Neonatal Stress on Adult Stress

¶ … Neonatal Stress on Adult Stress Response

The current study discusses the impact of neonatal stress on adult stress responses. There has been some suggestion that risk assessment defensive behaviors in rodents might resemble some of the behavioral/somatic symptoms of generalized anxiety in humans (Wall & Messier, 2001). Through the previous research conducted often utilizing elevated plus-maze (EPM). There are several hypothesis being tested, they include: STRESS animals will have less Closed arm entries then CONTROL animals, STRESS animals will have less Open arm entries then CONTROL animals, CONTROL animals will have a greater percentage of open arm entries (over total entries), then STRESS animals. STRESS animals will exhibit less Rearing Behavior then CONTROL animals, STRESS animals will spend more time in Closed arms then CONTROL animals, STRESS animals will spend less time in Open arm then CONTROL animals, CONTROL animals will spend a greater percentage of time on open arms (over total time), then STRESS animals. These hypotheses are tested in the current study utilizing previous research and results in order to clarify all prospective outcomes.

It is widely acknowledged that pregnancy is a state associated with drastic physiological and psychological changes. The alterations in maternal physiology that are initiated and maintained by pregnancy-related hormone secretions can, for the most part, be interpreted as biological adaptations to the needs of the developing fetus. (Field, McCabe, & Schneiderman, 1985, p. 161)

One of the most popular animal tests used is the EPM; during a five-year period, over 100 different research laboratories have reported on its use (Hogg, 1996). It is used as a screening tool for anxioselective effects of drugs. However, the use of this test has increased to include a use that allows for better understanding of the biological basis of emotionality as it relates to learning and memory, pain, hormones, addition and withdrawal, sub-types of anxiety disorders, anxiety phobias, and posttraumatic stress. The EPM provides evidence regarding altered emotionality in animals, as well as a tool successful in defining brain areas related to fear/anxiety. Advantages to the EPM include simplicity in design and bi-directional drug sensitivity, short training procedures, no need for food/water deprivation etc. There are a number of variables related to the use of the EPM are divided into two groups organismic and procedural feature of the EPM concerns the effect of prior test experience on subsequent behavioral and pharmacological responses (Carobez & Bertoglio, 2005).

Zellner & Ranaldi (2006), discuss their study, which addresses whether neonatal isolation affects acquisition of an operant response but did not address whether it affects motivation to respond after acquisition has occurred. Due to the strong connections between motivation and depression, and between early stress and depression, the researchers were interested in investigating whether or not neonatal isolation leads to changes in motivation to respond for natural reward, once the operant response is acquired. In the study, an operant conditioning procedure design was utilized to assess motivation for food. Results indicate that isolated male rats separated during the dark phase showed reduced responding for sucrose on a progressive ratio schedule when compared to non-handled controls, although rats isolated during the light phase showed normal responding.

As commonly used, the term "stressor" indicates a situation or event appraised as being aversive in that it elicits a stress response which taxes a person's physiological or psychological resources as well as possibly provokes a subjective state of physical or mental tension. As relevant scientific data have accumulated, however, a simple, universally accepted definition of stress has become increasingly elusive. (Anisman & Merali, 1999, p. 241)

Behavior of selectively bred lines of rats may provide evidence for genetic influences on EPM behavior. Acute stressors have also been reported to be influential on the behavior exhibited by animals on the EPM. Opposing evidence on the effects of repeated testing of rats and mice on behavior on the EPM exists. Some groups have reported an anxiogenic tendency, while others observed that repeated testing did not alter baseline behaviors. A significant determinant in the outcome of studies on the EPM is the method that is adopted for scoring the animals behavior, as it is this, which determines the numerical values on which conclusions are based (Hogg, 1996). The human stress response is influenced by a host of personality characteristics and life experiences that cannot be duplicated in animal studies. (Anisman & Merali, 1999, p. 241)

Because stressful stimuli often elicit cortisol secretion, some researchers have proposed the use of cortisol levels as an index of the stress response. (Anisman & Merali, 1999, p. 241)

Researchers have indicated that human and animal anxiety/stress profiles differ along cognitive behavioral lines. These findings are based on the idea that anxiety is understood as an affective (emotional) state in humans (Wall & Messier, 2001). Research was conducted regarding stress utilizing Rhesus monkeys. The study uses a hormone Adrenocorticotropic hormone (ACTH) which was injected into half of the pregnant Rhesus monkeys in the study. ACTH is secreted from the anterior pituitary in response to corticotropin-releasing hormone from the hypothalamus. It is secreted in response to various types of stress. Blood samples were collected from the controls and ACTH treated females to evaluate the effect of the injections at 1 and 2 weeks. The samples were obtained 4 hours after the injection, and the cortisol levels elicited on the final day of the 2-week treatment show ACTH markedly elevated adrenal activity in the pregnant female; the very high cortisol levels were comparable after both morning and afternoon injections. The saline control females continued to have normal, baseline levels of cortisol for this stage of pregnancy, and evinced the expected diurnal rhythm, with higher cortisol during the morning and lower titers in the early evening. (Lewis & Ramsay, 1999, p. 24) the research concluded that gestational length did not vary and pregnancies went normal to term.