Lesions of the dopaminergic nigrostriatal system in neonatal rats: effects on the electrophysiological activity of striatal neurons recorded during adulthood

The spontaneous activity of single striatal neurons was recorded extracellularly from 3-4-month-old adult rats that had been given dopamine (DA)-depleting brain lesions 3 days after birth. Behavioral observations made prior to recording indicated no gross sensorimotor deficits, yet subsequent biochemical analyses revealed that animals had sustained near-total DA depletions (greater than 99%). Electrophysiological results showed that the firing rates of type II striatal cells were greatly increased relative to control levels. This finding contrasts sharply with the effects of DA-depleting brain lesions given to adult animals, in which similarly high levels of striatal cell activity are invariably associated with akinesia.     

Reductions in spontaneous locomotor activity in aged male, but not female, rats in a model of early Parkinson's disease

The excessive loss of dopamine (DA) neurons that occurs with Parkinson's disease is usually confined to older individuals. While 6-hydroxydopamine (6-OHDA) is often used in animal models of DA neuron degeneration, there have been relatively few studies that have examined the effects of 6-OHDA in older animals. In the present study, we compared the effects of a bilateral, partial lesion with 6-OHDA in young (4 months), middle-aged (14 months), and aged (24 months) Fischer-344 rats of both sexes. Animals were given a single injection of vehicle or 100 mug 6-OHDA into the right lateral ventricle. Four weeks later, spontaneous locomotor activity was monitored. Microdialysis experiments were carried out 1 to 3 days later. The 6-OHDA treatments had no effect on horizontal activity or total distance traveled in young adults. However, with aged rats, there was a decrease in both measures in the vehicle-treated control rats compared to young adult controls, and a further decrease in the lesioned aged male rats. The 6-OHDA treatments led to significant decreases in both potassium- and amphetamine-evoked overflow of DA from the striatum in all groups. Thus, partial bilateral lesions of the nigrostriatal DA system led to decreases in evoked release of DA in the striatum of male and female rats of all three ages, but to changes in spontaneous activity only in the aged males. These results indicate that there are both age and sex differences in the brain's response to 6-OHDA, and imply that compensatory or neuroprotective mechanisms in the young brain and aged female brain are more efficient than in the aged male brain.     

Postural changes after lesions of the substantia nigra pars reticulata in hemiparkinsonian monkeys

Current neurosurgical strategies target overactive brain regions including the subthalamic nucleus, globus pallidus and thalamus to control various symptoms of Parkinson's disease. Subthalamotomy improves akinesia and can induce postural deficits in both parkinsonian humans and animals, pallidotomy improves limb dyskinesia and more variably, distal bradykinesia whilst thalamotomy improves tremor. Because the SNr also becomes overactive in PD and there are few surgical studies in parkinsonian primates, we therefore evaluated the effects of lesioning the SNr in hemiparkinsonian marmosets to establish the effects on symptomatology. Nine monkeys received unilateral 6-hydroxydopamine (6-OHDA) lesions. Seven weeks later, four received kainic acid lesions of the SNr. Behavioural tests were performed prior to 6-OHDA surgery and then fortnightly for 14 weeks. Unilateral 6-OHDA lesions induced ipsilateral postural bias, ipsilateral rotation after amphetamine injection and bradykinesia. Whilst, SNr lesions significantly altered the direction of head position and amphetamine-induced rotation relative to 6-OHDA lesions, there was no improvement in 6-OHDA-induced reaching deficits or sensorimotor neglect. Unbiased quantitation of the nigral lesions showed on average 88% loss of dopaminergic neurons after 6-OHDA lesions and 77% loss of non-dopaminergic neurons after SNr lesions. Our results demonstrate that the SNr is important in body orientation changes in parkinsonism.     

Short-term effects of dopamine-depleting brain lesions on spontaneous activity of striatal neurons: Relation to local dopamine concentration and behavior

The spontaneous activity of striatal neurons was measured after dopamine (DA)-depleting brain lesions were produced in rats by the neurotoxin 6-hydroxydopamine. The extent of DA depletion was determined using tissue punches from the same regions of striatum in which cell activity was recorded. Results showed that the spontaneous activity of Type II neurons in either the medial or lateral striatum increased only when local DA depletions exceeded 90%; when local depletions were less than 90%, spontaneous firing rates of Type II neurons were equivalent to control values. This finding was consistent with additional observations that ingestive and motor behaviors of the same animals were not disrupted until striatal DA depletions exceeded 90%. It also was found that spontaneous firing rates of neurons in the lateral but not the medial striatum could be at control levels in animals clearly exhibiting aphagia, adipsia and akinesia.     

Male rat copulation following 6-OHDA lesions of the medial preoptic area: resistance to repeated administration and rapid behavioral recovery

Dopamine (DA) in the medial preoptic and (MPOA) has been shown to facilitate male rat sexual behavior. However, injections of the catecholamine (CA) neurotoxin 6-OHDA into the MPOA did not impair copulation in tests 3 days after injection. In the present study, three weekly (serial) injections produced no copulatory deficits compared to animals that received a single injection or to preinjection copulatory behavior scores. However, blocking CA synthesis, which did not impair control rats, produced deficits in both single and serial lesion animals, with significantly fewer serial than single lesion animals initiating copulation. Biochemical analysis of tissue punches showed no difference in MPOA concentrations of dopamine, norepinephrine, epinephrine, or the dopamine metabolite DOPAC between the two groups. Additional animals were tested at earlier intervals after 6-OHDA injections into the MPOA. Tests conducted 30 min after an MPOA injection 6-OHDA revealed that all measures of copulation were impaired, relative to scores 24 h later. However, these scores were not significantly different from animals tested 30 min after a vehicle injection. A final group, tested 4 h after injection, showed impairment of all measures of copulation compared to vehicle injections and to tests 24 h later. Furthermore, in the tests 24 h later, 6-OHDA animals were not different from vehicle animals. Results from all experiments show that 6-OHDA injections into the MPOA impair copulation for at least 4 h, but that behavioral recovery is complete 24 h later. However, deficits can be reinstated by inhibiting DA synthesis, suggesting that increased synthesis in undamages terminals contributed to behavioral recovery.     

Subthalamic nucleus lesions are neuroprotective against terminal 6-OHDA-induced striatal lesions and restore postural balancing reactions

Inactivation of the subthalamic nucleus (STN) by deep brain stimulation or lesioning can ameliorate symptoms in Parkinson' disease (PD) and may alter the underlying progressive degenerative process. We evaluated the effects of STN lesions in a terminal lesion model of PD in rats. Multiple intrastriatal 6-OHDA injections (4 x 7 microg) resulted in a partial loss of striatal TH-positive innervation (-30 to -40%) and nigral dopaminergic neurons (-60%), which was associated with behavioral deficits as observed in drug-induced rotational asymmetry, side-stepping, and postural balancing reactions. Unilateral ibotenic acid lesions of the STN did produce a 50-60% loss of STN neurons based on stereological analysis, which did not induce a functional impairment in rotational asymmetry or spontaneous sensorimotor behaviors. When STN lesions were performed 1 week prior to the 6-OHDA terminal striatal lesions, a significant rescue effect (+23%) on nigral dopaminergic neurons against terminal 6-OHDA neurotoxicity could be demonstrated, whereas striatal TH-positive fiber loss was not attenuated in these animals. In addition, animals with combined STN and striatal lesions exhibited a significant recovery in postural balancing reactions induced by 6-OHDA terminal lesions and did not show a significant impairment in any of the other behavioral parameters examined. Taken together, STN lesions can exert neuroprotective effects on nigral dopamine neurons in a partial lesion model of PD which result in recovery of spontaneous sensorimotor behavior. These findings may therefore provide new insights into the functional interaction between the glutamatergic and the dopaminergic neurotransmitter systems and foster novel therapeutic concepts for the early and middle phases of Parkinson's disease.     

Sparing of behavior and basal extracellular dopamine after 6-hydroxydopamine lesions of the nigrostriatal pathway in rats exposed to a prelesion sensitizing regimen of amphetamine

Repeated administration of amphetamine leads to enduring augmentation of its behavioral-activating effects, enhanced dopamine (DA) release in striatal regions, and morphological changes in DA target neurons. Here we show that exposure to a 2-week escalating-dose regimen of amphetamine prevents behavioral asymmetries of forelimb use and spontaneous (drug-independent) turning behavior following unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal pathway made 7-14 days after termination of amphetamine treatment (Experiments 1-3). Exposure to three nonescalating injections of amphetamine 7 days before 6-OHDA lesions had no effect (Experiment 2). Prelesion amphetamine treatment led to normalization of basal extracellular levels of striatal DA as measured by microdialysis on days 11-14 and 25-28 after lesioning (Experiment 3). However, there were no significant differences between treatment groups in postmortem tissue levels of DA and its metabolites, indicating a dissociation between the DA depletion and the extracellular levels of DA as measured by microdialysis. Finally, rats exposed to the escalating amphetamine regimen had reduced lesion-induced loss of TH-IR cells in the ipsilateral DA cell body regions (Experiment 3). Thus, prelesion exposure to the escalating doses of amphetamine may render the cells resistant to the consequences of damage after subsequent 6-OHDA lesions, possibly by accelerating the development of compensatory changes in the DA neurons that typically accompany behavioral recovery. The potential role of amphetamine-induced endogenous neurotrophic factors in the behavioral sparing and normalization of basal extracellular DA levels observed after subsequent 6-OHDA lesions is discussed.     

Behavioural and biochemical effects of dopamine and noradrenaline depletion within the medial prefrontal cortex of the rat

The effects of 6-hydroxydopamine (6-OHDA) lesions of catecholamine terminals within the medial prefrontal cortex on spontaneous motor activity, dopamine (DA)-dependent stereotyped behaviour and subcortical dopamine turnover were investigated in the rat. Two types of lesions were examined, bilateral injection of 6-OHDA into the medial prefrontal cortex of untreated rats (6-OHDA alone), and bilateral injection of 6-OHDA into the medial prefrontal cortex of animals pretreated with the noradrenaline (NA) uptake blocking agent desmethylimipramine (6-OHDA/-DMI). Ten days after surgery the 6-OHDA lesions produced no significant change in spontaneous motor activity and had no overall effects on stereotyped behaviour induced by apomorphine or (+)-amphetamine. This lesion caused gross depletion of NA within the medial prefrontal cortex and curiously, elevated DA concentrations within this site. No changes in DA concentration were recorded within subcortical sites, although concentrations of DA metabolites within striatum and nucleus accumbens were reduced. In contrast, the 6-OHDA/DMI lesion of the medial prefrontal cortex significantly enhanced spontaneous motor activity and amphetamine-induced stereotyped behaviour. Apomorphine-induced stereotypy, on the other hand, was significantly reduced. Biochemically the lesion caused a large depletion of DA with relatively little loss of NA within the medial prefrontal cortex. In addition, from this and another study (ref. 33), increases in DA and its metabolite concentrations were measured in striatum and nucleus accumbens, together with an apparent increased in DA turnover within these subcortical sites. It is thus apparent that in the absence of a substantial portion of the DA innervation of the medial prefrontal cortex, with a largely intact NA innvervation, there is an increase in motor activity and amphetamine-induced stereotypy which may be related to functional changes in DA activity within subcortical telecephalic structures. Such a finding might suggest that DA within the frontal cortex has a behaviourally inhibitory role in the rat, although further work is required to substantiate this.     

Suppression of noradrenergic innervation compensates for behavioral deficits induced by lesion of dopaminergic terminals in the lateral septum

Spontaneous alternation which is disrupted by lesion of septal dopaminergic (DA) afferents was chosen as a behavioral marker for the study of functional interactions between DA and noradrenergic (NA) innervation of the lateral septum. Three groups of rats were studied: a solvent group which received only vehicle injection, and two lesioned groups, one with DA lesion and the second with simultaneous DA + NA lesion of the septal innervation. DA lesion was produced by infusing 6-hydroxydopamine (6-OHDA) into the lateral septum after pretreatment with desmethylimipramine (DMI) injected intraperitoneally. The DA + NA lesion was produced by infusing 6-OHDA without DMI pretreatment. The lesion of DA innervation alone led to a disturbance of alternation behavior in a Y-maze, but performance was not affected by the combined DA + NA lesion. The group with septal DA lesion was then injected with 6-OHDA into the pedunculus cerebellaris superior (PCS) in order to destroy NA efferents from the locus coeruleus. The two other groups were sham-operated. After post-operative recovery, the rats were retested for spontaneous alternation. The rats with the PCS NA lesion subsequent to the DA septal lesion displayed normal alternation behavior. Their performance was not different from that of animals with both NA and DA lesions in the septum. Thus the NA lesion appears to prevent the alternation deficits induced by the DA septal lesion, and also abolishes the deficits induced by the prior DA lesions. These results may have therapeutic implications.     

Dye-coupling in the neostriatum of the rat: I. Modulation by dopamine-depleting lesions

Evidence from experiments performed in turtle and fish retina suggests that dopamine (DA) modulates the permeability of gap junctions. The present experiment was aimed at determining if DA has a similar role in the mammalian neostriatum. Adults rats received one of four treatments: unilateral electrolytic substantia nigra lesions, unilateral injection of 6-hydroxydopamine (6-OHDA) into the substantia nigra, unilateral neocortical aspiration, or no treatment. After 3-5 weeks, neostriata from both sides of the brain were prepared for in vitro intracellular recordings. Recorded neurons (N approximately 150) were filled with Lucifer Yellow (LY), a low molecular weight dye that crosses gap junctions. In animals with electrolytic nigral lesions, dye-coupling in the ipsilateral neostriatum occurred after 38% of the intracellular injections. After 6-OHDA lesions, 19% of the injections produced dye-coupling in the ipsilateral neostriatum. This difference may have been accounted for by the fact that electrolytic lesions produced a greater degree of DA loss than 6-OHDA injections. Both of these percentages contrast with the very small percentage of dye-coupling found in intact animals or in animals with neocortical lesions. Dye-coupling occurred only between medium-sized spiny cells. No morphological differences between dye-coupled and non-dye-coupled cells were observed with light microscopy. Overall, passive and active electrophysiological properties of dye-coupled and single neurons were similar. The results suggest that DA may function in the neostriatum to control permeability of gap junctions.     

Regional depletion of central nervous system catecholamines: Effects on blood pressure and drinking behavior

The purpose of the present study was to identify which catecholamine-containing neurons (norepinephrine (NE) or dopamine (DA)) and which central nervous system (CNS) region(s) innervated by them might participate in the pressor and drinking responses produced by central drug stimulation. Forebrain NE was reduced in rats by injecting 4 micrograms of 6-hydroxydopamine (6-OHDA) into the ascending noradrenergic bundles. Spinal cord NE was depleted by intracisternal injection of 50 micrograms 6-OHDA. Depletion of forebrain DA was produced by bilateral injection of 4 micrograms 6-OHDA into the substantia nigra of desipramine-pretreated rats. Pressor responses to various doses of angiotensin II (AII), carbachol or hyperosmolar NaCl injected into the lateral ventricles (LVT); and drinking responses to LVT AII and carbachol were examined. Injection of 6-OHDA into the noradrenergic bundles reduced telencephalic and hypothalamic NE by more than 80% without significantly affecting brain DA or spinal cord NE. Intracisternal 6-OHDA depleted spinal cord NE by 80% and forebrain NE by 20-25% without reducing brain DA. Injection of 6-OHDA into the substantia nigra reduced telencephalic DA by 86% and NE by 29% without significantly affecting NE in other CNS regions. Substantia nigra 6-OHDA injected animals evidenced attenuated drinking to both LVT AII and carbachol. Pressor responses to LVT AII, carbachol and hypertonic saline were largely unaffected. Almost complete depletion of brain and/or spinal cord NE failed to alter centrally mediated drinking or pressor responses. These data indicate that the integrity of brain DA neurons is required for the behavioral but not hypertensive responses produced by central drug stimulation.     

Specificity of dopaminergic neuronal degeneration induced by intracerebral injection of 6-hydroxydopamine in the nigrostriatal dopamine system.

The neurotoxic specificity of injections of 6-hydroxydopamine (6-OHDA) into areas containing either dopamine (DA) cell bodies (substantia nigra) or DA axon terminals (striatum) was studied. This selective effect was compared to the unspecific effects of copper sulfate (CuSO4) injection and electrocoagulation. One to two days after unilateral nigral injection of 2 mug of either 6-OHDA or CuSO4 into the nigra the volume of the unspecific lesions around the tip of the cannula was very similar. Only the 6-OHDA-induced lesions were associated with elective degeneration of the nigral DA neurons. Ten days after the administration of the same compounds the gliosis in the substantia nigra was much more extensive in CuSO4-than in 6-OHDA-treated rats; however, the reduction of DA concentrations in the ipsilateral striatum was only noticeable after 6-OHDA (-62%). A somewhat similar decrease of striatal DA levels (-52%) was observed after large electrocoagulation of the substantia nigra. Ten days after 6-OHDA (8mug) or electrolytic lesion of the striatum the Km for DA, serotonin and choline uptakes were similar in the striata of both sides, suggesting that the uptake process in the non-damaged neurons of the lesioned side was functionally normal. Following electrolytic lesion of the striatum, serotonin and choline Vmax values were decreased to about the same extent as the striatal reduction in weight and DA levels. When directly administered into the striatum 6-OHDA also produced a decline in DA concentration and Vmax but in contrast did not affect serotonin and choline uptake (Vmax), suggesting that the drug specifically destroyed dopaminergic neurons. The present data confirm that selective DA denervation can be achieved when appropriate amounts of the drug are injected into brain tissue in order to limit the unspecific lesion.     

rAAV-mediated nigral human parkin over-expression partially ameliorates motor deficits via enhanced dopamine neurotransmission in a rat model of Parkinson's disease

We hypothesized that over-expressing the E3 ligase, parkin, whose functional loss leads to Parkinson's disease, in the nigrostriatal tract might be protective in the unilateral 6-hydroxydopamine (6-OHDA) rat lesion model. Recombinant adeno-associated virus (rAAV) encoding human parkin or green fluorescent protein (GFP) was injected into the rat substantia nigra 6 weeks prior to a four-site striatal 6-OHDA lesion. Vector-mediated parkin over-expression significantly ameliorated motor deficits as measured by amphetamine-induced rotational behavior and spontaneous behavior in the cylinder test but forelimb akinesia as assessed by the stepping test was unaffected. rAAV-mediated human parkin was expressed in the nigrostriatal tract, the substantia pars reticulata, and the subthalamic nucleus. However, in lesioned animals, there was no difference between nigral parkin and GFP-transduction on lesion-induced striatal tyrosine hydroxylase (TH) innervation or nigral TH positive surviving neurons. A second lesion experiment was performed to determine if striatal dopamine (DA) neurotransmission was enhanced as measured biochemically. In this second group of parkin and GFP treated rats, behavioral improvement was again observed. In addition, striatal TH and DA levels were slightly increased in the parkin-transduced group. In a third experiment, we evaluated parkin and GFP transduced rats 6 weeks after vector injection without DA depletion. When challenged with amphetamine, parkin treated rats tended to display asymmetries biased away from the treated hemisphere. Nigral parkin over-expression induced increases in both striatal TH and DA levels. Therefore, while parkin over-expression exerted no protective effect on the nigrostriatal DA system, parkin appeared to enhance the efficiency of nigrostriatal DA transmission in intact nigral DA neurons likely due to the observed increases in TH.     

Neurobehavioural, neurochemical and electrophysiological studies in 6-hydroxydopamine lesioned and neural transplanted rats

Unilateral injection of 6-hydroxydopamine (6-OHDA) into the caudate nucleus of rat caused degeneration of dopaminergic terminals, evidenced by significant (P⊂0.05) elevation of spontaneous and drug-induced motor behaviour, enhanced DA receptor binding and significant increase in the neuronal firing rate of caudate neurons, suggesting supersensitivity of dopaminergic receptors. Eight weeks following the transplantation of embryonic cell suspensions from caudate at the lesioned site, a significant restoration of the enhanced ³H spiperone binding and neuronal activity of caudate neurons was observed in comparison with lesioned rats.These results clearly demonstrate that transplanted embryonic neuronal tissue at the lesioned site is capable of restoring the neuronal deficits caused by 6-OHDA as evidenced by significant amelioration in neurochemical, behavioral and electrophysiological alterations.     

Lesions of noradrenergic neurons in rats with spontaneous generalized non-convulsive epilepsy.

The role of noradrenergic neurons in the control of a spontaneous generalized non-convulsive epilepsy (GNCE) was investigated. In rats with genetic spontaneous absence seizures, we produced lesions using 2 neurotoxins: 6-hydroxydopamine (6-OHDA) and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4). Lesions of noradrenergic neurons were made either in pups by neonatal 6-OHDA intraperitoneal (i.p.) injection (2 x 100 mg/kg) or in adult rats by i.p. administration of DSP4 (60 mg/kg) or bilateral microinjection of 6-OHDA in the locus coeruleus (LC) (4 micrograms/microliters, 2 microliters/side). Effectiveness of the lesions was controlled by measuring dopamine (DA) and noradrenaline (NA) contents in the brains. Neonatal 6-OHDA administration did not lead to any difference in seizures in adult animals, compared with control rats. DSP4 injections and LC lesions with local injections of 6-OHDA produced a transient increase of the seizures. Within one to two weeks, the seizure duration went back to prelesion levels. No seizure occurred when the same lesions were performed in non epileptic rats. These results suggest that NA is not involved in the genesis of this generalized non-convulsive epilepsy; they confirm that NA participates in the control of seizures in this model, but the rapid development of compensatory mechanisms shows that this control is not critical.     

Loss of Striatal DA Innervation Increases Striatal Trophic Activity Directed at DA Neurons in Culture

Male rats received intraventricular infusions of the dopamine (DA) neurotoxin 6-hydroxydopamine (6-OHDA; 0, 75, 150, and 250 μg) in order to determine if DA neuron loss was associated with an increase in striatal trophic activity. After 4 weeks, the animals were sacrificed and perfused with normal saline, and the brains were removed, immediately frozen, and processed. Intraventricular infusions of 6-OHDA were associated with a dose-dependent reduction in striatal DA content and tyrosine hydroxylase-immunoreactive (THir) cell counts in the substantia nigra while striatal DA activity ([HVA]/[DA]) was increased. Extracts of the striatum from these animals increased the survival of E15 primary, dissociated rostral mesencphalic cultures growing at low cell density. This growth effect was positively correlated with the dose of 6-OHDA infused. THir cell counts present in high-cell-density mesencephalic cultures following 72 h of extract incubation were similarly correlated to 6-OHDA dose but inversely correlated with striatal DA content and THir cell counts in the substantia nigra. Trophic activity in the cerebellar extracts from these animals was significantly lower than that present in striatal extracts and was not influenced by 6-OHDA lesions. These data suggest that loss of DA innervation in the striatum is associated with an increase in striatal trophic activity directed at DA neurons. A compensatory response to the loss of DA neurons involving increased striatal trophic activity may result in increased DA terminal sprouting of remaining viable DA neurons that, in turn, would serve to help reinstate normal DA tone.     

Progressive degeneration of dopamine neurons in 6-hydroxydopamine rat model of Parkinson's disease does not involve activation of caspase-9 and caspase-3

6-Hydroxydopamine (6-OHDA), a neurotoxin that causes the death of dopamine (DA) neurons, is commonly used to produce experimental models of Parkinson's disease (PD) in rodents. In the rat model of PD first described by Sauer and Oertel, DA neurons progressively die over several weeks following a striatal injection of 6-OHDA. It is generally assumed that DA neurons die through apoptosis after exposure to 6-OHDA, but data supporting activation of a caspase enzymatic cascade are lacking. In this study, we sought to determine if caspases involved in the intrinsic apoptotic cascade play a role in the initial stages of 6-OHDA-induced death of DA neurons in the progressively lesioned rat model of PD. We found that injection of 6-OHDA into adult rat striatum did not activate caspase-9 or caspase-3 or increase levels of caspase-dependent cleavage products in the substantia nigra at various survival times up to 7 days after the lesion, even though this paradigm produced DA neuronal loss. These data suggest that in the adult rat brain DA neurons whose terminals are challenged with 6-OHDA do not die through a classical caspase-dependent apoptotic mechanism.     

Neuroprotective and neurorescue effect of black tea extract in 6-hydroxydopamine-lesioned rat model of Parkinson's disease

In the present study, an attempt has been made to explore the neuroprotective and neuroreparative (neurorescue) effect of black tea extract (BTE) in 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease (PD). In the neuroprotective (BTE + 6-OHDA) and neurorescue (6-OHDA + BTE) experiments, the rats were given 1.5% BTE orally prior to and after intrastriatal 6-OHDA lesion respectively. A significant recovery in d-amphetamine induced circling behavior (stereotypy), spontaneous locomotor activity, dopamine (DA)-D2 receptor binding, striatal DA and 3-4 dihydroxy phenyl acetic acid (DOPAC) level, nigral glutathione level, lipid peroxidation, striatal superoxide dismutase and catalase activity, antiapoptotic and proapoptotic protein level was evident in BTE + 6-OHDA and 6-OHDA + BTE groups, as compared to lesioned animals. BTE treatment, either before or after 6-OHDA administration protected the dopaminergic neurons, as evident by significantly higher number of surviving tyrosine hydroxylase immunoreactive (TH-ir) neurons, increased TH protein level and TH mRNA expression in substantia nigra. However, the degree of improvement in motor and neurochemical deficits was more prominent in rats receiving BTE before 6-OHDA. Results suggest that BTE exerts both neuroprotective and neurorescue effects against 6-OHDA-induced degeneration of the nigrostriatal dopaminergic system, suggesting that possibly daily intake of BTE may slow down the PD progression as well as delay the onset of neurodegenerative processes in PD.     

Ultrastructural Changes in the Brain of Rats Administered with 6-Hydroxydopamine

Abstract: Adult Wistar rats were treated with 6-Hydroxydopamine (6-OHDA, 200–500 μg) by intraventricular injection. Two, five, seven or 14 days after the injection, the effects of 6-OHDA on rat behavior and the brain ultra-structure were observed. The increased irritability and the tendency of a decrease in self-grooming along with a reduced spontaneous movement were found in rats given 6-OHDA. The main ultrastructural alterations were observed in the nerve terminals localized in the catecholaminergic neurons, particularly the hypothalamic axon terminals. These ultrastructural changes might relate to the behavioral abnormalities in the animals.     

Behavioral and Cellular Protection of Rat Dopaminergic Neurons by an Adenoviral Vector Encoding Glial Cell Line-Derived Neurotrophic Factor

Previously, we observed that an adenoviral (Ad) vector encoding human glial cell line-derived neurotrophic factor (GDNF), injected near the rat substantia nigra (SN), protects SN dopaminergic (DA) neuronal soma from 6-hydroxydopamine (6-OHDA)-induced degeneration. In the present study, the effects of Ad GDNF injected into the striatum, the site of DA nerve terminals, were assessed in the same lesion model. So that effects on cell survival could be assessed without relying on DA phenotypic markers, fluorogold (FG) was infused bilaterally into striatae to retrogradely label DA neurons. Ad GDNF or control treatment (Ad mGDNF, encoding a deletion mutant GDNF, Ad lacZ, vehicle, or no injection) was injected unilaterally into the striatum near one FG site. Progressive degeneration of DA neurons was initiated 7 days later by unilateral injection of 6-OHDA at this FG site. At 42 days after 6-OHDA, Ad GDNF prevented the death of 40% of susceptible DA neurons that projected to the lesion site. Ad GDNF prevented the development of behavioral asymmetries which depend on striatal dopamine, including limb use asymmetries during spontaneous movements along vertical surfaces and amphetamine-induced rotation. Both behavioral asymmetries were exhibited by control-treated, lesioned rats. Interestingly, these behavioral protections occurred in the absence of an increase in the density of DA nerve fibers in the striatum of Ad GDNF-treated rats. ELISA measurements of transgene proteins showed that nanogram quantities of GDNF and lacZ transgene were present in the striatum for 7 weeks, and picogram quantities of GDNF in the SN due to retrograde transport of vector and/or transgene protein. These studies demonstrate that Ad GDNF can sustain increased levels of biosynthesized GDNF in the terminal region of DA neurons for at least 7 weeks and that this GDNF slows the degeneration of DA neurons and prevents the appearance of dopamine dependent motor asymmetries in a rat model of Parkinson's disease (PD). GDNF gene therapy targeted to the striatum, a more surgically accessible site than the SN, may be clinically applicable to humans with PD.