Fluoxetine hypophagia. Is there a role for serotonergic mechanisms in some circumstances?

Anxiolytic profile of fluoxetine as monitored following repeated administration in animal rat model of chronic mild stress

Background: Fluoxetine, a selective serotonin re-uptake inhibitor (SSRI), has been proposed to be more effective as an antidepressive drug as compared to other SSRIs. After chronic SSRI administration, the increase in synaptic levels of 5-HT leads to desensitization of somatodentritic 5-HT autoreceptors in the raphe nuclei. Chronic stress may alter behavioral, neurochemical and physiological responses to drug challenges and novel stressors. Methods: Twenty four male rats were used in this study. Animals of CMS group were exposed to CMS. Animals of stressed and unstressed group were administrated with fluoxetine at dose of 1.0 mg/kg s well as 5.0 mg/kg repeatedly for 07 days 1 h before exposed to CMS. The objective of the present study was to evaluate that repeated treatment with fluoxetine could attenuate CMS-induced behavioral deficits. Results: Treatment with fluoxetine attenuated CMS-induced behavioral deficits. Fluoxetine administration induced hypophagia in unstressed as well as CMS rats. Acute and repeated administration of fluoxetine increased motor activity in familiar environment but only repeated administration increased exploratory activity in open field. Anxiolytic effects of fluoxetine were greater in unstressed rats. These anxiolytic effects were produced as result of repeated administration not on acute administration of fluoxetine at 1.0 mg/kg as well as 5.0 mg/kg. Conclusion: The present study demonstrated that CMS exposure resulted into behavioral deficits and produced depressive-like symptoms. Fluoxetine, an SSRI, administration attenuated behavioral deficits induced by CMS. Anxiolytic effects of repeated fluoxetine administration were greater in unstressed than CMS animals.

Fluoxetine prevents 8-OH-DPAT-induced hyperphagia in Fischer inbred rats

Ovariectomized, Fischer rats were hormonally primed with 10 μg estradiol benzoate and 50 μg progesterone or were treated with the sesame seed oil vehicle. Food intake was measured 2 h and 24 h after treatment with 0.25 mg/kg of the 5-HT(1A) receptor agonist, (±)-8-hydroxy 2-(di-n-propylamino) tetralin (8-OH-DPAT), 5 mg/kg of the selective serotonin reuptake inhibitor, fluoxetine, or their combination. Consistent with prior studies, two hour food intake of rats given fluoxetine and 8-OH-DPAT did not differ from vehicle controls. 8-OH-DPAT-induced hyperphagia, evident at 2 h, was blocked by co-treatment with fluoxetine. However, in contrast to prior studies, 5 mg/kg fluoxetine, alone, had only modest effects on food intake. Differences in our experimental protocols and/or the strain of rat may account for the lower anorectic response to fluoxetine. Nevertheless, the absence of a significant response to fluoxetine, alone, coupled with the drug's attenuation of the hyperphagic effect of 8-OH-DPAT, leads to the suggestion that the behavioral response to the combined treatment is more complex than that of simple additivity. Consistent with this suggestion, 24 h food intake of rats given 8-OH-DPAT and fluoxetine was lower than that of vehicle or 8-OH-DPAT-treated rats.

Synergistic neurochemical and behavioral effects of fluoxetine and 5-HT1A receptor antagonists

We studied the ability of WAY 100635 [N-[4-(2-methoxyphenyl)-1-piperazinyl]-N-(2-pyridinyl) cyclo-hexanecarboxamide], 0.5 mg/kg, i.v. and (-)-5-Me-8-OH-DPAT [(-)-5-methyl-8-hydroxy-2-(di-n-propylamino)tetralin], 3 mg/kg, i.v. two selective 5-HT1A receptor antagonists, to potentiate: (1) the enhancement of extracellular 5-HT levels ([5-HT(ext)]) induced by a single administration of 5 mg/kg i.p. fluoxetine using in vivo microdialysis in the ventral hippocampus of conscious rats, (2) the decrease in food intake induced by this antidepressant drug in food-deprived rats. The effects of fluoxetine were significantly potentiated, by 30-40%, by WAY 100635 as well as by (-)-5-Me-8-OH-DPAT in the two sets of experiments. Thus, fluoxetine increased [5-HT(ext)] in serotonergic nerve terminal areas and consequently, induced hypophagia, both effects being limited by indirect activation of somatodendritic 5-HT1A autoreceptors.