Identification of Sodium-Dependent, High-Affinity Choline Uptake Sites in Rat Brain with [3H]Hemicholinium-3

[3H]Hemicholinium-3 (HC-3) was used to label sodium-dependent, high-affinity choline uptake sites in regions of rat brain. Autoradiography revealed a high density of [3H]HC-3 binding sites in brain regions with a high density of cholinergic terminals, such as the interpeduncular nucleus, caudate-putamen, and olfactory tubercle. This distribution of [3H]HC-3 binding sites was in close agreement with the amounts of choline acetyltransferase in specific nuclei and subregions of rat brain. Destruction of presynaptic cholinergic projections in the cerebral cortex and the basal ganglia by injection of excitotoxins reduced [3H]HC-3 binding by 40-50%. These data indicate that sodium-dependent [3H]HC-3 binding sites are related to the choline transport system present in cholinergic neurons.     

Dopamine receptors in the rat brain: quantitative autoradiographic localization using [3H]sulpiride

In vitro labeling of tissue sections with [³H]sulpiride has been utilized in the present study to autoradiographically localize D₂-dopamine receptors in the rat brain. Preliminary biochemical studies, using slide-mounted tissue sections, were performed to define the optimal labeling conditions for this binding. Autoradiograms were generated by apposition of the labeled tissue sections to tritium-sensitive film. Specific binding sites for [³H]sulpiride were localized to the caudate-putamen, nucleus accumbens, olfactory tubercle, glomerular layer of the olfactory bulb, pituitary, laminae I and III of the entorhinal cortex, substantia nigra, lateral mammillary nucleus and the stratum-lacunosum moleculare of the hippocampus. The high selectivity of [³H]sulpiride for the D₂-dopamine receptor indicates that it is a valuable tool for the autoradiographic localization and quantitation of neuroleptic receptors.     

Binding of [3H]SCH23390 in Rat Brain: Regional Distribution and Effects of Assay Conditions and GTP Suggest Interactions at a D1-Like Dopamine Receptor

The compound [9-3H]SCH23390 [R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7- ol] was synthesized, and the binding of this purportedly selective antagonist of D1 3,4-dihydroxyphenylethylamine (dopamine) receptors was characterized. The regional distribution of high-affinity, specific [3H]SCH23390 binding sites in the rat brain correlated well with levels of endogenous dopamine. Receptor densities were greatest in corpus striatum, nucleus accumbens, and olfactory tubercle; intermediate levels were found in several limbic and cortical areas, whereas few sites were detectable in cerebellum, brainstem, and ol-factory bulb. Specific binding in caudate-putamen was found to be both temperature- and pH-dependent, with optima at 25-30 degrees C and pH 7.8-8.0. Scatchard or Woolf analyses of binding in caudate-putamen suggest that most of the sites are either of a single class or of classes with similar characteristics (KD = 0.7 +/- 0.1 nM; Bmax = 347 +/- 35 fmol/mg of protein). Both dopamine and cis-flupenthixol altered the slope but not the intercept of lines generated by Scatchard analysis, suggesting a competitive mode of inhibition of [3H]SCH23390 binding. Competition for binding by dopamine or the D1 agonist SKF38393 was inhibited by guanine nucleotides, whereas GTP had little effect on the competition for binding by the antagonist cis-flupenthixol. The competition for [3H]SCH23390 binding sites by dopamine was much more sensitive to GTP than was competition for [3H]spiperone binding. These data support the hypotheses that [3H]SCH23390 binds to recognition sites that differ from those previously described using other radiolabeled dopamine antagonists and that these sites have the characteristics expected of dopamine receptors.     

Heterogeneity of D2 dopamine receptors in different brain regions.

The binding of [3H]spiperone has been examined in membranes derived from different regions of bovine brain. In caudate nucleus, nucleus accumbens, olfactory tubercle and putamen binding is to D2 dopamine and 5HT2 serotonin receptors, whereas in cingulate cortex only serotonin 5HT2 receptor binding can be detected. D2 dopamine receptors were examined in detail in caudate nucleus, olfactory tubercle and putamen using [3H]spiperone binding in the presence of 0.3 microM-mianserin (to block 5HT2 serotonin receptors). No evidence for heterogeneity among D2 dopamine receptors either between brain regions or within a brain region was found from the displacements of [3H]spiperone binding by a range of antagonists, including dibenzazepines and substituted benzamides. Regulation of agonist binding by guanine nucleotides did, however, differ between regions. In caudate nucleus a population of agonist binding sites appeared resistant to guanine nucleotide regulation, whereas this was not the case in olfactory tubercle and putamen.     

Autoradiographic distribution of high affinity muscarinic and nicotinic cholinergic receptors labeled with [3H]acetylcholine in rat brain

The relative distribution of muscarinic and nicotinic cholinergic receptors labeled with [3H]acetylcholine was determined using autoradiography. [3H]Acetylcholine binding to high affinity muscarinic receptors was similar to what has been described for an M-2 distribution: highest levels of binding occurred in the pontine and brainstem nuclei, anterior pretectal area and anteroventral thalamic nucleus, while lower levels occurred in the caudate-putamen, accumbens nucleus and primary olfactory cortex. Nicotinic receptors were labeled with [3H]acetylcholine to the greatest extent in the interpeduncular nucleus, several thalamic nuclei, medial habenula, presubiculum and superior colliculus, and to the least extent in the hippocampus and inferior colliculus. By using autoradiography to localize cholinergic binding sites throughout the brain it was observed that the distributions of high affinity muscarinic and nicotinic sites labeled with the endogenous ligand, [3H]acetylcholine are different from each other and are different from distributions of muscarinic and nicotinic sites labeled with muscarinic and nicotinic antagonists.     

Quantitative autoradiography of [3H]CTOP binding to mu opioid receptors in rat brain

[3H]H-D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 ([3H]CTOP), a potent and highly selective mu opioid antagonist, was used to localize the mu receptors in rat brain by light microscopic autoradiography. Radioligand binding studies with [3H]CTOP using slide-mounted tissue sections of rat brain produced a Kd value of 1.1 nM with a Bmax value of 79.1 fmol/mg protein. Mu opioid agonists and antagonists inhibited [3H]CTOP binding with high affinity (IC50 values of 0.2-2.4 nM), while the delta agonist DPDPE, delta antagonist ICI 174,864, and kappa agonist U 69, 593 were very weak inhibitors of [3H]CTOP binding (IC50 values of 234-3631 nM). Light microscopic autoradiography of [3H]CTOP binding sites revealed regions of high density (nucleus of the solitary tract, clusters in the caudate-putamen, interpeduncular nucleus, superior and inferior colliculus, subiculum, substantia nigra zona reticulata, medial geniculate, locus coeruleus and dorsal motor nucleus of the vagus) and regions of moderate labeling (areas outside of clusters in the caudate-putamen, cingulate cortex, claustrum and nucleus accumbens). The cerebral cortex (parietal) showed a low density of [3H]CTOP binding.     

Circadian rhythms in catecholamine metabolites and cyclic nucleotide production

Circadian rhythms in noradrenergic (NE) and dopaminergic (DA) metabolites and in cyclic nucleotide production were measured in discrete regions of rat brain. A circadian rhythm was found in the concentration of the NE metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), in the hippocampus. No MHPG rhythm was found in frontal, cingulate, parietal, piriform, insular or temporal cortex, or in hypothalamus. Circadian rhythms in the concentration of the NE metabolite, 3,4-dihydroxyphenylglycol (DHPG), occurred in occipital and parietal cortex and hypothalamus, with no rhythm observable in temporal or insular cortex, hippocampus, pons-medulla or cerebellum. The 24-hr mean concentration of MHPG varied 3.5-fold, highest in cingulate and lowest in parietal, temporal and occipital cortex. The 24-hr mean concentration of DHPG varied 6-fold, highest in hypothalamus and lowest in parietal cortex. Circadian rhythms in the concentration of the DA metabolite, homovanillic acid (HVA), were found in olfactory tubercle, amygdala and caudate-putamen, but not in nucleus accumbens. A circadian rhythm in the concentration of the DA metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), occurred in nucleus accumbens, but not in olfactory tubercle or caudate-putamen. The mean 24-hr concentration of HVA was highest in caudate-putamen, intermediate in nucleus accumbens, and lowest in olfactory tubercle and amygdala. The mean 24-hr concentration of DOPAC was highest in nucleus accumbens and lower in olfactory tubercle and caudate-putamen. Circadian rhythms were found in the concentration of cyclic GMP (cGMP) in all regions measured except parietal cortex. The mean 24-hr concentration varied 128-fold, highest in nucleus accumbens, frontal poles, and hypothalamus and lowest in cingulate cortex. Circadian rhythms in cyclic AMP (cAMP) concentration were found in piriform, temporal, occipital, cingulate, and parietal cortex, amygdala and nucleus accumbens. No rhythms were found in frontal or insular cortex, hypothalamus, hippocampus, caudate-putamen or olfactory tubercle. The 24-hr mean cAMP concentration varied 4-fold, highest in parietal cortex and lowest in caudate-putamen and amygdala. Norepinephrine metabolites and dopamine metabolites were rhythmic in few regions. It is, therefore, unlikely that the rhythmicity measured in adrenergic receptors is, in general, a response to rhythmic changes in adrenergic transmitter release. The putative second messenger response systems, especially cGMP, were more often rhythmic. The rhythms in cGMP are parallel in form and region to those in the alpha 1-adrenergic receptor and may act as 2nd messenger for that receptor.(ABSTRACT TRUNCATED AT 400 WORDS)     

Species Differences in the Brain Regional Distribution of Receptor Binding for Thyrotropin-Releasing Hormone

Abstract: A survey of the regional distribution of binding of 1 nM [³H](3-MeHis²)thyrotropin-releasing hormone ([³H]MeTRH) to TRH receptors in the brains of eight mammalian species revealed major species differences in both the absolute and relative values of TRH receptor binding in different brain regions. Several brain regions exhibited binding equal to or exceeding that in the anterior pituitary gland of the same species, including the amygdaia in the guinea pig and rat, the hypothalamus in the guinea pig, the nucleus accumbens in the rabbit, and all these and other regions in the cat and dog, for which pituitary binding was exceptionally low. Species could be divided into two groups according to which brain region appeared highest in binding: rabbits, sheep, and cattle had highest binding in the nucleus accumbens/septal area, whereas guinea pigs, rats, dogs, cats, and pigs had highest binding in the amygdala/temporal cortex area. The nucleus accumbens consistently exceeded the caudate-putamen in receptor binding. For most brain regions, rabbits, rodents, and sheep tended to be higher than carnivores, cattle, or pigs. Further regions that exhibited appreciable binding in most species included the olfactory bulb and tubercle, hippocampus, and various cortical and brain stem areas. In fact, essentially all brain regions appeared to have detectable levels of TRH receptors in at least some species, but no rat peripheral tissues have yet shown detectable receptor binding. The species differences appeared to reflect largely if not entirely differences in receptor density, although this was not tested in every species.     

Autoradiographic Localization of [3H]Zolpidem Binding Sites in the Rat CNS: Comparison with the Distribution of [3H]Flunitrazepam Binding Sites

The regional distribution of [3H]zolpidem, a novel imidazopyridine hypnotic possessing preferential affinity for the BZD1 (benzodiazepine subtype 1) receptor, has been studied autoradiographically in the rat CNS and compared with that of [3H]flunitrazepam. The binding of [3H]zolpidem to rat brain sections was saturable, specific, reversible, and of high affinity (KD = 6.4 nM). It occurred at a single population of sites whose pharmacological characteristics were similar to those of the benzodiazepine receptors labeled with [3H]flunitrazepam. However, ethyl-beta-carboline-3-carboxylate and CL 218,872 were more potent displacers of [3H]zolpidem than of [3H]flunitrazepam. The autoradiographic brain distribution of [3H]zolpidem binding sites was qualitatively similar to that previously reported for benzodiazepine receptors. The highest levels of [3H]-zolpidem binding sites occurred in the olfactory bulb (glomerular layer), inferior colliculus, ventral pallidum, nucleus of the diagonal band of Broca, cerebral cortex (layer IV), medial septum, islands of Calleja, subthalamic nucleus, and substantia nigra pars reticulata, whereas the lowest densities were found in parts of the thalamus, pons, and medulla. Comparative quantitative autoradiographic analysis of the binding of [3H]zolpidem and [3H]flunitrazepam [a mixed BZD1/BZD2 (benzodiazepine subtype 2) receptor agonist] in the CNS revealed that the relative density of both 3H-labeled ligands differed in several brain areas. Similar levels of binding for both ligands were found in brain regions enriched in BZD1 receptors, e.g., substantia nigra pars reticulata, inferior colliculus, cerebellum, and cerebral cortex lamina IV. The levels of [3H]zolpidem binding were five times lower than those of [3H]flunitrazepam binding in those brain regions enriched in BZD2 receptors, e.g., nucleus accumbens, dentate gyrus, and striatum. Moreover, [3H]zolpidem binding was undetectable in the spinal cord (which contains predominantly BZD2 receptors). Finally, like CL 218,872 and ethyl-beta-carboline-3-carboxylate, zolpidem was a more potent displacer of [3H]flunitrazepam binding in brain regions enriched in BZD1 receptors than in brain areas enriched in BZD2 receptors. The present data add further support to the view that zolpidem, although structurally unrelated to the benzodiazepines, binds to the benzodiazepine receptor and possesses selectivity for the BZD1 receptor subtype.     

Circadian rhythms in neurotransmitter receptors in discrete rat brain regions

Circadian rhythms were measured in alpha 1-, alpha 2- and beta-adrenergic, acetylcholine muscarinic (ACh), and benzodiazepine (BDZ) receptor binding in small regions of rat brain. Rhythms in alpha 1-receptor binding were measured in olfactory bulb, frontal, cingulate, piriform, parietal, temporal and occipital cortex, hypothalamus, hippocampus, pons-medulla, caudate-putamen and thalamus-septum. No rhythm was found in cerebellum. Rhythms in alpha 2-receptor binding were measured in frontal, parietal and temporal cortex, and pons-medulla. No rhythm was found in cingulate, piriform or occipital cortex, or hypothalamus. Rhythms in binding to beta-receptors were measured in olfactory bulb, piriform, insular, parietal and temporal cortex, hypothalamus and cerebellum. No rhythms were found in frontal, entorhinal, cingulate, or occipital cortex, hippocampus, caudate-putamen, or pons-medulla. Rhythms in ACh receptor binding were measured in olfactory bulb, parietal cortex and caudate-putamen. No rhythms were found in frontal or occipital cortex, nucleus accumbens, hippocampus, thalamus-septum, pons-medulla or cerebellum. Rhythms in BDZ receptor binding were measured in olfactory bulb, olfactory and occipital cortex, olfactory tubercle, nucleus accumbens, amygdala, caudate-putamen, hippocampus and cerebellum. No rhythms were found in parietal cortex, pons-medulla or thalamus-septum. The 24-hr mean binding to receptors varied between 3- and 10-fold, the highest in cortex and the lowest, usually, in cerebellum. The piriform cortex was particularly high in alpha 1- and alpha 2-adrenergic receptors; the nucleus accumbens and caudate, in ACh receptors; and the amygdala, in BDZ receptors. Most adrenergic and ACh receptor rhythms peaked in subjective night (the period when lights were off under L:D conditions), whereas most BDZ receptor rhythms peaked in subjective day (the time lights were on in L:D). Perhaps in the rat, a nocturnal animal, the adrenergic and ACh receptors mediate activity and the functions that accompany it, and the BDZ receptors mediate rest, and with it, sleep.     

Autoradiographic distribution of [3H]neurotensin receptors in rat brain: visualization by tritium-sensitive film

[3H]Neurotensin ([3H]NT) binds specifically to a single class of binding sites on slides-mounted sections of rat brain 1Kp = 5.1 nM; Bmax = 16.2 fmol/mg tissue). Bound [3H]NT can be displaced by nonradioactive NT and a series of its fragments and analogues with relative potencies that correlate closely (r = 0.89; p less than 0.01) to their potencies in the rat stomach strip bioassay. These results suggest that NT receptors are similar in both systems. [3H]NT binding sites were visualized by using tritium-sensitive LKB film analysed by computerized densitometry. [3H]NT receptors are highly concentrated in the external layer of the olfactory bulb, in the rhinal sulcus, in certain nuclei of the amygdala, in the substantia nigra, zona compacta and in the ventral tegmental area. The high density of [3H]NT receptors in the last two areas suggest an interaction between NT and brain dopaminergic systems such as the nigrostriatal and the mesolimbic pathways.     

Imaging the Dopamine Uptake Site with Ex Vivo [18F]GBR 13119 Binding Autoradiography in Rat Brain

We studied the binding of [18F]GBR 13119 (1-[[(4-[18F]fluorophenyl) (phenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine) to rat brain with autoradiography after intravenous injection. The rank order of binding was dorsal striatum greater than nucleus accumbens = olfactory tubercle greater than substantia nigra = ventral tegmental area greater than other areas. Binding was blocked by prior injection of dopamine uptake blockers but not by injection of dopamine receptor antagonists or drugs that bind to the dialkylpiperazine site. Unilateral 6-hydroxy-dopamine lesions of dopamine neurons caused a marked decrease in striatal and nigral binding on the side of the lesion. We conclude that intravenous injection of [18F]GBR 13119 provides a useful marker of presynaptic dopamine uptake sites.     

Receptor autoradiography of mu and delta opioid peptide receptors in spontaneously hypertensive rats.

The receptor autoradiographic distribution of opioid peptide receptors in spontaneously hypertensive rats (SHR) was compared to that of Sprague-Dawley (SD) rats, using the highly selective mu and delta opioid receptor ligands, [3H]DAGO (Tyr-D-Ala-Gly-NMe-Phe-Gly-ol) and [3H]DPDPE ([D-Pen2,D-Pen5]enkephalin), respectively. Although the distribution of these binding sites was similar in both strains, SHR showed significantly higher binding densities of mu receptors in 16 of 27 areas examined. These included the patch and matrix components of the caudate-putamen (CPu), olfactory tubercle, endopiriform nucleus, anterior cingulate cortex, ventral tegmental area lateroposteral thalamic nucleus and the ventral part of the dentate gyrus. In contrast, SHR had lower [3H]DAGO binding sites in the CA1 of the hippocampus. Conversely, SHR showed higher binding densities of delta receptors in 7 of 20 areas examined, including the CPu, CA2 and CA3 areas of the hippocampus and the central grey. High-to-low lateromedial gradients of striatal delta receptors were observed in both strains. Because opioid peptides are known to participate in locomotive behavior in rodents and in the control of blood pressure, the present results support a role of opioid peptidergic systems in the manifestation of hyperactivity and hypertension observed in SHR.     

Striatum Adenosine A2 Receptors Are Modified During Seizure: Effect of Cyclopentyladenosine Administration

Rat CNS adenosine A_2A receptors were studied after administration of the convulsant drug 3-mercaptopropionic acid (MP) and the adenosine analogue cyclopentyladenosine (CPA) by means of a quantitative autoradiographic method. Specific binding was quantified in striatum only. The highest density was found in caudate-putamen (2.50 fmol/mm²), followed by nuclei accumbens (1.85 fmol/mm²) and the lowest values in the olfactory tubercle (1.26 fmol/mm²). These differerences were statiscally significant. MP administration (150 mg/kg) caused significant increases (12–18%) in caudate-putamen and nuclei accumbens in both stages: seizure and postseizure and no changes in the olfactory tubercle. CPA administration (2 mg/kg) originated a rise of 16% in nuclei accumbens but no change in the other two regions. When CPA was injected 30 minutes before MP, an increase (18 to 45%) in caudate-putamen and nuclei accumbens at seizure and postseizure stages was observed. Saturation results, in striatal membrane fraction, indicate that receptor sites increased their maximal binding capacity (Bmax) while the apparent dissociation constant (Kd) remained unchanged. These results suggest the involvement of the adenosine A_2A receptors in convulsant activity and that CPA administration at the dose selected brings about a rise in neuronal excitability in this area.     

Adenosine and dopamine receptor antagonist binding in the rat ventral and dorsal striatum: lack of changes after a neonatal bilateral lesion of the ventral hippocampus.

There is experimental evidence from radioligand binding experiments for the existence of strong antagonistic interactions between different subtypes of adenosine and dopamine receptors in the striatum, mainly between adenosine A1 and dopamine D1 and between adenosine A2A and dopamine D2 receptors. These interactions seem to be more powerful in the ventral compared to the dorsal striatum, which might have some implications for the treatment of schizophrenia. The binding characteristics of different dopamine and adenosine receptor subtypes were analysed in the different striatal compartments (dorsolateral striatum and shell and core of the nucleus accumbens), by performing saturation experiments with the dopamine D1 receptor antagonist [125I]SCH-23982, the dopamine D2-3 receptor antagonist [3H]raclopride, the adenosine A1 receptor antagonist [3H]DPCPX and the adenosine A2A receptor antagonist [3H]SCH 58261. The experiments were also performed in rats with a neonatal bilateral lesion of the ventral hippocampus (VH), a possible animal model of schizophrenia. Both dopamine D2-3 and adenosine A2A receptors follow a similar pattern, with a lower density of receptors (40%) in the shell of the nucleus accumbens compared with the dorsolateral caudate-putamen. A lower density of adenosine A1 receptors (20%) was also found in the shell of the nucleus accumbens compared with the caudate-putamen. On the other hand, dopamine D1 receptors showed a similar density in the different striatal compartments. Therefore, differences in receptor densities cannot explain the stronger interactions between adenosine and dopamine receptors found in the ventral, compared to the dorsal striatum. No statistical differences in the binding characteristics of any of the different adenosine and dopamine receptor antagonists used were found between sham-operated and VH-lesioned rats.     

Tracer and maximal specific binding of tritiated spiperone or N-n-propylnorapomorphine to quantify dopamine receptors in rat brain regions in vivo

Specific tracer and maximal specific binding (Bmax) were determined in rat brain regions from radioactivity accumulation after intravenous administration of 3H N-n-propylnorapomorphine (NPA) or 3H spiperone at various specific activities. With NPA the highest Bmax-values (expressed in pmol.g-1 tissue) were found in the striatum (26 pmol.g-1) nucleus accumbens (about 27 pmol.g-1) and the olfactory tubercle (11 pmol.g-1). Saturable NPA binding was also found in the amygdaloid complex, medulla oblongata and inferior colliculi, but not in the frontal cortex. Bmax values for spiperone were high in the striatum (73 pmol.g-1), the nucleus accumbens (48 pmol.g-1), the olfactory tubercle (34 pmol.g-1) and the frontal cortex (18 pmol.g-1). A similar order was found for the tracer contents in these regions. There was no linear relationship between these contents and Bmax values. The possible implications of these findings and usefulness of NPA for brain imaging are discussed.     

Identification of D3 and σ Receptors in the Rat Striatum and Nucleus Accumbens Using (±)-7-Hydroxy-N,N-Di-n-[3H]Propyl-2-Aminotetralin and Carbetapentane

Abstract: Cross-reactions between dopamine D₃ and σ receptor ligands were investigated using (±)-7-hydroxy-N,N-di-n-[³H]propyl-2-aminotetralin [(±)-7-OH-[³H]DPAT], a putative D₃-selective radioligand, in conjunction with the unlabeled σ ligands 1,3-di(2-tolyl)guanidine (DTG), carbetapentane, and R(?)-N-(3-phenyl-1-propyl)-1-phenyl-2-aminopropane [R(?)-PPAP]. In transfected CCL1.3 mouse fibroblasts expressing the human D₃ receptor, neither DTG nor carbetapentane (0.1 µM) displaced (±)-7-OH-[³H]DPAT binding. R(?)-PPAP (0.1 µM) displaced 39.6 ± 1.0% of total (±)-7-OH-[³H]DPAT binding. In striatal and nucleus accumbens homogenates, (±)-7-OH-[³H]DPAT labeled a single site (15–20 fmol/mg of protein) with high (1 nM) affinity. Competition analysis with carbetapentane defined both high- and low-affinity sites in striatal (35 and 65%, respectively) and nucleus accumbens (59 and 41%, respectively) tissue, yet R(?)-PPAP identified two sites in equal proportion. Carbetapentane and R(?)-PPAP (0.1 µM) displaced ～20–50% of total (±)-7-OH-[³H]DPAT binding in striatum, nucleus accumbens, and olfactory tubercle in autoradiographic studies, with the nucleus accumbens shell subregion exhibiting the greatest displacement. To determine directly (+)-7-OH-[³H]DPAT binding to σ receptors, saturation analysis was performed in the cerebellum while masking D₃ receptors with 1 µM dopamine. Under these conditions (+)-7-OH-[³H]DPAT labeled σ receptors with an affinity of 24 nM. These results suggest that (a) (±)-7-OH-[³H]DPAT binds D₃ receptors with high affinity in rat brain and (b) a significant proportion of (±)-7-OH-[³H]DPAT binding consists of σ₁ sites and the percentages of these sites differ among the subregions of the striatum and nucleus accumbens.     

Characterization and visualization of cholecystokinin receptors in rat brain using [3H]pentagastrin

[³H]Pentagastrin binds specifically to an apparent single class of CCK receptors on slide-mounted sections of rat brain (K_D=5.6 nM; B_max=36.6 fmol/mg protein). This specific binding is temperature-dependant and regulated by ions and nucleotides. The relative potencies of C-terminal fragments of CCK-8(SO₃H), benzotript and proglumide in inhibiting specific [³H]pentagastrin binding to CCK brain receptors reinforce the concept of different brain and pancreas CCK receptors. CCK receptors were visualized by using tritium-sensitive LKB film analyzed by computerized densitometry. CCK receptors are highly concentrated in the cortex, dentate gyrus, granular and external plexiform layers of the olfactory bulb, anterior olfactory nuclei, olfactory tubercle, claustrum, accumbens nucleus, some nuclei of the amygdala, thalamus and hypothalamus.     

Regional distribution of binding sites for the nitric oxide synthase inhibitorl-[3H]Nitroarginine in rat brain

The regional distribution of N^G-nitro-l-[³H]arginine (L-[³H]NOARG) binding to different regions of rat brain was studied by quantitative autoradiography. These studies revealed highest density of binding sites in cerebellum, anterior olfactory nucleus, islands of Calleja and substantia nigra with appreciable binding site densities in inferior colliculus, superior colliculus, olfactory tubercle and dorsal tegmental nucleus. The regional distribution of L-[³H]NOARG binding, is in good agreement with the distribution of nitric oxide synthase studied previously by NADPH-diaphorase staining and immunohistochemistry using antibodies against neuronal nitric oxide synthase. The kinetics of L-[³H]NOARG binding to the cytosolic preparations of cerebral cortex, cerebellum, hippocampus and striatum was studied using an in vitro binding technique. Specific L-[³H]NOARG binding was of nanomolar affinity, saturable, and best fit to a single-site model in all four brain regions. These studies support the potential use of L-[³H]NOARG binding as a tool for further elucidation of the regional distribution and functional properties of NOS in the central nervous system.     

The distribution of a dopamine D2 receptor mRNA in rat brain

Based on the recently reported sequence of a dopamine D2 receptor cloned from rat brain, we prepared a series of cDNA probes to determine the distribution of mRNA encoding this receptor. Within the forebrain, D2 receptor mRNA is abundant in the caudate-putamen, accumbens nucleus and olfactory tubercle. Moderate to low levels of mRNA are observed in the medial habenular nucleus, diagonal band, lateral septal nucleus, claustrum, dorsal endopiriform nucleus, and entorhinal cortex. In the mesencephalon, D2 receptor mRNA is abundant within the substantia nigra, pars compacta, and the ventral tegmental area. Comparison of the distribution of the mRNA and ligand binding indicates that both presynaptic and postsynaptic D2 receptors of the nigrostriatal, mesolimbic and mesocortical pathways are derived from the same mRNA.