David J. Brunswick

Quantitative autoradiography of serotonin uptake sites in rat brain using [3H]cyanoimipramine

The binding of [3H]cyanoimipramine to serotonin uptake sites in rat brain slices was studied using quantitative autoradiography. Binding was of high affinity and was to a single class of binding site. This is in contrast to results previously obtained by others with [3H]imipramine where two binding sites were observed. The sites labeled by [3H]cyanoimipramine had properties consistent with this ligand labeling serotonin uptake sites, as: (1) binding is displaced by drugs which are potent inhibitors of serotonin uptake but not by drugs which are weak inhibitors of uptake; (2) binding is dependent on the presence of sodium ions as is the uptake of serotonin; (3) binding is almost completely eliminated in the brains of rats lesioned by the serotonin neurotoxin 5,7-dihydroxytryptamine; (4) the distribution of binding sites throughout the rat brain is highly correlated with that found previously for [3H]indalpine, a potent serotonin uptake inhibitor, and for [3H]imipramine. The properties of binding of [3H]cyanoimipramine make it an ideal ligand for the quantitative autoradiography of serotonin uptake sites.

[3H]Nisoxetine: a new radioligand for norepinephrine uptake sites in brain

[3H]Nisoxetine binds with high affinity (Kd = 0.7 nM) and selectivity to a homogenous population of sites associated with the uptake of norepinephrine. Specific [3H]nisoxetine binding to rat cortical homogenates was saturable, sodium-dependent and averaged 90% of total binding at its Kd concentration. Pretreatment with the neurotoxin DSP-4 resulted in 95% decrease in binding. [3H]Nisoxetine exhibits superior properties to radioligands previously used and appears to be the radioligand of choice for studies involving uptake sites for norepinephrine.

Lack of effect of high-dose cocaine on monoamine uptake sites in rat brain measured by quantitative autoradiography.

There have been a number of claims that high-dose administration of cocaine to rats leads to neurotoxic effects on dopamine neurons. In this study possible neurotoxic effects on monoamine neurons were examined by measuring the effects of cocaine (35 mg/kg daily for 10 days) on the binding of radioligands to uptake sites for dopamine, serotonin and norepinephrine using quatitative autoradiography. No effects of cocaine on any of the binding sites were observed and therefore, it is concluded that cocaine, unlike amphetamine derivatives which have similar pharmacologic properties, does not produce neurotoxic effects on monoamine neurons.

Prediction of steady‐state imipramine and desmethylimipramine plasma concentrations from single‐dose data

Tricyclic antidepressant plasma levels were measured in patients and healthy subjects after a single dose of desmethylimipramine (DM1) or imipramine (IMl) and after chronic dosing to steady states. Tricyclic plasma levels measured 24 hr after the single oral dose correlated with steady‐state plasma levels. In patients receiving DM1 there was a correlation (r = 0.97, n = 10) between 24‐hr and steady‐state DM1 levels, while in normal subjects receiving IMI the correlation was r = 0.92 (n = 20) between 24‐hr and steady‐state total tricyclic levels (IMI plus its metabolite, DMI). These results suggest the possibility that after a test dose of tricyclic antidepressant, a patient may be put on a “therapeutic” dosage regimen without delay.

Effects of high-dose methamphetamine administration on serotonin uptake sites in rat brain measured using [3H]cyanoimipramine autoradiography.

Repeated administration of high doses of methamphetamine (15 mg/kg given for 5 doses over 24 h) resulted in long-term decreases in the binding of [3H]cyanoimipramine ([3H]CN-IMI) to serotonin uptake sites measured using quantitative autoradiography. Seven days after termination of drug administration decreases were seen in 23 of 28 regions examined. This is consistent with previous studies indicating that methamphetamine and related amphetamines are neurotoxic to serotonin neurons. Significant decreases were still present in many brain areas on the same dosage schedule 30 days after drug administration. However, the number of areas affected was considerably less, consistent with some regrowth of serotonin neurons. At a lower dosage (7.5 mg/kg on the same schedule) no effects on [3H]CN-IMI binding were seen. The results of this study provide support for the serotonergic neurotoxicity of repeated methamphetamine administration in rats. They also show that the neurotoxicity is highly regional and dose dependent.

The effect of antidepressant drugs on regional cerebral glucose utilization in the rat

The 2-deoxyglucose (2-DG) technique is a potentially powerful method for assessing the effect of centrally acting drugs on local neuronal function in the brain. Since little is established on the effect of antidepressant drugs on local functional activity throughout the brain, we have employed this technique to study the effects of desmethylimipramine (DMI), a tricyclic antidepressant, and assessing the effect of centrally acting drugs on local neuronal function in the brain. Since little is established on the effect of antidepressant drugs on local functional activity throughout the brain, we have employed this technique to study the effects of desmethylimipramine (DMI), a tricyclic antidepressant, and assessing the effect of centrally acting drugs on local neuronal function in the brain. Since little is established on the effect of antidepressant drugs on local functional activity throughout the brain, we have employed this technique to study the effects of desmethylimipramine (DMI), a tricyclic antidepressant, and phenelzine, a monoamine oxidase inhibitor used clinically as an antidepressant, on local glucose utilization. The drugs were administered either as an acute dose, or repeatedly for 7 days, or chronically for 28 days. The local metabolic rate of glucose was determined in 30 regions of rat brain. Acute DMI increased glucose utilization in 11 regions whereas, in contrast, chronic DMI decreased glucose utilization in 7 regions of rat brain. Many of the areas affected are those of the telencephalon and diencephalon that receive prominent noradrenergic innervation. This is consistent with the notion that acute DMI treatment leads to enhanced and chronic DMI treatment leads to reduced noradrenergic functioning in the CNS. In contrast to these effects with DMI, phenelzine had little effects on glucose utilization either after acute or chronic dosing.

Plasma and erythrocyte electrolytes in affective disorders.

Plasma and erythrocyte sodium (Na+), total and free (ultrafiltrable) plasma magnesium (Mg2+) as well as erythrocyte magnesium were measured in patients with affective disorders and in healthy control subjects. Depressed and manic patients had higher total plasma Mg2+ than did hospitalized healthy control subjects, but concentrations of ultrafiltrable Mg2+ did not differ. Although erythrocyte Mg2+ was significantly elevated in the depressed subjects in comparison with that found in the non-hospitalized healthy controls, this difference was not seen between the depressives and the hospitalized healthy controls. Depressed, manic or healthy control subjects did not differ with respect to either plasma or erythrocyte.

Radioimmunoassay of imipramine and desmethylimipramine.

Abstract A sensitive radioimmunoassay has been developed for the determination of plasma levels of the tricyclic antidepressants imipramine and desmethylimipramine. Antisera were prepared by immunizing rabbits with N-succinylnortriptyline-bovine serum albumin conjugate. The assay required a preliminary extraction procedure to remove interfering metabolites and separate desmethylimipramine from imipramine. Using 3 H-imipramine as tracer, the radioimmunoassay can measure imipramine and desmethylimipramine levels down to 10 ng/ml using a 0.1 ml plasma sample. Agreement between the radioimmunoassay and a gas-chromatographic assay was excellent for both imipramine (r=0.97) and desmethylimipramine (r=0.99).

A Study of Growth Hormone Release in Depression

Interest in biogenic amine function in affective disorders has stimulated a variety of research strategies including the measurement of hormonal response to a variety of stimuli as an indirect method of investigating the integrity of aminergic function in clinically depressed patients. Apomorphine and levodopa are known to stimulate growth hormone release via a dopaminergic pathway in median eminence. Administration of these agents to groups of depressed patients and age, sex-matched normal control subjects did not indicate any significant abnormality in this dopaminergic system.

Fluoxetine and norfluoxetine plasma concentrations during relapse-prevention treatment

BACKGROUND Virtually no attention has been given to the relationship between antidepressant plasma drug concentrations and relapse-prevention during maintenance therapy. The purpose of this study was to investigate the relationship between steady-state plasma drug concentrations and outcome during relapse-prevention therapy with fluoxetine. METHODS The patients studied had responded to acute fluoxetine treatment for major depression (defined by DSM-III-R). Patients who met criteria for remission after 10-12 weeks of open-label acute fluoxetine therapy (N=395 of 839 patients), were randomly assigned to one of four treatment arms (50 weeks of fluoxetine, 38 weeks of fluoxetine followed by 12 weeks of placebo, 14 weeks of fluoxetine followed by 36 weeks of placebo and 50 weeks of placebo). Plasma fluoxetine and norfluoxetine concentrations were measured (1) after 4 and 8 weeks of open-label treatment and (2) at the beginning and after 14 weeks of double-blind, relapse-prevention therapy. RESULTS Mean drug plasma levels were stable throughout the study. There was no significant difference in steady state plasma levels for the patients who relapsed compared to those who completed fluoxetine therapy without relapsing after 14, 38 or 50 weeks of fluoxetine relapse-prevention treatment. In addition, time-to-relapse was not related to steady-state drug plasma levels. Finally, after dividing patients into two groups based on their drug plasma levels, no significant differences were seen in the cumulative proportions of patients staying well during relapse-prevention therapy. DISCUSSION Plasma concentrations of fluoxetine and/or its metabolite norfluoxetine, are not correlated with relapse in patients treated with a fixed dose of 20 mg/day fluoxetine. Fluoxetine plasma levels cannot be used to guide relapse-prevention treatment.