Penicillin-induced paroxysmal activity in brainstem neurons.
The spontaneous electrical activity of single mesencephalic and bulbar neurons was recorded in hemispherectomized rats, following topical application of the GABA-antagonist penicillin-G on the mesencephalon or on the rhombencephalon, to investigate whether these structures could develop a specific penicillin paroxysmal activity independently of the upper structures. Twenty minutes following penicillin-G, the mesencephalic neurons developed paroxysmal activity characterized by a significant increase in the spontaneous electrical activity, the appearance of multiunit activity and, frequently, phasic activity with rhythmical outbursts. The paroxysmal activity at bulbar level appeared later than that observed in the mesencephalon and was characterized by a significant increase of the spontaneous firing rate of the neurons, single short bursts and sometimes rhythmical outbursts. The bulbar outbursts always discharged at lower frequency than those at the mesencephalic level. Following a midcollicular transection the paroxysmal bulbar activity abruptly disappeared. This phenomenon might be explained by a loss of facilitation from superior structures on the bulbar neurons which in roditors show a poor GABA-receptor distribution. In other words, penicillin alone, due to the scarcity of GABA receptors, might not be sufficient to induce paroxysmal activity in bulbar neurons but the simultaneous presence of both the superior facilitation and the drug might enhance neuronal excitability to a critical level. However, the diffusion of the drug upwards to the mesencephalon, with consequent activation of a system allowing the downward propagation of paroxysmal activity, cannot be excluded. In conclusion, while the mesencephalic neurons demonstrate a proper ability to develop penicillin paroxysmal discharge, the bulbar neurons must be sustained by intact connections with upper structures to be able to do so.
Mameli
O
O
Institute of Human Physiology, University of Sassari, Italy.
Melis
F
F
Tolu
E
E
Caria
M A
MA
De Riu
P L
PL
Azzena
G B
GB
D000818:Animals; D001933:Brain Stem / Q000187:drug effects*; D004569:Electroencephalography / Q000187:drug effects*; D005071:Evoked Potentials / Q000187:drug effects; D008526:Medulla Oblongata / Q000187:drug effects; D008636:Mesencephalon / Q000187:drug effects*; D009434:Neural Pathways / Q000187:drug effects; D009474:Neurons / Q000187:drug effects; D010400:Penicillin G / Q000494:pharmacology*; D051381:Rats; D012154:Reticular Formation / Q000187:drug effects
D010400:Penicillin G