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Long-term synaptic depression (LTD) in cortico-striatal circuits is initiated by depolarization of striatal medium spiny neurons through a convergent cortical glutamatergic input. This produces retrograde endocannabinoid signaling to presynaptic cortical terminals and eventually results in long term (>30 min) decreases in glutamate release. These same circuits can also undergo short-term depression (STD) through a less well-defined process in which the magnitude of postsynaptic responses returns to baseline levels within 10 min. Additionally, the cortico-striatal circuit shows characteristics of a GABA A receptor-dependent low-pass filter, which results in significant attenuation of high frequency cortical inputs. The majority of in vitro studies of LTD have used a 100-Hz induction paradigm and it is unclear whether other frequencies, which may also have physiological relevance, have equivalent ability to induce this form of plasticity. Here we have investigated the effectiveness of a range of induction paradigms in producing LTD in cortico-striatal circuits, and demonstrate that some lower frequency paradigms, with perhaps more physiological relevance, are more effective at inducing LTD. We also show that GABA A receptor-dependent frequency filtering in this circuit is altered following the induction of LTD and STD suggesting an important role for synaptic depression in signal processing in these circuits. [ABSTRACT FROM AUTHOR]

Abstract: The phenomenon whereby the relative timing between presynaptic and postsynaptic spiking determines the direction and extent of synaptic changes in a critical temporal window is known as spike timing-dependent synaptic plasticity (STDP). We have previously reported that STDP profiles can be classified into two types depending on their layer-specific location along CA1 pyramidal neuron dendrites in the rat hippocampus, suggesting that there are differences in information processing between the proximal dendrite (PD) and distal dendrite (DD). However, how the different types of information processing interact at different dendritic locations remains unclear. To investigate how the temporal information of inputs to PD influences information processing at DD, PD stimulation was applied while the STDP protocol was simultaneously applied at DDs of CA1 pyramidal neurons. Synaptic plasticity induced by the STDP protocol at DDs was enhanced or depressed depending on the timing of the back-propagating action potentials (bAPs) and the excitatory and inhibitory postsynaptic potentials elicited by PD stimulation. These results suggested that bAPs function as carriers of temporal information of PD inputs to DD. Next, the influence of DD on PD was investigated using the same protocol. Synaptic plasticity at PD was modulated only if the pairing stimuli were applied to elicit coincidental timing of bAP and the excitatory postsynaptic potential. Such coding modulations could provide the basis for a novel learning rule and may be important factors in the integration of spatiotemporal input information in neural networks in the brain. [Copyright &y& Elsevier]