In vivo and in vitro measurement of brain phosphodiesterase 4 in rats after antidepressant administration.

Based largely on in vitro measurements, the mechanism of several antidepressant treatments is thought to involve upregulation of 3'-5'-cyclic adenosine monophosphate (cAMP) signal transduction cascade and a corresponding increase in phosphodiesterase (PDE) 4, the enzyme that metabolizes cAMP. To assess the in vivo status of PDE4, rats were chronically treated with imipramine and then studied with: (1) in vivo positron emission tomography (PET) measurement of (R)-[(11)C]rolipram binding, (2) in vitro measurement of [(3)H]rolipram binding in brain homogenates, and (3) Western blotting for protein levels of PDE4 isoforms. Imipramine administration caused no significant change in B(max)/K(d), for both in vivo measurements with (R)-[(11)C]rolipram and in vitro measurements with [(3)H]rolipram in frontal cortex, hippocampus, and diencephalon.

Quantification of brain phosphodiesterase 4 in rat with (R)-[11C]Rolipram-PET.

Objective: Phosphodiesterase 4 (PDE4) catabolizes the second messenger 3', 5'-cyclic adenosine monophosphate and may play a critical role in brain diseases. Our aim was to quantify PDE4 in rats with positron emission tomography (PET).

Methods: High (n = 6) and low specific activity (SA) (n = 2) higher affinity ((R)-[(11)C]rolipram) and high SA lower affinity ((S)-[(11)C]rolipram) (n = 2) enantiomers were intravenously administered to Sprague-Dawley rats.