Basal ganglia calcification induced by excitotoxicity: an experimental model characterised by electron microscopy and X-ray microanalysis

Activation of glutamate receptors induces an excitotoxic neurodegenerative process characterised in some brain areas by the formation of calcium precipitates. To examine the pathogenesis of basal ganglia calcification (BGC), an improved procedure of X-ray microanalysis was used to study experimental excitotoxic calcification in the rat. Three weeks after injection of ibotenic acid (IBO) in the rat basal forebrain, calcified inclusions within hypertrophied astrocytes were characterised. They appeared to form part of a filamentous structure localised in the cytoplasm in association with normal mitochondria and other organelles. Larger inclusions were surrounded by reactive microglia. The main inorganic components in these deposits were Ca and P, frequently accompanied by S. Al, Si and K. The shape and Ca/P molar ratio of the large deposits (>10 microm) indicate that they may be biological apatites. Aluminosilicates were detected as small deposits (<4 microm) free of other mineral constituents. To our knowledge this is the first report showing that IBO lesion induces brain accumulation of aluminosilicates similar to that described in Alzheimer's or Fahr's patients. Our data indicate that precipitation of Ca and Al may reduce their IBO-induced increased concentration. In conclusion, the experimental model and the improved efficiency of X-ray analysis described may help us to understand the pathogenesis of BGC.

Motor actions of cannabinoids in the basal ganglia output nuclei

The levels of CB1 cannabinoid receptors in the basal ganglia are the highest in the brain, comparable to the levels of dopamine receptors, a major transmitter in the basal ganglia. This localization of receptors is consistent with the profound effects on motor function exerted by cannabinoids. The output nuclei of the basal ganglia, the globus pallidus (GP) and substantia nigra reticulata (SNr), apparently lack intrinsic cannabinoid receptors. Rather, the receptors are located on afferent terminals, the striatum being the major source. Cannabinoids blocked the inhibitory action of the striatal input in the SNr. Furthermore, cannabinoids blocked the excitatory effect of stimulation of the subthalamic input to the SNr revealing, along with data from in situ hybridization studies, that this input is another likely source of cannabinoid receptors to the SNr. Similar actions of cannabinoids were observed in the GP. Behavioral studies further revealed that the action of cannabinoids differs depending upon which input to the output nuclei of the basal ganglia is active. The inhibitory striatal input is quiescent and the cannabinoid action is observable only upon stimulation of the striatum, while the noticeable effect of cannabinoids under basal conditions would be on the tonically active subthalamic input. These data suggest that the recently discovered endogenous cannabinergic system exerts a major modulatory action in the basal ganglia by its ability to block both the major excitatory and inhibitory inputs to the SNr and GP.

Neonatal iron exposure induces neurobehavioural dysfunctions in adult mice

Excess iron in the brain has been implicated in the pathogenesis of several human neurodegenerative disorders, i.e., Parkinson's and Alzheimer's disease. The neonatal period is critical for the establishment of normal iron content in the adult brain. In the present study, the long-term neurobehavioral effects of iron exposure during this period were assessed by treating NMRI mice orally with 0.0, 3.7, or 37.0 mg Fe(2+)/kg body wt on postnatal days 10-12. Spontaneous motor behavior and radial arm maze learning were tested at the age of 3 months. It was found that the mice treated with the higher dose of Fe(2+), 37.0 mg/kg body wt, were hypoactive during the first 20 min of testing but hyperactive during the final 20 min, showing an almost complete lack of habituation of spontaneous activity in the test chambers. These changes were also seen in animals treated with the lower dose of Fe(2+), 3.7 mg/kg body wt, but the effects were less pronounced, indicating a dose-response relationship. In the radial arm maze, the Fe(2+) 37.0 mg/kg group evidenced significantly both more errors in arm choices and longer latencies to acquire all eight pellets. Both dose groups showed attenuated performance increments on successive trials. Analysis of brain iron content indicated significantly more total iron (microgram/g) in the basal ganglia, but not frontal cortex, of the higher, 37 mg/kg, dose group. The knowledge of the long-term effects of iron entering the brain during this critical period of rapid brain growth is limited. Increased amounts of iron in the brain, especially in the basal ganglia, may contribute to neurodegenerative processes.

Distribution and cellular localization of the serotonin type 2C receptor messenger RNA in human brain

The regional and cellular distribution of serotonin type 2C receptor messenger RNA was investigated in autopsy samples of human brain by in situ hybridization histochemistry. The main sites of serotonin receptor type 2C messenger RNA expression were the choroid plexus, cerebral cortex, hippocampus, amygdala, some components of the basal ganglia, the substantia nigra, the substantia innominata and the ventromedial hypothalamus, suggesting that this receptor might be involved in the regulation of different brain functions. Interestingly, in all regions examined, the serotonin type 2C receptor messenger RNA was always restricted to subpopulations of cells, suggesting a specific role, perhaps determined by regionality. A comparison of the in situ hybridization results with those previously obtained by means of radioligand binding experiments suggested that in most of the areas analysed the serotonin type 2C receptors were located at axon terminals.

Increased basal ganglia iron levels in Huntington disease

OBJECTIVE

To quantify in vivo brain ferritin iron levels in patients with Huntington disease (HD) and normal control subjects.

DESIGN AND SUBJECTS

A magnetic resonance imaging method that can quantify ferritin iron levels with specificity in vivo was employed to study 11 patients with HD and a matched group of 27 normal controls. Three basal ganglia structures (caudate, putamen, and globus pallidus) and 1 comparison region (frontal lobe white matter) were evaluated.

RESULTS

Basal ganglia iron levels were significantly increased (P<.002) in patients with HD, and this increase occurred early in the disease process. This was not a generalized phenomenon, as white matter iron levels were lower in patients with HD.

CONCLUSIONS

The data suggest that increased iron levels may be related to the pattern of neurotoxicity observed in HD. Reducing the oxidative stress associated with increased iron levels may offer novel ways to delay the rate of progression and possibly defer the onset of HD.

Extrastriatal dopaminergic innervation of human basal ganglia

A tyrosine-hydroxylase immunohistochemical analysis of the brains of normal human individuals has revealed nigrostriatal axons providing collaterals that arborize in the pallidum and subthalamic nucleus. These thin and varicose collaterals emerge from thick and smooth axons that course backward along the main output pathways of the basal ganglia, including the ansa lenticularis, the lenticular fasciculus and Wilson's pencils. Many of these fibers run within pallidal medullary laminae before reaching the putamen, whereas others climb along the reticular thalamic nucleus to reach the caudate nucleus. This extrastriatal innervation, which allows nigral dopaminergic neurons to directly affect the pallidum and subthalamic nucleus, may play a crucial role in the functional organization of human basal ganglia, in both health and disease.

Localization of orphanin FQ (nociceptin) peptide and messenger RNA in the central nervous system of the rat

Orphanin FQ (OFQ) is the endogenous agonist of the opioid receptor-like receptor (ORL-1). It and its precursor, prepro-OFQ, exhibit structural features suggestive of the opioid peptides. A cDNA encoding the OFQ precursor sequence in the rat recently has been cloned, and the authors recently generated a polyclonal antibody directed against the OFQ peptide. In the present study, the authors used in situ hybridization and immunohistochemistry to examine the distribution of OFQ peptide and mRNA in the central nervous system of the adult rat. OFQ immunoreactivity and prepro-OFQ mRNA expression correlated virtually in all brain areas studied. In the forebrain, OFQ peptide and mRNA were prominent in the neocortex endopiriform nucleus, claustrum, lateral septum, ventral forebrain, hypothalamus, mammillary bodies, central and medial nuclei of the amygdala, hippocampal formation, paratenial and reticular nuclei of the thalamus, medial habenula, and zona incerta. No OFQ was observed in the pineal or pituitary glands. In the brainstem, OFQ was prominent in the ventral tegmental area, substantia nigra, nucleus of the posterior commissure, central gray, nucleus of Darkschewitsch, peripeduncular nucleus, interpeduncular nucleus, tegmental nuclei, locus coeruleus, raphe complex, lateral parabrachial nucleus, inferior olivary complex, vestibular nuclear complex, prepositus hypoglossus, solitary nucleus, nucleus ambiguous, caudal spinal trigeminal nucleus, and reticular formation. In the spinal cord, OFQ was observed throughout the dorsal and ventral horns. The wide distribution of this peptide provides support for its role in a multitude of functions, including not only nociception but also motor and balance control, special sensory processing, and various autonomic and physiologic processes.

Altered development of glutamate and GABA receptors in the basal ganglia of girls with Rett syndrome

Rett syndrome (RS), a genetic disorder found almost exclusively in females, is associated with psychomotor regression and stereotyped hand movements. To determine whether a defect in basal ganglia amino acid neurotransmission plays a role in RS, NMDA-, AMPA-, kainate (KA)-, and metabotropic (mGluR)-type glutamate receptors (GluRs) and GABA receptors were labeled autoradiographically in the caudate, putamen, and globus pallidus of postmortem brain slices from 9 RS girls and 10 age-related controls. The cases were divided into younger (8 years or younger) and older age groups to study age-related changes in receptor binding density. We found significant reductions in AMPA and NMDA receptor density in the putamen and in KA receptor density in the caudate of older RS cases compared to controls. In contrast, mGluR density in the basal ganglia of RS patients was not altered significantly. The density of GluRs in control subjects generally showed more limited changes with age than in RS cases. In contrast to ionotropic GluRs, GABA receptor density was significantly increased in the caudate of young RS patients. The effects on GluR density in the putamen, which serves a primary motor function, were consistent with the motor deficits observed in RS, while those on amino acid transmitter receptors in the caudate may account for some cognitive features. Our studies demonstrate regional, receptor-subtype, and age-specific alterations in amino acid neurotransmitter receptors in the basal ganglia of RS girls. These changes may correlate with age-related clinical stages observed in RS.

Iron in the basal ganglia in Parkinson's disease. An in vitro study using extended X-ray absorption fine structure and cryo-electron microscopy

Iron is found in high concentration in some areas of the brain, and increased iron in the substantia nigra is a feature of Parkinson's disease. The purpose of this study was to investigate the physical environment of brain iron in post-mortem tissue to provide information on the possible role of iron in neurodegeneration in Parkinson's disease. Iron has also been implicated as the cause of signal loss in areas of high brain iron on T2-weighted MRI sequences. Knowledge of the physical environment of the brain iron is essential in interpreting the cause of signal change. Post-mortem tissue was obtained from six cases of Parkinson's disease and from six age-matched controls. Iron levels were measured using absorption spectrophotometry. Extended X-ray absorption fine structure was used to evaluate the atomic environment of iron within the substantia nigra and both segments of the globus pallidus. Cryo-electron transmission microscopy was used to probe the iron storage proteins in these areas. Iron levels were increased in the parkinsonian nigra and lateral portion of the globus pallidus. Spectra from the extended X-ray absorption fine structure experiments showed that ferritin was the only storage protein detectable in both control and parkinsonian tissue in all areas studied. Cryo-electron transmission microscopy studies showed that ferritin was more heavily loaded with iron in Parkinson's disease when compared with age-matched controls. In summary we have shown that iron levels are increased in two areas of the brain in Parkinson's disease including the substantia nigra, the site of maximal neurodegeneration. This produces increased loading of ferritin, which is the normal brain iron storage protein. It is possible that increased loading of ferritin may increase the risk of free radical-induced damage. Differences in ferritin loading may explain regional differences in iron's effect on the T2 signal.

Cellular localization of brain-derived neurotrophic factor-like immunoreactivity in adult monkey brain

Immunohistochemical localization of brain-derived neurotrophic factor (BDNF) in the monkey brain was investigated using a polyclonal anti-BDNF antibody produced in our laboratory. The antibody recognized a single band in monkey brain homogenates, and the estimated molecular weight was approximately 14 kDa, which corresponds well to the molecular weight of BDNF monomer. BDNF-like immunoreactivity was observed in the somata and processes of discrete neuronal subpopulations in the monkey brain. BDNF-positive neurons were widely distributed in various structures of the brain, including the cerebral cortex, hippocampus, basal forebrain, basal ganglia, diencephalon, brainstem and cerebellum. In addition, immunopositive glial cells were found in some brain regions. These data suggest that BDNF may exist widely in the monkey brain, and may be concerned with various types of neurons in the monkey central nervous system.

Nucleus accumbens in the lizard Psammodromus algirus: chemoarchitecture and cortical afferent connections

To better understand the organization and evolution of the basal ganglia of vertebrates, in the present study we have analyzed the chemoarchitecture and the cortical input to the nucleus accumbens in the lacertid lizard Psammodromus algirus. The nucleus accumbens contains many gamma-aminobutyric acid (GABA)-positive neurons and calbindin-positive neurons, the majority of which may be spiny projection neurons, and a few dispersed neuropeptide Y-positive neurons that likely represent aspiny interneurons. The nucleus accumbens contains two chemoarchitectonically different fields: a rostromedial field that stains heavily for substance P, dopamine, GABA(A) receptor, and a caudolateral field that stains only lightly to moderately for them, appearing more similar to the adjacent striatum. Injections of biotinylated dextran amine were placed in either the medial, dorsomedial, or dorsal cortices of Psammodromus. The medial and the dorsal cortices project heavily to the rostromedial field of the accumbens, whereas they project lightly to moderately to the caudolateral field. Cortical terminals make asymmetric, presumably excitatory, synaptic contacts with distal dendrites and the head of spines. Our results indicate that the hippocampal-like projection to the nucleus accumbens is similar between mammals and reptiles in that cortical terminals make mainly excitatory synapses on spiny, putatively projection neurons. However, our results and results from previous investigations indicate that important differences exist between the nucleus accumbens of mammals and reptiles regarding local modulatory interactions between cortical, dopaminergic, and cholinergic elements, which suggest that the reptilian nucleus accumbens may be as a whole comparable to the shell of the mammalian nucleus accumbens.

Immunohistochemical localization of N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor subunits in the substantia nigra pars compacta of the rat

Ionotropic glutamate receptors in the substantia nigra pars compacta regulate the activity of dopamine neurons. We have used dual-label immunofluoresence and confocal laser microscopy to study the localization of subunits of two types of ionotropic receptors within the substantia nigra pars compacta of the rat. Immunostaining for N-methyl-D-aspartate receptor 1 and glutamate receptor 2/3 was prominent in the soma and proximal dendrites of all tyrosine hydroxylase-immunopositive cells, while only low amounts of N-methyl-D-aspartate receptor 2A and N-methyl-D-aspartate receptor 2B were present. Selective antibodies were used to determine the isoforms of N-methyl-D-aspartate receptor 1 present. Immunostaining for the N1, C1 and C2 variably spliced segments of N-methyl-D-aspartate receptor 1 were scarce in the substantia nigra pars compacta, while immunoreactivity for the alternative C2' terminus of N-methyl-D-aspartate receptor 1 was quite abundant. Staining for glutamate receptor 1 was heterogeneous; about half of the tyrosine hydroxylase immunopositive cells stained intensely, while the other half were immunonegative. The glutamate receptor 1-stained cells were concentrated in the ventral tier of the substantia nigra pars compacta. Glutamate receptor 4 was not found in tyrosine hydroxylase-immunopositive cells within the substantia nigra pars compacta. Together, these data demonstrate that dopaminergic neurons in the substantia nigra pars compacta express primarily glutamate receptor 1, glutamate receptor 2/3 and N-methyl-D-aspartate receptor 1 isoforms containing the alternative C2' terminus.

MR imaging of human brain at 3.0 T: preliminary report on transverse relaxation rates and relation to estimated iron content

PURPOSE

To determine the transverse relaxation rates R2 and R2' from several gray matter regions and from frontal cortical white matter in healthy human brains in vivo and to determine the relationship between relaxation rates and iron concentration [Fe].

MATERIALS AND METHODS

Six healthy adults aged 19-42 years underwent thin-section gradient-echo sampling of free induction decay and echo magnetic resonance (MR) imaging at 3.0 T. Imaging covered the mesencephalon and basal ganglia.

RESULTS

Relaxation rates (mean +/- SD) were highest in globus pallidus (R2 = 25.8 seconds-1 +/- 1.1, R2' = 12.0 seconds-1 +/- 2.1) and lowest in prefrontal cortex (R2 = 14.4 seconds-1 +/- 1.8, R2' = 3.4 seconds-1 +/- 1.1). Frontal white matter measurements were as follows: R2 = 18.0 seconds-1 +/- 1.2 and R2' = 3.9 seconds-1 +/- 1.2. For gray matter, both R2 and R2' showed a strong correlation (r = 0.92, P < .001 and r = 0.90, P < .001, respectively) with [Fe]. Although the slopes of the regression lines for R2' versus [Fe] and for R2 versus [Fe] were similar, the iron-independent component of R2' (2.2 seconds-1 +/- 0.6), the value when [Fe] = 0, was much less than that of R2 (12.7 seconds-1 +/- 0.7).

CONCLUSION

The small iron-independent component R2', as compared with that of R2, is consistent with the hypothesis that R2' has higher iron-related specificity.

Psychiatric symptoms as late onset of Wilson's disease: neuroradiological findings, clinical features and treatment

We describe a case of Wilson's disease with late psychiatric onset. Major depressive disorder was the first clinical manifestation at the age of 38 years. After pharmacotherapy with antidepressive agents, a manic episode was observed. Extrapyramidal hand tremor and micrography were the first neurological signs. Emotional lability occurred during worsening of extrapyramidal signs. Diagnosis was based on urinary and serum copper levels, ceruloplasmin serum level, Kayser-Fleischer ring, and liver biopsy that detected cirrhosis. Magnetic resonance imaging revealed basal ganglia hyperintensity on T1-weighted images, and hypodensity in the central part and hyperintensity in the peripheral part of the lentiform nucleus on T2-weighted images. Hyperintensity on T2-weighted images was also observed in the dorsal part of the midbrain. 123I-iodobenzamide single photon emission computed tomography (IBZM-SPECT) detected a normal distribution of the drug in the brain, with better signal in the right side and deficit of D2-dopaminergic receptors in the basal ganglia. Abnormal manganese erythrocyte level was observed. Treatment was based on penicillamine, zinc salts, low-copper diet, antidepressant agents, interpersonal psychotherapy and neurorehabilitation.

Localization of calcium-binding proteins and GABA transporter (GAT-1) messenger RNA in the human subthalamic nucleus

The distribution of messenger RNA encoding the human GAT-1 (a high-affinity GABA transporter) was investigated in the subthalamic nucleus of 10 neurologically normal human post mortem cases. Further, the distribution of messenger RNA and protein encoding the three neuronally expressed calcium-binding proteins (calbindin D28k, parvalbumin and calretinin) was similarly investigated using in situ hybridization and immunohistochemical techniques. Cellular sites of calbindin D28k, parvalbumin, calretinin and GAT-1 messenger RNA expression were localized using human-specific oligonucleotide probes radiolabelled with [35S]dATP. Sites of protein localization were visualized using specific anti-calbindin D28k, anti-parvalbumin and anti-calretinin antisera. Examination of emulsion-coated tissue sections processed for in situ hybridization revealed an intense signal for GAT-1 messenger RNA within the human subthalamic nucleus, indeed the majority of Methylene Blue-counterstained cells were enriched in this transcript. Further, a marked heterogeneity was noted with regard to the expression of the messenger RNA's encoding the three calcium-binding proteins; this elliptical nucleus was highly enriched in parvalbumin messenger RNA-positive neurons and calretinin mRNA-positive cells but not calbindin messenger RNA-positive cells. Indeed, only an occasional calbindin messenger RNA-positive cell was detected within the mediolateral extent of the nucleus. In marked contrast, numerous parvalbumin messenger RNA-positive cells and calretinin messenger RNA-positive cells were detected and they were topographically distributed; parvalbumin messenger RNA-positive cells were highly enriched in the dorsal subthalamic nucleus extending mediolaterally; calretinin messenger RNA-positive cells were more enriched ventrally although some degree of overlap was apparent. Computer-assisted analysis of the average cross-sectional somatic area of parvalbumin, calretinin and GAT-1 messenger RNA-positive neurons revealed them all to be in the range of 300 microm2. The unique patterns of calcium-binding protein gene expression were similarly reflected at the protein level; an abundance of parvalbumin- and calretinin-immunopositive neurons were observed whereas only occasional intensely-labelled calbindin-immunopositive fibres were seen, no calbindin-immunopositive cells were detected. Single and double labelling studies show that parvalbumin-immunopositive neurons were mainly localized in the dorsal region of the nucleus, and calretinin-immunopositive neurons were mainly localized in the ventral region although there was overlap with double-labelled neurons located in the middle and dorsal regions. The significance of these findings, in particular the expression of GAT-1, a high-affinity GABA uptake protein, for basal ganglia signalling is discussed.

High signal in the adenohypophysis on T1-weighted images presumably due to manganese deposits in patients on long-term parenteral nutrition

Hypermanganesaemia is reported in patients on long-term parenteral nutrition. Deposition of manganese, giving high signal on T1-weighted images, may involve the basal ganglia. MRI in nine patients (mean age 51 years, range 31-75 years) on long-term parenteral nutrition (mean duration 30 months, range 6-126 months), demonstrated high signal in the anterior pituitary gland on T1-weighted sagittal and coronal images. The gland appeared normal on T2-weighted images. Signal intensity in the basal ganglia on T1-weighted images was increased in all patients. Endocrine assessment showed no significant abnormality. Neurological examination showed a mild parkinsonian movement disorder in one patient. Hypermanganaesemia was present in all nine (1.3-2.8 micromol/l, mean 1.87 micromol/l). The high signal in the anterior pituitary gland was probably related to deposition of paramagnetic substances, especially manganese.

Targeted expression of a toxin gene to D1 dopamine receptor neurons by cre-mediated site-specific recombination

Idiopathic Parkinson's disease involves the loss of midbrain dopaminergic neurons, resulting in the presynaptic breakdown of dopaminergic transmission in the striatum. Huntington's disease and some neurodegenerative diseases with Parkinsonian features have postsynaptic defects caused by striatal cell death. Mice were generated in which an attenuated form of the diphtheria toxin gene (tox-176) was expressed exclusively in D1 dopamine receptor (D1R)-positive cells with the aim of determining the effect of this mutation on development of the basal ganglia and on the locomotor phenotype. Transgenic mice expressing Cre, a site-specific DNA recombinase, were crossed with a second line in which a transcriptionally silenced tox-176 gene was inserted into the D1R gene locus by homologous recombination. Young doubly transgenic mutant mice expressing the tox-176 gene displayed bradykinesia, dystonia, and had falls caused by myoclonic jerks. The mutant brain had evidence of apoptosis and reactive gliosis and, consistent with the D1R expression pattern, the striatum was reduced in volume, and the Islands of Calleja were absent. In contrast, the cortex was of normal thickness. D1Rs were not detectable in mutants by in situ hybridization or ligand autoradiography, whereas D2 dopamine receptor (D2R) mRNA and protein was present in the striatum. In addition, substance P and dynorphin, neuropeptides known to be expressed in D1R-positive striatonigral projection neurons were not detectable. Enkephalin, a marker found in D2-positive striatopallidal projection neurons was expressed in the mutant brain. The mutant represents a novel neurodegenerative disease model with a dramatic extrapyramidal phenotype.

Immunohistochemical localization of adenosine A2A receptors in the rat central nervous system

The A2A adenosine receptor (A2A-AR) transcript and radioligand binding sites have a distinct distribution in rat brain, restricted primarily to the striatum, nucleus accumbens and olfactory tubercles. We describe here the use of purified recombinant human A2A-ARs to generate a monoclonal antibody that has been used to better resolve the distribution of A2A-ARs in rat brain. The antibody can detect 1 ng of purified recombinant receptor by Western blotting and is potent (EC50 = 0.62 microg/ml) and highly selective for the A2A-AR subtype. By Western blotting, the apparent molecular mass of recombinant and rat striatal receptors shifts upon deglycosylation from 43-48 to 42 kilodaltons. Analyses of chimeric A1/A2A-ARs and synthesis of a blocking peptide pinpointed the epitope (SQPLPGER) of the antibody to the center of the third intracellular loop of the receptor. Incubation of rat striatal membranes with antibody reduces receptor coupling to G-proteins. In rat brain, dense A2A-AR-like immunoreactivity that is eliminated by the blocking peptide was found in the neuropil of the striatum, nucleus accumbens (rostral pole, core and shell), cell bridges of the striatum, olfactory tubercles, and areas of extended amygdala with somewhat lighter labeling in the globus pallidus and nucleus of the solitary tract. Light perikaryal labeling was found in other areas of the brain, including the cortex, hippocampus, thalamus, cerebellum, and portions of the hindbrain. The observed distribution of A2A-AR immunoreactivity throughout the neuraxis is consistent with the receptors' role in modulating dopaminergic neurotransmission and central control of cardiovascular function.

Drug-induced changes in the concentration of 5-OR indolyl compounds in cerebrospinal fluid and caudate nucleus

The effects of reserpine and imipramine on the concentration of indolyl compounds bearing an OR group in position 5 (5-OR indolyl compounds) in the cerebrospinal fluid and the caudate nucleus of the dog have been studied. Reserpine was shown to produce an increase in the concentration of these compounds in the cerebrospinal fluid. In the caudate nucleus reserpine produced a fall in the concentration of the basic 5-OR indolyl compounds accompanied by an equivalent increase in the concentration of acidic 5-OR indolyl compounds. No significant change in the concentration of 5-OR indolyl compounds in the cerebrospinal fluid was observed after treatment with imipramine.

Correlative ultrastructural distribution of neurotensin receptor proteins and binding sites in the rat substantia nigra

Neurotensin (NT) produces various stimulatory effects on dopaminergic neurons of the rat substantia nigra. To gain insight into the subcellular substrate for these effects, we compared by electron microscopy the distribution of immunoreactive high-affinity NT receptor proteins (NTRH) with that of high-affinity 125I-NT binding sites in this region of rat brain. Quantitative analysis showed a predominant association of immunogold and radioautographic labels with somata and dendrites of presumptive dopaminergic neurons, and a more modest localization in myelinated and unmyelinated axons and astrocytic leaflets. The distributions of immunoreactive NTRH and 125I-NT binding sites along somatodendritic plasma membranes were highly correlated and homogeneous, suggesting that membrane-targeted NTRH proteins were functional and predominantly extrasynaptic. Abundant immunocytochemically and radioautographically labeled receptors were also detected inside perikarya and dendrites. Within perikarya, these were found in comparable proportions over membranes of smooth endoplasmic reticulum and Golgi apparatus, suggesting that newly synthesized receptor proteins already possess the molecular and conformational properties required for effective ligand binding. By contrast, dendrites showed a proportionally higher concentration of immunolabeled than radiolabeled intracellular receptors. A fraction of these immunoreactive receptors were found in endosomes, suggesting that they had undergone ligand-induced internalization and were under a molecular conformation and/or in a physical location that precluded their recognition by and/or access to exogenous ligand. Our results provide the first evidence that electron microscopic immunocytochemistry of the NT receptor identifies sites for both the binding and trafficking of NT in the substantia nigra.

Cannabinoid receptor and WIN-55,212-2-stimulated [35S]GTP gamma S binding and cannabinoid receptor mRNA levels in the basal ganglia and the cerebellum of adult male rats chronically exposed to delta 9-tetrahydrocannabinol

The inhibition of motor behavior in rodents caused by the exposure to plant or synthetic cannabinoids has been reported to develop tolerance after repeated exposure. This tolerance seems to have a pharmacodynamic basis, since downregulation of cannabinoid receptors in motor areas, basal ganglia and cerebellum, has been demonstrated in cannabinoid-tolerant rats. The present study was designed to further explore this previous evidence by analyzing simultaneously in several motor areas of delta 9-tetrahydrocannabinol- (delta 9-THC)-tolerant rats: 1. Cannabinoid receptor binding, by using [3H]WIN-55,212-2 autoradiography; 2. Cannabinoid receptor activation of signal transduction mechanisms, by using WIN-55,212-2-stimulated [35S]-guanylyl-5'-O-(gamma-thio)-triphosphate ([35S]-GTP gamma S) autoradiography; 3. Cannabinoid receptor mRNA expression, quantitated by in situ hybridization. Results were as follows. As expected, the exposure to delta 9-THC for 5 d resulted in a decrease of cannabinoid receptor binding in the molecular layer of the cerebellum, medial, and lateral caudate-putamen and, in particular, entopeduncular nucleus. We also found decreased cannabinoid receptor binding in the superficial and deep layers of the cerebral cortex, two regions used as a reference to test the specificity of changes observed in motor areas. There were only two brain regions, the globus pallidus and the substantia nigra, where the specific binding for cannabinoid receptors was unaltered after 5 d of a daily delta 9-THC administration. However, in the substantia nigra, the magnitude of WIN-55,212-2-stimulated [35S]-GTP gamma S binding was lesser in delta 9-THC-tolerant rats than controls, thus suggesting a possible specific change at the level of receptor coupling to GTP-binding proteins. This was not seen neither in the globus pallidus nor in the lateral caudate-putamen, where agonist stimulation produced similar [35S]-GTP gamma S binding levels in delta 9-THC-tolerant rats and controls. Finally, animals chronically exposed to delta 9-THC also exhibited a decrease in the levels of cannabinoid receptor mRNA in the medial and lateral caudate-putamen, but there were no changes in the cerebellum (granular layer) and cerebral cortex. In summary, the chronic exposure to delta 9-THC resulted in a decrease in cannabinoid receptor binding and mRNA levels in the caudate-putamen, where cell bodies of cannabinoid receptor-containing neurons in the basal ganglia are located. However, this decrease particularly affected the receptor binding levels in those neurons projecting to the entopeduncular nucleus, but not in those projecting to the globus pallidus and substantia nigra, although, in this last region, a specific decrease in the efficiency of receptor activation of signal transduction mechanisms was seen in delta 9-THC-tolerant rats. The chronic exposure to delta 9-THC also resulted in decreased cannabinoid receptor binding in the cerebellum, although without affecting mRNA expression.

Magnetic resonance imaging and 11C-N-methylspiperone/positron emission tomography studies in a patient with the interval form of carbon monoxide poisoning

Magnetic resonance (MR) and (11)C-N-methylspiperone ((11)C-NMSP)/positron emission tomography (PET) imagings were repeatedly performed in a 50-year-old man with the interval form of carbon monoxide (CO) poisoning. In MR images obtained when delayed neuropsychiatric symptoms developed (two months after poisoning), the inner segments of the bilateral globus pallidus appeared as high signal intensities in the T1-weighted and low signal intensities in the T2-weighted images, suggesting prior focal hemorrhage in these areas. A PET study with (11)C-NMSP performed at that time showed an increase in dopamine D2 receptor binding in the caudate and putamen. Treatment with bromocriptine was very effective and five months after the poisoning, MR and (11)C-NMSP/PET images showed improvement, concomitantly with the disappearance of the neuropsychiatric symptoms.

Proton magnetic resonance spectroscopy in primary blepharospasm

Single-volume proton magnetic resonance spectroscopy, localized to basal ganglia, was carried out in 10 patients with primary blepharospasm (PB) to assess the levels of N-acetyl aspartate (NAA), creatine-phosphocreatine, and choline-containing compounds. NAA was reduced significantly in patients compared with control subjects. This result suggests a striatal neuronal loss in PB.

Guanosine 5'-(gamma-[35S]thio)triphosphate autoradiography allows selective detection of histamine H3 receptor-dependent G protein activation in rat brain tissue sections

Histamine elicits its biological effects via three distinct G protein-coupled receptors, termed H1, H2, and H3. We have used guanosine 5'-(gamma-[35S]thio)triphosphate (GTPgamma[35S]) autoradiography to localize histamine receptor-dependent G protein activation in rat brain tissue sections. Initial studies revealed that in basal conditions, adenosine was present in tissue sections in sufficient concentrations to generate an adenosine A1 receptor-dependent GTPgamma[35S] signal in several brain regions. All further incubations therefore contained 8-cyclopentyl-1,3-dipropylxanthine (10 microM), a selective A1 receptor antagonist. Histamine elicited dose-dependent increments in GTPgamma[35S] binding to discrete anatomical structures, most notably the caudate putamen, cerebral cortex, and substantia nigra. The overall anatomical pattern of the histamine-evoked binding response closely reflects the known distribution of H3 binding sites and was faithfully mimicked by N(alpha)-methylhistamine, (R)-alpha-methylhistamine, and immepip, three H3-selective agonists. In all regions examined, the GTPgamma[35S] signal was reversed with thioperamide and clobenpropit, two potent H3-selective antagonists, whereas mepyramine, a specific H1 antagonist, and cimetidine, a prototypic H2 antagonist, proved ineffective. These data indicate that in rat brain tissue sections, GTPgamma[35S] autoradiography selectively detects H3 receptor-dependent signaling in response to histamine stimulation. As the existing evidence suggests that GTPgamma[35S] autoradiography preferentially reveals responses to G(i/o)-coupled receptors, our data indicate that most, if not all, central H3 binding sites represent functional receptors coupling to G(i/o), the inhibitory class of G proteins. Besides allowing more detailed studies on H3 receptor signaling within anatomically restricted regions of the CNS, GTPgamma[35S] autoradiography offers a novel approach for functional in vitro screening of H3 ligands.