Effect of phenobarbital pretreatment on cardiac neural discharge and pentylenetetrazol-induced epileptogenic activity in the cat

Carnel SB, Schraeder PL, and Lathers CM(1985) Effect of phenobarbital pretreatment on car- diac neural discharge and pentylenetetrazol-induced epileptogenic activity in the cat. Phar- macology 30:4 225–40.

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Abstract: The effect of phenobarbital on autonomic function associated with ictal discharges and interictal spikes (IS) was examined. Phenobarbital (20 mg/kg, i.v.) was infused over 10 min; 1 h later, pentylenetetrazol (PTZ) 10, 20, 50, 100, 200, and 2,000 mg/kg was given intravenously at 10-min intervals. 10 mg/kg PTZ produced IS in only 3 of 9 phenobarbital-pretreated cats; when used alone, 10 mg/kg of PTZ produced IS in 8 of 9 cats. Ictal discharges first appeared at 20 mg/kg PTZ in 6 of 9 phenobarbital-pretreated cats; all 9 cats receiving only PTZ exhibited ictal discharges after 20 mg/kg. Phenobarbital pretreatment depressed heart rate, blood pressure and postganglionic cardiac sympathetic neural discharge. Maximal ictal discharges in the cats pretreated with phenobarbital occurred with 100 mg/kg PTZ. This discharge was associated with a 10 mm Hg increase in blood pressure and a slight decrease in heart rate, followed by a subsequent return to baseline. The concurrent sympathetic neural discharge increased. When maximal ictal discharges occurred in the cats receiving PTZ alone, blood pressure, heart rate, and sympathetic neural discharge increased significantly. Cardiac vagal neural discharge was not altered after PTZ even in phenobarbital-pretreated cats. Although phenobarbital suppressed PTZ-induced epileptogenic activity and the associated changes in blood pressure and heart rate, a X2 test indicated no significant difference in the incidence of arrhythmias between the two groups. Since phenobarbital did not prevent the changes in cardiac neural discharge and the arrhythmias associated with epileptogenic activity, its effectiveness in decreasing autonomic dysfunction is questionable.

Keywords: cardiac autonomic neural discharge, arrhythmia, Pentylenetetrazol, Phenobarbital, epileptogenic activity, cat

Context

• Early animal study of the effects of phenobarbitol (PB) and the seizure-provoking agent pentylenetetrazol (PTZ). Phenobarbitol decreased the rate of epileptiform activity, as well as heart rate and blood pressure. Autonomic response to the seizure-provoking agent was altered by the presence of PB; heart rate increased significantly in the presence of PTZ alone but decreased slightly when PTZ was given after PB. Phenobarbitol did not decrease the incidence of arrhythmias. This article is very similar to Lathers et al.