p-Chloroamphetamine: evidence against a serotonin mediated learning deficit in PKU

Progress in experimental phenylketonuria: a critical review

Experimental progress in the development of an accurate and useful model of phenylketonuria (PKU) during the last 15 years is reviewed in detail. From this review it is clear that the recent emergence of models using the combined administration of phenylalanine (phe) and p-chlorophenylalanine (PCPA) constitutes a major success that lays the groundwork for future research into the pathogenesis and treatment of PKU. Biochemical evidence on the pathophysiology of PKU is also briefly reviewed in the context of the behavioral and biochemical adequacy of the models used. It appears that in the past biochemical investigations into PKU have been impaired by use of inadequate models, a situation that should now change if the best of the phe-PCPA models are more widely adopted. New trends in PKU research involve the role of large neutral amino acids other than phe as potential aids in the treatment of PKU and the appearance of a new model based on the use of alpha-methylphenylalanine (AMPhe) combined with phe. It appears that PKU research may be on the brink of a new and productive era as investigations into these promising areas unfold and as new emerge through the full utilization of existing models.

Facilitation of avoidance acquisition in rats produced by P-chlorophenylalanine or P-chloroamphetamine

The effects of reducing brain serotonin using p-chlorophenylalanine (PCPA) were examined as a follow up to our previous report that reducing serotonin with p-chloroamphetamine (PCA) facilitated Y-maze avoidance acquisition and reduced open field activity. In the current work, PCPA was also found to facilitate Y-maze avoidance acquisition, while open field activity, although reduced, was not reduced significantly. In a second experiment, we re-examined PCA, except that the apparatus was changed in order to test the generality of the effect of PCA on avoidance performance in a task other than the Y-maze. Testing was also run at varying shock intensities to determine if this was a significant determinant of the effect. PCA reliably facilitated shuttle-box avoidance acquisition and did so at all shock intensities tested. Finally, in a third experiment, the time course of the onset of the PCA-induced avoidance facilitation was examined and found to develop 8--10 hours following drug treatment and not at a shorter drug to test interval of 4 hours. The present data, in conjunction with our previous data support the concept that lowered brain serotonin content facilitates avoidance acquisition regardless of the specific method used to reduce serotonin or to assess avoidance acquisition.

Rapid tolerance to the motor effects of p-chloroamphetamine in rats

Studies were designed to test the hypothesis that tolerance to the effect of p-chloroamphetamine (PCA) on motor activity in rats would develop with repeated injections. In related biochemical studies the effects of single or repeated doses of PCA on the in vitro synaptosomal uptake of 3H-NE and 3H-DA and on the in vivo metabolism of intraventricularly administered 3H-NE and 3H-DA were investigated. The administration of 10 mg/kg of PCA induced a complex behavioral syndrome, which was quantified by scoring specific symptoms after direct observation. In agreement with previous data, this syndrome appears to be mediated by a release of 5-HT since pretreatment with PCA prevented its development on subsequent injection of the drug. After the administration of lower doses of PCA, total motor activity as measured in activity cages increased, and tolerance to this effect also developed rapidly. For example, pretreatment with 5 mg/kg of PCA greatly attenuated the stimulant effect of a subsequent dose of 3 or 5 mg/kg of the drug. Moreover, the degree of tolerance was the same if the time between the 2 injections was 1 day or 2 weeks, suggesting that 5-HT release is also involved in the tolerance to the motor effects of lower doses of the drug. Moreover, biochemical studies of the response of catecholaminergic neurons to PCA suggest that tolerance does not develop to the effects on DA and NE neurons on repeated injection of PCA.

Induced PKU in rats: effects of age and melatonin treatment

Newborn rats injected on Days 1-8 of life with L-phenylalanine (2 g/kg) and p-chlorophenylalanine (80 mg/kg) displayed biochemical symptoms analogous to human phenylketonuria (PKU) and maze learning impairments. The behavioral effects were less evident in rats treated on Days 9-16 or 7-24. None of the symptoms observed were alleviated by simultaneous administration of melatonin (10 mg/kg/day).

A comparative study of different amphetamines on copulatory behavior and stereotype activity in the female rat

The influence of D- and L-amphetamine, fenfluramine, and p-chloroamphetamine on female copulatory behavior (lordosis response) and the induction of stereotype activity was compared. Lordosis response in the female rat has been shown to be inhibited by increased central nervous serotonergic (5-HT) as well as dopaminergic (DA) activity. A dose-dependent inhibitory effect on the estrogen- + progesterone-induced lordosis response in ovariectomized rats was demonstrated after treatment with the four amphetamines. In contrast, only D- and L-amphetamine induced a stereotype activity, which is considered to be mediated by DA mechanisms. A decrease in DA receptor activity, achieved by pimozide pretreatment, abolished the effect of D-amphetamine on lordosis behavior, but the effect of L-amphetamine was only slightly diminished and the action of fenfluramine and p-chloroamphetamine was unaffected. On the other hand, both L- and D-amphetamine-induced stereotype activity was prevented by pimozide treatment. The data suggest that the D-amphetamine effect on lordosis behavior is mediated by increased DA receptor activity. Although it induces stereotype activity by increased DA activity, L-amphetamine, like fenfluramine and p-chloroamphetamine, inhibits the lordosis response by some other action presumably related to serotonergic mechanisms.