Relation between responsiveness to neurotransmitters and complexity of epileptiform activity in rat hippocampal CA1 neurons.
OBJECTIVE
Our previous works suggested that sensitivity of neurons with chaotic firing patterns to stimuli is significantly greater than that in neurons with periodic firing patterns, which shows that responsiveness of neurons may depend on the complexity of the firing series. This study was performed to determine the relation between responsiveness of the hippocampal CA1 neurons with epileptiform activity (EA) to neurotransmitters and their complexity of firing series.


METHODS
Firing series of CA1 neurons were recorded extracellularly in rat hippocampal slice. Approximate entropy was used to describe the complexity of the interspike interval (ISI) series. EA was induced by local application of penicillin (1,000 IU/ml). The change of firing rate induced by neurotransmitters (glutamate and gamma-aminobutyric acid) was compared with that of the degree of complexity of ISI series in the process of EA.


RESULTS
The excitatory responses to glutamate and the inhibitory responses to gamma-aminobutyric acid in CA1 neurons appeared to be decreased during the process of penicillin-induced EA. However, during this same process, the approximate entropy of the ISI series also was decreased significantly.


CONCLUSIONS
The results suggest that the reduced responses to neurotransmitters of the CA1 neurons appear to be closely related to the onset of EA. Furthermore, these neurons show that the changes in responsiveness are closely parallel to the decrease of degree of complexity of firing series during penicillin epileptogenesis.
Yang
Hong-Jun
HJ
Institute of Neuroscience, The Fourth Military Medical University; and School of Civil Engineering and Mechanics, Xi'an Jiaotong University, Xi'an Peaple's Republic of China. sjhu@fmmu.edu.cn
Hu
San-Jue
SJ
Han
Sheng
S
Liu
Guo-Peng
GP
Xie
Yong
Y
Xu
Jian-Xue
JX
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D019277:Entropy; D004827:Epilepsy / Q000139:chemically induced / Q000503:physiopathology*; D018698:Glutamic Acid / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects* / Q000503:physiopathology*; D066298:In Vitro Techniques; D008297:Male; D009474:Neurons / Q000187:drug effects* / Q000502:physiology*; D010406:Penicillins; D051381:Rats; D017207:Rats, Sprague-Dawley; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D010406:Penicillins; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid