Effect of 2-(p-chlorophenyl)cyclopropylamine on 5-hydroxyindole concentration and monoamine oxidase activity in rat brain.

p-Chloroamphetamine (PCA) causes a rapid and long-lasting depletion of serotonin in rat brain [l]. PCA is thought to affect serotonin neurons acutely by (a) inhibition of tryptophan hydroxylation, (b) release of vesicular bound serotonin, (c) inhibition of serotonin reuptake from the synaptic cleft, and (d) inhibition of serotonin oxidation by monoamine oxidase, and to produce neurotoxic degeneration of some serotonin neurons resulting in a chronic decrease in tryptophan hydroxylase activity, serotonin and S-hydroxyindoleacetic acid (S-HIAA) concentration, and serotonin uptake capacity (variables associated specifically with serotonin neurons). Among the analogs of PCA that have been studied [I], N-cyclopropyl-PCA is characterized by being a potent irreversible inhibitor of monoamine oxidase [2]. Its relatively greater inhibition of monoamine oxidase than that by PCA results in serotonin concentration not being decreased initially (during the first 24 hr), whereas at 1 week, when the monoamine oxidase-inhibiting effects have diminished, serotonin concentration is decreased [2]. 5HIAA concentration decreases rapidly and remains decreased at 1 week after N-cyclopropyl-PCA injection [2]. Thus, N-cyclopropyl-PCA (a) inhibits monoamine oxidase and (b) has PCA-like serotonin-depleting activity. These two actions have been dissociated first by giving harmaline, which protects against the irreversible inactivation of type A monoamine oxidase by N-cyclopropylPCA and exposes its ability to deplete serotonin earlier (31, and second by giving fluoxetine. which inhibits Ncyclopropyl-PCA uptake into serotonin neurons and thus prevents its depletion of serotonin but permits monoamine oxidase inhibition to occur [4]. We are describing here studies on a PCA analog similar in structure to N-cyclopropyl-PCA but with the cyclopropyl group interposed between the p-chlorophenyl group and the amino group. The structure of this compound. 2-(pchlorophenyl) cyclopropylamine (PCCA), is shown in Fig. 1 compared to PCA and N-cvclopropvl-PCA. In these experiments, 13&20dg male Wistar rats from Harlan Industries, Cumberland, IN, were used. The rats were housed in hanging wire cages in a light-controlled room (12 hr light/l2 hr dark) and had free access to food and water. PCCA hydrochloride was synthesized at the Smith Kline & French Laboratories. Chromatographic and spectral data indicated that it consists of 77.6% tram and 22.4% cls isomers. Harmaline hydrochloride was purchased from the Sigma Chemical Co., St. Louis, MO. PCCA was injected at a dose of 0.05 mmole/kg, the same as that used previously for N-cyclopropyl-PCA [2]. Both drugs were injected i.p. in aqueous solutions. Rats were decapitated after treatment, and brains were rapidly excised. split longitudinally along with the midline. and frozen on dry ice. Tissue samples were stored at 15” prior to analysis. Serotonin and 5-hydroxyindoleacetic acid concentrations were determined spectrofluorometrically after extraction and reaction with o-phthalaldehyde by the method of Miller et al. [5]. Monoamine oxidase activity was assayed with 100 pM [14C]serotonin or 80 pM [“C]phenylethylamine (from New England Nuclear. Boston, MA) as substrate [6]. The effects of PCCA on 5-hydroxyindole concentrations in rat brain at various times are shown in Table 1. Within p-Chloroamphetamine (PCA)