The relationship between loss of dopamine nerve terminals, striatal [3H]spiroperidol binding and rotational behavior in unilaterally 6-hydroxydopamine-lesioned rats

Simultaneous Measurement of Striatal Dopamine and Hydrogen Peroxide Transients Associated with L-DOPA Induced Rotation in Hemiparkinsonian Rats

Parkinson's disease (PD) is a neurodegenerative disorder commonly treated with levodopa (L-DOPA), which eventually induces abnormal involuntary movements (AIMs). The neurochemical contributors to these dyskinesias are unknown; however, several lines of evidence indicate an interplay of dopamine (DA) and oxidative stress. Here, DA and hydrogen peroxide (H2O2) were simultaneously monitored at discrete recording sites in the dorsal striata of hemiparkinsonian rats using fast-scan cyclic voltammetry. Mass spectrometry imaging validated the lesions. Hemiparkinsonian rats exhibited classic L-DOPA-induced AIMs and rotations as well as increased DA and H2O2 tone over saline controls after 1 week of treatment. By week 3, DA tone remained elevated beyond that of controls, but H2O2 tone was largely normalized. At this time point, rapid chemical transients were time-locked with spontaneous bouts of rotation. Striatal H2O2 rapidly increased with the initiation of contraversive rotational behaviors in lesioned L-DOPA animals, in both hemispheres. DA signals simultaneously decreased with rotation onset. The results support a role for these striatal neuromodulators in the adaptive changes that occur with L-DOPA treatment in PD and reveal a precise interplay between DA and H2O2 in the initiation of involuntary locomotion.

Context-driven changes in L-DOPA-induced behaviours in the 6-OHDA lesioned rat

Both contralateral rotational behaviour and dyskinetic abnormal involuntary movements (AIMs) are induced by the administration of l-DOPA in the unilateral 6-OHDA lesioned rat model of Parkinson's disease. Since rotational responses can be conditioned to environmental cues we have investigated the extent to which drug-induced AIMS may also be conditioned by exteroceptive cues and experience. In Experiment I, 6-OHDA lesioned rats received repeated daily injections of l-DOPA either in their home cage (control) or in association with a brief (20 mins) exposure to the rotometers (paired). To assess conditioning, all animals then received two tests in the rotometer bowls. Following injection of saline the paired group both rotated more contralaterally and displayed manifest AIMs, neither of which were exhibited by the control rats. Moreover, following injection of l-DOPA, the paired group showed a trend for increased AIMs compared to controls. Two further studies provided longer exposure to the conditioning environments in counterbalanced designs. Although, using these parameters, re-exposure in the presence of saline did not induce context-dependent AIMs, a strong context-specific component of the sensitised response to l-DOPA was seen; chronic administration of drug produced a significantly stronger behavioural response in animals paired with a particular environment for drug administration than controls. This data suggests that part of the sensitisation of behavioural responding to l-DOPA administration is not solely a pharmacological phenomenon, but is also conditioned to the environmental context in which the drug is administered. This has clear implications for the clinical observation and experimental measurement of drug-induced dyskinesia in Parkinson's disease patients and animal models.

Different striatal D2-like receptor function in an early stage after unilateral striatal lesion and medial forebrain bundle lesion in rats

Unilateral striatal lesion and complete medial forebrain bundle (MFB) lesion by 6-hydroxydopamine in rats have been widely used as Parkinson disease (PD) models. However, the difference of pre- and post-synaptic dopamine (DA) system in these two models are not well concerned. In order to investigate the pathophysiologic difference between the MFB lesion rats and striatal lesion rats, we studied the variation of pre-synaptic DA transporter and post-synaptic D(2)-like receptor in nigrostriatal DA system using binding assay, behavioral test and a small animal PET. Our data showed that there was a same tendency of the striatal DA transporter decrease both in MFB lesion rats and striatal lesion rats 4 weeks after lesion, however, it showed increase (up-regulation) of D(2)-like receptor in the MFB lesion rats, whereas showed decrease (down-regulation) in the striatal lesion rat. This finding strongly indicated the different dynamic pathophysiologic process between the MFB lesion model and striatal lesion model. MFB lesion model mimics an early stage of PD, whereas striatal lesion model mimics Parkinson syndrome, such as vascular Parkinson syndrome. Such difference should be taken into account in the selection of these model systems.

The stepping test and its learning process in different degrees of unilateral striatal lesions by 6-hydroxydopamine in rats

Four different levels of the nigrostriatal dopamine system lesions were produced by injections of 6-hydroxydopamine at one-, two-, three-, or four-sites in the striatum and drug-induced rotational movement and stepping test were performed to evaluate behavioral impairments in the rat model of Parkinson's disease. A dose-dependent progressive loss of tyrosine hydroxylase-positive cells in the substance nigra pars compacta was observed in rats with striatal lesion from one- to four-sites. Though the differences in the rotational behavior and stepping test between the lesioned and control rats were highly significant, there were no differences in those behaviors among four groups of lesioned rats. During observation of these behavioral tests, the authors found that the times of trials required for acquisition of the stepping test on the first day of training, which reflected learning acuity, increased in a dose-dependent manner in the lesioned rats as compared with the controls. On the contrary, the times of trials on the next day and in the next week, which reflected retention of the acquired memories, were not different among the groups. In conclusion, the rotational movement and stepping test were not sensitive enough to distinguish severity of the striatal lesions, and learning acuity, but not retention of memories, was disturbed by the striatal lesions.

Olfactory ensheathing glial co-grafts improve functional recovery in rats with 6-OHDA lesions

Olfactory ensheathing cells (OEC) transplanted to the site of a spinal cord injury can promote axonal sparing/regeneration and functional recovery. The purpose of this study was to investigate if OEC enhance the effects of grafted dopamine-neuron-rich ventral mesencephalic tissue (VM) in a rodent model of Parkinson's disease. We co-grafted VM with either OEC or astrocytes derived from the same olfactory bulbs as the OEC to rats with a unilateral 6-hydroxydopamine lesion of the nigrostriatal system. Co-grafting fetal VM with OEC, but not with astrocytes enhanced dopamine cell survival, striatal reinnervation and functional recovery of amphetamine- and apomorphine-induced rotational behaviour compared with grafting embryonic VM alone. Grafting OEC or astrocytes alone had no effects. Intriguingly, only in the presence of OEC co-grafts, did dopamine neurons extend strikingly long neurites that reached peripheral striatal compartments. Comparable results were observed in a co-culture system where OEC promoted dopamine cell survival and neurite elongation through a mechanism involving both releasable factors and direct contact. Cell type analysis of fetal VM grafts suggested that dopamine neurons of the substantia nigra rather than of the ventral tegmental area were increased in the presence of OEC co-grafts. We conclude that the addition of OEC enhances efficacy of grafted immature dopamine neurons in a rat Parkinson's disease model.

Behavioral differences in a rotenone-induced hemiparkinsonian rat model developed following intranigral or median forebrain bundle infusion

A mitochondrial complex-I inhibitor, rotenone was unilaterally infused into the substantia nigra pars compacta (SNpc) or median forebrain bundle (MFB) to create hemiparkinsonian animal models and investigated spontaneous and drug-induced stereotypic rotations, as well as certain postural behaviors in Sprague-Dawley rats. Animals infused intranigrally, but not intra-MFB, with rotenone exhibited spontaneous contralateral rotations immediately after recovery from anesthesia. Head position bias and elevated body swing test showed insignificant contralateral bias in animals with nigral damage but a significant ipsilateral bias in MFB-lesioned rats. General motor activity of the animals was reduced in both the groups as indicated by reduced performance on a Plus-Maze. Intranigrally, rotenone-infused animals exhibited progressive ipsilateral rotations when challenged with d-amphetamine on the 7th, 14th, 21st, and 28th days or with apomorphine on 9th, 16th, 23rd, and 30th days. However, animals that received rotenone in MFB exhibited ipsilateral or contralateral rotations when challenged respectively with d-amphetamine or apomorphine only in the 5th week (28th and 30th days). Stereotaxic administration of rotenone into SNpc or MFB caused a significant loss of dopamine in the ipsilateral striatum (>80% in SNpc; >95% in MFB), when assayed employing an HPLC equipped with electrochemical detector on the 32nd day. Neuronal loss in SNpc was confirmed in coronal sections stained with cresyl violet and revealed extension of lesion towards SN pars reticulata, in SNpc-infused animals. Our results demonstrate that rotenone-induced neurodegeneration is a slow, yet progressive process similar to that in idiopathic Parkinson's disease and unlike that observed in other classical neurotoxin-mediated lesions which are abrupt and developed in few hours to days. Thus, intranigral or intra-MFB infusion of rotenone could be used for producing hemiparkinsonian animal models in rats. These findings further suggest that, while both d-amphetamine and apomorphine-induced stereotypic rotations could be used as a valuable behavioral assay procedure to test novel drugs against Parkinson's disease, yet apomorpine-induced contralateral bias in turning is a reliable indicator of specific destruction in nigrostriatal pathway and development of postsynaptic dopamine receptor supersensitivity.

Pharmacokinetic and pharmacodynamic analyses, based on dopamine D2-receptor occupancy of bromocriptine, of bromocriptine-induced contralateral rotations in unilaterally 6-OHDA-lesioned rats

Bromocriptine is a selective agonist for dopamine D2-receptors and is used in the treatment of Parkinson's disease. In this study, we performed pharmacokinetic and pharmacodynamic (PK/PD) analyses of the antiparkinsonian effect of bromocriptine and evaluated drug-induced contralateral rotations in rats in which unilateral striatal lesions had been generated by microinjection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle. The plasma concentration (Cp) and D2 receptor occupancy (Phi(D2)) were quantitated by HPLC and with an in vivo back-titration method using [(3)H]-raclopride, respectively. Bromocriptine induced contralateral rotations (E(rot)) in a dose-dependent manner following intraperitoneal administration in an animal model of Parkinson's disease. The Cp of bromocriptine peaked at 15-30 min after the administration and decreased time-dependently, whereas the Phi(D2) of bromocriptine increased gradually for 180 min after administration. The relationship between Cp and E(rot) exhibited an anticlockwise hysteresis, whereas the relationship between Phi(D2) and E(rot) showed a linear correlation. These results suggest that in vivo Phi(D2) is a good pharmacological indicator of the effect of a D2 agonist.

A role for presynaptic mechanisms in the actions of nomifensine and haloperidol

Psychomotor stimulants and neuroleptics exert multiple effects on dopaminergic signaling and produce the dopamine (DA)-related behaviors of motor activation and catalepsy, respectively. However, a clear relationship between dopaminergic activity and behavior has been very difficult to demonstrate in the awake animal, thus challenging existing notions about the mechanism of these drugs. The present study examined whether the drug-induced behaviors are linked to a presynaptic site of action, the DA transporter (DAT) for psychomotor stimulants and the DA autoreceptor for neuroleptics. Doses of nomifensine (7 mg/kg i.p.), a DA uptake inhibitor, and haloperidol (0.5 mg/kg i.p.), a dopaminergic antagonist, were selected to examine characteristic behavioral patterns for each drug: stimulant-induced motor activation in the case of nomifensine and neuroleptic-induced catalepsy in the case of haloperidol. Presynaptic mechanisms were quantified in situ from extracellular DA dynamics evoked by electrical stimulation and recorded by voltammetry in the freely moving animal. In the first experiment, the maximal concentration of electrically evoked DA ([DA](max)) measured in the caudate-putamen was found to reflect the local, instantaneous change in presynaptic DAT or DA autoreceptor activity according to the ascribed action of the drug injected. A positive temporal association was found between [DA](max) and motor activation following nomifensine (r=0.99) and a negative correlation was found between [DA](max) and catalepsy following haloperidol (r=-0.96) in the second experiment. Taken together, the results suggest that a dopaminergic presynaptic site is a target of systemically applied psychomotor stimulants and regulates the postsynaptic action of neuroleptics during behavior. This finding was made possible by a voltammetric microprobe with millisecond temporal resolution and its use in the awake animal to assess release and uptake, two key mechanisms of dopaminergic neurotransmission. Moreover, the results indicate that presynaptic mechanisms may play a more important role in DA-behavior relationships than is currently thought.

Relationships between various behavioural abnormalities and nigrostriatal dopamine depletion in the unilateral 6-OHDA-lesioned rat

While rotational asymmetry is used as a characteristic behavioural sign of striatal dopamine (DA) loss in unilateral animal models of Parkinson's disease (PD), there is relatively little analysis of how other common behavioural deficits relate to nigrostriatal DA depletion. We analysed the relationships between several deficits induced by unilateral 6-OHDA lesions and striatal neurochemistry, as well as neuronal loss in the dopaminergic substantia nigra (SN). Behaviour was evaluated from before until 6 weeks after surgery and abnormalities appeared in body axis, head position and sensorimotor performance as well as apomorphine-induced rotation. As expected, rotational behaviour correlated with striatal DA loss and not with other striatal neurotransmitters measured. Similar observations were found for sensorimotor deficits ('disengage task'). Both deficits were observed in rats with >70% loss of TH+ nigral neurons and >80% loss of striatal DA. Additional postural abnormalities appeared with mean losses of 87% of nigral DA neurons and 97% striatal DA, consistent with observations in patients with advanced PD. The data show that the repertoire of behavioural abnormalities manifested by hemiparkinsonian rats relate directly to the degree of nigrostriatal DA loss and, therefore, mimic features of PD. Analysis of such behaviours are relevant for chronic therapeutic studies targeting PD.

Dopamine depletion causes fragmented clustering of neurons in the sensorimotor striatum: evidence of lasting reorganization of corticostriatal input

Firing during sensorimotor exam was used to categorize single neurons in the lateral striatum of awake, unrestrained rats. Five rats received unilateral injection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle to deplete striatal dopamine (DA; >98% depletion, postmortem assay). Three months after treatment, rats exhibited exaggerated rotational behavior induced by L-dihydroxyphenylalanine (L-DOPA) and contralateral sensory neglect. Electrode track "depth profiles" on the DA-depleted side showed fragmented clustering of neurons related to sensorimotor activity of single body parts (SBP neurons). Clusters were smaller than normal, and more SBP neurons were observed in isolation, outside of clusters. More body parts were represented per unit volume. No recovery in these measures was observed up to one year post lesion. Overall distributions of neurons related to different body parts were not altered. The fragmentation of SBP clusters after DA depletion indicates that a percentage of striatal SBP neurons switched responsiveness from one body part to one or more different body parts. Because the specific firing that characterizes striatal SBP neurons is mediated by corticostriatal inputs (Liles and Updyke [1985] Brain Res. 339:245-255), the data indicate that DA depletion resulted in a reorganization of corticostriatal connections, perhaps via unmasking or sprouting of connections to adjacent clusters of striatal neurons. After reorganization, sensory activity in a localized body part activates striatal neurons that have switched to that body part. In turn, switched signals sent from basal ganglia to premotor and motor neurons, which likely retain their original connections, would create mismatches in these normally precise topographic connections. Switched signals could partially explain parkinsonian deficits in motor functions involving somatosensory guidance and their intractability to L-DOPA therapy-particularly if the switching involves sprouting.

Evidence for Target-Specific Nerve Fiber Outgrowth from Subpopulations of Grafted Dopaminergic Neurons: A Retrograde Tracing Study Using in Oculo and Intracranial Grafting

Efforts have been made to counteract the symptoms of Parkinson's disease by substituting the loss of dopaminergic neurons with fetal ventral mesencephalic grafts. One of the postulated limiting factors in this treatment is the relatively poor cell survival and limited graft-derived fiber outgrowth. Recent results documenting enhanced survival of grafted dopaminergic neurons showed no positive correlation to enhanced innervation of the striatal target. Therefore this study was undertaken to investigate whether all surviving grafted dopaminergic neurons projected to the striatal target. Hence, fetal ventral mesencephalic tissue was implanted adjacent to mature versus immature striatal tissue using in oculo and intraventricular grafting techniques. In in oculo grafting, fetal ventral mesencephalon was implanted simultaneously with fetal lateral ganglionic eminence (immature striatal target) or to already matured striatal in oculo grafts (mature striatal target). Furthermore, fetal ventral mesencephalon was implanted into the lateral ventricle adjacent to mature dopamine-depleted striatum. The retrograde tracer fluorogold was injected into the striatal portion of the in oculo cografts and into reinnervated areas of the adult brain. Immunohistochemistry revealed that a significantly larger proportion of tyrosine hydroxylase-positive neurons in the ventral mesencephalic graft was innervating in oculo immature striatal tissue, and hence was fluorogold-positive, in comparison with the number of tyrosine hydroxylase-positive neurons innervating mature striatal tissue. Moreover, intracranial transplantations showed that tyrosine hydroxylase-positive neurons were distributed within the grafts in dense clusters of cells. In most clusters tyrosine hydroxylase-positive cells were fluorogold-negative but calbindin-positive. In a few tyrosine hydroxylase-positive cell clusters, neurons were coexpressing fluorogold but were calbindin-negative. In conclusion, significantly more dopamine neurons projected to immature than to mature striatal tissue and thus, a subpopulation of grafted dopaminergic neurons was not projecting into adult striatum. Thus, the results from this study show that further attempts to enhance survival of grafted dopamine neurons in purpose to enhance graft-derived fiber outgrowth and efficacy should also consider different subtypes of dopamine neurons.

Nigrostriatal dopaminergic denervation enhances dopamine D(4) receptor binding in rat caudate-putamen

Radioligand binding to dopamine (DA) D(4) receptors was examined in adult rat forebrain 5 weeks after unilateral 6-hydroxydopamine (6-OHDA) lesioning of substantia nigra to remove ascending nigrostriatal dopaminergic projections. D(4) receptor binding was increased by up to 47% in denervated caudate-putamen (CPu) in rats that rotated away from the lesioned side with apomorphine challenge, with lesser changes in rats that failed to rotate with apomorphine. Functional significance of D(4) receptor upregulation induced by the lesions was investigated by examining behavioral effects of the highly selective D(4) agonist CP-226,269 and antagonist CP-293,019. Neither agent induced rotation at doses as high as 30 mg/kg ip. Pretreatment with the D(4) antagonist CP-293,019 did not affect rotation induced by either a D(1)-like (SKF-38393) or D(2)-like receptor (quinpirole) agonist. These findings provide the first evidence that D(4) receptors can be upregulated by nigrostriatal dopaminergic denervation. They also suggest that, unlike D(1) and D(2) receptors, D(4) receptors do not play a pivotal role in rotational behavior in rats with unilateral dopaminergic lesions.

Partial, graded losses of dopamine terminals in the rat caudate-putamen: an animal model for the study of compensatory adaptation in preclinical parkinsonism

Procedures to lesion dopamine (DA) neurons innervating the rat caudate-putamen (CP) in a partial, graded fashion are described in this study. The goal is to provide a lesion model that supports intra-animal comparisons of voltammetric recordings used to investigate compensatory adaptation of DA neurotransmission. Lesions exploited the topography of mesostriatal DA neurons, microinjections of the neurotoxin 6-hydroxydopamine (6-OHDA) into the medial and lateral edges of the ventral mesencephalon containing DA cell bodies and microdissection of the CP into six regions. Analysis of tissue DA content in these regions by HPLC-EC demonstrated that 6-OHDA injected into the lateral substantia nigra results in a significantly greater loss of DA in lateral versus medial regions of the CP. The direction of the graded loss of DA was reversed (i.e. a medial to lateral lesion gradient) by the injection of 6-OHDA into the ventral tegmental area near the medial SN. Extracellular concentrations of electrically evoked DA could be measured across the mediolateral axis of the CP in a single animal using the technique of in vivo voltammetry. More importantly, graded decreases in the amplitude of evoked DA levels generally followed the direction of the tissue DA gradient in lesioned animals. These results suggest that the graded loss of DA terminals in the CP, coupled to a spatially and temporally resolved technique for monitoring extracellular DA, is a viable tool for investigating compensatory adaptation in the mesostriatal DA system.

The effect of intrastriatal single injection of GDNF on the nigrostriatal dopaminergic system in hemiparkinsonian rats: behavioral and histological studies using two different dosages

Glial cell line-derived neurotrophic factor (GDNF) is a member of the transforming growth factor-beta superfamily and acts as a neurotrophic factor for the nigrostriatal dopamine (DA) system. Although previous studies have shown that pretreatment with GDNF could prevent degenerative changes of nigrostriatal DA system by DA neurotoxin 6-hydroxydopamine (6-OHDA), it is not really known whether GDNF can induce recovery of nigrostriatal DA system after partial lesioning by 6-OHDA. Substantia nigra has been commonly chosen as injection site for GDNF but a limited number of studies have used striatum as injection site where neural transplantation is commonly performed. Unilateral intrastriatal administration of 6-OHDA was performed in Sprague-Dawley rats to create partial lesion of the nigrostriatal DA system. These hemiparkinsonian model rats received a 10- or 100-microg single injection of human recombinant GDNF into the same portion of the striatum 4 weeks after 6-OHDA treatment. Both animals that received a 10- or 100-microg single injection of GDNF showed decreased apomorphine-induced rotation at 2 weeks after injection. More potent and prolonged functional recovery was observed in animals receiving 100 microg of GDNF than in those receiving 10 microg of GDNF. Tyrosine hydroxylase (TH) immunocytochemistry revealed that TH positive DA fiber density in the striatum and the number of DA cell bodies in the substantia nigra were greater in animals receiving 10 or 100 microg of GDNF than those receiving saline. These immunocytochemical results have also shown that 100 microg of GDNF was more potent than 10 microg of GDNF. These morphological and functional results indicate that GDNF treatment 4 weeks after 6-OHDA lesioning could induce recovery of nigrostriatal DA system. Striatum was a good site for GDNF administration for hemiparkinsonian rats and a single injection of 100 microg of GDNF was more potent than 10 microg of GDNF.

N-type calcium channel blockers - tools for modulation of cerebral functional units?

According to in vitro and in vivo studies, the direct application of N-type calcium channel blockers as for instance omega-conotoxin GVIA (omega-ctx) potently inhibits the release of neurotransmitters like dopamine. To find out whether this effect could be used for modulation of neurological functions, omega-ctx was used for continuous infusion into the functionally well characterized rat striatum. Over the 2-week time course of intrastriatal application, rats developed a decrease in spontaneous motor activity, spontaneous rotational asymmetry towards the side of application, and behavioral supersensitivity to apomorphine. After the end of infusion period, all functional deficits showed reversibility. The pattern of spontaneous neurological deficits - in particular supersensitivity to apomorphine - points to a substantial unilateral alteration of dopaminergic transmission due to omega-ctx, which is suggested also by an increase in dopamine receptor protein expression within the ipsilateral striatum. Time course and reversibility of neurological deficits caused by omega-ctx, as well as a lack of dopamine depletion contrast findings after selective destruction of dopaminergic neurons and support a functional modulation of dopaminergic transmission. The present study suggests that omega-ctx is an effective potent tool for the unilateral and reversible intracerebral modulation of neuronal circuits. Intracerebral application of omega-ctx could possibly open the way to therapeutic interventions.

Dopaminergic pharmacology and antioxidant properties of pukateine, a natural product lead for the design of agents increasing dopamine neurotransmission

The dopaminergic and antioxidant properties of pukateine [(R)-11-hydroxy-1,2-methylenedioxyaporphine, PUK], a natural aporphine derivative, were analyzed in the rat central nervous system. At dopamine (DA) D1 ([3H]-SCH 23390) and D2 ([3H]-raclopride) binding sites, PUK showed IC50 values in the submicromolar range (0.4 and 0.6 microM, respectively). When the uptake of tritiated dopamine was assayed by using a synaptosomal preparation, PUK showed an IC50 = 46 microM. In 6-hydroxydopamine unilaterally denervated rats, PUK (8 mg/kg but not 4 mg/kg) elicited a significant contralateral circling, a behavior classically associated with a dopaminergic agonist action. When perfused through a microdialysis probe inserted into the striatum, PUK (340 microM) induced a significant increase in dopamine levels. In vitro experiments with a crude rat brain mitochondrial suspension showed that PUK did not affect monoamine oxidase activities, at concentrations as high as 100 microM. PUK potently (IC50 = 15 microM) and dose-dependently inhibited the basal lipid peroxidation of a rat brain membrane preparation. As a whole, PUK showed a unique profile of action, comprising an increase in extracellular DA, an agonist-like interaction with DA receptors, and antioxidant activity. Thus, PUK may be taken as a lead compound for the development of novel therapeutic strategies for Parkinson disease.

Characterization of behavioral and neurodegenerative changes following partial lesions of the nigrostriatal dopamine system induced by intrastriatal 6-hydroxydopamine in the rat

Partial lesions of the nigrostriatal dopamine system have been investigated with respect to their ability to induce consistent long-lasting deficits in movement initiation and skilled forelimb use. In eight different lesion groups 6-hydroxydopamine (6-OHDA) was injected at one, two, three, or four sites into the lateral sector of the right striatum, in a total dose of 20-30 microgram. Impairments in movement initiation in a forelimb stepping test, and in skilled paw use in a paw-reaching test, was seen only in animals where the severity of the lesion exceeded a critical threshold, which was different for the different tests used: single (1 x 20 microgram) or two-site (2 x 10 microgram) injections into the striatum had only small affects on forelimb stepping, no effect on skilled paw use. More pronounced deficits were obtained in animals where the same total dose of 6-OHDA was distributed over three or four sites along the rostro-caudal extent of the lateral striatum or where the injections were made close to the junction of the globus pallidus. The results show that a 60-70% reduction in tyrosine hydroxylase (TH)-positive fiber density in the lateral striatum, accompanied by a 50-60% reduction in TH-positive cells in substantia nigra (SN), is sufficient for the induction of significant impairment in initiation of stepping. Impaired skilled paw-use, on the other hand, was obtained only with a four-site (4 x 7 microgram) lesion, which induced 80-95% reduction in TH fiber density throughout the rostrocaudal extent of the lateral striatum and a 75% loss of TH-positive neurons in SN. Drug-induced rotation, by contrast, was observed also in animals with more restricted presymptomatic lesions. The results indicate that the four-site intrastriatal 6-OHDA lesion may be a relevant model of the neuropathology seen in parkinsonian patients in a manifest symptomatic stage of the disease and may be particularly useful experimentally since it leaves a significant portion of the nigrostriatal projection intact which can serve as a substrate for regeneration and functional recovery in response to growth promoting and neuroprotective agents.

Somatic delivery of catecholamines in the striatum attenuate parkinsonian symptoms and widen the therapeutic window of oral sinemet in rats

Guidelines for clinical transplantation studies for Parkinson's disease emphasize that transplants should be considered as an adjunct to systemic L-DOPA, yet few preclinical studies have specifically assessed the potential of transplants as an adjunct to the clinical gold standard treatment. The objectives of the present study were to determine if encapsulated PC12 cells implanted in rats with severe unilateral dopamine depletions: (i) have a direct therapeutic effect on measures of parkinsonian symptoms; and/or (ii) increase the therapeutic window of oral sinemet in this model. Rats with severe unilateral dopamine depletions received striatal implants of encapsulated PC12 cells producing dopamine and L-DOPA. These rats were tested on a battery of behavioral measures of parkinsonian symptoms, at a range of doses of oral sinemet (0, 12, 24, and 36 mg/kg). Stereotypies/dyskinesias were also quantified after high doses of oral sinemet (36 and 50 mg/kg). The results confirm that parkinsonian symptoms can be quantified in rats with severe dopamine depletions, and the validity and clinical relevance of these measures are supported by the fact that the clinical gold standard treatment, oral sinemet, attenuates these parkinsonian symptoms. Somatic delivery of dopamine and L-DOPA, directly to the dopamine-depleted striatum, also attenuates parkinsonian symptoms. In fact, the magnitude of the therapeutic effect produced by continuous, site-specific, somatic delivery of dopamine and L-DOPA was larger than the effect produced by acute, systemic, oral sinemet. The beneficial effects of oral sinemet and striatal implants of catecholamine-producing devices were additive, but there were no adverse effects related to striatal catecholamine-producing devices, and these devices did not increase the adverse effects related to oral sinemet. Therefore, striatal implants of catecholamine-producing devices have direct therapeutic effects which are fairly robust, and they widen the therapeutic window of oral sinemet.

Infusions of tyrosine hydroxylase antisense oligodeoxynucleotide into substantia nigra of the rat: effects on tyrosine hydroxylase mRNA and protein content, striatal dopamine release and behaviour

Modulation of the transcriptional message of tyrosine hydroxylase was investigated in vivo in the rat nigrostriatal dopamine system with unmodified antisense oligodeoxynucleotide, mismatch oligodeoxynucleotide or vehicle controls. Oligodeoxynucleotide was infused (0.5 microgram/0.5 microliter/h) unilaterally into the substantia nigra by an osmotic minipump system over 14 days. The presence of oligodeoxynucleotide in the brain was verified by in situ hybridization and fluorescence labelling. Animals treated with unmodified antisense oligodeoxynucleotide showed ipsilateral turning behaviour when challenged systemically with the indirect dopamine agonist amphetamine, whereas mismatch- and vehicle-infused rats showed no such behavioural asymmetries. In the substantia nigra, antisense treatment had no effects on tyrosine hydroxylase mRNA, but it led to a reduction in tyrosine hydroxylase protein content. Tissue levels of dopamine, measured in postmortem tissue punches of the neostriatum and substantia nigra, were reduced in the oligodeoxynucleotide-treated hemisphere. Furthermore, basal extracellular levels of dopamine, monitored by in vivo microdialysis, were also lower in the neostriatum ipsilateral to antisense infusion and showed a weaker response to an amphetamine challenge when compared with the contralateral side. These effects were not observed after infusion of mismatch oligodeoxynucleotide or vehicle into the substantia nigra. Finally, the GABAergic enzyme glutamate decarboxylase was not affected in the antisense-treated substantia nigra, indicating that non-specific damage in this area was not caused by this treatment. Our results indicate that antisense oligodeoxynucleotide treatment against tyrosine hydroxylase in the substantia nigra has behavioural and neurochemical effects that are comparable with known actions of dopamine neurotoxins, which are conventional pharmacological tools for the depletion of dopamine. Furthermore, our data show the potential of antisense targetting to reveal new relationships between neurotransmitter-related enzymes and behavioural parameters, because the possibility of selectively and discretely manipulating tyrosine hydroxylase function is likely to produce new insights into the physiological and behavioural functions of the dopaminergic nigrostriatal system.

Pretreatment with neurokinin substance P but not with cholecystokinin-8S can alleviate functional deficits of partial nigrostriatal 6-hydroxydopamine lesion

The neuropeptide substance P (SP) has been implicated in the control of various neuro-behavioral functions including reinforcement and learning processes. It also exerts neurotrophic and regenerating effects in vitro and in vivo. A previous study indicated a potential therapeutic effect of SP in rats with partial 6-hydroxydopamine lesions of the nigrostriatal dopamine system when SP was administered after the lesion. The purpose of the present study was to determine whether prelesion treatment with SP would also interact with the effects of unilateral 6-hydroxydopamine lesion of the substantia nigra. Thus, SP (50 micrograms/kg) was administered i.p. on 8 consecutive days prior to unilateral lesion of the substantia nigra. Furthermore, we investigated the effects of prelesion treatment with cholecystokinin-8S (CCK; 1 microgram/kg), another neuropeptide, which is closely related to dopaminergic neurons, and which also can have neurotrophic and neuroprotective functions. Our results show that animals with partial neostriatal dopamine depletions (residual dopamine levels of more than 10%) did not show turning asymmetries when pretreated with SP, whereas animals pretreated with vehicle exhibited an initial ipsiversive asymmetry from which they recovered. In contrast, behavioral asymmetries were most pronounced in animals which had been pretreated with CCK. These peptide treatments did not affect the degree of neostriatal dopamine depletion; however, dihydroxyphenylacetic acid/dopamine ratios were enhanced in the neurostriatum of animals with partial dopamine damage after SP- and CCK-pretreatment, and in the ventral striatum of SP-pretreated animals. These data provide evidence that prelesion treatment with SP, but not with CCK, can alleviate functional deficits induced by a partial nigro-striatal dopamine lesion. This effect may be related to enhanced ventral striatal dopamine activity and/or to the peptide's known effects on learning, motivation, and emotion.

Dopaminergic control of light-adaptive synaptic plasticity and role in goldfish visual behavior

Dopamine has been implicated in processes of retinal light and dark adaptation. In goldfish retina, horizontal cell dendrites elaborate neurite processes (spinules) into cone terminals, in a light- and dopamine-dependent manner. However, the functions of retinal dopamine and the horizontal cell spinules in visual behavior are unknown. These issues were addressed in behavioral, electroretinographic, and anatomical studies of normal fish and those with unilateral depletion of retinal dopamine induced by intraocular (i.o.) injections with 6-hydroxydopamine (6-OHDA). Dopamine interplexiform cells (DA-IPC) disappear within 2 weeks after 6-OHDA injection; cell bodies appear at the marginal zone within 6 weeks at which time neurites slowly reinnervate the retina with a sparse plexus over the next 12 months. We found that dopamine depletion increased light sensitivity at photopic but not scotopic backgrounds by 2.5 log units, an effect mimicked by i.o. injections of dopamine D1 and D2 antagonists. The ERG b-wave increment thresholds were the same for control and dopamine depleted eyes, indicating a normal transition from rod to cone systems in the ON pathway. Light-dependent spinule formation was reduced by about 60% in dopamine-depleted retinas, but returned to normal by 3 months and 9 months after injection in the entire retina, even areas not directly innervated with DA-IPC processes. Spinule formation in vivo was inhibited 50% with i.o. injection of SCH 23390 in control retinas as well as throughout 3 month 6-OHDA injected retinas, including DA-IPC free areas. This latter result indicates a volume effect of dopamine, diffusing laterally through the retina over several millimeters, in regulating spinules. We conclude that DA-IPCs regulate sensitivity to background at photopic levels not via the ON pathway, but perhaps the OFF pathway. Goldfish display both increased sensitivity to light and a normal Purkinje shift in the ERG b-wave whether or not horizontal cell spinules are present, indicating that dopamine control of photopic vision in fish is not mediated through light-induced spinule formation of horizontal cell dendrites.

Decline in striatal dopamine D1 and D2 receptor activation in aged F344 rats

Aging differentially affects receptor function. In the present electrophysiological study we compared neuronal responsiveness to locally applied dopamine D1 and D2 receptor agonist in the striatum of female Fischer 344 rats aged 3 and 26-27 months. In a subgroup of the old rats, the nigrostriatal dopamine bundle was destroyed unilaterally with 6-hydroxydopamine (6-OHDA) to assess receptor plasticity in response to denervation. Spontaneous firing rate of striatal neurons was higher in aged compared to young rats. Higher doses of the D1 agonist SKF 38393 or the D2 agonist quinpirole were required to elicit a 50% change in firing rate in aged compared to young rats. No difference with SKF 38393 or quinpirole was detected between 6-OHDA denervated and control (nonlesioned) striatum in aged rats. Supersensitivity to D2 agonists has been reported following 6-OHDA lesions in young rats. These observations suggest that D2 receptors in aged rat striatum might not be as plastic as in younger rats.

Modulation of dopaminergic neurotransmission in the 6-hydroxydopamine lesioned rotational model by peptidomimetic analogues of L-prolyl-L-leucyl-glycinamide

Melanocyte stimulating hormone release inhibiting factor (MIF-1), also known as L-prolyl-L-leucyl-glycinamide (PLG), has previously been found to have the ability to modulate dopamine D2-receptor agonist binding both in the striatum and limbic regions. In the present study the 6-hydroxydopamine unilateral lesion model of apomorphine-induced rotational behaviour, in Wistar rats, was used to assess the dopaminergic modulatory activity of PLG and two novel analogues, L-prolyl-L-prolyl-L-prolinamide (analogue A) and (2S, 5R, 7R)-1-Aza-7[3'(S)-1-(2',5'-dioxo-pyrrolidino[2,1-c]piperazino++ +)] -8-oxo-4-thiabicyclo[3.30]octane-2-carboxamide (analogue B). PLG and the two novel analogues showed a bell-shaped dose-response relationship, suggesting that analogue A, B and PLG all manifest their effect through a similar mechanism and exhibit a window of therapeutic efficacy. Analogue A was a 100 times, while analogue B was 10 times, more potent than PLG in increasing the contralateral rotational response when given in combination with apomorphine. Analogue A was also more efficacious than PLG or analogue B at increasing apomorphine-induced contralateral rotations. Intrastriatal administration of either analogue A or B resulted in a greater increase in apomorphine-induced rotations than the most efficacious intraperitoneally delivered dose. The results of the present study suggest that PLG and its two novel analogues are able to modulate dopamine receptor activity and may be possible therapeutic agents for the treatment of Parkinsonian symptoms as well as tardive dyskinesia.

The effect of dopamine D1 receptor stimulation on the up-regulation of histamine H3-receptors following destruction of the ascending dopaminergic neurones

1. The binding of [3H]-(R)alpha-methylhistamine and [3H]-N alpha-methylhistamine to histamine H3-receptors, [3H]-SCH23390 to dopamine D1-receptors, and [3H]-YM09151-2 to dopamine D2-receptors was investigated by quantitative receptor autoradiography in the rat brain following 6-hydroxydopamine injection into the substantia nigra. 2. The levels of [3H]-(R)alpha-methylhistamine binding sites in the denervated striatum and substantia nigra were significantly higher than those in the contralateral side from 1 week to 12 weeks after nigral lesions. The H3-receptor binding was maximal at 3 weeks after nigral lesions and maintained until 12 weeks. 3. The increased number of histamine H3-receptors was decreased to the level of the contralateral side by chronic treatment with a selective dopamine D1 agonist, SKF38393, but not modified by a selective dopamine D2 agonist, quinpirole. 4. Dopamine D1- and D2-receptors in the striatum were similarly up-regulated after unilateral nigral lesion. On the other hand, the number of dopamine D2-receptors in the substantia nigra was markedly decreased after administration of 6-hydroxydopamine. 5. The treatment with (S)alpha-fluoromethylhistidine increased the H3-receptor binding in both the ipsilateral and contralateral sides. As a result, the magnitude of the ratio of the H3-receptor binding between ipsilateral and contralateral sides was partially attenuated by treatment with (S)-alpha-fluoromethylhistidine. 6. These results strongly suggest that the expression of histamine H3-receptors in the striatum and substantia nigra is influenced through D1-receptors by tonic nigrostriatal dopaminergic inputs.

Unilateral 6-hydroxydopamine lesions of meso-striatal dopamine neurons and their physiological sequelae

One of the primary approaches in experimental brain research is to investigate the effects of specific destruction of its parts. Here, several neurotoxins are available which can be used to eliminate neurons of a certain neurochemical type or family. With respect to the study of dopamine neurons in the brain, especially within the basal ganglia, the neurotoxin 6-hydroxydopamine (6-OHDA) provides an important tool. The most common version of lesion induced with this toxin is the unilateral lesion placed in the area of mesencephalic dopamine somata or their ascending fibers, which leads to a lateralized loss of striatal dopamine. This approach has contributed to neuroscientific knowledge at the basic and clinical levels, since it has been used to clarify the neuroanatomy, neurochemistry, and electrophysiology of mesencephalic dopamine neurons and their relationships with the basal ganglia. Furthermore, unilateral 6-OHDA lesions have been used to investigate the role of these dopamine neurons with respect to behavior, and to examine the brain's capacity to recover from or compensate for specific neurochemical depletions. Finally, in clinically-oriented research, the lesion has been used to model aspects of Parkinson's disease, a human neurodegenerative disease which is neuronally characterized by a severe loss of the meso-striatal dopamine neurons. In the present review, which is the first of two, the lesion's effects on physiological parameters are being dealt with, including histological manifestations, effects on dopaminergic measures, other neurotransmitters (e.g. GABA, acetylcholine, glutamate), neuromodulators (e.g. neuropeptides, neurotrophins), electrophysiological activity, and measures of energy consumption. The findings are being discussed especially in relation to time after lesion and in relation to lesion severeness, that is, the differential role of total versus partial depletions of dopamine and the possible mechanisms of compensation. Finally, the advantages and possible drawbacks of such a lateralized lesion model are discussed.

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.

Relationship of the ipsilateral rotation in night period and striatal dopamine content reduction in unilateral nigrostriatal 6-OHDA lesioned rats

In order to discriminate well-lesioned rats after unilateral microinjection of 6-OHDA into the nigrostriatal dopamine system, we measured the spontaneous rotation in the night period and calculated the rate of ipsilateral rotation movement. The rate of ipsilateral rotation movement increased along with the total rotation movement. The rats with over 95% of ipsilateral rotation kept the rate relatively constant for 4 weeks after 6-OHDA lesion and showed a significant increase of contralateral rotation (253.2 +/- 37.9) as compared with the rat that had lower than 95% ipsilateral rotation (3.6 +/- 1.4) after the injection of apomorphine (0.25 mg/kg, s.c.). The reduction percentages of striatal DA contents in animals with unilateral rotation over 95% and under 95% to the lesioned side were 97.8 +/- 0.6% and 59.6 +/- 5.8% (P < 0.001), respectively. The rats with over 90% reduction of striatal DA levels corresponded nicely to rats with 95% ipsilateral rotation among rats injected with apomorphine. These results suggested that the evaluation of ipsilateral rotation, taken the level of 95% rotation to the lesioned side as a standard, was able to discriminate well-lesioned rats without apomorphine treatment after unilateral nigrostriatal 6-OHDA application.

Specific lesions in the extrapyramidal system of the rat brain induced by 3-nitropropionic acid (3-NPA)

The irreversible mitochondrial toxin 3-nitropropionic acid (3-NPA) is a specific inhibitor of succinate dehydrogenase. We performed stereotaxic unilateral injections of 3-NPA into the nigrostriatal dopaminergic pathway in rats in order to examine its specific effects on the dopamine system. The 3-NPA-treated rats displayed unidirectional apomorphineinduced rotations, suggesting that 3-NPA selectively damages dopaminergic neurons when injected into the nigrostriatal pathway. In situ hybridization 7 weeks postinjection indicated a decrease in tyrosine hydroxylase (TH) mRNA to 30% of the noninjected side in the substantia nigra pars compacta (P < 0.05) and decreased to 62% of the noninjected side in the ventral tegmental area (VTA) (nonsignificant) of 3-NPA-lesioned rats. The number of TH mRNA positive cells showed statistically significant decreases in substantia nigra and VTA (P < 0.001) within the lesioned side. In contrast, expression of mRNAs encoding choline acetyltransferase, p75 low-affinity NGF receptor, neurotrophin tyrosine kinase receptors Trk and TrkB, and brain-derived neurotrophic factor showed neuronal sparing in several other regions of the brain. The results suggest that the nigrostriatal dopaminergic system might be selectively vulnerable to 3-NPA and demonstrate that it is possible to employ 3-NPA in a model of partial lesion of the nigrostriatal dopaminergic system resembling early stages of Parkinson's disease.

Long-term effects of human-to-rat mesencephalic xenografts on rotational behavior, striatal dopamine receptor binding, and mRNA levels

Fetal ventral mesencephalic grafts have been used as a tool to counteract the symptoms of Parkinson's disease. In this study human fetal ventral mesencephalic xenografts were implanted into the lateral ventricle of unilaterally dopamine-depleted immunosuppressed rats. Rotational behavior elicited by low doses of apomorphine, host striatal dopamine receptor binding, and mRNA levels were investigated. Rotational behavior was reduced beginning 2 months after grafting. After 4 months only a small number of rotations, lasting approximately 30 min, were recorded. Seven months after transplantation, the rotational behavior was completely eleminated. Dopamine D2 receptor binding revealed significantly increased levels in sham-operated 6-hydroxydopamine- (6-OHDA) lesioned control striata. These increased levels decreased, and although still significantly higher at 4 months, normalized at the survival time of 7 months postgrafting. Regional differences were still obvious at 7 months in the dorsolateral quadrant of dorsal striatum. Dopamine D2 receptor mRNA revealed significantly increased levels in the lateral aspects of 6-OHDA-lesioned control striata, reversing by 4 months postgrafting. The D1 receptor binding revealed a moderately reduced signal in striata of lesioned animals. After grafting, this reduction became significantly lower than that seen in the control side, with a continous decrease over time. The same pattern was detected using in situ hybridization for dopamine D1 receptor mRNA, that is, moderate decreases after dopamine depletion and a significant decrease in the dorsomedial part of dorsal striatum 7 months postgrafting. Dopamine D3 receptor binding was increased after dopamine depletion, but reversed already by 4 months postgrafting. Taken together, human ventral mesencephalic xenografts are able to completely reverse apomorphine-induced rotational behavior, provided the grafts are left in vivo for a sufficient time. The increased striatal D2 receptors are reversed after grafting, but the human xenograft further suppressed the D1 receptor subtype both at binding and at mRNA levels. There was no strict correlation in the time courses of dopamine receptor changes and reduction of rotational behavior.

Behavioral asymmetries and recovery in rats with different degrees of unilateral striatal dopamine depletion

A detailed behavioral analysis during the first postoperative week was performed in rats which had sustained various degrees of unilateral neostriatal dopamine (DA) lesions by administration of the neurotoxin 6-hydroxydopamine into the substantia nigra. These animals were assigned to different groups according to their residual DA levels in the damaged neostriatum (as percentage of the intact side). On the first day after toxin injection into the substantia nigra, turning asymmetries (tight turns) toward the side of the lesion were observed in animals with a mean residual DA level of 32% or less. Out of these, the strongest asymmetries were observed in animals with a mean residual DA of 3%. After one week, the asymmetry in tight turns had totally recovered except in those groups with mean residual DA levels of 17% or less. Partial recovery was found in animals with mean residual DA of 9 and 17%, whereas no indication for recovery was found in animals with the most severe lesions (mean residual DA 3%). Measurement of thigmotactic scanning also revealed an asymmetry for the side of the lesion on the first post-operative day. This asymmetry was observed over a wider range of DA lesion than that observed in turning, namely up to a mean residual DA level of 78%. Furthermore, recovery to symmetry was observed in all lesion-groups except in those with more severe lesions (mean residual DA 17% or less). In contrast to turning, the strongest asymmetries were not displayed by the animals with the most severe lesions. Furthermore, locomotor activity was affected by the lesion, since on the first postoperative day locomotion was reduced in animals with mean residual DA of 39% or less. On day 7, this lesion-dependent deficit had recovered to control levels. Finally, the analysis of net turns allowed the prediction of lesion size in animals with residual DA levels of less than 15%. These results are discussed with respect to mechanisms of recovery, the role of lesion size, and the value of different behavioral measures to predict the degree of DAergic lesion.

Motor fluctuations in levodopa treated parkinsonian rats: relation to lesion extent and treatment duration

The pathogenesis of the motor fluctuations that complicate levodopa treatment of most parkinsonian patients remains uncertain. To evaluate the contribution of the degree of dopamine neuron loss and the duration of levodopa exposure, rats whose nigrostriatal system had been previously lesioned unilaterally by 6-hydroxydopamine received twice daily levodopa (25 mg/kg) injections for three weeks. The magnitude of the rotational response to levodopa more than doubled during the first week of treatment (P < 0.01), but remained essentially constant thereafter. Rats with over 95 percent loss of dopaminergic neurons evidenced a progressive shortening in the duration of levodopa's motor effects (P < 0.01) as well as a failure of nearly 8 percent of levodopa injections to elicit any response after the first week of treatment. In contrast, response changes resembling those associated with end of dose deterioration and on-off fluctuations in parkinsonian patients did not occur in the less severely lesioned rats. These results suggest that the extent of a dopamine neuron loss must exceed a relatively high threshold before intermittent levodopa treatment produces changes favoring the rapid appearance of motor fluctuations of the wearing-off and on-off types.

Intracellularly recorded response of rat striatal neurons in vitro to fenoldopam and SKF 38393 following lesions of midbrain dopamine cells

The effect of long-term (6-19 weeks) 6-hydroxydopamine-induced (6-OHDA) lesions of midbrain dopamine cells on dopamine D1-like agonist-induced changes in the excitability of rat striatal neurons was investigated in vitro using tissue slices and intracellular recording techniques. Fenoldopam and (+/-)-SKF 38393 predominantly decreased excitability in control preparations including striatal neurons located contralateral to 6-OHDA injection sites and neurons obtained from rats receiving sham injections or no treatment. Fenoldopam also inhibited neurons ipsilateral to lesions of midbrain dopamine cells. (+/-)-SKF 38393, unlike fenoldopam, produced predominantly increases in the excitability of ipsilateral striatal neurons. Superfusion of the D1 receptor antagonist, SCH 23390, blocked fenoldopam-induced decreases in excitability but not the (+/-)-SKF 38393-induced excitation of neurons ipsilateral to the lesion. Sequential application of fenoldopam and quinpirole, a D2/D3 receptor agonist, produced responses to both drugs in a majority of neurons. The results demonstrate that inhibitory responses to fenoldopam are mediated by D1 receptors, while excitatory effects of (+/-)-SKF 38393 in the striatum ipsilateral to the lesion are apparently not dependent on D1 receptor activation. These findings also suggest that dopamine D1 and D2/D3 receptors are able to concurrently influence the excitability of striatal neurons in the dopamine deafferentated striatum. Similar regulation of striatal neurons in vivo may contribute to dopaminergic regulation of basal ganglia output and the ability of dopaminomimetic agents to ameliorate symptoms of dopaminergic deficiency in Parkinson's disease.

Marked increase in histamine H3 receptors in the striatum and substantia nigra after 6-hydroxydopamine-induced denervation of dopaminergic neurons: an autoradiographic study

The bindings of [3H](R) alpha-methylhistamine to histamine H3 receptors were investigated in rat brain following intranigral treatment with 6-hydroxydopamine (6-OHDA) by quantitative receptor autoradiography. The levels of [3H](R) alpha-methylhistamine binding sites in the denervated striatum (dorsomedial and dorsolateral) and substantia nigra were significantly higher than those in the contralateral side 21 days after nigral lesions. Saturation kinetic analysis revealed that the maximum binding capacities were up-regulated to about 1.7- and 1.2-fold those in the contralateral substantia nigra and striatum, respectively. These results strongly suggest that H3 receptors in the striatum and substantia nigra are influenced by tonic dopaminergic inputs.

Glutamate receptor expression in rat striatum: effect of deafferentation

The cerebral cortex is the primary source of glutamatergic afferents to the neostriatum. We used in situ hybridization to examine the effect of removal of the glutamatergic input to the striatum by unilateral frontal cortical ablation on the expression of genes encoding subunits from three families of glutamate receptors: N-methyl-D-aspartate receptors (NMDAR1, NMDAR2A, and NMDAR2B); alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors (GluR1-4, flip and flop splice variants); and metabotropic receptors (mGluR1-5). Significant changes were restricted to the dorsolateral quadrant of the ipsilateral striatum, the main projection area of the sensorimotor cortex. The expression of those messages which are normally abundant, NMDAR1, NMDAR2A, GluR1-4 flop and mGluR1, 3 and 5, was decreased in the deafferented dorsolateral striatum by 10-39% at 3 days after cortical ablation and subsequently increased to 120-165% of control at 15 and 60 days. mRNAs encoding the flip isoforms of GluR1-4, mGluR2 and 4, and an alternatively spliced region of NMDAR1 (Insertion I) which are undetectable or present at low levels in the striatum were not induced by cortical ablation. In contrast, both glial fibrillary acid protein and beta-actin mRNA expression were markedly enhanced at 3 and 15 days, returning to near normal at 60 days. Striatal NMDA, AMPA and metabotropic type 1 ligand binding sites were increased as early as 3 days after cortical ablation, reached a peak at 15 days and remained increased for up to 60 days, while metabotropic type 2 binding was slightly but significantly reduced at 3 and 15 days and [3H]kainate binding did not change significantly. These results demonstrate that cortical ablation, and subsequent loss of glutamatergic afferents to the striatum, results in alterations in the expression of genes encoding glutamate receptor subunits in striatal neurons. The regulation of these genes appears to be coordinate, so that the relative abundance of the different messages is preserved.

Dopamine receptors: molecular biology, biochemistry and behavioural aspects

The description of new dopamine (DA) receptor subtypes, D1-(D1 and D5) and D2-like (D2A, D2B, D3, D4), has given an impetus to DA research. While selective agonists and antagonists are not generally available yet, the receptor distribution in the brain suggests that they could be new targets for drug development. Binding characteristics and second messenger coupling has been explored in cell lines expressing the new cloned receptors. The absence of selective ligands has meant that in vivo studies have lagged behind. However, progress has been made in understanding the function of DA-containing discrete brain nuclei and the functional consequence of the DA's interaction with other neurotransmitters. This review explores some of the latest advances in these various areas.

Possible noradrenergic dysfunction in schizophrenia

In spite of extensive studies over the last 2 decades to find direct evidence in support of the dopamine hypothesis of schizophrenia, no undisputed experimental data has been obtained. In contrast, estimation of noradrenalin (another major catecholamine) and its metabolites in postmortem brain and in the cerebrospinal fluid appears to be producing consistent results. To understand the meaning of this change for the pathogenesis of the illness, we have carried out animal experiments in which reproducibility of schizophrenic signs and symptoms by noradrenergic dysfunction, and treatability of the disorder by modulation of noradrenergic activity were studied. First, psychophysiological signs in skin conductance responsiveness (nonhabituating or nonresponding change) and smooth pursuit eye movement (spiky or stepwise pursuit) could be reproduced by enhancing or suppressing central noradrenergic activity. Behavioral abnormalities resembling schizophrenic symptoms are known to be reproducible by over- or underactivity of the system (overarousal or underarousal syndrome). Secondly, the action of various drugs capable of modulating schizophrenic symptoms was analyzed in relation to noradrenergic activity. Haloperidol, in particular, had a potent suppressing effect on skin conductance activity (spontaneous fluctuation rate and habituation rate) when administered chronically, suggesting its inhibitory action on noradrenergic activity.

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.

Correlation of apomorphine- and amphetamine-induced turning with nigrostriatal dopamine content in unilateral 6-hydroxydopamine lesioned rats

In the unilateral 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease, controversy exists concerning the use of apomorphine- or D-amphetamine-induced rotations as reliable indicators of nigrostriatal dopamine depletion. Our objective was to evaluate which, if either, drug-induced behavior is more predictive of the extent of nigrostriatal dopamine depletion. Fischer 344 and Sprague-Dawley rats were unilaterally injected with 9 micrograms/4 microliters/4 min 6-hydroxydopamine into the medial forebrain bundle. The animals were behaviorally tested with apomorphine (0.05 mg/kg, s.c.) and D-amphetamine (5.0 mg/kg, s.c.). Following testing, the brains were removed and the right and left striata, substantia nigra and ventral tegmental area were dissected free and quickly frozen at -70 degrees C for analysis of catecholamine content by high performance liquid chromatography coupled with electrochemical detection. Our results indicate that an animal which has greater than a 90% depletion of dopamine in the striatum might not rotate substantially on apomorphine, without a concomitant depletion of > 50% of the DA content in the corresponding substantia nigra. No correlations were seen involving depletions of the ventral tegmental area and the extent of the lesions to the striatum. Submaximally lesioned (75-90% depleted) rats were found to rotate on D-amphetamine but not on apomorphine. In addition, control rats that did not receive lesions were often seen to rotate extensively on D-amphetamine. We therefore conclude that maximal lesions of the striatum and substantia nigra are required to generate rotations demonstrable with low dose apomorphine but not with D-amphetamine.(ABSTRACT TRUNCATED AT 250 WORDS)

The intrastriatal 6-hydroxydopamine model of hemiparkinsonism: quantitative receptor autoradiographic evidence of correlation between circling behavior and presynaptic as well as postsynaptic nigrostriatal markers in the rat

Unilateral injections of 6-hydroxydopamine into the striatum resulted in almost immediate ipsilateral amphetamine (AMPH)- and delayed contralateral apomorphine (APO)-induced circling behavior in rats. APO-induced rotation correlated positively with that caused by AMPH. In these animals, there was an almost complete disappearance of dopamine uptake sites as well as increases in DA D2 receptors in specific subdivisions of the ipsilateral caudate-putamen (CPu). Both the rate of AMPH- and APO-induced rotation correlated with the percentage of DA terminal loss in the total aspect and in various quadrants of the striatum. In contrast, AMPH- and APO-induced rotation correlated with the percentage increase in striatal D2 receptors only in the dorsolateral (DL) aspect of the CPu. These results indicate that both AMPH- and APO-induced rotation can be used to determine the extent of DA terminal loss in the rat basal ganglia. The positive correlation of circling behavior to only changes in DA D2 receptors observed in the DL striatal subdivision provides further evidence for the heterogeneity of the basal ganglia. This model of hemiparkinsonism in the rat which uses a distant intrastriatal approach to the destruction of nigral DA cell bodies may be a more appropriate model to study the regenerative properties of the nigrostriatal DA system. This approach could also be used to more specifically localize peptidergic receptors on midbrain dopamine cell bodies.

Dissociation of the striatal D-2 dopamine receptor from adenylyl cyclase following 6-hydroxydopamine-induced denervation

Intracellular cyclic AMP accumulation following exposure to dopamine (DA) agonists and and antagonists was measured in striatal slices from rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion of the nigrostriatal pathway and which showed contralateral circling to apomorphine. Both DA (10-320 microM) and the D-1 agonist SKF 38393 (0.1-32 microM) increased cyclic AMP accumulation in striatal slices from the lesioned and intact hemispheres. The EC50 for DA to increase cyclic AMP accumulation in slices was greater in the 6-OHDA-lesioned striata compared to the intact striatum, but the EC50 for SKF 38393 was not affected. The D-1 antagonist SCH 23390 (10 microM) completely inhibited the ability of DA and SKF 38393 to increase cyclic AMP accumulation in striatal slices from both denervated and intact sides of the brain. In slices from the intact hemisphere the increase in DA-induced cyclic AMP accumulation was enhanced by the D-2 antagonist (+/-)-sulpiride (50 microM) but (+/-)-sulpiride had no effect on the DA response in slices from the lesioned side. Similarly, the ability of SKF 38393 to enhance cyclic AMP accumulation was blocked by the D-2 agonist quinpirole (10 microM) in striatal slices from the intact hemisphere but not in tissue from the lesioned side. The density of striatal D-1 and D-2 receptors assessed by [3H]SCH 23390 and [3H]spiperone binding did not differ between the hemispheres although there was an increase in the affinity of D-1 receptors for [3H]SCH 23390 in the lesioned striatum. After striatal deafferentiation there appears to be an uncoupling of the "inhibitory" D-2 receptor from the D-1 receptor-associated adenylyl cyclase.

Preoperative operant circling training facilitates recovery following unilateral substantia nigra lesion in rats

This study was undertaken to examine (1) whether pre- and/or postoperative training, using water reinforcement, to turn in circles (rotation) affects the behavioral symptoms induced by unilateral 6-hydroxydopamine (6-OHDA)-induced DA denervation of the rat substantia nigra (SN); (2) whether there was any influence of this training on the temporal pattern of recovery; and (3) whether the rotational training influences turning induced by systemic injection of dopaminergic drugs. In the first experiment, rats were trained either ipsi- or contraversive (TI or TO) to the side to be damaged 11 days before and 23 days after lesion, and tested in an open field for rotational behavior following systemic administration of apomorphine and amphetamine. In the second experiment rats were trained only before the lesion was made and tested in the open field for spontaneous circling and thigmotactic behavior. The results of the first experiment indicated maintenance of the training performance after the lesion. At the 14th day after the lesion, the ipsiversive trained group showed a higher contraversive circling frequency after apomorphine injection in relation to the contralateral trained group. In the second experiment, rats trained only before the surgery, showed asymmetrical spontaneous circling in the trained direction before and 14 days after surgery, indicating, in a drug free condition, that training direction can be restored after unilateral SN lesions, even to the contralateral body side. Moreover, thigmotactic behavior indicated a lack of habituation in an open field in unilateral lesion rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiographic study of striatal D1 and D2 dopamine receptors in 6-OHDA-lesioned rats receiving foetal ventral mesencephalic grafts and chronic treatment with L-dopa and carbidopa

Foetal dopamine cell suspensions or sham preparations were implanted into the denervated striatum of rats with a unilateral 6-hydroxy-dopamine (6-OHDA) lesion of the medial forebrain bundle. Some animals were also treated with L-DOPA (200 mg/kg/24 h) and carbidopa (25 mg/kg/24 h) in the drinking water for 5 weeks, followed by a 3-week drug-free period. Rotational responses to apomorphine and (+)-amphetamine were assessed, and the density of D1 and D2 dopamine receptors was evaluated autoradiographically in striatal slices exposed to [3H]SCH 23390 or [3H]spiperone. Foetal grafts reduces apomorphine-induced contralateral rotation and prevented the development of apomorphine-induced stereotypy. Foetal grafts abolished (+)-amphetamine-induced ipsilateral rotation. These effects of the grafts were not altered by treatment with L-DOPA. A unilateral 6-OHDA lesion of the nigrostriatal pathway resulted in an ipsilateral increase in D2 receptor density most marked in the lateral and dorsomedial quadrants of the striatum compared with the contralateral side. Foetal ventral mesencephalic grafts implanted into the lesioned striatum decreased D2 receptor density to levels found in the contralateral intact striatum. Chronic L-DOPA and carbidopa treatment did not alter the effect of the grafts. A 6-OHDA lesion resulted in a reduction of D1 receptor density in the lateral areas of the lesioned striatum at Level 2. The presence of a foetal ventral mesencephalic graft either alone or together with L-DOPA treatment did not alter the lesion-induced changes in D1 binding density.