Discriminative stimulus effects of the type-4 phosphodiesterase inhibitor rolipram in rats.
BACKGROUND
Rolipram, an inhibitor of cyclic AMP phosphodiesterase (PDE4) produces discriminative stimulus effects in rats. These effects may be related to a wide range of central nervous system effects described previously.


OBJECTIVE
The purposes of the present study were to: (i) assess the specificity of the discriminative stimulus effects of rolipram; (ii) examine the role of beta adrenergic receptors; (iii) assess the effects of imipramine and nisoxetine; and (iv) determine whether SKF 38393, a compound which also increases cAMP levels, substitutes for rolipram.


METHODS
Rats were trained to discriminate 0.1 mg/kg rolipram from its vehicle in a two-lever task. Following discrimination training, substitution and antagonism tests were carried out.


RESULTS
In generalization tests, the PDE4 inhibitors ICI 63,197 and Ro 20-1724 substituted for rolipram in a dose-dependent manner (substitution at 0.3 mg/kg and 3 mg/kg, respectively). The selective inhibitors of PDE1, PDE2, and PDE5/6 did not substitute for rolipram; however, a dose of 10 mg/kg of the PDE3 inhibitor milrinone did substitute. The beta adrenergic agonists clenbuterol and dobutamine at least partially substituted for rolipram (0.1 mg/kg and 18 mg/kg, respectively). By contrast, the D1 dopaminergic agonist SKF 38393 and the monoamine uptake inhibitors imipramine and nisoxetine were ineffective (at doses up to 3, 10, and 10 mg/kg, respectively).


CONCLUSIONS
The present results indicate that the discriminative stimulus effects of rolipram are related to the inhibition of the hydrolytic activity of PDE4. Generalized increases in cyclic nucleotides do not appear to be sufficient for producing rolipram-like effects. It appears that a mechanism involving beta adrenergic receptors may contribute to the effects of rolipram, consistent with previous neuropharmacological data. Finally, the discriminative stimulus effects of rolipram appear to be unrelated to its antidepressant-like effect, but may provide a surrogate marker for central nervous system-related side effects of PDE4 inhibitors.
Makhay
M M
MM
Acadia Pharmaceuticals, 3911 Sorrento Valley Boulevard, San Diego, CA 92121-1402, USA. mmakhay@acadia-pharm.com
Houslay
M D
MD
O'Donnell
J M
JM
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000818:Animals; D054677:Cyclic Nucleotide Phosphodiesterases, Type 1; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; D004192:Discrimination, Psychological / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D008297:Male; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D020889:Rolipram / Q000494:pharmacology*
D010726:Phosphodiesterase Inhibitors; D011943:Receptors, Adrenergic, beta; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054677:Cyclic Nucleotide Phosphodiesterases, Type 1; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; D020889:Rolipram