Elsevier

Brain Research Bulletin

Volume 57, Issue 2, 15 January 2002, Pages 205-209
Brain Research Bulletin

Analysis of gene expression with cDNA microarrays in rat brain after 7 and 42 days of oral lithium administration

https://doi.org/10.1016/S0361-9230(01)00744-4Get rights and content

Abstract

The gene expression profile in rat brain was examined using microarrays in rats fed lithium chloride for 7 days (subacute) or 42 days (chronic). Brain lithium concentrations were 0.39 mM and 0.79 mM (therapeutically relevant), at 7 and 42 days, respectively. Of the 4132 genes represented in the microarrays, 25 genes were downregulated by at least twofold and none was upregulated after 7 days of treatment. Expression of 50 genes was downregulated by at least two-fold at 42 days, without any being upregulated. Lithium treatment for 7 days did not affect at a measurable extent expression of 37 of the 50 genes that were downregulated at 42 days. Genes whose expression was changed at 42 days coded for a number of receptors, protein kinases, transcription and translation factors, markers of energy metabolism, and signal transduction. Thus, chronic lithium at a therapeutically relevant concentration reduced expression of a large number of genes involved in multiple signaling and other pathways, without increasing expression at a comparable extent.

Introduction

Bipolar disorder (BD) is a common psychiatric condition characterized by cycling periods of mania and severe depression. The established efficacy of lithium in the treatment and prophylaxis of BD is well known 7, 13. Many cellular effects of lithium have been described, although the basis of its therapeutic action is not agreed upon [24]. Several signal transduction pathways have been suggested to contribute to lithium’s action, in particular, guanine-nucleotide-binding proteins [28], adenylyl cyclase [10], protein kinase C isoenzymes [39], phosphoinositide cycle 1, 15, and the balance of neurotransmitter signaling [23]. Studies also suggest that lithium is neuroprotective, as it increases Bcl-2 and decreases p53 and Bax expression 9, 30. Additionally, we reported that therapeutically relevant brain concentrations of lithium (about 0.7 mM) [20] reduced, by 80%, the turnover of arachidonic acid within brain phospholipids of awake rats [8]. The mRNA and protein levels of an AA-selective cytosolic PLA2 (cPLA2, type IV) also were reduced, consistent with reduced AA turnover 22, 33.

Lithium’s action as a mood stabilizer generally requires weeks to develop 20, 29, suggesting alterations at the genomic level 17, 31. However, changes occurring over such a long time frame could also result from translational and post-translational modifications, or as a consequence of protein/RNA half-life modification.

Gene expression monitoring with cDNA arrays 11, 14 provides a simple way to explore the biochemical effects of lithium and therefore elucidate its potential therapeutic and negative side effects. We used this approach to determine the effect of feeding lithium chloride (LiCl) [8] to rats for periods of 7 days (subacute) and 42 days (chronic) on brain expression of 4132 genes. We report that the changes induced by subacute lithium do not overlap with the more chronic alterations in gene expression. The latter are more likely related to lithium’s mood-stabilizing effect, considering the latency in onset of therapeutic action, which is not immediately reversed upon discontinuation 17, 18. These findings have significant implications for understanding mechanisms of BD and identifying targets for treating it.

Section snippets

Lithium administration

The protocol conformed to the Guideline for the Care and Use of Laboratory Animals (NIH Publication No. 80-23). Adult male Fischer-344 rats (200–250 g; Charles River Laboratories, Wilmington, MA, USA) were acclimatized for 2 weeks, and then fed ad lib Purina chow (containing 1.70 g LiCl per kg chow for 7 days or 1.70 g LiCl per kg chow for 4 weeks followed by a diet containing 2.55 g LiCl per kg chow for 2 weeks, or LiCl-free chow [controls]) [8]. To prevent hyponatremia, water and NaCl

Results

Using atomic absorption spectrometry, lithium was not detected in plasma or brain of control rats fed a LiCl-free diet, whereas the lithium concentration (mean ± SEM, n = 4) was 0.39 ± 0.01 mM in brain and 0.56 ± 0.02 mM in plasma of rats fed LiCl for 7 days, and 0.79 ± 0.07 mM in brain and 0.74 ± 0.03 mM in plasma of rats fed LiCl for 42 days. The latter concentrations are therapeutically relevant [3]. As shown in Fig. 1, the brain lithium concentration became equivalent to the plasma

Discussion

In this study we used a high-density filter-based cDNA microarray, representing over 4000 known human genes, to determine the effects of subacute (7 days) and chronic (42 days) oral lithium administration on rat brain gene expression, compared with control brain. We identified many genes that were downregulated by a factor of at least 2 by chronic but not by subacute lithium, whereas no gene was upregulated by this factor at either time point. The expression of 11 genes was downregulated after

Acknowledgements

We thank Dr. Barry Horwitz for statistical help.

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    Current address: NeuroLogic, Inc., Functional Genomics, 15010 Broschart Road, Rockville, MD 20850, USA.

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