Brian E. Kalmbach, PhD - US grants

DESCRIPTION (provided by applicant): The input/output properties of a neuron are modifiable. Characterizing changes in input/output properties is imperative to understanding how neural activity changes in response to ongoing changes in network activity. While there are several examples of input-driven changes in neural excitability, it is not known how ongoing synaptic activity modulates the input/output properties of a neuron. The long-term goal of the proposed research is characterize how ongoing synaptic input affects the integrative properties of layer V pyramidal neurons in prefrontal cortex (PFC). The first specific aim of this proposal will further test the initial observation that low rates of synaptic stimulation produce changes in the excitability of pyramidal neurons in layer V of PFC. These experiments will identify the conductances and neurotransmitter receptors involved in the observed changes. These experiments involve whole-cell patch clamp recordings from the soma of layer V PFC neurons. The second specific aim will test the hypothesis that the changes occur in the dendrites in a manner that depends on the frequency and site of stimulation. Completion of this aim will provide insight into whether the plasticity is short-term or long-term and whether it is homeostatic or putatively involved in learning. These experiments will involve both whole-cell somatic and dendritic recordings. The third specific aim will test for differences in changes in the properties of two classes of neurons with different repertoires of membrane conductances: those that project within the cortex and those that project subcortically. The overriding hypothesis of this specific aim is that changes in input/output properties depend on the specific membrane conductances available to be modified. PUBLIC HEALTH RELEVANCE: Understanding how ongoing synaptic input affects the input/output properties of a neuron could have implications for treatment strategies for a variety of disorders associated with changes in neural excitability including epilepsy. In addition, the prefrontal cortex is involved in several cognitive processes such as action planning and working memory. Thus, characterizing changes in prefrontal neurons is vital for developing treatment strategies for a host of neurological disorders associated with deficits in these cognitive processes, including: Alzheimer's disease, attention disorders such as ADHD, autism, and schizophrenia.

The long-term goal of this project is to determine the consequences of cell-type specific expression of ion channel and neuromodulator receptor genes on primate neocortical function. The human brain is composed of an astonishing number of cell types. Molecular profiling suggests that upwards of ~75 unique neuronal cell types reside in a given neocortical area, and that each area has exclusive types. How do differences in gene expression translate into a neuron?s phenotypic identity? Solving this problem is crucial because several emerging lines of evidence suggest that human brain disorders may have cell type-specific etiologies, wherein different classes of neurons make distinct contributions to the pathophysiology of the disease. We propose to examine in human and nonhuman primates how mRNA expression in two broad categories of neocortical infragranular pyramidal neurons translates into their unique physiology, morphology and response to neuromodulation. Employing a state-of-the-art patch clamping technique, Patch-seq, we can genetically identify physiologically probed neurons from human and non-human primate neocortex. We test hypotheses about how specific ion channels and neuromodulator receptors shape the unique input-output properties of these neurons. We also utilize viral tools to prospectively label neurons, in particular the layer 5 (L5) extratelenephalic (ET)-projecting neurons (which send axonal projections to subcerebral regions). Several types of L5 ET neurons are not found in the rodent brain (e.g., Betz cells of motor cortex). Three factors make this proposal especially relevant for human health and disease. First, L5 ET neurons represent the sole direct output of the neocortex to many subcerebral structures and are implicated in several neurological disorders including Alzheimer?s disease and amyotrophic lateral sclerosis (ALS). Second, we will be directly working in non-human primate and human brain slices rather than the traditional rodent models. The latter point is especially pertinent given recent published findings of major differences in murine and human pyramidal neuron physiology. Experiments with monkey tissue will provide direct access to long-range axonal projection targets in vivo (which isn?t feasible for human brain slices), as well as the ability to study brain areas rarely available in the human from surgical specimens (e.g., primary motor cortex). Finally, this proposal lays the foundational knowledge necessary for eventual development of cell type-specific genetic and pharmacological treatment of disease.