Anatomically, along with cholinergic

inputs, glutamatergic afferents from brain structures such as pedunculopontine tegmental nucleus (PPTg), subthalamic nucleus (STN), and prefrontal cortex (PFC) provide main forms of excitatory inputs to the midbrain DA neurons (Grace et al., 2007). NMDA receptors (NMDARs), members of the ionotropic glutamate receptor family, are important regulators of DA neuron activity. First, synaptic plasticity in the glutamatergic afferents to DA neurons depends on NMDARs (Bonci and Malenka, 1999, Overton et al., 1999 and Ungless et al., 2001). This plasticity can be modulated by experiences, environmental factors, and psychostimulant drugs (Bonci and Malenka, 1999, Kauer and Malenka, 2007 and Saal et al., 2003). Second, iontophoretic administration of NMDAR antagonists, but not AMPAR-selective antagonists, attenuated phasic firing of DA neurons, Selisistat chemical structure an activity linked to reward/incentive salience (Schultz, 1998), without changing the frequency of tonic firing (Overton and Clark, 1992). Third, in drug addiction studies, NMDARs in DA neurons are essential for developing nicotine-conditioned place preference (Wang et al., 2010) and likely also involved in cocaine-conditioned place preference (Engblom et al., 2008 and Zweifel et al., 2008). Thus, we postulated that modulation

of DA neurons by NMDARs might be important in engaging DA neurons in the habit learning. Here, HIF activation we set out to examine the roles of NMDARs in DA neurons, by generating DA neuron-specific NR1 knockout mice and testing them in a variety of habit-learning paradigms (Devan and White, 1999, Dickinson et al., 1983, Packard et al., 1989 and Packard and McGaugh, 1996). In order to understand the

cellular mechanisms, we also recorded the DA neurons in these mice using multielectrode in vivo neural-recording techniques (Wang and Tsien, 2011). These mice, named “DA-NR1-KO,” were produced by crossing floxed NR1 (fNR1) mice (Tsien et al., 1996) with Slc6a3+/Cre transgenic mice that express Cre recombinase under DA transporter promoter ( Zhuang et al., 2005) ( Figures 1A and 1B). The DA neuron-specific deletion of the NR1 gene was confirmed by both the reporter gene method ( Figure 1C) and immunohistochemistry ( Figure 1D), which showed that the gene deletion was restricted to the dopaminergic neurons in regions such as the VTA and the substantia nigra. (-)-p-Bromotetramisole Oxalate No obvious changes were observed in the expression pattern of tyrosine hydroxylase (TH), the catecholamine neuronal marker, suggesting that there was no obvious loss of dopaminergic neurons (see Figure S1 available online). DA-NR1-KO mice were born in the expected Mendelian ratios and visually indistinguishable from the controls. Additionally, they were normal in locomotor activities in a novel open field (Figure 2A), in learning the rotarod tests (Figure 2B), in an anxiety test using the elevated plus maze (Figure 2C), and in the novel object recognition tests (Figure 2D).