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Keywords:

  • amyloid β-protein fragment 31–35;
  • long-term potentiation;
  • hippocampus;
  • fEPSP;
  • paired pulse facilitation;
  • rats

Abstract

Effects of fragment 31–35 of amyloid β-protein (AβP31–35) on the baseline synaptic transmission, shown as fEPSPs, and the long-term potentiation (LTP) induced by high-frequency stimuli (HFS) were investigated in vivo in the hippocampal CA1 region of rats; a longer fragment of AβP, i.e., AβP25–35, which had been generally accepted as the active center in AβP, was also tested comparatively along with AβP31–35. The results showed that: (1) the baseline fEPSPs induced by test stimuli were not changed by i.c.v. injection of AβP31–35, while application of either AβP31–35 or AβP25–35 with the same molar concentration (50 nmol) significantly and similarly suppressed the HFS-induced LTP; (2) higher concentration of AβP31–35 or longer time of AβP exposure exhibited stronger suppression on LTP, indicating a dose- and time-dependent trends; (3) no significant effects could be found on the paired-pulse facilitation (PPF) following AβP31–35 injection; (4) pretreatment with verapamil (2.5 mg/kg, i.p., 1 h prior to HFS), a blocker of L-type Ca2+ channels, did not affect the baseline fEPSPs, while it exhibited a significant suppression on LTP induced by HFS; and (5) surprisingly enough, coapplication with verapamil and AβP31–35 exhibited a similar suppression on LTP just as both of these two agents were used alone. These results indicate that: (1) AβP31–35, similar to AβP25–35, possesses potent suppressive effects on hippocampal LTP in vivo, supporting our proposal that the fragment AβP31–35 might be to date the shortest active sequence in full-length of AβP molecule; (2) AβP31–35-induced LTP suppression is not mediated by affecting the presynaptic processes; and (3) L-type Ca2+ channels might be one of the main pathways by which AβP31–35 insults LTP. Synapse 60:307–313, 2006. © 2006 Wiley-Liss, Inc.