Calcium hopantenate (HOPA-Ca), which is obtained by substituting the beta-alanine of pantothenic acid for gamma-amino butyric acid (GABA), is a therapeutic drug for mental retardation and cerebrovascular dementia. HOPA-Ca is known to produce convulsive seizures in some patients although it is also true that this improves EEG abnormalities and suppresses epileptic seizures. Thus, clinical observations suggest that HOPA-Ca exerts a paradoxical influence on epilepsy. In order to gain further insight into the influence of HOPA-Ca on epilepsy, we examined its effects on the generalized seizure-triggering threshold (GST) of kindled amygdaloid (AM) seizure and on the rate of AM kindling in rats. Male Wistar rats weighing 200-250 g were used. Under pentobarbital anesthesia, a bipolar electrode, made of twisted stainless steel wire 0.2 mm in diameter, was stereotaxically implanted into the left AM. Daily electrical stimulation was given at the intensity of afterdischarge threshold (ADT). Electrical stimulation was continued until at least five consecutive generalized convulsions were evoked. Subsequently, the stimulus intensity was daily lowered by 20-microA steps and the last stimulus intensity for evoking generalized convulsion was designated as the GST. Experiment 1. Influence of HOPA-Ca on the GST; HOPA-Ca was dissolved in saline as a vehicle. Injections of 50, 100, 250, 500 mg/kg HOPA-Ca were given intraperitoneally 60 min before the stimulation at the GST. The GST never changed with vehicle injection. The GST increase was never observed with any amount of HOPA-Ca. However, the GST dropped flowing HOPA-Ca infection independent of its amount. The GST reduction was always 20-microA.(ABSTRACT TRUNCATED AT 250 WORDS)