Depressed patients have decreased binding of tritiated imipramine to platelet serotonin "transporter"

The high-affinity tritiated (3H) imipramine binding sites are functionally (and perhaps structurally) associated with the presynaptic neuronal and platelet uptake sites for serotonin. Since there is an excellent correlation between the relative potencies of a series of antidepressants in displacing 3H-imipramine from binding sites in human brain and platelet, we have examined the binding of 3H-imipramine to platelets from 14 depressed patients and 28 age- and sex-matched controls. A highly significant decrease in the number of 3H-imipramine binding sites, with no significant change in the apparent affinity constants, was observed in platelets from the depressed patients compared with the controls. These results, coupled with previous studies showing a significant decrease in the maximal uptake of serotonin in platelets from depressed patients, suggest that an inherited or acquired deficiency of the serotonin transport protein or proteins may be involved in the pathogenesis of depression.

Quinolones, theophylline, and diclofenac interactions with the gamma-aminobutyric acid receptor

Epileptic seizures and hallucinations, which are rare in patients receiving quinolones, have been observed more frequently in patients receiving both quinolones and either theophylline or nonsteroidal anti-inflammatory drugs. Inhibition of gamma-aminobutyric acid (GABA) binding to the GABA receptor, resulting in general excitation of the central nervous system, may be the underlying mechanism of these adverse phenomena. We demonstrate here that ciprofloxacin displaced a GABA-like substance (muscimol) from the GABA receptor when administered in concentrations of greater than 10(-4) M. These concentrations were lower than those needed by pefloxacin, ofloxacin, and nalidixic acid to reach a concentration that inhibits 50% of binding. The combination of ciprofloxacin and theophylline was additive in reducing the level of muscimol binding to the GABA receptor, whereas a diclofenac-ciprofloxacin combination had no effect. The concentrations of both ciprofloxacin and the other quinolones used were much higher than those observed in human serum and cerebrospinal fluid in a clinical setting; however, different human GABA receptor affinities, preexisting GABA excitation, or underlying central nervous system disease may amplify the excitatory side effects observed by the co-administration of quinolones and theophylline. Attention should be paid to the possible epileptogenic activity of the simultaneous administration of quinolones with aminophylline, nonsteroidal anti-inflammatory drugs, or other unpredictable drugs.

High-affinity imipramine binding and serotonin uptake in platelets of eight adolescent and ten adult obsessive-compulsive patients

The authors evaluated high-affinity [3H]imipramine binding and [3H]serotonin uptake to platelets in eight adolescent and 10 adult patients who met DSM-III criteria for obsessive-compulsive disorder in comparison with those of normal control subjects of similar ages. The maximal binding of [3H]imipramine was significantly lower in adults and adolescents with obsessive-compulsive disorder than in the control subjects. No differences between groups in the affinity of [3H]imipramine to its binding sites or in serotonin uptake kinetic measures were detected. The lower density of [3H]imipramine binding sites in platelet membrane in patients with obsessive-compulsive disorder might implicate involvement of the serotonergic system or might represent an adaptive response to a chronic disease.

Amitriptyline: long-term treatment elevates alpha-adrenergic and muscarinic receptor binding in mouse brain

The effects of long-term treatment of the tricyclic antidepressant drug, amitriptyline, on alpha-adrenergic, muscarinic and dopaminergic receptor binding were studied in mouse brain. No changes could be observed after 7 or 14 days of amitriptyline administration, but after 21 days a two-fold increase in alpha-adrenergic binding was detected in the medulla pons and in the hippocampus using [3H]WB-4101 as the binding ligand. In the same two regions, a moderate increase in muscarinic receptor binding (25%) as measured by [3H]4NMPB was seen, while no change was detected in dopaminergic receptor binding measured by [3H]spiperone. Scatchard analysis reveals that the increases in receptor densities are not a result of changes in the dissociation constants of the tritiated drugs for their receptors. It is suggested that the increase in alpha-adrenergic as well as in muscarinic binding is a consequence of a chronic blockade of these two types of receptors by amitriptyline in vivo.

High-affinity binding of [3H]desipramine to rat brain: a presynaptic marker for noradrenergic uptake sites

High-affinity binding sites (apparent KD = 1.5 nM) for [3H]desipramine have been demonstrated and characterized in membranes prepared from rat brain. The binding of [3H]desipramine was found to be saturable, reversible, heat-sensitive, sodium-dependent, and regionally distributed among various regions of the brain. High concentrations of [3H]desipramine binding sites were found in the septum, cerebral cortex, and hypothalamus, whereas lower concentrations were found in the medulla, cerebellum, and corpus striatum. A very good correlation (r = 0.81, P less than 0.001) was observed between the potencies of a series of drugs in inhibiting high-affinity [3H]desipramine binding and their capacity to block norepinephrine uptake into synaptosomes. In 6-hydroxydopamine-lesioned rats there was a marked decrease in [3H]norepinephrine uptake and [3H]desipramine binding with no significant alterations in either [3H]serotonin uptake or [3H]imipramine binding. These results suggest that the high-affinity binding of [3H]desipramine to rat brain membranes is pharmacologically and biochemically distinct from the high-affinity binding of [3H]imipramine, and that there is a close relationship between the high-affinity binding site for [3H]desipramine and the uptake site for norepinephrine.

Opposite modulatory effects of ovarian hormones on rat brain dopamine and serotonin transporters

The present study was designed to investigate the modulatory effect of gonadal steroids on brain dopamine (DA) and serotonin (5-HT) presynaptic transporters in female and male rats. Female and male rats were castrated and treated with either vehicle or gonadal hormones. The pharmacodynamic characteristics of the DA and 5-HT transporters were analyzed by [3H]BTCP and [3H]imipramine binding respectively. Ovariectomy (OVX) resulted in an upregulation of the striatal DA transporter and this alteration was prevented by estradiol (E2) or E2 + progesterone (P) treatment but not by P alone. In contrast to the DA transporter, the hypothalamic 5-HT transporter was down-regulated by OVX in female rats and this decrease was reversed by the administration of E2, P or their combination. The striatal DA transporter and the hypothalamic 5-HT transporter in male rat were not affected by orchidectomy or by administration of testicular hormone. Our findings indicate that ovarian, but not testicular, steroid hormones may play an important role in the regulation of brain DA and 5-HT transporters. It appears that ovarian hormones modulate rat brain 5-HT and DA transporters in opposite directions. These interactions between ovarian steroids and presynaptic transporters may be relevant to DA- and 5-HT-related neuropsychiatric disorders.

Modulatory effect of agents active in the presynaptic dopaminergic system on the striatal dopamine transporter

We have investigated the effects of agents active in the presynaptic dopaminergic system on the characterization of the rat striatal dopamine transporter. The dopamine transporter was characterized by high-affinity [3H]GBR 12935 (1-[2-diphenylmethoxy)-ethyl]-4-(3-phenylpropyl)-piperazine) binding to a membrane preparation and by [3H]dopamine uptake into striatal synaptosomes. Subchronic treatment with reserpine (2.5 mg/kg, 4 days), a monoamine depletor, caused a significant decrease in both [3H]GBR 12935 binding (20%) and [3H]dopamine uptake (51%). In contrast, amantadine (a dopamine releaser) treatment (20 mg/kg, 21 days) induced an increase (28%) in the maximal number of [3H]GBR 12935 sites. Chronic levo-dopa (dopamine precursor) treatment combined with carbidopa (50 mg/kg and 5 mg/kg respectively, 21 days) as well as benztropine (dopamine uptake inhibitor) treatment (10 mg/kg, 21 days) did not affect the striatal dopamine transporter characteristics. The present results showed that the striatal dopamine transporter is sensitive to changes in dopaminergic neurotransmission caused by agents that do not interact directly with the dopamine carrier.

Effects of tetrazole derivatives on [3H]diazepam binding in vitro: correlation with convulsant potency

A series of 8 tetrazole derivatives which differ more than one hundred-fold in their potencies as convulsants were tested for their abilities to inhibit [3H]diazepam binding to benzodiazepine receptors in vitro. The concentrations of drug necessary to inhibit 50% of specifically bound [3H]diazepam ranges from 18 micro M for undecamethylenetetrazole to 20 mM for trimethylenetetrazole. A comparison of the minimum convulsive doses for the 8 tetrazole derivatives tested with their relative potencies in displacing [3H]diazepam binding in vitro revealed a highly significant correlation (r = 0.98, P less than 0.001). In contrast, several representative tetrazole derivatives were found to have no inhibitory effects on beta-adrenergic, alpha-adrenergic or muscarinic cholinergic receptors in the same membrane preparation. These results suggest that pentamethylenetetrazole and related tetrazole derivatives may elicit their convulsant effects by interaction with the benzodiazepine receptor.

Upregulation of imipramine binding and serotonin uptake by estradiol in female rat brain

This report describes the effect of chronic estradiol treatment on the serotonin transporter in the female rat brain. Both [3H]imipramine binding and [3H]serotonin uptake increased by 20-30% in the frontal cortex and hypothalamus of ovariectomized rats after 12 days of 17 beta-estradiol treatment. No differences were observed in the binding and uptake parameters as a function of the rats' estrous cycle or in untreated ovariectomized rats, as compared to controls. Estradiol in vitro, inhibits [3H]imipramine binding as well as serotonin uptake in rat brain and human platelets. Like serotonin, estradiol decreases the dissociation rate in vitro of [3H]imipramine from its binding site in a dose-dependent manner.

Role of the orbital cortex and of the serotonergic system in a rat model of obsessive compulsive disorder

The serotonergic system and the orbitofrontal cortex have been consistently implicated in the pathophysiology of obsessive compulsive disorder. Yet, the relations between these two systems and the ways they interact in producing obsessions and compulsions are poorly understood. The present study tested the hypothesis that pathology of the orbitofrontal cortex leads to a dysregulation of the serotonergic system which is manifested in compulsive behavior, using a new rat model of this disorder. In the model, 'compulsive' behavior is induced by attenuating a signal indicating that a lever-press response was effective in producing food. We found that lesion to the rat orbital cortex led to a selective increase in compulsive lever-pressing that was prevented by the serotonin re-uptake inhibitor, paroxetine, and was paralleled by an increase in the density of the striatal serotonin transporter, assessed using high affinity [3H]imipramine binding. These results suggest that the serotonergic system is involved in orbital lesion-induced compulsivity, and provide a possible account for the observed association between obsessions and compulsions and dysfunction of the orbitofrontal cortex and of the serotonergic system in obsessive compulsive disorder.

Anticholinesterase and antiacetylcholine activity of 1-phenylcyclohexylamine derivatives

The antiacetylcholine and anticholinesterase potencies of four 1-phenylcyclohexylamine derivatives were estimated by measuring their antagonism to the contractile response of smooth and striated muscles and their inhibition of cholinesterase activity. In addition, their affinities towards the central muscarinic receptor from mouse brain homogenate were determined by competition experiments in vitro. Relative to atropine, these drugs exerted mild antimuscarinic activity in both isolated smooth muscle and in the competition experiments. On the other hand, they were found to exert antinicotinic potencies equal to that of d-tubocurarine in the striated muscle. The concentration of (3H)-phencyclidine taken up by mouse brain in vivo could be correlated with its dissociation constants from the central muscarinic binding sites, as well as with the Ki values for acetylcholinesterase inhibition, both determined in vitro. Since these drugs have a similar rigid spatial molecular structure, it is proposed that the variations in the potency of their cholinergic interactions stemmed mainly from the structural changes in the region of the 'cationic head'.

High affinity [3H]imipramine binding and serotonin uptake to platelets of adolescent females suffering from anorexia nervosa

High affinity [3H]imipramine binding and [3H]serotonin uptake to platelets were investigated in 17 anorexic females aged 15-18 years as compared to 15 healthy females of similar ages. A significant decrease in the density of [3H]imipramine binding sites was observed in anorexics as compared to controls (368 +/- 40 vs 517 +/- 38 fmoles/mg protein, p less than 0.01). No alteration in Kd values or in the kinetic parameters of serotonin uptake (Vmax, Km) were noted. The fact that the decrease in imipramine binding is not accompanied by a parallel reduction in serotonin uptake might indicate that anorexia nervosa is not ultimately related to major depression and that the imipramine binding site is not identical to the serotonin uptake site.

Regulation of rat brain vesicular monoamine transporter by chronic treatment with ovarian hormones

Ovarian steroids play an important role in neuroregulation and in the pathophysiology of various neuropsychiatric disorders. Most of the studies focused on the impact of gonadal steroids on post-synaptic receptors and plasma membrane transporters. In the present study, we evaluated the effect of chronic treatment with ovarian steroids on the expression of rat brain vesicular monoamine transporter (VMAT2). Ovariectomized rats were treated for 21 days with estradiol, progesterone or both. VMAT2 gene expression was assessed on the protein level by high affinity [3H]dihydrotetrabenazine ([3H]TBZOH) binding using autoradiography and on the mRNA level by in situ hybridization. Progesterone administration led to a decrease in [3H]TBZOH binding in the middle striatum and in the nucleus accumbens and to a parallel decrease in VMAT2 mRNA level in the substantia nigra pars compacta and dorsal raphè nuclei. Chronic estradiol treatment reduced VMAT2 mRNA level in the dorsal raphè and [3H]TBZOH binding in middle part of the striatum and nucleus accumbens but did not affect VMAT2 mRNA level in the substantia nigra pars compacta. Simultaneous administration of both ovarian steroids did not modulate VMAT2 mRNA in the substantia nigra pars compacta as well as [3H]TBZOH binding in the striatum or the nucleus accumbens but reduced VMAT2 mRNA level in the dorsal raphè. It appears that ovarian steroids may play a crucial role in the regulation of VMAT2 gene expression in the dopamine and serotonin systems. This modulatory activity may be relevant to synaptic and neuronal plasticity as well as to the molecular and cellular pathophysiology of gender-specific neuropsychiatric disorders.

Genome-wide expression profiling of human lymphoblastoid cell lines implicates integrin beta-3 in the mode of action of antidepressants

Selective serotonin reuptake inhibitors (SSRIs) are the first-line treatment for major depression. However, the link between inhibition of serotonin reuptake and remission from depression remains controversial: in spite of the rapid onset of serotonin reuptake inhibition, remission from depression takes several weeks, presumably reflecting synaptogenesis/neurogenesis and neuronal rewiring. We compared genome-wide expression profiles of human lymphoblastoid cell lines from unrelated individuals following treatment with 1 μM paroxetine for 21 days with untreated control cells and examined which genes and microRNAs (miRNAs) showed the most profound and consistent expression changes. ITGB3, coding for integrin beta-3, showed the most consistent altered expression (1.92-fold increase, P=7.5 × 10(-8)) following chronic paroxetine exposure. Using genome-wide miRNA arrays, we observed a corresponding decrease in the expression of two miRNAs, miR-221 and miR-222, both predicted to target ITGB3. ITGB3 is crucial for the activity of the serotonin transporter (SERT), the drug target of SSRIs. Moreover, it is presumably required for the neuronal guidance activity of CHL1, whose expression was formerly identified as a tentative SSRI response biomarker. Further genes whose expression was significantly modulated by chronic paroxetine are also implicated in neurogenesis. Surprisingly, the expression of SERT or serotonin receptors was not modified. Our findings implicate ITGB3 in the mode of action of SSRI antidepressants and provide a novel link between CHL1 and the SERT. Our observations suggest that SSRIs may relieve depression primarily by promoting neuronal synaptogenesis/neurogenesis rather than by modulating serotonin neurotransmission per se.

Demonstration of endogenous "imipramine like" material in rat brain

The extraction and partial purification of an endogenous "imipramine- like" material from rat brain is described. The endogenous factor obtained after gel filtration and silica chromatography inhibits [3H] imipramine specific binding and mimics the inhibitory effect of imipramine on [3H] serotonin uptake in both brain and platelet preparations. The effects of the endogenous material are dose-dependent and it inhibits [3H] imipramine binding in a competitive fashion. The factor is unevenly distributed in the brain with high concentration in the hypothalamus and low concentration in the cerebellum.

Sparing by rasagiline (TVP-1012) of cholinergic functions and behavior in the postnatal anoxia rat

Rasagiline (N-propargyl-1(R)aminoindan) is a selective and potent MAO-B inhibitor currently under development as the mesylate salt (TVP-1012) for the treatment of various neurologic disorders. Preliminary work in adult and senescent rats, either normal or hypoxia-lesioned, showed that chronic rasagiline treatment improved performance in memory and learning tasks, suggesting some beneficial effect on central cholinergic function. We have now used the postnatal anoxia-lesioned rat as a model of cholinergic dysfunction. In the neonatal rat, anoxia strongly affects the cholinergic system, which has not yet reached full maturation at this state of life. Rasagiline mesylate was administered from day 1 to completion of the study (day 60), first through nursing mother milk until weaning (day 21), then in drinking water, at the rate of 0.5 mg/kg/day. Drug access to the CNS was verified by analysis of MAO activity in brain (at 21 days). Treatment improved the juvenile hyperactivity syndrome associated with anoxia (at day 28). It improved performance in the passive avoidance test to normal control level (at day 40). It improved spatial memory performance in the Morris water maze to normal control level (at day 50). The untreated anoxia group failed in these tasks and was significantly inferior to either the normal control and rasagiline-treated anoxia groups. Determination of ChAT activity in the caudate and hippocampus of rats from each of these groups gave the following results (pmol ACh/mg protein/min). Caudate: normal control, 588 +/- 56; anoxia, 398 +/- 54; rasagiline-treated anoxia, 536 +/- 35. Hippocampus: normal control, 380 +/- 31; anoxia, 275 +/- 47; rasagiline-treated anoxia, 325 +/- 35. Results are mean +/- SD from each of seven to nine different donors in a group. Thus, improvement in memory and learning tasks of the rasagiline-treated anoxia group finds correspondence in the activity of the cholinergic marker ChAT in two brain regions that have prominent cholinergic innervation.

Subcellular distribution of high affinity [3H]imipramine binding and [3H]serotonin uptake in rat brain

The binding of [3H]imipramine to various subcellular fractions of rat brain was investigated. Using sodium free buffer or 0.5 microM chlorimipramine to define nonspecific binding, the specific binding was found to be associated with the synaptosomal fraction, as was the uptake of [3H]serotonin. A significant quantity of 'displaceable' binding was observed in the myelin and nuclear fractions when 'specific' binding was defined using only one concentration of [3H]imipramine and a large molar excess of chlorimipramine. This 'pseudospecific' binding was of low affinity and was not affected by the presence or absence of sodium.

Characterization of high-affinity [3H]TBZOH binding to the human platelet vesicular monoamine transporter

The present study indicates that human platelets can be used as an accessible peripheral model not only for the plasma membrane serotonin transporter, but also for the vesicular monoamine transporter. The vesicular monoamine transporter (VMAT2) is responsible for the accumulation of monoamines in the synaptic vesicles. VMAT2 differs from the plasma membrane transporters in its capability to recognize serotonin, histamine, norepinephrine and dopamine with almost the same affinity. Dihydrotetrabenazine (TBZOH) is a very potent inhibitor of VMAT2 that binds with high affinity to this transporter. [3H]TBZOH has been used as a ligand to label VMAT2 in human, bovine and rodent brain. In this study we characterized the pharmacodynamic and pharmacokinetic parameters of [3H]TBZOH binding in human platelets as compared to rat brain. The density (Bmax) and affinity (Kd) of [3H]TBZOH specific binding was assessed by Scatchard analysis. Association and dissociation rate constants (k(on), K(off)) were assessed by kinetic binding studies. In this study high-affinity and saturable binding sites for [3H]TBZOH were demonstrated in human platelets. Both the affinity of [3H]TBZOH to its binding site in platelets (Kd = 3.2+/-0.5 nM) and the kinetic rate constants (K(on) = 2.8 x 10(7) M(-1) min(-1); K(off) = 0.099 min(-1)) were similar to that in rat brain (Kd(striatum) = 1.5 nM; Kd(cerebral cortex) = 1.35 nM; K(on) = 2 x 10(7) M(-1) min(-1); K(off) = 0.069 min(-1)). Only the VMAT2 blockers tetrabenazine and reserpine inhibited [3H]TBZOH specific binding.