Heterosynaptic Neuroplasticity of Cortical Inhibitory Circuits

皮層抑制性環路的異突觸神經可塑性

Student thesis: Doctoral Thesis

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Detail(s)

Awarding Institution
Supervisors/Advisors
  • Jufang HE (Supervisor)
  • Ying Shing Chan (External person) (External Co-Supervisor)
Award date2 Jul 2021

Abstract

This study explored the effects of high-frequency laser stimulation (HFLS) and low-frequency laser stimulation (LFLS) on GABAergic neurons. To specifically target GABAergic neurons, we injected AAV-mDlx-DIO-Chronos-mCherry-pA into the auditory cortex of GABA-Cre mice. HFLS of GABAergic neurons induced inhibitory long-term potentiation (i-LTP). Inhibitory postsynaptic currents (IPSCs) were recorded from pyramidal neurons using whole-cell patch-clamp recordings before and after HFLS or LFLS to measure the alterations in inhibitory transmission. The amplitude of IPSCs remained stable after LFLS (from 100.00% ± 0.13% to 103.10 ± 4.52%), whereas the IPSCs increased dramatically after HFLS (from 100.09% ± 0.13% to 143.03% ± 4.52%), indicating i-LTP was induced by HFLS of GABAergic neurons. Spontaneous IPSCs (sIPSCs) revealed that after HFLS of GABAergic neurons, the amplitudes of sIPSCs increased from 43.78 pA ± 2.94 pA to 51.80 pA ± 3.39 pA, whereas the frequency8 of sIPSCs did not exhibit a difference, indicating that the modification mainly occurred at postsynaptic neurons.

Second, GABAergic cholecystokinin (CCK) neurons contributed to HFLS-induced i-LTP. We examined three major types of GABAergic interneurons: CCK interneurons, parvalbumin (PV) interneurons, and somatostatin (SST) interneurons. By combining optogenetics with in vitro whole-cell recordings, IPSCs were recorded from pyramidal neurons by laser activation of Chronos-expressing CCK, PV, and SST interneurons before and after HFLS. The results demonstrated that HFLS caused a growth in IPSC amplitudes only by activating CCK interneurons (from 102.15% ± 3.65% to 175.70% ± 51.26%), indicating that CCK was the key neuromodulator in the induction of i-LTP. The sIPSCs results showed that after HFLS of CCK interneurons, the amplitude of sIPSCs were increased (from 47.92 pA ± 2.80 pA to 52.43 pA ± 2.40 pA), and the frequency of sIPSCs exhibited no difference, indicating that the modification mainly occurred at postsynaptic neurons.

Third, CCK 8S enhanced the inhibitory effect of PV and SST interneurons on pyramidal neurons. IPSCs were recorded from pyramidal neurons by laser activation of Chronos-expressing PV and SST interneurons before HFLS. Then, CCK 8S (400 nM) dissolved in normal artificial cerebrospinal fluid (ACSF) was infused into the recording chamber for 5 min. IPSCs were recorded for another 25 min. After HFLS and infusion of CCK 8S, the amplitudes of IPSCs were dramatically increased by activating both PV interneurons (from 100.39% ± 0.93% to 142.86% ± 4.13%) and SST interneurons (from 100.00% ± 0.00% to 128.51% ± 5.13%). Furthermore, we tested the effect of CCK 8S when LFLS was applied to PV interneurons and SST interneurons. IPSCs were increased after LFLS and CCK 8S infusion but showed no significant change after LFLS. Collectively, these results indicate that CCK 8S enhanced the inhibitory effects of PV and SST interneurons on pyramidal neurons, regardless of whether HFLS or LFLS was applied to these two types of interneurons.

Finally, HFLS of CCK interneurons increased the inhibitory effect of both CCK interneurons and PV interneurons to the same pyramidal neurons and enabled heterosynaptic neuroplasticity. In this experiment, we crossed the CCK-Cre mice and PV-FlpO mice to generate CCK-Cre-PV-FlpO mice. By injecting two kinds of viruses, AAV9-mDlx-DIO-Chronos-mCherry-WPRE-pA, and AAV9-EF1α-fDIO-ChrmosonR-EYFP-WPRE-pA, into the auditory cortex of CCK-Cre-PV-FlpO mice, CCK interneurons expressed Chronos-mCherry and PV interneurons expressed ChrmosonR-EYFP. A 473 nm blue laser could activate Chronos, and a 594 nm red laser could activate ChrimsonR. Thus, we could independently activate CCK interneurons and PV interneurons by blue and red lasers, respectively. When we applied HFLS to both CCK interneurons and PV interneurons, we found that the amplitudes of CCK interneurons induced IPSCs (CCK-IPSCs) and PV interneurons induced IPSCs (PV-IPSCs) were increased when recorded on the same pyramidal neurons (CCK-IPSCs: 100% ± 0.00 before vs. 143.20% ± 11.39% after; PV-IPSCs: 100.09% ± 0.09% before vs. 133.07 % ± 7.66 % after), whereas applied HFLS to PV interneurons and LFLS to CCK interneurons failed to increase the CCK-IPSCs (99.88% ± 0.39% before vs. 100.32% ± 4.96% after) and PV-IPSCs (100.24% ± 0.31% before vs. 98.39% ± 3.00% after). Interestingly, after the application of HFLS to CCK interneurons and LFLS to PV interneurons, CCK-IPSCs (100% ± 0.01% before vs. 125.61% ± 6.57% after) and PV-IPSCs (100.06% ± 0.06% before vs. 132.99% ± 8.92% after) were significantly increased.

In summary, we found that HFLS of GABAergic neurons induced an increase in IPSCs, indicating that HFLS of GABAergic neurons induced i-LTP. Next, we examined three main types of GABAergic interneurons, CCK interneurons, PV interneurons, and SST interneurons, and found an increase in IPSCs evoked by activating GABAergic neurons after HFLS, mainly because of CCK interneurons. We demonstrated that CCK8S also increased the inhibitory effects of PV interneurons and SST interneurons on pyramidal neurons. Furthermore, HFLS of CCK interneurons increased the inhibitory effect of both CCK interneurons and PV interneurons to the same pyramidal neurons and enabled heterosynaptic neuroplasticity.

    Research areas

  • cholecystokinin, parvalbumin interneurons, somatostatin interneurons, auditory cortex, i-LTP, heterosynaptic neuroplasticity