Sequence-independent effects of phosphorothiolated oligonucleotides on synaptic transmission and excitability in the hippocampus in vivo.
Antisense oligodeoxynucleotides (ODNs) have the potential to be a powerful tool for regulating gene expression and mRNA translation in spatially and temporally restricted domains. Prior to investigating the effects of antisense ODNs on hippocampal long-term potentiation, we investigated whether there are any non-specific effects of ODNs on perforant path synaptic transmission in the dentate gyrus of both pentobarbital-anaesthetized and awake, freely moving rats. Single injections of phosphorothioated antisense ODNs (4 nmol) to the immediate early gene zif/268 caused a rapid (within minutes) and long-lasting (>24 hr) profound depression of the perforant path evoked field potentials. This depressive effect was due to the phosphorothioate modification since a depression was not seen with unmodified antisense ODNs, relative to saline controls. Furthermore, the effect was not sequence-specific since modified sense ODNs caused the same degree of depression. The depression caused by the modified antisense ODNs was dose-dependent and specific to synaptic transmission, since antidromic population spikes elicited by mossy fibre stimulation were relatively unaffected compared to the orthodromic responses. A second unexpected side-effect of the modified ODNs was cellular hyperexcitability, such that bursts of epileptiform spikes in the EEG occurred both spontaneously and as a result of synaptic stimulation. While the mechanism of the synaptic depression remains unknown, these results indicate that phosphorothioate-modified ODNs exert profound non-specific effects on synaptic transmission in the hippocampus, that have the potential to seriously compromise any corresponding behavioural or electrophysiological studies.
Abraham
W C
WC
Department of Psychology, Neuroscience Research Centre, University of Otago, Dunedin, New Zealand. cabraham@psy.otago.ac.nz
Logan
B
B
Thompson
V L
VL
Williams
J M
JM
Tate
W P
WP
D000818:Animals; D004305:Dose-Response Relationship, Drug; D006624:Hippocampus / Q000187:drug effects*; D017774:Long-Term Potentiation / Q000187:drug effects; D008297:Male; D016376:Oligonucleotides, Antisense / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000187:drug effects*
D016376:Oligonucleotides, Antisense