Search

The creation of seizure-prone (Fast) and seizure-resistant (Slow) rat strains via selective breeding implies genetic control of relative seizure vulnerability, yet ample data also advocates an environmental contribution. To investigate potential environmental underpinnings to the differential seizure sensitivities in these strains, the authors compared amygdala kindling profiles in adult male Fast and Slow rats raised by (a) their own mother, (b) a foster mother from the same strain, or (c) a foster mother from the opposing strain. Ultimately, strain-specific kindling profiles were not normalized by cross-fostering. Instead, both strains became more seizure-prone regardless of maternal affiliation (i.e., cross-fostered groups from both strains kindled faster than uncrossed controls). Interhemispheric seizure spread was also facilitated in cross-fostered Slow rat groups and was associated with increased commissural cross-sectional areas, giving them a Fast-like profile. It is important to note, however, that all Fast groups remained significantly more seizure-prone than Slow groups, suggesting that although the postnatal environment strongly influenced seizure disposition in both strains, it did not wholly account for their relative dispositions. Investigation into mechanisms fundamental to cross-fostering-induced seizure facilitation should help prevent postnatal worsening of pathology in already seizure-prone individuals. Keywords: kindling, cross-fostering, seizure susceptibility, epigenetic

Fischer and Lewis rat strains often serve as animal vulnerability models for drug abuse and addiction. When these strains respond for drugs of abuse, several measures, including total drug intake, response rate and progressive-ratio breakpoints, have been reported to be strain-dependent, a result suggesting genetic differences in drug reactivity and vulnerability. The present study extends these strain comparisons to a previously untested measure--demand analysis. In Experiment 1, four Fischer and four Lewis rats earned their daily food ration by lever pressing under a fixed-ratio schedule, the size of which was increased every three sessions from 3 to 1,000 in logarithmic steps. Consumption was plotted as a function of ratio size, and modeled by the exponential-demand equation (Harsh & Silberberg, 2008). Experiment 2 replicated Experiment 1 except that different rats were used, and cocaine reinforced lever pressing. A between-experiment comparison showed a commodity-by-strain interaction: Fischer rats defended consumption with greater vigor when cocaine served as the reinforcer than did Lewis rats; for food, this relation was reversed. However, for both strains, defense of consumption of food exceeded that of cocaine. Keywords: exponential model of demand, cocaine, food, Fischer rats, Lewis rats

Clinical and epidemiological studies provide strong data for a relationship between prenatal ethanol exposure and the risk for abuse in adolescent and young adult humans. However, drug-acceptance results in response to fetal exposure have differed by study, age at evaluation, and experimental animal. In the present study, the authors tested whether voluntary ethanol intake was enhanced in both the infantile and adult rat (15 and 90 days of age, respectively), as a consequence of chronic fetal drug experience. Experimental rats were exposed in utero by administering ethanol to a pregnant dam in a liquid diet during gestational Days 6-20. Compared with those for isocaloric pair-fed and ad lib chow control animals, the results for experimental animals demonstrated that fetal exposure significantly increased infantile affinity for ethanol ingestion without affecting intake patterns of an alternative fluid (water). Heightened affinity for ethanol was absent in adulthood. Moreover, the results argue against malnutrition as a principal factor underlying the infantile phenomenon. These data add to a growing literature indicative of heightened early postnatal acceptance patterns resulting from maternal use or abuse of ethanol during pregnancy. Keywords: fetal ethanol exposure, postnatal ethanol affinity, ethanol abuse, ethanol drinking behavior, fetal learning

The study describes a novel method for tinnitus screening in rats by use of gap detection reflex procedures. The authors hypothesized that if a background acoustic signal was qualitatively similar to the rat's tinnitus, poorer detection of a silent gap in the background would be expected. Rats with prior evidence of tinnitus at 10 kHz (n = 14) exhibited significantly worse gap detection than controls (n = 13) when the gap was embedded in a background similar to their tinnitus. No differences between tinnitus and control rats were found with 16 kHz or broadband noise backgrounds, which helped to rule out explanations related to hearing loss or general performance deficits. The results suggest that gap detection reflex procedures might be effective for rapid tinnitus screening in rats. Keywords: tinnitus, screening, behavior, gap detection, startle