Beschreibung
The objective of this study was to investigate the effects of TNF-? and its two receptors (TNFR1 and TNFR2) on neuronal activity. Current studies show sometimes contradictory results on stimulating or inhibitory effects. Most of these studies are performed with animals, tissue, or cell cultures, that are treated with TNF-?, TNFR1 or TNFR-2 agonists or antagonists for some minutes to several hours. This allows to draw conclusions on acute effects of TNF-? and its receptors. To gather more information on the chronic effects of TNF-? and its receptors, organotypic hippocampal cultures (OHCs) of TNF-?-overexpressing, as well as TNFR1-ko and TNFR2-ko mice strains were compared to OHCs of wt mice in this study. Additionally, connections between TNF-? and microglia on their activation and on neuronal activity were investigated, using OHCs from the same mice strains.
OHCs from all four mice strains were prepared and their activity was investigated using multielectrode arrays (MEAs). For this the OHCs were stimulated with carbachol (Cch) and KCl. The mean spike frequency was recorded as well as some burst parameters, like the duration of bursts, the frequency of spikes within the bursts and the interburst interval. All results were compared using statistical analysis.
After stimulation with Cch the mean spike-frequency in OHCs obtained from TNFtg mice (OHC-TNF) was increased compared to OHCs from wt mice (OHC-WT). The spike frequency in OHCs from TNFR1-ko mice (OHC-TNFR1-ko) and OHC-TNFR2-ko was even higher than in OHC-TNF. However, the spike frequency in OHC-TNFR1-ko did not differ from the spike frequency in OHC-TNFR2-ko.
Concerning burst parameters, OHC-TNF showed a reduced activity compared to OHC-WT, which was characterized by a reduced spike frequency and a prolonged interburst interval. In OHC-TNFR1-ko there was a reduction in spike frequency during bursts. There was no difference in spike frequency in between OHC-TNFR1-ko and OHC-TNFR2-ko. The interburst interval was prolonged in OHC-TNFR1-ko compared to OHC-WT as well as OHC-TNFR2-ko.
After stimulation with KCl OHC-TNF showed a reduced local field potential (LFP) frequency compared to OHC-WT. The LFP frequency in OHC-TNFR1-ko was increased, whereas OHC-TNFR2-ko also showed a reduction in LFP frequency compared to OHC-WT.
Immunofluorescence was used to investigate the number and activation of microglia in OHCs of the different mice strains. Number as well as activation of microglia in OHC-TNF was increased compared to OHC-WT. In OHC-TNFR1-ko there was a reduction in number and activation of microglia. In OHC-TNFR2-ko there was also a reduction in microglial activation, but the number of microglia was comparable to OHC-WT.
To put it in a nutshell, these results show a difference in between the chronic influence of TNF-? on neuronal activity and acute effects of TNF-?. The two TNFRs often show overlapping results. In case their effects differ, there is an anticonvulsive and protective effect of TNFR2 and a proconvulsive and degenerative effect of TNFR1 also with chronically increased levels of TNF-?.
