Figure 7. Chronic chemogenetic activation of CamKIIα-positive forebrain excitatory neurons during the early postnatal window alters excitatory and inhibitory spontaneous currents in the hippocampi of adult male mice.

(A) Shown is a schematic of the experimental paradigm to induce chronic CNO-mediated hM3Dq DREADD activation in CamKIIα-positive forebrain excitatory neurons using bigenic CamKIIα-tTA::TetO-hM3Dq mouse pups that were fed CNO (PNCNO; 1 mg/kg) or vehicle from P2 to P14 and then left undisturbed for 3 months prior to electrophysiological analysis, in acute hippocampal slices derived from adult male mice. Whole-cell patch clamp was performed to record sEPSCs/mEPSCs and sIPSCs/mIPSCs in the somata of CA1 pyramidal neurons. R – Recording electrode. (B) Shown are representative sEPSC traces of CA1 pyramidal neurons from vehicle and PNCNO-treated mice. (C) PNCNO-treated mice showed significantly altered cumulative probability of sEPSC amplitude with a small increase at lower amplitudes (<30 pA) and a significant decline in large-amplitude events as compared to vehicle-treated controls. (D) PNCNO-treated mice showed a significant decline in the cumulative probability of sEPSC interevent intervals as compared to vehicle-treated controls (n = 8 cells for vehicle; n = 5 cells for PNCNO). (E) Shown are representative mEPSC traces of CA1 pyramidal neurons from vehicle and PNCNO-treated mice. (F) PNCNO-treated mice showed significantly enhanced cumulative probability of sEPSC amplitude as compared to vehicle-treated controls. (G) No significant change was observed in the cumulative probability of sEPSC interevent intervals in PNCNO-treated mice as compared to vehicle-treated controls (n = 5 cells for vehicle; n = 6 cells for PNCNO). (H) Shown are representative sIPSC traces of CA1 pyramidal neurons from vehicle and PNCNO-treated mice. PNCNO-treated mice showed a significant increase in the cumulative probability of sIPSC amplitude (I), along with a significant decline in the cumulative probability of sIPSC interevent intervals (J) as compared to vehicle-treated controls (n = 8 cells for vehicle; n = 7 cells for PNCNO). (K) Shown are representative mIPSC traces of CA1 pyramidal neurons from vehicle and PNCNO-treated mice. (L) PNCNO-treated mice showed a significant decline in the cumulative probability of mIPSC amplitude as compared to vehicle-treated controls (n = 6 cells for vehicle; n = 7 cells for PNCNO). (M) No significant change was observed in the cumulative probability of mIPSC interevent intervals across treatment groups. Results are expressed as cumulative probabilities. *p<0.001 as compared to PNCNO-treated group using the Kolmogorov-Smirnov two-sample comparison.

Figure 7—figure supplement 1. Chronic chemogenetic activation of CamKIIα-positive forebrain excitatory neurons during the early postnatal window does not change intrinsic excitability but alters spontaneous network activity in the hippocampi of adult male mice.

(A) Shown is a schematic of the experimental paradigm to induce chronic CNO-mediated hM3Dq DREADD activation in CamKIIα-positive forebrain excitatory neurons using bigenic CamKIIα-tTA::TetO-hM3Dq mouse pups that were fed CNO (PNCNO; 1 mg/kg) or vehicle from P2 to P14 and then left undisturbed for 3 months prior to electrophysiological analysis, in acute hippocampal slices derived from adult male mice. Whole-cell patch clamp was performed to record sPSCs and input-output characteristics in the somata of CA1 pyramidal neurons. R – Recording electrode. (B) Shown are representative traces of spikes generated by CA1 pyramidal neurons following a current injection of 100 pA in vehicle and PNCNO-treated adult male mice. (C) No significant change was observed in the input-output characteristics of CA1 pyramidal neurons in acute hippocampal slices derived from PNCNO-treated mice as compared to vehicle-treated controls (n = 18 cells for vehicle; n = 25 cells for PNCNO). Results are expressed as the mean ± S.E.M. (D) Shown are representative sPSC traces of CA1 pyramidal neurons from vehicle and PNCNO-treated mice. (E) PNCNO-treated mice showed significantly enhanced cumulative probability of sPSC amplitude in addition to the presence of a long-tail as compared to vehicle-treated controls. (F) PNCNO-treated mice showed a significant decline in the cumulative probability of sPSC interevent intervals as compared to vehicle-treated controls (n = 8 cells for vehicle; n = 6 cells for PNCNO). Results are expressed as cumulative probabilities. *p<0.001 as compared between vehicle and PNCNO-treated group using the Kolmogorov-Smirnov two-sample comparison.

Figure 7—figure supplement 2. Effect of chronic chemogenetic activation of CamKIIα-positive forebrain excitatory neurons during the early postnatal window on the distribution of spontaneous network events in hippocampi of adult male mice.

(A) Shown is a schematic of the experimental paradigm to induce chronic CNO-mediated hM3Dq DREADD activation in CamKIIα-positive forebrain excitatory neurons using bigenic CamKIIα-tTA::TetO-hM3Dq mouse pups that were fed CNO (PNCNO; 1 mg/kg) or vehicle from P2 to P14 and then left undisturbed for 3 months prior to electrophysiological analysis, in acute hippocampal slices derived from adult male mice. Whole-cell patch clamp was performed to record sPSCs in the somata of CA1 pyramidal neurons. R – Recording electrode. (B) Shown is an example trace of a large-amplitude spontaneous network event observed in a CA1 pyramidal neuron of a PNCNO-treated mouse. (C) Distribution plot for sPSC amplitudes showing a long-tail of large-amplitude events in PNCNO-treated mice. (D) Quantification of percent of total events with amplitude >100 pA and >200 pA. No event >200 pA was observed in vehicle-treated controls.