Tenofovir disoproxil fumarate: toxicity, toxicokinetics, and toxicogenomics analysis after 13 weeks of oral administration in mice.

Tenofovir disoproxil fumarate (TDF) is a prodrug of tenofovir that exhibits activity against HIV and hepatitis B. The goals of this study were to evaluate the molecular mechanism of TDF-induced toxicity in mice after 13 weeks of daily oral administration (50-1000 mg/kg) by correlating transcriptional changes with plasma drug levels and traditional toxicology end points. Plasma levels and systemic exposure of tenofovir increased less than dose proportionally and were similar on days 1 and 91. No overt toxicity was observed following the completion of TDF administration. The kidneys of TDF-treated mice were histopathologically normal. This result is consistent with the genomic microarray results, which showed no significant differences in kidney transcriptional levels between TDF-treated animals and controls. In liver, after 4 and 13 weeks, cytomegaly was observed in mice treated with 1000 mg/kg of TDF, but mice recovered from this effect following cessation of administration. Analysis of liver transcripts on day 91 reported elevated levels of Cdkn1a in TDF-treated animals compared with controls, which may have contributed to the inhibition of liver cell cycle progression.

The conditioning of dyspneic suffocation fear. Effects of carbon dioxide concentration on behavioral freezing and analgesia.

Previous studies in our laboratory have shown that a single exposure to 100% carbon dioxide (CO2) can serve as an effective unconditioned stimulus (US) in a Pavlovian aversive-context conditioning paradigm in rats. Although the US exposure parameters employed in the initial studies were sufficient for producing a context-specific enhancement of behavioral freezing and analgesia, it had yet to be determined whether variations of these CO2 conditioning procedures would produce other conditioning effects. Thus, the purpose of the following experiment was to investigate the intensity of the US on the conditioned response (CR). The findings confirm that variations in CO2 concentrations produce changes in the CR that are consistent with principles of Pavlovian conditioning. The findings lend additional support to the tenability of a dyspneic suffocation fear theory of panic disorder, a theory that postulates that at least one type of panic attack could be a consequence of Pavlovian conditioning.

Central nervous system effects of caffeine and adenosine on fatigue.

Caffeine ingestion can delay fatigue during exercise, but the mechanisms remain elusive. This study was designed to test the hypothesis that blockade of central nervous system (CNS) adenosine receptors may explain the beneficial effect of caffeine on fatigue. Initial experiments were done to confirm an effect of CNS caffeine and/or the adenosine A(1)/A(2) receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) on spontaneous locomotor activity. Thirty minutes before measurement of spontaneous activity or treadmill running, male rats received caffeine, NECA, caffeine plus NECA, or vehicle during four sessions separated by approximately 1 wk. CNS caffeine and NECA (intracerebroventricular) were associated with increased and decreased spontaneous activity, respectively, but caffeine plus NECA did not block the reduction induced by NECA. CNS caffeine also increased run time to fatigue by 60% and NECA reduced it by 68% vs. vehicle. However, unlike the effects on spontaneous activity, pretreatment with caffeine was effective in blocking the decrease in run time by NECA. No differences were found after peripheral (intraperitoneal) drug administration. Results suggest that caffeine can delay fatigue through CNS mechanisms, at least in part by blocking adenosine receptors.

Differential release of corticotropin-releasing hormone (CRH) in the amygdala during different types of stressors.

The purpose of this study was to determine if differences exist between the effects of acute treadmill running and restraint stress on corticotropin-releasing hormone (CRH) release within the amygdala of rats. Extracellular CRH immunoreactivity (CRH-IR) was measured in microdialysate collected from the central nucleus of the amygdala (CeA) during exposure to an inactivated treadmill (TC), during 1 h treadmill running to exhaustion (RUN), and 1 h restraint (RES). Extracellular CRH-IR increased from control levels during the first 20-min period for TC, RUN, and RES, with the largest increase during RES. During the second 20-min period, only RES maintained levels higher than control values. CRH release was higher than control during the third 20-min period of RES and RUN. A second experiment consisted of four groups of either cage controls (CC), TC, RUN, or RES. Immediately following the 60-min treatment, brains were removed and trunk blood collected for analysis of tissue CRH-IR and plasma corticosterone. While amygdala tissue CRH-IR was not different in the CC, TC and RUN rats, these groups had significantly lower levels than the RES animals. Hypothalamic tissue CRH-IR was not different between the CC and TC rats, but the levels were significantly higher in the RES and RUN rats than in the two control groups. Plasma corticosterone levels were elevated only in RES and RUN rats. Results from tissue analysis indicate that increased tissue CRH-IR in the amygdala and hypothalamus can be elicited by RES, while only the hypothalamus shows an increase following RUN. Further, extracellular CRH release in the CeA is increased throughout the period of RES, when rats are placed on the treadmill, and when the animals are approaching physical exhaustion. No increase is observed during the running period between placement on the treadmill and intense exertion. Overall, the data suggest that amygdala CRH release is regulated differently during treadmill running and restraint.