RESUMO
Long-term memory (LTM) formation requires new protein synthesis and new gene expression. Based on our work in Aplysia, we hypothesized that the rRNA genes, stimulation-dependent targets of the enzyme Poly(ADP-ribose) polymerase-1 (PARP-1), are primary effectors of the activity-dependent changes in synaptic function that maintain synaptic plasticity and memory. Using electrophysiology, immunohistochemistry, pharmacology and molecular biology techniques, we show here, for the first time, that the maintenance of forskolin-induced late-phase long-term potentiation (L-LTP) in mouse hippocampal slices requires nucleolar integrity and the expression of new rRNAs. The activity-dependent upregulation of rRNA, as well as L-LTP expression, are poly(ADP-ribosyl)ation (PAR) dependent and accompanied by an increase in nuclear PARP-1 and Poly(ADP) ribose molecules (pADPr) after forskolin stimulation. The upregulation of PARP-1 and pADPr is regulated by Protein kinase A (PKA) and extracellular signal-regulated kinase (ERK)--two kinases strongly associated with long-term plasticity and learning and memory. Selective inhibition of RNA Polymerase I (Pol I), responsible for the synthesis of precursor rRNA, results in the segmentation of nucleoli, the exclusion of PARP-1 from functional nucleolar compartments and disrupted L-LTP maintenance. Taken as a whole, these results suggest that new rRNAs (28S, 18S, and 5.8S ribosomal components)--hence, new ribosomes and nucleoli integrity--are required for the maintenance of long-term synaptic plasticity. This provides a mechanistic link between stimulation-dependent gene expression and the new protein synthesis known to be required for memory consolidation.
Assuntos
Potenciação de Longa Duração/genética , Memória de Longo Prazo/fisiologia , Plasticidade Neuronal/genética , Poli(ADP-Ribose) Polimerases/biossíntese , Sinapses/genética , Animais , Colforsina/administração & dosagem , Proteínas Quinases Dependentes de AMP Cíclico/biossíntese , Proteínas Quinases Dependentes de AMP Cíclico/genética , Expressão Gênica/efeitos dos fármacos , Hipocampo/efeitos dos fármacos , Hipocampo/fisiologia , Potenciação de Longa Duração/efeitos dos fármacos , Potenciação de Longa Duração/fisiologia , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Sistema de Sinalização das MAP Quinases/genética , Camundongos , Plasticidade Neuronal/fisiologia , Poli(ADP-Ribose) Polimerase-1 , Poli Adenosina Difosfato Ribose/biossíntese , Poli Adenosina Difosfato Ribose/genética , Poli(ADP-Ribose) Polimerases/genética , RNA Ribossômico 28S/biossíntese , RNA Ribossômico 28S/genética , Sinapses/fisiologiaRESUMO
Brain tissue slices can be maintained within metabolically stable conditions for long periods of time (hours). This experimental setting has been productive for investigating long-term neural function in vitro. Here, we utilize this experimental approach to describe the recovery of functional connectivity in slices from the mouse hippocampus. Hippocampal slices were cut up bisecting the CA1 region (parietal cut) and each severed half placed adjacent to the other. Stimulation and recording electrodes were placed on each side of the cut; with one electrode stimulating one hemi-slice (20 V, 0.033 Hz) and the other electrode recording the evoked response from the adjacent hemi-slice. As expected, no evoked response was observed shortly after the beginning of stimulation. However, 20-40 min after the initiation of stimulation a large depolarization signal was detected. Right after that, fiber volley potentials were observed in the adjacent hemi-slice. After 1h excitatory postsynaptic potentials (EPSP) were detected. Based on this observation, we hypothesize that recovery of functional connectivity is enhanced by constant delivery of electrical pulses at low frequency to the damaged neural tissue. The described in vitro slice system may become a very suitable experimental method to investigate strategies to enhance the recovery of neural connectivity after brain injury.
Assuntos
Potenciais Evocados/fisiologia , Hipocampo/fisiologia , Técnicas In Vitro/métodos , Modelos Biológicos , Recuperação de Função Fisiológica/fisiologia , Animais , Estimulação Elétrica , Técnicas Histológicas/métodos , CamundongosRESUMO
An unexpected and novel finding is described and discussed here concerning the synaptic physiology of hippocampal slices during the period of recovery after brain dissection. Contrary to the common notion that the amplitude of synaptic responses recovers in a single exponential rising fashion, we found that synaptic response amplitude displayed an oscillatory pattern. The period of oscillation was of 6h and its frequency depended on the input frequency of stimulation. Based on these preliminary data we can make an assumption that the recovery-associated oscillatory behavior of synaptic responses may be hippocampus specific. These data suggest the existence of a previously undescribed element that modifies the electrical properties underlying the modulation of synaptic responses in a neuronal population. The article hypothesizes a mechanism for this phenomenon.
