Effect of excess leucine on tryptophan oxygenase, 3-hydroxyanthranilate oxygenase and leucine aminotransferase in livers of young rats

Hepatic tryptophan oxygenase (EC 1.13.1.12) 3-hydroxyanthranilate oxygenase (EC 1.13.1.6) and leucine aminotransferase (EC 2.6.1.6) activities were determined in livers of rat pups of various ages whose mothers were fed on diets with or without excess leucine. Tryptophan oxygenase activity was detectable on the 20th day in both the groups and thereafter increased with age. Low activity of 3-hydroxyanthranilate oxygenase was observed at birth, the levels increased on the 10th day and thereafter remained unaltered on both diets. Leucine aminotransferase activity was highest at birth and thereafter decreased with age. Tryptophan oxygenase and leucine aminotransferase activities were significantly higher at all ages in livers of pups born to mothers given excess leucine in their diet.

Effect of acute and chronic pentylenetetrazol treatment on benzodiazepine and cholinergic receptor binding in rat brain

The binding of [3H] diazepam and [3H] flunitrazepam in rat cerebral cortex was not altered by either acute or chronic administration of pentylenetetrazol except in rats made to convulse 30 min before sacrifice. Rats treated for up to 6 months with doses of pentylenetetrazol which are below seizure threshold in naive rats, became increasingly sensitive to the CNS stimulant effect of pentylenetetrazol as demonstrated by the development of myoclonus and convulsions during treatment periods. These effects were not correlated with any changes in benzodiazepine binding in cerebral cortex or cerebellum and [3H] quinuclidinyl benzilate binding in cerebral cortex. Acute convulsant doses of pentylenetetrazol increased benzodiazepine binding in cerebral cortex, but only in those rats which actively convulsed. Benzodiazepine and cholinergic receptors of the cortex, and benzodiazepine receptors of the cerebellum, therefore, do not appear to change with either the acute or chronic subconvulsive administration of pentylenetetrazol.

Effectiveness of nantradol in blocking narcotic withdrawal signs through nonnarcotic mechanisms

Male rats were made narcotic dependent through continuous intravenous infusion of morphine. During withdrawal, nantradol, clonidine, and morphine were found to block withdrawal signs in a dose-dependent manner. Almost complete alleviation of withdrawal occurred with nantradol or clonidine at 0.16 mg/kg and with morphine at 40 mg/kg. The effectiveness of morphine, but not of nantradol or clonidine, was reversed by naloxone. Likewise, in naive rats given castor oil, naloxone did not block the antidiarrheal effect of nantradol or clonidine. In order to compare possible subjective effects of nantradol with other antiwithdrawal drugs, naive rats were trained to discriminate either morphine, cyclazocine, or clonidine from vehicle by selecting different levers for reinforcement. Nantradol failed to produce any generalization to morphine, cycloazocine, or clonidine, suggesting that this drug does not produce central subjective effects like those of the training drugs. In additional testing in behavioral experiments, nantradol failed to produce any sign of anxiogenic activity.

Nonnarcotic antidiarrheal action of clonidine and lofexidine in the rat

Clonidine (0.01 to 0.16 mg/kg) and lofexidine (0.01 to 0.64 mg/kg) produced a dose-dependent inhibition of diarrhea induced by castor oil treatment in the rat. Both drugs were more potent and longer acting than diphenoxylate. Pre- and posttreatment with naloxone (5 mg/kg) failed to prevent or antagonize the antidiarrheal effect of clonidine and lofexidine. These data suggest that clonidine and lofexidine may provide potent antidiarrheal activity of a nonnarcotic nature.

Discriminative response control by naloxone in morphine pretreated rats

In an operant procedure using a lever press response 12 male, hooded rats were trained to discriminate 1.25 mg/kg naloxone from a saline injection. On certain days, according to a counterbalanced training schedule, naloxone was administered 8 h after 40 mg/kg morphine and 10 min prior to a trail in which food was available on an FR10 schedule from one of two levers in a dual lever operant chamber. On other days saline was administered 10 min prior to a trial in which food was made available by pressing the other lever. After criterion performance for acquisition of the discrimination had been reached, tests were carried out to determine its nature. Discrimination of naloxone was dose-dependent and was significantly diminished when naloxone was administered 36 h after morphine. Partial generalization of cyclazocine with naloxone was observed. Spontaneous withdrawal from morphine, tested during trials preceeded by an injection of saline instead of naloxone at various time intervals after morphine, did not generalize with the naloxone discriminative stimulus.

Effectiveness of lofexidine in blocking morphine-withdrawal signs in the rat

Discontinuation of chronic morphine infusion in rats resulted in the reliable occurrence of withdrawal body shakes. This sign of narcotic withdrawal was dose-dependently reduced by lofexidine (0.04-0.64 mg/kg) and clonidine (0.01-0.16 mg/kg). As with clonidine, the activity of lofexidine was not prevented by naloxone (5 mg/kg). In addition, diarrhea induced by naloxone (5 mg/kg) in morphine dependent rats was also prevented by lofexidine or clonidine pretreatment. These data suggest that lofexidine, like clonidine, may reduce the narcotic withdrawal syndrome in humans.

Discriminative stimulus properties of pentylenetetrazol and bemegride: some generalization and antagonism tests

In an operant procedure of lever pressing on a FR 10 schedule of food reinforcement, male hooded rats were trained to respond with a lever on one side of a food cup following a drug injection, and to respond with a lever on the alternate side following a 1 ml/kg saline injection. All of 14 subjects learned to discriminate reliably between the effects of 20 mg/kg pentylenetetrazol (PTZ) and saline. Seven of eight rats learned to discriminate between the effects of bemegride (5 mg/kg) and saline. None of 14 rats learned to discriminate between 5mg/kg PTZ and saline. The bemegride discriminative stimulus generalized to PTZ (20mg/kg) and was antagonized by chlordiazepoxide (10 mg/kg). Chlordiazepoxide, diazepam, flurazepam, clobazam, and meprobamate were all effective antagonist of PTZ in a dose-dependent manner. Bemegride and cocaine generalized to the PTZ discriminative stimulus in a dose-dependent manner, but d-amphetamine, methylphenidate, and nicotine did not. Since bemegride and PTZ are convulsants at higher doses, the discriminative stimulus properties of these drugs might be based on a subtle convulsive brain state. The anxiolytic properties of benzodiazepines and meprobamate suggest that the discriminative stimulus produced by these convulsants is related to an "anxiety-inducing" action.

Antinociceptive activity of clonidine and its potentiation of morphine analgesia

The activity of clonidine and its interaction with morphine was assessed in the mouse tail flick assay. In this assay, clonidine was found to be 10 times more potent than morphine. Clonidine potentiated morphine antinociceptive activity approximately five-fold and morphine potentiated clonidine activity four-fold. Clonidine's agonstic activity was not reversed by naloxone hydrochloride (10 mg/kg) while the potentiating effect of clonidine by morphine was. Tolerance to the antinociceptive effect of morphine was observed in morphine pellet-implanted mice but no cross tolerance was observed for clonidine. These data indicate that clonidine-induced analgesia is not a result of an interaction at morphine receptors; but rather, common pathway(s) are present which appear to complement the agonistic interaction of each.

Lack of tolerance development to benzodiazepines in antagonism of the pentylenetetrazol discriminative stimulus

In an operant procedure of lever pressing on FR 10 schedule of food reinforcement male hooded rats were trained to respond on a lever on one side of a food cup following a 20 mg/kg pentylenetetrazol (PTZ) injection and to respond on a lever on the alternate side following a 1 ml/kg saline injection. Upon acquisition of the PTZ-saline discrimination, diazepam and chlordiazepoxide were tested and found to antagonize the PTZ discriminative stimulus. The animals were then injected with 10 mg/kg diazepam or chlordiazepoxide for ten consecutive days. New dose-response curves obtained following this treatment indicated that tolerance did not develop to the antagonism of the PTZ discriminative stimulus by these benzodiazepines.