Dopamine release from neurons in the ventral tegmental area (VTA) assists in learning goal-oriented behaviors and mediates the pleasurable aspects of most drugs of abuse. Understanding how the excitability of VTA neurons is regulated by synaptic inputs and membrane properties is crucial if one is to understand how dopamine release is controlled. 5'-Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a master enzyme that regulates cellular metabolism. When activated by a falling AMP/ATP ratio, AMPK promotes biochemical pathways that increase energy production while reducing energy expenditure. Although AMPK is widely regarded as an energy sensor, recent studies suggest it also influences neuronal excitability. Preliminary data from our lab suggest that activators of AMPK potentiate the hyperpolarizing current evoked by ATP-sensitive K+ (K-ATP) channels, reduce the desensitization of dopamine D2 autoreceptors, and inhibit the influence of excitatory synaptic transmission in VTA neurons. The over-arching hypothesis of our proposed studies is that AMPK activation augments inhibitory influences on VTA neurons. Patch pipettes will be used to record whole-cell currents and potentials in single VTA neurons in slices of rat midbrain. Western immunoblot will be used to quantify levels of phosphorylated and total AMPK in midbrain slices that have been incubated in the presence and absence of AMPK activators and/or inhibitors.
Aim #1 will characterize the effect of AMPK activators on currents evoked by the K-ATP opener diazoxide.
Aim #2 will investigate second messenger systems and identify transmitter receptors that mediate the ability of AMPK activators to reduce dopamine D2 autoreceptor desensitization.
Aim #3 will investigate mechanisms and sites of action by which AMPK inhibits glutamate-mediated synaptic transmission in the VTA.
Aim #4 will characterize mechanisms by which AMPK activation inhibits burst firing in VTA dopamine neurons. Results of these studies may suggest new pharmacological strategies for treating dopamine-dependent disorders.
The brain region called the ventral tegmental area (VTA) contains dopamine neurons that project to structures that are involved in emotional and cognitive behaviors. Dopamine released from these neurons assists in the learning of goal-oriented behaviors and it mediates the pleasurable effects of drugs of abuse such as morphine and amphetamine. Understanding how the excitability of VTA neurons is regulated is crucial if one is to understand mechanisms that control dopamine release. 5'-Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a master enzyme that regulates cellular metabolism. Preliminary data from our lab suggest that activators of AMPK reduce VTA neuronal excitability by inhibiting glutamate synaptic input while increasing the function of inhibitory membrane properties. The present research will use neurophysiological methods in rodent tissue to define actions of AMPK on VTA dopamine neurons. Results may suggest new pharmacological strategies for the treatment of mood disorders, learning disorders, and drug abuse.
|Wu, Yan-Na; Shen, Ke-Zhong; Johnson, Steven W (2017) Differential actions of AMP kinase on ATP-sensitive K+ currents in ventral tegmental area and substantia nigra zona compacta neurons. Eur J Neurosci 46:2746-2753|
|Shen, Ke-Zhong; Wu, Yan-Na; Munhall, Adam C et al. (2016) AMP kinase regulates ligand-gated K-ATP channels in substantia nigra dopamine neurons. Neuroscience 330:219-28|