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, 128 (2), 107-13

No Effect of Acute Tryptophan Depletion on Phosphodiesterase Inhibition--Related Improvements of Short-Term Object Memory in Male Wistar Rats

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No Effect of Acute Tryptophan Depletion on Phosphodiesterase Inhibition--Related Improvements of Short-Term Object Memory in Male Wistar Rats

E L van Donkelaar et al. Acta Psychiatr Scand.

Abstract

Objective: To further explore the implication of the serotonin (5-HT) system in the improvement of rat short-term object recognition after administration of the type 2 phosphodiesterase inhibitor (PDE-I) BAY 60-7550 and the type 5 PDE-I vardenafil, the effect of PDE2 and PDE5 inhibition upon central amino acid levels, 5-HT, and related parameters were measured after applying acute tryptophan depletion (ATD).

Method: Wistar rats were orally administered saline or a protein-carbohydrate mixture with or without tryptophan (TRP). TRP-depleted animals additionally received an oral vehicle injection or the PDE inhibitors BAY 60-7550 or vardenafil at a dose known to improve object memory performance.

Results: Although ATD significantly decreased TRP levels in the hippocampus 2 h after administration, 5-HT levels appeared only moderately affected, without any changes observed in the amount of 5-HIAA or 5-HT turnover rate. Moreover, no effects of PDE inhibition upon 5-HT or related parameters were observed.

Conclusion: Changes in 5-HT neurotransmitter activity might be excluded as a potential underlying mechanism of the previously reported ability of PDE inhibitors to improve short-term object memory in rats. It is suggested that a decrease in cerebral blood flow potentially underlies ATD-induced object memory deficits, most likely due to decrease in NO synthesis.

Keywords: acute tryptophan depletion; phosphodiesterase inhibitors; rat object memory; serotonin.

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