neuroprotection Nitrous oxide is neurotoxic and long-term or habitual use can cause severe neurological damage. Like other NMDA receptor antagonists, it has been suggested that produces neurotoxicity in the form of Olney's lesions in rodents upon prolonged (several hour) exposure. New research has arisen suggesting that Olney's lesions do not occur in humans, however, and similar drugs such as ketamine are now believed not to be acutely neurotoxic. It has been argued that, because is rapidly expelled from the body under normal circumstances, it is less likely to be neurotoxic than other NMDAR antagonists. Indeed, in rodents, short-term exposure results in only mild injury that is rapidly reversible, and neuronal death occurs only after constant and sustained exposure. Nitrous oxide also may cause neurotoxicity after extended exposure because of hypoxia. This is especially true of non-medical formulations such as whipped-cream chargers (also known as "whippets" or "nangs"), which never contain oxygen, since oxygen makes cream rancid. In heavy (≥400 g or ≥200 L of gas in one session) or frequent (regular, e.g. daily or weekly) users reported to poison control centers, signs of peripheral neuropathy have been noted: the presence of ataxia (gait abnormalities) or paresthesia (perception of abnormal sensations, e.g. tingling, numbness, prickling, mostly in the extremities). These are considered an early sign of neurological damage and indicates chronic toxicity. Nitrous oxide at 75% by volume reduces ischemia-induced neuronal death induced by occlusion of the middle cerebral artery in rodents, and decreases NMDA-induced Ca2+ influx in neuronal cell cultures, a critical event involved in excitotoxicity. DNA damage Occupational exposure to ambient nitrous oxide has been associated with DNA damage, due to interruptions in DNA synthesis. This correlation is dose-dependent and does not appear to extend to casual recreational use; however, further research is needed to confirm the duration and quantity of exposure needed to cause damage. Oxygen deprivation If pure nitrous oxide is inhaled without oxygen, oxygen deprivation can occur, resulting in low blood pressure, fainting, and even heart attacks. This can occur if the user inhales large quantities continuously, as with a strap-on mask connected to a gas canister. It can also happen if the user engages in excessive breath-holding or uses any other inhalation system that cuts off a supply of fresh air. Vitamin B deficiency Long-term exposure to nitrous oxide may cause vitamin B deficiency. This can cause serious neurotoxicity if the user has preexisting vitamin