ABSTRACTThe nucleus accumbens (NAc) is a mesocorticolimbic structure that integrates cognitive, emotional and motor functions. Although its role in psychiatric disorders is widely acknowledged, the understanding of its circuitry is not complete. Here we combined optogenetic and whole-cell recordings to draw a functional portrait of excitatory disambiguated synapses onto D1 and D2 medium spiny neurons (MSNs) in the adult mouse NAc core. Comparing synaptic properties of ventral hippocampus (vHipp), basolateral amygdala (BLA) and prefrontal cortex (PFC) inputs revealed a hierarchy of synaptic inputs and feedforward inhibition that depends on the identity of the postsynaptic target MSN. Thus, the BLA is the dominant excitatory pathway onto D1 MSNs (BLA > PFC = vHipp) while PFC inputs dominate D2 MSNs (PFC > vHipp > BLA). Feedforward inhibition of MSN firing too, was input and cell-type specific: while minimal at vHipp-D1 and vHipp-D2 inputs; it inhibited with similar efficacy BLA-D1 or BLA-D2 inputs, was minimal at PFC-D1 but maximal at PFC-D2 inputs. We also tested the hypothesis that endocannabinoids endow excitatory circuits with pathway- and cell-specific plasticity. Thus, while CB1 receptors (CB1R) uniformly depress excitatory pathways irrespective of MSNs identity, TRPV1 receptors (TRPV1R) bidirectionally control inputs onto the NAc core in a pathway-specific manner. Finally, we show how the interplay of TRPV1R/CB1R shapes plasticity at identified BLA-NAc synapses. Together these data shed new light on synapse and circuit specificity in the adult NAc core and illustrate how endocannabinoids contribute to pathway-specific synaptic plasticity.SIGNIFICANCE STATEMENTWe examined the impact of connections from the ventral hippocampus (vHipp,) basolateral amygdala (BLA) and prefrontal cortex (PFC) onto identified medium spiny neurons (MSN) in the adult accumbens core. We found BLA inputs were strongest at D1 MSNs while PFC inputs dominate D2 MSNs. We evaluated the role of the endocannabinoid system in pathway- and cell-specific plasticity and found that CB1 receptors (CB1R) and TRPV1 receptors (TRPV1R) bidirectionally control synaptic transmission and plasticity onto accumbens’ MSNs in a pathway- and cell-specific manner. Finally, we clarify how the interplay of TRPV1R/CB1R shapes plasticity at identified BLA-NAc synapses.
Projections from ventral hippocampus to medial prefrontal cortex but not nucleus accumbens remain functional after fornix lesions in rats