Salomon Z. Langer

Preferential metabolism of (—)-3H-norepinephrine through the deaminated glycol in the rat vas deferens

Abstract A method for separation of norepinephrine (NE) and its metabolites by the combined use of Alumina and Dowex columns is described. The most commonly used eluents, 0·2 N acetic acid, 0·04 N perchloric acid or 0·2 N HC1, were found to elute 3,4-dihydroxyphenylglycol (DOPEG) together with NE from Alumina. The use of Dowex columns for further separation of NE from DOPEG was essential to measure labeled NE without contamination. With the use of the method described in this publication, the metabolism of (—)− 3 H-NE released spontaneously from the rat vas deferens was studied. 3 H-DOPEG was the main metabolite in the spontaneous outflow, and it accounted for 70 per cent of the total radioactivity. In the presence of cocaine (10 −5 M), there was a decrease in the percentage of DOPEG while the proportion of NE rose significantly. Phenoxybenzamine (3 × 10 −5 M) elicited an increase in total outflow of radioactivity which was mainly composed of the deaminated glycol, DOPEG.

Characterization of [3H]paroxetine binding to rat cortical membranes

Paroxetine is a selective and potent inhibitor of 5-hydroxytryptamine uptake into serotonergic neurons. The specific binding of [3H]paroxetine to rat cortical membranes at 22 degrees C was examined in this study. Our results indicate the presence of a single saturable high affinity binding component for [3H]paroxetine. Scatchard analysis revealed a Kd of 0.15 +/- 0.01 nM, and a Bmax of 549 +/- 36 fmol/mg protein. The kinetically derived dissociation constant was 0.034 +/- 0.008 nM. [3H]Paroxetine binding was inhibited selectively by 5-HT uptake blockers, and a good correlation was demonstrated between the potency of various drugs to inhibit [3H]paroxetine binding and [3H]5-hydroxytryptamine uptake. Also, lesions performed with the neurotoxin, 5,7-dihydroxytryptamine resulted in a 94% decrease in endogenous 5-hydroxytryptamine levels and concomitantly, a 90% reduction in [3H]paroxetine binding when compared to sham controls. These results indicate that the binding site labelled by [3H]paroxetine is associated with the neuronal 5-hydroxytryptamine transporter complex.

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.

Specific 3H-imipramine binding in human platelets

SummaryHuman platelets have been shown to possess high-affinity binding sites for 3H-imipramine. These binding sites have a similar affinity and drug specificity to those already described in rat brain. The platelets from healthy volunteers show no difference in 3H-imipramine binding between the sexes but there is a decrease in maximal 3H-imipramine binding with increasing age of the donor.

Sodium dependent [3H]cocaine binding associated with dopamine uptake sites in the rat striatum and human putamen decrease after dopaminergic denervation and in Parkinsons disease.

SummaryThe binding of radiolabelled cocaine, an inhibitor of dopamine uptake, to the post-mortem human putamen was studied and compared to that in the rat striatum. Saturation analysis of [3H]cocaine binding to the human putamen revealed the presence of a high affinity component of binding with a Kd of 0.21 μmol/l and a Bmax of 1.47 pmol/mg protein. In addition a low affinity component (Kd=26.4 μmol/l) was demonstrated, having a Bmax of 42.2 pmol/mg protein. Also in the rat striatum [3H]cocaine binding was both of high affinity (Kd=0.36 μmol/l, Bmax=5.56 pmol/mg protein) and low affinity (Kd=25.9 μmol/l, Bmax=35.6 pmol/mg protein). A pharmacological characterisation of high affinity [3H]cocaine binding to rat striatal membranes clearly indicates an association with the neuronal dopamine transporter. The IC50 values of 8 selected drugs for inhibition of [3H]cocaine binding in the rat striatum were highly significantly correlated with their potency to inhibit [3H]dopamine uptake into slices of the rat striatum. [3H]Cocaine binding was stereospecifically inhibited by (+)nomifensine and (+)diclofensine which were 50–80-fold more active than their respective (-)isomers. Drugs with dopamine releasing activity were more potent at inhibiting [3H]dopamine uptake than at competing for the high affinity site of [3H]cocaine binding. A highly significant correlation was found between IC50 values for [3H]cocaine binding in the rat striatum and the human putamen. Further evidence in support of an association of [3H]cocaine binding in the rat striatum with the dopamine transporter was obtained from lesion studies. Thus, intranigral 6-hydroxydopamine administration produced a marked (67%) decrease in striatal [3H]cocaine binding. Also in the human putamen high affinity [3H]cocaine binding sites appear localized on dopaminergic nerve terminals as evidenced by a prominent decrease in binding in the putamen obtained from subjects with Parkinsons disease. It is concluded that [3H]cocaine may be a useful ligand to examine the dopamine transporter in the rat striatum and the human putamen. Therefore it offers a new and valuable approach in the study of drug effects and neuropsychiatric diseases.

Pharmacological profile of the imidazopyridine zolpidem at benzodiazepine receptors and electrocorticogram in rats

SummaryZolpidem is a novel non-benzodiazepine related hypnotic, which possesses an imidazopyridine structure. This drug has preferential affinity for the3H-diazepam binding site in the rat cerebellum, while it is only weakly active at inhibiting3H-Ro 5-4864 binding to the rat kidney. The potency of zolpidem at displacing3H-Ro 15-1788 binding to rat cerebral cortex membranes is enhanced in the presence of GABA. On the sleep pattern of the electrocorticogram in the curarised rat, zolpidem induces a physiological type of slow wave sleep with rapid onset of action. Zolpidem differs from classical benzodiazepine drugs, in possessing an atypical binding profile to3H-benzodiazepine receptors, and because it does not affect the sleep patterns.

Localisation of tricyclic antidepressant binding sites on serotonin nerve terminals.

Abstract: High‐affinity specific [3H]imipramine binding has been demonstrated in the brain and platelets of various species including man. Electrolytic lesion of the rat dorsal raphe, which resulted in a significant decrease in the endogenous levels of serotonin produced a reduction in the density of [3H]imipramine binding sites in the hypothalamus and cortex. The affinity constants were unchanged. These results suggest that [3H]imipramine binding sites are located on serotonin nerve terminals.

High-affinity binding of 3H-imipramine in brain and platelets and its relevance to the biochemistry of affective disorders

Abstract Specific high-affinity binding of 3 H-imipramine has been demonstrated in the brain of various species including man. These binding sites have many of the characteristics to be expected for a pharmacological receptor and appear to be associated with the neuronal uptake mechanism for serotonin. Different antidepressant treatments like chronic administration of tricyclic antidepressants, chronic electroshock or sleep-deprivation result in decreases in the density of 3 H-imipramine binding sites in normal animals. 3 H-imipramine binding sites have also been found in blood platelets from different species including man. These sites are identical to those described in the brain. Clinical studies have shown that untreated severely depressed patients have a lower density of 3 H-imipramine binding sites in their platelets when compared with control volunteers of the same age and sex. Longitudinal studies indicate that the low density of 3 H-imipramine binding sites does not change during treatment with tricyclic antidepressant drugs and the subsequent clinical recovery from depression. 3 H-imipramine binding in brain and platelets is proposed as a useful research tool in biochemical and clinical studies in affective disorders.

Complex Inhibition of [3H]Imipramine Binding by Serotonin and Nontricyclic Serotonin Uptake Blockers

Abstract: Tricyclic antidepressant drugs inhibit [3H]imipramine binding to the rat brain cortex in a competitive manner, giving linear Hofstee plots and Hill coefficients of approximately 1.0. Serotonin, the only neurotransmitter to inhibit [3H]imipramine binding, does so in a complex manner, exhibiting a Hill coefficient of 0.40‐0.50. Nontricyclic inhibitors of serotonin uptake such as fluoxetine, paroxetine, norzimelidine, and citalopram inhibit [3H]imiprarnine binding in the same complex manner as serotonin. These results are interpreted as suggesting that [3H]imipramine binds to a site associated with the serotonin uptake system but different from either the substrate recognition site for serotonin or the site of action of the nontricyclic inhibitors of neuronal uptake of serotonin.

High-affinity 3H-imipramine binding in platelets from untreated and treated depressed patients compared to healthy volunteers

Specific high-affinity binding of 3H-imipramine to human platelets possesses very similar characteristics to the sites previously described in animal and human brains. In a study comparing the binding of 3H-imipramine in platelets obtained from 39 control volunteers with 37 hospitalized, untreated, severely depressed patients, the maximal binding of 3H-imipramine was found to be significantly lower in the depressed population. There were no differences in the KD values. After 7–15 days of treatment with tricyclic antidepressant drugs, there was an improvement in the degree of the depression but no significant change in the maximal 3H-imipramine binding. After an average of 50 days treatment, Hamilton ratings had returned to normal, but the 3H-imipramine binding values remained unchanged.