Stereoselective accumulation of hydroxylated metabolites of amphetamine in rat striatum and hypothalamus.

The stereoselective accumulation of alpha-methyl-p-tyramine (AMPT) and alpha-methyl-p-octopamine (AMPO) in rat striatum and hypothalamus after acute and chronic administration of the (+)- and (-)-isomers of amphetamine (Amphet) and the acute administration of (+)- and (-)-AMPT has been investigated by chemical ionization gas chromatography mass spectrometry (c.i.g.c.m.s.). Two h after the administration of (+)- or (-)-AMPT (5 mg kg-1 i.p.), the concentrations of the isomers in striatal tissue were approximately equal; 18 h later, the concentration of the (+)-isomer was 10 times that of the (-)-isomer. The concentrations of AMPO in the striatum and hypothalamus 20 h after administration of (+)-AMPT were 68 ng g-1 and 484 ng g-1 respectively. After the administration of the (-)-isomer of AMPT, small quantities of AMPO were detected in both brain areas. Twenty h after the last of 7 daily injections of (+)-Amphet (5 mg kg-1, i.p.), the concentration of AMPO in the hypothalamus was 5.4 times the concentration at 20 h after one injection. In the striatum, the corresponding ratio for AMPO was 3.5 and for AMPT was 2.5. These data indicate that, although both isomers of AMPT formed from Amphet administered systemically, cross the blood brain barrier, the (+)-isomers AMPT and AMPO are preferentially stored in striatal and hypothalamic aminergic nerve terminals. The accumulations of AMPT and AMPO in rat striatum and hypothalamus after chronic administration of Amphet demonstrates that these metabolites persist in neuronal storage in these brain areas for days after administration. The half-lives of (+)-AMPT and (+)-AMPO in striatal neuronal storage, calculated from this data, were 1.5 days and 2.5 days, respectively. The corresponding half-life for hypothalamic (+)-AMPO was 7 days. 7. These findings suggest the involvement of accumulated AMPT and AMPO in the development of behavioural augmentation to repeated injections of Amphet (Randrup & Munkvad, 1970).

Effect of chlordimeform and clonidine on the turnover of P-octopamine in rat hypothalamus and striatum.

The effect of the invertebrate octopamine agonists chlordimeform and clonidine on the concentration and turnover of p-octopamine and m- and p-tyramine was determined in rat hypothalamus and striatum. Clonidine (0.25 mg/Kg, s.c.) did not alter the concentration of p-octopamine in the hypothalamus or p-tyramine in the striatum. Administration of chlordimeform (50 mg/Kg, i.p.) resulted in an increase in p- and m-tyramine concentrations in the striatum but not that of p-octopamine in the hypothalamus. This increase in the tyramine isomers is consistent with the ability of chlordimeform and its metabolite, demethylchlordimeform, to inhibit monoamine oxidase (MAO). The concurrent administration of chlordimeform (50 mg/Kg, i.p.) and pargyline (75 mg/Kg, i.p.) produced a significant decrease in the accumulation of octopamine in the hypothalamus but not in the striatum. In contrast, the concurrent administration of clonidine (0.25 mg/Kg, s.c.) and pargyline (75 mg/Kg, i.p.) caused a significant decrease in the accumulation of octopamine in the striatum but not hypothalamus. These results show that the turnover of octopamine in the hypothalamus and striatum is decreased by chlordimeform and clonidine, respectively. Further, clonidine is known to modulate the turnover of amines in mammalian noradrenergic nerve terminals by an action at presynaptic adrenergic receptors. These data suggest that two mechanisms, one involving presynaptic adrenergic receptors in the striatum, and the other involving as yet unidentified receptors in the hypothalamus, modulate the turnover of octopamine in the mammalian brain.

Octopamine receptors in the molluscan aortic bulb: effects of clozapine and chlordimeform.

The presence of specific, stereo-selective octopamine receptors has been demonstrated in the non-spontaneously beating accessory ventricle (aortic bulb) of the clam Tapes watlingi. Analogues of octopamine with a single chloro group in either the para or meta positions of the benzene ring were 10 times less potent than octopamine in their agonist activity. In low concentrations (less than 200 microM), phentolamine, chlordimeform and clozapine were octopamine antagonists. In high concentrations (greater than 200 microM), clozapine, clonidine and chlordimeform induced changes in aortic tone similar to that produced by p-octopamine. This activity may result from the chloro-substituted phenamidine skeleton in both clozapine and chlordimeform.