2001 — 2004 |
Steffensen, Scott C |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Neuropharmacological Subsrates of Alcohol Addiction @ Brigham Young University
Recently we have demonstrated that a homogeneous population of gamma-aminobutyric acid (GABA) neurons in the ventral tegmental area (VTA) undergo adaptation in association with ethanol dependence. The overall objective of this proposal is to evaluate the role, whether contributory or reflective, of VTA GABA neurons in mediating the reinforcing properties of ethanol, under non-dependent and dependent conditions. The core thesis underlying this proposal is that adaptive changes in VTA GABA neuron excitability result from repeated exposure to acute intoxicating levels of ethanol and contribute to the dysregulation of mesolimbic dopamine homeostasis that accompanies ethanol reinforcement. Our proposed studies are designed to test three major hypotheses: 1) That persistent alterations in VTA GABA neuron excitability, N-methyl-D-aspartate (NMDA) and/or GABA receptor-mediated neurotransmission occur in association with ethanol dependence; 2) That enhancement of VTA GABA neuron excitability, NMDA and/or GABA neurotransmission anticipates ethanol self-administration (SA); and 3) That adaptation of VTA GABA neuron excitability, NMDA and/or GABA neurotransmission parallels the continuum of ethanol intoxication, aversion, reinforcement and dependence. We will employ electrophysiological methods to determine if VTA GABA neuron firing rate, axonal excitability and/or NMDA and GABA receptor- mediated synaptic input undergo adaptation to chronic ethanol. We will evaluate VTA GABA neuron firing rate, axonal excitability and response to afferent synaptic input during ethanol self- administration and in the ethanol operant runway paradigms. These studies will determine if VTA GABA neurons or their corticolimbic inputs undergo plasticity during ethanol reinforcement. VTA GABA neurons may act as unique integrators of convergent information from sensory, cortical and limbic areas subserving ethanol addiction.
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0.958 |
2006 — 2011 |
Steffensen, Scott C |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Neuropharmacological Substrates of Alcohol Addiction @ Brigham Young University
DESCRIPTION (provided by applicant): We have identified a homogeneous population of y-aminobutyric acid (GABA) neurons in the ventral tegmental area (VTA) that undergo adaptation in association with ethanol dependence. We have recently reported that VTA GABA neurons form part of a larger electrical network of ventral brain GABA neurons linked by connexin-36 gap junctions whose electrical coupling is enhanced by dopamine via D2 receptor-mediated activation of adenylate cyclase, and sensitive to low-dose ethanol. We hypothesize that VTA GABA neurons, and the electrical network they form, may act as unique integrators of convergent information from sensory, cortical and limbic areas subserving ethanol addiction. The overall objective of this application is to extend our evaluation of the role of this specific class of mesocorticolimbic GABA neurons in mediating the intoxicating and rewarding properties of ethanol. The core thesis underlying this proposal is that VTA GABA neurons underlie ethanol self-administration and that adaptive changes in VTA GABA neuron excitability and electrical synaptic transmission result from repeated exposure to contingent and/or non-contingent ethanol and contribute to the dysregulation of mesolimbic homeostasis that accompanies alcohol addiction. Our proposed in vivo and in vitro studies are designed to test four major hypotheses: 1) That VTA GABA neuron activity correlates with ethanol self-administration; 2) That lesioning VTA GABA neurons disrupts ethanol self-administration; 3) That gap junction transmission between VTA GABA neurons, or glutamate (GLU), GABA, or DA synaptic modulation of VTA GABA neuron gap junctions, is sensitive to ethanol; and 4) That persistent alterations in the gene expression of NMD A, non-NMDA, GABA, DA receptors, or connexin-36 gap junction proteins parallels the plasticity in synaptic adaptation that underlies the physiological manifestations of alcohol reward and dependence.
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0.958 |
2012 — 2016 |
Steffensen, Scott C |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Neuroplasticity With Alcohol Dependence @ Brigham Young University
DESCRIPTION (provided by applicant): The prevailing view is that enhancement of dopamine transmission in the mesocorticolimbic system underlies the rewarding properties of alcohol. This system consists of dopamine neurons in the midbrain ventral tegmental area (VTA) that innervate the nucleus accumbens and other limbic structures. Dopamine neurotransmission is controlled by local-circuit GABA interneurons. We have identified a homogeneous population of GABA neurons in the VTA that are excited by low-dose ethanol, but inhibited by moderate to high-dose ethanol, become tolerant to chronic ethanol, evince hyperexcitabililty during withdrawal, and accelerate in anticipation of ethanol self-reward. These correlative studies are complemented by our recent studies demonstrating a causal role for VTA GABA neurons in ethanol self-administration. VTA GABA neurons are widely accepted to be critical regulators of DA neurotransmission, but they may serve as unique and independent integrators of convergent information from sensory, cortical and limbic areas subserving alcohol reward and dependence. The core thesis underlying this proposal is that repeated exposure to alcohol causes adaptive changes in GABA(A) receptor [GABA(A)R]-mediated inhibition of VTA GABA neurons and contributes to the dysregulation of mesolimbic DA homeostasis that accompanies alcohol dependence (Gilpin and Koob, 2008; Koob and Le Moal, 1997). Based on previous work and preliminary results, we hypothesize that adaptation of VTA GABA neurons to chronic ethanol exposure and accompanying dependence results from a molecular switch in GABA(A)Rs on VTA GABA neurons, similar to what has been reported in our studies of opiate dependence (Laviolette et al., 2004; Vargas-Perez et al., 2009). We will employ multidisciplinary behavioral, electrophysiological, molecular and novel fluorescent imaging approaches to evaluate the adaptive effects of short-term and long-term ethanol exposure on GABA(A)R-mediated inhibition and glutamate (GLU) NMDAR-mediated excitation, and receptor expression, as well as the role of brain-derived neurotrophic factor (BDNF) tyrosine kinase B (TrkB) receptors in mediating the functional switch of GABA(A)Rs during ethanol dependence. Our studies will test the following hypotheses: 1) Withdrawal from a single exposure to ethanol (non-dependent condition) will enhance NMDAR-mediated GLU excitation of VTA GABA neurons, while withdrawal from chronic ethanol (dependent condition) will reduce GABA(A)R-mediated inhibition of VTA GABA neurons; 2) Withdrawal from chronic ethanol exposure will modify the expression of GABA(A)Rs; and 3) Withdrawal from chronic exposure to ethanol will result in a functional switch in GABA(A)R-mediated inhibition of VTA GABA neurons that is mediated by BDNF TrkB receptor activation. To test these hypotheses, we propose three Specific Aims in GAD GFP mice, wherein GABA neurons can be identified and characterized unambiguously. We will focus on mechanistic approaches in order to characterize the synaptic substrates in VTA GABA neurons that adapt in response to a single exposure (short-term) or multiple exposures to ethanol (long-term), and the role of BDNF and its high- affinity TrkB receptor in mediating the long-term adaptation of GABA(A)Rs. To test these hypotheses, we propose three Specific Aims in GAD GFP mice, wherein GABA neurons can be identified and characterized electrophysiologically: 1) We will evaluate spontaneous and evoked inhibitory and excitatory synaptic transmission, paired-pulse responses, total charge transfer, AMPAR/NMDAR ratio and AMPA rectification index using patch clamp electrophysiology. These studies will be accomplished by recording IPSCs and EPSCs from brain slices during withdrawal from a single injection of ethanol administered to mice 24 hrs previous (non-dependent condition) or in mice consuming ethanol in the forced liquid ethanol diet procedure (dependent condition); 2) We will evaluate the GABA(A)R subunit, NMDAR subunit, tyrosine hydroxylase, Cx36, and TrkB receptor transcript expression in VTA GABA neurons using single-cell quantitative RTPCR; and 3) We will evaluate the effects of BDNF TrkB receptor antagonists and TrkB depletion with siRNA TrkB on GABA(A)R-mediated inhibitory and NMDAR-mediated excitatory synaptic responses as in Aim 1. In addition, we will evaluate the hypothetical switch in GABA(A)R using the perforated patch procedure for individual VTA GABA neurons and using the novel Clomeleon fluorescent imaging procedure for populations of VTA GABA neurons. The proposed studies will provide important new insights into the role of GABA(A)Rs on VTA GABA neurons in alcohol dependence. VTA GABA neurons evince neuroadaptive responses in association with opiate dependence, characterized by a switch in functionality from being hyperpolarized by GABA to being depolarized. This switch appears to involve BDNF, as it triggers long-term changes in the functionality of GABA(A) receptors and a state of dependence without chronic opioids. We anticipate that the studies we propose will provide important new insights into the contributory role of VTA GABA neurons and their functional connectivity in ethanol consumption and the role of BDNF in mediating a switch in the functionality of GABA(A) receptors on VTA GABA neurons with alcohol dependence. Results from this study could provide a preclinical pharmacologic rationale for considering drugs that act selectively on GABA(A) receptor subtypes or on BDNF TrkB receptors as putative therapeutic agents for the treatment of alcohol dependence. PUBLIC HEALTH RELEVANCE: Alcoholism is a chronic relapsing disorder that has enormous impact on society. A major goal of research on alcoholism is to characterize the critical neural substrates that are most sensitive to alcohol, adapt in association with chronic alcohol and drive subsequent alcohol-seeking behavior. Currently, there are no evidence-based, clinically useful, pharmacotherapeutic interventions that might reverse the neuroadaptive effects of alcohol dependence. The long-term objective of our research program is to advance our understanding of the neural basis of alcohol reward and dependence and, subsequently, to identify therapeutic agents whose mechanisms of action would be predicted to have clinical utility in treating it. A population of GABA neurons in the midbrain that regulate dopamine neurons in the reward pathway appear to be promising candidates, as they are especially sensitive to alcohol, their activity correlates with rewarding behaviors and recent evidence indicates that they play a causal role in alcohol self-administration. Most importantly, they show remarkable adaptation to alcohol dependence. Thus, elucidating the molecular substrates that underlie this adaptation may suggest treatments to reverse alcohol dependence.
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0.958 |
2014 — 2018 |
Steffensen, Scott C |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Nicotine and Alcohol Co-Dependence @ Brigham Young University
ABSTRACT The prevailing view is that enhancement of dopamine (DA) transmission in the mesocorticolimbic system underlies the rewarding properties of alcohol and nicotine (NIC). The mesolimbic DA system consists of DA neurons in the midbrain ventral tegmental area (VTA) that innervate the nucleus accumbens (NAc). Dopamine neurotransmission is regulated by inhibitory VTA GABA neurons, whose excitability is a net effect of glutamate (GLU) and GABA neurotransmission that are modulated by NIC cholinergic receptors (nAChRs) on afferent terminals. We have shown that these neurons are excited by low-dose ethanol (Steffensen et al., 2009), but inhibited by moderate to high-dose ethanol (Gallegos et al., 1999; Ludlow et al., 2009; Steffensen et al., 2009; Stobbs et al., 2004; Yang et al., 2010), and adapt to chronic ethanol (Gallegos et al., 1999), evincing marked hyperexcitability during withdrawal. Based on our previous studies and data presented here, we propose that VTA GABA neurons are a common substrate for the acute actions of ethanol and NIC. The core thesis underlying this proposal is that ¿6*-nAChRs on GABA terminals mediate acute ethanol inhibition of VTA GABA neurons and DA release in the NAc. In addition, VTA GABA neuron hyperexcitability during withdrawal from chronic ethanol results from adaptations in presynaptic ¿6*-nAChRs and postsynaptic GABA(A)R-mediated inhibitory synaptic transmission to these neurons, which contributes to the dysregulation of mesolimbic DA homeostasis that accompanies dependence on ethanol and co-dependence on NIC. We will study of the role of ¿6*-nAChRs in acute and chronic effects of ethanol on VTA GABA neurons and on DA release. Our proposed studies constitute a focused investigation into the role of ¿6*-nAChRs in mediating acute ethanol effects on these neurons and their adaptation with alcohol dependence. Our studies will test the following specific hypotheses: 1) Acute ethanol inhibition of VTA GABA neuron activity and phasic DA release results from enhancement of GABA release via ¿6*-nAChRs on GABA terminals; 2) Lack of ¿6*-nAChRs results in disrupted ethanol consumption and reward; and 3) Hyperexcitability of VTA GABA neurons during withdrawal from chronic ethanol results from adaptation of ¿6*-nAChRs and subsequent reduction of DA release at terminals in the NAc. To test these hypotheses, we propose three Specific Aims, which involve electrophysiological, behavioral, neurochemical and molecular experiments with acute and chronic ethanol exposure in GAD GFP knock-in mice, and in wild type (WT) and ¿6*-nAChR KO mice: 1) Define the role of ¿6*-nAChRs in acute ethanol actions on VTA neurons and dopamine release in the NAc; 2) Define the role of ¿6*-nAChRs in mediating ethanol consumption and reward; and 3) Define the role of ¿6-nAChRs in mediating the hyperexcitability of VTA GABA neurons and lowered dopamine release in the NAc during withdrawal from chronic ethanol. We will show preliminary evidence that ¿6*-nAChRs mediate ethanol enhancement of NIC currents in recombinant nAChRs expression systems,that ethanol enhancement of GABA inhibition to VTA GABA neurons and ethanol reduction in DA release in the NAc, and compromised ethanol reward in ¿6*- nAChR KO mice. The proposed studies constitute a thorough and systematic investigation into the role of VTA GABA neurons in mediating the acute effects of ethanol and NIC and the role of ¿6*-nAChR in modulating GABA neurotransmission to these neurons that critically regulate DA neurotransmission in the mesolimbic system implicated in alcohol reward and dependence. Results from this study could provide a preclinical pharmacologic rationale for considering drugs that act selectively on ¿6*-nAChR as putative therapeutic agents for the treatment of alcohol dependence and alcohol and NIC co-dependence.
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0.958 |