) and the substantia nigra pars reticulata (SNpr) on the intact side of the brain, but resulted in pronounced expression in these structures on the lesioned side. These findings demonstrate that unilateral dopamine depletion results in a pathophysiological state in which some responses to amphetamine are attenuated while others are paradoxically potentiated. One explanation of these effects is that amphetamine may indirectly activate excitatory inputs to the SNpr and the EPN on both sides of the brain. On the intact side, these effects would be opposed by the simultaneous activation of inhibitory pathways arising in the striatum and the GP, with the result that little Fos expression would be seen. On the dopamine-depleted side, however, engagement of these inhibitory pathways would be attenuated and the unopposed effects of the excitatory inputs mobilized by amphetamine would result in exaggerated Fos synthesis.

Effects of sex and laterality on the rotatory swimming behavior of normal mice

Clockwise and counterclockwise full turns are commonly used to assess lateralization in circling behavior. Although previous studies have reported that the rotatory swimming (ROSW) test is simple and reliable, little is known about lateralization of turns lower than 360 degrees and the amount of turning close to the wall, and even less is known about alternation of direction during a session. Here we investigated the effects of consistency of laterality and sex on 30 degree turns in center and in periphery of the swimming apparatus, and on alternation of direction upon three sessions. Approximately 80% of the turns occurred when mice swam along the wall. In side-consistent turners, this suggests the existence of an intrinsic sensorimotor asymmetry that determines the adhesion to the preferred side. Regarding categorization of side preferences, there was a high percentage of agreement between center and periphery, as well as between full turns and extra 30 degree turns (30 degree turns that do not contribute to full turns). Therefore, behavioral asymmetry in the ROSW can be assessed using 30 degree turns. There was no significant directional bias in the population, and side preference was found to be independent of sex. By contrast, after the second minute of each session, males exhibited a significantly higher number of reversal of direction (RD) as well as a higher number of RD per turn than females. The amount of RD presented by each animal is not predicted by the animal's side preference. Thus, RD is independent of preferred side of turning and depends on sex.

Pathogenesis of Tourette's syndrome

This review presents a models of disease pathogenesis in the context of CNS development. It begins with an exploration of the clinical features and natural history of Tourette's syndrome. This is followed by a consideration of the role of genetic and nongenetic factors. An effort is then made to review the anatomical organization of the basal ganglia and related cortical sites. These circuits are intimately involved in the normal processing of sensorimotor, cognitive, and emotionally laden information. Evidence implicating these circuits in the pathobiology of Tourette's syndrome is then considered. The review closes with the prospects for advances in interdisciplinary research and therapeutics using this model as a guide.

Three cases of symptom change in Tourette's syndrome and obsessive-compulsive disorder associated with paediatric cerebral malignancies

OBJECTIVE

To correlate behaviour manifestations with tumour location in three children who had Gilles de la Tourette's syndrome (GTS), obsessive-compulsive disorder (OCD), and primary cerebral malignancies.

METHOD

Cases were ascertained from a chart review in a GTS and OCD specialty clinic. For each case the temporal progression of change in neuropsychiatric symptoms was qualitatively correlated with radiographic documentation of tumour progression.

RESULTS

The change in symptom severities during tumour progression and treatment, together with prior neurobiological studies of GTS, suggest that the ventral striatum, corpus callosum, thalamus, and midbrain are potentially important neural substrates in the formation or modulation of tic symptoms. The limbic system, including the hypothalamus and cingulate, and the caudate nucleus, seem to be important in the neurobiology of OCD. All structures are neuroanatomically and functionally related to the corticostriato-thalamocortical circuitry that is thought to subserve symptom generation in both GTS and OCD.

CONCLUSION

Although the malignancies were not likely to have caused the tic and OCD symptoms in these children, the locations of these intracranial lesions provide important clues in identifying brain regions that may contribute to the determination of tic and OCD severities.

Bilateral 6-hydroxydopamine-induced lesion of the nigrostriatal dopamine pathway reproduces the effects of unilateral lesion on substance P but not on enkephalin expression in rat basal ganglia

This study compared the effects of unilateral and bilateral 6-hydroxydopamine-induced lesions of the nigrostriatal dopaminergic neurons on substance P and enkephalin expression in the rat striatum and its main target structures by means of quantitative in situ hybridization and immunocytochemistry. In animals with bilateral lesion, substance P mRNA levels were decreased in the striatum, and this was matched by parallel reductions in substance P immunoreactivity in the striatum and in the striatonigral terminals at substantia nigra level in both hemispheres. These changes were similar to those observed ipsilaterally to unilateral lesion. In contrast, whereas increased striatal enkephalin immunoreactivity and mRNA levels and decreased immunoreactivity in the globus pallidus were observed on the lesioned side after unilateral lesion, no significant change in these enkephalin markers occurred in animals with bilateral lesion. These data suggest that the effects of dopamine deafferentation on substance P expression in the striatonigral system may be due primarily to removal of direct dopamine influence, whereas the effects on enkephalin expression in the striatopallidal system may involve complex interhemispheric adaptive mechanisms. The present finding that bilateral dopamine lesion does not simply reproduce the effects of unilateral lesion but creates a new functional state may have a critical bearing on the understanding and treatment of Parkinson's disease.

A direct observational measure of whole body turning bias

The directional preference for spontaneous turning in humans has previously been documented using an electronic device (rotometer). We used a simple, inexpensive, and well-controlled test of turning behaviour in 41 adults with no psychiatric diagnoses. In this test, the direction in which subjects turned is recorded as they complete each one of what they think is a series of evaluations of gait, in a room symmetrically spacious and free of distracters. A substantial majority of our right-handed subjects (N = 27) showed a significant leftward turning bias, while non-right handed group (N = 14) did not show this bias. Test-retest reliability for this measure in 17 individuals tested twice at different times was high (rho = 0.73).

Lateralization of rotational behavior in developing and adult hamsters

Rotational asymmetries were studied in developing and adult hamsters, and compared to verify if early lateralization is a predictor of the animals' later performance. Animals were divided into two groups: group I (GI) was tested from P46 (P1 = day of birth) to P62, and group II (GII) was tested daily from P2 to P60. They were placed in a cylindric arena for 5 min under video recording, and their 90 degree right and left displacements were counted and normalized. Since adult animals of both groups did not differ significantly in the distribution of asymmetries, the data were pooled together: 38.8% were non-lateralized (NL), 39.4% were right-rotators (RR), and 21.8% were left-rotators (LR). No significant difference was discerned between males and females. Distribution of asymmetries in GII animals between P2 and P10 showed a predominance of lateralized (64.7% RR and 21.5% LR) over NL animals (13.8%). The proportion of pups that maintained their classification into adulthood was only 46%, and the kappa coherence coefficient for these data was only 0.09. We conclude that: (1) most adults are lateralized, RR being more frequent; (2) the proportion of lateralized adults is not significantly altered by early testing; (3) there is no significant difference between males and females; (4) most developing hamsters are lateralized, right-rotators being more frequent; and (5) the animals' early classification is not a good predictor of their preference as adults.

Interhemispheric modulation of dopamine receptor interactions in unilateral 6-OHDA rodent model

A critical assumption in the unilateral 6-hydroxydopamine (6-OHDA) model is that interactions between the intact and denervated hemispheres do not influence the response to insult. The present study examined this issue by assessing the effects of unilateral substantia nigra 6-OHDA lesions in rats that previously had received corpus callosum transections, a treatment designed to minimize interhemispheric influences. Quantitative autoradiography in the caudate-putamen ipsilateral to the lesion revealed that corpus callosum transection did not alter the increase in D2-like receptors ([125I]-epidepride-labeled sites) that is induced by unilateral 6-OHDA lesion. There were no effects of either 6-OHDA lesion or transection on D1 receptor density ([125I]-SCH23982 autoradiography). As a functional endpoint, dopamine-stimulated cAMP efflux was measured in superfused striatal slices. In this paradigm, the net effect of dopamine (DA) represents a combination of D1 receptor-mediated stimulation and D2 receptor-mediated inhibition. 6-OHDA lesion increased cAMP efflux induced by exposure to 100 microM DA alone; corpus callosum transection did not alter this effect. An interaction between 6-OHDA lesion and transection status was revealed, however, by comparison of results obtained with DA alone vs. DA plus the D2 antagonist sulpiride (to block the D2 inhibitory effects of 100 microM DA). This comparison revealed two important effects of 6-OHDA lesion in rats with an intact corpus callosum: 1) a moderate decrease in dopamine D1 receptor-mediated stimulation; and 2) a dramatic decrease in the ability of D2 receptors to inhibit this stimulation. Corpus callosum transection prevented these effects of 6-OHDA. These results provide a biochemical demonstration of D1:D2 receptor uncoupling in unilateral 6-OHDA lesioned rats, and suggest that interhemispheric influences (e.g., contralateral cortico-striatal glutamatergic projections) may contribute to lesion-induced alterations in D1:D2 receptor interactions.

Asymmetrical orientation to edges of an openfield: modulation by striatal dopamine and relationship to motor asymmetries in the rat

Rats with unilateral 6-hydroxydopamine (6-OHDA, 4 or 8 micrograms) or sham lesions of the substantia nigra were examined (undrugged) for asymmetrical orientation to edges of a large openfield. Lesioned rats preferentially aligned with the edge such that the intact striatum was contralateral to the edge. The magnitude of this asymmetry was greatest in rats lesioned with the highest dose of 6-OHDA. There was no population left/right hemispheric asymmetry in the extent to which unilateral striatal dopamine (DA) depletion produces this behavioral bias. In sham-lesioned rats, endogenous imbalances in striatal DA activity (DOPAC/DA) were related to the direction of edge orientation, such that the more active striatum tended to be contralateral to the edge. Also in shams, the direction of this orientational asymmetry was not significantly related to the direction of motor bias measured as amphetamine- and apomorphine-induced turning behavior in rotometers (having no edges). However, the magnitudes of sensorimotor (edge behavior) and motor (turning) asymmetries were negatively correlated. The results extend previous findings that asymmetrical edge behavior is a sensitive index of imbalances in striatal DA activity, not only in DA-depleted rats, but in intact rats as well. Furthermore, sensorimotor and motor asymmetries, while both under DAergic influence, are largely independent processes.