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Mechanisms of Nicotine Modulation in Midbrain Doparminergic Neurons

Using electrophysiological approaches to study the mechanisms of nicotine reward and addiction, this project is investigating how nicotine modulates somatodendritic and presynaptic nAChRs in the neurons of the ventral tegmental area (VTA). Single-cell patch-clamp recordings, slice patch-clamp recordings and single-unit recordings from anesthetized rodents are used for evaluation of nicotine reward and reinforcement. We also perform electrophysiological recordings in nAChR subunit (e.g., α7 or β2 subunit) knockout mice. (Phillip Morris External Research Grant. Dr. Wu, Principal Investigator)

 

Development of New Compounds for Smoking Cessation

This project involves collaboration with several research groups focused on screening a series of compounds that act as nAChR agonists or antagonists using patch-clamp recordings in heterologously expressed nAChR subunit combinations (e.g., α4β2, α4β4, and α7) in a human epithelia cell line. (NIH U19 Grant, Dr. Wu, Co-investigator)

 

α6-nAChR Expression and Function in the Rodent VTA

In the ventral tegmental area, naturally-expressed nAChRs on both dopaminergic (DA) and nonDA neurons, and on afferent nerve terminals or boutons, exist as diverse subtypes. These receptors play crucial roles in mediation of nicotine-induced reward and dependence. Expression of the α6 nAChR subunit is most abundant in the ventral tegmental area, but the function, pharmacology, and the roles that nAChRs containing the α6 subunit (α6*-nAChR) play in nicotine reinforcement are not well defined.

The objective of this project is to evaluate the roles of α6*-nAChRs in modulation of GABA release in the ventral tegmental area. The work uses patch-clamp recordings combined with cellular and molecular techniques to study acutely dissociated rodent ventral tegmental area DAergic neurons. A novel procedure is used to generate mechanically dissociated (no enzyme treatment) single neurons that maintain functional presynaptic boutons on DA neurons.

 

Mechanisms of Amyloid Peptide Toxicity

Alzheimer’s disease is a neurodegenerative dementia characterized by increased Aβ and degeneration of neurons of the basal forebrain, hippocampus and neocortex and by a gradually developing learning and memory deficit. It has been postulated that an abnormally high level of Aβ may contribute to the pathogenesis in Alzheimer’s disease, but the mechanism of Aβ-induced neurodegeneration remains unclear. Nicotinic acetylcholine receptors (nAChRs) are important mediators of cholinergic signaling in the basal forebrain, hippocampus and neocortex. One of the earliest events in the pathogenesis in Alzheimer’s disease patients or Alzheimer’s disease model animals is a significant increase of mRNA and protein expressions of α7 nAChRs. However, no consensus has emerged about how these enhanced α7 nAChRs play a role in the mediation of Aβ-induced neuronal degeneration and death.

The objective of this proposal is to show the mechanisms by which Aβ harms hippocampal neurons. We are using multiple experimental approaches (electrophysiology, cellular and molecular biology) to test a novel hypothesis that α7 nAChR in Alzheimer’s disease may be an important target involved in Alzheimer’s disease pathogenic process and therapy. (Barrow Neurosciece Foundation Grant. Dr. Wu, Principal Investigator)

 

Mechanisms of Nicotine-Induced Excitatory Synaptic Plasticity in VTA Dopaminergic Neurons

Nicotine, the major addictive substance in tobacco, acts on various subtypes of nicotinic acetylcholine receptors (nAChRs), activating the reward circuitries within and/or external to the ventral tegmental area. Increasing evidence indicates that a single systemic exposure to nicotine triggers glutamatergic synaptic plasticity on dopamine (DA) neurons in the ventral tegmental area—an early neural adaptive response—and may play an important role in developing nicotine reinforcement and reward. However, the cholinergic mechanisms of this nicotine-induced neural adaptation remain elusive.

The objective of this project is to determine how different nAChR subtypes mediate systemic nicotine-induced glutamatergic synaptic plasticity in ventral tegmental area DA neurons. The central hypothesis is that diverse nAChR subtypes with different properties, including distribution, function, and pharmacology within the ventral tegmental area, play important roles in mediating systemic nicotine-induced glutamatergic synaptic plasticity in ventral tegmental area DA neurons. To test this hypothesis, patch-clamp whole-cell recordings will be employed using ventral tegmental area slices or dissociated neurons prepared from rat and α7-/- and β2-/- knockout mice. To monitor glutamatergic synaptic plasticity, we will measure the ratio of AMPA receptor-mediated excitatory postsynaptic currents (EPSCs) to NMDA receptor-mediated EPSCs (AMPA/NMDA ratio) from ventral tegmental area DA neurons by stimulation of their excitatory afferents. (Barrow Neuroscience Foundation Grant. Dr. Wu, Principal Investigator)

 

Epileptogenesis of Human Gelastic Seizures with Hypothalamic Hamartoma

Hypothalamic hamartomas (HH) are rare developmental malformations of the hypothalamus often associated with hallmark gelastic (laughing) seizures, which are refractory to treatment with antiepileptic drugs. HH is known to be intrinsically epileptogenic, but the mechanisms by which the malformation causes gelastic seizures are largely unknown.

The objective of this project is to elucidate how these spontaneously firing, small HH neurons synapse onto their target cells to form a neuronal network, which ultimately drives hyperexcitation and synchronization within HH lesions. This study is conducted by performing electrophysiological recordings, along with cellular and molecular biological approaches, from single neurons or tissue slices prepared from fresh, surgically-resected specimens from patients with HH who have gelastic seizures. (NIH R21 Grant and Barrow Neuroscience Foundation Grant. Dr. Wu, Principal Investigator)

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