H. Peter Pfister

The glucocorticosterone response to novelty as a psychological stressor

Abstract The 11-hydroxycorticosterone response in non-pregnant and pregnant rats to novelty as a psychological stressor was examined. Past studies have mostly emphasized short duration of exposure to the novel environment. The present study aimed at investigating the elevation and habituation of the 11-hydroxycorticosterone response to repeated exposures (30 min daily) to the novel environment. It was found that on Day 1 of exposure in non-pregnant and pregnant rats the 11-hydroxycorticosterone elevation is approximately four fold, and then gradually habituating over days. No significant elevation above control levels were obtained after 5 days of exposure to the novel environment in nulliparous animals. Novelty is a powerful but simple tool in psychological stress research.

Corticosterone and prolactin responses to predictable and unpredictable novelty stress in rats.

Prolactin along with corticosterone is a stress responsive hormone. The present study examined the effect of predictable and unpredictable psychological stress on corticosterone and prolactin secretion. Repeated unpredictable exposure to the novelty cage produced a more substantial increase in the level of corticosterone than predictable exposure to the same novelty apparatus. In contrast, predictable novelty stress induced a more substantial elevation in prolactin levels than unpredictable stress. Furthermore, it was observed that both corticosterone and prolactin returned to control levels 30 minutes after the fifth exposure to the novelty cage. It was concluded that the pattern of exposure to novelty is an important paradigm which effects the magnitude of hormonal responding. An important relationship between corticosterone release and prolactin secretion is also indicated.

Time course of the corticosterone and prolactin response following predictable and unpredictable novelty stress in Rattus norvegicus

Marked changes in corticosterone and prolactin levels are observed following repeated psychological stress. Furthermore, these responses appear to be affected by the pattern of exposure to the stressor. The present study examined the time course of the corticosterone and prolactin responses following predictable and unpredictable novelty stress. On the fifth day of stress treatment, predictable and unpredictable exposure to the novelty apparatus produced a peak corticosterone response after 15 min of stress treatment. Although corticosterone levels began to decline for both these treatment groups after 15 min, substantially higher levels were observed following unpredictable stress. The steroid levels of animals receiving unpredictable stress treatment continued to be significantly higher than those receiving predictable stress until 30 min post-stress. Predictable stress failed to significantly alter prolactin levels from controls at any of the time points examined. However, unpredictable exposure to the novel apparatus produced high baseline prolactin levels and a subsequent suppression of this response during exposure to the stressor. It was concluded that the differences obtained between animals receiving predictable and unpredictable exposure to novelty reflect a difference in the magnitude of these responses rather than a difference in their temporal pattern.

Prenatal exposure to predictable and unpredictable novelty stress and oxytocin treatment affects offspring development and behavior in rats.

Prenatal stress in rats usually results in behavioral and developmental changes in offspring. This experiment assessed body weight during the first three weeks postpartum and subsequent behavior of the offspring when tested as adults. Pregnant females allocated to the stress condition were exposed during the third week of pregnancy to either predictable (NOV1) or unpredictable (NOV2) psychological novelty stress. At this time, pregnant rats were also treated with various doses of oxytocin or vehicle solution. The exposure to unpredictable novelty stress during the third week of pregnancy resulted in pups which were significantly heavier at birth than either control animals or those which had received predictable exposure to the novelty stress. In contrast, oxytocin treatment appeared to lower body weight of offspring compared to control animals. This effect was observed right up until Day 21 postpartum for animals exposed to the larger dose (11.6 I.U.) of oxytocin. When tested as adults, NOV1 and NOV2 offspring were found to defecate more in the open field setting suggesting the they were more emotional than control animals. It was concluded that psychological stress during pregnancy has a subtle effect on development and subsequent effects on later emotionality of the offspring when tested as adults.

Influence of exogenously administered oxytocin on the corticosterone and prolactin response to psychological stress.

Prolactin along with corticosterone is a stress responsive hormone. Evidence suggests that oxytocin (OXT) modulates not only ACTH secretion but also prolactin release. The present study was therefore designed to examine the possible role of oxytocin in the corticosterone and prolactin response to predictable and unpredictable novelty stress. Repeated stress and oxytocin treatment produced a substantial increase in corticosterone. A greater increase was obtained for the larger OXT dose (11.6 IU/kg) than for the smaller dose (5.8 IU/kg). In addition, for the smaller oxytocin dose only, unpredictable exposure to the novelty apparatus produced a more substantial increase in corticosterone than predictable exposure to the same stressor. In contrast, oxytocin produced a significant suppression of the prolactin response in all OXT treated animals. No significant interaction between stress and oxytocin was obtained. It was concluded that an important role exists for oxytocin in the modulation of both corticosterone and prolactin secretion.

Differential preference for and activation by the odoriferous compartment of a shuttlebox in fear-conditioned and naive rats.

Adult, male Wistar rats were either fear conditioned in a Plexiglas tube or were subjected to a control procedure. Each animal was subsequently placed in a two-compartment shuttlebox and tested for activity and time spent in the compartment of the shuttlebox which contained odoriferous fecal materials generated by other fear-conditioned rats. The results showed that fear-conditioned rats were significantly less active than control animals and spent significantly less time than control animals in the odoriferous compartment of the shuttlebox. In addition, control animals spent significantly more time in the odoriferous compartment than in the nonodoriferous compartment. These findings suggest that odors generated by stressed rats do not have alarm pheromone properties.

α-Melanocyte-stimulating hormone conditioned suppression of a lipopolysaccharide-induced fever ☆

Recent investigations have demonstrated the susceptibility of various components of the immune system to behavioral conditioning, using a conditioned taste aversion (CTA) paradigm. In Experiment 1 the effective antipyretic dose (40 micrograms/kg) and duration of antipyretic action (up to 4 hr) of alpha-melanocyte-stimulating hormone (alpha-MSH) was determined in rats tested with lipopolysaccharide (LPS). In the second experiment, alpha-MSH was used as the unconditioned stimulus (UCS) and paired with a novel-tasting saccharin solution (0.1%) to elicit a conditioned antipyretic response to a fever induced one hour previously by LPS. Both the antipyretic effect of alpha-MSH and the pyrogenic effect of LPS were found to be significantly conditionable. The conditioning of fever/antipyretic responses demonstrates for the first time that still another aspect of the host response can be influenced by conditioning procedures.

Prenatal psychological stress effects on offspring behaviour in rats

Prenatal stress experienced by the mother usually results in behavioural changes in the offspring. The first part of this study is concerned with the mothers, who were either psychologically stressed or were subjected to a control procedure, during pregnancy. At weaning one-half of each group of mothers was used to establish the glucocorticosterone levels (11-OHCS), which were found to be lower for females of the stress group than the females of the control group. The other half of the mothers of the two groups was used to establish short term stress levels of the glucocorticosterone response. Similar elevations in the stress response for both groups of mothers were obtained. The second part of the study examined the behaviour of the offspring using the open-field. One set of offspring was tested at 45 days of age while another set was tested at 90 days of age. Both ambulation and defecation measures were taken. In addition glucocorticosterone levels were also obtained before and after the open-field testing. The ambulation measure revealed habituation both for animals tested at 45 and 90 days of age. With respect to the defecation measure no significant difference between the groups was obtained at 45 days of age. However, those animals tested at 90 days have a significantly lower defecation score for rats of the stress group as compared to those of the control graup. The major finding of this study is in the glucocorticosterone response. Animals tested at 45 days of age responded with a significant elevation of glucocorticosterone for rats of the stress group as compred with those of the control group. This finding is reversed for those animals tested at 90 days of age. The decrease of glucocorticoids in stressed animals, tested at 90 days of age, can be explained in terms of the traditional view in prenatal psychological stress research, i.e., high levels of 11-OHCS during the prenatal period resulted in a decreased 11-OHCS responsiveness. This is inconsistent with the results obtained at 45 days of age. An alternative explanation is examined which suggests that stressed mothers habituated quickly to the stressor and that during pregnancy pups were subjected to less rather than more of the circulating steroids.

New Technology for Administering Group Tests

Abstract With the emergence of laptop computers, one could have expected to see large-scale group testing to be switched from paper and pencil to computers. Yet little evidence is available which would suggest that testing has followed that trend. One of the main reasons is “keyboard phobia”. This paper examines how one can overcome this keyboard problem by employing barcode technology that enables one to use computer processing without the problems associated with keyboards or screens. The paper highlights some of the advantages and disadvantages associated with this new technology and discusses new measures associated with computer testing. In addition, test publishing and the possible use of barcode technology in the interactive testing mode is also discussed.

Conversion between control mechanisms in simulated flight: an ab initio quasi-transfer study

Skill acquisition in simulated flight was examined to identify differences between transfer effects facilitated by yoke and joystick flight control systems. Flight naive participants (N = 32) twice completed 15 consecutive visual landing approach trials in a low fidelity fixed based synthetic flight trainer. Acquisition and transfer phases were completed one week apart with either the prior or alternate control. Vertical deviations from a constant three degree glideslope angle were analysed. Results revealed evidence of positive transfer. The results are discussed in relation to similarity based transfer theories and avenues for future research are proposed.