Selective degeneration of central dopaminergic systems after injection of 6-hydroxydopamine in the ventral mesencephalic tegmentum of the rat. Demonstration by the Fink-Heimer strain

Torsin-mediated protection from cellular stress in the dopaminergic neurons of Caenorhabditis elegans

Parkinson's disease (PD) is linked genetically to proteins that function in the management of cellular stress resulting from protein misfolding and oxidative damage. Overexpression or mutation of alpha-synuclein results in the formation of Lewy bodies and neurodegeneration of dopaminergic (DA) neurons. Human torsinA, mutations in which cause another movement disorder termed early-onset torsion dystonia, is highly expressed in DA neurons and is also a component of Lewy bodies. Previous work has established torsins as having molecular chaperone activity. Thus, we examined the ability of torsinA to manage cellular stress within DA neurons of the nematode Caenorhabditis elegans. Worm DA neurons undergo a reproducible pattern of neurodegeneration after treatment with 6-hydroxydopamine (6-OHDA), a neurotoxin commonly used to model PD. Overexpression of torsins in C. elegans DA neurons results in dramatic suppression of neurodegeneration after 6-OHDA treatment. In contrast, expression of either dystonia-associated mutant torsinA or combined overexpression of wild-type and mutant torsinA yielded greatly diminished neuroprotection against 6-OHDA. We further demonstrated that torsins seem to protect DA neurons from 6-OHDA through downregulating protein levels of the dopamine transporter (DAT-1) in vivo. Additionally, we determined that torsins protect robustly against DA neurodegeneration caused by overexpression of alpha-synuclein. Using mutant nematodes lacking DAT-1 function, we also showed that torsin neuroprotection from alpha-synuclein-induced degeneration occurs in a manner independent of this transporter. Together, these data have mechanistic implications for movement disorders, because our results demonstrate that torsin proteins have the capacity to manage sources of cellular stress within DA neurons.

Experimental models of Parkinson's disease: from the static to the dynamic

The experimental models of Parkinson's disease (PD) available today can be divided into two categories according to the mode of action of the compound used: transient pharmacological impairment of dopaminergic transmission along the nigrostriatal pathway or selective destruction by a neurotoxic agent of the dopaminergic neurons of the substantia nigra pars compacta. The present article looks at the relative merits of each model, the clinical symptoms and neuronal impairment it induces, and the contribution it could make to the development of a truly dynamic model. It is becoming more and more clear that there is an urgent need for a chronic model integrating all the clinical features of PD including resting tremor, and reproducing the gradual but continuous nigral degeneration observed in the human pathology. Discrepancies have been reported several times between results obtained in classic animal models and those described in PD, and it would seem probable that such contradictions can be ascribed to the fact that animal models do not, as yet, reproduce the continuous evolution of the human disease. Dynamic experimental models which come closer to the progressive neurodegeneration and gradual intensification of motor disability so characteristic of human PD will enable us to investigate crucial aspects of the disease, such as compensatory mechanisms and dyskinesia.

Ventral tegmental (A10) system: neurobiology. 1. Anatomy and connectivity

The VTA contains the A10 group of DA containing neurons. These neurons have been grouped into nuclei to be found on the floor of the midbrain tegmentum--Npn, Nif, Npbp and Nln rostralis and caudalis. The VTA is traversed by many blood vessels and nerve fibers. Close to its poorly defined borders are found DA (A8, A9, A11) and 5-HT containing neurons (B8). Efferent projections of the VTA can be divided into 5 subsystems. The mesorhombencephalic projects to other monoaminergic nuclei, the cerebellum and a fine projection descends to other tegmental nuclei as far as the inferior olive. Fibers to the spinal cord have not been demonstrated. The mesodiencephalic path projects to several thalamic and hypothalamic nuclei and possibly the median eminence. Functionally important examples are the anterior hypothalamic-preoptic area, N. medialis dorsalis and reuniens thalami. These two subsystems are largely non-dopaminergic. A minor mesostriatal projection is overshadowed by the large mesolimbic projection to the accumbens, tuberculum olfactorium, septum lateralis and n. interstitialis stria terminalis. There are also mesolimbic connections with several amygdaloid nuclei (especially centralis and basolateralis), the olfactory nuclei and entorhinal cortex. A minor projection to the hippocampus has been detected. The mesocortical pathway projects to sensory (e.g. visual), motor, limbic (e.g. retrosplenial) and polysensory association cortices (e.g. prefrontal). Prefrontal, orbitofrontal (insular) and cingulate cortices receive the most marked innervation from the VTA. A more widespread presence of DA in other cortices of rodents becomes progressively more evident in carnivores and primates. Most but not all projections are unilateral. Some neurons project to more than one area in mesodiencephalic, limbic and cortical systems. The majority of these fibers ascend in the MFB. Most areas receiving a projection from the VTA (DA or non-DA) project back to the VTA. The septohippocampal complex in particular and the limbic system in general provide quantitatively much less feedback than other areas. The role of the VTA as a mediator of dialogue with the frontostriatal and limbic/extrapyramidal system is discussed under the theme of circuit systems. The large convergence of afferents to certain VTA projection areas (prefrontal, entorhinal cortices, lateral septum, central amygdala, habenula and accumbens) is discussed under the theme of convergence systems.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of gamma-aminobutyric acid-immunoreactive neurons in the septal region of the rat brain

The distribution of gamma-aminobutyric acid-immunoreactive (GABA-I) elements was examined in the septal region of the rat brain. The indirect peroxidase-antiperoxidase technique was used with anti-GABA antibodies in normal and colchicine-pretreated rats, with or without use of detergent in the incubation medium. Intraventricular injection of colchicine did not result in any change in the staining of neuronal perikarya. Intraseptal injections increased the intensity of labelling of GABA-I cell bodies in the lateral septal nucleus and increased the number of labelled cells in the medial septal nucleus and diagonal band of Broca (dbB). Triton X-100 added to the incubation media decreased the intensity of staining and number of GABA-I somata in all septal nuclei with a concentration-dependent effect. No change was observed concerning GABA-I varicosities. The septal area, including the lateral, medial, and triangular septal nuclei; the anterior rudiment of the hippocampus; the island of Calleja magna; the septofimbrial nucleus; the bed nucleus of the stria terminalis; and the dbB showed a strong reaction to anti-GABA antibodies with regard to GABA-containing surrounding structures. GABA-I axonal varicosities were observed in all the regions with an uneven distribution. The highest density was found in the dorsal and ventral parts of the lateral septal nucleus and in a band situated between the dbB and the nucleus accumbens. Labelled varicosities were frequently observed surrounding GABA-I and nonimmunoreactive cell bodies. GABA-I somata ranged from 10 to 30 micron in diameter. Small neurons were present in great number at the ventricular border and in the zona limitans. Medium-size and large neurons were mostly observed in the medial part of the dorsal lateral nucleus and in the intermediate lateral nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of the locus coeruleus induced by selective stimulation of the ventral tegmental area

The effects of selective stimulation of perikarya, but not axons of passage, within the ventral tegmental area (VTA) on the locus coeruleus (LC) noradrenergic system were examined. Anterograde and combined retrograde-immunohistochemical studies indicated both dopaminergic and non-dopaminergic projections to the region of the LC originating from the VTA. Kainic acid (KA) stimulation of the VTA resulted in a dose-dependent increase in the levels of the dopamine metabolite dihydroxyphenylacetic acid (DOPAC) in the prefrontal cortex, and also elevated levels of the norepinephrine (NE) metabolite 3-methoxy-4-hydroxyphenolglycol (MHPG). Prefrontal cortical MHPG levels did not increase in response to vehicle injection or KA infusion into the hippocampus, nor did concentrations of this metabolite increase in the prefrontal cortex in response to intra-VTA KA in animals with neurotoxic lesions of the VTA. KA injection into the VTA resulted in increased MHPG levels in the hippocampus, but not the hypothalamus. Dorsal noradrenergic bundle knife cuts prevented the KA-elicited prefrontal cortical MHPG increase. These data suggest that stimulation of the mesocoeruleo dopaminergic projection arising from the VTA results in selective excitation of the LC-derived dorsal bundle noradrenergic system.

Further studies on the effects of intravenously administered 6-hydroxydopamine on the median eminence of the rat

6-Hydroxydopamine (6-OHDA) given i.v. in a dose of 150 mg/kg to adult male Sprague-Dawley rats produces at 24 h a complete depletion of median eminence (ME) and neurointermediate lobe (NIL) catecholamines (CA), as judged by Falck-Hillarp fluorescence histochemistry, leaving the remainder of the hypothalamus substantially unaltered. Restoration of a normal fluorescence histochemical appearance took place over 35 days, apparently due to regeneration of CA-containing terminals. Administration of desipramine prior to 6-OHDA injection modified its effect; depletion was largely confined to the midline region of the external layer of the ME and to the NIL, suggesting that these regions contain dopaminergic terminals. Microspectrofluorometric methods were used in an attempt to verify this conclusion. It is suggested that this technique provides a model for establishing the role of ME and NIL CA-containing structures in control of pituitary gland function.

Terminal degeneration demonstrated by the Fink-Heimer method following lateral ventricular injection of 6-hydroxydopamine

Degenerating terminals were mapped by the Fink-Heimer method after lateral or fourth ventricular administration of 6-hydroxydopamine (60OHDA). This method marks dopaminergic terminals and has the advantage that noradrenergic terminals are not stained. Fink-Heimer stained degeneratig terminals were seen bilaterally in specific patterns in many nuclei known to have a dopaminergic innervation: neostriatum, nucleus accumbens, olfactory tubercle, the dorsolateral and ventral parts of the bed nucleus of the stria terminalis, laterla septal nucleus, amygdala, and layers II-III of anterior cingulate cortex. Detailed maps are provided of the dopaminergic innervation in the bed nucleus of the atria terminalis in relatin to the cytoarchitectural subdivisions of this nucleus. A Fink-Heimer stained field was discovered in the lateral parabrachial nucleus, suggesting the presence of a previously unreported dopaminergic innervation of this nucleus. It was also noted that nonspecific degeneration near the injection site was much worse after lateral ventricle than after fourth ventricle injection.

Light and electron microscopic identification of monoaminergic terminals in the central nervous system

A brief critical survey of methods used for light and electron microscopic examination of amine-containing pathways within the CNS. Light microscopic techniques such as fluorescence histochemistry, immunocytochemistry, autoradiography, silver degeneration techniques, and retrograde tracing technique are suitable for studying the topography of pathways but, due to limits of resolution, they are inadequate for identifying terminals. Electron microscopy which is adequate to visualize terminals does not provide an overall view. This review considers various methods which have been devised to specifically detect aminergic nerve terminals. Electrolytic and chemical induced degenerations are described in noradrenergic, dopaminergic, and serotoninergic terminals. Although the individual degenerative alterations are not specific for aminergic terminals, the degenerative process when considered as a whole can be informative. At present no single technique can provide complete information about the origin, course, connections, and terminals of aminergic systems. Concurrent application of light and electron microscopy, experimental surgery, histochemistry, and microsample biochemistry would provide a complete description.

Neuropharmacological studies on the nigro-striatal and raphe-striatal system in the rat

The responses of single neostriatal neurones to substantia nigra (SN) and dorsal raphe nucleus (DRN) stimulation and iontophoretic administration of several drugs were studied in urethane-anaesthetised rats. Stimulation of the SN-evoked excitation followed by inhibition in striatal neurones. In some cells only inhibition of firing was evoked indicating that there may be separate nigrostriatal inhibitory and excitatory pathways. DRN stimulation evoked mainly inhibition of striatal cell firing. The activity of most neurones responding to SN and DRN stimulation was depressed by iontophoretically administered dopamine, 5-hydroxytryptamine and GABA and increased by acetylcholine. Studies with antagonist revealed that alpha-flupenthixol reduced responses to dopamine and 5-hydroxytryptamine and inhibition evoked by SN and DRN stimulation. Bicuculline methochloride only reduced responses to GABA. Methysergide selectively reduced responses to 5-hydroxytryptamine and also reduced DRN-but not SN-evoked inhibition. It was concluded that the SN-evoked inhibition was probably mediated by dopamine and DRN-evoked inhibition by 5-hydroxytryptamine.

Behavioral effects of lesions in the A10 dopaminergic area of the rat

Experiments have been carried out with 150 rats in order to study some psychophysiological functions of the mesencephalocortico limbic dopaminergic A10 group. Lesions in the A10 area were made by using 6-hydroxydopamine (6-OHDA) local injections; 2 small volumes of injections were used at the same concentration (2 mug/1 mul or 1 mug/0.5 mul). In a first experiment the effects of these two injections were tested on locomotor activity measured in a circular corridor, 10 and 30 days after surgery. Injections provoked hyperactivity, mainly during nocturnal basal activity periods, but not during initial exploratory activity periods. The larger the injection, the more important the hyperactivity was. The larger injections induced important food spillage evidence through the wire floor of the home cage and perturbation in a passive avoidance learning. There was no change in body weight or in amount of ingested food. In a second experiment, the effects of local injection of 6-OHDA in the other CA structures or bundles situated in or near the ventral tegmental area were tested. Injections in the substantia nigra compacta, in the noradrenergic ventral bundle, in the dorsal periventricular system-tegmental radiations did not provoke locomotor hyperactivity. In a third experiment, a possible role of the median raphe (MR) nucleus in the A10-lesion induced hyperactivity was tested: first, radiofrequency MR lesions were made and no durable significant hyperactivity was recorded; secondly, 6-OHDA (1 mug/0.5 mul) was injected into the A10 area and activity was measured 10 days later: these injections provoked significant hyperactivity during the nocturnal basal and the diurnal basal activity periods. It might be concluded that neither the neighboring CA fibers nor the MR were directly involved in the ventral tegmental -- 6-OHDA lesions syndrome. Anatomical controls by using the Fink-Heimer silver impregnating method have demonstrated, first, that the 6-OHDA injections did not destroy fibers other than catecholaminergic and secondly, that the degenerations are found in the forebrain and cortical limbic A10 projections. Hypotheses are made about a possible general inhibitory role of the A10 in behavior, in the sence of selective and attentive arousal processes, often impaired in some mental illnesses.

Silver impregnation of dopaminergic systems after radiofrequency and 6-OHDA lesions of the rat ventral

Nauta and Fink-Heimer silver impregnation techniques were used to study the anterior degeneration produced by radiofrequency (RF) or 6-OHDA lesions in the medial and lateral ventral mesencephalic tegmentum (VMT), substantia nigra and dorsalis tegmental decussation (DTD) in rats. Both Nauta and Fine-Heimer impregnating methods showed that RF lesion of the VNT produced degeneration in three major pathways: a ventral pathway corresponding to the fasciculus medialis prosencephali (FMP), an intermediate pathway projecting to the ventral thalamus, and a dorsal pathway to the medio-dorsal thalamus and to the nucleus lateralis habenulae. In addition, the Fink-Heimer method demonstrated prejections of the dopaminergic A10 and A9 cell group in the VMT to the nucleus caudatus after RF or 6-OHDA lesions. Projections to nucleus accumbens, tuberculum olfactorium, stria terminalis, and cortex frontalis were observed only after 6-OHDA lesion of the A10 cell group. Degeneration in cortex cinguli and entorhinalis was seen mainly after 6-OHDA lesion of the A9 cell group. The limbic forebrain cortical projections of the A10 group provide a coherent anatomical basis for the behavioral syndrome provoked by RF and 6-OHDA lesions in the VMT.

Excitatory nature of dopamine in the nigro-caudate pathway

Inputs from the substantia nigra (SN) to the caudate nucleus (Cd) and the effects of electrophoretic dopamine on Cd neurones were studied in cats anaesthetized with pentobarbitone with intracellular techniques. Single shock electrical stimulation of the SN or the medial forebrain bundle (MFB) induced monosynaptic EPSPs in Cd neurones. Dopamine depolarized Cd neurones and chlorpromazine suppressed the SN or MFB induced EPSPs. Appropriate controls indicate that the drug effects were not artifactual. Some recorded neurones were identified by procion yellow dye injection as the medium-size intrinsic Cd neurones.

An additional silver impregnation method for demonstration of degenerating nerve cells and processes in the central nervous system

A new silver impregnation technique for frozen and paraffin sections of formalin-fixed nervous tissue has been devised by modifying the Fink-Heimer14 and De Olmos-Ingram6 methods. The modified versions have been combined into a single staining procedure. Cobalt or lead nitrate are substituted for uranyl nitrate. Silver nitrate in the impregnating solution is replaced by silver lactate or protargol. This procedure results in a preferential impregnation of degenerating perikarya, dendrites, axons and synaptic endings. It affords a more complete impregnation of 'preterminal' axonal arborizations than previous methods. The method is effective for the demonstration of degenerating terminals in the rat cerebellar cortex. Emphasis has been laid on the usefulness of the method for the study of drug-induced CNS lesions.