Social Modulation during Songbird Courtship Potentiates Midbrain Dopaminergic Neurons

Synaptic transmission onto dopaminergic neurons of the mammalian ventral tegmental area (VTA) can be potentiated by acute or chronic exposure to addictive drugs. Because rewarding behavior, such as social affiliation, can activate the same neural circuitry as addictive drugs, we tested whether the intense social interaction of songbird courtship may also potentiate VTA synaptic function. We recorded glutamatergic synaptic currents from VTA of male zebra finches who had experienced distinct social and behavioral conditions during the previous hour. The level of synaptic transmission to VTA neurons, as assayed by the ratio of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) to N-methyl-D-aspartic acid (NMDA) glutamate receptor mediated synaptic currents, was increased after males sang to females, and also after they saw females without singing, but not after they sang while alone. Potentiation after female exposure alone did not appear to result from stress, as it was not blocked by inhibition of glucocorticoid receptors. This potentiation was restricted to synapses of dopaminergic projection neurons, and appeared to be expressed postsynaptically. This study supports a model in which VTA dopaminergic neurons are more strongly activated during singing used for courtship than during non-courtship singing, and thus can provide social context-dependent modulation to forebrain areas. More generally, these results demonstrate that an intense social encounter can trigger the same pathways of neuronal plasticity as addictive drugs

Cocaine triggered AMPA receptor redistribution is reversed in vivo by mGluR-dependent long-term depression

Drugs of abuse induce long-lasting changes in neural circuits that may underlie core components of addiction. Here we focus on glutamatergic synapses onto dopamine (DA) neurons of the ventral tegmental area (VTA). Using an 'ex vivo' approach in mice, we show that a single injection of cocaine caused strong rectification and conferred sensitivity to the polyamine Joro spider toxin (JST) of AMPAR-mediated excitatory postsynaptic currents (AMPAR EPSCs), indicating the recruitment of receptors that lack GluR2. This qualitative change in transmission was paralleled by an increase in the AMPAR:NMDAR ratio and was prevented by interfering with the protein interacting with C kinase-1 (PICK1) in vivo. Activation of metabotropic glutamate receptors (mGluR1s) by intraperitoneal injection of a positive modulator depotentiated synapses and abolished rectification in slices of cocaine-treated mice, revealing a mechanism to reverse cocaine-induced synaptic plasticity in vivo