Influence of ifenprodil on the ACTH-induced behavioral syndrome in rats

The influence of nicardipine and ifenprodil on the brain free arachidonic acid level and behavior in hypoxia-exposed rats

1. The effects of the calcium channel blockers, nicardipine and ifenprodil, on the brain free arachidonic acid level and learning ability in rats exposed to hypoxia were examined. 2. Adult rats were injected with 0.003; 0.01; 0.03; 0.1; 0.3 or 1.0 mg/kg of tested drugs i.p. Thirty min later the learning ability was tested in a passive avoidance task according to the step-through procedure. Immediately after the training trial, the animals were subjected to a period of oxygen deprivation hypoxia until the loss of the righting reflex. The retention trial was carried out 24 hr later. 3. The other groups of animals were pretreated with mentioned substances before hypoxia-exposure. Fifteen min after the loss of the righting reflex they were decapitated and brains were frozen in liquid nitrogen. The brain free arachidonic acid level was quantified by gas chromatography. 4. Both nicardipine and ifenprodil were effective in preventing a memory decline in hypoxia-exposed rats but did not prevent the accumulation of the brain free arachidonic acid in hypoxia-exposed rats. 5. The protective effects of both substances in behavioral studies during acute brain damage caused by hypoxia could not be explained by the prevention of the increase of the brain free arachidonic acid, but by some other mechanism.

Blockade of the polyamine site of NMDA receptors produces antinociception and enhances the effect of morphine, in mice

The possible effect of ifenprodil--a potent antagonist at the polyamine site of the NMDA receptor complex--on nociceptive threshold and morphine analgesia was investigated in mice. In the hot plate test, the intraperitoneal (i.p.) injection of ifenprodil significantly prolonged the reaction time of mice at the dose of 30 mg/kg, and increased the analgesic effect of morphine. In the phenylquinone writhing test, ifenprodil reduced the number of abdominal constrictions of mice starting from the dose of 2.5 mg/kg i.p., and increased the effect of morphine. The effect of ifenprodil on pain threshold was prevented by naloxone. Moreover, ifenprodil antagonized the pain threshold-reducing effect of alpha-melanocyte-stimulating hormone (0.05 microgram/mouse, intracerebroventricularly). These data show that blockade of the polyamine site of the NMDA receptor complex produces analgesia and increases the analgesic effect of morphine.

Nitric oxide is involved in the ACTH-induced behavioral syndrome

In many animal species, the ICV injection of ACTH and of several shorter sequences of the ACTH molecule (melanocortin peptides) induces a peculiar behavioral syndrome mainly characterized by excessive grooming and by repeated acts of stretching and yawning. In adult males, spontaneous penile erections with ejaculation are also induced. We have studied the effect of NO synthase inhibition on this behavioral syndrome. The IP injection of the NO synthase inhibitor L-NG-nitroarginine methyl ester (NAME) significantly prevented--at the doses of 50 and 100 mg/kg--all the behavioral symptoms induced by the ICV administration of ACTH(1-24) (4 micrograms/rat). On the other hand, the ICV injection of NAME (up to 300 micrograms/rat) had no influence on the ACTH-induced excessive grooming and stretching, while significantly inhibited the display of yawnings and penile erections. These data indicate that brain NO synthase is involved in the mechanism of ACTH-induced yawning and penile erections, whereas peripheral NO synthase is involved in the induction of stretching and grooming.