Relationship between interhemispheric nigrostriatal projections and the direction of rotational behavior induced by amphetamine

The grid-walking test: assessment of sensorimotor deficits after moderate or severe dopamine depletion by 6-hydroxydopamine lesions in the dorsal striatum and medial forebrain bundle

The present study aims to evaluate the applicability of the grid-walking test in rats with moderate or severe dopamine-depletion incurred by unilateral nigro-striatal 6-hydroxydopamine (6-OHDA) lesions. Striatum samples were analyzed by high pressure liquid chromatography coupled to electrochemical detection (HPLC-EC) after behavioral testing. In Experiment 1, 2 weeks after the injection of 6-OHDA into the medial forebrain bundle, adult Wistar rats were divided into an l-3,4-dihydroxyphenylalanine (L-dopa) and a vehicle treatment group and their behaviors on the grid were compared. The severely lesioned animals (mean dopamine depletion of 92%) did not exhibit behavioral asymmetry in the number of contralateral foot-slips. However, L-dopa administration selectively reduced the number of foot-slips of the contralateral forelimb when compared with the vehicle group. In Experiment 2, 6-OHDA was injected into the dorsal striatum and foot-slips on the grid were analyzed 4, 9 and 13 days following the lesion. The rats with moderate dopamine-depletion (mean depletion of 54%) exhibited more contralateral forelimb-slips on all testing days. Compared with naive rats, hemiparkinsonian rats also showed more forelimb-slips. These results suggest that the grid-walking test should be a powerful and sensitive behavioral assay for sensory-motor deficits in rat models of nigro-striatal dopamine lesions.

Behavioral analysis of asymmetries induced by unilateral 6-OHDA injections into the substantia nigra

The intent of this study was to perform a detailed analysis of behavioral asymmetries (turning behavior) exhibited by animals which had sustained a unilateral lesion of the substantia nigra (SN). Rats were tested for behavior asymmetries over 16 days, once before, and 7 times after 6-OHDA had been injected into one SN. On the basis of the number of narrow diameter ipsiversive half turns produced during testing, they were then assigned to one of three groups: (a) those which showed an initial asymmetry from which they recovered, (b) those which were asymmetrical throughout testing, and (c) those in which the asymmetry only emerged during the testing period. We examined several different aspects of turning behavior. Recovery from asymmetry was associated with an increase in the number of contraversive, as well as a decrease in the number of ipsiversive narrow-angle turns. The average diameter of these ipsiversive turns also increased. Animals which recovered showed a contraversive asymmetry for wide-diameter turns which increased during testing. Narrow-diameter contraversive turns decreased during testing in the two nonrecovery groups. Both nonrecovery groups showed a contraversive asymmetry for wide-diameter turns. Asymmetry was attributable to a tendency to circle and move ipsiversively in the two nonrecovery groups, whereas it was due to circling behavior in animals which showed recovery. Additionally, more cells, labeled by HRP injected into the ipsilateral caudate putamen, were found in the damaged SN of animals which recovered.

Behavioral concomitants of regional changes in the brain's biogenic amines after apomorphine and amphetamine

Behavioral and neurochemical changes were analyzed in rats after systemical injections of the dopamine receptor agonist apomorphine (0.5 mg/kg) or the indirect agonist amphetamine (1.0 mg/kg). As expected, amphetamine led to an increase in locomotion, whereas apomorphine resulted in decreases in locomotion, rearings, and grooming. The analysis of biogenic amines in tissue samples showed that amphetamine decreased 3,4-dihydroxy-phenylacetic acid (DOPAC) levels and DOPAC/dopamine ratios in the neostriatum, and resulted in a lower 5-hydroxyindole-3-acetic acid (5-HIAA)/5-hydroxytryptamine (5-HT) ratio in the ventral mesencephalon. Apomorphine decreased the dopamine metabolites [DOPAC, homovanillic acid (HVA), 3-methoxy-tyramine (3-MT)] and their respective metabolite/transmitter ratios and increased dopamine levels in the neostriatum. Similar decreases in dopamine metabolites or their ratios were found in the ventral mesencephalon, septum, and frontoparietal cortex but not the thalamus. In addition to its effects on dopamine, apomorphine decreased norepinephrine in the ventral neostriatum and 5-HT and 5-HIAA in the cortex. Correlations between behavioral activity and neurochemical metabolism (using the metabolite-transmitter ratios for the latter) revealed relationships between locomotion and serotonergic activity in the thalamus of animals treated with amphetamine. Evidence for a relationship between locomotion or rearings and dopaminergic activity was found in all six brain areas analyzed. Here, the pattern of correlation was dependent on the kind of treatment and the behavioral and neurochemical measures. These results support earlier findings on the neurochemical effects of apomorphine and amphetamine in the neostriatum and ventral mesencephalon, and add new evidence for an action on the septal area, thalamus, and frontoparietal cortex.

Changes in the nigrostriatal projection associated with recovery from lesion-induced behavioral asymmetry

Possible neuronanatomical changes correlated with recovery from lesion-induced behavioral asymmetry were examined. Rats, with 6-OHDA injected into the substantia nigra (SN) on one side, were either assigned to a group with a 48-hour survival period, or one with a 15-day recovery period. Control groups, without a lesion, were also included. All animals were tested for behavioral asymmetry and, at the end of the survival period, had horseradish peroxidase (HRP) deposited in the caudate-putamen (CPU) ipsilateral to the lesion (right or left CPU in the controls). Both substantia nigrae of all animals were examined for HRP-labeled cells. Animals given a 15-day recovery period had more HRP-labeled cells in the SN ipsilateral to the HRP deposition site than those given a 1-day recovery period. Also animals which showed behavioral recovery had more HRP-labeled cells in their ipsilateral SN than either those which showed no recovery or those which were not given time to recover. Thus, our results suggested that behavioral recovery from lesion-induced asymmetry was associated with an increase in HRP uptake and retrograde transport by the remaining nigrostriatal terminals. Animals which recovered showed the expected decrease in ipsiversive, and increase in contraversive turning with time. Unexpectedly, animals which did not recover exhibited an increase in ipsiversive, and a decrease in contraversive turning with time.

Possible interaction between the inferior colliculus and the substantia nigra in audiogenic seizures in Wistar rats

Male Wistar rats were tested for sensitivity to audiogenic seizures (AS; 110 dB), using an audiogenic severity index (SI). Sensitive (S) animals were subjected to bilateral lesion of the inferior colliculus (IC) and/or the lateral lemniscus (LL). Resistant (R) animals were subjected to bilateral lesions of the IC, unilateral sequential lesions of the substantia nigra reticulata (SN) and/or IC (contralateral to one another), and unilateral thalamic and sham lesions. Bilateral lesions of the IC and LL abolish AS in S rats. Lesion of the SN resulted in more pronounced sensitivity to AS than unilateral lesion of IC, in R rats. When the SN lesion was contralateral to a previous IC lesion, the effect was not only an increase in the SI, but also a reversal of the asymmetry generated by IC lesion. Although the behavioral effects resulting from IC lesions are due to alterations in the primary structures involved in the origin of AS, unilateral SN lesions can alter critical substrates of sensorimotor integration involved in the control and expression of AS.

Asymmetries in thigmotactic scanning: evidence for a role of dopaminergic mechanisms

In two experiments, the influence of spontaneous asymmetries in thigmotactic scanning was analyzed on spontaneous and drug-induced behavior in the rat. The side of the face with which an animal performed more scanning in a baseline test was defined as the dominant vibrissae side. In experiment 1, repeated testing of either spontaneous thigmotactic scanning, or scanning after apomorphine or amphetamine, yielded no evidence that rats would preferably use one side of the face for scanning, when re-exposed to the same environment. However, an asymmetry in turning was observed both under apomorphine and amphetamine, that is, turning away from the dominant vibrissae side. In experiment 2, an influence of spontaneous asymmetries in scanning was found on behavioral asymmetries induced by unilateral vibrissae removal. Only animals, in which the vibrissae of the non-dominant side had been removed, showed more scanning with the intact vibrissae side, both undrugged and after apomorphine. Turning under apomorphine was more pronounced in animals in which the vibrissae on the dominant side had been removed. These animals showed an asymmetry in turning towards the intact vibrissae side. Furthermore, in both experiments we found evidence for left/right differences in turning or scanning. The results are discussed with respect to possible endogenous substrates of asymmetry, such as within the mesostriatal dopamine system.

The basal ganglia-orofacial system: studies on neurobehavioral plasticity and sensory-motor tuning

We have employed the unilateral removal of the vibrissae as a tool to examine ensuing behavioral changes in relation to concomitant changes in the central nervous system. In this paper we review a series of studies showing that unilateral removal of the vibrissae leads to behavioral asymmetries (e.g., in thigmotactic scanning) from which rats recover over time. Time-related to these behavioral changes we found neuronal alterations in striatal afferents, that is, in uncrossed and crossed projections from the substantia nigra and the tuberomammillary nucleus. The involvement of dopaminergic mechanisms was indicated by results showing that dopaminergic agonists can induce asymmetries in thigmotactic scanning and turning; the direction of these asymmetries was also dependent on time after vibrissae removal. Furthermore, it was shown that endogenous preferential use of one vibrissae side in thigmotactic scanning interacts with the expression of spontaneous and drug-induced behavioral asymmetries exhibited after unilateral vibrissae removal. Neurochemical studies indicated that both unilateral vibrissae removal and unilateral perioral stimulation can have lateralized effects on biogenic amines in the brain. Finally, using electrical stimulation of the substantia nigra, evidence was found for a lateralized and bidirectional interaction between basal ganglia and the orofacial systems, indicating an involvement in mechanisms of motivation and particular stimulation. These results are important from several perspectives. One, they indicate functional links between the orofacial systems and the basal ganglia. Two, they raise the possibility that unilateral removal of the vibrissae can serve as a model (a) to investigate the dynamics of recovery of function after CNS insults, in general, and specifically, (b) to study neuronal plasticity in the nigrostriatal and tuberomammillary-striatal pathways, and (c) to investigate the neuropharmacology of catecholamine systems in the brain.

Asymmetries in crossed and uncrossed nigrostriatal projections dependent on duration of unilateral removal of vibrissae in rats

The influence of unilateral removal of vibrissae on the crossed and uncrossed nigrostriatal projections was examined with the horseradish peroxidase tract tracing technique. Hemivibrissotomy mainly affected the projections arising from the rostral part of the substantia nigra. One to three days after clipping the vibrissae, rats were found to have more labeled neurons in the crossed projection to the caudate-putamen (CPU) on the same side as vibrissae removal than in the crossed projection to the CPU opposite to vibrissae removal. A reversed asymmetry was seen in rats examined 4-20 days after vibrissae removal. These animals had more labeled cells in the crossed and uncrossed projections terminating in the CPU opposite to the shaved side, i.e. in the hemisphere deprived of vibrissal sensory input. This time-course of neural alterations is similar to that of the recovery from behavioral asymmetries seen after hemivibrissotomy. Similar time-dependent alterations in the nigrostriatal projection had been found after unilateral injection of 6-OHDA into the substantia nigra.

Ventral mesencephalic neurons containing both cholecystokinin- and tyrosine hydroxylase-like immunoreactivities project to forebrain regions

The coexistence of cholecystokinin- and tyrosine hydroxylase-like immunoreactivities within neurons of the rat ventral mesencephalon was analyzed by using an indirect immunofluorescence technique for the simultaneous demonstration of two antigens in the same tissue section. A high degree of colocalization was observed in the substantia nigra pars compacta, in which 80-90% of all labeled neurons at rostral and up to 70% at intermediate levels contained both cholecystokinin and tyrosine hydroxylase. At caudal levels, the incidence of colocalization declined to approximately 30-50%. All of the immunoreactive perikarya in the substantia nigra pars lateralis were labeled with both substances. Other areas of the ventral midbrain that exhibited a moderate proportion of neurons immunoreactive for both cholecystokinin and tyrosine hydroxylase included the ventral tegmental area, interfascicular nucleus, and rostral and caudal linear nuclei. In addition, coexistence was occasionally observed within neurons of the central and ventral periaqueductal gray matter, supramammillary region, peripeduncular region, retrorubral field, and extremely rarely, within the substantia nigra pars reticulata. Cell bodies containing tyrosine hydroxylase-like immunoreactivity (indicative of dopamine) usually outnumbered those containing the peptide except in the supramammillary region and in the ventral periaqueductal gray matter, where the cholecystokinin perikarya were present in higher numbers. The double-labeling colocalization technique was combined with fluorescence retrograde tracing to determine some of the forebrain projections of these neurons. Ventral midbrain neurons containing both cholecystokinin and tyrosine hydroxylase were found to project to the caudate-putamen, nucleus-accumbens, prefrontal cortex, and amygdala. These projections originated from neurons located predominantly in the substantia nigra pars compacta and the ventral tegmental area. Thus, cholecystokinin occurs within the well-known dopaminergic nigrostriatal pathway in the rat. Overall, these results demonstrate that a significant proportion of the dopamine neurons giving rise to the ascending mesotelencephalic projections also contain the peptide cholecystokinin.

Video image analysis of behavior by microcomputer: categorization of turning and locomotion after 6-OHDA injection into the substantia nigra

The automated video image analyzing system (VIAS) measures locomotion in meters and turning behavior of rats by digitized video image and microcomputer evaluation. To measure turning behavior the number of 1/4, 1/2, 3/4 and complete turns are recorded. The turns are classified in different diameter classes. To test the validity of this system rats were administered unilateral 6-OHDA lesions of the substantia nigra and were observed by human rater and VIAS in parallel. Correlation coefficients for the data obtained by both methods were r = 0.98 for locomotion, r = 0.93 for half turns with diameter greater than or equal to 30 cm. Recovery from lesion-induced turning of animals with striatal dopamine depletion of 81.4% to 87.2% was described in detail by VIAS with respect to the diameter of the turns. It is concluded that VIAS provides a potent tool for the analysis of turning behavior and locomotion.

Amygdala kindling modifies interhemispheric dopaminergic asymmetry

Brain dopamine is known to retard the development of kindled seizures, but it is uncertain whether kindling affects dopamine function. In the present study, rats were screened for cerebral dominance by recording their preferred direction of rotation when injected with d-amphetamine. Bipolar stimulating electrodes were then implanted in the amygdaloid complex of either the dominant or nondominant hemisphere (i.e., respectively, contra- and ipsilateral to the preferred direction of rotation; the dominant hemisphere identified in this way has been shown to contain higher concentrations of dopamine than the nondominant hemisphere). Kindling stimulation (or sham-kindling, in control rats) was applied through the electrodes two or three times daily for 21 days, and the rats were reassessed for amphetamine- and apomorphine-induced rotation, during and after the course of treatment. Kindling of the originally dominant hemisphere caused a diminution of rotational asymmetry as measured in tests 2 to 3 h after stimulation sessions, and in some rats led to a reversal in the preferred direction of amphetamine-induced rotation. Kindling of the nondominant hemisphere tended to accentuate the original amphetamine-induced asymmetry. The direction of rotation induced by a direct postsynaptic DA-receptor agonist (apomorphine) was not significantly affected by kindling of either hemisphere. It appears that kindling stimulation brings about a relatively inferior level of DA function on the stimulated vs. the nonstimulated side of the brain, and that this process depends mainly on changes occurring at a presynaptic level.

Neuronal plasticity in the nigrostriatal system of the rat after unilateral removal of vibrissae

The vibrissae of rats were shaved from one side of the face daily for 10 days. To see whether or not this treatment had an effect on crossed and uncrossed striatal afferent connections from the midbrain, the tract tracer horseradish peroxidase was applied to the caudate-putamen on day 11. When the tracer was deposited on the side opposite the vibrissae removal, more labeled cells were found in the contralateral substantia nigra than when it was applied on the same side as the vibrissae removal, or placed in animals with intact vibrissae. Unilateral removal of vibrissae did not affect uptake of the tracer by the cells which give rise to the homolateral nigrostriatal projections. These changes in HRP labeling in the crossed projection from the substantia nigra were seen after 10 days of unilateral removal of the vibrissae; i.e., at a time when the animals have had opportunity to learn to compensate for vibrissotomy-induced behavioral asymmetries.

Dissociation of crossed and uncrossed nigrostriatal projections with respect to site of origin in the rat

In the present study we have investigated the relative rostrocaudal position of the neurons in the substantia nigra, which project to the ipsilateral or contralateral neostriatum. The retrograde tract tracer horseradish peroxidase was implanted into the striatum on one side. The substantia nigra, ventral tegmental area and retrorubral area ipsilateral and contralateral to the site of implantation were examined for labeled cells. The distributions of the cells which give rise to the crossed and uncrossed nigrostriatal projections were found to be inverse. More labeled cells were found in the rostral than the caudal part of the substantia nigra ipsilateral to the site of horseradish peroxidase implantation. In contrast, there was a greater likelihood of finding labeled cells in the middle and caudal parts of the contralateral substantia nigra than in the rostral part. Sparse projections from the ipsilateral and contralateral retrorubral area and ventral tegmental area were also found.

Lack of relationship between the direction of operant turning and horseradish peroxidase uptake by crossed nigro-striatal projections

We examined the effect of training rats to perform an operant turning response on the crossed nigro-striatal projections. Rats were reinforced for circling behavior with water. After 7 days of reinforced circling, the animals were implanted with horseradish peroxidase in the striatum either ipsilateral or contralateral to the direction in which they had been trained to turn. Subsequently, the substantia nigra, ventral tegmental area, and retrorubral area in both hemispheres were examined for labeled cells. This analysis failed to reveal any relationship between the direction of reinforced circling and efferents from these areas to the striatum.

Effect of forebrain commissurotomy on recovery from unilateral 6-OHDA lesions of the substantia nigra and circling induced by apomorphine

We studied the influence of transection of the interhemispheric fiber systems between the anterior and posterior commissures on recovery from turning behavior induced by a unilateral substantia nigra lesion in rats. It has been argued that the crossed nigrostriatal projection is involved in this recovery, and its site of crossing has been suggested to lie within the region split. Animals which received this transection did not differ from controls with respect to time-course and extent of recovery from lesion-induced asymmetries within the 7 postlesion days examined. Additionally, the commissurotomy did not prevent apomorphine-induced contraversive circling.