Gain in sensitivity and loss in temporal contrast of STDP by dopaminergic modulation at hippocampal synapses

Abstract

Spike-timing-dependent plasticity (STDP) is considered a physiologically relevant form of Hebbian learning. However, behavioral learning often involves action of reinforcement or reward signals such as dopamine. Here, we examined how dopamine influences the quantitative rule of STDP at glutamatergic synapses of hippocampal neurons. The presence of 20 M dopamine during paired pre-and postsynaptic spiking activity expanded the effective time window for timing-dependent long-term potentiation (t-LTP) to at least ؊45 ms, and allowed normally ineffective weak stimuli with fewer spike pairs to induce significant t-LTP. Meanwhile, dopamine did not affect the degree of t-LTP induced by normal strong stimuli with spike timing (ST) of ؉10 ms. Such dopamine-dependent enhancement in the sensitivity of t-LTP was completely blocked by the D1-like dopamine receptor antagonist SCH23390, but not by the D2-like dopamine receptor antagonist sulpiride. Surprisingly, timing-dependent long-term depression (t-LTD) at negative ST was converted into t-LTP by dopamine treatment; this conversion was also blocked by SCH23390. In addition, t-LTP in the presence of dopamine was completely blocked by the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid, indicating that D1-like receptor-mediated modulation appears to act through the classical NMDA receptor-mediated signaling pathway that underlies STDP. These results provide a quantitative and mechanistic basis for a previously undescribed learning rule that depends on pre-and postsynaptic ST, as well as the global reward signal.dopamine receptor ͉ synaptic plasticity ͉ learning ͉ memory ͉ reward A ctivity-dependent synaptic plasticity through long-term potentiation (LTP) and long-term depression (LTD) is believed to serve as the cellular substrate for various forms of learning and memory (1, 2). For neurons experiencing spiking activity, it has been found that the direction of subsequent synaptic plasticity can be determined by near coincident pre-and postsynaptic firing: LTP is induced when presynaptic firing precedes postsynaptic spike, and paring in the converse order results in LTD (3, 4). Such spike-timing-dependent plasticity (STDP) has been widely used in modeling naturally occurring synaptic plasticity (5). Meanwhile, several lines of evidence show that the quantitative rule of STDP can vary across synapses in different brain areas, and even on the same dendrites, or axons (3, 4). Also, the STDP rule can be dynamically regulated by the activity of adjacent synapses (6) or by the activation of ␤-adrenergic receptors and M1 muscarinic cholinergic receptor (7,8). Therefore, rather than being a stereotypic learning rule, it is clear that STDP is influenced or modulated by various intrinsic and external factors.Behavioral learning often involves reward processes. In such learning, the activity of dopamine neurons has been shown to code for prediction error and uncertainty (9). Animal experiments have shown that blockade of dopamine receptors impairs learning and memory, and dopamin...

Functional Requirements for Reward-Modulated Spike-Timing-Dependent Plasticity

“…1 A). Overall, the interaction of the Hebbian eligibility trace with a global success factor is an example of a three-factor rule (Reynolds et al, 2001;Jay, 2003) applied to spiking neurons (Seol et al, 2007;Pawlak and Kerr, 2008;Zhang et al, 2009).…”

“…Thus, the amount of plasticity cannot be decomposed into an STDP curve and a multiplicative factor that determines the amplitude of STDP. Another recent study in hippocampal cell cultures indicates, moreover, that an increase in dopamine level can convert the LTD (post-before-pre) component of STDP into LTP, whereas the LTP (pre-before-post) component remains unchanged in amplitude but changes its coincidence requirements (Zhang et al, 2009). Similar effects have been observed for the interaction of STDP with other neuromodulators (Seol et al, 2007).…”

“…From a theoretical perspective (Dayan and Abbott, 2001), these forms of plasticity relate to unsupervised learning rules, i.e., the behavioral relevance of synaptic changes is not taken into account. Recently, however, it was shown that the outcome of many plasticity experiments, including STDP, depends on neuromodulation (Seol et al, 2007), in particular the presence of dopamine (Jay, 2003;Pawlak and Kerr, 2008;Wickens, 2009;Zhang et al, 2009), a neuromodulator known to encode behavioral reward signals (Schultz et al, 1997). Inspired by these findings, a number of theoretical studies have investigated the hypothesis that reward-modulated STDP could be the neuronal basis for reward learning (Seung, 2003;Xie and Seung, 2004;Farries and Fairhall, 2007;Florian, 2007;Izhikevich, 2007;Legenstein et al, 2008).…”

“…Moreover, synaptic plasticity in general (Reynolds and Wickens, 2002;Jay, 2003) and STDP in particular (Pawlak and Kerr, 2008;Zhang et al, 2009) are subject to dopaminergic modulation.…”

Activation of β2-adrenoceptor enhances synaptic potentiation and behavioral memory via cAMP-PKA signaling in the medial prefrontal cortex of rats

“…Because the timing between pre-and postsynaptic firing specifies synaptic change, tLTP has become an attractive mechanism to model naturally occurring plasticity, particularly in learning-induced changes in cortical cells. The threshold, magnitude, timing window, and gating of tLTP is influenced by catecholaminergic inputs in the cortex and the hippocampus (Lin et al 2003;Seol et al 2007;Zhang et al 2009;Xu and Yao 2010;Edelmann and Lessmann 2012). In the present study, we examined the role of prefrontal cortical b2-AR in tLTP with timing-dependent stimulation of pre-and postsynaptic activity.…”