Brain 5-HT1 binding sites in depressed suicides

5-HT₁ and 5-HT_1A binding sites were measured in brain tissue obtained at postmortem from 19 suicides, with definite evidence of depression, and 19 sex and age-matched controls. Thirteen of the depressed suicides had not been prescribed psychoactive drugs recently (drug-free suicides); six had been receiving antidepressant drugs, alone or in combination with other drugs (antidepressant-treated suicides). No significant differences were found in the number or affinity of 5-HT₁ and 5-HT_1A binding sites in frontal or temporal cortex between drug-free suicides and controls. The number of 5-HT₁ sites was significantly lower (by 20%), affinity unaltered, in hippocampus and the affinity significantly lower (by 33%), number unaltered, in amygdala of drug-free suicides than controls. The number of 5-HT₁ binding sites tended to be higher and the affinity lower in the antidepressant-treated compared to drug-free suicides, and significantly so in hippocampus. The present results, together with our previous studies, provide no evidence of altered cortical 5-HT markers in depressed suicides, but further emphasise abnormalities in the hippocampus.     

Specific tricyclic antidepressant binding sites in rat brain characterised by high-affinity 3H-imipramine binding

The specific binding of ³H-imipramine to various brain regions of the rat is of high affinity (Kd = 4.0 nM), rapid and reversible. It was inhibited by tricyclic antidepressants at nanomolar concentrations and by atypical antidepressants at micromolar concentrations. The binding does not seem to be directly related to known neurotransmitter receptor systems. Specific ³H-imipramine binding sites were unequally distributed between the various brain regions and undetectable in the heart and vas deferens. Rats chronically treated with desipramine for three weeks had significantly less specific ³H-imipramine binding sites in the cortex than did control animals. It is concluded that these ³H-imipramine binding sites may be important in the study of depression and of the mechanism of action of antidepressant drugs.     

Age alters the observed response of imipramine binding sites to chronic antidepressant treatment in female rats

Age alters hypothalamic imipramine binding sites in female rats. Older females have increased levels of imipramine binding with decreased affinity. The response of hypothalamic imipramine binding sites to chronic antidepressant treatment varies depending on the age of the animals treated. In juvenile female rats imipramine binding sites decrease after antidepressant treatment, consistent with previous reports. However, in young females chronic imipramine treatment produces no change in levels of imipramine binding with a slight decrease in binding affinity. In middle-aged female rats, the same treatment causes an apparent increase in levels of imipramine binding sites along with a decrease in affinity. These decreases in the affinity of imipramine binding sites in older female rats, and the concomitant changes in the levels of imipramine binding are the result of imipramine metabolites remaining in the tissue after antidepressant treatment and interfering with the binding assay, despite extensive washing of the membrane preparation. Thus, the observed changes in the response of imipramine binding sites to chronic imipramine treatment with age are probably due to age-related alterations in the metabolism of imipramine in female rats.     

Decreased numbers of progenitor cells but no response to antidepressant drugs in the hippocampus of elderly depressed patients

Imaging studies have consistently documented hippocampal volume reductions in depression. Although depressive disorders are traditionally considered to have a neurochemical basis, recent studies suggest that impairments of structural plasticity contribute to the volume reductions and the related cognitive changes. This might result from repeated periods of stress that are a wellknown risk factor for depression. Adult neurogenesis is a prominent example of neuroplasticity that in rodents, is reduced by stress but stimulated by antidepressant drugs. Although reductions in neurogenesis have been proposed to contribute to the etiology of depression, only two studies have so far examined hippocampal cytogenesis in depression, but this was in a limited number of subjects with considerable interindividual variation, and these studies came to different conclusions. We therefore collected hippocampal tissue of 10 elderly control subject and 10 well-matched depressed patients that were highly comparable in terms of age, sex, pH-CSF and postmortem delay, and tested whether the numbers of MCM2-positive progenitors and PH3-positive proliferating cells were altered by depression or antidepressant treatment. A significant reduction was found in MCM2-, but not PH3-immunopositive cells in depression. Although this result is consistent with the concept that structural plasticity is decreased in depression, we could not confirm that antidepressant drugs had a stimulatory effect on these cells. This discrepancy may relate to anatomical differences, in medication, to neurogenesis-independent mechanisms of antidepressant action, or the age of the patients that was higher than in previous studies. Whether the reduction is a cause or consequence of depression awaits to be determined.     

[11C]Mirtazapine binding in depressed antidepressant nonresponders studied by PET neuroimaging

Rationale  Lack of benefit from antidepressant drug therapy is a major source of human suffering, affecting at least 25% of people with major depressive disorder. We want to know whether nonresponse to antidepressants can be linked to aberrant neuroreceptor binding. Objective  This study aims to assess the antidepressant binding in brain regions of depressed nonresponders compared with healthy controls. Materials and methods  Healthy volunteers and depressed subjects who had failed to benefit from at least 2 antidepressant treatments were recruited by newspaper advertisements. All subjects had received no antidepressant medication for at least 2 months before positron emission tomography (PET) that was carried out with [¹¹C]mirtazapine. Kinetic parameters of [¹¹C]mirtazapine were determined from PET data in selected brain regions by the simplified reference tissue model. Results  Binding potentials of [¹¹C]mirtazapine in cerebral cortical regions were lower in depressed nonresponders than in healthy controls. Removal rates of [¹¹C]mirtazapine were higher in diencephalic regions of depressed nonresponders than in healthy controls. Conclusions  PET neuroimaging with [¹¹C]mirtazapine showed aberrant neuroreceptor binding in brain regions of depressed subjects who had failed to benefit from treatment with antidepressant drugs.     

Modifications of central 5-hydroxytryptamine binding sites in synaptic membranes from rat brain after long-term administration of tricyclic antidepressants.

The effects of single and long-term administration of tricylic antidepressants, imipramine, desmethylimipramine (desipramine), amitriptyline and dimetacrine on 5-hydroxytrptamine (5-HT) binding sites in synaptic membranes from rat brain were studied. There were two types of specific [³H]-5-HT binding sites; one with high affinity and the other with low affinity. Intraventricular injection of 5,6-dihydroxytryptamine did not modify the binding parameters. In in vitro experiments, 5-HT, tryptamine derivatives and 5-HT antagonists were found to be effective displacers of [³H]-5-HT binding while all antidepressants studied were ineffective in displacing the binding at 10^?6 M. Single i.p. administration of antidepressants did not affect significantly the specific binding. In contrast, administration of antidepressants for 3 weeks produced a significant decrease in the maximal numbers of binding sites, without affecting the dissociation constants of the specific binding. It is suggested that the modification of central 5-HT binding sites caused by long-term administration of tricylclic antidepressants is due to persistent exposure of the binding sites to elevated concentrations of 5-HT, a consequence of the 5-HT uptake inhibition by the antidepressants. These observations could have some implication for the new theory proposed recently that in depression, there is an involvement of synaptic 5-HT with a hypersensitive receptor in the postsynaptic membranes.     

Corticotropin-releasing factor receptor blockade enhances conditioned aversive properties of cocaine in rats

The behavioral profile of corticotropin-releasing factor (CRF) in mediating anxiogenic-like and aversive responses to stressors may be particularly relevant for dependence and withdrawal in drug-experienced organisms. Moreover, stressful aspects of drug exposure in the drug naive organism may also induce CRF system activation. In the present studies, the dependence of aversive properties of cocaine on activation of endogenous CRF systems has been evaluated in rats using taste conditioning and runway self-administration paradigms. Systemic cocaine administration (20 mg/kg IP) produced a conditioned saccharin aversion which was dose-dependently potentiated by central administration of the CRF receptor antagonist, D-phe CRF (12–41). In addition, IV cocaine administration (0.75 mg/kg per injection IV) produced runway goal-box avoidance and conditioned place avoidance responses which were significantly accelerated by CRF antagonist treatment. In contrast, CRF receptor stimulation using CRF itself abolished cocaine-induced increases in goal latency in the runway paradigm. This generalized involvement of CRF systems in cocaine-related motivational/associative states is consistent with the comprehensive role of CRF in mediating emotional responses to non-drug stressors. Received: 3 June 1997/Final version: 28 August 1997     

Heterogeneity of cerebral beta-adrenoceptor binding sites in various vertebrate species.

[3H]-Dihydroalprenolol ([3H]-DHA) binds to cerebral membranes of the frog, chick, rat, mouse, rabbit and human with a dissociation equilibrium constant (KD) of about 1 nM and displays binding characteristics indicative of an interaction with beta-adrenoceptors. However, the maximum number of specific binding sites labelled by this beta-adrenoceptor ligand varies substantially between the species with the chick and mouse having the highest, and the frog the lowest density. The structure--activity relationships of adrenergic agents to inhibit specific [3H]-DHA binding suggests that whereas the membrane sites from all the species had similar affinities for non-selective beta-adrenergic agents, several drugs that have been reported to show selectivity for beta1-adrenoceptors demonstrated considerably higher affinities for mammalian rather than avian or amphibian membrane sites. By this pharmacological criteria it is likely that all the beta-adrenoceptor binding sites in frog and chick cerebral tissue have properties resembling beta2-receptors. However, in mammalian cerebral cortex, evidence is presented that beta1- and beta2-adrenoceptors coexist in a ratio of 70%/30% respectively.     

Clonazepam-induced up-regulation of serotonin1 binding sites in frontal cortex of rat

Chronic administration of the benzodiazepine, clonazepam, increased the number of [3H]5-hydroxytryptamine (5-HT1) binding sites in the frontal cortex of the rat. The increase reflected a change in the maximum density of binding sites (Bmax) with no change in ligand affinity (Kd). Increased binding occurred after continued exposure (10 days) to large (5.0 mg/kg) doses of clonazepam. The changes in [3H]5-HT binding were regional in that they occurred in membranes from the frontal cortex but not the brainstem. The effects were also at least partially selective for 5-HT receptors since the binding of the beta-adrenergic radioligand, [3H]dihydroalprenolol, was not affected by clonazepam. A second benzodiazepine, diazepam, did not affect the binding of [3H]5-HT at doses of 30 mg/kg per day. The latter data suggest that the effects of benzodiazepines on serotonin 5-HT1 receptors are unique to clonazepam.     

Affinities of some common opioid analgesics towards four binding sites in mouse brain

Summary The selectivities of morphine, codeine, l-methadone and d-propoxyphene, towards the binding sites in mouse brain membranes labelled by ³H-dihydromorphine (DHM), ³H-ethylketocyclazocine (EKC) and ³H-D-Ala²-Leu⁵-enkephalin (DALE), were investigated. Of the four binding sites identified, three correspond to mu-, kappaand delta-opioid binding sites or receptors, respectively. The fourth site has a high capacity and binds EKC with a high affinity, DHM with a very low affinity and does not bind DALE. In displacement studies, the relative affinities of morphine and methadone were quite similar towards the tree sites with highest affnity (mu kappa delta). Codeine and d-propoxyphene were mu-selective but did not differentiate between kappa-and delta-sites. At high concentrations I-methadone (K_d=6.7 M), and d-propoxyphene (K_d=40 M) bound to the fourth site, while morphine, codeine and naloxone were practically inactive. The binding selectivities of these drugs were quite different from those of metkephamid and U-50, 488 H, substances that are thought to exert their antinociceptive effects through delta-and kappa-receptors, respectively. It was concluded that while d-propoxyphene and codeine may partly act througg other receptors than morphine, this is probably not the case for l-methadone.     

Identification of multiple nitrobenzylthioinosine binding sites in guinea pig platelets: Comparison with binding in guinea pig erythrocytes

The novel existence of multiple binding sites for the potent nucleoside transporter Probe, [³H]nitrobenzylthioinosine, was identified in guinea pig platelet membranes and the binding characteristics compared to those of guinea pig erythrocyte membranes. Scatchard analysis of the binding in platelets reveled two high affinity binding sites with affinity constant (K_D) of 0.94 ± 0.07 nM and 83 ± 13 nM with corresponding maximal binding capacities (B_max) of 21 ± 7 and 110 ± 25 fmol/mg protein, respectively. In comparison, guinea pig erythrocyte membranes revealed a homogeneous population of the binding sites with K_D of 0.17 ± 0.04 nM and a B_max value of 73 ± 11 fmol/mg protein. Biphasic semi-log plots of the binding site heterogeneity in erythrocytes not reveled by Scatchard plots. Determination of the potencies of selected drugs in inhibiting the binding showed evidence of differential interacitons with the binding sites by various agents which may be exploited pharmacologically. © 1993 Wiley-Liss, Inc.     

抑郁症信号转导通路研究

长期给予抗抑郁剂可以增加脑内cAMP依赖性PKA的表达水平,继而激活cAMP反应元件结合蛋白。CREB可以调节脑源性神经生长因子的表达。大量的研究表明cAMP和BDNF是多种抗抑郁剂的共同通路,现就此进行综述,探讨其与抗抑郁剂之间的关系,为精神药理和新药研发提供依据。     

GABA receptor-mediated modulation of 3H-diazepam binding in rat cortex.

Three membrane preparations of rat cortex were used to examine the effects of GABA, bicuculline and bicucine on specific 3H-diazepam binding. In the crude synaptosomal fraction, GABA had no effect on either the maximal binding capacity (Bmax) or dissociation constant (KD) of 3H-diazepam binding. Bicuculline and bicucine both decreased binding affinity. This was antagonized by adding GABA. In the repeatedly washed membrane preparation, and in the washed, frozen and thawed preparation, GABA increased binding affinity and, at high concentrations, increased Bmax. Increased binding affinity was observed with as little as 10(-8) M GABA in the washed, frozen and thawed preparation. Bicuculline inhibited the effect of GABA on 3H-diazepam binding. It was found that about 3 X 10(-5) M GABA was present in the assay medium containing crude synaptosomal fraction. These results suggest endogenous GABA is present in, and influences the results of 3H-diazepam binding assays. Furthermore, it appears that GABA and bicuculline affect 3H-diazepam binding through their binding to the specific GABA binding site.     

The effects of PK 11195, a ligand for benzodiazepine binding sites, in animal tests of anxiety and stress

PK 11195 (1-(2-chlorophenyl)-N-methyl-(1-methylpropyl)-3-isoquinolinecarboxami de, a potent ligand for peripheral benzodiazepine binding sites, was unable to reverse the anxiogenic effects of Ro 5-4864 (chlorodiazepam) in the social interaction test or in the punished drinking test. However, at 90 mg/kg PK 11195 also reduced social interaction, indicating an anxiogenic effect. Both PK 11195 (30-120 mg/kg) and Ro 5-4864 (20-60 mg/kg) significantly increased the plasma corticosterone concentrations of rats left in their home cages after injection, and in those placed in novel apparatus. Because both drugs had effects in the same direction and because the doses were far higher than those needed to saturate the peripheral receptor, it is unlikely that these behavioural actions are mediated by peripheral benzodiazepine binding sites. It is suggested that the effect of PK 11195 could even be mediated by the classical CNS benzodiazepine binding sites.     

A comparison of the binding of nicotine and nornicotine stereoisomers to nicotinic binding sites in rat brain cortex

Summary Both stereoisomers of nicotine and nornicotine were tested for their ability to competitively displace ³H(-)-nicotine and ³H-acetylcholine (in the presence of atropine), in rat cortex tissue. ³H-acetylcholine was displaced from two binding sites, super-high and high, by (+)-nicotine, (-)-nornicotine and (+)-nornicotine but from a high affinity site by (-)-nicotine. ³H-nicotine was displaced from two sites, high and low affinity by nicotine and nornicotine stereoisomers. The high-affinity ³H(-)-nicotine binding site showed similar binding characteristics to one of the sites labelled by ³H-acetylcholine. IC₅₀ values showed (-)-nicotine to be 13 and 25-fold more potent than (+)-nicotine for displacing ³H-(-)nicotine and ³H-acetylcholine, respectively, but no difference was observed for nornicotine stereoisomers. While (-)-nicotine preferentially bound to the high affinity site of ³H-(-)-nicotine (+)-nicotine preferred the low affinity site. The study provides further evidence for multiple nicotine receptors in brain. Send offprint requests to A. Nordberg at the above address     

Characterization of non-adrenergic [3H]clonidine binding sites in rat stomach: high affinity of imidazolines,guanidines and sigma ligands

We have identified and characterized non-adrenergic [³H]clonidine binding sites in rat stomach. The binding of [³H]clonidine was rapid, reversible, partly specific (as defined by cirazoline 0.1 mmol/l; 68% specific binding at [³H]clonidine 10 nmol/l), saturable and of high affinity. The specific binding of [³H]clonidine to rat stomach membranes was concentration-dependently inhibited by various imidazolines and guanidines including the sigma site ligand 1,2-di-(2-tolyl)guanidine (DTG), by the butyrophenone derivative haloperidol and by the piperidine derivative (+)-3-PPP[(R)-3-(3-hydroxyphenyl)-N-propylpiperidine]; the latter two compounds are also known to exhibit affinity for sigma sites. In contrast, rauwolscine, histamine, ranitidine and the non-hydrolysable GTP-analogue Gpp(NH)p (5 guanylylimidodiphosphate) did not, or with negligible affinity, inhibit [³H]clonidine binding. In most cases, the competition curves were best fitted to a two-site model. The rank order of affinity for the high affinity site (in a few cases for a single detectable site) was as follows: cirazoline>idazoxanDTG>(+)-3-PPP> clonidine>guanabenz>haloperidol. This rank order is not compatible with the pharmacological properties of either I₁- or I₂-imidazoline binding sites. However, the ability of haloperidol, (+)-3-PPP and DTG to displace [³H]clonidine (the latter two with high affinity) suggests that the [³H] clonidine binding sites in rat stomach may be related to sigma-like sites.     

Imidazoline/guanidinium binding sites and their relation to inhibition of KATP channels in pancreatic B-cells

To elucidate the β-cytotropic effect of imidazoline compounds their inhibitory effect on ATP-dependent K⁺ channels (K_ATP channels) in pancreatic B-cells was compared with their binding to membranes from insulin-secreting HIT T15 cells. K_ATP channels in inside-out patches from B-cells were closed with the following rank order of efficacy at 10 μM: guanabenz > phentolamine = alinidine > clonidine > idazoxan > rilmenidine = amiloride. The last four compounds achieved an incomplete inhibition only. In contrast to sulfonylureas, the inhibitory action of imidazolines was not enhanced by ADP. With intact cells the site which mediates inhibition is less easily accessible for protonated compounds, suggesting a location at the inner face of the plasma membrane. Competition binding experiments were performed by masking α-adrenoceptors and using [³H]clonidine as ligand. Homologous displacement of [³H]clonidine revealed two distinct binding sites in HIT cell membranes characterized by dissociation constants of 38 nM and 4,911 nM and maximal binding capacities of 118 fmol/mg protein and 18 pmol/ mg protein. Generally, ligands for I₂ imidazoline receptors were more potent than ligands for I₁ imidazoline receptors to displace [³H]clonidine from the high affinity site, which does not fit into the current classification of imidazoline receptors. Binding to the second site had affinities in the micromolar range, similar to the concentrations necessary to inhibit K_ATP channels in B-cells. However, alinidine and phentolamine inhibited K_ATP channels already at concentrations at which they displaced [³H] clonidine only from the high affinity site, but not yet from the low affinity site. Since the proportion of the low and high affinity site varied in dependence of the competitor, the imidazoline binding sites in HIT cells may not be independent, but may rather represent two interacting or interconvertible sites both of which may be involved in K_ATP channel closure. Received: 1 April 1997 / Accepted: 2 June 1997