Luis Gil

Inbred Roman High- and Low-Avoidance Rats: Differences in Anxiety, Novelty-Seeking, and Shuttlebox Behaviors

In the present study, male inbred animals (from the 10th generation of an inbreeding program that has been carried out in parallel to that of the outbred Roman high- and low-avoidance rat lines), were compared for emotionality in different testing situations, exploratory behavior in the holeboard and two-way, active-avoidance acquisition. Compared to the inbred Roman high-avoidance (RHA-I/Verh) rats, inbred Roman low-avoidance (RLA-I-Verh) rats showed higher emotionality in the open field (reduced distance travelled and number of rearings, and increased self-grooming behavior), in the elevated plus-maze test (increased number of total and open-arm entries, reduced distance travelled in the open arms, and increased self-grooming behavior), and during the habituation period in the shuttle box (decreased number of crossings, increased self-grooming behavior and defecations). Results from the hyponeophagia test were not conclusive, probably due to the test-dependent hyperactivity shown by RHA-I/Verh rats. In the holeboard apparatus, RHA-I/Verh rats explored more than RLA-I/Verh rats, especially when novel objects were located beneath the holes. Finally, RHA-I/Verh animals rapidly acquired active, two-way (shuttlebox) avoidance, whereas RLA-I/Verh animals required four 50-trial sessions to achieve an assymptotic level of 30-40% avoidance. Thus, the behavioral patterns of the Roman inbred strains were very similar to those previously reported for the RHA/Verh outbred lines. Differences in locomotor activity, exploratory, and self-grooming behavior were actually greater between the inbred strains than between the outbred lines. Differences in defecation, however, although still significant, were not so pronounced as those noted previously at this laboratory with the outbred lines.

Enduring effects of environmental enrichment on novelty seeking, saccharin and ethanol intake in two rat lines (RHA/Verh and RLA/Verh) differing in incentive-seeking behavior

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.

Fearfulness and sex in F2 Roman rats: males display more fear though both sexes share the same fearfulness traits.

The pattern of sex differences in a large sample (about 400 for each sex) of F2-generation rats, derived from inbred Roman high- and low-avoidance strains differing in fearfulness and brain functioning, was investigated. We obtained measures from responses to a battery of novel/threatening tests [open field (OF), plus maze (PM), hole board (HB), activity (A), and acoustic startle reflex (ASR)] as well as learned fear paradigms [classical fear conditioning (CFC) and shuttlebox avoidance conditioning (SAC)]. The results showed that almost all behaviors assessed fit with a pattern of unidirectional sex effects characterized by male rats as being more fearful than females: males defecated more than females in the OF, PM, HB, ASR, and CFC; ambulated less in the OF, PM, A, and SAC; showed more self-grooming in PM and HB; explored the open arms of the PM and the holes of the HB less; displayed enhanced ASR; and showed poorer performance in the SAC task. We applied two factor analyses to each sex showing that, in general, they shared a common three-factor structure: a Learned Fear Factor comprising SAC and CFC responding, a Fear of Heights/Open Spaces Factor with the highest loadings for open arm behavior in the PM, and an Emotional Reactivity Factor, mainly grouping defecations, ambulation, and self-grooming. These results indicate that the essential components of fearful behavior are similar for both sexes in an inbred but genetically heterogeneous population.

Genetically-based behavioral traits influence the effects of Shuttle Box avoidance overtraining and extinction upon intertrial responding: a study with the Roman rat strains

In the present study, we evaluated the effects of extended exposure procedures to contextual fear cues as a way of reducing intertrial responses (ITRs), a characteristic stereotyped behavior displayed in 2-way Shuttle Box avoidance overtraining. We used rat strains psychogenetically selected for efficient (Roman high-avoidance; RHA) versus poor 2-way Shuttle Box performance (Roman low-avoidance; RLA), the former being fearless/impulsive relative to the latter. Additionally, Sprague-Dawley (SD) rats were compared with RHAs to have a measure of the ITRs exhibited by another, non-selected group of animals. The main findings were that after extended exposure RHAs diminished their ITRs without affecting avoidance performance, although they emitted a pattern of ITRs somewhat excessive as compared with SDs. We concluded that three factors could influence the expression of ITRs in RHA rats: (1) the repetitive and stereotyped responding induced by 2-way Shuttle Box overtraining; (2) contextual fear conditioning; and (3) a genetic background associated with high impulsiveness.

Differences between two psychogenetically selected lines of rats in a swimming pool matching-to-place task: long-term effects of infantile stimulation.

The present study explored the effects of infantile stimulation (i.e., neonatal handling or NH) on the performance of 18-month-old Roman high-avoidance (RHA/Verh) and low-avoidance (RLA/Verh) rats in a swimming pool matching-to-place (SPMP) test. This test (also called repeated acquisition and place learning-set paradigm) consists of administering pairs of consecutive trials in the Morris water maze. The difference between each “odd” and the consecutive “even” trial of a trial pair is considered to be a measure of working memory. The same rats were first tested for exploration and novelty-seeking in a hole-board test in the presence of novel objects, which showed that RHA/Verh rats were more explorative than their RLA/Verh counterparts, and that NH treatment augmented exploration in RLA/Verh rats, generally eliminating the genetically-based differences between the lines. RHA/Verh rats performed less efficiently than RLA/Verh rats in the SPMP test, and NH facilitated acquisition in the early stages of training in both rat lines, an effect that was presumably due to an improvement in the acquisition of spatial reference information. Performance during training also indicated that RHA/Verh rats showed less differentiated behavior between odd and even trials, indicating a relative working memory deficit at advanced ages in that rat line.

Differential Effects of Cohort Removal Stress on the Acoustic Startle Response of the Roman / Verh Rat Strains

Male and female rats of the inbred Roman/Verh strains, which have been psychogenetically selected and bred for good (RHA-I/Verh) and extremely poor (RLA-I/Verh) two-way avoidance acquisition, were evaluated in an acoustic startle response test. One half of the rats of each strain and sex were previously subjected to 30 min of isolation by removal of their cage partners (“cohort removal”). During the testing session each animal received 40 acoustic stimuli at interstimulus intervals of 30 seconds. The hyperemotional RLA-I/Verh rats (especially the males) showed stronger acoustic startle responses than did their RHA-I/Verh counterparts. Startle amplitudes of the RLA-I/Verh males were further enhanced by the stress of 30 min isolation, whereas cohort removal did not significantly affect startle response amplitudes in RHA-I/Verh rats of either sex or in females of the RLA-I/Verh strain.