Ian A. Oldenburg - US grants

DESCRIPTION (provided by applicant): The striatum is the primary input to the basal ganglia, a collection of structures involved in initiation of voluntary movements and motor learning. This structure is involved in many movement and cognitive disorders. The principle output of striatum is through the GABAergic medium spiny neurons (MSNs). Cholinergic interneurons (CINs) of the striatum fire tonically and provide the sole source of the neuromodulator acetylcholine (Ach) to the striatum. In vitro, Ach presynaptically inhibits corticostriatal EPSCs in MSNs. This provides a powerful opportunity for regulation of MSN activity. However, it has been difficult to assess the role of CIN firing on this inhibition. Furthermore, CINs are thought to correspond to tonically active neurons (TANs) reported in vivo. These cells briefly cease firing to rewarding stimuli and stimuli that predict reward, suggesting the possibility that this pause reduces Ach relieving this inhibition. In this project we seek to link the activity of CINs to changes in MSN firing and corticostriatal EPSCs both in vitro and in vivo. We selectively control the firing of CINs using virally delivered light activated membrane proteins, channelrhodopsin (ChR2) and halorhodopsin (HR). We have validated that we can control the firing of CINs in vivo and in vitro. We can now investigate how both the timing of CIN action potential and their firing rate affects EPSCs in MSNs in the acute slice. And, with HR we now have the ability to briefly pause CINs in striatum. We will observe any changes to corticostriatal EPSCs, allowing us to make predictions on the function of TAN pauses. Additionally, using implanted fiberoptics and in vivo recording devices we can activate and pause CINs in vivo. By comparing evocable CINs to apparent TANs we can identify if CINs are in fact TANs. And by recording the activity of the surrounding MSNs we can identify the net effect of CIN activity or pause on spontaneous and cortically driven activity. This approach allows the first opportunity to observe the effects of cholinergic interneuron activity, and provides the first insight to a function of the behaviorally important pause in TAN firing. PUBLIC HEALTH RELEVANCE: Acetylcholine in striatum is critically involved in voluntary movement and associative learning. However, the mechanisms of this control are not well understood. The new techniques that we develop in this proposal will help us understand how acetylcholine release controls the behaviors of other cells, aiding in our understanding of normal cognition as well as the pathophysiology of brain disorders such as Parkinson's Disease, Alzheimer's Disease, Huntington's Disease, and Schizophrenia.

Project Summary: Neural computation requires the coordinated effort of thousands of interrelated and often genetically similar neurons. These neurons form physically intermingled networks and subnetworks that act together to amplify and strengthen sensory perceptions or select motor action. Such co-active ensembles are known to be preferentially interconnected, and may represent a functional element of neural processing with unique properties, such as pattern completion and competition between ensembles. In this proposal I will gain a mechanistic understanding of how ensembles of co-active neurons interact by probing the function of individual and groups of neurons in an awake mouse. I will examine: how ensembles of pyramidal cells interact with other pyramidal cells and local inhibitory neurons in a visual task, how these ensembles influence motor behavior, and how specific ensembles respond to information from other cortical areas. Despite the potential importance of ensembles in cortical coding, the intermixed nature of these groups has made them particularly hard to study. While conventional optogenetic techniques can manipulate genetically identified neurons in a region, they are incapable of selectively manipulating intermingled neurons that differ only by their functional properties. Critically, new multiphoton optogenetic techniques are beginning to allow manipulation of cells chosen by their activity alone, however such techniques require further development. In the K99 phase of this proposal, I will continue my training through the development of novel optical systems for multiphoton stimulation and through use of these technique understand cortical function. By combining these new optical techniques with novel opsins designed for in vivo multiphoton use that I have already developed, I now have the ability to write in or edit neural activity across many neurons with a precision never before possible. By altering ensemble activity during visual perception I will determine the causal contributions of individual neurons as well as populations of neurons to sensory coding. In the R00 phase, through manipulations in motor cortex I will unravel the behavioral impact of these groups, probing the role motor ensembles play in motor action, and study how neurons interact across modalities. The ability to both edit and monitor the activity of neural subnetworks is critical to gaining a mechanistic understanding of perception and action. The conclusions we draw from this proposal will help to describe how all information is presented in the cortex, but can only be reached with advanced techniques.