Chronic use of marijuana decreases cannabinoid receptor binding and mRNA expression in the human brain

Chronic exposure to Cannabis sativa (marijuana) produced a significant down-regulation of cannabinoid receptor in the postmortem human brain. The significant decrease in maximal binding capacity was not accompanied by changes in the affinity constant. [3H]SR141716A binding was reduced in the caudate nucleus, putamen and in the accumbens nucleus. A significant decrease of binding sites was seen in the globus pallidus. Also in the ventral tegmental area and substantia nigra pars reticulata quantitative analysis of the density of receptors shows a significant reduction in [3H]SR141716A binding. In Cannabis sativa user brains, compared with normal brains [3H]SR141716A binding was reduced only in the hippocampus. The density of cannabinoid receptor 1 mRNA-positive neurons was significantly lower in Cannabis sativa users than in control brains for the caudate nucleus, putamen, accumbens nucleus and hippocampal region (CA1-CA4, areas of Ammon's horn). No hybridization was seen in the mesencephalon and globus pallidus.

An immunohistochemical study of the distribution of brain-derived neurotrophic factor in the adult human brain, with particular reference to Alzheimer's disease

Brain-derived neurotrophic factor is a member of the family of neuronal differentiation and survival-promoting molecules called neurotrophins. Neuronal populations known to show responsiveness to the action of brain-derived neurotrophic factor include the cholinergic forebrain, mesencephalic dopaminergic, cortical, hippocampal and striatal neurons. This fact has aroused considerable interest in the possible contribution of an abnormal brain-derived neurotrophic factor function to the aetiology and physiopathology of different neurodegenerative disorders, such as Alzheimer's disease. This report describes the cellular and regional distribution of brain-derived neurotrophic factor in post mortem control human brain and in limited regions of the brain in patients with Alzheimer's disease, as was revealed by immunohistochemistry. Brain-derived neurotrophic factor is widely expressed in the control human brain, both by neurons and glia. In neurons, brain-derived neurotrophic factor was localized in the cell body, dendrites and axons. Among the structures showing the most intense immunohistochemical labeling were the hippocampus, claustrum, amygdala, bed nucleus of the stria terminalis, septum and the nucleus of the solitary tract. In the striatum, immunoreactivity was more intense in striosomes than in the matrix. Many labeled neurons were found in the substantia nigra pars compacta. The large putatively cholinergic neurons in the basal forebrain showed no immunoreactivity. The general pattern of labeling was similar in individuals with Alzheimer's disease. Brain-derived neurotrophic factor-immunoreactive material was found in senile plaques, and some immunoreactive cortical pyramidal neurons showed neurofibrillary tangles, suggesting that brain-derived neurotrophic factor may be involved in the process of neuronal degeneration and/or compensatory mechanisms which occur in this illness.

[125I]EGF binding in basal ganglia of patients with Parkinson's disease and progressive supranuclear palsy and in MPTP-treated monkeys

Since EGF is known to protect and stimulate the activity of dopaminergic neurons, an autoradiographic study of [125I]EGF binding sites was performed in the striatum and pallidal complex in parkinsonian syndromes. The analysis was performed on postmortem brain tissues of three control subjects, three patients with Parkinson's disease, and three patients with progressive supranuclear palsy, another parkinsonian syndrome in which dopaminergic neurons also degenerate. Since all six patients had been treated with L-Dopa, we also analyzed the effects of this drug in an animal model of Parkinson's disease. Quantitative analysis of [125I]EGF binding was performed on the brains of three control monkeys, nine monkeys rendered parkinsonian by MPTP intoxication, three of which were treated with L-Dopa. An increased density of [125I]EGF binding was observed at anterior levels in the dorsal striatum, but not in the pallidum, of patients with Parkinson's disease and progressive supranuclear palsy. [125I]EGF binding was unchanged in parkinsonian monkeys whether or not they had been treated with L-Dopa. The data suggest an increased expression of EGFRs in the striatum in chronic parkinsonian syndromes but not in acute models of the disease.

Neuroanatomy of the basal ganglia

This article deals with the neuroanatomic aspects of the basal ganglia with regard to different neurotransmitter systems and to different diseases. A general scheme of these circuits with the overall distinction between limbic-associative and motor components and circuits is presented.

Consequence of nigrostriatal denervation and L-dopa therapy on the expression of glutamic acid decarboxylase messenger RNA in the pallidum

To examine the consequences of nigrostriatal denervation and L-dopa treatment on the basal ganglia output system, we analyzed, by quantitative in situ hybridization, the messenger RNA coding for glutamic acid decarboxylase (Mr 67,000) (GAD67 mRNA) in pallidal cells from patients with Parkinson's disease (PD), monkeys rendered parkinsonian by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) receiving or not receiving L-dopa, and their respective control subjects. In MPTP-treated monkeys, the expression of GAD67 mRNA was increased in cells from the internal pallidum, and this effect was abolished by L-dopa treatment. There were no differences in the levels of GAD67 mRNA between patients with PD, who were all treated with L-dopa, and control subjects. These results indicate that the level of GAD67 mRNA is increased in the cells of the internal pallidum after nigrostriatal dopaminergic denervation and that this increase can be reversed by L-dopa therapy.

Regional distribution of monoamine vesicular uptake sites in the mesencephalon of control subjects and patients with Parkinson's disease: a postmortem study using tritiated tetrabenazine

The distribution of the vesicular monoamine transporter was investigated post mortem in the human ventral mesencephalon of control subjects (n = 7) and patients with Parkinson's disease (n = 4) using tritiated dihydrotetrabenzine binding and autoradiography. Tritiated dihydrotetrabenazine binding was characterized by a single class of sites with a Kd of 7 nM and a Bmax of 180 fmol/mg of protein in the substantia nigra. Tritiated dihydrotetrabenazine binding sites were heterogeneously distributed in the mesencephalon of control subjects: the density of tritiated dihydrotetrabenazine binding sites was high in the substantia nigra pars compacta, locus coeruleus and nucleus raphe dorsalis, moderate in the ventral tegmental area and low in the substantia nigra pars reticulata and catecholaminergic cell group A8. Within the substantia nigra, a zone with maximal density of tritiated dihydrotetrabenazine binding, two times higher than the mean estimate for the whole substantia nigra pars compacta, was detected in the medial part of the structure. The anatomical organization of the human ventral mesencephalon was analyzed on adjacent sections stained for acetylcholinesterase histochemistry and tyrosine hydroxylase immunohistochemistry. Tritiated dihydrotetrabenazine binding displayed the same characteristic regional pattern of distribution as that observed with tyrosine hydroxylase immunohistochemistry except in the nucleus raphe dorsalis, where no tyrosine hydroxylase immunoreactivity was detected. In parkinsonian brains, the level of tritiated dihydrotetrabenazine binding was dramatically decreased in all regions of the ventral mesencephalon analyzed except in the substantia nigra pars reticulata. In the substantia nigra pars compacta, the reduction was by 55% for the whole structure and by 65% in its medial zone, where binding site density was maximal. In most nigral subsectors analyzed, the decrease in density of tritiated dihydrotetrabenazine binding sites reached the level expected given the loss of tyrosine hydroxylase-positive cells observed. By contrast, the ratio of [3H]dihydrotetrabenazine binding to the number of tyrosine hydroxylase positive neurons was significantly increased in the zone of high [3H]dihydrotetrabenazine binding sites. This relative sparing of tritiated dihydrotetrabenazine binding sites may be due either to the contribution of other monoaminergic neurons such as serotoninergic neurons or more likely to hyperactivity of the still surviving dopaminergic neurons.

Autoradiographic localization and density of [125I]ferrotransferrin binding sites in the basal ganglia of control subjects, patients with Parkinson's disease and MPTP-lesioned monkeys

Degeneration of the nigro-striatal dopaminergic neurons occurring in Parkinson's disease is associated with an increase in iron concentrations in the substantia nigra. As this metal catalyzes the production of free radicals, and oxidative stress may participate in the cascade of events ending in cell death, this increase in iron content may be involved in dopaminergic neuronal death. The localization and number of receptors for transferrin were investigated postmortem by quantitative autoradiography of iodinated-ferrotransferrin binding in the basal ganglia from controls, parkinsonian patients and MPTP-lesioned monkeys. In human controls, specific [125i] ferrotransferrin binding-site density was highest in the putamen and the caudate nucleus, and lowest in the globus pallidus. In parkinsonian patients, it was increased in the putamen and caudate nucleus, while in MPTP-intoxicated monkeys, there was a tendency for levels to decrease in these two regions. An inverse relationship between binding density and iron content reported in the studied regions supports the assumption of a possible capture of iron at the level of dopaminergic terminals and, in parkinsonian patients, on other cellular elements as well. These results suggest an involvement of transferrin receptors in iron uptake in the striatum of patients with Parkinson's disease, with differences between the 'acute' nigro-striatal MPTP-induced degeneration syndrome and the chronic long lasting human disease.

Effects of nigrostriatal denervation and L-dopa therapy on the GABAergic neurons in the striatum in MPTP-treated monkeys and Parkinson's disease: an in situ hybridization study of GAD67 mRNA

The effects of nigrostriatal denervation and L-dopa therapy on GABAergic neurons were analysed in patients with Parkinson's disease and in monkeys rendered parkinsonian by MPTP intoxication. The expression of the messenger RNA coding for the 67 kDa isoform of glutamic acid decarboxylase (GAD67 mRNA), studied by quantitative in situ hybridization, was used as an index of the GABAergic activity of the striatal neurons. A significant increase in GAD67 mRNA expression, generalized to all GABAergic neurons, was observed in MPTP-treated monkeys compared to control monkeys in the putamen and caudate nucleus (+44 and +67% respectively), but not in the ventral striatum. L-Dopa therapy significantly reduced GAD67 mRNA expression in the putamen and caudate nucleus to levels similar to those found in control monkeys. However, the return to normal of GAD67 mRNA expression was not homogeneous across all neurons since it was followed by an increase of labelling in one subpopulation of GABAergic neurons and a decrease in another. These data suggest that in MPTP-treated monkeys the degeneration of nigrostriatal dopaminergic neurons results in a generalized increase in GABAergic activity in all the GABAergic neurons of the striatum, which is partially reversed by L-dopa therapy. As the expression of GAD67 mRNA is less intense in the ventral than in the dorsal striatum, this increase in striatal GABAergic activity may be related to the severity of nigrostriatal denervation. In parkinsonian patients who had been chronically treated with L-dopa, GAD67 mRNA expression was significantly decreased in all GABAergic neurons, in the caudate nucleus (by 44%), putamen (by 43.5%) and ventral striatum (by 26%). The opposite variation of GAD67 mRNA in patients with Parkinson's disease, compared with MPTP-treated monkeys, might be explained by the combination of chronic nigrostriatal denervation and long-term L-dopa therapy.

Alterations of GABAergic neurons in the basal ganglia of patients with progressive supranuclear palsy: an in situ hybridization study of GAD67 messenger RNA

We analyzed postmortem GABAergic neurons in the basal ganglia of three patients with progressive supranuclear palsy (PSP) and four matched controls by means of glutamic acid decarboxylase (M(r) 67,000 [GAD67]) mRNA in situ hybridization. In PSP, we found a 50 to 60% decrease in the number of neurons expressing GAD67 mRNA in the caudate nucleus, ventral striatum, and the external and internal pallidum. The expression of GAD67 mRNA per neuron was reduced in the caudate nucleus and putamen (-43%), the ventral striatum (-55%), and the external and internal pallidum (-59% and -68%). Our data indicate that striatal and pallidal GABAergic neurotransmission is markedly reduced in PSP and we suggest that this alteration may account for the motor and cognitive symptoms observed in PSP. Furthermore, the destruction of the basal ganglia output systems may explain the lack of responsiveness to L-dopa therapy of PSP patients.

Loss of striatal high affinity NGF binding sites in progressive supranuclear palsy but not in Parkinson's disease

125I-Nerve growth factor (NGF) binding sites were analyzed by autoradiography in the striatum of 3 control subjects, 3 patients with Parkinson's disease and 3 patients with progressive supranuclear palsy. A high level of 125I-NGF binding was observed (0.3-0.4 fmol/mg of tissue equivalent) in the striatum and the nucleus basalis of Meynert of control patients. Pockets of lower 125I-NGF binding corresponding to acetylcholinesterase-poor striosomes were detected in the striatum of control subjects and patients with Parkinson's disease or progressive supranuclear palsy. When compared to controls, the density of 125I-NGF binding sites was reduced by 30% in the striatum of patients with progressive supranuclear palsy but not reduced in that of patients with Parkinson's disease. 125I-NGF binding was not significantly decreased in the nucleus basalis of Meynert in either diseases. Since NGF receptors are thought to be localized on cholinergic neurons in the striatum, the decrease in NGF binding is compatible with the loss of cholinergic neurons reported in the striatum from PSP patients.

Monoamine vesicular uptake sites in patients with Parkinson's disease and Alzheimer's disease, as measured by tritiated dihydrotetrabenazine autoradiography

The monoaminergic innervation of the caudate nucleus, putamen and ventral striatum was investigated post mortem, in patients with Parkinson's and Alzheimer's disease as compared to control subjects, by autoradiographic detection of tritiated dihydrotetrabenazine (3H-TBZOH), a specific high affinity ligand of the vesicular monoamine transporter. The binding of 3H-TBZOH was specific and saturable (Kd 5.3 nM). In control striatum, the pattern of distribution of 3H-TBZOH binding was heterogeneous, with higher binding levels in the 'matrix' than in the 'striosome' compartment. Changes in ligand binding levels were observed in the pathological brains compared to controls. In Parkinson's disease (PD), characterized by a severe damage of mesostriatal dopaminergic neurons, the density of 3H-TBZOH binding was reduced. A severe decrease in 3H-TBZOH binding was observed in all parts of the striatum (caudate nucleus: -80%, putamen: -86%, ventral striatum: -94%) in PD brains. The data corroborate the deficiency in striatal dopaminergic transmission and suggest that in PD brains dopaminergic terminals have disappeared and/or no longer contain synaptic vesicles. In Alzheimer's disease (AD), 3H-TBZOH binding was significantly reduced by 57% in the ventral striatum and not in the caudate nucleus and putamen. The specific decrease of monoaminergic transporter levels in the ventral striatum confirm that this nucleus is a target area in AD.

Autoradiographic study of [125I]epidermal growth factor-binding sites in the mesencephalon of control and parkinsonian brains post-mortem

Epidermal growth factor (EGF) is assumed to act as a neurotrophic factor on dopaminergic nigrostriatal neurons in cell cultures and animal brain. This led us to consider its possible role in the pathophysiology of Parkinson's disease. An autoradiographic study of the distribution of EGF-binding sites was performed in the mesencephalon of controls and patients with Parkinson's disease, a neurodegenerative disease associated with dramatic damage to the mesostriatal dopaminergic neurons. Scatchard analysis revealed a single type of binding sites with a high affinity constant, in the various mesencephalic dopaminergic areas examined. The characteristics and density of [125I]EGF-binding sites were similar in controls and parkinsonian patients. This suggests that EGF receptors in the mesencephalon are unaffected in Parkinson's disease and may therefore contribute to the increased activity and survival of the remaining dopaminergic neurons.

Distribution of 125I-ferrotransferrin binding sites in the mesencephalon of control subjects and patients with Parkinson's disease

Iron is abnormally accumulated in the substantia nigra pars compacta of patients with Parkinson's disease (PD). Because neuronal and glial iron uptake seems to be mediated by the binding of ferrotransferrin to a specific high-affinity receptor on the cell surface, the number of transferrin receptors could be altered in this disease. The regional distribution of specific binding sites for human 125I-diferric transferrin has been studied in the mesencephalon, on cryostat-cut sections from autopsy brains of control subjects and parkinsonian patients by in vitro autoradiography. Densities of binding sites were highest in the central gray substance (approximately 10 fmol/mg of tissue equivalent), intermediate in the catecholaminergic cell group A8, superior colliculus, and ventral tegmental area, and almost nonexistent in the substantia nigra. The density of 125I-transferrin binding sites was not significantly different between parkinsonian and control brains in any region analyzed. These results show that in the mesencephalon the regional density of transferrin binding sites is lowest in the dopaminergic cell groups, which are the most vulnerable to PD, and suggest that iron does not accumulate through an increased density of transferrin receptors at the level of the substantia nigra.