PERGAMON Journal of Psychiatric Research 32 (1998) I II-1 15 J OUFLNALOF PSYCHIATRIC RESEARCH CAMP-dependent phosphorylation system after short and long- term administration of moclobemide S. Mori”, R. Zanardi”, M. Popolia,b, S. Garbini”, N. Brunellod, E. Smeraldi” G. Racagni”,‘, J. Perez”.“%* d Center oj ;I’,,,,~pllarn?acnl~g~, Institute oj Pharmacological Sciences, L’nirersir> qf’Milan, Italy h Laboratory of ,Veurochemistg~. II School of Medicine, tiniversity of~aples, It& ’ Istituto Scientifico H. San Raffirele. Department gf iVertrop.~~~chiatric Sciences. School qf&f~dicittc. Unwersit), of‘ Milan. Ital), ’ Deportment c~/ Pharmaceutical Sciences. Unirersir>~ ofA4odenu. Ital}, ’ I.R.C.C.S. Crrttro San Giorxmni di Dio-Fatc~bertefi-atelli. Istituto Sac?-0 Cuore di Grsu. Erestiu, Italy Received 7 February 1997; accepted 14 October 1997 Abstract Accumulating evidence suggested that signal transduction cascade including protein phosphorylation is implicated in the neu- rochemical action of antidepressant agents. Clinical data indicated that moclobemide, a short acting and reversible inhibitor of monoamino oxidase type A. is an effective antidepressant medication. However. little is known about the intracellular effects of this compound. Thus, in the present study we assessed the binding of CAMP to CAMP-dependent protein kinasc (PKA) in rat cerebral cortex following short and long-term administration of moclobemide. The results showed that 21 days of treatment with moclobemide significantly increased the specific [3’P]-cAMP covalent binding into the soluble 52-54 kDa CAMP-receptor. This effect w-as not seen following 1, 5 and 12 days of treatment. These findings suggest that PKA could be implicated in the biochemical effects of moclobemide. lc 1998 Elsevier Science Ltd. All rights reserved. 1. Introduction It is well established that inside the ccl1 the CAMP- dependent protein kinase (PKA) plays a pivotal role in the regulation of monoaminergic neurotransmission (Walaas & Greengard, 1991) and evidence has accumu- lated mainly during the last decade suggesting its involve- ment in the mechanism of action of antidepressant drugs (Racagni et al., 1992; Hyman & Nestler, 1996). It has been reported that the binding of CAMP to the regulatory subunits of PKA as well as the activity of this enzyme were altered following prolonged administration of different antidepressants (Perez et al.; 1989; Nestler et al., 1989;Perez et al., 1991). Moreover, it has been shown that chronic administration of antidepressants elicited changes in the phosphorylation state or in the levels of some PKA substrates (Perez et al., 1989: Guitart & Nestler, 1992; Perez et al., 1995; Nibuya et al., 1996; Duman et al., 1997). Preclinicai and clinical data have indicated that moclo- bemide, a short acting and reversible inhibitor of * Corresponding author. Tel.: 0039-z-26433379; fax: 0039-2- 264333265. 0022-3956!98 $19.00 c 1998 Elsevier Science Ltd. All rights reserved. PII: 50022~3956(98)00003~X monoamino oxidase type A, is an effective antidepressant medication (Burkard et al., 1989; Da Prada et al., 1989; Angst & Stabl, 1992). However, the possiblerole of PKA in the action of this compound has not been examined so far. Hence, the aim of the present study was to assess whether the CAMP-dependent phosphorylation system could be relevant in the biochemical action of this anti- depressantagent. 2. Materials and methods Moclobemide was a gift from F. Hoffman-LaRoche (Easel, Switzerland). Male Sprague-Dawley rats were pur- chased from Charles River laboratories (Calco. Italy). EDTA, morpholin ethanesulfonic acid (MES), piperazine N,N’(2-ethanesulfonic acid) (PIPES), 3-isobutyl-l- rnethylxantine (IBMX), aprotinin, pepstatin A, phe- nylmethylsulfonyl fluoride (PMS-F), GTP, CAMP, glycerol and Tween-80 were from Sigma Chemical Corporation. S-Azido[j’P]-CAMP (&N,.[“P] CAMP) (66.7 ciimmol) was from ICN (Irvine, CA, U.S.A.) Y-[~~P]-ATP (30 Ci/