The Antimetabolite ara-CTP Blocks Long-Term Memory of Conditioned Taste Aversion

Abstract

We examined the hypothesis that processes related to DNA recombination and repair are involved in learning and memory. Rats received intracerebroventricular (icv) infusions of the antimetabolite 1-beta-D-arabinofuranosylcytosine triphosphate (ara-CTP) or its precursor cytosine arabinoside (ara-C) 30 min prior to conditioned taste aversion (CTA) training. Both ara-CTP and ara-C caused significant impairments in long-term memory (LTM) of CTA. Control experiments indicate that the effect of ara-CTP on CTA memory is related to interference with learning. Furthermore, as it was previously demonstrated for the protein synthesis inhibitor anisomycin, ara-CTP had no effect on CTA memory when it was injected 1 h after training. Importantly, although both ara-CTP and anisomycin significantly blocked LTM in the task, short-term memory (STM) measured 1 h after training was not affected by either of the drugs. Finally, ara-CTP had no effect on in vitro transcription, but it did effectively block nonhomologous DNA end joining (NHEJ) activity of brain protein extracts. We suggest that DNA ligase-mediated DNA recombination and repair processes are necessary for the expression of LTM in the brain.

An Inhibitor of DNA Recombination Blocks Memory Consolidation, But Not Reconsolidation, in Context Fear Conditioning

“…ANI was dissolved in PBS, and the pH was adjusted to 7.4 with 1N HCl. As in our previous studies (Wang et al, 2003), the dose of ara-C used in the intracerebral studies was 1 mM.…”

“…Pooled tissue was stored at Ϫ80°C until used for protein extraction. Protein extracts were prepared as described by us previously (Ren and Peña de Ortiz, 2002;Wang et al, 2003). Tissues were homogenized in extraction buffer [30 mM HEPES/KOH, pH 7.9, 0.5 M KCl, 5 mM MgCl 2, 1 mM EDTA, 2 mM dithiothreitol (DTT), 20% glycerol, 1 mM phenylmethylsulfonyl fluoride (PMSF), and 1 g/ml each of leupeptin and aprotinin] and incubated for 1 h in ice.…”

“…Protein extracts were stored at Ϫ80°C until used. The protein concentration of the extract was determined by the Bradford method as detailed by us previously (Ren and Peña de Ortiz, 2002;Wang et al, 2003;Santini et al, 2004).…”

“…The fact that the effects of ara-CTP on CTA consolidation were observed as early as 4 h after training suggested that its effects were related to blockade of DNA recombination, rather than replication and neurogenesis (Wang et al, 2003). Here, we questioned whether recombination processes sensitive to ara-CTP are involved in the consolidation of context fear conditioning, a task that is independent of neurogenesis (Shors et al, 2002;Pham et al, 2005).…”

“…Our previous studies showed that the expression of the gene encoding terminal deoxynucleotidyl transferase (TdT), a template-independent DNA polymerase involved in V(D)J recombination, is upregulated in brain neurons by learning and is required for the beneficial cognitive effects of enriched experiences . Finally, we demonstrated that the nucleoside analog 1-␤-D-arabinofuranosylcytosine triphosphate (ara-CTP) inhibited brain NHEJ and impaired LTM, but not STM, of conditioned taste aversion (CTA) in rats when infused intracereventricularly before learning (Wang et al, 2003). The amnesic effects of ara-CTP were also observed with its precursor agent, cytosine arabinoside (ara-C; 1-␤-D-arabinofuranosylcytosine).…”