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Two Wistar rat lines, selectively bred for high-anxiety-related behavior (HAB) and low-anxiety-related behavior (LAB) in the elevated plus-maze test, were tested for the susceptibility of their behavioral characteristics to anxiolytic treatment and for their endocrine and physiological reactivity to different stressors. Injection of 1 mg/kg diazepam failed to affect line differences in coping strategy but resulted in a marked (20-fold) decrease in plus-maze anxiety in HAB rats; whereas, the anxiolytic effect was less pronounced in LAB animals. Biotelemetrical measurements revealed that HAB and LAB rats do not significantly differ in their baseline body temperature, locomotor activity, food and water intake, or in stress-induced alterations of the diurnal rhythms in these parameters. However, line differences were found in acute changes in body temperature and locomotor activity following stress exposure, LAB rats responding with a greater, albeit shorter, increase in body temperature and activity than HAB animals. Basal ACTH and corticosterone plasma levels as well as pituitary reactivity to intravenously administered CRH (40 ng/kg) were similar in both lines, although, especially in response to plus-maze exposure, HAB rats tended toward higher ACTH secretion than LAB rats. These data confirm that animals with high or low basal levels of anxiety may be a promising model for studying the mechanisms of action of anxiolytic substances. Nevertheless, the endocrine findings support the notion that the reactivity of the hypothalamo-pituitary-adrenocortical system and anxiety-related behavior can be regulated independently.

Over the past years, two breeding lines, derived originally from outbred Wistar rats, have been established that differ markedly and consistently in their anxiety-related behaviour in the elevated plus-maze. At the age of ten weeks, rats were tested once on the elevated plus-maze and the males and females displaying the most anxious and the least anxious behaviour were sib-mated to start a new generation of the high anxiety-related behaviour (HAB) and the low anxiety-related behaviour (LAB) lines, respectively. The resulting difference in emotionality between these two lines was also evident in an open field test and correlated with differences in the forced swim test. In the open field, the HAB rats tended to be less active and explored the central zone of the open field much less than the LAB animals. In the forced swim test, HAB rats started floating earlier, spent significantly more time in this immobile posture and struggled less than LAB rats. However, in an olfactory-cued social discrimination task there was no difference between male and female animals from either line. The overall performance in these various behavioural tests suggests that selective breeding has resulted in rat lines not only differing markedly in their innate anxiety-related behaviour in the plus-maze, but also in other stress-related behavioural performances, suggesting a close link between the emotional evaluation of a novel and stressful situation and an individual's coping strategy.

In order to test the hypothesis that prenatal hormones influence the emotional maturation of the offspring, the hypothalamo-pituitary-adrenal (HPA) axis activity was studied at the end of pregnancy in two rat breeding lines differing consistently in their innate anxiety-related behaviour in the elevated plus-maze. Virgin and pregnant rats were fitted with a chronic jugular vein catheter and tested 5 days later. The high basal level of anxiety-related behaviour (HAB) described in males and females of the HAB breeding line persists in pregnancy as indicated by a significantly reduced number of entries into and time spent on the open arms of the elevated plus-maze between days 18 and 20 of pregnancy compared with pregnant rats of the breeding line with low anxiety-related behaviour (LAB). In general, an increase in anxiety was found in both breeding lines in pregnancy compared with the respective virgin controls. With respect to HPA axis activity, increased basal levels of adrenocorticotropin (ACTH) and corticosterone have been found in pregnant rats of the HAB line compared with pregnant LAB rats. ACTH and corticosterone secretion in response to emotional and complex physical stressors (exposure to the elevated plus-maze and forced swimming, respectively) did not differ between virgin and pregnant rats of either breeding line. However, independent of the inborn emotionality of the animals, a general attenuation in the HPA axis response to stressors and to exogenous CRH could be confirmed in pregnant rats. The basal and stress-induced activity of the hypothalamo-neurohypophysial system secreting oxytocin and vasopressin was also tested, and no differences were found relating to the emotionality or reproductive state of the animals except for a reduced vasopressin secretion in pregnant HAB rats after forced swimming. The elevated basal activity of the HPA axis, including enhanced circulating concentrations of corticosterone in pregnant HAB rats, may influence both the neuroendocrine and emotional development of their offspring. Thus, the passing-on of maternal behavioural characteristics via prenatal, hormonal 'imprinting' has to be considered as a possible contribution to emotional maturation during an individual's development.

In order to study the dynamics of ethanol drinking behaviour, male Wistar rats were given the free choice between tap water, and 5, 10 and 20% ethanol solutions. After 8 weeks of continuous access, the animals were repeatedly deprived of the ethanol solutions for 3 days every 4 weeks. In the first experiment, drinking patterns were recorded for 24 h with an electronic drinkometer device, at different time-points of ethanol experience and after an ethanol deprivation episode. The preference for more highly concentrated ethanol solutions as well as ethanol consumption increased with continuing ethanol experience. Furthermore, after the ethanol deprivation episode, the animals immediately and preferentially drank from the 20% ethanol solution, the most highly concentrated ethanol solution offered. Additionally, the number of drinking bouts, particularly at the 10 and 20% ethanol solutions, was increased during the first hour after ethanol re-presentation. In a second experiment, the effects of repeated ethanol deprivation experience, inherent in this self-administration paradigm, on anxiety-related behaviour were tested on the elevated plus-maze. Repeated ethanol deprivation proved to be more anxiogenic than the first deprivation experience. Taken together, these findings suggest that ethanol deprivation is anxiogenic in long-term voluntarily ethanol-drinking rats, which is increased by repeated ethanol deprivation experience. The possibility that anxiety during ethanol deprivation might contribute to the 'relapse'-like drinking behaviour is discussed.

Arginine vasopressin (AVP) or its V1 receptor antagonist d(CH2)5Tyr(Me)AVP was administered directly into the septal brain area of adult male rats by means of inverse microdialysis. Immediately after a 30-min dialysis period, during which either approximately 0.25 ng AVP or 5 ng of the V1 antagonist were delivered into the brain tissue, anxiety-related behaviour of the animals was measured on an elevated plus-maze apparatus. While synthetic AVP failed to alter plus-maze behaviour compared to vehicle-treated controls, animals treated with the V1 receptor antagonist made more entries into (P < 0.01) and spent more time on the open arms (P < 0.05), indicating reduced anxiety. Since administration of neither AVP nor the V1 antagonist significantly influenced general locomotor activity of the rats on the plus-maze and in an open field, these data point towards a critical involvement of intraseptally released AVP in the emotional evaluation of novel situations.

We studied the role of central amygdala CRH receptors in behavioral responses to an anxiogenic stimulus. An antisense oligodeoxynucleotide corresponding to the rat CRH1 receptor mRNA was infused chronically into the central amygdaloid nucleus of male rats via osmotic minipumps (0.25 micrograms/0.5 microliters/h). Control groups received infusions of either a scrambled sequence oligodeoxynucleotide or vehicle. On the 4th day of treatment, rats were subjected to 10 min of social defeat and immediately afterwards tested on the elevated plus-maze. Antisense oligodeoxynucleotide-treated rats spent significantly more time exploring the open arms of the plus-maze than scrambled sequence- and vehicle-treated animals, both of which did not differ from each other. The social discrimination test, on the other hand, revealed no difference in juvenile recognition abilities among the treatment groups. Using in situ hybridization and receptor autoradiography, we were not able to detect clear signals of CRH1 receptor mRNA and CRH binding sites in the central amygdaloid nucleus of either group, confirming the reportedly low expression and density of CRH receptors in this brain area. The present data support the view that CRH receptors in the central nucleus of the amygdala are involved in the mediation and expression of anxiety-related behavior, but simultaneously raise questions as to the mechanisms of antisense oligodeoxynucleotide action.