CHAPTER 1
 INTTRODUCTION

 Annually, approximately 6.6% of the national adult population suffers from

depression (Kessler et al., 2003). It is a wide-spread illness that interferes with the ability

to eat, sleep, work, and enj oy formerly pleasurable activities. The economic impact of

this devastating disorder is high, but the cost in human distress cannot be estimated.

 The 4th Edition of the Diagnostic and Statistical Manual of Mental Disorders

(1994) defines depression according to the following criteria, with at least Hyve of the

symptoms present on a daily basis for at least 2 weeks: depressed mood, loss of interest

or pleasure, significant weight loss or gain, insomnia or hypersomnia, psychomotor

agitation or retardation, fatigue, undue guilt and/or feelings of worthlessness,

indecisiveness, recurrent thoughts of death, and significant distress or impairment in

social or occupational functioning. These symptoms must represent a change from the

individual' normal level of interpersonal function.

 Maj or depression is also clinically characterized by altered hormonal function

stemming from ongoing elevations in overall organism distress. It has been well

established that chronic emotional stress plays a pivotal role in the genesis of many

psychiatric disorders such as depression (for review, see Agid et al., 2000). Chronic

stress weighs on the physiological systems that maintain homeostasis and produces

changes in the operating limits of those hormonal systems. Allostatic load, or the strain

from the elevated activity of systems under maj or stress, can predispose an animal to

many psychiatric disorders, including depression (McEwen and Stellar, 1993). The