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The Roman high- and low-avoidance (RHA/Verh and RLA/Verh) rat lines represent, respectively, low emotional/anxious and high novelty seeker vs. high emotional/anxious and low novelty seeker profiles. In the present study, RLA/Verh and RHA/Verh rats, either reared in pairs from weaning (untreated) or reared in groups of 8-10 in an enriched environment until the age of 7 months, were tested for exploratory and novelty-seeking behavior in the hole board (including novel objects under the holes), as well as for their preference for saccharin-water and ethanol-water in a two-bottle free-choice paradigm. Testing started when rats were 20 months old in order to study the long-lasting effects of differential rearing. RHA/Verh rats explored more and showed greater preference for (and intake of) saccharin as well as for ethanol than RLA/Verh rats, thus confirming their validity as a rat model for sensation/reward seeking. Environmental enrichment (EE) increased head-dipping behavior (i.e., novelty seeking) in both rat lines, without affecting locomotor activity. EE treatment increased the preference for, and volume intake of, saccharin (especially at the higher concentrations tested) in the relatively low saccharin-preferring RLA/Verh rats, and also enhanced ethanol consumption in both rat lines. Thus, the results demonstrate consistent and enduring effects of EE on incentive-seeking behavior and further the analysis of how individual differential predispositions for the need of novelty and contact with (or consumption of) rewarding substances arise through either biological (genetic) or early environmental factors, or both.

The effect of infantile handling stimulation and/or perinatal flumazenil (Ro 15-1788; a benzodiazepine receptor antagonist; 3.7 mg/kg/day) administration on exploratory and emotional-related behavior was investigated using adult females from the Roman high- and low-avoidance (RHA/Verh and RLA/Verh) lines. When rats (6 months old) were exposed to a hexagonal tunnel maze including an illuminated central arena, it was found that RHA/Verh rats were more active, explored more maze area, showed more outward preference, and more frequently entered the illuminated center than RLA/Verh rats. In addition, postnatal stimulation decreased emotional-related behavior in both lines of rats, as expressed by increased entry into, and time spent in, the central arena. Perinatal flumazenil treatment decreased entry into the maze central arena in both rat lines but this effect was counteracted by postnatal (handling) stimulation. Thus, the present study extends to adult RHA/Verh and RLA/Verh rats the positive long-lasting effects of postnatal handling and shows postnatal handling × flumazenil interactions in some behavioral parameters related to the pattern of exploration and exploratory efficiency.

The frequency of shock-induced fighting, posturing and “no reaction” (running/ jumping or freezing), after acute SC injections of 0, 0.1, 0.2 and 0.4 mg/kg nicotine, was measured in 38 pairs of male and 12 pairs of female rats. Sensitivity of footshock was also measured, at the same nicotine doses, in males. Nicotine inhibited shock-induced fighting in 32 pairs of high-frequency fighting males in a dose-dependent fashion, with fighting being gradually replaced by posturing at the 0.1 and 0.2 mg/kg doses. There was a significant increase in the “no reaction” category (especially freezing behavior) only at 0.4 mg/kg, indicating that reduced activity may have been partly responsible for the reduction in fighting seen at that dose. None of the doses had a significant effect on sensitivity to footshock. Nicotine had no effect on shock-induced fighting in the six low-frequency fighting male pairs, and affected the female pairs only at the 0.4 mg/kg level, where fighting was also decreased due to an increase in the “no reaction” category. It could be concluded that small doses of nicotine, under favorable conditions, were capable of inhibiting shock-induced fighting in rats without altering shock sensitivity or depressing activity.

The behavior of male rats with chronic end-to-side portacaval shunts or control surgery were evaluated in a complex enclosed maze, an open-field arena, and a swim canal. Subsequently, serotonin and 5-hydroxyindoleacetic acid levels were measured for hypothalamus, striatum, hippocampus, and midbrain-medulla. Chronic portacaval anastomosis did not significantly alter any of the behavioral parameters evaluated in the diverse test situations studied, despite a significant elevation of 5-hydroxyindoleacetic acid levels in all brain regions analyzed and the elevation of serotonin levels in hypothalamus and midbrain-medulla.