Opposite effects of intranigral ibotenic acid and 6-hydroxydopamine on motor behavior and on striatal neuropeptide Y neurons

Participation of the substantia nigra dopaminergic neurons in the occurrence of gastric mucosal erosions

Previous reports indicate that dopaminergic systems play an important role on gastric mucosal erosions. In the present study, the participation of intrinsic neurons of the substantia nigra (SN) and ventral tegmental area (VTA) on the occurrence of stomach ulceration was investigated. It was found that bilateral microinfusions of a neurotoxic dose (20 microg/microl) of N-methyl-D-aspartate (NMDA) into the SN, but not in the VTA, lead to gastric erosions 24 h after the surgery. A decrease in dopamine levels in the caudate 24 h after the microinfusion of NMDA into the SN was also observed. Destruction of SN cell bodies with 6-hydroxydopamine (6-OHDA) did not induce gastric ulceration or changes in dopamine levels in the caudate nucleus 24 h after the lesioning procedure. NMDA neurotoxicity is mediated by the acute excitatory or activational effects, in contrast to 6-OHDA, suggesting that the occurrence of gastric ulceration after the infusion of NMDA into the SN is not due to the cell death per se but is related to an overactivation of these cells that precede their death. Taken together, these results suggest that modulation of dopaminergic levels by neurons located within the SN may play an important role for the development of gastric erosions.

Increased neuropeptide Y mRNA expression in striatum in Parkinson's disease

High levels of neuropeptide Y (NPY) are found in basal ganglia where it is co-localised with somatostatin (SOM) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH/d) in a population of striatal GABA containing interneurones. Although alterations occur in the levels of various neuropeptides in basal ganglia in Parkinson's disease (PD), it is not known whether NPY is affected. Using in situ hybridisation immunohistochemistry, we have examined the distribution of NPY mRNA in the caudate nucleus, putamen and nucleus accumbens of normal individuals and patients with PD. NPY mRNA was weakly expressed in the caudate nucleus, putamen and nucleus accumbens in normal individuals with a scattered labelling of neurones. However, there was no regional localisation within any brain area and no obvious differences between brain regions. In PD, the number of NPY mRNA-expressing cells was increased as was the density of the silver grains overlying each positive cell. The increase was more pronounced in the nucleus accumbens and in the ventral part of the caudate nucleus. The increase in NPY mRNA expression observed in patients with PD may reflect the loss of dopaminergic tone on striatal NPY containing interneurones, although a role for chronic L-DOPA therapy cannot be ruled out.

Complex motor disturbances in a sequential double lesion rat model of striatonigral degeneration (multiple system atrophy)

This study characterizes paw reaching, stepping and balance abnormalities in a double lesion rat model of striatonigral degeneration, the core pathology underlying levodopa unresponsive parkinsonism associated with multiple system atrophy. Extensive unilateral nigral or striatal lesions induced by 6-hydroxydopamine or quinolinic acid, respectively, produced a similarly marked contralateral paw reaching deficit without further deterioration following a secondary (complementary) lesion of ipsilateral striatum or substantia nigra. Contralateral stepping rates were reduced by unilateral 6-hydroxydopamine lesions without further deterioration following the secondary striatal lesion. In contrast, initial unilateral striatal quinolinic acid injections induced bilateral stepping deficits that significantly worsened contralaterally following the secondary nigral lesion. Contralateral sidefalling rates were significantly increased following primary nigral and striatal lesions. Secondary nigral but not secondary striatal lesions worsened contralateral sidefalling rates. Histological studies revealed subtotal (>90%) depletion of dopaminergic neurons in substantia nigra pars compacta and variable degrees of striatal degeneration depending on the lesion sequence. Animals pre-lesioned with 6-hydroxydopamine showed significantly larger residual striatal surface areas following the secondary striatal quinolinic acid lesion compared to animals with primary striatal quinolinic acid lesions (P<0.001). These findings are in line with previous experimental studies demonstrating that striatal dopamine depletion confers neuroprotection against subsequent excitotoxic injury. Whether loss of dopaminergic neurons protects against the striatal disease process occurring in multiple system atrophy (Parkinson-type) remains to be elucidated. In summary, this is the first experimental study to investigate spontaneous motor behaviour in a unilateral double lesion rat model. Our observations are consistent with a complex interaction of nigral and striatal lesions producing distinct behavioural and histological changes depending on the lesion sequence. Tests of forelimb akinesia and complex motor behaviour appear to provide a reliable tool that will be helpful for monitoring the effects of interventional strategies such as embryonic neuronal transplantation in the rat model of striatonigral degeneration.

Effects of the prototypical mGlu(5) receptor antagonist 2-methyl-6-(phenylethynyl)-pyridine on rotarod, locomotor activity and rotational responses in unilateral 6-OHDA-lesioned rats

In the present study, we evaluated the effect of the prototypical metabotropic glutamate receptor 5 (mGlu(5)) antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) on motor behaviour in rats using the accelerating rotarod, spontaneous locomotor activity and the 6-hydroxy-dopamine (6-OHDA) lesion model to assess its treatment potential for Parkinson's disease. The data indicate that MPEP at doses between 7.5 and 300 mg/kg, p.o. did not disrupt endurance performance on the accelerating rotarod (4-40 rpm in 300 s) which indicates that MPEP has a relatively high safety margin. However, while ineffective at doses of 3.75, 7.5 and 15 mg/kg (p.o.) MPEP inhibited spontaneous locomotor activity at doses of 30 and 100 mg/kg (p.o.). In the 6-OHDA rat rotation model, at doses of 7.5, 15 and 30 mg/kg (p.o.), MPEP induced a dose-dependent ipsilateral rotational response that reached statistical significance at the highest dose tested. This effect was relatively small but consistent. In combination with direct or indirect dopamine agonists, i.e. apomorphine (0.25 mg/kg, s.c.) and D-amphetamine (2.5 mg/kg, i.p.), MPEP (7.5, 15 or 30 mg/kg, p.o.) was found to significantly inhibit these dopamine receptor mediated rotational responses. MPEP injected at a dose of 30 mg/kg also inhibited the rotational response induced by L-DOPA (25 mg/kg, i.p.). (+)MK-801 was used in these rotation experiments as the reference compound. In view of these findings, it could be concluded that MPEP and potentially other mGlu(5) receptor antagonists are probably not appropriate drug candidates for the symptomatic treatment of Parkinson's disease.

Composition of ibotenic acid-induced calcifications in rat substantia nigra

Agonists of the excitatory neurotransmitter glutamate have neurotoxic properties and are, therefore, frequently used to place locally circumscript brain lesions. In certain vulnerable brain areas, especially the substantia nigra and globus pallidus, the ensuing neurodegeneration is accompanied by the formation of calcium deposits. In the present study, we investigated the structure and chemical composition of calcium deposits formed in rat substantia nigra upon local application of ibotenic acid. Using scanning and transmission electron microscopy in combination with X-ray analysis and analysis of the electron diffraction patterns, we demonstrate that the inorganic components of the calcifications consist of calcium and phosphate. The calcium phosphate is deposited in a polycrystalline manner in degenerating neurons and in a matrix surrounding the degenerated complexes. New matrix is continuously added around the enlarging calcium deposits. Content of inorganic material is always higher in the center of the deposits than in the margin, but in every case the diffraction pattern reveals that the calcium phosphates are present in the form of hydroxyapatite. Thus, organic and inorganic components of the calcifications are subject to a continuous process of growth and maturation. The ibotenic acid-induced calcium deposits in rat substantia nigra provide a reliable model system to study the pathogenesis of non-arteriosclerotic calcifications.

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.

The placement of a striatal ibotenic acid lesion affects skilled forelimb use and the direction of drug-induced rotation

The motor consequences of excitotoxic striatal damage have been evaluated extensively in the rat, using tests of whole body motor asymmetry and of deficits in skilled paw and limb movements. However conflicting results of both the type and extent of behavioural deficits have been reported, particularly in the direction of rotation observed in response to the dopamine receptor agonist, apomorphine. The present study investigated the effect of unilateral ibotenic acid lesions in the dorsal striatum of the adult rat, placed at either anterior, posterior, medial, or lateral loci, on rotation in response to both amphetamine and apomorphine, and in the "staircase test" of skilled forelimb use. In a 2 x 2 matrix design experiment, adult female albino rats received a double unilateral lesion of 0.5 microliter 0.06 M ibotenic acid injected at each of two sites either anterior (medial and lateral), posterior (medial and lateral), medial (anterior and posterior), or lateral (anterior and posterior). Rats that received posterior lesions showed a marked ipsilateral rotation in response to both amphetamine and apomorphine, while animals receiving anterior lesions showed little ipsilateral or a slight contralateral bias. Rats receiving lateral lesions showed a marked impairment of contralateral paw use on the "staircase test," while animals with medial lesions showed no significant difference to control unoperated animals. These results confirm the somatotopic organisation of the dorsal striatum in its control of motor functions, and indicate the need to take into account the locus of an excitotoxic lesion in the design of lesion and transplantation studies if we are to achieve reliable tests of the behavioural deficits and recovery.

Impairments and compensatory adjustments in spontaneous movement after unilateral dopamine depletion in rats

Rats with unilateral dopamine (DA) depletions (hemi-Parkinson rats) display directional biases in their locomotion in spontaneous and drug induced tests. These biases have been explained as being due either to changed responsiveness to sensory stimulation, changes in motor ability, or to central changes, but as yet their basis is not fully understood. The purpose of the present experiment is to examine the posture of immobility and the posture and strategies of locomotion in rats with unilateral DA depletions. The rats are found to display impairments in their bad limbs (contralateral-to-lesion limbs) in adjusting posture and moving. They compensate by supporting themselves mainly on their good hindlimb, using the bad hindlimb and tail for balance and by disproportionately relying upon their good limbs to turn and to walk. Thus, their center of gravity is shifted to the good side and movement is preferentially directed toward the good side, in part to maintain equilibrium and in part to remove weight from the bad limbs so that they can enter the swing phase of the stepping cycle. It is proposed that the bad limbs may be unable to apply force to adjust posture and produce movement. These results provide a basis for predicting the movements that the animals will use in various situations and they expand the test repertoire this hemi-Parkinson model provides for studying recovery processes after loss of dopamine.

Synaptic reorganisation in the rat striatum after dopaminergic deafferentation: an ultrastructural study using glutamate decarboxylase immunocytochemistry

The ultrastructure of GABAergic and non-GABAergic synapses in the adult rat neostriatum was examined 6-8 months after unilateral removal of the nigrostriatal dopaminergic pathway by 6-hydroxydopamine injection into the medial forebrain bundle. GABAergic profiles were identified by preembedding glutamate decarboxylase (GAD) immunocytochemistry performed on parasagittal vibratome sections. In three representative fields of the striatum, the nature and number of boutons and their postsynaptic partners were determined and the differences between the striata ipsi- and contralateral to the lesion analyzed. The percentage of GAD-immunoreactive boutons was increased from 23% on the intact side to 28% on the lesioned side. In addition, the GABAergic boutons underwent significantly more multiple contacts with several independent postsynaptic profiles, preferentially with dendritic spines. This could reflect a lesion-induced sprouting of local GABAergic axon terminals. On the other hand, although the vast majority of GABAergic boutons underwent synaptic contacts with dendrites (77% vs. 80%), the number of boutons per dendrite or per dendritic circumference remained unchanged. Thus, the higher frequency of GABAergic boutons may simply reflect the loss of the dopaminergic nerve endings, without a heterosynaptic replacement by GABAergic boutons. The deafferentation also induced structural changes of the postsynaptic profiles. Some dendritic spines had a shortened neck; others were completely integrated in the dendrite which now contained a spine apparatus and was contacted by boutons with the features of axospinous synapses. The spine retraction resulted in a quantitative decrease in the number of spines. Analysis of the synaptic curvature revealed that only spines with a flat contact zone were lost. Concurrently, the number of dendrites was increased, of the GAD-containing in particular, suggesting that the denrites of GABAergic interneurons tend to elongate and/or arborize. Taken together, the results of the present study show that the dopaminergic denervation caused a remodeling of the postsynaptic neurons. The relative increase of the number of GABAergic boutons and their synaptic contacts suggests that an altered wiring of the intrinsic GABAergic system contributes to the changes in the striatal output activity.

Reversal of the adaptive response of neuropeptide Y neurons in the rat striatum to nigrostriatal dopamine deafferentation by the N-methyl-D-aspartate antagonist dizocilpine maleate

This study examined the effects of systemic treatments with dizocilpine maleate alone or in combination with unilateral 6-hydroxydopamine-induced lesion of the nigrostriatal dopaminergic neurons on the number and staining intensity of neuropeptide Y-immunoreactive neurons in the rat striatum. In the combined condition, short-term and long-term treatments with dizocilpine maleate were started 19 days and 12 days after the lesion of the nigrostriatal dopaminergic pathway, respectively. As reported previously, the unilateral dopaminergic lesion elicited an increase in both the number and staining intensity of neuropeptide Y-immunoreactive neurons in the ipsilateral striatum. Short-term treatment with dizocilpine maleate at the dose of 0.2 mg/kg (four injections, 6 h apart, sacrifice 2 h after the final dose), which by itself did not modify neuropeptide Y immunostaining, totally suppressed the effect of the dopaminergic deafferentation on the number of neuropeptide Y-positive neurons but not that on the intraneuronal amount of labelling. When administered twice a day for eight days at the same dose of 0.2 mg/kg, dizocilpine maleate by itself elicited an increase in the number of neuropeptide Y-immunodetectable cells, paradoxically concomitant with a decrease in the levels of intraneuronal labelling. After combination of this treatment with unilateral lesion of the nigrostriatal dopaminergic pathway, the changes related to either the dizocilpine maleate treatment or the 6-hydroxydopamine-induced lesion totally disappeared, so that the number and staining intensity of neuropeptide Y-immunoreactive neurons in that condition did not differ from control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Ibotenic acid-induced calcium deposits in rat substantia nigra. Ultrastructure of their time-dependent formation

The excitotoxin ibotenic acid (IBO) induces local calcium deposits upon injection into rat substantia nigra. Their formation has been investigated at the ultrastructural level in a time course study from 2 days to 8 weeks survival. Potassium bichromate stain was used to visualize pathological calcium accumulation. Two days after IBO application, reaction product for calcium was observed in mitochondria of degenerating perikarya and dendrites, but not in axons, boutons or glia. Four days after the lesion, calcium stain was found, in addition, in a seemingly free form in a few dendrites, especially those still contacted by intact boutons and not sequestrated by invading glia. Two days later, most of these calcium-accumulating dendrites were separated by astroglia from their synaptic partners. At the border between glia and dendrite a fibrillar matrix was formed which further accumulated calcium. During the following weeks this matrix enlarged stepwise and was infiltrated with calcium, thus giving a picture resembling the annual growth rings of trees. The evolving bodies incorporated smaller deposits in their vicinity, finally representing the large concretions seen at the light microscopic level from the 4th postoperative week onward. Similarities and dissimilarities of these observations with the results from other ultrastructural studies on excitotoxin lesions are detailed. It is suggested that the different outfit of neuronal subpopulations and of glia with ligand-gated and metabotropic glutamate receptors in the single brain region, as well as the local response repertoire of glial cells towards the excitotoxic injury with the subsequent formation of a calcium-accumulating matrix provide the molecular basis for the formation of calcium deposits.