[3H]Spiperone binding sites in brain: autoradiographic localization of multiple receptors

Olfactory Bulb D2/D3 Receptor Availability after Intrastriatal Botulinum Neurotoxin-A Injection in a Unilateral 6-OHDA Rat Model of Parkinson's Disease

Olfactory deficits occur as early non-motor symptoms of idiopathic Parkinson's disease (PD) in humans. The first central relay of the olfactory pathway, the olfactory bulb (OB), depends, among other things, on an intact, functional crosstalk between dopaminergic interneurons and dopamine receptors (D2/D3R). In rats, hemiparkinsonism (hemi-PD) can be induced by unilateral injection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle (MFB), disrupting dopaminergic neurons of the substantia nigra pars compacta (SNpc). In a previous study, we showed that subsequent injection of botulinum neurotoxin-A (BoNT-A) into the striatum can reverse most of the pathological motor symptoms and normalize the D2/D3R availability. To determine whether this rat model is suitable to explain olfactory deficits that occur in humans with PD, we examined the availability of D2/D3R by longitudinal [18F]fallypride-PET/CT, the density of tyrosine hydroxylase immunoreactivity in the OB, olfactory performance by an orienting odor identification test adapted for rats, and a connectome analysis. PET/CT and immunohistochemical data remained largely unchanged after 6-OHDA lesion in experimental animals, suggesting that outcomes of the 6-OHDA hemi-PD rat model do not completely explain olfactory deficits in humans. However, after subsequent ipsilateral BoNT-A injection into the striatum, a significant 8.5% increase of the D2/D3R availability in the ipsilateral OB and concomitant improvement of olfactory performance were detectable. Based on tract-tracing meta-analysis, we speculate that this may be due to indirect connections between the striatum and the OB.

Increased Dopamine Type 2 Gene Expression in the Dorsal Striatum in Individuals With Autism Spectrum Disorder Suggests Alterations in Indirect Pathway Signaling and Circuitry

Autism spectrum disorder (ASD) is behaviorally defined and diagnosed by delayed and/or impeded language, stereotyped repetitive behaviors, and difficulties with social interactions. Additionally, there are disruptions in motor processing, which includes the intent to execute movements, interrupted/inhibited action chain sequences, impaired execution of speech, and repetitive motor behaviors. Cortical loops through basal ganglia (BG) structures are known to play critical roles in the typical functioning of these actions. Specifically, corticostriate projections to the dorsal striatum (caudate and putamen) convey abundant input from motor, cognitive and limbic cortices and subsequently project to other BG structures. Excitatory dopamine (DA) type 1 receptors are predominantly expressed on GABAergic medium spiny neurons (MSNs) in the dorsal striatum as part of the "direct pathway" to GPi and SNpr whereas inhibitory DA type 2 receptors are predominantly expressed on MSNs that primarily project to GPe. This study aimed to better understand how this circuitry may be altered in ASD, especially concerning the neurochemical modulation of GABAergic MSNs within the two major BG pathways. We utilized two classical methods to analyze the postmortem BG in ASD in comparison to neurotypical cases: ligand binding autoradiography to quantify densities of GABA-A, GABA-B, 5-HT₂, and DA type 1 and 2 receptors and in situ hybridization histochemistry (ISHH) to quantify mRNA for D1, D2 receptors and three key GABAergic subunits (α1, β2, and γ2), as well as the GABA synthesizing enzymes (GAD65/67). Results demonstrated significant increases in D2 mRNA within MSNs in both the caudate and putamen, which was further verified by proenkephalin mRNA that is co-expressed with the D2 receptor in the indirect pathway MSNs. In contrast, all other GABAergic, serotonergic and dopaminergic markers in the dorsal striatum had comparable labeling densities. These results indicate alterations in the indirect pathway of the BG, with possible implications for the execution of competing motor programs and E/I imbalance in the direct/indirect motor feedback pathways through thalamic and motor cortical areas. Results also provide insights regarding the efficacy of FDA-approved drugs used to treat individuals with ASD acting on specific DA and 5-HT receptor subtypes.

Molecular identity of periglomerular and short axon cells

Within glomeruli, the initial sites of synaptic integration in the olfactory pathway, olfactory sensory axons terminate on dendrites of projection and juxtaglomerular (JG) neurons. JG cells form at least two major circuits: the classic intraglomerular circuit consisting of external tufted (ET) and periglomerular (PG) cells and an interglomerular circuit comprised of the long-range connections of short axon (SA) cells. We examined the projections and the synaptic inputs of identified JG cell chemotypes using mice expressing green fluorescent protein (GFP) driven by the promoter for glutamic acid decarboxylase (GAD) 65 kDa, 67 kDa, or tyrosine hydroxylase (TH). Virtually all (97%) TH+ cells are also GAD67+ and are thus DAergic-GABAergic neurons. Using a combination of retrograde tracing, whole-cell patch-clamp recording, and single-cell three-dimensional reconstruction, we show that different JG cell chemotypes contribute to distinct microcircuits within or between glomeruli. GAD65+ GABAergic PG cells ramify principally within one glomerulus and participate in uniglomerular circuits. DAergic-GABAergic cells have extensive interglomerular projections. DAergic-GABAergic SA cells comprise two subgroups. One subpopulation contacts 5-12 glomeruli and is referred to as "oligoglomerular." Approximately one-third of these oligoglomerular DAergic SA cells receive direct olfactory nerve (ON) synaptic input, and the remaining two-thirds receive input via a disynaptic ON-->ET-->SA circuit. The second population of DAergic-GABAergic SA cells also disynaptic ON input and connect tens to hundreds of glomeruli in an extensive "polyglomerular" network. Although DAergic JG cells have traditionally been considered PG cells, their interglomerular connections argue that they are more appropriately classified as SA cells.

Distribution of D2 dopamine receptor in the olfactory glomeruli of the rat olfactory bulb

Dopamine plays key roles in the processing of the olfactory information that takes place in the olfactory glomeruli. Previous studies using autoradiography demonstrate that, at the glomerular level, these actions are mainly mediated via activation of D2 dopamine receptors. Moreover, it has been suggested that D2 receptors could be present in the olfactory nerve, where they might modulate the entrance of olfactory input into the brain. Nevertheless, the precise subcellular localization of D2 receptors in the glomerular neuropil has not been investigated. In this report, we show the subcellular distribution of D2 receptors in the glomerular circuits of Wistar rats, using pre-embedding immunogold-silver labelling and electron microscopy. Present results demonstrate for the first time the presence of D2 dopamine receptors into the terminals of the olfactory axons. In addition, we demonstrate that D2 receptors are located into presynaptic elements of the glomerular neuropil other than the olfactory axons. These elements include the dendrites of the mitral/tufted cells and the dendrites of a subset of periglomerular cells that are GABAergic and dopaminergic. This distribution pattern provides anatomical support for a wide range of actions of dopamine in the glomerular circuits through presynaptic mechanisms mediated by D2 receptors. These actions would include: (i) modulation of the glutamate release from the olfactory axons to the dendrites of mitral/tufted cells and periglomerular cells; (ii) modulation of glutamatergic synapses from the dendrites of mitral/tufted cells to the dendrites of periglomerular cells and (iii) modulation of the neurotransmission from a subset of GABAergic/dopaminergic periglomerular cells to mitral/tufted cells.

Effects of long-term biogenic amine transporter blockade on receptor/G-protein coupling in rat brain

This study examines the effect of long-term elevation of brain monoamine levels on receptor/G-protein coupling by chronic administration of a highly potent tropane analog, WF-23 (2beta-propanoyl-3beta-(2-naphthyl) tropane). WF-23 blocks dopamine, serotonin and norepinephrine transporters with high affinity in vitro, and blocks transporters for at least two days following a single in vivo administration. Rats were chronically treated for 15 days with 1mg/kg WF-23, injected i.p. every two days. Receptor activation of G-proteins was determined by [35S]GTPgammaS autoradiography in brain sections for D2, 5-HT1A and alpha2-adrenergic receptors, as well as mu opioid receptors as a non-monoamine receptor control. Chronic treatment with WF-23 produced significant reductions in D2, 5-HT1A, and alpha2-adrenergic receptor-stimulated [35S]GTPgammaS binding in caudate/putamen, hippocampus and amygdala, respectively. There were no effects of WF-23 treatment on mu opioid-stimulated [35S]GTPgammaS binding. Additionally, there was no effect of WF-23 treatment on D2 receptor binding, as determined by [3H]spiperone autoradiography. These data show that chronic blockade of monoamine transporters produces specific uncoupling of receptors and G-proteins in specific brain regions in the absence of receptor downregulation.

Time-dependent changes in receptor/G-protein coupling in rat brain following chronic monoamine transporter blockade

The potent tropane analog, WF-23 [2beta-propanoyl-3beta-(2-naphthyl) tropane], blocks dopamine, serotonin, and norepinephrine transporters with high affinity in vitro and blocks transporters for at least 2 days following a single in vivo administration. Previous studies demonstrated desensitization of monoamine receptor-coupled G-proteins in brain following chronic treatment of rats with WF-23. The current study sought to determine the time course of this desensitization and the behavioral effects of receptor desensitization. Rats were treated with 1 mg/kg WF-23 and injected i.p. every 48 h for 1 to 21 days. Receptor activation of G-proteins was determined by guanosine 5'-O-(3-[(35)S]thiotriphosphate) ([(35)S]GTPgammaS) binding in brain sections for monoamine receptors, as well as mu opioid receptors as a nonmonoamine receptor control. Chronic treatment with WF-23 produced significant reductions in D(2), 5-hydroxytryptamine 1A, and alpha(2)-adrenergic receptor-stimulated [(35)S]GTPgammaS binding; however, the time course of desensitization varied with different receptors. There was no effect of WF-23 treatment on mu opioid-stimulated [(35)S]GTPgammaS binding at any time point. Consistent with previous studies, there was no effect of WF-23 treatment on D(2) receptor binding, as determined by [(3)H]spiperone autoradiography. Locomotor activity was significantly increased for up to 48 h following acute administration of WF-23, demonstrated by increased photocell beam interruptions. WF-23-induced increases in locomotor activity occurred following repeated administration, as above, for up to 7 days. Following 7 days of treatment, there was a significant decrease in WF-23-increased locomotor activity. This reduction occurred at the same time point as the decrease in D(2) receptor/G-protein coupling, suggesting a role of D(2) desensitization in producing tolerance to WF-23-mediated behavior.

GABAB receptor expression and function in olfactory receptor neuron axon growth

Neurotransmitters have been implicated in regulating growth cone motility and guidance in the developing nervous system. Anatomical and electrophysiological studies show the presence of functional GABAB receptors on adult olfactory receptor neuron (ORN) nerve terminals. Using antisera against the GABAB R1a/b receptor isoforms we show that developing mouse olfactory receptor neurons express GABAB receptors from embryonic day 14 through to adulthood. GABAB receptors are present on axon growth cones from both dissociated ORNs and olfactory epithelial explants. Neurons in the olfactory bulb begin to express glutamic acid decarboxylase (GAD), the synthetic enzyme for GABA, from E16 through to adulthood. When dissociated ORNs were cultured in the presence of the GABAB receptor agonists, baclofen or SKF97541, neurite outgrowth was significantly reduced. Concurrent treatment of the neurons with baclofen and the GABAB receptor antagonist CGP54626 prevented the inhibitory effects of baclofen on ORN neurite outgrowth. These results show that growing ORN axons express GABAB receptors and are sensitive to the effects of GABAB receptor activation. Thus, ORNs in vivo may detect GABA release from juxtaglomerular cells as they enter the glomerular layer and use this as a signal to limit their outgrowth and find synaptic targets in regeneration and development.

Intrastriatal Dopamine-rich Implants Reverse the Increase of Dopamine D2 Receptor mRNA Levels Caused by Lesion of the Nigrostriatal Pathway: A Quantitative In Situ Hybridization Study

Changes in striatal dopamine D2 receptor mRNA levels provoked by unilateral 6-hydroxydopamine-induced lesion of the nigrostriatal dopamine pathway were studied by in situ hybridization. The influence of embryonic dopaminergic neurons implanted into the dopamine-depleted striatum on the lesion-induced changes was also examined. Changes in D2 mRNA levels were compared with changes in D2 receptor densities measured in the same animals by receptor autoradiography using [3H]spiperone or [3H]SDZ 205-501 as ligands. The distribution of D2 mRNA in the striatum of control animals closely paralleled that of the D2 receptor itself, as assessed by autoradiography, and the highest density of D2 mRNA occurred in the lateral part of the striatum. One month after lesion, levels of D2 mRNA were 34% higher in the dorsolateral part of the dopamine-depleted striatum than in the corresponding region of the contralateral control striatum. D2 receptor density in this region was increased by 40% relative to the control level. No significant increases could be measured in the medial part of the striatum. The increases in the lateral part were similar at 7 months post-lesion; however, at this time the increase in both D2 mRNA and receptor levels had spread to the medial part of the striatum as well. In the graft-bearing striatum levels of both D2 mRNA and D2 receptors reverted to control levels. This study shows that the post-lesion increase in striatal dopamine receptor and mRNA level is a biphasic phenomenon with a late-occurring component in the medial striatum. It also shows that once the increase in striatal D2 receptor gene expression is accomplished, it is maintained unchanged for long periods, similar to that of D2 receptor levels themselves. Moreover, grafts of embryonic dopaminergic neurons are able to modulate the expression of the dopamine D2 receptor gene.

Decreased [(3)H]spiperone binding in the anterior cingulate cortex of schizophrenia patients: an autoradiographic study

Abnormalities in the anterior cingulate cortex have been reported in patients with schizophrenia, and have been implicated in the pathophysiology of this disorder. In the present study, we have examined antipsychotic-sensitive binding sites in the left anterior cingulate cortex of schizophrenia patients and controls. Using quantitative autoradiography and [(3)H]spiperone as a ligand, both saturation and competition experiments were performed in post-mortem brain tissue obtained from six schizophrenia and six control cases. Saturation experiments revealed that the maximum number of [(3)H]spiperone binding sites was significantly reduced by 31% in the schizophrenia group as compared to the control group (65.3+/-5.6 fmol/mg tissue versus 94.2+/-7.3 fmol/mg tissue). Increased dissociation constant was also observed in the schizophrenia group (2.2+/-0.4 nM versus 1.3+/-0.2 nM), but was not statistically significant (P=0.07). Competition experiments were performed in order to examine the pharmacological profile of [(3)H]spiperone binding, and revealed that: (i) displacement of [(3)H]spiperone binding by clozapine and mianserin was significantly reduced in the schizophrenia group as compared to the control group (-26% and -16% respectively); (ii) the order of displacement potency of the drugs tested was: haloperidol>mianserin>butaclamol approximately risperidone>clozapine>2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene. Our results suggest a reduction of antipsychotic-sensitive binding sites in the anterior cingulate cortex of patients with schizophrenia. Such abnormality could lead to an imbalance in neurotransmitter regulation in the anterior cingulate cortex which may contribute to the emergence of some symptoms of schizophrenia.

Age-related changes of dopamine receptors in the rat hippocampus: a light microscope autoradiography study

Hippocampus is a brain region involved in learning and memory and is particularly sensitive to ageing. It is supplied with a dopaminergic innervation arising from the midbrain, which is part of the mesolimbic dopaminergic pathway. Dysfunction of the dopaminergic mesolimbic system is probably involved in the pathophysiology of psychosis and behavioural disturbances occurring in the elderly. The present study was designed to assess the density and localisation of dopamine D1- and D2-like receptor subtypes in the hippocampus of male Sprague-Dawley rats aged 3 months (young), 12 months (adult) and 24 months (old). Dopamine D1-like receptors, labelled by [3H]-SCH 23390, in young rats displayed a dentate gyrus-CA1 subfield gradient. The expression was increased in the cell body of dentate gyrus, CA4 and CA3 subfield of old rats compared to younger cohorts, as well as in the neuropil of dentate gyrus. A decreased density of dopamine D1-like receptors was found in the stratum oriens of CA1 and CA3 subfields. Dopamine D2-like receptors, labelled using [3H]-spiperone as radioligand, were expressed rather homogeneously throughout different subfields of the hippocampus. In old rats, the density of dopamine D2-like receptors was decreased in the dentate gyrus, unchanged in the CA4 and CA1 subfields and increased in the CA3 subfield. The above results indicate the occurrence of inhomogeneous changes in the density of dopamine D1- and D2-like receptors in specific portions of hippocampus of old rats. These findings support the hypothesis of an involvement of dopaminergic system in behavioural abnormalities or psychosis occurring in ageing.

Haloperidol-induced catalepsy is absent in dopamine D(2), but maintained in dopamine D(3) receptor knock-out mice

We have previously found that mice homozygous for the deletion of the dopamine D(2) receptor gene (D(2)(-/-) mice) do not present spontaneous catalepsy when tested in a "bar test". In the present study, we sought to analyse the reactivity of D(2) receptor mutant mice to the cataleptogenic effects of dopamine D(2)-like or D(1)-like receptor antagonists. In parallel, we assessed the cataleptogenic effects of these antagonists in dopamine D(3) receptor mutant mice. D(2)(-/-) mice were totally unresponsive to the cataleptogenic effects of the dopamine D(2)-like receptor antagonist haloperidol (0.125-2 mg/kg i.p.), while D(2)(+/-) mice, at the highest haloperidol doses tested, showed a level of catalepsy about half that of wild-type controls. The degree of haloperidol-induced catalepsy was thus proportional to the level of striatal dopamine D(2) receptor expression (0.50, 0.30 and 0.08 pmol/mg protein as measured at 0.25 nM [3H]spiperone for D(2)(+/+), D(2)(+/-) and D(2)(-/-) mice, respectively). However, D(2)(-/-) and D(2)(+/-) mice were as sensitive as their wild-type counterparts to the cataleptogenic effects of the dopamine D(1)-like receptor antagonist R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4, 5-tetrahydro-1H-3-benzazepine hydrochloride (SCH 23390: 0.03-0.6 mg/kg s.c.). Striatal dopamine D(1) receptor expression (as measured using [3H]SCH 23390 binding) was not significantly affected by the genotype. The ability of SCH 23390 to induce catalepsy in D(2)(-/-) mice suggests that their resistance to haloperidol-induced catalepsy is due to the absence of dopamine D(2) receptors, and not to the abnormal striatal synaptic plasticity that has been shown by others to occur in these mice. In agreement with the observation that dopamine D(2) and dopamine D(1) receptor expression was essentially identical in D(3)(+/+), D(3)(+/-) and D(3)(-/-) mice, dopamine D(3) receptor homozygous and heterozygous mutant mice, on the whole, did not differ from their controls in the time spent in a cataleptic position following administration of either haloperidol (0.5-2 mg/kg i.p.) or SCH 23390 (0.03-0.6 mg/kg s.c.). Also, dopamine D(3) receptor mutant mice were no more responsive than wild-type controls when co-administered subthreshold doses of haloperidol (0.125 mg/kg) and SCH 23390 (0.03 mg/kg), suggesting that dopamine D(3) receptor knock-out mice are not more sensitive than wild-types to the synergistic effects of concurrent blockade of dopamine D(2) and dopamine D(1) receptors in this model. These results suggest that the dopamine D(2) receptor subtype is necessary for haloperidol to produce catalepsy, and that the dopamine D(3) receptor subtype appears to exert no observable control over the catalepsy produced by dopamine D(2)-like, D(1)-like and the combination of D(1)-like and D(2)-like receptor antagonists.

Olfactory receptor neurons express D2 dopamine receptors

The role of the dopamine (DA) in the olfactory bulb (OB) was explored by determining which of the potential target cells express dopamine receptors (DARs). Previously, it was reported that D2-like DAR (D2, D3, and D4 subtypes) radioligand binding is restricted to the outer layers of the OB. The neuronal elements present only in these layers are the axons of the olfactory receptor neurons (ORNs) and the juxtaglomerular (JG) neurons of the glomerular layer. Based on this pattern of D2-like ligand binding, it was suggested that D2-like receptors might be located presynaptically on ORN terminals. The present study was undertaken to investigate this hypothesis. In the outer bulb layers of rats in which the ORNs were destroyed by nasal lavage with ZnSO(4), D2-like radioligand binding was reduced severely. The receptor subtype D2 mRNA, but not D3 mRNA, was detected in adult rat olfactory epithelial tissue. By using in situ hybridization, this D2 mRNA was located preferentially in epithelial layers that contain ORN perikarya. D2 mRNA was eliminated after bulbectomy, a manipulation known to cause retrograde degeneration of the mature ORNs. Taken together, the surgical manipulations indicate that mature ORNs express D2 DARs and are consistent with the hypothesis that functional receptors are translocated to their axons and terminals in the bulb. This suggests that dopamine released from JG interneurons could be capable of presynaptically influencing neurotransmission from the olfactory nerve terminals to OB target cells through the D2 receptor.

Effects of chronic treatment with typical and atypical antipsychotic drugs on the rat striatum

Human MRI studies have demonstrated that treatment with typical antipsychotics may increase the volume of the caudate nucleus while clozapine treatment is associated with either no change or a reversal of the previous volume increase. In this study four groups of seven rats were treated for 8 months with either the typical antipsychotic haloperidol, the atypical antipsychotic clozapine, the D2/D3 receptor antagonist raclopride, or vehicle (plain drinking water). Striatal sections were prepared using D1-like and D2-like receptor ligand autoradiography. Images (4-6 sections per rat, per ligand) were digitized and the area of the striatum was measured on each section. Rats treated with haloperidol did not have a larger mean striatum area than the control group on either D1- or D2-like ligand autoradiograms. Using the D2-like ligand autoradiograms, the clozapine treated animals had a smaller mean striatum area than the control group. Mean left striatum area was larger than mean right striatum area in each treatment group and in the control group. In contrast to the MRI findings reported in schizophrenia, the area of the striatum was not increased in rats treated with typical antipsychotic agents, but the clozapine-associated area reduction may parallel the clinical studies.

Differential regulation of dopamine receptors after chronic typical and atypical antipsychotic drug treatment

Changes in dopamine receptor subtype binding in different brain regions were examined after 28 days treatment of rats with haloperidol, raclopride, clozapine or SCH23390 using in vitro receptor autoradiography. [3H]7-hydroxy-N,N-di-n-propyl-2-aminotetralin binding to dopamine D3 receptors was not changed in any brain region by any of the drug treatments. [3H]SCH23390 was only increased by chronic SCH23390 treatment. Haloperidol significantly increased [3H]nemonapride and [3H]spiperone binding to dopamine D2-like receptors in the caudate putamen. In contrast, haloperidol caused a small, significant increase in [3H]raclopride binding in the lateral caudate putamen only. Raclopride also elevated, but to a lesser extent [3H]nemonapride and [3H]spiperone binding in caudate putamen, whereas it did not affect [3H]raclopride binding. Clozapine did not significantly change D2-like striatal binding of [3H]nemonaipride, [3H]spiperone or [3H]raclopride. The differences in radioligand binding suggest that [3H]nemonapride and [3H]spiperone may be binding to additional subsets of dopamine D2-like receptors (including D4-like receptors) that are not recognized by [3H]raclopride, which has high affinity for D2 and D3 receptors only. Quantification of [3H]nemonapride or [3H]spiperone binding in the presence of 300 nM raclopride (to block D2 and D3 receptors) revealed that haloperidol, raclopride and clozapine up-regulated D4-like receptors in the caudate putamen using either radioligand. These results suggest that D4-like receptors may be a common site of action of both typical and atypical antipsychotics.

Effect of aging on dopaminergic receptors and uptake sites in the rat brain studied by receptor autoradiography

We studied the age-related alterations of dopaminergic receptors in the brain of Fisher 344 rats with various age (3 weeks and 6, 12, 18 and 24 months) using in vitro receptor autoradiography. [3H]SCH 23390, [3H]spiperone and [3H]nemonapride, and [3H]mazindol were used to label dopamine D1 receptors, dopamine D2 receptors and dopamine uptake sites, respectively. In immature rats (3 weeks old), [3H]SCH 23390 binding showed a significant increase in most brain regions compared to adult animals (6 months old), whereas [3H]spiperone and [3H]nemonapride bindings showed no significant alteration in any brain areas. In contrast, [3H]mazindol binding showed a significant decline in most brain regions. On the other hand, the age-related alterations in [3H]SCH 23390 binding were not observed in any brain regions. [3H]Spiperone and [3H]nemonapride bindings also showed no significant alteration in the brain during aging, except for a transient alteration in [3H]spiperone binding in the nucleus accumbens and hippocampus of 12 months old rats. However, [3H]mazindol binding showed a significant reduction in most brain areas of 12 months old rats. Thereafter, the age-related reduction in [3H]mazindol binding was observed in most brain regions of 18 and 24 months old rats. The results demonstrate that dopamine uptake sites are more susceptible to the aging process than both dopamine D1 and D2 receptors. Furthermore, our results suggest that dopaminergic receptors and dopamine uptake sites may develop with different patterns and speeds after birth. Our studies may provide valuable information concerning the effect of aging on dopaminergic systems.

Differential effects of haloperidol and two anxiolytic drugs, buspirone and lesopitron, on c-Fos expression in the rat striatum and nucleus accumbens

We have studied the effects of the neuroleptic haloperidol and the non-benzodiazepine anxiolytics buspirone and lesopitron on the expression of c-Fos immunoreactivity in the rat forebrain. Haloperidol and buspirone administration resulted in a significant quantitative increase in the number of Fos-immunoreactive neurons in the lateral striatum and a presumable qualitative increase in the nucleus accumbens. In contrast, lesopitron did not lead to a significant increase in the c-Fos expression in the striatum. The induction of c-Fos immunoreactivity by buspirone is compatible with an interaction of this compound with D2 dopamine receptors, as documented for haloperidol. The lack of effects after lesopitron administration suggests that, in contrast with buspirone, this compound has no dopaminergic blocking activity.

Effects of cerebral ischemia on dopamine receptors in the gerbil striatum

Dopamine D1 and D2 receptors and uptake sites were studied in the gerbil striatum and frontal cortex 1 h to 7 days after 10 min of cerebral ischemia caused by occlusion of the bilateral common carotid arteries. [3H]SCH23390 ([N-methyl-3H]R[+]-8-chloro-2, 3,4,5-tetrahydro-3-methyl-5-phenyl-7-ol-benzazepine), [3H]nemonapride and [3H]mazindol were used as markers of dopamine D1 receptors, D2 receptors and uptake sites, respectively. A significant reduction in [3H] SCH23390 binding was found in the striatum from 48 h after ischemia. In contrast, during the recirculation periods, [3H]nemonapride and [3H]mazindol binding was mostly unaffected in this region which was the most vulnerable to ischemia. The frontal cortex, where ischemic neuronal damage was mild, also showed no significant changes in [3H]SCH23390, [3H]nemonapride and [3H]mazindol binding after ischemia. Thus, cerebral ischemia that was associated with cell loss in the striatum resulted in a selective reduction of dopamine D1 receptors and not D2 receptors. No changes in dopamine D1 or D2 receptors were observed in frontal cortex. If massive dopamine release occurs with cerebral ischemia, it is not reflected by modification in the number of uptake sites located on dopamine terminals.

Development of dopamine receptors in the forebrain of the domestic chick in relation to auditory imprinting. An autoradiographic study

The rostro-medial neostriatum/hyperstriatum ventrale (MNH) and the neostriatum dorsocaudale (Ndc) are forebrain regions which play a role in auditory filial imprinting. Both regions receive a distinct dopaminergic input from the mesencephalon and we were interested to investigate if the dopaminergic system, which is known to play a role in associative learning processes and neuronal plasticity is involved in auditory imprinting. Using ligand autoradiography we studied the distribution and density of dopamine receptors (D1 and D2 type) in the forebrain of socially isolated chicks during the first postnatal week and compared these data with the values of age-matched imprinted chicks. D1- and D2-receptors were present in the chick forebrain on the day of hatching and they showed in general, the same distribution until postnatal day 7. Between days 0 and 2 the D2-receptor density increased significantly in the lobus parolfactorius and paleostriatum augmentatum while for D1-receptor density no significant changes were detectable. The receptor densities in the investigated forebrain regions did not differ significantly between imprinted and control chicks. These results suggest that auditory imprinting does not induce alterations of dopamine receptor density, however, more subtle changes can not be excluded. The presented detailed data about the developmental profile of dopamine receptors within distinct brain regions is a further step towards a more specific interpretation of behavioral effects of dopamine receptor agonists or antagonists at different postnatal ages.

Synthesis, in vitro binding profile and biodistribution of a 125I-labeled N-benzyl pyrrolidinyl benzamide derivative: a potential radioligand for mapping dopamine D2 receptors

cis-N-(1-Benzyl-2-methylpyrrolidine-3-yl)-5-iodo-2-methoxy-4-(methylamin o) benzamide (IYM), a YM-09151-2 analog iodinated at the 5-position of the benzoyl moiety, was synthesized and evaluated as a potential radiopharmaceutical for investigating brain dopamine D2 receptors by single photon emission computer tomography (SPECT). [125I]IYM was synthesized by a halogen exchange reaction and purified by high-performance liquid chromatography (HPLC). An in vitro competitive binding study with [3H]spiperone using rat striatal synaptosomal membranes revealed that IYM had higher affinity for dopamine D2 receptors than did YM-09151-2 or spiperone. In a saturation binding study using rat striatal synaptosomal membranes, IYM had a Kd of 0.04 nM. Biodistribution studies in mice disclosed that [125I]IYM exhibited high and specific striatal uptake, with the striatal/cerebellar uptake ratio being 14 at 120 min after injection. Furthermore, the striatal uptake of [125I]IYM was saturable, and [125I]IYM was displaced only by dopaminergic compounds. Ex vivo autoradiographic studies in rats further confirmed the high uptake and retention of this agent in the striatum and total blockade of its uptake by YM-09151-2. Thus, IYM showed specific binding to dopamine D2 receptors in the rodent striatum and therefore holds great potential for use in in vivo dopamine D2 receptor studies.

Effects of chronic treatment with haloperidol on [3H]PK 11195 binding in the rat brain and peripheral tissues

The effects of chronic treatment with haloperidol on [3H]PK 11195 binding and labelling of the peripheral-type benzodiazepine receptor (PBR) in the rat brain and peripheral tissues were investigated using an in vitro receptor binding technique. The intraperitoneal injection with haloperidol (0.3 or 1.0 mg/kg) for 21 days produced a significant increase in the specific [3H]PK 11195 binding only in the olfactory bulb, but not in the other brain areas or peripheral tissues, while single or subchronic (4 days or 7 days) administration with the drug (0.3 mg/kg, i.p.) failed to increase the binding in the olfactory bulb. Scatchard analysis revealed a significant increase in the maximum number of [3H]PK 11195 binding sites in the olfactory bulb after chronic treatment with haloperidol, showing no change in the affinity of the binding. These results suggest that there is an interaction between PBR and the pharmacological actions of haloperidol in the brain area, and that some compensatory mechanism may be involved in the PBR changes.

Quantitative autoradiographic analysis of D1 and D2 dopamine receptors in rat brain in early and late pregnancy

This study examined the levels of D1 and D2 dopamine receptors in the rat brain during pregnancy, a physiologically unique and important naturally occurring state. We are particularly interested in changes in the dopamine receptor complement of the brain during pregnancy because these receptors might support some components of the immediate postpartum onset of normal maternal behavior. Quantitative in vitro receptor autoradiography was applied particularly focusing on brain areas that control maternal behavior. The D1 dopamine receptor selective antagonist -3H-SCH23390 and the D2 dopamine receptor selective antagonist [3H]spiperone were used as the ligands. We examined the levels of binding to D1 and D2 dopamine receptors in brains in females on day 2 (early pregnancy) and day 21 (late, but prepartum pregnancy) of pregnancy. In addition, brains from females on diestrus-1 and from males provided reference points to the existing literature. Late in pregnancy females had significantly 18-27% lower levels of binding to D1 dopamine receptors in the lateral striatum, the medial striatum, and the nucleus accumbens when compared to all other groups. Late in pregnancy, females had also significantly 11-25% lower levels of binding to D2 dopamine receptors in the lateral striatum, the anterior striatum, the nucleus accumbens and the olfactory tubercle compared to all other experimental groups. We examined all of the brain regions already established to be important for maternal behavior, and found that dopamine receptor binding changed across pregnancy only in one such region, the nucleus accumbens. Thus pregnancy, perhaps the hormones of pregnancy, reduces the levels of D1 and D2 dopamine receptors in the striatum, and the nucleus accumbens, but not in other brain regions.

Dopamine D2-like receptors labeled by [3H]YM-09151-2 in the rat hippocampus: characterization and autoradiographic distribution

Dopamine D2-like receptor labeled by [3H]YM-09151-2 in the rat hippocampus proper was examined by in vitro receptor autoradiography. In the dorsal hippocampus, [3H]YM-09151-2 bindings were high in the whole layers of CA1, the stratum pyramidale of CA4 and the stratum molecular of gyrus dentatus, moderate in the stratum oriens of CA3 and hilus of the gyrus dentatus, and low in remaining CA3 and the subiculum. In the ventral hippocampus, the binding densities were high in the stratum oriens and the stratum radiatum of CA1, the stratum pyramidale of CA4, and the stratum moleculare of gyrus dentatus, moderate in the stratum lacnosum moleculare of CA1 and the hilus of the gyrus dentatus. Saturation analysis using hippocampal sections demonstrated that the Kd value was about five times higher than that using striatal sections. The rank order potency of competition on [3H]YM-09151-2 binding by dopaminergic ligands in the hippocampus was YM-09151-2 > (+)-butaclamol > dopamine > sulpiride > SCH-23390; which shows the appropriate dopamine D2-like receptor profile. The hippocampal [3H]YM-09151-2 binding did not represent serotonergic receptors (5-HT1A and 5-HT2) and sigma receptor, since Ki values of ketanserine, serotonin, 8-OH-DPAT and DTG were much lower than D2-like receptor antagonists. These findings suggest tha [3H]YM-09151-2 binds hippocampal D2-like receptor site with different association kinetics of striatal D2-like receptor site, and demonstrates widespread distribution of D2-like receptor in the hippocampus with distinct region-specific profile.

Autoradiographic distribution of [3H]YM-09151-2, a high-affinity and selective antagonist ligand for the dopamine D2 receptor group, in the rat brain and spinal cord

We determined the regional distribution of the dopamine D2 receptor group in the rat central nervous system by quantitative receptor autoradiography with a high-affinity and selective antagonist, [3H]YM-09151-2. Saturation and competition experiments demonstrated that the binding of [3H]YM-09151-2 to striatal sections was saturable (Bmax = 37.3 fmol/section), of high affinity (Kd = 0.315 nM), and was inhibited selectively by prototypic D2 ligands. The anatomical localization of binding sites was determined by comparison of autoradiograms and the original 3H-ligand-exposed sections stained with cresyl violet. Very high levels of [3H]YM-09151-2 binding were found in the caudate-putamen, nucleus accumbens, tuberculum olfactorium and the insula of Calleja, to each of which midbrain dopaminergic neurons project densely. High levels of binding were also observed in other regions rich in dopaminergic neurons and fibers including the glomerular layer of the olfactory bulb, the intermediate lobe of the pituitary, lateral septum, substantia nigra pars compacta, interfascicular nucleus, dorsal raphe nucleus, locus coeruleus, and nucleus of the solitary tract. Some regions poor in dopaminergic innervation, however, had high levels of [3H]YM-09151-2 binding including the molecular layer of gyrus dentatus, all layers of CA1 and the nonpyramidal layer of CA4 of hippocampus, and the deeper layer of medial entorhinal cortex. Motor neurons present in brainstem motor nuclei and spinal ventral horn were also strongly labeled. Neocortical, cerebellar, and thalamic regions had low levels of binding, except lobules 9-10 of the cerebellum, the olivary pretectal nucleus, zona incerta and lateral mammillary nucleus, in which moderate to high levels of binding were detected. Our findings concerning the widespread but region-specific localization of [3H]YM-09151-2 binding sites in the brain and spinal cord may prove useful for analyzing various dopaminergic functions in the central nervous system.

Savoxepine fails to selectively influence glucose metabolism in the rat limbic system

The [14C]-2-deoxyglucose method was used to map the in vivo metabolic response of glucose to savoxepine, a novel tetracyclic cyano-dibenzoxepino-azepine. Savoxepine is reported to have higher affinity for dopamine (DA) receptors in the hippocampus than in the striatum and hence should have dose-dependent, anatomically selective actions. Two doses of savoxepine (0.05 mg/kg and 0.5 mg/kg) were compared with haloperidol (1 mg/kg) to test the hypothesis that low doses of savoxepine would display a selective action on limbic brain areas. Results failed to show that low dose savoxepine selectively modifies glucose utilization in the limbic system as previous biochemical studies suggested. In fact, low doses of the drug displayed a potent activity quite similar to haloperidol in effect and localization. The low dose did not produce significantly altered glucose metabolism in the nucleus accumbens or in the lateral habenular nucleus as observed with most other neuroleptics, suggesting a lack of antipsychotic action at this dose. Our findings demonstrate the difficulty of designing a neuroleptic with a preferential blockade of limbic DA receptors and point to the need for functional assessment of regional receptor binding differences.

Alterations of neurotransmitter receptors and neurotransmitter transporters in progressive supranuclear palsy

Neurotransmitter receptors and neurotransmitter transporters were studied postmortem in the brains of 9 PSP patients by receptor autoradiography. Densities of dopamine uptake sites and neurotensin receptors were significantly reduced in striatum and substantia nigra consistent with a localization of these binding sites on degenerating dopaminergic nigrostriatal projection neurons. The densities of dopamine D1 receptors were unchanged. Dopamine D2 receptors were unaltered when labeled by [125I]-Iodosulpride or [3H]-CV 205 502, but appeared to be significantly reduced when labeled by [3H]-spiperone. Levels of D2 mRNA were comparable to control levels, suggesting that only subtypes of Dopamine D2-like receptors may be affected in PSP. Serotonin (5-HT) uptake sites and 5-HT receptors were not altered. The density of muscarinic receptors was reduced in striatum, possibly related to a degeneration of cholinergic striatal interneurons, but increased in internal globus pallidus. GABAA/BZ receptor binding sites were significantly reduced in both segments of globus pallidus, probably as a consequence of severe degeneration of intrinsic pallidal neurons in PSP. Binding of substance P in striatum tended to be decreased but failed to reach statistical significance. Compared to Parkinson's disease, the densities of more neurotransmitter receptors were altered in PSP. With the exception of increased muscarinic receptor binding sites in medial globus pallidus, the alterations seen in PSP seem to reflect cell loss rather than functional changes.

Alterations in striatal and extrastriatal D-1 and D-2 dopamine receptors in the MPTP-treated common marmoset: an autoradiographic study

In adult common marmosets (Callithrix jacchus), MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) treatment induced almost total depletion of cells in the substantia nigra pars compacts (SNc) but partial cell loss in the ventral tegmental area (VTA). There was severe depletion of [3H]-mazindol binding to dopamine (DA) uptake sites in the caudate, putamen, and SNc. The loss of [3H]-mazindol binding in the nucleus accumbens (NAc) and olfactory tubercle (OT) was less marked. [3H]-mazindol binding in the body of caudate nucleus showed a small but significant recovery with increasing post-lesion survival times. The specific binding of [3H]-SCH 23390 to D-1 DA receptor sites was increased after MPTP treatment in all subregions of both caudate and putamen but was unaltered in the NAc and OT. Substantia nigra pars reticulata (SNr), frontal cortex, and medial segment of globus pallidus (GPm) all demonstrated moderate levels of [3H]-SCH 23390 binding in control animals, which were unaffected by MPTP treatment. Specific [3H]-spiperone binding to D-2 DA receptor sites was not altered by MPTP treatment in the subregions of caudate-putamen. Moderate levels of [3H]-spiperone binding were observed in control animals in the NAc, OT, SNc, and the lateral segment of globus pallidus (GP1). [3H]-spiperone binding in the SNc and OT was partially decreased in MPTP-treated animals. The changes in specific [3H]-spiperone and [3H]-SCH 23390 binding induced by MPTP-treatment did not alter with post-lesion survival times. These results demonstrate that MPTP treatment causes greater dopaminergic denervation of the caudate-putamen than in NAc/OT. This resulted in an increase in postsynaptic D-1 DA receptor sites in the caudate-putamen but not in the NAc/OT. Also, there appeared to be loss of presynaptic D-2 DA receptor sites in the SNc and OT. In the caudate-putamen, the loss of presynaptic D-2 DA receptor sites may have masked postsynaptic D-2 DA receptor upregulation.

Autoradiographic studies of RP 62203, a potent 5-HT2 receptor antagonist. In vitro and ex vivo selectivity profile

In this study, quantitative autoradiography was used to determine the selectivity of RP 62203, a novel naphtosultam derivative, for 5-HT2 receptors in vitro and ex vivo, using [125I]7-amino-8-iodo-ketanserin ([125I]AMIK) and [3H]mesulergine as radioligands. The density of [125I]AMIK or [3H]mesulergine binding sites was determined by quantitative image analysis. In in vitro experiments, RP 62203 displaced [125I]AMIK from 5-HT2 receptors with an IC50 of 0.21 nM in rat frontal cortex. Its affinity for 5-HT1C receptors was 100-fold lower (IC50 25 nM versus [3H]mesulergine in rat choroid plexus). RP 62203 showed moderate affinity for alpha 1-adrenoceptors in the rat thalamus (IC50 14 nM) and for histamine H1 receptors in the guinea-pig cerebellum (IC50 13 nM). The tetrabenazine sites were not affected by RP 62203 at a concentration of 30 nM. In ex vivo experiments, RP 62203 was about 4 times more potent than ritanserin in displacing [125I]AMIK from 5-HT2 receptors (ED50 0.58 mg/kg p.o.). A dose of 10 mg/kg of RP 62203 did not displace [3H]mesulergine from 5-HT1C receptors or [125I]AMIK from alpha 1-adrenoceptors and tetrabenazine sites in the rat brain and from histamine H1 receptors in the guinea-pig brain. These results demonstrate that RP 62203 specifically recognizes 5-HT2 receptors in rodent brain.

Autoradiographic studies of RP 62203, a potent 5-HT2 receptor antagonist. Pharmacological characterization of [3H]RP 62203 binding in the rat brain

The binding properties and localization of [3H]RP 62203, a novel ligand for 5-HT2 receptors, were investigated on rat brain sections. The specific binding of this 5-HT2 receptor antagonist was reversible and could be displaced by ritanserin (1 microM). Saturation experiments revealed a single class of binding sites with a KD of 0.128 +/- 0.018 nM and a Bmax of 1.67 +/- 0.06 pmol/mg protein. Pharmacological specificity was demonstrated by the potency order of displacing agents: RP 62203 > ritanserin > spiperone > methysergide > mianserin > pipamperone > cinanserin > 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). Quantitative autoradiography showed a heterogeneous distribution of [3H]RP 62203 binding sites, with the highest densities in the frontal, parietal and auditory cortices (layer IV), claustrum and olfactory bulb. Binding densities in the occipital cortex, caudate putamen and thalamic nuclei were moderate, whereas the hippocampus and substantia nigra displayed a very low density of binding sites. The cerebellar cortex appeared almost devoid of [3H]RP 62203 binding sites. The anatomical distribution of binding sites demonstrated that [3H]RP 62203 essentially bound only to rat brain regions known to contain 5-HT2 receptors. This ligand could thus be a useful tool to visualize 5-HT2 receptors.

Differential visualization of dopamine D2 and D3 receptor sites in rat brain. A comparative study using in situ hybridization histochemistry and ligand binding autoradiography

At least five members of the dopamine receptor family have been characterized at the gene level. D2, D3 and D4 dopamine receptors are related pharmacologically. In order to visualize the differential expression of D1, D2 and D3 receptors in rat brain we have combined in situ hybridization histochemistry with receptor autoradiography. Regions enriched with D3 messenger RNA (mRNA) included the islands of Calleja (ioC) and nucleus accumbens. Very low or undetectable levels were present in the caudate-putamen. In contrast, no D2 transcripts were observed in the islands of Calleja, but there were high levels in the nucleus accumbens, caudate-putamen (CP) and pyramidal layer of the olfactory tubercle. A comparison of the binding pattern of six dopamine receptor radioligands hitherto regarded as D2 receptor-selective showed that the islands of Calleja were intensely labelled by [125I]iodosulpride, [3H]CV 205 502 and [3H]SDZ 205 501, while the binding of [3H]spiperone, [3H]raclopride and [3H]YM 09151-2 was much lower or undetectable. Pharmacological analysis of the binding of D2/D3 ligands to the islands of Calleja and caudate-putamen suggests that binding sites in these two regions are of different pharmacology, consistent with the presence of D3 sites in the islands of Calleja and the predominance of D2 sites in the caudate. These results demonstrate the expression of D3 binding sites in the rat brain and provide a procedure to differentiate D2 and D3 receptor populations in binding studies.

Hypotensive effects of 5-HT1A receptor activation: ventral medullary sites and mechanisms of action in the rat

Serotonin-1A (5-HT1A) binding sites were previously localized in several regions of the ventral medulla associated with neural regulation of the cardiovascular system. Some of these binding sites were associated with serotonergic neurons of the ventral medulla. The purpose of these studies was to assess and characterize hypotensive responses to a 5-HT1A agonist, (8-hydroxy-dipropylaminotetraline, 8-OH-DPAT), administered to the ventral medulla of the rat, to correlate the responsive ventral medullary sites with the distribution of 3H-8-OH-DPAT binding sites, and to assess the role of serotonergic systems in mediating the hypotensive responses. Ventral medullary application of 8-OH-DPAT caused dose-related reductions in mean arterial pressure and heart rate which were mediated by the autonomic nervous system. The hypotensive response to 8-OH-DPAT was attenuated by pretreatment with the 5-HT1A antagonists, spiperone or NAN-190. Microinjections of 8-OH-DPAT into ventral medullary structures revealed that 8-OH-DPAT responsive sites included the raphe pallidus, the parapyramidal region, and the rostral ventrolateral medulla. The role of serotonergic terminals in mediating the responses of 8-OH-DPAT was evaluated in animals pretreated with the serotonin nerve toxin, 5,7-dihydroxytryptamine (5,7-DHT). Cardiovascular responses to ventral medullary application of 8-OH-DPAT were unaffected by the selective depletion of serotonin. Thus, whereas the hypotensive responses elicited by 8-OH-DPAT in the raphe pallidus and parapyramidal region may involve serotonergic neurons, other non-serotonergic sites (e.g. the rostral ventrolateral medulla) can mediate the hypotensive actions of 8-OH-DPAT.

Autoradiographic study on dopamine uptake sites and their correlation with dopamine levels and their striata from patients with Parkinson disease, Alzheimer disease, and neurologically normal controls

An autoradiographic study of labeled mazindol binding to presumed dopamine (DA) uptake sites in the striatum was done in 7 Parkinson (PD), 6 Alzheimer (AD), 1 Huntington disease (HD), and 4 neurologically normal cases. Large and significant decreases of specific binding were found in PD in both caudate (to 32% of control) and putamen (to 16%), with no significant effect in AD or HD. Nonspecific binding was a large proportion of total binding in all cases. In the 12 cases where both binding data and DA levels were available, they showed highly significant linear correlations in both caudate and putamen. Autoradiographic studies on D1, D2, and muscarinic binding sites in the PD, AD and control striata revealed no significant group differences.

Synthesis and evaluation of high affinity, aryl-substituted [18F]fluoropropylbenzamides for dopamine D-2 receptor studies

The potent dopamine D-2 ligands (S)-2,3-dimethoxy-N-[(1-ethyl-2-pyrrolidinyl)methyl]-5(3- [18F]fluoropropyl)benzamide (18F-1) and (S)-2,3-dimethoxy-N-[(1-ethyl-2-pyrrolidinyl)methyl]-5-(3- [18F]fluoropropyl)-6-hydroxybenzamide (18F-2) were prepared in high specific activity and 5-25% overall radiochemical yields. Benzamide 1 possessed a lower in vitro binding affinity for the D-2 receptor than salicylamide 2, but the in vivo striatal-to-cerebellar radioactivity concentration ratios (St/Cb) in rats and dogs were nearly identical for the two compounds. Compound 18F-2 was more lipophilic than 18F-1, and its increased penetration into and retention by striatal tissue was matched by an increase in non-specific binding in the cerebellum. Cerebral cortex radioactivity concentration levels in dogs were similar to cerebellum levels. The binding of 18F-labelled 1 and 2 displayed regional brain distribution patterns consistent with known dopamine D-2 receptor densities and was selectively blocked in the striatum of rats by dopamine D-2 antagonists. The binding of 18F-1 was found to be stereoselective, as the 18F-labelled (R)-enantiomer displayed no selective retention in the striatum of dogs. High levels of radioactivity were found in the bones of rats following the injection of 18F-1 and 18F-2, indicating that in vivo defluorination had occurred; however, no bone radioactivity was observed in dogs following the injection of these radioligands. Compound 18F-1 was displaced from the striatum of dogs by both d-amphetamine-stimulated dopamine release and haloperidol at doses of 1 and 0.5 mg/kg, respectively, while compound 18F-2 was displaced from the dog striatum only by haloperidol at these doses. The radioligand 18F-2 holds promise for positron emission tomography studies of the dopamine D-2 receptor system based upon its selective, potent binding and resistance to displacement by endogenous dopamine.

Effects of hypoxic-ischemic brain damage on dopaminergic markers in the neonatal rat: a regional autoradiographic analysis

Dopamine has been implicated as an endogenous substance that may mediate neuronal death after hypoxic-ischemic insult. Using semiquantitative autoradiography, we studied the effect of perinatal hypoxic-ischemic injury on dopamine binding sites in rat brain. Experimental injury resulted in a substantial decrease in dopamine type-1 (D1) and forskolin (adenylate cyclase) binding sites. In contrast, markers for dopamine type-2 (D2) sites and for dopamine uptake were unaffected in lesioned animals. Changes within dopaminergic pathways were variable, with reduction in binding being encountered mainly in components of the extrapyramidal motor system: caudate-putamen, -61%; globus pallidus, -64%; entopeduncular nucleus, -60%; and substantia nigra, -69%. Furthermore, the topography of D1 receptor loss within the caudate-putamen was not uniform, with the greatest decrement in dorsolateral regions. Reduced D1 versus D2 receptor activation may underlie extrapyramidal movement disorders that appear as a consequence of perinatal hypoxic-ischemic insult.

Autoradiographic mapping of neurotransmitter system receptors in mammalian brain

Regional localization of neurotransmitter system receptors was visualized in the gerbil grain and in the rat brain using receptor autoradiography. [3H]Quinuclidinyl benzilate (QNB), [3H]cyclohexyladenosine (CHA), [3H]muscimol, [3H]MK-801, [3H]SCH 23390, [3H]PN200-110, [3H]spiperone, and [3H]naloxone were label muscarinic receptors, adenosine A1 receptors, GABAA receptors, N-methyl-D-aspartate (NMDA) receptors, dopamine D1 receptors, L-type calcium channels, spirodecanone receptors, and opioid receptors, respectively. Regional localization of [3H]QNB, [3H]muscimol, [3H]MK-801, [3H]SCH 23390, and [3H]PN200-110 binding sites in the gerbil brain was relatively similar to that in the rat brain. In contrast, the autoradiographic distribution of [3H]spiperone and [3H]naloxone binding sites in the gerbil was quite different from that in the rat. This phenomenon was found especially in the hippocampus and the cerebellum. The results suggest that the gerbil differs from the rat with respect to spirodecanone and opioid binding sites in the hippocampus and the cerebellum. This finding may help to further elucidate the species differences and relationships for brain function and behavioral pharmacology.

Autoradiographic localization of dopamine uptake sites in the rat brain with3H-GBR 12935

The regional distribution of dopamine (DA) uptake sites in the rat brain has been studied by quantitative autoradiography using [3H]GBR 12935 as a ligand. The binding of [3H]GBR 12935 to striatal sections was saturable and of high affinity (Kd = 1.6 nM); it occurred at a single population of sites and possessed the pharmacological features of the DA uptake sites. The highest densities of [3H]GBR 12935 binding sites were found in the caudate-putamen, nucleus accumbens, olfactory tubercle, ventral tegmental area and substantia nigra (especially in the pars compacta). Moderate levels of [3H]GBR 12935 binding were observed in globus pallidus, thalamus, hypothalamus, hippocampus, amygdala (basolateral nucleus) and prefrontal and singular cortices. This regional distribution of [3H]GBR 12935 binding closely correlated with the reported distribution of dopaminergic nerve terminals. The topographical distribution of [3H]GBR 12935 has also been studied in detail in striatal subregions and this distribution was compared, using quantitative TH immunoreactivity, to the density of striatal dopaminergic nerve terminals. There is good overlapping between these two regional distributions, the highest density of both markers was found in the lateral part of the striatum and a similar rostro-caudal gradient has been observed. A dopaminergic denervation caused a complete loss of [3H]GBR 12935 in basal ganglia ipsilateral to the lesion.

Intrastriatal dopamine-rich implants reverse the changes in dopamine D2 receptor densities caused by 6-hydroxydopamine lesion of the nigrostriatal pathway in rats: an autoradiographic study

The aim of the present study was to test whether intrastriatal implants of embryonic dopaminergic neurons are able to normalize the lesion-induced hypersensitivity of striatal dopaminergic receptors. The ascending dopaminergic pathway of adult rats was unilaterally lesioned using 6-hydroxydopamine. Three weeks later a cell suspension obtained from the mesencephali of ED 14 rat embryos was implanted into the denervated striatum. Rotational responses to dopaminergic agonists were tested five months after implantation. One month later animals were killed and striatal dopaminergic receptor densities were quantified using autoradiography, the dopaminergic reinnervation of the host striatum being visualized with [3H]GBR 12935, a ligand labelling dopamine uptake sites. The lesion induced a behavioural hypersensitivity to dopaminergic agonists and lesioned animals displayed a strong rotation contralateral to the lesion in response to a test dose of the D1 agonist compound SKF 38393 (2.5 mg/kg) or of the D2 agonist LY 171555 (0.15 mg/kg). These responses were completely abolished by the graft. The normal distribution of D1 and D2 dopaminergic receptors in the rat striatum was similar to that described previously. Seven months after the lesion of the nigrostriatal dopaminergic pathway, the density of D1 receptors was not significantly affected while the density of D2 receptors was increased by about 25-50%. The implantation of embryonic dopaminergic neurons into the denervated striatum led to a slight decrease of D1 receptor densities and to a reversal of the lesion-induced increase of striatal dopaminergic D2 receptors six months later. Moreover, this reversal concerned not only the reinnervated striatal region but also extended into non-reinnervated areas of the striatum. It is concluded that grafts of embryonic dopaminergic neurons can normalize the density of dopaminergic D2 receptors.

Effects of aging on signal transmission and transduction systems in the gerbil brain: Morphological and autoradiographic study

The Mongolian gerbil was used as a model of aging because of its relatively short lifespan, genetic homogeneity and the fact that data had been collected previously. Furthermore, gerbils have been widely used in biomedical investigations of stroke and epilepsy. Age-related differences in signal transmission and transduction systems were investigated in brains of three-, 11- and 21-month-old gerbils by morphological and in vitro receptor autoradiographic studies. Morphometric analysis revealed a decreased number of neurons in layer III of the occipital cortex and also a decrease in cerebellar Purkinje cells in 21-month-old animals. However, no statistical differences were observed in the hippocampal formation, the dorsolateral striatum and layer III of the frontal cortex. Autoradiography was used to map muscarinic cholinergic (labeled with [3H]quinuclidinyl benzilate), serotonin2 ([3H]spiperone), dopamine D2 ([3H]spiperone), adenosine A1 ([3H]cyclohexyladenosine), GABAA ([3H]muscimol), naloxone ([3H]naloxone), protein kinase C ([3H]phorbol 12,13-dibutyrate), adenylate cyclase ([3H]forskolin), cyclic AMP ([3H]cyclic AMP) and L-type Ca2+ channels ([3H]PN200-110). Muscarinic cholinergic receptor and protein kinase C, cyclic AMP and L-type Ca2+ channels were significantly decreased in the cerebral cortex and/or in the CA1 subfield of the hippocampus in the 21-month-old group. Muscarinic cholinergic receptor and L-type Ca2+ channel binding sites were significantly reduced in the dentate gyrus. In contrast, protein kinase C was increased in this area in the 21-month-old group. Also, naloxone binding sites were increased in the CA3 subfield, hilus, dentate gyrus and molecular layer of the cerebellum in the 11- and 21-month-old groups. Muscarinic cholinergic, serotonin2 and dopamine D2 receptors and adenylate cyclase were significantly decreased in the striatum. On the other hand, adenosine A1 and GABAA receptors remained unchanged in the 21-month-old group. Although age-related histopathological abnormalities were only observed in the occipital cortex and in the cerebellum, alterations of signal transmission and transduction systems were noticed in all areas examined (e.g. cerebral cortex, CA1 subfield, dentate gyrus and striatum). These data indicate that changes in these receptors and binding sites may be related to dysfunction of learning and memory and to the loss of motor function. The aged gerbil model is a good system for studying aging and is of value for simulating aging after epilepsy and stroke.

Effect of ferric nitrilotriacetate on rostral mesencephalic cells

After murine fetal cells from the rostral mesencephalic tegmentum were isolated, prepared, and cultured; neuronal and glial cells in primary mixed cell cultures were exposed to ferric nitrilotriacetate (Fe-NTA) at varying concentrations. Studies were performed at 23 days in culture after 14 day exposure to Fe-NTA. In addition to morphologic studies, biochemical assays including specific [3H]flunitrazepam (FLU) binding, clonazepam (CLO)-displaceable [3H]-FLU binding, Ro5-4864-displaceable [3H]-FLU binding, [3H]-FLU binding, [3H]dopamine (DA) uptake, [3H]haloperidol (HAL) binding, [3H]spiperone (SP) binding, glutamine synthetase activity (GS), and protein determinations were performed. The data demonstrate that chelated ferric iron has an adverse effect on these cells. The data also demonstrate that increasing concentrations of Fe-NTA resulted in massive neuronal dropout leaving the culture population virtually all glial; however, the specific binding of [3H]HAL and [3H]SP increased. There was a concomitant decrease in both glutamine synthetase activity and overall protein content. The mechanism of enhancement in the presence of Fe-NTA of [3H]HAL and [3H]SP binding is unknown and may be unique, but may be related to the known increase in D2 receptor ligand affinity in the presence of other multivalent cations (Ca2+ and Mg2+).

Effect of unilateral perinatal hypoxic-ischemic brain injury in the rat on dopamine D1 and D2 receptors and uptake sites: a quantitative autoradiographic study

The effect of a unilateral perinatal hypoxic-ischemic brain injury on dopamine D1 and D2 receptors and uptake sites was investigated in rats by using in vitro quantitative binding autoradiography, 2-3 weeks after the insult. We observed significant decreases in the Bmax and KD for [3H]SCH 23390-labeled D1 and in the Bmax for [3H]spiperone-labeled D2 receptors in the lesioned caudate-putamen in rats with moderate brain injury (visible loss in hemispheric volume ipsilateral to the injury) compared with the nonlesioned contralateral caudate-putamen or with control rats. Changes in [3H]SCH 23390 and [3H]spiperone binding predominated in the dorsolateral part of the lesioned caudate-putamen. Pronounced reduction in [3H]SCH 23390 binding was also observed in the substantia nigra pars reticulata on the side of the lesion. In contrast, we did not observe any significant change in Bmax or KD for [3H]mazindol-labeled dopamine uptake sites. Similarly, no significant changes in the levels of dopamine or its metabolites were found on the side of the lesion. The observed reductions in striatal dopamine D1 and D2 receptors are a reflection of striatal cell loss induced by the hypoxic-ischemic injury. The absence of changes in [3H]mazindol binding or dopamine levels in the lesioned caudate-putamen indicates that the dopaminergic presynaptic structures are preserved.

Dopamine D2-receptors mediate hypothermia in mice: ICV and IP effects of agonists and antagonists

The effect of centrally and peripherally administered dopamine D1 and D2 specific compounds on core body temperature in mice was investigated. Quinpirole (LY-17155), a D2 agonist, induced a dose-dependent fall in body temperature (2.4-11.6%; p less than 0.003) when injected intraperitoneally (ip, 0.3-3.0 mg/kg) and intracerebroventricularly (icv, 0.1 mg/kg). This quinpirole-induced (1.0 mg/kg, ip) hypothermia was reversed by the central and peripheral administration of the D2 antagonists S-(-)-sulpiride (3.0-30.0 mg/kg, ip; 0.1-3.0 mg/kg, icv) and spiperone (0.03 and 0.1 mg/kg, ip; 0.03-3.0 mg/kg, icv). Domperidone, a D2 antagonist which does not cross the blood brain barrier, had no effect on quinpirole-induced hypothermia (1.0-10.0 mg/kg, ip). Domperidone partially reversed quinpirole-induced hypothermia at 0.1-30.0 mg/kg, icv. The D1 agonist, SKF-38393 at a high dose of 10.0 mg/kg, ip mildly attenuated quinpirole-induced hypothermia (a 1.8% increase in temperature). SKF-38393 at 10.0 mg/kg, icv potentiated quinpirole-induced hypothermia. SCH-23390 (0.1-3.0 mg/kg, ip), a D1 antagonist, had no effect on quinpirole-induced hypothermia and potentiated the hypothermia when administered icv. An ineffective icv dose of spiperone (0.01 mg/kg) in reversing quinpirole-induced hypothermia was rendered effective by prior administration of SCH-23390 (0.1-3.0 mg/kg, icv) but not by SKF-38393 (1.0-10.0 mg/kg, icv). These data suggest a central D2 receptor mechanism mediating hypothermia in mice which is capable of being modulated by the D1 receptor.

Presynaptic parkinsonism in olivopontocerebellar atrophy: clinical, pathological, and neurochemical evidence

The substrate for olivopontocerebellar atrophy parkinsonism is obscure due to the lack of clinical and pathological reports and the absence of studies on dopamine receptors in this entity. We describe a patient with olivopontocerebellar atrophy whose clinical presentation was levodopa-responsive parkinsonism in whom pathological examination disclosed pronounced nigral cell loss with no striatal damage. Autoradiographic labeling with 3H-spiperone showed normal densities of D2 dopamine striatal receptors. These data show that indistinguishable nigral, presynaptic parkinsonism occurs in patients with idiopathic Parkinson's disease and in patients with olivopontocerebellar atrophy, and also how a favorable response to levodopa is neither synonymous with idiopathic Parkinson's disease, nor does it exclude multiple-system, atrophy-related parkinsonism.

Effect of unilateral perinatal hypoxic-ischemic brain injury on striatal dopamine uptake sites and D1 and D2 receptors in adult rats

The effect of unilateral perinatal hypoxic-ischemic brain injury on striatal dopamine uptake sites and on D1 and D2 receptors was investigated in rat by using in vitro quantitative receptor binding autoradiography, 9-11 weeks after the insult. Saturation experiments revealed a significant 20% decrease in maximal binding capacity (Bmax) for [3H]spiperone-labeled D2 receptors on the side of the lesion in comparison to the non-lesioned contralateral side or to either side of control animals. There was no significant change in [3H]mazindol-labeled dopamine uptake sites or in [3H]SCH 23390-labeled D1 receptor characteristics (Bmax and Kd) on the lesioned side. We conclude that the decrease in D2 receptor binding previously observed in immature animals is persistent, whereas the decrease in D1 binding is not.

ACTH/MSH-like peptides inhibit the binding of dopaminergic ligands to the dopamine D2 receptor in vitro

ACTH-(1-24) decreased the binding of the dopamine D2 receptor agonist, [3H]N-propylnorapomorphine ([3H]NPA), to rat striatal membranes in a concentration-dependent manner, with a Ki of 5 x 10(-7) M. Saturation curves for [3H]NPA binding in the presence of increasing concentrations of ACTH-(1-24) were performed. Scatchard analysis in the presence of ACTH-(1-24) revealed an increased dissociation constant (Kd), while the binding capacity (Bmax) was not affected by the peptide, suggesting an apparent competitive interaction between ACTH-(1-24) and [3H]NPA. ACTH-(1-24) also reduced the binding of the dopamine D2 receptor antagonist [3H]spiperone to striatal membranes, with a Ki of 10(-6) M. Much higher concentrations of ACTH-(1-24), up to 10(-4) M, were needed for the displacement of appropriate radiolabelled ligands from dopamine D1 receptors, serotonin 5-HT1A, serotonin 5-HT1B, muscarinic M1 acetylcholine and histamine H1 receptors. ACTH-(1-24) also inhibited the binding of [3H]spiperone to dopamine D2 receptors in membranes of the pituitary gland, the septum and the substantia nigra. ACTH-(1-39) and most ACTH fragments and analogs were less potent than ACTH-(1-24) in displacing [3H]NPA from the dopamine D2 receptor in striatal membranes. In general there was a relationship between displacing potency and chain length. ACTH-(7-16)-NH2 and benzyloxycarbonyl-ACTH-(8-16)-NH2, however, were more potent than ACTH-(1-24) in reducing the binding of [3H]NPA to dopamine D2 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Olfactory deprivation increases dopamine D2 receptor density in the rat olfactory bulb

Unilateral olfactory deprivation during postnatal development results in significant anatomical and neurochemical changes in the deprived olfactory bulb. Perhaps the most dramatic neurochemical change is the loss of dopaminergic expression by neurons of the glomerular region. We describe here the effects of early olfactory deprivation on other elements of the bulb dopaminergic system, namely the dopamine receptors of the olfactory bulb. Rat pups had a single naris occluded on postnatal day 2 (PN2). On PN20 or PN60, animals were sacrificed and the bulbs were examined for catecholamine levels or D2 and D1 dopamine receptor binding. Receptor densities were quantified by in vitro autoradiography using the tritiated antagonists spiperone (D2) and SCH23390 (D1). Dopamine uptake sites were similarly examined using tritiated mazindol. No significant specific labeling of D1 or mazindol sites was observed in the olfactory bulbs of control or experimental animals at either age. Normal animals displayed prominent labeling of D2 sites in the glomerular and nerve layers. After 60 days of deprivation, deprived bulbs exhibited an average increase in D2 receptor density of 32%. As determined by Scatchard analysis, the mean values for Kd and Bmax were 0.134 nM and 293 fmol/mg protein in normal bulbs, and 0.136 nM and 403 fmol/mg protein in deprived bulbs. The results suggest that, as in the neostriatum, dopamine depletion in the olfactory bulb leads to an upregulation of D2 receptor sites. This change may represent an attempt by the system to adapt neurochemically to reduced dopaminergic activity and thereby maintain bulb function.

Quantitative image analysis with densitometry for immunohistochemistry and autoradiography of receptor binding sites--methodological considerations

Major technical progress in the development of computer-based image analysis has made possible the entry of autoradiography and immunohistochemistry into a new era where quantification by densitometry has become easily accessible. Autoradiography could become quantitative and displayed adequate reproducibility with the help of emulsion-coated films and the use of scales of standards of known radioactivity exposed and analyzed in parallel to the tissue sections. Immunohistochemistry after revelation by a color-based enzymatic technique can also become quantitative, providing that standardization of the crucial steps of the procedure and calibration through a parallel treatment of a scale of antigen standards can be ensured. Such an approach is described here in the rat with reference to tyrosine hydroxylase (TH), the main synthesizing enzyme for catecholamines, and with dopamine (DA) itself, a catecholaminergic neurotransmitter. The different parts of the procedure, which can influence the results, such as the fixation of the animals by perfusion and the evaluation of the fluctuations via the calibration curve, are discussed in detail. Biological validation of the proposed procedure is described by reference to experiments already well documented biochemically, such as the induction effect of reserpine on TH in the rat locus coeruleus and the depleting effect of alpha-methyltyrosine (AMPT), a well-known blocker of TH activity, on rat striatal DA content. Finally the importance of restricting the measurements to the (pseudo)linear portion of the calibration curve is illustrated by the autoradiographic identification of the differential intrastriatal repartition of the dopaminergic D1 and D2 receptor sites, particularly the dual patch-matrix compartments.

Retrograde degeneration of nigrostriatal neurons induced by intrastriatal 6-hydroxydopamine injection in rats

Quantitative receptor autoradiography was used to assess the effects of unilateral intrastriatal injections of 6-hydroxydopamine (6-OHDA) on the distribution of D1 and D2 dopamine (DA) receptors and of DA uptake sites in the mesostriatal pathway. [3H]Mazindol-labeled DA uptake sites were reduced both in the striatum (-97%) and in the substantia nigra pars compacta (SNpc) (-88%) on the injected side. There were also significant decreases of dopamine uptake sites in the nucleus accumbens (NAc) (-73%) and in the ventral tegmental area (VTA) (-70%). Changes in [3H]mazindol binding were also found within the contralateral VTA (-30%) and SNpc (-13%) but not in the contralateral-striatum. [3H]SCH23390-labeled D1 receptors were significantly reduced in the dorsomedial (-18%) and ventromedial (-14%) aspects of the striatum ipsilateral to the side of the lesions. In contrast, the concentration of [3H]spiperone-labeled D2 receptors was not altered. There were also significant decreases in D1 (-18%) and of D2 (-27%) receptors in the SNpc and of D1 (-10%) in the SN pars reticulata (SNpr). These results suggest that oxyradical-induced damage in striatal DA terminals could lead to retrograde changes in the SNpc. In addition, the data indicate that unilateral striatal damage can result in bilateral changes in the SNpc, thus confirming the interdependence of the two nigrostriatal pathways in rats.