Theta activity paradoxically boosts gamma and ripple frequency sensitivity in prefrontal interneurons

Fast oscillations in cortical circuits critically depend on GABAergic interneurons. Which interneuron types and populations can drive different cortical rhythms, however, remains unresolved and may depend on brain state. Here, we measured the sensitivity of different GABAergic interneurons in prefrontal cortex under conditions mimicking distinct brain states. While fast-spiking neurons always exhibited a wide bandwidth of around 400 Hz, the response properties of spike-frequency adapting interneurons switched with the background input’s statistics. Slowly fluctuating background activity, as typical for sleep or quiet wakefulness, dramatically boosted the neurons’ sensitivity to gamma and ripple frequencies. We developed a time-resolved dynamic gain analysis and revealed rapid sensitivity modulations that enable neurons to periodically boost gamma oscillations and ripples during specific phases of ongoing low-frequency oscillations. This mechanism predicts these prefrontal interneurons to be exquisitely sensitive to high-frequency ripples, especially during brain states characterized by slow rhythms, and to contribute substantially to theta-gamma cross-frequency coupling.

Human Stem Cell-Derived GABAergic Interneurons Establish Efferent Synapses onto Host Neurons in Rat Epileptic Hippocampus and Inhibit Spontaneous Recurrent Seizures

Epilepsy is a complex disorder affecting the central nervous system and is characterised by spontaneously recurring seizures (SRSs). Epileptic patients undergo symptomatic pharmacological treatments, however, in 30% of cases, they are ineffective, mostly in patients with temporal lobe epilepsy. Therefore, there is a need for developing novel treatment strategies. Transplantation of cells releasing γ-aminobutyric acid (GABA) could be used to counteract the imbalance between excitation and inhibition within epileptic neuronal networks. We generated GABAergic interneuron precursors from human embryonic stem cells (hESCs) and grafted them in the hippocampi of rats developing chronic SRSs after kainic acid-induced status epilepticus. Using whole-cell patch-clamp recordings, we characterised the maturation of the grafted cells into functional GABAergic interneurons in the host brain, and we confirmed the presence of functional inhibitory synaptic connections from grafted cells onto the host neurons. Moreover, optogenetic stimulation of grafted hESC-derived interneurons reduced the rate of epileptiform discharges in vitro. We also observed decreased SRS frequency and total time spent in SRSs in these animals in vivo as compared to non-grafted controls. These data represent a proof-of-concept that hESC-derived GABAergic neurons can exert a therapeutic effect on epileptic animals presumably through establishing inhibitory synapses with host neurons.

Reprogramming Human Adult Fibroblasts into GABAergic Interneurons

Direct reprogramming is an appealing strategy to generate neurons from a somatic cell by forced expression of transcription factors. The generated neurons can be used for both cell replacement strategies and disease modelling. Using this technique, previous studies have shown that γ-aminobutyric acid (GABA) expressing interneurons can be generated from different cell sources, such as glia cells or fetal fibroblasts. Nevertheless, the generation of neurons from adult human fibroblasts, an easily accessible cell source to obtain patient-derived neurons, has proved to be challenging due to the intrinsic blockade of neuronal commitment. In this paper, we used an optimized protocol for adult skin fibroblast reprogramming based on RE1 Silencing Transcription Factor (REST) inhibition together with a combination of GABAergic fate determinants to convert human adult skin fibroblasts into GABAergic neurons. Our results show a successful conversion in 25 days with upregulation of neuronal gene and protein expression levels. Moreover, we identified specific gene combinations that converted fibroblasts into neurons of a GABAergic interneuronal fate. Despite the well-known difficulty in converting adult fibroblasts into functional neurons in vitro, we could detect functional maturation in the induced neurons. GABAergic interneurons have relevance for cognitive impairments and brain disorders, such as Alzheimer’s and Parkinson’s diseases, epilepsy, schizophrenia and autism spectrum disorders.

Cholinergic control of striatal GABAergic microcircuits

Cholinergic interneurons (CINs) are essential elements of striatal circuits and behaviors. While acetylcholine signaling via muscarinic receptors (mAChRs) have been well studied, more recent data indicate that postsynaptic nicotinic receptors (nAChRs) located on GABAergic interneurons (GINs) are equally critical. One demonstration is that CINs stimulation induces large disynaptic inhibition of SPNs mediated by nAChR activation of striatal GINs. While these circuits are ideally positioned to modulate striatal output activity, the neurons involved are not definitively identified due largely to an incomplete mapping of CINs-GINs interconnections. Here, we show that CINs optogenetic activation evokes an intricate dual mechanism involving co-activation of pre- and postsynaptic mAChRs and nAChRs on four GINs populations. Using multi-optogenetics, we demonstrate the participation of tyrosine hydroxylase-expressing GINs in the disynaptic inhibition of SPNs likely via heterotypic electrical coupling with neurogliaform interneurons. Altogether, our results highlight the importance of CINs in regulating GINs microcircuits via complex synaptic/heterosynaptic mechanisms.

The Role for GABAergic Interneurons Subtypes in the Antidepressant Efficacy of Traditional Chinese Medicine Formula Lily Bulb and Rehmannia Decoction

Background Depression is associated with reduced γ-aminobutyric acid (GABA) and alterations of GABAergic interneurons in medial prefrontal cortex (mPFC), which can be normalized by traditional Chinese medicine formula lily bulb and Rehmannia decoction (LBRD) standard decoction. However, the impact of GABAergic interneurons subtypes including parvalbumin (PV), somatostatin (SST), and vasoactive intestinal peptide (VIP), in depressive episodes as well as in the LBRD standard decoction antidepressant effects remains to be elucidated. Methods We assessed the effects of LBRD standard decoction intervention on the expression of GABA associated miRNA/mRNA and GABAergic subtype-specific markers in chronic stress induced depression by western blot and qRT-PCR. The lncRNA/miRNA/GABA regulatory axis was verified by luciferase reporter assay, RNA immunoprecipitation, RNA pull-down assay and then detect its changes in LBRD standard decoction administration with use of immunofluorescence staining and RNA-fluorescence in situ hybridization (FISH). Results In the current study, we found that LBRD standard decoction exerted antidepressant effects based on the results of behavioral tests. Meanwhile, LBRD also revised the reduced GABA levels in depression by increasing the expression of lncRNA Neat1 and Malat1, as well as decreasing miRNA-144-3p and miRNA-15b-5p. Moreover, the expression of SST mRNA and protein in the mPFC tissues from depression group, was significantly lower than those in the control cases, while LBRD standard decoction treatment revised these changes. Whereas, neither chronic stress nor treatment can obviously change the level of PV and VIP mRNA and protein expression. In the SST-positive neurons of mPFC tissues, treatment with LBRD standard decoction resulted in the elevation of Gad-67, VGAT, GAT-3 and an reduction of miRNA-144-3p expression. Conclusion Taken together, these findings suggest that SST interneurons may be served as a preferentially vulnerable GABAergic neuronal subtype in depression and LBRD standard decoction antidepressant activities potentially relate to against the SST cells deficits by regulating the miRNA-144-3p mediated GABA synthesis, release.

Presynaptic HCN channels constrain GABAergic synaptic transmission in pyramidal cells of the medial prefrontal cortex

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are widely expressed in neurons in the central nervous system. It has been documented that HCN channels regulate the intrinsic excitability of pyramidal cells in the medial prefrontal cortex (mPFC) of rodents. Here, we report that HCN channels limited GABAergic transmission onto pyramidal cells in rat mPFC. The pharmacological blockade of HCN channels resulted in a significant increase in the frequency of both spontaneous and miniature inhibitory postsynaptic currents (IPSCs) in mPFC pyramidal cells, whereas potentiation of HCN channels reversely decreases the frequency of mIPSCs. Furthermore, such facilitation effect on mIPSC frequency required presynaptic Ca2+ influx. Immunofluorescence staining showed that HCN channels expressed in presynaptic GABAergic terminals, as well as in both soma and neurite of parvalbumin-expressing (PV-expressing) basket cells in mPFC. The present results indicate that HCN channels in GABAergic interneurons, most likely PV-expressing basket cells, constrain inhibitory control over layer 5-6 pyramidal cells by restricting presynaptic Ca2+ entry.