Effects of amphetamines on the metabolism of catecholamines in the rat brain

Protracted 'pro-addictive' phenotype produced in mice by pre-adolescent phenylpropanolamine

For decades, the sympathomimetic phenylpropanolamine (PPA; +/- -norepinephrine) was an active ingredient found in popular children's over-the-counter (OTC) cold, cough, and allergy medications. To examine the possibility that pre-adolescent PPA exposure may induce neuroadaptations that influence behavioral and neurochemical responding to cocaine, C57BL/6J mice were pretreated with PPA (0-40 mg/kg) during postnatal days 21-31. The behavioral and neurochemical responses to acute and repeated cocaine (4 x 15 mg/kg) were then assessed in adulthood when the mice were 10 weeks of age. Whereas pre-adolescent PPA exposure did not influence the acute locomotor response to 15 mg/kg cocaine, PPA pre-exposure dose-dependently enhanced the expression of cocaine-induced place conditioning, reduced the expression of locomotor sensitization, but did not influence cocaine-induced stereotypy. Pre-adolescent PPA exposure completely prevented the capacity of cocaine to elevate extracellular levels of catecholamines in the nucleus accumbens, but facilitated the development of cocaine-induced glutamate sensitization. Neither acute nor repeated cocaine altered extracellular GABA levels in the accumbens of control mice; however, 15 mg/kg cocaine lowered GABA levels by approximately 40% in PPA pretreated mice and this effect showed tolerance with repeated cocaine administration. These data provide the first evidence that early exposure to an OTC compound produces protracted effects upon cocaine-induced changes in nucleus accumbens neurotransmission that may contribute to a 'pro-addictive' phenotype in adulthood.

Lack of involvement of 4-hydroxynorephedrine in phenylpropanolamine-induced anorexia in rats

The anorexic effects of phenylpropanolamine (PPA) appear to be qualitatively different in humans and rats. One factor that may account for these differences is that PPA is excreted essentially unchanged in humans, while nearly 30% is metabolized into 4-hydroxynorephedrine (4-OHN) in rats. To investigate the contribution of 4-OHN to the anorexic properties of PPA, this experiment compared the effects of equal doses (0.0-20.0 mg/kg, IP) of both drugs on eating and drinking during restricted feeding trials in the same group of food-deprived, female rats. Both 15.0 and 20.0 mg/kg of PPA significantly decreased eating when compared to saline vehicle, while 5.0-20.0 mg/kg of the drug reduced prandial drinking. In comparison, only the highest dose of 4-OHN (20.0 mg/kg) significantly suppressed food and water intake. When the percentage of reduction produced by corresponding doses of the two drugs was compared, PPA proved to be more than twice as potent as 4-OHN. It is concluded that, at the doses used, 4-OHN is unlikely to significantly contribute to reductions in deprivation-induced eating produced by the acute administration of PPA.

Effects of phenylpropanolamine on regulatory and nonregulatory ingestion in adult rats

This experiment examined the effects of phenylpropanolamine (0.0, 5.0, 10.0, 20.0 mg/kg PPA) on regulatory (RG) and nonregulatory (NRG) eating and drinking in rats using a within-subjects design. Administration of PPA produced dose-dependent reductions in eating in animals deprived to 80-85% of baseline weight, and reduced drinking after 23.5-h of water deprivation. Nonregulatory eating, elicited by tail pinch in nondeprived animals, was similarly inhibited. Nonregulatory drinking was elicited in the schedule-induced polydipsia (SIP) paradigm. Water consumption, locomotion, licking, lick efficiency (licks/ml water), and entries into the food magazine were simultaneously measured. At the lowest dose, only locomotion was significantly reduced. At 10.0 mg/kg, lick efficiency and entries into the food magazine were also significantly reduced, while all measured behaviors, including licking and water consumption, were decreased by the highest dose of PPA. The reduction in lick efficiency suggested a PPA-induced motor impairment in the capacity for licking. Considered together, these results indicated that the observed decreases in regulatory and nonregulatory eating and drinking could be at least partially accounted for by the drug's effects on behaviors contributing to ingestion, as well as apparent motor impairments in ingestive behavior at higher doses.

A review of the physiological bases of the anorexic action of phenylpropanolamine (d,1-norephedrine)

Phenylpropanolamine (PPA) is a phenethylamine that induces a variety of effects including anorexia and weight loss. The present review compares the acute anorexic effects of PPA with those of amphetamine in animals and humans, describes the persistent chronic effects of PPA on feeding as well as differences in anorexic potency between the norephedrine enantiomers (d-norephedrine less than 1-norephedrine) and summarizes the generality of PPA anorexia. The review also describes the putative mechanisms by which PPA is thought to reduce feeding behavior including alteration of gastric emptying and interaction with central nervous system neurons.

Norepinephrine elevations in cerebrospinal fluid after d- and l-amphetamine

We continuously collected cerebrospinal fluid (CSF) from the lateral ventricles of monkeys and gave them from 0.1 to 1.0 mg/kg d- or l-amphetamine intravenously. The norepinephrine (NE) content of their CSF had a small circadian rhythm and a large increase after amphetamine. 1.0 mg/kg amphetamine gave a four-fold rise in CSF-NE which remained elevated for 33 h, smaller doses gave proportionately lesser responses. Both d- and l-amphetamine caused similar NE elevations except for minor differences at the highest dose. If there are differences in behavioral effects of moderate doses of d- and l-amphetamine, they are probably not due to a general difference in central NE release from these stereoisomers.