The article deals with synaptic plasticity. Synapses undergo activity-dependent changes of their ultrastructure. These changes of synaptic connections are referred to as synaptic plasticity which is the basis of learning and memory processes.
The aim of this study was to investigate the role for GABAB receptors in frequency-dependent long-term synaptic modifications of developing GABA-ergic synapses on hippocampal CA1 pyramidal cells (the frequency of synaptic stimulation is critical for determining the polarity of long-term modification of excitatory synapses).
The author's attention was focused on the developing rat hippocampal synapses during the first few postnatal weeks, a period in which GABA-ergic synapses may undergo extensive activity-dependent refinement.
GABAB receptors are largely located in extrasynaptic sites and can be activated by GABA spillover during high frequency GABA-ergic synaptic activity. Activity-induced synaptic modification can be attributed to changes in either the amount of evoked neurotransmitter release or the postsynaptic response to the released neurotransmitter, or both.
The data showed that long-term modification of developing rat hippocampal GABA-ergic synapses that was induced by repetitive coincident presynaptic and postsynaptic spiking (i.e. coincident stimulation of the presynaptic and postsynaptic cell) was frequency dependent. Spiking at 20-50 Hz resulted in synaptic potentiation, whereas spiking at 5 Hz led to synaptic depression. The long-term potentiation was abolished by pharmacological blocking GABAB receptors, whereas the depression was independent of GABAB receptors activation and could be converted to potentiation by elevating GABAB receptors activity.
The potentiation could be attributed to a local postsynaptic increase in Na+/K+/2Cl- co-transporter activity near activated synapses. The activity of postsynaptic Ca2+/calmodulin-dependent protein kinase II was necessary for long-term potentiation of these developing GABA-ergic synapses.
Together with the data that activation of GABAB receptors is frequency dependent, these results indicate that postsynaptic GABAB receptors activation mediates frequency-dependent potentiation of developing GABA-ergic synapses. The results extend the knowledge of the function of GABAB receptors to the postsynaptic regulation of long-term synaptic plasticity of developing GABA-ergic synapses.