Zane R. Hollingsworth

Excitatory amino acid binding sites in the basal ganglia of the rat: A quantitative autoradiographic study

Quantitative receptor autoradiography was used to determine the distribution of excitatory amino acid binding sites in the basal ganglia of rat brain. alpha-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid, N-methyl-D-aspartate, kainate, quisqualate-sensitive metabotropic and non-N-methyl-D-aspartate, non-kainate, non-quisqualate glutamate binding sites had their highest density in striatum, nucleus accumbens, and olfactory tubercle. Kainate binding was higher in the lateral striatum but there was no medial-lateral striatal gradient for other binding sites. N-Methyl-D-aspartate and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid binding sites were most dense in the nucleus accumbens and olfactory tubercle. There was no dorsal-ventral gradient within the striatal complex for the other binding sites. Other regions of the basal ganglia had lower densities of ligand binding. To compare binding site density within non-striatal regions, binding for each ligand was normalized to the striatal binding density. When compared to the striatal complex, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and metabotropic binding sites had higher relative density in the globus pallidus, ventral pallidum, and subthalamic nucleus than other binding sites. Metabotropic binding also had a high relative density in the substantia nigra. Non-N-methyl-D-aspartate, non-kainate, non-quisqualate glutamate binding sites had a high relative density in globus pallidus, ventral pallidum, and substantia nigra. N-Methyl-D-aspartate binding sites had a low relative density in pallidum, subthalamic nucleus, substantia nigra and ventral tegmental area. Our data indicate heterogeneous distribution of excitatory amino acid binding sites within rat basal ganglia and suggest that the character of excitatory amino acid-mediated neurotransmission within the basal ganglia is also heterogeneous.

Dopamine transmission in DYT1 dystonia: A biochemical and autoradiographical study

Abstract—Indices of dopamine transmission were measured in the postmortem striatum of DYT1 dystonia brains. A significant increase in the striatal 3,4-dihydroxyphenylacetic acid/dopamine ratio was found. Quantitative autoradiography revealed no differences in the density of dopamine transporter or vesicular monoamine transporter-2 binding; however, there was a trend toward a reduction in D1 receptor and D2 receptor binding. One brain with DYT1 parkinsonism was similarly evaluated and marked reductions in striatal dopamine, 3,4-dihydroxyphenylacetic acid, and homovanillic acid content as well as the density of binding of all four dopaminergic ligands were measured.

Excitatory amino acid binding sites in the hippocampal region of Alzheimer's disease and other dementias

Quantitative receptor autoradiography was used to measure muscarinic cholinergic, benzodiazepine, kainate, phencyclidine (PCP), N-methyl-D-aspartate (NMDA) (measured in Tris acetate), quisqualate-sensitive, non-quisqualate-sensitive and total glutamate (measured in Tris chloride buffer) binding sites in adjacent sections of the hippocampal region of 10 Alzheimers disease, nine control, and six demented, non-Alzheimers disease postmortem human brains. The measurements were compared to the number of neurofibrillary tangles as revealed by Congo red staining of adjacent sections. All assays and measurements were done by observers blinded to the clinical diagnoses. Binding was decreased significantly for all ligands except quisqualate in stratum pyramidale of CA1 of the Alzheimers disease brains. The binding loss was significantly greater for the non-quisqualate and NMDA sites than for the muscarinic, benzodiazepine and kainate sites with the total glutamate and PCP site losses being intermediate. Only the loss of benzodiazepine binding was significantly correlated with the number of neurofibrillary tangles. Lesser binding losses were seen in adjacent areas. This difference in the degree of binding decrease is consistent with the hypothesis that NMDA receptors are located on more distal dendrites of hippocampal neurons. There they may be relatively more vulnerable than the other receptors to the pathological process.

Glutamate receptors in the substantia nigra of Parkinson's disease brains

Glutamic acid and its analogs are excitotoxins that might contribute to the pathogenesis of Parkinsons disease (PD). We measured four subtypes of glutamate binding sites autoradiographically in 20-μm sections from control and PD midbrains. N-Methyl-D-aspartate (NMDA) binding sites (eight control, eight PD) were very low in control (20 ± 7 [SEM] fmol/mg protein) and were reduced in the PD pars compacta (2.6 ± 1.1 fmol/mg protein; p < 0.02). NMDA binding was also reduced in the red nucleus but not in periaqueductal gray (PAG). We measured α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), metabotropic, and non-NMDA, nonkainate, non-quisqualate (NNKQ) sites in 10 PD and 12 control midbrains. AMPA binding sites were reduced from 175 ± 20 to 99 ± 16 (p < 0.05) fmol/mg protein in PD pars compacta, NNKQ sites from 86 ± 10 to 50 ± 12 (p < 0.05) fmol/mg protein in total nigra, and metabotropic sites (15 ± 5 fmol/mg protein) were unchanged. AMPA, metabotropic, and NNKQ binding were unchanged in red nucleus and PAG. The very low number of NMDA binding sites suggests that factors other than excitotoxicity mediated via NMDA receptors on nigral cell bodies play roles in the pathogenesis of PD. There may be a generalized loss of NMDA receptors in PD brains. AMPA and NNKQ binding sites appear to be located on dopamine neurons, although the role of NNKQ sites in normal nervous system function and human disease is unknown.

The Relationship Between CAG Repeat Length and Age of Onset Differs for Huntington's Disease Patients with Juvenile Onset or Adult Onset

Age of onset for Huntingtons disease (HD) varies inversely with the length of the disease‐causing CAG repeat expansion in the HD gene. A simple exponential regression model yielded adjusted R‐squared values of 0.728 in a large set of Venezuelan kindreds and 0.642 in a North American, European, and Australian sample (the HD MAPS cohort). We present evidence that a two‐segment exponential regression curve provides a significantly better fit than the simple exponential regression. A plot of natural log‐transformed age of onset against CAG repeat length reveals this segmental relationship. This two‐segment exponential regression on age of onset data increases the adjusted R‐squared values by 0.012 in the Venezuelan kindreds and by 0.035 in the HD MAPS cohort. Although the amount of additional variance explained by the segmental regression approach is modest, the two slopes of the two‐segment regression are significantly different from each other in both the Venezuelan kindreds [F(2, 439) = 11.13, P= 2 × 10−5] and in the HD MAPS cohort [F(2, 688) = 38.27, P= 2 × 10−16]. In both populations, the influence of each CAG repeat on age of onset appears to be stronger in the adult‐onset range of CAG repeats than in the juvenile‐onset range.

Excitatory amino acid binding sites in the periaqueductal gray of the rat

We used receptor autoradiography to determine the distribution of excitatory amino acid (EAA) binding site subtypes in the periaqueductal gray (PAG) of the rat. N-Methyl-D-aspartate (NMDA), kainate, quisqualate-ionotropic, and quisqualate-metabotropic binding sites were all present in the PAG. Distribution was inhomogeneous with greatest density of all binding site subtypes in the dorsolateral subdivision and lowest density in the ventrolateral subdivision. Relative to regions of brain with high densities of EAA binding site subtypes, quisqualate-metabotropic binding sites had the highest relative density and NMDA binding sites the least. The presence of all subtypes of EAA binding sites in the PAG suggests that EAA action within the PAG is likely to be complex.

Dopamine‐receptor autoradiography of human narcoleptic brain

Although the pathology of human narcolepsy is unknown, studies of human and canine narcolepsy have suggested that dopamine metabolism may be disturbed. We used quantitative autoradiography to assess dopamine D1- and D2-receptor binding in basal ganglia and amygdala of five narcoleptic and 17 control human brains. In caudate, narcoleptic brains had a statistically significant increase of 57% in D1- receptor binding, and large but not significant increases of 54% in medial globus pallidus D1 binding, 63% in caudate D2-receptor binding, 95% in lateral globus pallidus D2 binding, and 93% in lateral amygdala D2 binding. We found no major changes in the putamen or in the basal or accessory basal nuclei of the amygdala. These results suggest that narcolepsy is associated with upregulation of dopamine receptors in specific areas of the brain, although medications used prior to death may have contributed to the findings.

Differential D1 and D2 receptor-mediated effects on immediate early gene induction in a transgenic mouse model of Huntington's disease.

The diminished expression of D1 and D2 dopamine receptors is a well-documented hallmark of Huntingtons disease (HD), but relatively little is known about how these changes in receptor populations affect the dopaminergic responses of striatal neurons. Using transgenic mice expressing an N-terminal portion of mutant huntingtin (R6/2 mice), we have examined immediate early gene (IEG) expression as an index of dopaminergic signal transduction. c-fos, jun B, zif268, and N10 mRNA levels and expression patterns were analyzed using quantitative in situ hybridization histochemistry following intraperitoneal administration of selective D1 and D2 family pharmacological agents (SKF-82958 and eticlopride). Basal IEG levels were generally lower in the dorsal subregion of R6/2 striata relative to wild-type control striata at 10-11 weeks of age, a finding in accord with previously reported decreases in D1 and adenosine A2A receptors. D2-antagonist-stimulated IEG expression was significantly reduced in the striata of transgenic animals. In contrast, D1-agonist-induced striatal R6/2 IEG mRNA levels were either equivalent or significantly enhanced relative to control levels, an unexpected result given the reduced level of D1 receptors in R6/2 animals. Understanding the functional bases for these effects may further elucidate the complex pathophysiology of Huntingtons disease.

Localization of dopaminergic markers in the human subthalamic nucleus

The potential role for dopamine in the subthalamic nucleus was investigated in human postmortem tissue sections by examining; (1) immunostaining for tyrosine hydroxylase, the rate‐limiting enzyme in catecholamine synthesis; (2) binding of [3H]‐SCH23390 (D1‐like), [3H]‐YM‐09151‐2 (D2‐like), and [3H]‐mazindol (dopamine uptake); and (3) expression of dopamine D1 and D2 receptor mRNAs. Immunostaining for tyrosine hydroxylase was visualized in Bouins‐fixed tissue by using a monoclonal antibody and the avidin‐biotin‐complex method. The cellular localization of the dopamine D1 and D2 receptor mRNAs was visualized by using a cocktail of human specific oligonucleotide probes radiolabeled with 35S‐dATP. Inspection of immunostained tissue revealed a fine network of tyrosine hydroxylase‐immunostained fibers traversing the nucleus; no immunopositive cells were detected. Examination of emulsion‐coated tissue sections processed for D1 and D2 receptor mRNA revealed, as expected, an abundance of D1 and D2 mRNA‐positive cells in the caudate nucleus and putamen. However, no D1 or D2 receptor mRNA‐expressing cells were detected in the subthalamic nucleus. Further, semiquantitative analysis of D1‐like, D2‐like and dopamine uptake ligand binding similarly revealed an enrichment of specific binding in the caudate nucleus and putamen but not within the subthalamic nucleus. However, a weak, albeit specific, signal for [3H]‐SCH23390 and [3H]‐mazindol was detected in the subthalamic nucleus, suggesting that the human subthalamic nucleus may receive a weak dopaminergic input. As weak D1‐like binding is detected in the subthalamic nucleus, and subthalamic neurons do not express dopamine D1 or D2 receptor mRNAs, together these data suggest that the effects of dopaminergic agents on the activity of human subthalamic neurons may be indirect and mediated via interaction with dopamine D1‐like receptors. J. Comp. Neurol. 421:247–255, 2000.

Phospholipase A2 Modulates Different Subtypes of Excitatory Amino Acid Receptors: Autoradiographic Evidence

Abstract: Exogenous phospholipases have been used extensively as tools to study the role of membrane lipids in receptor mechanisms. We used in vitro quantitative autoradiography to evaluate the effect of phospholipase A2 (PLA2) on N‐methyl‐D‐aspartate (NMDA) and non‐NMDA glutamate receptors in rat brain. PLA2 pretreatment induced a significant increase in α‐[3H]amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate ([3H]AMPA) binding in the stratum radiatum of the CA1 region of the hippocampus and in the stratum moleculare of the cerebellum. No modification of [3H]AMPA binding was found in the stratum pyramidale of the hippocampus at different ligand concentrations. [3H]‐Glutamate binding to the metabotropic glutamate receptor and the non‐NMDA‐, non‐kainate‐, non‐quisqualate‐sensitive [3H]glutamate binding site were also increased by PLA2 pretreatment. [3H]Kainate binding and NMDA‐sensitive [3H]glutamate binding were minimally affected by the enzyme pretreatment. The PLA2 effect was reversed by EGTA, the PLA2 inhibitor p‐bromophenacyl bromide, and prolonged pretreatment with heat. Bovine serum albumin (1%) prevented the increase in metabotropic binding by PLA2. Arachidonic acid failed to mimic the PLA2 effect on metabotropic binding. These results indicate that PLA2 can selectively modulate certain subtypes of excitatory amino acid receptors. This effect is due to the enzymatic activity but is probably not correlated with the formation of arachidonic acid metabolites. Independent of their possible physiological implications, our results provide the first autoradiographic evidence that an enzymatic treatment can selectively affect the binding properties of excitatory amino acid receptors in different regions of the CNS.