Synaptic transmission and hippocampal long-term potentiation in olfactory cyclic nucleotide-gated channel type 1 null mouse

Field potential recording was used to investigate properties of synaptic transmission and long-term potentiation (LTP) at Schaffer collateral-CA1 synapses in both hippocampal slices of mutant mice in which the α-subunit of the olfactory cyclic nucleotide-gated channel (α3/OCNC) 1 was rendered null and also in slices prepared from their wild-type (Wt) littermates. Several measures of basal synaptic transmission were unaltered in the OCNC1 knockout (KO), including maximum field excitatory postsynaptic potential (fEPSP) slope, maximum fEPSP and fiber volley amplitude, and the function relating fiber volley amplitude to fEPSP slope and paired-pulse facilitation. When a high-frequency stimulation protocol was used to induce LTP, similar responses were seen in both groups [KO: 1 min, 229 ± 50% (mean ± SE), 60 min, 123 ± 10%; Wt: 1 min, 287 ± 63%; 60 min, 132 ± 19%]. However, on theta-burst stimulation, the initial amplitude of LTP was smaller (1 min after induction, 147 ± 16% of baseline) and the response decayed faster in the OCNCl KO (60 min, 127 ± 18%) than in Wt (1 min, 200 ± 14%; 60 min, 169 ± 19%). Analysis of waveforms evoked by LTP-inducing tetanic stimuli revealed a similar difference between groups. The development of potentiation throughout the tetanic stimulus was similar in OCNC1 KO and Wt mice when high-frequency stimulation was used, but OCNC1 KO mice showed a significant decrease when compared with Wt mice receiving theta-burst stimulation. These results suggest that activation of cyclic nucleotide-gated channels may contribute to the induction of LTP by weaker, more physiological stimuli, possibly via Ca²⁺ influx.