Paul R. Paetsch

Effects of chronic antidepressant treatment of β-adrenoceptor subtype binding in the rat cerebral cortex and cerebellum

The effects of desipramine, tranylcypromine, and phenelzine on beta-adrenoceptor subtype binding were measured in rat cerebral cortex and cerebellum. The drugs were administered to male Sprague Dawley rats for 28 d sc via 2ML4 Alzet osmotic minipumps (desipramine HCl 10, tranylcypromine HCl 1, phenelzine sulfate 5, 10 mg kg-1/d). Binding of [3H]CGP 12177 was measured to determine total beta-adrenoceptor density in each brain region. The relative densities of beta 1- and beta 2-adrenoceptors were directly calculated from competition analysis using ICI 89406 to displace [3H]CGP 12177. beta 1-Adrenoceptor density was decreased in cortical tissue following each antidepressant treatment, but no effects on beta 2-adrenoceptor density were evident. With cerebellar tissue, despite a higher density of beta 2-adrenoceptors in this area, no effects of antidepressants on beta 2-adrenoceptor density were evident. The present data confirm and extend previous reports of beta 1- but not beta 2-adrenoceptor downregulation in brain following chronic antidepressant drug treatment.

β-adrenoceptors and antidepressants: Possible 2-phenylethylamine mediation of chronic phenelzine effects

Effects of chronic administration of antidepressant drugs on beta-adrenoceptor function were assessed. Tricyclics (imipramine 30 mg/kg/day, desipramine 5 and 10 mg/kg/day) and monoamine oxidase inhibitors [(+/-)-tranylcypromine 1 mg/kg/day, phenelzine 5 and 10 mg/kg/day] were administered to Male Sprague-Dawley rats (n = 8), via Alzet 2ML2 osmotic minipumps for 28 days. Pumps were implanted subcutaneously in the interscapular region and replaced after 14 days. On days 21 and 22 motor-suppressant actions of the beta-adrenoceptor agonist salbutamol (3 mg/kg intraperitoneally [IP]) were assessed as a measure of beta-adrenergic receptor sensitivity. On day 28 the animals were killed and their brains used for measurement of drug levels and monoamine oxidase activity. Liver tissue was used to measure the trace amine 2-phenylethylamine. Each drug induced a decrease in the response to salbutamol. With phenelzine the decreased response to salbutamol was not observed at the lower dose. Differences in monoamine oxidase inhibition following phenelzine did not correspond to differential effects on functional beta-adrenergic sensitivity. Levels of 2-phenylethylamine, an endogenous amine that is also a metabolite of phenelzine, were significantly higher in the 10-mg/kg/day phenelzine group. These data suggest that 2-phenylethylamine may be one mediator of the chronic actions of phenelzine on beta-adrenoceptors.

Electron-capture gas chromatographic procedure for simultaneous determination of amphetamine and N-methylamphetamine.

An electron-capture gas chromatographic procedure for the simultaneous determination of amphetamine and N-methylamphetamine in biological samples is described. The method employs extraction with the ion-pairing reagent bis(2-ethylhexyl)phosphoric acid, and back-extraction with 0.5 M hydrochloric acid. The hydrochloric acid phase is basified, and the amphetamines and the internal standard benzylamine are derivatized with pentafluorobenzenesulfonyl chloride prior to analysis on a gas chromatograph equipped with a capillary column. Levels of amphetamine and N-methylamphetamine have been determined in the urine and liver of rats treated chronically with (-)-deprenyl.

β-Adrenergic Effects on Plasma and Brain Large Neutral Amino Acids Are Unaltered by Chronic Administration of Antidepressants

Abstract: Effects of isoproterenol (3 mg kg−1, i.p. for 60 min) and salbutamol (3, 10 mg kg−1, i.p. for 60 min) on large neutral amino acid concentrations in rat plasma and brain were assessed. Phenylalanine, leucine, isoleucine, and valine were measured by gas chromatography with electron‐capture detection; tyrosine and tryptophan were measured by HPLC with electrochemical detection. These drugs induced increases in brain tryptophan, tyrosine, phenylalanine, and valine and decreases in plasma tryptophan, tyrosine, leucine, isoleucine, and valine. Effects of salbutamol (3 mg kg−1, i.p. for 60 min) were assessed following chronic administration of phenelzine sulfate and desipramine · HCl (each drug 10 mg kg−1 per day, s.c. via Alzet 2ML4 osmotic minipumps for 28 days). There were no effects of these antidepressants on basal levels of large neutral amino acids in brain and plasma. In both brain and plasma, salbutamol‐induced changes in large neutral amino acids were unaffected by these antidepressants. The results indicate that β‐adrenoceptor‐regulated availability of plasma and brain large neutral amino acids is unaffected by chronic administration of tricyclic or monoamine oxidase inhibitor antidepressants.

Effects of chronic antidepressant treatment on dopamine-related [3H]SCH 23390 and [3H]Spiperone binding in the rat striatum

Summary1.The effects of chronic administration of antidepressants on dopaminerelated [3H]SCH 23390 and [3H]spiperone binding to rat striatal membranes were assessed.2.The monoamine oxidase inhibitors phenelzine (5 or 10 mg kg−1/day) and tranylcypromine (1 mg kg−1/day) and the tricyclic desipramine (10 mg kg−1/day) were administered for 28 days by constant subcutaneous infusion using Alzet (2ML4) osmotic minipumps.3.These treatments did not alterKd estimates for either [3H]SCH 23390 or [3H]spiperone binding sites. The monoamine oxidase inhibitors induced a decrease in theBmax values for both [3H]SCH 23990 and [3H]spiperone binding sites. Desipramine induced a decrease in theBmax value for [3H]SCH 23390 binding but had no effect on theBmax value for [3H]spiperone binding.

Down-regulation of beta-adrenergic and dopaminergic receptors induced by 2-phenylethylamine.

Summary1.The effects of chronic administration (28 days s.c. via Alzet osmotic minipumps) of 2-phenylethylamine·HC1 (10 mg kg−1 per day) and/or ( − )-deprenyl⋅HC1 (1 mg kg−1 per day) on dopamine and noradrenaline receptor subtypes have been measured in rat brain.3H-CGP 12177 was used to labelβ-adrenoceptors;3H-spiperone and3H-SCH 23390 were used to label D2-like and D1-like receptors.2.Total corticalβ-adrenoceptor density was reduced by ( − )-deprenyl but not 2-phenylethylamine alone. Combined administration of 2-phenylethylamine and ( − )-deprenyl resulted in a significantly larger decrease than ( − )-deprenyl alone. Subtype density analysis by competition experiments with ICI 89406 revealed that the ( − )-deprenyl effect in cortex was due to a decrease inβ1-adrenoceptor density. The combination of 2-phenylethylamine and ( − )-deprenyl resulted in a significant decrease in both corticalβ1- and corticalβ2-adrenoceptors. Cerebellarβ-adrenoceptor density was not altered by the present drug treatments. TheKd values for totalβ-adrenoceptor densities andKi values forβ-adrenoceptor subtype densities were not altered by drug treatment in either cortex or cerebellum.3.Administration of 2-phenylethylamine and of ( − )-deprenyl resulted in a decrease in the density of D1-like3H-SCH 23390 but not D2-like3H-spiperone binding to dopamine receptors in the striatum. The effects of combined 2-phenylethylamine and ( − )-deprenyl treatment on3H-SCH 23390 binding were additive. These drug treatments did not alterKd values for these binding sites.4.The down-regulation of catecholamine receptors following chronically increased availability of 2-phenylethylamine may be due to the catecholamine releasing or uptake blocking effects of this amine. These effects may also be attributable to a direct neuromodulatory action of 2-phenylethylamine on catecholamine receptors.5.The parallels between effects of increased 2-phenylethylamine availability and effects of administration of MAO inhibitor antidepressants on catecholamine receptor systems indicate that this substrate for MAO may mediate some of the effects of MAO inhibitor antidepressants.

Failure to detect amphetamine or 1-amino-3-phenlypropane in humans or rats receiving the MAO inhibitor tranylcypromine

BACKGROUND There have been conflicting reports in the literature about whether or not tranylcypromine is metabolized to amphetamine. In the current report, we investigated this possible route of metabolism in both rats and humans. Body fluid samples from patients and rats and brain, liver and heart samples from rats were analyzed for levels of amphetamine and 1-amino-3-phenylpropane, another potential product of cleavage of the cyclopropyl ring of tranylcypromine after administration of tranylcypromine. Extracted samples were reacted with pentofluorobenzenesulfonyl chloride and analyzed using electron-capture gas chromatography. RESULTS Amphetamine or 1-amino-3-phenylpropane were not found in any of the samples, indicating that opening of the cyclopropyl ring of tranylcypromine is not a significant route of metabolism for this drug at usual doses. LIMITATIONS The assay procedure did not permit analysis of 1-amino-2-phenylpropane (another possible product of cleavage of the cyclopropyl ring of tranylcypromine) or of N-methylamphetamine. CONCLUSIONS These studies support the growing body of evidence indicating that opening of the cyclopropyl ring of tranylcypromine to form amphetamine, a drug of abuse, is not significant at usual doses of tranylcypromine.

Chronic antidepressant drug treatment attenuates motor-suppressant effectsof apomorphine without changing [3H]GBR 12935 binding

The effects of chronic administration (28 days s.c. via osmotic minipumps) of the antidepressants phenelzine sulphate, desipramine hydrochloride and clomipramine hydrochloride (each at 10 mg/kg per day) on dopamine function have been measured in rats. Both phenelzine and desipramine attenuated the suppression of locomotor activity induced by apomorphine hydrochloride (0.05 mg/kg s.c. 15 min). Clomipramine did not affect the behavioural response to apomorphine. Analyses of brain tissue from these animals using the radioligand [3H]GBR 12935 revealed that there were no changes in dopamine uptake site density or affinity following the administration of phenelzine, desipramine or clomipramine. Analyses of brain monoamine oxidase activity and tricyclic levels were used to confirm the efficacy of the drug administration protocol. These data indicate that changes in dopamine uptake site density do not mediate antidepressant-induced changes in behavioural responses to apomorphine.

A rapid procedure for the analysis of phenylalanine in brain tissue utilizing electron-capture gas chromatography

A rapid procedure has been developed for the analysis of phenylalanine in brain tissue. Perchloric acid extracts of brain tissue were made basic, and benzoyl chloride was added to derivatize the amine function. The aqueous layer was retained and made slightly acidic. To derivatize the carboxylic acid group, a solution of pentafluorobenzyl alcohol was added in the presence of the coupling agent dicyclohexylcarbodiimide and chloroform. After shaking for 15 min, the organic phase was retained and taken to dryness. The residue was taken up in toluene, washed, and an aliquot used for analysis on a gas chromatograph equipped with an automatic injector, a capillary column and an electron-capture detector. The procedure has been utilized for analysis of phenylalanine in brains of rats treated with vehicle or phenylalanine.

Monoamine oxidase inhibitors: effects on tryptophan concentrations in rat brain

It has been suggested that inhibition of tryptophan (Trp) pyrrolase and a subsequent elevation of brain Trp may contribute to the actions of antidepressant drugs. In our laboratories, we have conducted a series of experiments measuring brain Trp levels in the rat after both acute and chronic administration of several monoamine oxidase (MAO) inhibitors. The drugs studied during the course of the long-term (28 day) experiments were phenelzine, N2-acetylphenelzine, tranylcypromine, 4-fluorotranylcypromine, 4-methoxytranylcypromine and (-)-deprenyl. High-pressure liquid chromatography with electrochemical detection was employed to measure Trp levels in brains of both MAO inhibitor- and vehicle-treated animals. No significant increases in brain Trp levels were observed as a consequence of MAO inhibitor treatment. Acute time-response (up to 24 h) and dose-response studies were conducted following the administration of phenelzine and tranylcypromine. Only after administration of high doses of these drugs was an elevation in brain Trp observed and the increase was relatively short-lived. These results suggest that elevation of brain Trp may be an important factor in the actions of MAO inhibitors only at high doses of these drugs.