Disrupted Activity in the Hippocampal–Accumbens Circuit of Type III Neuregulin 1 Mutant Mice

Neuregulin 1 (Nrg1), a schizophrenia susceptibility gene, is involved in fundamental aspects of neurodevelopment. Mice lacking any one of the several isoforms of Nrg1 have a variety of schizophrenia-related phenotypes, including deficits in working memory and sensorimotor gating, loss of spines in pyramidal neurons in the ventral subiculum, loss of dendrites in cortical pyramidal cells, loss of parvalbumin-positive interneurons in the prefrontal cortex, and altered plasticity in corticolimbic synapses. Mice heterozygous for a disruption in exon 7 of the Nrg1 gene lack Type III (cysteine-rich-domain-containing) isoforms and have sensorimotor gating deficits that may involve changes in the activity of a circuit involving projections from the ventral hippocampus (vHPC) to medium spiny neurons in the nucleus accumbens (nACC). To explore the neural basis of these deficits, we examined electrophysiological activity in the nACC and vHPC of these mice. Under urethane anesthesia, bursts of spontaneous activity propagated from the vHPC to the nACC in both wild-type and mutant mice. However, these bursts were weaker in mutant nACC, with reduced local field potential amplitude and spiking activity. Single units in mutant nACC fired less frequently within the bursts, and more frequently outside of the bursts. Moreover, within-burst nACC spiking was less modulated by vHPC activity, as determined by phase-locking to the low-frequency oscillatory components of the bursts. These data suggest that the efficacy of vHPC input to the nACC is reduced in the Type III Nrg1 heterozygotes, supporting a role for Nrg1 in the functional profile of hippocampal–accumbens synapses