['NMDA receptor antagonists, like ketamine, produce a rapid-acting and long-lasting antidepressant effect. Although the mechanism is not completely understood, ketamine is thought to preferentially target NMDA receptors on fast-spiking parvalbumin (PV)-containing interneurons. The function of PV-containing interneurons is dependent on perineuronal nets, a specialized form of extracellular matrix that surrounds these cells.', 'Chondroitinase was used to enzymatically degrade perineuronal nets surrounding PV-containing interneurons in the ventral hippocampus (vHipp), a region that is involved in the antidepressant response to ketamine. Rats were tested on the forced swim test 30 minutes and one week after ketamine administration.', 'Thirty minutes after ketamine injection, both chondroitinase-treated and control animals had a decrease in immobility. One week later, however, the antidepressant-like response observed with ketamine was completely abolished in the chondroitinase-treated animals.'] Are hippocampal perineuronal nets required for the sustained antidepressant effect of ketamine?