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Psychology Basics Endocrine System TYPE OF PSYCHOLOGY: Biological bases of behavior FIELDS OF STUDY: Endocrine system Behavior, by definition, includes physiological events which are responses to internal and external stimuli; the endocrine system, through the action of hormones and in cooperation with the nervous system, plays a necessary role in bringing about these reactions in animals and humans. KEY CONCEPTS ∙ adrenal glands ∙ biopsychology ∙ endocrine system ∙ ethology ∙ hormone ∙ hypothalamus ∙ pituitary gland Curiosity about behavior, both animal and human, is of long standing. The suspicion that substances in the body contribute to behavior also has a long history. During the fifth century B.C.E., Hippocrates suggested, in his humoral theory, that personality was determined by four body fluids: phlegm, black bile, yellow bile, and blood. The dominance of one or another of the fluids was associated with a behavior pattern. A proportionate distribution of the fluids resulted in a balanced personality. This theory has contributed terms such as phlegmatic, sanguine, bilious, and good- or bad-humored to describe personality types and states of mind. Aristotle (384-322 B.C.E.) is reported to have performed castration experiments on both fowl and men in order to alter behavior. He believed that something produced by the testes caused typically male behavior. Several nineteenth century researchers continued the study of the connection between the testes and male reproductive behavior. In 1849, Arnold Adolphe Berthold initiated a series of experiments on cockerels. He removed the testes from six birds and noted their loss of "male" behavior. Testes were transplanted into the abdomens of half the castrated birds. Successful transplantation restored the typical male crowing and combativeness. During the late nineteenth and early twentieth centuries, the sciences became more organized. Interest in behavior and its causes continued. The science of ethology, which focuses on animal behavior, came into existence. In the early 1900's, John B. Watson founded a branch of psychology that became known as behavior science. This area of psychology concentrated on human behavioral studies. Eventually, ethology and behavior science contributed to biopsychology, a new branch of psychology which incorporates and applies data from neuroscience, genetics, endocrinology, and physiology in the quest for biological explanations of behavior. Biopsychology embraces several subdivisions. Physiological psychology focuses on nervous system and endocrine system research. Psychopharmacology specializes in the effects of drugs on the nervous system and, ultimately, on behavior. The development of therapeutic drugs is a goal of this discipline. The neuropsychologist studies the effects of brain damage on behavior. Psychophysiology differs from physiological psychology in that the psychophysiologist uses only human subjects while the physiological psychologist experiments on laboratory animals, especially rats. Early research in physiological psychology focused on the nervous system, but it soon became evident that the endocrine system also influenced behavior and that the effects of the two systems were interrelated contributors to behavior. The endocrine system essentially consists of ductless glands that produce chemical substances called hormones. The hormones elicit physiological reactions, either locally or at some distant target site. When acting at a distance, the hormones travel to the site by way of the circulatory system. Hans Selye, a Canadian scientist, proposed a direct connection between the endocrine system and behavior. In 1946, he described physiological events that were triggered by stress. This set of bodily changes became known as the general adaptation syndrome. The syndrome involved the mobilization of the autonomic nervous system, the adrenal glands, and the anterior lobe of the pituitary. As research continued, data on the role of the endocrine system in determining behavior began to accumulate. Researchers continue to look to the endocrine system to provide clues about the causes of psychiatric diseases and the efficacy of hormone therapy in treating the diseases, as well as in altering behavior patterns. INVERTEBRATES Among most invertebrates (animals without backbones), endocrine glands are not in evidence. Specialized cells known as neurosecretory cells serve as endocrine tissue. The cells, which resemble neurons (the functional cells of the nervous system) are hormone producers. In invertebrate animals such as the hydra and planaria, the secretions (hormones) of the neurosecretory cells seem to influence growth and may be the underlying cause of the tremendous powers of regeneration possessed by the animals. There are indications that the development of sexuality, the laying of eggs, and the release of sperm may be under hormonal control in these animals. Attempts to establish the link between hormones and invertebrate behavior when the hormones are produced by neurosecretory cells have inherent problems. A common method of studying hormone influence involves removal of the secreting organ, which causes a hormone deficit. Changes in physiology and/or behavior are observed. A hormone is then provided to the animal to see if the original condition can be restored. Utilization of this method is complicated by the difficulty in removing all the functioning neurosecretory cells. In addition, the cells regenerate rapidly. This prevents an accurate assessment of the effects of hormone deficit. Hormone effects are observable and measurable in the more developed invertebrates such as the Arthropoda. Studies carried out on insects and crustaceans indicate the presence of both neurosecretory cells and endocrine glands. Among the behaviors and activities controlled by the hormones released from either the cells or the glands are molting, sexual differentiation, sexual behavior, water balance, and diapause. Since arthropods are encased in an outer skeletal structure, it is necessary for the animals to shed their outer structure in order to grow. During the growth years, the animals go through cycles of shedding the outer skeleton or molting, growing, and reforming an outer coat. There is evidence that insects are under hormonal control when they enter a state of diapause, or arrested behavior in adverse times. VERTEBRATES All vertebrates (animals with backbones) have a well-developed and highly organized endocrine system. The system consists of the following glands: the pituitary, the pineal, the thyroid, the thymus, the pancreas, a pair of adrenals (each adrenal actually acts as two glands-the adrenal cortex produces unique hormones and functions independently of the adrenal medulla), a pair of parathyroids, and a pair of ovaries or testes. Endocrine tissue in the gastrointestinal tract readies the system for the digestive process. During a pregnancy, the placental tissue assumes an endocrine function. Although the kidneys do not produce a hormone directly, they release an enzyme which converts a blood protein into a hormone that stimulates red blood cell production. All vertebrates have a pituitary. The pituitary is a small, round organ found at the base of the brain. This major endocrine gland interacts with the hypothalamus of the nervous system. Together they control behavior. The hypothalamus keeps aware of physiological events in the body by monitoring the composition of the blood. In turn, the hypothalamus signals the pituitary by either a nerve impulse or a chemical messenger. The pituitary responds by releasing or ceasing to release hormones that will have a direct effect on physiology or will stimulate other endocrines to release their hormones in order to alter the physiological event and influence behavior. The endocrine system exerts its effects on a biochemical level. The human endocrine system is typical of vertebrate endocrine systems and their effect on behavior, although certain hormones may have a more pronounced and obvious effect in other vertebrates. For example, melanocyte-stimulating hormone, which is generated by the anterior lobe of the pituitary, greatly increases skin pigmentation in amphibians. This creates a protective coloration. In humans, the darkening effect is not achieved unless excessive hormone is administered. The protective function is not apparent. There are enough similarities among human and animal endocrine functions and effects, however, to warrant the use of data from both ethology and human behavioral studies in determining the biological bases for behavior. INFLUENCE ON REPRODUCTIVE BEHAVIOR The influence of the endocrine system on behavior has been studied on many levels. Much of the work has been done on animals; laboratory rats have been the most frequently used subjects. There is, however, a growing body of information on hormonal effects on a variety of human behaviors, including reproductive and developmental behavior, reaction to stress, learning, and memory. Studies carried out in reproductive and developmental biology on both animal and human subjects have substantiated the belief that hormones influence mating behavior, developmental events including sexual differentiation, and female and male sexuality. Castration experiments have linked the testes with a male mating behavior pattern in animals. The sexually active adult male animal aggressively seeks and attempts to mount the female whether she is receptive or not. The castrated male retains the ability to mount a female but loses the aggressiveness and persistent pursuit of females. The male may assume the more submissive female behavior and even engage in homosexual encounters. Normally, the release of reproductive hormones in the male is noncyclic, whereas in the female it is cyclic. Castrated animals begin to exhibit the female, cyclic pattern of hormone release. The hormonal influence is confirmed by administering androgens (male hormones) to the castrated animals. Male mating behavior and the noncyclic release of hormones returns. The presence of male hormones has an effect on the female cycle and sexual receptivity. Pheromones are substances secreted on the body of one individual which influence the behavior of another. These chemical messengers function during mate attraction, territoriality, and episodes of fear. Their existence and functions are well documented throughout the animal kingdom, especially among insects and mammals. In experiments using rats, it was shown that the pheromones act in conjunction with male hormones in bringing the female to a state of receptivity. The urine of noncastrated male rats contains androgens. When a male rat is introduced into a cage of sexually inactive females, the male sends off chemical signals by way of pheromones and the androgen-containing urine. The result is the accelerated onset of estrus, or sexual receptivity, on the part of the females. Castrated males produce pheromones but do not have androgens in the urine. When castrated males are introduced into a cage of inactive females, the estrous cycle is not affected. Female mammals, with the exception of monkeys, apes, and humans, also experience estrus. Under hormonal control, the female is receptive to the male once or twice a year, when her eggs are available for fertilization. This period of receptivity is known as the estrous phase, or heat. Research shows that the particular female hormone which induces estrus is progesterone. HORMONAL INFLUENCES The work done by researchers in developing contraceptives clarified the role of hormones in the functioning of the human female reproductive system. The system operates in a monthly cycle during which ovarian and uterine changes occur under hormonal control. These hormones do not affect the human female's receptivity, which is not limited to fertile periods. Testosterone derivatives known as anabolic steroids are illegally used by some athletes in an attempt to increase muscularity, strength, and performance. While both sexes do experience the desired effects, long-term, high-dosage usage has undesirable consequences. This is particularly true in the female, who begins to exhibit a deepening of the voice, a male body shape, and increased body and facial hair. Both males and females can become sterile. Psychotic behaviors and states such as depression and anger have been recorded. Rosemary Scheirer See AlsoEmotions; Hormones and Behavior; Memory: Animal Research; Stress: Physiological Responses. |
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