Chronic stress is a risk factor for the development of psychopathologies characterized by cognitive dysfunction and deregulated social behaviours. Emerging evidence suggests a role for cell adhesion molecules, including ​nectin-3, in the mechanisms that underlie the behavioural effects of stress. We tested the hypothesis that proteolytic processing of nectins by matrix metalloproteinases (MMPs), an enzyme family that degrades numerous substrates, including cell adhesion molecules, is involved in hippocampal effects induced by chronic restraint stress. A reduction in ​nectin-3 in the perisynaptic CA1, but not in the CA3, compartment is observed following chronic stress and is implicated in the effects of stress in social exploration, social recognition and a CA1-dependent cognitive task. Increased ​MMP-9-related gelatinase activity, involving N-methyl-D-aspartate receptor, is specifically found in the CA1 and involved in ​nectin-3 cleavage and chronic stress-induced social and cognitive alterations. Thus, ​MMP-9 proteolytic processing emerges as an important mediator of stress effects in brain function and behaviour.