Drug interactions in the reinforcing effects of over-the-counter cough syrups.

Drug interactions in reinforcin effects of over-the-counter cough syrups were investigated by utilizing place preference conditioning in rats. Dihydrocodeine (2 mg/kg, IP) induced a small, non-significant place preference. On the other hand, concurrent dosing of dihydrocodeine (2 mg/kg, IP) and a mixture (SC) of methylephedrine (4 mg/kg), caffeine (4 mg/kg) and chlorpheniramine (0.8 mg/kg) produced a significant place preference, the mean conditioning score in this group being about 3 times higher than that in the dihydrocodeine alone group. The potentiation of dihydrocodeine-conditioned place preference was observed by combination with chlorpheniramine (0.8 mg/kg, SC) alone as well as with the mixture, but neither with methylephedrine (4 mg/kg, SC) nor with caffeine (4 mg/kg, SC). Chronic infusion of the dopamine D1 receptor antagonist SCH23390 (1.0 mg/kg/day, SC) during conditioning abolished the appetitive effects of dihydrocodeine combined with chlorpheniramine. In conclusion, it is suggested that the potentiation of appetitive effects of dihydrocodeine is mostly due to chlorpheniramine among three ingredients in the cough syrups, and that the dopaminergic system, especially D1 receptor, may play an important role in the potentiation effect of chlorpheniramine on the reinforcing effects of dihydrocodeine.

Differential modification of the rewarding effects of methamphetamine and cocaine by opioids and antihistamines.

We previously reported that the reinforcing effects of opioids are enhanced in combination with antihistamines. In the present study, effects of opioids and antihistamines on the reinforcing effects of psychostimulants such as methamphetamine and cocaine were investigated by utilizing the conditioned place preference procedure in rats. The place preference induced by methamphetamine was enhanced in combination with either morphine or chlorpheniramine, which produced additive and potentiative effects, respectively. In contrast, although the preference for cocaine was also enhanced by combination with these two drugs, morphine caused a potentiative effect and chlorpheniramine an additive one. In other words, the reinforcing effect of methamphetamine was differentially enhanced by opioids and antihistamines as compared to that of cocaine. These results suggest that the mechanism of reinforcing effect of methamphetamine is different from that of cocaine, resembling rather those of opioids.

Potentiation of pentazocine conditioned place preference by tripelennamine in rats.

The effects of tripelennamine on place preference conditioning in rats with pentazocine were investigated. Pentazocine at a dose of 2 mg/kg (IP) slightly, but not significantly, induced a place preference. Concurrent dosing of pentazocine (2 mg/kg, IP) and tripelennamine (2.5 mg/kg, SC) significantly and prominently produced a place preference, although administration of tripelennamine (2.5 mg/kg, SC) alone did not. Chronic infusion of a dopamine D1 receptor antagonist, SCH23390 (1.0 mg/kg/day) during conditioning abolished the appetitive effect of pentazocine potentiated by the combination with tripelennamine. In conclusion, it is suggested that the dopaminergic system, especially at the D1 receptor, plays an important role in the potentiation effect of tripelennamine on the pentazocine-induced place preference.

Relationship between covalently bound ceramides and transepidermal water loss (TEWL).

The stratum corneum, which is the outermost layer of the skin, functions as an important barrier to maintain biological homeostasis. The multilamellar structures formed by intercellular lipids present in the stratum corneum are considered to play an important role in barrier function. Most intercellular lipids are unbound and can be extracted by organic solvents, but some intercellular lipids are covalently bound to cornified envelope proteins. Decreases in unbound lipid levels reduce the barrier function of the stratum corneum, but the relationship between bound lipid and the barrier function of the stratum corneum is not well understood. In this study, we examined the relationship between the amount of covalently bound ceramide, the main bound lipid, and the barrier function of the stratum corneum. A single dose of UVB irradiation (2 x MED), or continuous UVB irradiation (0.5 x MED/day for 14 days) to the back, or feeding with an essential fatty acid-deficient (EFAD) diet for 8 weeks caused a significant elevation of TEWL and a significant reduction in covalently bound ceramides in hairless rats. Transmission electron microscopy revealed that the intercellular multilamellar structures in the stratum corneum of treated rats were incomplete (folding, defects, unclear images) compared to the structures seen in the stratum corneum of non-UVB-irradiated and non-EFAD rats. These results suggest that the amount of covalently bound ceramides is highly correlated with the barrier function of the skin, and that covalently bound ceramides play an important role in the formation of lamellar structures, and are involved in the maintenance of the barrier function of the skin.

Preferences for opioids by the weight pulling method in rats.

The preference for morphine and codeine was studied by means of the antagonistic conflict behavior between the positive drive of drug intake and the negative drive of weight pulling in rats. An apparatus was developed in which rats were compelled to pull the weight for the intake of drug-admixed food. The experiments began with the preadministration of the drug through the repetition of CFF schedule. The schedule consisted of one choice trial between the intake of normal food and drug-admixed food followed by two consecutive forced trials, in which the rats were forced to take the drug-admixed food only. In the test trial, the findings were that the rats which had already shown a drug seeking behavior toward morphine or codeine pulled weight to take each drug and that the reinforcing effects of these drugs on the drug seeking behavior depended on the treatment period of these drugs. The reinforcing effect of codeine was weaker than one of morphine. It is suggested that the reinforcing effects of these opioids can be evaluated quantitatively by the weight pulling method in rats.

Preference for cocaine by the weight pulling method in rats.

The purpose of the present study is to show the efficiency of the weight pulling method in evaluating quantitatively the positive reinforcing effect of cocaine. Rats were trained to pull the weight in order to eat the drug-admixed food (DAF). The experiments began with the preexposure of the drug through the repetition of CFF schedule. The schedule consisted of one choice trial (C) between the intake of normal food and DAF followed by two consecutive forced trials (F), in which the rats were forced to take the DAF only. The study consisted of Experiment I, where cocaine concentration in DAF was varied while the period of cocaine preexposure was kept constant and Experiment II, where the period of preexposure was varied while the cocaine concentration was kept constant. Results show that the reinforcing effect of cocaine was dependent on cocaine intake. On the other hand, the reinforcing effect of cocaine was independent of cocaine preexposure period. The effect of cocaine on the drug-seeking behavior was evident on the first day of cocaine exposure. It is concluded that the weight pulling method is sufficient to evaluate quantitatively the reinforcing effects of cocaine in rats, and this method may be useful for the prediction of dependence potential in man.

5-HT3 receptor antagonists block cocaine- and methamphetamine-induced place preference.

The effects of 5-HT3 receptor antagonists, MDL72222 and ICS205-930, on cocaine- and methamphetamine-induced place preference were examined. Cocaine (0.5-4.0 mg/kg, ip) and methamphetamine (0.25-2.0 mg/kg, ip) induced a dose-dependent place preference. The cocaine (4 mg/kg)-induced place preference was blocked by both MDL72222 and ICS205-930 (0.1 mg/kg, ip). On the other hand, the dose (0.1 mg/kg) of 5-HT3 antagonists did not block the methamphetamine (2 mg/kg)-induced place preference, although a higher dose (1.0 mg/kg) of 5-HT3 receptor antagonists did block it. The difference in sensitivity may reflect a difference in attack point in dopaminergic system of these two psychostimulants. Our findings suggest that the rewarding effects of cocaine and methamphetamine may be indirectly regulated by 5-HT3 receptor; cocaine being more sensitive to 5-HT3 receptor antagonists than methamphetamine.

Effects of calcium antagonists on the cocaine- and methamphetamine-induced conditioned place preference.

The effects of calcium antagonists (nifedipine, flunaridine and diltiazem) on the cocaine- and methamphetamine-induced place preference were examined. Calcium antagonists alone induced neither place preference nor place aversion. Nifedipine markedly antagonized and flunarizine and diltiazem reduced the cocaine-induced place preference. The methamphetamine-induced place preference was reduced by nifedipine and diltiazem, but not by flunarizine. These results suggest the possibility that the cocaine-induced place preference is strongly influenced by dihydropyridine sensitive calcium channels, whereas the methamphetamine-induced place preference is not.

Low neurotoxicity of LJC 10,627, a novel 1 beta-methyl carbapenem antibiotic: inhibition of gamma-aminobutyric acidA, benzodiazepine, and glycine receptor binding in relation to lack of central nervous system toxicity in rats.

The toxicity of LJC 10,627 to the central nervous system of rats was evaluated by examining the effects of the compound on gamma-aminobutyric acidA, benzodiazepine, and glycine receptor binding in rat synaptic membranes and on the induction of behavioral convulsions by intraventricular administration to rats. The concentrations of this compound needed to inhibit specific [3H]muscimol binding, specific [3H]diazepam binding, and specific [3H]strychnine binding were greater than those of imipenem, as demonstrated by the 50% inhibitory concentrations (IC50S of LJC 10,627, greater than 10 mM for each; IC50S of imipenem, 0.6, 1.9, and 0.2 mM, respectively). These results reflect the fact that LJC 10,627 does not evoke severe convulsions or cause death, even when it is administered intraventricularly at a high dose (300 micrograms per rat), and suggest that the low neurotoxic potential of LJC 10,627 may be attributed to the chemical structure of this compound, which has a methyl radical at the 1 beta site and a triazolium radical at the side chain of the second site.

[The effects of constituents of an antitussive and expectorant preparation on physical dependence on and antitussive activity of dihydrocodeine].

The effects of constituents of an antitussive and expectorant preparation on physical dependence potential and antitussive activity of dihydrocodeine (DC) were studied. Rats were treated with DC, methylephedrine (ME), chlorpheniramine (CP), and caffeine (CA) singly or simultaneously admixed with food (DC 0.125, ME: 0.25, CP: 0.05, CA: 0.25 mg /g of food) for 7 days. Subsequently, rats were treated with naloxone (0.5 mg/kg, sc) and withdrawal signs produced were observed. Naloxone-precipitated body weight loss in DC-treated rats was suppressed by simultaneous administration of the three drugs (ME, CP and CA) or CP, which is a H1-receptor antagonist. In abrupt withdrawal, the withdrawal signs were also suppressed by CP. Moreover, tripelennamine, the same kind of H1-receptor antagonist, suppressed naloxone-precipitated withdrawal signs, but cimetidine H2-receptor antagonist, did not suppress them. These results may suggest that H1-receptor antagonists suppress the development of physical dependence on DC, and that H1-receptors play an important role in the physical dependence. On the other hand, the cough reflex was induced by electric stimulation in order to evaluate the influence of ME, CP, and CA on antitussive effect of DC in guinea pigs. ME enhanced the effect of DC. These experimental findings suggest that the constituents of the antitussive and expectorant preparation suppress the development of physical dependence on DC, though they increase the antitussive effect of DC.

[Effect of methamphetamine on morphine preference].

The effect of methamphetamine on preference for morphine was studied in rats by the drug-admixed food (DAF) method. The preference rates for morphine-admixed food gradually increased by the repetition of choice and forced trials and then became stable at the level of 70%. On the other hand, the preference rates for morphine-admixed food combined with methamphetamine did not so increase compared with the case of morphine alone. From the taste aversion test, it was assumed that combination of morphine and methamphetamine did not enhance taste aversion, although methamphetamine suppressed development of preference for morphine. In the case of combination of morphine and cocaine or caffeine, preference rates for these drugs increased like the case of morphine. This result indicated that the suppression of the preference for morphine which was induced by methamphetamine was not produced by the general effect of CNS stimulants. We found that methamphetamine suppressed the development of the preference for morphine. These findings suggest that the suppression resulted from neither taste aversion nor the general effect of CNS stimulants. Furthermore, acute toxicity and other effects were enhanced by the combination of morphine and methamphetamine, and it might participate with the suppression.

The role of mu- and kappa-opioid receptors in cocaine-induced conditioned place preference.

Effects of buprenorphine, U-50,488H, naltrexone and lithium chloride on cocaine conditioned place preference were examined. Buprenorphine, a mixed opioid agonist-antagonist, blocked the cocaine-induced place preference. Furthermore, the kappa-receptor agonist U-50,488H and the mu-receptor antagonist naltrexone both antagonized the cocaine preference. U-50,488H or naltrexone alone induced a place aversion in a dose-dependent manner. However, the cocaine-induced conditioned place preference was not blocked by lithium chloride, although the latter induced a conditioned place aversion, indicating that the antagonism of cocaine-induced place preference by U-50,488H or naltrexone does not result from a functional antagonism. These results suggest that mu- and kappa-opioid receptors may be involved in cocaine-induced conditioned place preference.