Specific bindings of prostaglandin D2, E2 and F2α in postmortem human brain

Binding activities specific for each of [³H]prostaglandin (PG) D₂, E₂ and F_2α were detected in the P₂ fraction of the human brain homogenates. The bindings were time-dependent, saturable and of high affinity;K_dvalues were 30 nM for all the PG bindings. Regional distribution of these binding activities was determined by measuring specific bindings with 10 nM [³H]PG-D₂, [³H]PG-E₂ and [³H]PG-F_2α in the P₂ fractions from 17 brain regions. The PG-D₂ binding activity was high in the hypothalamus, amygdala and hippocampus followed by cerebellar nuclei, thalamus, nucleus accumbens and cerebral cortex. The PG-E₂ binding sites were similarly concentrated in the hypothalamus and the limbic system, but, unlike the PG-D₂ binding, no significant binding of [³H]PG-3₂ was observed in cerebellar nuclei, cerebellar cortex and putamen. Compared with these two PG bindings, PG-F_2α binding activity was low in many areas, but significant binding was detected in the amygdala, cingulate cortex, cerebellar medulla, hippocampus, nucleus accumbens, midbrain and hypothalamus. These results suggest the presence and specific distribution of three distinct types of PG binding activities, i.e. specific binding of PG-D₂, PG-E₂ and PG-F_2α, in the human brain.     

Alpha 2-adrenoceptors in the brain of suicide victims: increased receptor density associated with major depression.

To examine directly in the brain the status of the alpha 2-adrenoceptor in major depression, the specific binding of the agonists [3H]clonidine and [3H]UK 14304 was quantitated in various brain regions of suicide victims with a retrospective diagnosis of depression or other psychiatric disorders. In depressed suicides, the binding capacity of [3H]clonidine was found to be increased in the hypothalamus (Bmax 35%-55% greater), and to a lesser extent in the frontal cortex, as compared with that in matched controls, schizophrenic suicides, or suicides with various diagnosis. The binding capacity of [3H]UK 14304 also was found increased in the frontal cortex (Bmax 30% greater), and to a lesser extent in the hypothalamus, of depressed suicides. In other brain regions such as the amygdala, hippocampus, and cerebellum there also was a tendency for an increased receptor density associated with suicide. Moreover, in the frontal cortex of suicides, the potency of norepinephrine in displacing the binding of the antagonist [3H]idazoxan also was found increased (Ki decreased eight-fold). The results indicate that the density and affinity of alpha 2A-adrenoceptors in the high-affinity state are increased in the brain of depressed suicides.     

Quantitative light microscopic autoradiographic localization of alpha 2-adrenoceptors in the human brain.

In the present work the anatomical distribution of alpha 2-adrenoceptors in the human central nervous system was studied in detail by quantitative autoradiography using the selective alpha 2 agonist [3H]bromoxidine ([3H]UK-14304) as a ligand. Only postmortem tissues from subjects free of neurological disorders were used in this study. Very high or high densities of alpha 2-adrenoceptors were found along layers I and III in non-visual neocortex, layers III and IVc of the visual cortex, CA1 field--stratum lacunosum-moleculare--and dentate gyrus--stratum granularis--at the hippocampal formation, nucleus arcuatus at the hypothalamus, locus ceruleus, nucleus dorsalis of vagus and at the stratum granularis of the cerebellar cortex. Relevant densities of alpha 2-adrenoceptors were also observed along the remaining layers of neocortex, nuclei centralis, medialis and corticalis at the amygdala, anterior thalamic group and rotundocellularis nuclei, paraventricular and ventromedial hypothalamic nuclei, substantia innominata, superior colliculus--stratum zonale--and lateral periaqueductal area at the midbrain, nucleus tractus solitarii and dorsal horn--substantia gelatinosa--of the spinal cord. [3H]Bromoxidine specific binding was very low or negligible in the remaining brain areas. Although a general parallelism between the distribution of these receptors could be observed for the rat and human brain, dramatic species differences in the level of alpha 2-receptors were found in several brain areas, such as thalamus, amygdala or cerebellar cortex. In general, the distribution of alpha 2-adrenoceptors in the human brain found here was parallel to that described for the noradrenergic presynaptic terminals in the mammalian central nervous system, lending some weight to the proposed predominant presynaptic localization of these receptors. The relevance of the anatomical distribution of alpha 2-adrenoceptors in the human brain for a better knowledge of the neurochemistry of neuropsychiatric disorders is discussed.     

Quantitative autoradiography of M2 muscarinic receptors in the rat brain identified by using a selective radioligand [3H]AF-DX 116

Muscarinic receptors of the M2 type have been studied in the rat brain using quantitative autoradiography with the selective ligand, [3H]AF-DX 116. High specific binding of [3H]AF-DX 116 was found in areas such as laminae IV and V of the parietal cerebral cortex, thalamus and hypothalamus and dentate gyrus. Intermediate [3H]AF-DX 116 binding was found in the frontal cortex, hippocampus, caudate-putamen, nucleus accumbens, and claustrum as well as in certain brainstem nuclei such as the nucleus of the solitary tract and the dorsal motor nuclei of the vagus. In contrast, the accessory olfactory nucleus, globus pallidus and cerebellum contained very low concentrations of M2 receptors. The present study demonstrates a unique regional distribution of M2 receptors in the rat brain.     

Modulation of rat brain alpha- and beta-adrenergic receptor populations by lesion of the dorsal noradrenergic bundle

Bilateral lesion of the ascending noradrenergic fibers in the dorsal bundle of adult Wistar rats with 4 micrograms 6-hydroxydopamine caused extensive depletion of norepinephrine in all forebrain areas, but led to a 54% increase in norepinephrine levels in the cerebellum. beta-Adrenergic receptor binding of [3H]dihydroalprenolol was significantly increased in all forebrain areas depleted of norepinephrine except hypothalamus. The increase in [3H]dihydroalprenolol binding was due to 62% and 34% increases in the number of beta-receptor sites in the frontal cerebral cortex and hippocampus respectively. Binding of [3H]WB-4101 to alpha 1-adrenergic receptors after dorsal bundle lesion was augmented generally to a lesser extent than beta-receptor binding, with significantly increased numbers of sites only in the frontal cortex (74%), thalamus (20%) and septum. Both alpha 1- and beta-receptor binding sites were reduced in number by 25-28% in the cerebellum of dorsal bundle-lesioned rats, whereas intraventricular administration of 6-hydroxydopamine to adult rats, which depletes norepinephrine in the cerebellum by 96%, increased cerebellar alpha 1- and beta-receptor binding by 33-40%. Binding of [3H]clonidine to forebrain alpha 2-adrenergic receptors was significantly elevated in the frontal cortex, but reduced in the amygdala and septum, after dorsal bundle lesion.     

Autoradiographic distribution of alpha 2 adrenoceptors, NAIBS, and 5-HT1A receptors in human brain using [3H]idazoxan and [3H]rauwolscine.

The regional distribution of [3H]idazoxan and [3H]rauwolscine was studied autoradiographically in human brain. [3H]Idazoxan binds with high affinity to alpha 2 adrenoceptors as well as to non-adrenergic sites (NAIBS). [3H]Rauwolscine, besides binding to alpha 2 adrenoceptors, also binds to 5-HT1A receptors. Both radioligands labelled the same population of alpha 2 adrenoceptors, defined as the epinephrine-displaceable binding component. The highest densities of alpha 2 adrenoceptors occur in the leptomeninges, cerebral cortex and claustrum; lower densities were visualised in the basal ganglia, thalamus, pons, substantia nigra, cerebellum and medulla oblongata; no alpha 2 adrenoceptors were detected in amygdala and nucleus ruber. NAIBS were present in all the examined brain areas, with the highest densities found in the basal ganglia and substantia nigra. The finding that certain brain regions, such as the amygdala, contained NAIBS but no detectable alpha 2 adrenoceptors, suggests that the binding sites are independent from each other. The regional distribution of 5-HT1A receptors labelled by [3H]rauwolscine is in agreement with previous studies using [3H]8-OH-DPAT.     

Galanin/alpha2-adrenoceptor interactions in telencephalic and diencephalic regions of the rat

The aim of this study was to evaluate whether galanin could affect central alpha2-adrenoceptors in telencephalic and diencephalic regions in the rat using quantitative receptor autoradiography with the alpha2 agonist radioligand [3H]p-aminoclonidine. Galanin 1 nM significantly and substantially increased the Kd value of the [3H]p-aminoclonidine binding sites in the medial hypothalamus and amygdala by 86% (p < 0.01) and 73% (p < 0.05) respectively. The Bmax value was only significantly increased with 3 nM galanin in the amygdala and the medial hypothalamus (both p < 0.05). The antagonist M35 counteracted the increase of the Kd values of the alpha2-adrenoceptor agonist binding sites produced by galanin 1 nM in the amygdala and the medial hypothalamus (both p < 0.001). These findings suggest the existence of an antagonistic galanin/alpha2 adrenoceptor interaction in the medial hypothalamus and amygdala that may be of relevance for alpha2-adrenoceptor-regulated neuroendocrine functions and food intake.     

Characteristics of [3H]prazosin binding to guinea pig brain alpha-adrenergic receptors: effects of estradiol and progesterone

[3H]Prazosin was found to bind to sites on guinea pig brain membranes with alpha 1-adrenergic receptor characteristics. Treatment of ovariectomized guinea pigs with estradiol benzoate (EB) or EB followed by progesterone (P) did not affect [3H]prazosin binding to membranes from hypothalamus, preoptic area, amygdala or cerebral cortex. When added to the incubation mixture of the assay, estradiol, P, and other steroids decreased [3H]prazosin binding but only at high concentrations. These results do not support the idea that estrogen and progestin influence reproductive physiology through effects on brain alpha 1-receptors, although limitations of the methodology employed do not completely rule out this possibility.     

Impact of food deprivation on alpha 1- and alpha 2-noradrenergic receptors in the paraventricular nucleus and other hypothalamic areas

Hypothalamic norepinephrine may modulate normal eating behavior through activation of alpha 2-noradrenergic receptors, localized in the paraventricular nucleus (PVN). We investigated whether these receptors, which stimulate food ingestion, may in turn be altered by the nutritional state of the organism. Thus the impact of food deprivation, on the specific binding of [3H]-p-aminoclonidine ([3H]PAC) to alpha 2-noradrenergic receptors in discrete hypothalamic areas, was examined in rats. The results of our first experiment revealed that 48 hr food deprivation reduced (by 50%) the maximum number of binding sites (Bmax) of the high affinity component of [3H]PAC binding to alpha 2 receptors. This effect occurred exclusively in the medial hypothalamus (which includes the PVN), without any change in the affinity (Kd) of these receptors. A smaller decline was seen in the low affinity binding sites of the medial hypothalamus, whereas no changes were observed in the density or affinity of the high and low affinity alpha 2 receptor sites in the lateral hypothalamus or frontal cortex. The alpha 1-noradrenergic receptor sites, as defined by [3H]prazosin and [3H]WB-4101 binding, were also unaffected in the different brain areas by 48 hr food deprivation. An additional analysis of alpha 2 receptors in discrete hypothalamic nuclei demonstrated that the deprivation-induced decline in alpha 2-receptor binding: occurred specifically in the PVN; was apparent after as little as 3 hr food deprivation; and occurred only when this brief deprivation fell at the onset of the dark cycle, as opposed to at the end of the dark cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional distribution of high-affinity [H]somatostatin binding sites in the human brain

The distribution of high-affinity binding sites for [³H]somatostatin has been studied in membrane preparations from a number of regions of normal human brain. The highest densities of binding sites (> 48 fmol/mg protein) were found in the cerebral and cerebellar cortices and the hippocampus, with intermediate binding densities (30–46 fmol/mg protein) being present in the basal ganglia, amygdala, septum and claustrum. The lowest densities of binding sites (<14 fmol/mg protein) were observed in the hypothalamus, thalamus and substantia nigra. The binding of [³H]somatostatin in both the frontal cortex and cerebellar cortex demonstrated pharmacological specificity, since somatostatin-28, but not somatostatin-28_1–12 or Des AA^{1,2,4,5,12,13}, -Trp⁸-somatostatin, competed for the binding sites. Scatchard analysis of the binding in both frontal cortex and cerebellar cortex revealed the presence of two classes of high-affinity binding sites.     

3H]Rauwolscine binding sites in the brains of male tree shrews are related to social status.

The aim of the present study was to investigate the influence of social status on central nervous alpha 2-adrenoceptors. Using the specific alpha 2-adrenoceptor antagonist [3H]rauwolscine, binding sites in the brains of dominant and subordinate male tree shrews were quantified by in vitro autoradiography. In 5 of the 14 brain structures investigated, subordinates had significantly lower numbers of binding sites than dominants. These structures were the solitary tract nucleus, the dorsal motor nucleus of the vagus, the periaqueductal gray, the perifornical region of the hypothalamus and the medial nucleus of the amygdala. These brain areas are all intimately involved in the regulation of autonomic functions and of emotional behavior. Also the affinities for [3H]rauwolscine differed between the groups. In 3 nuclei, the solitary tract nucleus, the periaqueductal gray and the medial nucleus of the amygdala, dominants had significantly higher Kd-values than subordinates. This demonstrates the presence of low affinity binding sites in dominants which do not exist in subordinates. It is suggested that the low number of [3H]rauwolscine binding sites in subordinates results from down-regulation of alpha 2-adrenoceptors by high levels of noradrenaline and/or adrenaline. The disappearance of low affinity [3H]rauwolscine binding sites may play an important role in the etiology of psychosocial stress.     

Chronic desipramine treatment reduces regional neuropeptide Y binding to Y2-type receptors in rat brain.

Chronic treatment of rats with desipramine and imipramine (5 mg/kg/twice daily/i.p.) for 14 days caused a significant reduction in the binding of [3H]propionyl NPY to membranes prepared from frontal cortex, nucleus accumbens, hypothalamus and hippocampus. There was no change in binding of [3H]propionyl NPY in the parieto-occipital cortex, striatum or amygdala. Scatchard analysis of binding data from frontal cortical and hippocampal membranes showed that [3H]propionyl NPY bound to a single site with a Kd of approximately 0.3 nM. The loss of [3H]propionyl NPY binding in hippocampal and frontal cortical membranes revealed that chronic tricyclic antidepressant treatment produced a reduction in the number of binding sites with no change in the affinity for the ligand. Chronic desipramine treatment did not alter the ability of NPY (0.01-25 microM) to stimulate inositol phosphate accumulation in rat frontal cortical slices as compared to saline-treated animals. The lack of change of NPY-induced inositol phosphate accumulation following chronic desipramine treatment showed that there was no change to Y1 NPY-type receptors which are linked to the hydrolysis of inositol phospholipids. However, the ability of NPY (0.05-0.5 microM) to inhibit forskolin (1 microM) stimulated adenylate cyclase via Y2 NPY-type receptors in rat frontal cortical slices was significantly reduced following chronic desipramine treatment. This finding suggests that the reduction of [3H]proprionyl NPY binding in selective brain regions may be the result of an antidepressant-induced loss of Y2-type NPY receptors which are negatively linked to adenylate cyclase.     

Down-regulation of alpha 2-adrenoceptors involved in growth hormone control in the hypothalamus of infant rats receiving short-term clonidine administration

In infant rats short-term administration of the alpha 2-adrenoceptor agonist, clonidine (CLO), induces refractoriness to the growth hormone (GH)-releasing effect of an acute CLO challenge. CLO reportedly stimulates GH release via increased release of GH-releasing hormone (GHRH) from the hypothalamus. Based on these premises, in this study we investigated the possibility that repeated CLO administration may induce down-regulation of hypothalamic alpha 2-adrenoceptors, involved in GH control, thus prohibiting the GH-releasing effect of the drug. alpha 2-Adrenoceptor binding was determined in different brain regions of 10-day-old rats pretreated for 5 days with CLO (150 micrograms/kg, b.i.d.) and killed 14 h after last CLO administration. [3H]p-Aminoclonidine [( 3H]PAC) was used as the specific ligand of alpha 2-adrenoceptors. Treatment with CLO decreased by about 30% the maximum number of binding sites (Bmax) in areas of the mediobasal hypothalamus (MBH) involved in the stimulatory control of GH secretion, i.e. nucleus periventricularis arcuatus, nucleus ventromedialis hypothalami and nucleus lateralis hypothalami. Reduction of Bmax for [3H]PAC binding was observed also in the nucleus periventricularis hypothalami, an area involved in the inhibitory control of GH secretion and, among extrahypothalamic areas, only in the cortex piriformis. In no brain areas was the affinity constant (Kd) for [3H]PAC binding significantly changed after CLO pretreatment. Binding studies performed with a specific ligand of alpha 1-adrenoceptors, [3H]prazosin, showed that the effect of CLO was specific since no changes in the Bmax or Kd were present in either hypothalamic or extrahypothalamic regions.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of spinal cord transection on the development of cholinergic and adrenergic sympathetic neurons.

The regional distribution and properties of the sodium-independent “specific” binding of [³H]GABA to membranes prepared from human brains (control and Parkinsonian patients) have been investigated. The affinity of [³H]GABA for the binding site was similar for human cerebellar cortex (K_d = 3.4 × 10^?7 M) and whole rat brain (K_d = 5.1 x 10^?7 M) and was inhibited by bicuculline (ID₅₀ = 2.2 x 10^-5 M). In the normal human brain the cerebellar cortex demonstrated the highest number of binding sites, in accordance with the large number of GABA interneurons in this structure. The hippocampus also displayed a high capacity to bind [³H]GABA, whereas cerebral cortical areas showed a lesser capacity. [³H]GABA binding was similar in many regions of the basal ganglia (amygdala, putamen, caudate or accumbens) but was lower than that for the cortical regions. The binding of [³H]GABA to membranes from the substantia nigra, thalamus and internal or external pallidum was lower than for the above regions. Subcortical white matter did not exhibit specific binding for [³H]GABA. In membranes prepared from Parkinsonian patients [³H]GABA binding was greatly decreased in the substantia nigra, but not in other brain areas examined. From this observation it was concluded that there are [³H]GABA binding sites on the cell bodies (or dendrites) of the nigral dopamine neurons.     

Distribution of cocaine recognition sites in monkey brain: I. In vitro autoradiography with [3H]CFT.

The cocaine analog [3H]CFT ([3H]WIN 35,428) was used to map and characterize cocaine recognition sites in the squirrel monkey brain by quantitative autoradiography. Coronal tissue sections were incubated with 5 nM [3H]CFT to measure total binding or with [3H]CFT in the presence of 30 microM (-)-cocaine to measure nonspecific binding. High densities of [3H]CFT binding sites were present in dopamine-rich brain regions, including the caudate nucleus, putamen, nucleus accumbens, and olfactory tubercle. In each of these regions specific binding was greater than 90% of total binding. Several additional brain regions exhibited intermediate densities of [3H]CFT binding, including the substantia nigra, the zona incerta, the amygdala, and the hypothalamus. Low, though measurable levels of binding were observed in the bed nucleus of the stria terminalis, the ventral tegmental area, the medial preoptic area, the pineal, the hippocampus, and thalamic central nuclei. Near-background levels of binding were found in white matter, cortical regions, globus pallidus, and cerebellum. The pharmacological specificity of [3H]CFT binding in various brain regions was determined in competition studies using [3H]CFT and a range of concentrations of selected monoamine uptake inhibitors. In all brain regions examined, stereoselective inhibition of [3H]CFT binding was observed for the (-) over the (+) isomer of cocaine. For other drugs tested, competition experiments indicated a rank order of potency of GBR 12909 greater than or equal to CFT greater than bupropion, suggestive of binding of [3H]CFT to elements of the dopamine transport system. The results demonstrate that although densities of [3H]CFT binding sites are highest in the caudate nucleus, putamen, and nucleus accumbens/olfactory tubercle, significant levels of binding can be detected in other brain regions that may contribute to the behavioral and physiological effects of cocaine.     

Characterization of [3H] CCK4 binding sites in mouse and rat brain

We have investigated the possible occurrence of distinct CCK8 and CCK4 binding sites in the brain by comparing the binding characteristics of [3H] CCK4 to those of the CCK8 analogue, [3H] Boc (Nle28,31]CCK27-33 (BDNL-CCK7). [3H] CCK4 and [3H] BNDL-CCK7 were shown to interact with mouse brain membranes with very similar maximal binding capacities 31.7 +/- 2.1 fmol/mg prot (KD = 3.78 +/- 0.47 nM) and 38.9 +/- 2.2 fmol/mg prot (KD = 0.26 +/- 0.02 nM) respectively. The apparent affinities of five CCK analogues for the sites labelled by both probes were almost identical. Autoradiographic studies revealed that the distribution of [3H] CCK4 binding sites in rat forebrain was the same as that of [3H] BDNL-CCK7, with high densities of receptors in the cortex, nucleus accumbens, olfactory bulb and the medial striatum, moderate densities in the amygdala, the hippocampus, several nuclei of the thalamus and hypothalamus. However in the interpenduncular nucleus where there was moderate binding of [3H]BDNL-CCK7, no [3H]CCK4 labelling was observed. These studies demonstrated the occurrence of one class of high affinity binding sites for [3H] CCK4 in mouse and rat brain, with characteristics similar to those already reported with CCK33, CCK8 and pentagastrin probes. Nevertheless the presence of a small amount of very high affinity binding sites for [3H]CCK4 cannot be excluded.     

A topographic quantitative method for measuring brain tissue pH under physiological and pathophysiological conditions

The autoradiographic regional localization of [3H]beta-endorphin binding in rat brain differed from that of either [3H]dihydromorphine or [3H]D-Ala2-D-Leu5-enkephalin. Comparisons were made from sequential sections through 3 regions of rat brain: striatum, hypothalamus/thalamus, and brainstem. [3H]beta-endorphin labeled some clusters as well as the subcallosal streak in the striatum, the nucleus accumbens, lamina IV of the cortex, medial regions of the thalamus, hippocampus, inferior colliculus, dorsal raphe, median raphe and pontine nuclei. White matter regions had little binding. Although many of these structures were also labeled with either [3H]dihydromorphine or [3H]D-Ala2-D-Leu5-enkephalin, the overall pattern of [3H]beta-endorphin labeling appeared unique, consistent with the proposal of central epsilon receptors.     

Transient elevation of amygdala alpha 2 adrenergic receptor binding sites during the early stages of amygdala kindling

Enhanced noradrenergic neurotransmission retards but does not prevent the development of kindling. We previously reported that locus coeruleus (LC) alpha 2 adrenergic receptor binding sites are transiently elevated during the early stages of kindling development. Since the firing activity of LC noradrenergic neurons is partially regulated via an alpha 2 receptor-mediated recurrent inhibition, the transient elevation in LC alpha 2 receptors could decrease LC activity and consequently facilitate the development of kindling. Transient elevation of alpha 2 receptor binding sites during early stages of kindling may also occur on noradrenergic axon terminals projecting to forebrain sites. Using in vitro neurotransmitter autoradiography techniques, we investigated this hypothesis by measuring specific [3H]idazoxan binding in 5 different areas of rat forebrain at 2 different stages of kindling development. After 2 class 1 kindled seizures, specific [3H]idazoxan binding was elevated significantly in the amygdala, but not in other forebrain regions. No differences in specific [3H]idazoxan binding were observed in any of the 5 brain regions in rats kindled to a single class 5 kindled motor seizure. Saturation of binding experiments indicated that the increase in amygdala [3H]idazoxan binding, following 2 class 1 kindled motor seizures, was due to an increase in the total number of alpha 2 receptor binding sites without a change in the affinity of the binding sites for [3H]idazoxan. Thus, the transient increase in alpha 2 receptors that occurs in the LC in the early stages of kindling also occurs in the forebrain region in which the kindled seizure originates.     

Specific binding of [H]prostaglandin E2 to rat brain membranes and synaptosomes

There is saturable, reversible and specific binding for [3H]prostaglandin E2 (PGE2) to rat brain membranes. This binding is of high affinity, selectively distributed with a maximum in the hypothalamus, the amygdala and the posterior pituitary, and is associated subcellularly with the synaptosomal fraction. This specific PGE2 binding has the characteristics expected for receptors, so opening new perspectives which might clarify the role of PGs in the brain.