This is a book about behavioral neuroscience. As a subdiscipline of both biology and psychology, behavioral neuroscience spans the breadth of neuroscience (Gallistel, 1980). Neuroscience itself is a new discipline, a hybrid intellectual entity derived from a number of other disciplines, including physiological psychology (Lashley, 1938; Stellar, 1954), psychobiology (Richter, 1943; Beach, 1948), and ethology (Tinbergen, 1969; Lorenz, 1981), as well as neuroanatomy, neurophysiology, neuroendocrinology, neuropsychology, logic, linguistics, and philosophy.

Specifically, this book focuses on how hormones influence behavior by their actions in the brain. Phylogenetically ancient chemical messengers produced by endocrine glands and the brain, hormones exert their influences throughout the body. Biologists separate them into two major classes: peptide hormones, which typically act on cell membranes to produce their effects, and steroid hormones, which act on the nuclei of cells to promote protein synthesis. The effects of the first class usually are rapid, whereas those of the second class are slow, although these distinctions between peptides and steroids and their rapid and delayed behavioral effects are beginning to become blurred (e.g., Wehling, Eisen, and Christ, 1992). Both peptide and steroid hormones have profound effects on behavior.

Hormones such as insulin, cholecystokinin, and bombesin (essential for feeding behavior and food regulation) are produced in gastrointestinal organs. Aldosterone, angiotensin, and atrial natriuretic factor (hormones involved in mineral and water balance) are produced in the adrenal glands, kidney, and heart.