The overall objectives of this project are to:
Objective 1 – Examine HA-induced changes in the excitability of layer 5 PYR, PV, and SOM neurons
Objective 2 – Test HA-mediated modulation of synaptic plasticity in layer 5 PYR, PV, and SOM connections
and predict regulation of microcircuit oscillatory dynamics
Objective 3 – Quantify HA regulation of NMDA-evoked potentials in layer 5 PYR, PV, and SOM neurons
Work Package 1: I have previously shown using detailed simulations that neuromodulatory signaling can decrease the excitability of layer 5 PYR neurons during low-frequency network activity . However, the impact of HA on the electrical properties of distinct layer 5 cell-types is unknown. In WP1, I investigated the specific effects of HA on the electrical properties of layer 5 PYR, PV, SOM neurons during slow wave network activity in ~300 µm thick coronal visual cortex slices obtained from male and female adult mice. Through whole-cell recordings in layer 5 PYR, PV, SOM and VIP neurons combined with optogenetic stimulation of HA neurons, I quantified HA regulation of electrical properties such as resting membrane potential, input resistance, and membrane time constant; and firing properties such as action potential (AP) amplitude, AP frequency, adaptation index, and inter-spike interval. HA modulation of electrical properties was investigated by combining photo-stimulation of RFP labeled HA neurons in HDC-ChR2 mice with targeted somatic whole-cell recordings in PYR, PV, SOM and VIP neurons. For comparison, electrical properties were quantified both with and without photo-stimulation in male and female mouse brain slices. Pharmacological experiments with HA agonists such as betazole and betahistine, and antagonists such as pyrilamine and ranitidine identified the location and expression of HA receptors – H1, H2, and H3 that modulate electrical activity in layer 5 cell-types.
Work package 2: It is known that neuromodulation differentially controls the synaptic properties of neocortical neurons . However, the mechanisms of HA neuromodulation of synaptic transmission are poorly understood. In this study, I measured the effect of HA on layer 5 PYR, PV, and SOM synaptic connections, using paired whole-cell recordings to characterize the efficacy and short-term depression and facilitation of synaptic transmission. I characterized the regulation of synaptic transmission by HA in ~300 μm thick coronal visual cortex slices from male and female adult mice. By combining photo-stimulation of RFP labeled HA neurons in HDC-ChR2 mice, and paired whole-cell recordings, I measured synaptic properties by somatic depolarization of the presynaptic neuron to elicit a single AP or a frequency-dependent train of APs, while simultaneously measuring sub-threshold membrane potential changes in the postsynaptic neuron. Synaptic properties such as the amplitude and time course of postsynaptic responses, latencies, rise and decay times, transmission failures, response variability, short-term facilitation and depression were characterized with and without photo-activation of HA axons in brain slices from male and female mice. Acquired data on HA-induced changes in cellular and synaptic physiology were utilized to construct an in silico network model comprising multicompartmental neurons to investigate how HA regulates the emergence of rhythmic microcircuit oscillatory dynamics in the gamma-band. Experimental data on HA modulation of the excitability of PYR, PV and SOM neurons were used to build and validate computational models in the NEURON simulation environment using an open-source framework. Data on HA-induced changes in the synaptic plasticity of PYR, PV and SOM neurons were utilized to construct models of HA regulation of synaptic transmission. The cellular and synaptic models were integrated into an in silico model of visual cortex microcircuitry to study how HA synchronizes the activity of populations of excitatory and inhibitory neurons shape rhythmic oscillations in the gamma-band.
