Depression is a devastating mental disease that affects up to 10% of the population. Its neurobiological basis is unknown. Traditionally, depression was thought to be caused by a deficiency in the monoamine neurotransmitter molecules, such as serotonin. Based on that assumption, antidepressant drugs were developed to prevent the breakdown of monoamines. However, recent advances in neuroscience have demonstrated that the effects of antidepressants on monoamine levels are immediate, whereas actual changes in mood take many weeks, which means the ability of antidepressants to effectively treat depression is likely due to long term changes in other systems. There is growing evidence linking depression to the endocannabinoid system – a group of molecules and their receptors that act as a modulatory system, fine-tuning the body's responses to a variety of stimuli. Various studies have suggested that endocannabinoids may be reduced in depression and that use of antidepressants may act to increase them. Mathew Hill is examining the relationship between endocannabinoid and antidepressants. He is specifically interested in determining if increasing endocannabinoid activity is a common response to all types of antidepressants; if changes in the endocannabinoid system are required for antidepressants to work; and if increasing endocannabinoid activity alone is sufficient to elicit an antidepressant response. Results from his study will contribute to a better understanding of the neurobiology of depression and ultimately may lead to a new class of antidepressants.