Effect of the radioprotector WR-2721 on operant behavior in the rat

Radiation-induced cognitive dysfunction: The protective effect of ethyol in young rats

PURPOSE

To evaluate the protective learning and memory effect of Ethyol in irradiated young rats.

METHODS AND MATERIALS

One hundred twenty-eight 45-day-old Wistar rats received whole brain fractionated radiation (30 Gy), whereas 48 rats received sham irradiation. Four irradiated subgroups were defined: saline, 37.5 mg/kg, 75 mg/kg, and 150 mg/kg Ethyol. Sequential behavioral studies including one-way and two-way avoidance tasks were undertaken before and after radiation.

RESULTS

Before radiation, the performances of all groups were similar. For the one-way avoidance task, at 1, 3, and 6 months postradiation, saline-irradiated rats had a lower percentage of avoidance than sham- or Ethyol- (75 or 150 mg/kg) irradiated rats (p <or= 0.001). Nevertheless, lower percentage of avoidance (p <or= 0.001) was only seen at 1 month postradiation in saline-irradiated rats, after comparison with their preradiation values. For the two-way avoidance task, performed only after radiation, saline-irradiated rats had a lower percentage of avoidance than sham- or Ethyol- (150 or 75 mg/kg) irradiated rats at 1, 2.5, 4.5, and 7.5 months (p = 0.000). Rats treated with Ethyol did not differ from sham-irradiated rats in both avoidance tasks, except for the 37.5 mg/kg-Ethyol group which showed lower performances 6 months postradiation (p = 0.005, one-way avoidance).

CONCLUSIONS

Treatment with 75 or 150 mg/kg of Ethyol prevents radiation-induced learning and transitory memory dysfunction in young rats.

Dopaminergic modulation of ventilation in obese Zucker rats

To investigate the hypothesis that the impaired respiratory drive noted in morbid obesity was attributable to altered dopaminergic mechanisms acting on peripheral and/or central chemoreflex sensitivity, seven obese and seven lean Zucker rats were studied at 11 wk of age. Ventilation (VE) was measured by the barometric technique during hyperoxic (100% O(2)), normoxic (21% O(2)), hypoxic (10% O(2)), and hypercapnic (7% CO(2)) exposures after the administration of vehicle (control), haloperidol [Hal, 1 mg/kg, a central and peripheral dopamine (Da) receptor antagonist], or domperidone (Dom, 0.5 mg/kg, a peripheral Da receptor antagonist). In both lean and obese rats, Hal increased tidal volume and decreased respiratory frequency during hyperoxia or normoxia, resulting in an unchanged VE. In contrast, Dom did not affect tidal volume, frequency, or VE during hyperoxia or normoxia. During hypoxia, however, VE significantly increased from 1,132 +/- 136 to 1,348 +/- 98 ml. kg(-1). min(-1) (P < 0.01) after the administration of Dom in obese rats, whereas no change was observed in lean rats. Hal significantly decreased VE during hypoxia compared with control in lean but not obese rats. In both lean and obese rats, Hal decreased VE in response to hypercapnia, whereas Dom had no effect. Our major findings suggest that peripheral chemosensitivity to hypoxia in obese Zucker rats is reduced as a result of an increased dopaminergic receptor modulation in the carotid body.

Comparison of behavioral and radioprotective effects of WR-2721 and WR-3689

The behavioral effects of the radioprotectant agents ethiofos, S-2-(3-aminopropylamino)ethylphosphorothioic acid (WR-2721) and S-2-(3-methylaminopropyl)aminoethylphosphorothioic acid (WR-3689) were evaluated in rats trained to respond under a multiple fixed-interval 120-s, fixed-ratio 50-response (mult FI FR) schedule of milk reinforcement. Each compound produced dose-dependent reductions in responding under both schedules over the same dose range (100-180 mg/kg, IP); ED50s indicated that WR-3689 was slightly more potent than WR-2721. On several performance measures, WR-3689 produced greater decrements during a second dose-effect determination, whereas WR-2721 had more pronounced effects during the initial one. In a second series of studies, low (56 mg/kg) and high (180 mg/kg) doses of both drugs were tested for radioprotective effects in rats responding under an FR-50 schedule of milk reinforcement and exposed to a nonlethal (5 gray, Gy) or lethal (10 Gy) dose of ionizing radiation (60Co gamma rays). Neither dose of radiation altered FR response rates on the day of exposure (day 1). Five Gy of gamma radiation produced a 25-40% reduction in response rates on days 2-5 (24-72 h) after exposure. Neither dose of WR-2721 or WR-3689 provided significant protection against these performance decrements. All groups exposed to 10 Gy experienced a progressive decline in FR responding on days 2-5 after exposure. Performance of groups that received pretreatment with the 180-mg/kg dose of either drug or the 56-mg/kg dose of WR-3689 was maintained at significantly higher levels than saline-treated controls on days 4-5 after exposure to 10 Gy; however, even at these higher levels of performance response rates remained below 50% of preirradiation control levels. Subsequently, 56 and 180 mg/kg WR-3689 and 180 mg/kg WR-2721 were found to provide protection against the lethal consequences of the 10-Gy exposure. Thus, neither WR-2721 nor WR-3689 afforded any significant short-term protection against radiation-induced performance decrements when these drugs were administered at either behaviorally ineffective or behaviorally disruptive doses. Rather, the beneficial effects of these drugs paralleled their ability to antagonize radiation-induced lethality.