Saizo Yanaura

Changes in the serotonin and 5-hydroxyindoleacetic acid contents in rat brain after ethanol and disulfiram treatments

Disulfiram (700 mg/kg, p.o.) significantly increased the brain levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in rats. Ethanol (1 g/kg and 2 x 1.5 g/kg, i.p.) did not affect the 5-HT level, but at the higher dose it significantly increased the 5-HIAA level. When disulfiram was given in combination with ethanol, the brain level of 5-HT was significantly higher and, conversely, the 5-HIAA level was significantly lower, as compared to the results with disulfiram alone. These results suggest that the biogenic aldehyde derived from 5-HT may influence 5-HT metabolism and the elimination of 5-HIAA from the brain.

Effect of p-chlorophenylalanine on diazepam withdrawal signs in rats

The effect of p-chlorophenylalanine (PCPA), a specific serotonin (5-HT) depleter, on diazepam withdrawal signs was studied. Rats were made dependent on diazepam by the chronic administration of this drug in the diet. At the time of diazepam withdrawal, the animals were treated with PCPA (200 mg/kg, IP) or the corresponding vehicle (control). After diazepam withdrawal, the maximal body weight losses of control and PCPA-treated animals were 4.1% and 9.0%, respectively. In naive animals, PCPA did not cause any change in body weight. These results suggest that depletion of central 5-HT by PCPA may potentiate the severity of diazepam withdrawal signs.

Effect of opioid agonist-antagonist interaction on morphine dependence in rats.

Morphine dependence was induced by treatment with morphine-admixed food (0.25mg/g of food) for 7 days. Withdrawal was precipitated by injecting naloxone (0.5mg/kg, s.c.). Rats treated with morphine exhibited body weight loss upon the naloxone injection. When morphine-dependent rats were injected subcutaneously with morphine, codeine, meperidine and pentazocine 30 min before the naloxone injection, these drugs significantly suppressed the naloxone-precipitated loss of body weight in a dose-dependent manner. However, body weight loss induced through coadministration of naloxone and Mr-2266 BS were not suppressed by morphine pretreatment. These results suggest that opioids protect against naloxone-precipitated loss of body weight, and that mu and kappa opiate receptors play an important role in the protection against naloxone-precipitated withdrawal.

Experimental barbiturate dependence

A method for testing a rats physical-dependence liability to sedaditive-hypnotic agents and for evaluating that dependence was studied by using the method. Rats received phenobarbital- or barbital-admixed food on a graded-increase dosage schedule over 30–40 days. Manifestations of CNS-suppressing action of either drug (e.g., systemic muscle relaxation, motor incoordination, staggering gait, and ptosis) persisted day and night during the drug medication. Twenty-four to 48 h after withdrawal of either drug, abstinence symptoms (e.g., muscle fasciculation, nuchal twitching, vocalization, increased irritability, ataxia, hyperthermia, and clonic-tonic and grand mal-type convulsions) were evidenced in all animals (N=6), some of which died after convulsions. These withdrawal signs in rats were classified and found to be closely correlated with the magnitude of weight loss during the withdrawal. The classification provides a basis for quantitatively assessing physical-dependence liability. The data obtained in the present study suggest that rats, like dogs and monkeys, are suitable experimental animals for tests in early stages of dependence liability, and that the administration of drug-admixed food is a useful method of developing dependence on both barbiturate and morphine-type drugs.

Sex differences in physical dependence on pentobarbital in four inbred strains of rats

1. In Lewis (LEW), Fischer 344 (F344), Spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats, pentobarbital (PB)-induced sleep time was much longer in female than in male rats. 2. At the time of awakening, brain levels of PB were significantly higher in the female F344 than in the male rats, but there was no sex differences in other strains. 3. Each strain of rats was treated with PB-admixed food for 47 days. There were significant sex differences in mean drug intake of the SHR and LEW strains, but not the WKY and F344 strains during the final concentration. 4. Only female rats exhibited moderate to severe motor impairment by PB. 5. After PB treatment ended, various signs of PB withdrawal occurred in female, but not male, rats. These marked sex differences were observed in all four inbred strains. 6. The sex differences in physical dependence on PB may be due mainly to differences in rates of drug metabolism for the LEW, SHR and WKY rats, and to differences in CNS sensitivity for the F344 rats.

Synergistic effect of prostaglandin E1 and disulfiram on the prolongation of hexobarbital hypnosis

A possible role of a deaminated metabolite of 5-hydroxytryptamine (5-HT) on hexobarbital hypnosis was studied in rats. Pretreatment with either prostaglandin E1 (PGE1) or disulfiram prolonged hexobarbital hypnosis, and a combined administration of both drugs strongly prolonged hexobarbitai hypnosis and drastically reduced brain hexobarbital content on awakening. PGE1 was found to enhance 5-HT synthesis without altering the elimination of 5-hydroxyindoleacetic acid. The results suggest that elevation of steady state level of 5-hydroxyindoleacetaldehyde potentiates hexobarbital hypnosis. In 1973, Haubrich et al.~ suggested that the sleep induced by prostaglandin E1 (PGE1) may be related to the increased formation of deaminated metabolites of 5-hydroxytryptamine (5-HT) in brain. In addition, Bhattacharya et al. 1 demonstrated that the potentiation of hexobarbital hypnosis by PGE1 might be mediated by serotonergic system. On the other hand, disulfiram was shown to prolong barbiturate hypnosis without any inhibition of liver drug metabolizing enzymesT,XL Recently, we demonstrated that this effect of disulfiram might be related to the elevation of steady state level of 5-hydroxyindoleacetaldehyde (5-HIAAld), one of the deaminated metabolites of 5-HT 3,7. In the present study, we examined the effect of a combined administration of PGE1 and disulfiram on hexobarbital hypnosis, and investigated the possible role of a deaminated metabolite of 5-HT in the alteration of brain susceptibility to hexobarbital. Male, Wistar rats weighing 130-150 g were used in this study. PGE~ was dissolved in absolute ethanol and diluted with 0.2 M phosphate buffer (pH 6.5). This solution was administered intraperitoneally at a dose of 1 mg/kg 15 min before

Relationship between chronic treatment with morphine and sex-dependent low molecular weight protein excretion

Abstract Chronic administration of morphine caused a marked decrease in the urinary excretion of low molecular weight proteins (LMWP) including α2u-globulin (E.L. Stanley and O.W. Neuhaus, Biochim. Biophys. Acta, 257 , 461–470, 1972), which exist only in male rats. Levels of urinary high molecular weight proteins, such as albumin and γ-globulin, however, were not significantly changed by morphine treatment. The amount of excreted LMWP was observed to decrease 3 days after giving morphine, 0.5 mg/g food, and to recover to the control level within 6 days after withdrawal of morphine. These findings suggest that the decrease of excreted LMWP may be related to the development of morphine dependence in male 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.

Experimental dependence on barbiturates

Feeding rats on food containing phenobarbital (PhB) (1 and 2 mg/g) for 13 consecutive days resulted in the inhibition of motor coordination (by rotarod test) for 7 days, followed by a gradual decrease in the inhibition. PhB level in the serum reached a peak on the third day of feeding and then gradually decreased. PhB level in the brain, unlike that in the serum, gradually increased up to the seventh day and then decreased until the thirteenth day of feeding. Thus, alterations of the inhibited rotarod performance were depended on PhB level in the brain rather than on that in the serum.PhB level in the serum increased parallel to the graded increment in dosage from 0.5 and 1.0 mg/g to 4.0 mg/g, while that in the brain did not increase above the level on the seventh day of feeding on 1 and 2 mg/g food but remained relatively stable.PhB-dependent rats ate small amounts of drug-containing food incessantly day and night, and PhB levels in the serum und brain remained high and stable throughout the day.These phenomena suggest that the development of dependence on PhB is more intimately correlated with the length of application of the drug than with the magnitude of its dosage.

Effect of tryptophol on pentylenetetrazol and picrotoxin induced convulsion in mice.

Abstract The effect of treatment of mice with tryptophol (TOL), a neutral metabolite of tryptophan, on drug-induced convulsion was studied. TOL effectively suppressed both pentylenetetrazol and picrotoxin induced convulsion. Diphenylhydantoin (DPH), a potent inhibitor of brain aldehyde reductase, significantly reduced the anticonvulsant effect of TOL, however, TOL level in brain of DPH-treated mice was rather higher than that of control one. These results strongly suggest that the manifestation of the anticonvulsant effect of TOL requires the conversion of TOL to its active metabolite, indoleacetaldehyde.