Eijiro Tagashira

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.

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.

Effects of central monoamine compounds on tranylcypromine-induced barbital-withdrawal convulsions

Challenge with tranylcypromine (Tcp) during barbital (B) withdrawal induces dose-related clonic-tonic convulsion (C-TC), which is also related to the severity of withdrawal signs and their changes with the passage of time. The effects of neuropharmacological agents on the Tcp-induced convulsions were observed. dl-Propranolol, phentolamine, phenoxybenzamine and methysergide had been administered intraperitoneally 20 approximately 30 minutes before Tcp challenge. B-withdrawn rats had been pretreated with alpha-methyl-p-tyrosine, 5-hydroxytryptophan, p-chlorophenylalanine or reserpine, or with the combination of iproniazid and reserpine (5 hrs after iproniazid administration) before Tcp challenge. alpha-MT and dl-propranolol inhibited B withdrawal convulsion markedly, though high doses of dl-propranolol rather tended to show a less effect on the convulsion. alpha-Adrenoceptor blockers scarcely inhibited the convulsion. Methysergide or 5-HTP failed to inhibit, but PCPA intensified the convulsion. Reserpine, when administered alone, aggravated the convulsion, but when administered after iproniazid, inhibited it significantly. These findings suggested that the balance between the activities of noradrenergic and serotonergic neurons might be of importance in the manifestation of B withdrawal convulsions, the former probably being excitatory and the latter, inhibitory.

Screening method for drug dependence liability using drug-admixed food (DAF) method.

In the present study, we used drug-admixed food (DAF) to induce dependence on morphineand barbIturate-type drugs by continuous exposure of the animal to these agents By utilizing th~s simplified techmque for producing dependence, we present in this experiment some quantltaUve aspects of abstinence symptoms and also on drug-seelang behawor by the twoor three-food container choice test Each group of rats included six male Sprague-Dawley strata rats (purchased from Charles R,ver, Japan), 5-7 weeks of age. Rats were housed ind|vldually in cages (21 × 25 × 12 cm) with two food containers, eqm-distant from the water bottle To prepare the DAF, each test drug was mixed with a powdered food (CA-1 powder, manufactured by Japan Clea, Tokyo) m a mortar. Body weight and food intake were measured once daily. The position of the food contamers was changed daily and food and water was provided ad Ubitum.

Specific action of tranylcypromine to precipitate barbital withdrawal convulsions

This research was designed to determine whether the convulsion-eliciting action of tranylcypromine (TCP) during barbital (B) withdrawal was specific to physical dependence on B, and to compare the findings with the action of pentetrazol (PTZ). Challenge with 15–20 mg/kg IP TCP at 48 h of B withdrawal resulted in the elicitation of clonictonic convulsion (CTC) in all rats (N=6) within 10 min. Another challenge with 5–20 mg/kg TCP led to the doserelated precipitation and intensification of CTC. The CTC-inducing action of TCP was relatively reduced as the B withdrawal signs were gradually mitigated. In other words, when challenge with the drug was made at 72h of B withdrawal, the time of CTC onset was prolonged, and the incidence was reduced to 50% in parallel with abolition of the other withdrawal signs. A challenge at 120 h of B withdrawal when the vital signs had almost recovered to prewithdrawal level failed to induce even the prodromal signs of convulsion. In all rats exhibiting only mild to moderate withdrawal signs (such as hyperirritability, hyper-reflexia, anorexia, weight loss), 40 mg/kg TCP was required to induce CTC during B withdrawal, which was twice the dose required in severely dependent rats. Other monoamine oxidase inhibitors, i.e., pargyline, iproniazid, and clorgyline, elicited no CTC during B withdrawal. Methamphetamine was without effect on B withdrawal convulsions. From these findings, the convulsive threshold for TCP during B withdrawal proved well correlated to the grade of B-dependence and the duration of B-withdrawal signs.