Pl. Deriu et al., CEREBELLAR AND MESENCEPHALIC INFLUENCE ON BULBAR PENICILLIN-G EPILEPTOGENESIS IN RATS, Physiology & behavior, 56(4), 1994, pp. 715-721
The influence of the cerebellum and mesencephalon on epileptic bulbar
discharge induced by topical application of penicillin-G on the floor
of the IVth ventricle was analyzed in rats. Bulbar multiunit activity
was recorded at different depths. The animals were divided into two ma
in groups: totally cerebellectomized rats (Group I) and lobus anterior
cerebellectomized rats (Group II). Each main group was further subdiv
ided into two subgroups: animals with intact mesencephalon and animals
with transected mesencephalon. In Group I: the total cerebellectomy,
in intact mesencephalic rats (first subgroup) induced a sudden disappe
arance of bulbar epileptic discharge. The mid-collicular transection (
second subgroup) produced the immediate disappearance of bulbar paroxy
sms and the total cerebellectomy, subsequently performed, further decr
eased the spontaneous firing rate. In Group II: (first subgroup) the l
obus anterior ablation in rats with intact mesencephalon, significantl
y enhanced me paroxysmal discharge. In the second subgroup, where the
midcollicular transection had provoked the disappearance of bulbar par
oxysms, the lobus anterior ablation induced the immediate reappearance
of the paroxysmal activity. The penicillin-G epileptogenic activity s
howed a different intensity at different depths in the bulb with a max
imum intensity at the level of the vestibular nuclei. In conclusion, t
he present study shows that both the mesencephalon and the cerebellum
have a facilitating influence on bulbar epileptic discharge induced by
the topical application of the GABA antagonist. However, not all the
cerebellum has a facilitating effect, because the anterior lobus was f
ound to have an inhibitory influence on bulbar discharge. The higher r
esponsiveness to the paroxysmal action of GABA antagonists found at th
e level of the vestibular nuclei may be due to an increased number of
GABA receptors present in the vestibular neuron membrane, compared to
those in the membrane of the remaining bulbar cells.