Neuroprotective agents or neuroprotectants are drugs intended to protect the brain or spinal cord from damage caused by neurological diseases or injury. The mechanisms by which they reduce damage are not yet fully understood, although it is believed that antioxidants protect neurons from toxic levels of amino acids. Neuroprotectants often greatly increase the chances of recovery and are used to treat various neurological conditions such as stroke, Alzheimer’s Disease, Parkinson’s Disease, etc.
The cannabinoids THC and CBD are examples of neuroprotective agents. In test scenarios, cortical neuron cultures in rats were exposed to toxic levels of glutamate (a neurotransmitter). After administering THC/CBD to the rats, both chemicals proved to reduce neurotoxicity levels.
(Reference: http://www.cannabis.net/cannabinoids/neuroprotectant.html)