Protein Synthesis Inhibition Blocks the Induction of Mossy Fiber Long-Term PotentiationIn Vivo

Abstract

Protein synthesis inhibitors block the maintenance of NMDA receptor-dependent long-term potentiation (LTP) both in vivo and in vitro. Protein synthesis inhibitors block mossy fiber(MF) LTP maintenance in vitro, but little is known about the effect of protein synthesis inhibitors on either induction or maintenance in MF-LTP in vivo. Here we study the role of protein synthesis in the induction of long-term potentiation at the mossy fiber-CA3 hippocampal synapse in vivo in anesthetized rats. The protein synthesis inhibitor anisomycin was administered at different doses (0.04, 10, or 40 nmol) into area CA3 15 min before delivering high-frequency stimulation (two times at 100 Hz, 1 sec). Anisomycin blocked MF-LTP induction in a dose-dependent manner; both 40 and 10 nmol blocked MF-LTP induction, but a lower dose of 0.04 nmol was without effect. The inhibitory effect of anisomycin on protein synthesis was determined by measuring the incorporation of [35 S]methionine into the newly synthesized proteins. Percentages of protein synthesis inhibition were determined by comparing [35 S] incorporation of anisomycin-treated samples with vehicle controls. Doses of 0.04, 10, or 40 nmol of anisomycin produced 21, 82, or 83% inhibition of [35 S]methionine incorporation, respectively. The effect of anisomycin was verified using a single dose of the protein synthesis inhibitor cycloheximide (40 nmol). Cycloheximide also blocked MF-LTP induction. These results suggest that protein synthesis plays an important role in the induction of mossy fiber long-term potentiation in vivo.

Memory Consolidation for the Discrimination of Frequency-Modulated Tones in Mongolian Gerbils Is Sensitive to Protein-Synthesis Inhibitors Applied to the Auditory Cortex

“…However, the discrimination deficit was monitored after intracortical injections of 113 mM or 66 mM solutions of ANI, whereas administrations of a 0.04 mM solution of ANI were ineffective. In rat hippocampus, application of 1 µl of a 10 mM solution of ANI has been shown to cause more than 80% inhibition of protein synthesis, whereas a 0.04 mM solution had only a marginal effect (Barea-Rodriguez et al 2000). Therefore, the amnesic action of ANI monitored in the present study was dose-dependent and occurred with dosages that, as deduced from literature data, should induce more than 80% inhibition of protein synthesis in the target region.…”

“…This dose was shown to cause only a non-significant inhibition of protein synthesis following injection into rat hippocampus (Barea-Rodriguez et al 2000). In contrast to injections of 113 mM ANI, administrations of 0.04 mM ANI to the gerbil auditory cortex did not affect FM discrimination learning during the subsequent three days of training (D of session 1 to session 4, 0.04 mM ANI: 5.50 ± 1.26, 12.17 ± 1.54, 14.00 ± 2.27, 15.17 ± 1.58; D of session 1 to session 4, saline: 0.50 ± 1.28, 10.67 ± 2.88, 10.50 ± 1.61, 15.50 ± 2.92; means ± s.e.m., n = 6 per group).…”

“…Specifically, the highest dose (113 mM) of ANI was chosen based on previously published studies showing 80% suppression of protein synthesis in rat cerebral cortex and hippocampus after injections of 100 µg ANI per hemisphere (Rosenblum et al 1993;Meiri and Rosenblum 1998). During the course of our experiments, data were published showing that even lower doses of ANI are sufficient to induce >80% suppression of protein synthesis in rat hippocampus (Barea-Rodriguez et al 2000). Therefore, in subsequent experiments the dose of ANI was reduced to 66 mM as indicated.…”

“…To control for amnesic effects of ANI apart from those caused by protein-synthesis inhibition, the lowest dose (0.04 mM) was used. This dose was shown to induce only a nonsignificant inhibition of protein synthesis following injection into rat hippocampus (Barea-Rodriguez et al 2000). The dose of EME was chosen based on previous studies on chicks showing a highly localized inhibition of protein synthesis after intracranial injections (Patterson et al 1986).…”

Locus Ceruleus Activation Initiates Delayed Synaptic Potentiation of Perforant Path Input to the Dentate Gyrus in Awake Rats: A Novel β-Adrenergic- and Protein Synthesis-Dependent Mammalian Plasticity Mechanism

“…The latter has been examined at all synapses in the tri-synaptic hippocampal pathway . This form of LTP also depends on the cAMP-protein kinase A cascade Abel et al, 1997) and protein synthesis (Krug et al, 1984;Frey et al, 1988;Barea-Rodriguez et al, 2000). ␤-Adrenergic receptor activation is a requirement for tetanus-induced late-phase LTP at both the lateral and medial perforant path-dentate gyrus synapses (Bramham et al, 1997), at the mossy fiber-CA3 synapse , and for late-phase LTP in the lateral amygdala (Huang et al, 2000).…”