Sven Kroener - US grants

[unreadable] DESCRIPTION (provided by applicant): Cortical activity in the intact brain is characterized by intermittent sustained membrane depolarizations called "up-states". The task-specific computations of a given cortical region are superimposed on top of this heightened activity. In the case of the prefrontal cortex (PFC), recurrent excitation of deep layer neurons is thought to underlie sustained activity during working memory. Dopamine (DA) modulates working memory, however, it has not been feasible to investigate its detailed biophysical effects in the awake animal. Instead, most of our knowledge about dopamine's effects on membrane excitability or synaptic transmission derives from recordings in "quiet" acute brain slice preparations. However, up-states and sustained activity are a network phenomenon and the asynchronous firing that occurs across neurons results from the interplay between intrinsic excitability and recurrent synaptic transmission. The present proposal investigates DA modulation of active cortex using an organotypic co-culture preparation of the PFC, hippocampus and ventral tegmental area (VTA). These cultures exhibit sustained activity (up-states) and possess key inputs required for working memory, namely the hippocampus and the DA input from the VTA. The present proposal tests two hypotheses generated from in vitro brain slice preparations and computational modeling studies. The first hypothesis posits that sustained activity during up-states can be modulated by DA in a dose-dependent manner. Experiments in Specific Aim 1 will use whole-cell current clamp recordings to test whether there is an "optimal" range of DA modulation in which action-potential firing and up-state duration are enhanced, while outside of this optimal range sustained activity will be reduced. Control experiments will assess the contribution of tonic vs. phasic release of DA from the VTA, and will test whether DA has network specific effects. The concentration of DA in the slice will be monitored simultaneously via fast-scan cyclic voltammetry. The second hypothesis states that DA acts on GABA and NMDA currents to modulate persistent activity during up-states. Combined voltage-clamp and calcium imaging experiments will be used to measure the modulation of GABA and NMDA currents by a high dose or low dose of DA, respectively. These studies will provide insights into the architecture of sustained activity and DA modulation of active PFC networks; information critical for our understanding of the normal and pathological conditions of the PFC. [unreadable] [unreadable] [unreadable]

? DESCRIPTION (provided by applicant): Drug addiction is a chronic, relapsing condition characterized by compulsive drug seeking and substance use despite harmful consequences. Evidence suggests that drugs of abuse diminish the ability of the prefrontal cortex (PFC) to exert supervisory control over impulsive behaviors related to drug-seeking and relapse to drug taking. The transition from social drinking where inhibitory control by the PFC is intact, to addiction and dependence where the inhibitory control by the PFC is lost, may reflect fundamental changes in the integrative capacities of the PFC itself. However, a direct test of this theory and an analysis of the cellular mechanisms involved are still forthcoming. Glutamate-mediated excitatory neurotransmission plays an important role in the behavioral effects of acutely administered EtOH, as well as the neuroadaptations associated with prolonged EtOH exposure that underlie EtOH dependence. The NMDA subtype of glutamate receptors is a major target for the effects of alcohol in the brain. We have recently shown that (passive) chronic EtOH exposure selectively upregulates NMDAR function in the PFC, leading to a shift in the NMDA/AMPA current ratio and a dysregulation of long-term synaptic plasticity. The experiments outlined in this proposal expand on these findings to further test the theory that EtOH-induced changes in synaptic plasticity lead to impairments in PFC function, which in turn may lead to further increases in alcohol drinking after a period of abstinence, thus making alterations in glutamatergic plasticity predictive for the propensity for relapse. Specifically, we will study the predicted changes in an operant self-administration model of alcohol addiction and we will correlate changes in behavior (alcohol drinking, and performance in an Attentional Set-Shifting task, respectively) with changes in synaptic plasticity at critical points in the addiction cycle (.e. after prolonged exposure, after withdrawal, and after relapse drinking). Therefore, we perform voltage-clamp recordings (measuring NMDA/AMPA ratios, spontaneous AMPA and GABA currents) in brain slices of adult animals that self- administer EtOH in an operant paradigm in which animals respond for EtOH rewards either under goal- oriented or habit-promoting reinforcement schedules (Aim 1). In Aim 2 we will test the hypothesis that the widely prescribed anti-craving drug acamprosate can normalize the EtOH-induced changes in glutamatergic transmission (i.e. restore the NMDA/AMPA ratio) to restore cognitive flexibility, thus reducing the propensity for relapse. The results of these experiments will inform us how EtOH-induced aberrant glutamatergic plasticity in the PFC contributes to the loss of behavioral flexibility and shift towards sensory-driven compulsive behaviors in alcohol abuse. Moreover, in concert with previous and ongoing experiments in our lab that use a dependence model of alcohol addiction (chronic intermittent ethanol exposure, CIE) these experiments will allow us to study how learning and motivational factors can differentially affect our behavioral and physiological measures of PFC dysfunction.

Drug addiction is a chronic, relapsing condition characterized by compulsive drug seeking and substance use despite harmful consequences. Persistent relapse to addictive drugs constitutes the most challenging problem in addiction therapy, and is linked to impaired prefrontal cortex regulation of motivated behaviors that involve the nucleus accumbens. Learning to inhibit drug seeking can be an important strategy to reduce the risk of relapse. Treatments are sought that can aid in these learning processes. Here we will explore vagus nerve stimulation (VNS) as a means to facilitate extinction learning (i.e. the inhibition of a response to a previously learned stimulus) and to reduce reinstatement of drug seeking (relapse) in an animal model of cocaine addiction. Vagus nerve stimulation is a FDA- approved treatment for epilepsy and depression and its mechanisms of action likely involve release of norepinephrine in the cortex and amygdala. The proposed research is based on recent data which show that VNS can induce cortical plasticity and can enhance extinction of fear memories. Because brief VNS affords tight temporal control over neuromodulator release, our approach provides context-specificity and may target the brain areas and synapses that support extinction of drug memories more efficiently than drug-based treatments can. If VNS holds promise as a novel approach to the treatment of drug addiction, the mechanisms of action need to be better understood. We propose the following 3 Aims to test the effects of VNS on extinction training and reinstatement in cocaine self-administering rats: In Aim 1 the effect of VNS on drug extinction training and reinstatement will be investigated in cocaine self- administering rats using a short-access paradigm. In Aim 2 we will study the network that underlies the effect of VNS on operant behavior, and specifically changes in synaptic plasticity (LTP and LTD) in the projection from the medial prefrontal cortex (mPFC) to the nucleus accumbens (NAc) using extracellular local field recordings in-vivo. We predict that combining VNS with extinction training restores the ability to induce LTP in the mPFC-NAc pathway, and that it suppresses the induction of LTD more than extinction training does by itself. These effects should be positively correlated to the inhibition of cocaine seeking produced by extinction. In Aim 3 we will perform patch-clamp recordings from medium spiny neurons in the NAc in vitro and use optogenetic stimulation of identified inputs from the mPFC to further examine changes in glutamate receptor function (measured as changes in the AMPAR/NMDAR current ratio) and alterations in presynaptic release that underlie VNS' effects on metaplasticity in the extinction circuit. The proposed research will test a novel approach to aid consolidation of extinction learning and it will elucidate important basic questions of how a potential therapy works.