Spreading Depolarization Induces a Transient Potentiation of Excitatory Synaptic Transmission.

ABSTRACT

Spreading depolarization (SD) is a slowly propagating wave of prolonged activation followed by a period of synaptic suppression. Some prior reports have shown potentiation of synaptic transmission after recovery from synaptic suppression and noted similarities with the phenomenon of long-term potentiation (LTP). Since SD is increasingly recognized as participating in diverse neurological disorders, it is of interest to determine whether SD indeed leads to a generalized and sustained long-term strengthening of synaptic connections. We performed a characterization of SD-induced potentiation, and tested whether distinctive features of SD, including adenosine accumulation and swelling, contribute to reports of SD-induced plasticity. Field excitatory postsynaptic potentials (fEPSPs) were recorded in the hippocampal CA1 subregion of murine brain slices, and SD elicited using focal microinjection of KCl. A single SD was sufficient to induce a consistent potentiation of slope and amplitude of fEPSPs. Both AMPA- and NMDA-receptor mediated components were enhanced. Potentiation peaked ∼20 min after SD recovery and was sustained for ∼30 min. However, fEPSP amplitude and slope decayed over an extended 2-hour recording period and was estimated to reach baseline after ∼3 h. Potentiation was saturated after a single SD and adenosine A1 receptor activation did not mask additional potentiation. Induction of LTP with theta-burst stimulation was not altered by prior induction of SD and molecular mediators known to block LTP induction did not block SD-induced potentiation. Together, these results indicate an intermediate duration potentiation that is distinct from hippocampal LTP and may have implications for circuit function for 1-2 h following SD.