Serum phenobarbital and barbital concentrations in rats on a limited food regimen

Pharmacological and neuroethological studies of three antiepileptic drugs in the Genetic Audiogenic Seizure Hamster (GASH:Sal)

Epilepsy modeling is essential for understanding the basic mechanisms of the epileptic process. The Genetic Audiogenic Seizure Hamster (GASH:Sal) exhibits generalized tonic-clonic seizures of genetic origin in response to sound stimulation and is currently being validated as a reliable model of epilepsy. Here, we performed a pharmacological and neuroethological study using well-known and widely used antiepileptic drugs (AEDs), including phenobarbital (PB), valproic acid (VPA), and levetiracetam (LEV). The intraperitoneal administration of PB (5-20mg/kg) and VPA (100-300mg/kg) produced a dose-dependent decrease in GASH:Sal audiogenic seizure severity scores. The administration of LEV (30-100mg/kg) did not produce a clear effect. Phenobarbital showed a short plasmatic life and had a high antiepileptic effect starting at 10mg/kg that was accompanied by ataxia. Valproic acid acted only at high concentrations and was the AED with the most ataxic effects. Levetiracetam at all doses also produced sedation and ataxia side effects. We conclude that the GASH:Sal is a reliable genetic model of epilepsy suitable to evaluate AEDs.

Functional tolerance to the hypothermic effect of phenobarbital in rats

Phenobarbital elicits a hypothermic effect in rats. To determine if functional tolerance develops to this effect on temperature, rats were treated twice daily with IP injections of sodium phenobarbital (PheB) or saline. The PheB doses were increased over 21 days and then were held constant for another 23 days. On the next day (day 45) animals from both groups were given 80, 110 or 160 mg/kg PheB IP and the decrease in rectal temperature after 2 h was determined. Animals were decapitated after the temperature measurement and brain PheB levels were determined. A 1.51-fold shift in the relationship between brain level and response was found for the group given chronic PheB. These results show functional tolerance occurs to the hypothermic effect of PheB. This experiment was done in animals that were on a restricted food regimen. Rats given chronic PheB lost more weight than the group given chronic saline unless extra food was provided. We found that this occurred because the rats given chronic PheB lost more food through the wire cage floor than rats given chronic saline.

Barbiturate dependence and drug preference

Rats exposed to a daily 3-hr session of intermittent food delivery ingested physical-dependent levels of a 1 mg/ml sodium phenobarbital solution. This chronic, voluntary, high level of session phenobarbital intake had no effect on 21-hr home cage barbiturate preference. Substitution of water for phenobarbital during the session after 7.5 weeks precipitated various spontaneous withdrawal signs in some of the animals by the 24th hr of drug withdrawal but no change was found in home-cage barbiturate preference at any time. Physical dependence alone does not seem to play a crucial role in the maintenance of drug intake behavior.