The effects of metoprine, an inhibitor of histamine N-methyltransferase, on open field
activity and brain regional histamine (HA) content were examined in rats with mixed,
absence and audiogenic, epilepsy (WAG/Rij-AGS), rats with audiogenic epilepsy (Wistar-AGS)
and in non-epileptic control rats (Wistar-nAGS). HA content was increased by metoprine
(20mg/kg, i.p.) in the cortex, striatum, thalamus, hypothalamus and hippocampus of
the rats from all three tested groups. However, WAG/Rij rats showed a lower rate of
metoprine-induced HA accumulation in the striatum and thalamus than Wistar rats. For
the open field test, the main effect of metoprine (20mg/kg, i.p.) was a general increase
of locomotor activity although distinctive features, such as hyperlocomotion and exaggerated
sniffing, were characteristic for the epileptic rats (WAG/Rij-AGS and Wistar-AGS,
respectively). Individual rats from all the groups showed stereotyped behavior of
shuttle type and head bobbing. Electroencephalographic data obtained in WAG/Rij-AGS
rats confirmed that metoprine-induced behavioral activation was accompanied by suppression
of spike-wave discharges, the main hallmark of absence seizures. Taken together, these
results show that inhibition of the histamine catabolism may induce motor activation
of particular patterns in epileptic rats and provoke stereotyped behavior.