Exposure of stress precipitates a coordinated series of responses which may lead to changes in brain functions. Most of the changes in brain function are mediated by stress-induced activation of neurotransmitter systems in the brain, which include neurotransmitter receptors and these receptors-mediated signal transduction pathways. The signal transduction pathways are ultimately responsible for stress-induced changes in neuronal functions. Some of these changes are beneficial, however, depending upon the nature and duration of stressful stimuli, the changes in neuronal functions may be harmful, which may lead to many disorders. In the present chapter, we describe comprehensively the effects of stress on neurotransmitter receptors and various molecules of signal transduction pathways in brain. © 2005 Elsevier B.V. All rights reserved.