S-33 John Cade Symposium on Lithium - Part 2

total number of spikes. to increase c-fos expression in DA target areas.Thus 5-HT2-receptor antagonism should facilitate information process­ing through frontal DA innervated circuits. In contrast. a l-adrenoceptorantagonism by prazosin was found to reduce phasi, but not tonic activityin mesolimbic DA neurons and to effectively antagonize the MK-80levokedDArelease in nucleus accumbens, without changing basal release.Although blockade of DA receptors appears critical for antipsychotic ac­tivity. antagonism of 5-HT2A-receptors and a l-adrenoceptors may help tonormalize central DA system perturbations in psychosis at a presynapticlevel.

IS-33 I John Cade Symposium onLithium - Part 2

18-33-1 I Actions of.Lithium on Brain Adenylyl Cyclase: Roleof MagneSium

A. Merk, Department of Neurobiology. Pharmacological Research. H.Lundbeck AlS. Copenhagen-Valby. Denmark

Lithium affects cAMP formation in the brain [1]. There is now evi­dence of 9 different types of adenylyl cyclase. having distinct regulatorycharacteristics [2]. Type 1,III and VIII adenylyl cyclases are sensitive tocalcium-calmodulin (Ca2+-CaM) and are thus stimulated by physiologicalconcentrations of Ca2+. Magnesium (Mg2+) regulates adenylyl cyclasesthroughtwo independent cation sites; one Mg2+ site modulates the activityof G proteins. and a second Mg2+ site on the catalytic proteins regulatesthe catalytic activities. The in vitro and chronic effects of lithium onbrain adenylyl cyclase have been studied. Chronic lithium was studiedby treating rats for 4 weeks. yielding serum-lithium of 0.7-0. 8 rnmol/l.Lithium inhibited Ca2+-CaM-stimulated adenylyl cyclase activity, indi­cating altered activity of the catalytic protein independent of the proteinkinase C arm. The inhibitory effect of lithium in vitro on cAMP forma­tionstimulated by noradrenaline, Gpp(NH)p. forskolin, or Ca2+ -CaM wasfoundto be counterac ted by increasing concentrations of Mg2+ , indicatingthat lithium in situ inhibits adenylyl cyclases by displacing Mg2+ from itsregulatory ion site. However, following chronic treatment. Mg2

+ did notantagonize the inhibitory effect of lithium. suggesting that the acute andchronic effects of lithium on adenylyl cyclases are exerted by differentmechanisms.

[1] Moerk A. Geisler A,1. Neurochern. 65(1995) 134-139.[2] Cooper DMF, Mons N,Karpen lW, Nature 374 (1 995)421 -424.

18-33-21 Marcks: A Key to the long-TermTherapeuticAction of Mood Stabilizers in the Brain?

R.H. Lenox, D.G. Watson, R.K. McNamara. Departments ofPsychiatry,Pharmacology and Neuroscience, University of Florida College ofMedicine, Gainesville, Florida, U.S.A.

Ongoing studies in our laboratory and others have provided evidencefor a role of PKC in mediating the effects of chronic lithium in thebrain (Manji and Lenox, 1994). We have reported that chronic lithium atclinically relevantconcentrations significantly reduces the expression of amajor PKC substrate, MARCKS (Myristoylated Alanine-Rich C-KinaseSubstrate), in rat hippocampus (Lenox et al, 1992). This protein hasbeen implicated in synaptic signaling and cytoskeletal remodeling. andrecent studies in our laboratory have mapped the constitutive MARCKSgene expression in the hippocampal formation. Exposure of immortal­ized hippocampal cells (HN33) in culture to phorbol esters induces adown-regulation of MARCKS protein via a PKC-dependent mechanism(Watson et al, 1994). Similar studies in HN33 cell exposed to lithiumresults in a time-dependent reduction in MARCKS expression (Lenox etal, 1993). which we have now shown to be dependent upon the relativeconcentrations of lithium and inositol, as well as the level of muscarinicreceptor activation. We have compared the effects of chronic exposureto lithium, valproate and carbamazepine, on the expression of MARCKSprotein in HN33 cells. Sodium valproate exposure produced a significantdose-dependent but inositol-independent reduction in MARCKS protein

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in both the soluble and membrane fractions following long-term exposure(3- 7 days). In contrast. no changes in MARCKS protein levels weredetected following long-term exposure to carbamazepine or followingacute exposure to any of these three agents. Regulation of MARCKSprotein may represent a pharmacological property shared by selectivemood stabilizers with therapeutic efficacy in the prophylactic treatmentof manic-depressive illness and may provide an important avenue forelucidating the pathobiology of this illness •

Supportedby NIMH Grant # MH50105.

I8-33-31Regulation ofTransmembrane Signalling Systemsby Mood Stabilizing Agents: TherapeuticImplications

Husseini K. Manji . Molecular Pathophysiology Program. Wayne StateUniversity School ofMedicine

Lithium. valproic acid (VPA), and Carbamazepine (CBZ) are widely usedin the treatment for bipolar affective disorder, but despite their efficacy.the molecular mechanisms underlying their therapeutic actions have notfully been elucidated. In recent years it has become increasingly clearthat rather than any single neurotransmitter system being responsible fordepression or mania, multiple interacting and overlapping systems areinvolved in regulating mood, and that most effective drugs may exert theirtherapeutic efficacy by affecting the functional balance between interact­ing systems. In this context. signal transduction pathways are in a pivotalposition in the CNS and represent attractive targets to explain the efficacyof these mood-stabilizing agents in treating multiple aspects oft he illness.We have found that in both platelets from healthy volunteers, and ratprefrontal cortex. chronic lithium affects both basal and post-receptoradenylyl cyclase activity, and significantly increases pertussis-catalyzed[32p]ADP-ribosylation. Preliminary studies from our laboratory suggest

that chronic lithium administration impairs the ability of GTPyS to dis­sociate Gi, suggesting a post-translational process stabilizing the inactivebeterotrimeric (apy ) form of the protein. Chronic lithium also producesa significant decrease in f3HjPDBU binding in several hippocampalstructures (most notably subiculum and CAI region), effects which aredue to isozyme-specific decrease in levels of membrane-associated PKCa and {3 ; in view of lithium's significant effects on PKC outlined above,we have also investigated the effecrs of VPA on various aspects ofthis family of enzymes. Chronic VPA (0.5 mM) produces a significantdecrease in PKC activity in both the membrane and cytosolic fractionsof C6 glioma cells; these effects are accompanied by isozyme-selectivedecreases in the levelsofPK C Cl' and p.Consistent with its effects on PKCisozyrnes, we findthat VPAexerts majoreffects on a major PKC substrate(MARCKS), and on the activity of AP-l (a transcriptional factor knownto be regulated by PKC). We have also investigated CBZ's effects 0 0

signal transduction pathways and have found a concentration-dependentattenuation of both basal and post-receptor (Forskolin, cholera toxinor pertussis toxin) stimulated cyclic AMP accumulation. Using in vivomicrodialysis, we have found that similar to what was observed in vitro.CBZ concentration-dependently reduced FSK stimulated cAMP levels inrat prefrontal cortex. We have used a FSK affinity column to purify ACsfrom rat brain. and findthat CBZ also exerts a significant inhibitory effecton the purified ACs. Overall, the results suggest that signal transductionpathways are targets for the actions of mood stabilizing agents; giventheir key roles in the amplification and integration of signals in the centralnervous system, these findings have clear implications not only for re­search into the etiology/pathophysiology of manic-depressive illness. butalso for thc development of innovative treatment strategies.

18-33-4 1The Inositol Depletion Hypothesis: Promise andProblems

R.H. Belmaker. Division ofPsychiatry. Ben Gurian UniversityBeersheva, Israel

Lithium (Li) inhibits inositol monophosphatase and reduces brain in­ositol. This effect was proposed as a mechanism of Li action. sincereduced inositol could compromise resynthesis of phosphatidylinositol(PI) and thus moderate the second messenger response to agonists thatwork by breakdown of PI to IP3. However, many authors found that