Trigeminal and olfactory pathways mediating isolation distress and companion comfort responses in rat pups.

Isolation in a novel test cage elicits ultrasonic vocalization (USV) in 12-13-day-old rat pups, and the presence of an anesthetized littermate companion reduces USV while eliciting body contact. These responses were studied in pups with surgical lesions of trigeminal snout afferents and after olfactory denervation by nasal ZnSO4 perfusion. With lesions of only one system, body contact with the passive companion was reduced by 20%, and interpup orientation was differentially affected by the two types of lesions. However, USV rates were no different from littermate controls in the presence of the companion or when tested alone. Combined lesions of both systems reduced contact time 55% and eliminated any reduction in USV rates by the companion while leaving intact USV and locomotor responses to isolation. These results suggest that different sensory pathways may mediate isolation distress and companion comfort responses.