Role of DA in the stimulant effect of DITA in mice; comparison with d-amphetamine

Behavioural microanalysis of the role of dopamine in amphetamine anorexia

A microstructural analysis paradigm was used to study amphetamine anorexia. Doses above 0.40 mg/kg significantly reduced food intake by reducing eating time; in contrast, eating rate was increased at these doses. Examination of the frequency distribution of interresponse times (IRTs) revealed a significant shift to shorter IRTs at doses as low as 0.125 mg/kg. Pimozide blocked amphetamine anorexia at 0.5 and 1.0 mg/kg, suggesting that at both doses amphetamine anorexia has a dopaminergic substrate. However, the atypical neuroleptic thioridazine did not antagonize amphetamine. Furthermore, effects of amphetamine were additive with those of apomorphine, administered at a dose known to suppress feeding by inhibiting mesolimbic DA neurons. These results provide evidence against an involvement of the mesolimbic DA system in amphetamine anorexia.

Central and peripheral contributions to the enhancement of amphetamine anorexia by desmethylimipramine (DMI)

Intrahypothalamic administration of amphetamine to rats increased food intake, but pre-treatment with the alpha-receptor antagonist phentolamine unmasked an anorexic effect commensurate with that seen after peripheral amphetamine administration. Pretreatment with systemic DMI increased anorexia after peripheral or central amphetamine administration, but the enhancement of centrally-induced anorexia was small. It is concluded that enhancement of the anorexic effect of peripherally administered amphetamine by DMI is primarily a peripheral phenomenon, with interactions within the central nervous system making a relatively minor contribution.

Catecholamine mechanisms in the stimulation of mouse locomotor activity by nitrous oxide and morphine

Nitrous oxide, like morphine, produces a significant increase in mouse locomotor activity. This stimulation of locomotor activity is antagonized by the narcotic antagonist naloxone (10 mg/kg). The catecholamine synthesis inhibitor alpha-methyl-p-tyrosine (300 mg/kg) also significantly reduced the nitrous oxide stimulation of mouse locomotor activity. Administration of naloxone (10 mg/kg) to mice previously treated with alpha-methyl-p-tyrosine resulted in a further decrease in nitrous oxide stimulated activity levels. Haloperidol (0.08-0.64 mg/kg), a potent dopamine receptor antagonist, dose dependently reduced the activity stimulation resulting from exposure to nitrous oxide. Administration of haloperidol (0.08 mg/kg) in conjunction with naloxone (10 mg/kg) further reduced the nitrous oxide effect. In view of the fact that morphine's activity stimulating effects are reduced by alpha-methyl-p-tyrosine and haloperidol, the results reported here suggest additional similarities in the pharmacology of morphine and nitrous oxide. The stimulation of mouse locomotor activity produced by nitrous oxide appears to be mediated by both endogenous opioid and catecholamines.

Microstructural analysis of the involvement of beta-receptors in amphetamine anorexia

Rats were trained to take food by pushing the door of the pellet dispenser in an operant chamber. Log survivor analysis of the inter-response time frequency distribution was used to determine whether or not an animal was eating, at any time during a thirty minute session. This information was used to compute eating time, eating rate, and the mean length of bouts of eating and gaps between eating bouts. Video-recordings confirmed that the method discriminated eating from not eating with an accuracy of approximately ninety percent. Amphetamine (0.5 mg/kg) significantly reduced total food intake and eating time, and increased gap length; propranolol (5 mg/kg) significantly increased eating time and bout length. Following propranolol pretreatment, amphetamine significantly reduced eating time and bout length but also significantly increased eating rate; as a result there was no significant decrease in total food intake. The possible mediation of these effects by beta-adrenergic and dopaminergic systems is discussed.

The effect of propranolol phentolamine and pimozide on drug-induced anorexia in the mouse

Pimozide was a potent antagonist of (+)amphetamine, diethylpropion, mazindol and phentermine anorexia in the mouse. Phentolamine and propranolol produced no such antagonism, but either potentiated or had no effect on the drug-induced anorexia. Although the mechanism of action of the four anorectic agents appears to involve dopamine receptor agonist activity, an antagonist or partial agonist effect at noradrenergic receptors may also be involved.

Studies on the capacity of mazindol and dita to act as uptake inhibitors or releasing agents for 3H-biogenic amines in rat brain tissue slices

The effects of the anorexic and stimulant agents mazindol and dita on 3H-biogenic amine uptake and release were determined. Mazindol and dita were very potent inhibitors of 3H-norepinephrine uptake into rat brain occipital cortex slices with ED50 values (point of 50% inhibition of uptake) of 1.5 X 10(-9) M and 3.2 X 10(-9) M, respectively. Mazindol (ED50 of 2.8 X 10(-7) M) and dita (ED50 value of 8.5 X 10(-7) M) were also potent inhibitors of 3H-dopamine uptake into rat neostriatal slices and of 3H-serotonin uptake into whole brain slices (ED50 values of 5.5 X 10(-7) M and 5.1 X 10(-7) M for mazindol and dita respectively). Both compounds proved however to be extremely weak releasing agents for the 3H-biogenic amines in the respective brain areas. The effects of mazindol and dita on uptake may help to explain some of their pharmacological properties.

Role of dopamine in the anorexigenic effect of DITA; comparison with d-amphetamine

The effects of d,1-alpha-methyltyrosine (alphaMT), haloperidol, phenoxybenazmine, propranolol, methysergide and cyproheptadine on the anorexigenic activities of DITA and d-amphetamine were studied in male mice. The pretreatment of mice with methysergide (10 mg/kg, s.c.), cyproheptadine (5 mg/kg, i.p.), phenoxybenzamine (10 mg/kg, i.p.), and propranolol (5 mg/kg, i.p.) failed to alter the anorexigenic effect of DITA and d-amphetamine. On the other hand, alphaMT (32 mg/kg, i.p.) and haloperidol (0.5 mg/kg, i.p.) significantly antagonized the anorexigenic effect of DITA and d-amphetamine. Our data indicate that the anorexigenic activities of DITA and d-amphetamine are mediated mainly through the dopaminergic system.