Probing the neural circuit basis of normal and disease-relevant cognitive function in mice

National Institute Of Neurological Disorders And Stroke

Investigators

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Abstract

In the last fiscal year, we enhanced our ability to conduct high-quality electrical recordings from multiple brain areas in active mice. We improved electrode design/implantation and data analysis pipelines. We expanded our mouse colony to include diverse dual- and triple-transgenic strains. We refined our use of simultaneous optogenetic manipulation with various neuronal recording techniques in behaving mice. Additionally, we fine-tuned our process for high-resolution confocal imaging and analysis of excitatory synapses in specific neuronal populations. We applied these and other tools to advance understanding in three key domains: 1. Oscillatory synchrony and SWM in mouse models relevant to psychiatric disease. Dysregulated GSK3 signaling is linked to schizophrenia and other psychiatric disorders. We previously showed that early-life treatment with a nonselective GSK3 (alpha and beta isoform) inhibitor rescues deficits in SWM task acquisition and vHPC-mPFC synchrony in adult male Df(16)A+/- mice. Considering isoform-specific and sex-divergent GSK3 signaling, we tested the effects of selective GSK3-alpha and beta inhibitors on SWM and vHPC-mPFC synchrony in male and female wildtype (WT) and Df(16)A+/- mice. GSK3-beta inhibition from P7-P28 improved SWM task acquisition in adult male but not female Df(16)A+/- mice, and modulated task-related vHPC-mPFC theta coherence. Conversely, GSK3-alpha inhibition didnt improve task acquisition but enhanced task performance under higher SWM demand in Df(16)A+/- mice of both sexes. RNA sequencing of mPFC and vHPC tissue is revealing sex-, genotype- and age-specific transcriptomic profiles underlying our behavioral and neurophysiological findings. Heterozygous null mutations of SETD1A are associated with increased risk for schizophrenia. Mice with similar mutations reportedly show SWM deficits. We investigated synchrony between the mPFC, vHPC, dorsal hippocampus, and nucleus reuniens (Re) of the thalamus during a SWM task. Despite reported SWM deficits in Setd1a+/- mice, our results showed Setd1a+/- mice performed similarly to WT controls in the SWM task. We included female mice, who performed similarly to males. Neural recordings indicated Setd1a+/- mice had altered vHPC-mPFC, vHPC-Re, and Re-mPFC synchrony compared to WT mice. Ongoing analyses are exploring changes in phase-locking of mPFC neuronal firing to hippocampal and thalamic neural oscillations. These findings implicate disruptions in prefrontal-thalamo-hippocampal synchrony in SETD1A-related genetic predisposition to schizophrenia. 2. vHPC-mPFC microcircuit interactions and plasticity. Inhibiting somatostatin-positive interneurons (SST-INs) in mPFC or vHPC-mPFC inputs during SWM encoding impaired vHPC-mPFC synchrony, mPFC neuron spatial encoding, and task performance, mimicking impairments in Df(16)A+/- mice. This phenotypic convergence raised three questions: (1) How do vHPC inputs interact with mPFC inhibitory microcircuits in vivo? (2) Are these interactions disrupted in Df(16)A+/- mice? And (3) are these interactions plastic, offering a potential path to correcting circuit dysconnectivity? To investigate these questions, we optically examined in vivo dynamics and activity-induced plasticity of mPFC interneuron population responses to vHPC input stimulation in wildtype and Df(16)A+/- mice. Using fiber photometry, we monitored SST-, VIP-, and PV-INs Ca2+ responses to optogenetic vHPC stimulation. Baseline SST-IN responses were weak in both mouse types but strengthened over 50 days of periodic stimulation. This potentiation was diminished in Df(16)A+/- compared to WT mice but improved with additional high-frequency vHPC stimulation. Conversely, VIP- and PV-INs had strong initial responses that waned with high-frequency stimulation in both mouse types. Ongoing work is exploring the effects of these plasticity forms at the ensemble, synaptic, and behavioral levels. By reshaping recruitment of mPFC INs by long-range inputs, these forms of plasticity stand to bias the routing of pathway-specific information through mPFC and may be leveraged to influence cognition-relevant circuit function and dysfunction. 3. Real-time modulation of cognition-relevant oscillatory synchrony. Dynamic changes in vHPC-mPFC synchrony correlate with various behaviors, but the causal contributions of such synchrony to behavior is unclear. Our prior work explored causal contributions of theta-frequency synchrony to avoidance behavior using sinusoidal open-loop optogenetic stimulation of vHPC-mPFC projections during exploration of the elevated plus maze. We found a privileged role for vHPC-mPFC theta-frequency communication in generating avoidance behavior and showed direct evidence that synchronized oscillations can facilitate neural transmission and behavior. Expanding on this, we used open-loop sinusoidal optogenetic stimulation to characterize properties of vHPC-mPFC oscillatory dynamics more richly. We recorded local field potentials (LFP) and/or single units from vHPC and mPFC during sinusoidal stimulation of ChR2 in vHPC-mPFC inputs. By systematically varying the frequency and amplitude of the optical stimulation, we revealed sensitivities of the vHPC-mPFC physiological response to our oscillatory manipulations. mPFC and vHPC oscillatory power increased preferentially to sinusoidal stimulation at frequencies below 15 Hz and above 10 Hz, respectively. vHPC-mPFC coherence was preferentially increased at frequencies above 10 Hz. These findings reveal a frequency-biased responsivity in vHPC-mPFC circuits, suggesting vHPC-mPFC input activity might foster synchrony more at higher frequencies than lower ones. To robustly test the causal contributions of long-range synchrony to cognitive function, we would need to modulate endogenous task-relevant oscillatory activity in real-time. We created a closed-loop optogenetic stimulation method, activating vHPC projections to mPFC based on ongoing vHPC theta-frequency oscillations. We expressed ChR2 or GFP in vHPC-mPFC terminals in WT mice and governed laser output in the mPFC by the theta-filtered vHPC LFP, allowing for phase delays relative to ongoing vHPC theta oscillations. Near-synchronous stimulation with vHPC theta increased vHPC-mPFC theta coherence in ChR2 mice, less so with greater phase delays. We applied this approach in mice performing a SWM task, hypothesizing that in-phase stimulation will enhance SWM performance, and that phase-shifted stimulation will impair it. Neither in-phase nor phase-shifted stimulation affected SWM performance. However, stimulation enhanced mPFC theta power, particularly when applied in-phase. Light-induced changes in theta coherence were phase- and delay-dependent, and more evident in ChR2 than GFP mice. We are currently examining stimulation effects on mPFC unit phase-locking to vHPC theta. Overall, our data show the behavioral state-dependent impact of closed-loop optogenetic stimulation on long-range synchrony. Ongoing collaborations. The INS also engaged in four formal collaborations with intramural and extramural groups. These include projects with: (1) Dr. Marisela Morales from NIDA studying the ultrastructural synaptic connectivity of vHPC inputs with mPFC SST+, PV+, and VIP+ INs in WT and Df(16)A+/- mice. (2) Dr. Yi Gu at NINDS examining neural dynamic stability within the medial entorhinal cortex and its impact on spatial learning behavior (submitted to Neuron, Sept. 2023). (3) Dr. Nikki Crowley at Penn State Univ. testing the effects of SST peptide-induced neuronal hyperpolarization in the mPFC on exploratory behavior (published in Cell Reports, Aug. 2023). (4) Dr. Hugo Tejeda at NIMH exploring how mPFC SST action influences SWM and long-range neural synchrony.