Long-term increase in excitability induced by Mg(2+)-free medium in the absence of afferent stimulation in CA1 area of mouse hippocampal slices.
Omission of Mg ions from the perfusion fluid of hippocampal slices unblocks the N-methyl-D-aspartate (NMDA) type of glutamate receptor/channel, and induces long term enhancement of synaptic responses. In order to test the role of afferent activation in induction of long term potentiation in CA1 area by this process, we switched off stimulation during the time of perfusing the slices with Mg(2+)-free medium (30 min). In addition to a short lasting increase in synaptic activation we observed a long term increase in population spike amplitude in all slices tested (n = 5), which lasted for at least 2 h. This process was antagonized by 50-100 microM DL-2-amino-5-phosphonovalerate, a specific NMDA receptor antagonist (n = 8), but not by isolating CA1-CA3 areas prior to the testing (n = 5). These results suggest that the resting levels of the endogenous excitatory neurotransmitter(s) can induce long term increase in firing probability of CA1 pyramidal cells, when NMDA channels are unblocked, in the absence of afferent stimulation and irrespective of CA3 area prior excitation.
Psarropoulou
C
C
Department of Physiology, Medical School, University of Patras, Greece.
Kostopoulos
G
G
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D003470:Culture Media; D004558:Electric Stimulation; D004594:Electrophysiology; D006624:Hippocampus / Q000502:physiology*; D008274:Magnesium / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology; D013997:Time Factors
D003470:Culture Media; D016194:Receptors, N-Methyl-D-Aspartate; D015763:2-Amino-5-phosphonovalerate; D008274:Magnesium