Autor(es): Diógenes, Maria José ; Fernandes, Catarina Cunha ; Sebastião, Ana M ; Ribeiro, Joaquim A.
Data: 2004
Origem: Repositório da Universidade de Lisboa
Assunto(s): Adenosine receptors; Brain-derived neurotrophic factor (BDNF); Hippocampus; Synaptic transmission; Neuromodulation; Neurotrophic factors
Both brain-derived neurotrophic factor (BDNF) and adenosine influence neuronal plasticity. We now investigated how adenosine influences the action of BDNF on synaptic transmission in the CA1 area of the rat hippocampal slices. Alone, BDNF (20 –100 ng/ml) did not significantly affect field EPSPs (fEPSPs). However, a 2 min pulse of high-K+ (10 mM) 46 min before the application of BDNF (20 ng/ml)triggered an excitatory action, an effect blocked by the TrkB receptor inhibitor K252a (200 nM), by the adenosine A2A receptor antagonist ZM241385 (50 nM), and by the protein kinaseAinhibitor H-89 (1µM). Presynaptic, rather than postsynaptic depolarization was required to trigger the BDNF action because after K+ depolarization BDNF also increased EPSCs recorded from pyramidal neurons voltageclamped at -60 mV, and transient postsynaptic depolarization was unable to unmask the BDNF action. A weak theta burst stimulation of the afferents could elicit potentiation of synaptic transmission only when applied in the presence of BDNF. Activation of adenosineA2A receptors with CGS 21680 (10 nM), or the increase in extracellular adenosine levels induced by 5-iodotubercidin (100 nM) triggered the excitatory action of BDNF, a process prevented by ZM 241385 and by H-89. In the presence of dibutyryl-cAMP (0.5 mM), BDNF also increased fEPSPs but postsynaptic cAMP (0.5mM) was unable to trigger the BDNF action. It is concluded that presynaptic activity-dependent release of adenosine, through activation of A2A receptors, facilitates BDNF modulation of synaptic transmission at hippocampal synapses.
