Previous research in rodents and humans has implicated the ventral hippocampus in regulating anxiety. However, many rodent studies examining ventral hippocampal neuronal pathways have utilized lesions that create nonspecific and/or nonreversible damage to the region. The present study sought to characterize the role of ventral hippocampal glutamatergic pyramidal neurons in modulating anxiety-like behavior during exposure to a variety of threatening stimuli. Five weeks prior to testing, male Long-Evans hooded rats received ventral hippocampal viral-vector infusions expressing either pAAV-CaMKIIα-hM4D-mCherry (DREADD) or pAAV-CaMKIIa-EGFP (GFP). DREADD transfection allowed for the specific, noninvasive and temporary inhibition of ventral hippocampal glutamatergic neurons immediately before threat presentation. Rats were evaluated for behaviors congruent with anxiety- or fear-like defensive states (e.g., freezing, risk assessment, avoidance, etc.) during testing in the elevated plus-maze and light-dark exploration test, or footshock-induced contextually conditioned fear, respectively. Analyses revealed a significant effect of DREADD inhibition that was dependent on the type of threat exposure. Specifically, compared to GFP controls, DREADD-induced silencing of ventral hippocampal glutamatergic neurons reduced anxiety-like behavior in the elevated plus-maze and light-dark test, without reliably affecting the expression of conditioned fear. The present results confirm that ventral hippocampal glutamatergic pyramidal neurons are recruited in rats during exposure to anxiety-inducing stimuli. These data add to a growing literature implicating the ventral hippocampus as a key region involved in modulating anxiety-like behaviors in rodents, primates and humans
