Presentation on theme: "Marina E. Wolf Chicago Medical School Rosalind Franklin University of Medicine & Science How do drugs of abuse rewire the motivational circuitry?"— Presentation transcript:
Marina E. Wolf Chicago Medical School Rosalind Franklin University of Medicine & Science How do drugs of abuse rewire the motivational circuitry?
Acute effects of cocaine and amphetamine: interference with monoamine reuptake Addiction: long-lasting adaptations triggered by increased monoamine levels These adaptations “rewire” the motivational circuitry, facilitating the formation of new habits that center around drug-seeking, usually at the expense of more appropriate behaviors.
Hypothesis Addiction is a form of neuronal plasticity. The adaptations leading to addiction involve the same glutamate-dependent cellular mechanisms that enable learning and memory.
Glutamate-dependent plasticity and addiction Animal model of addiction (behavioral sensitization) Behavioral changes blocked by glutamate antagonists or lesions of glutamate pathways Behavioral changes are associated with changes in glutamate receptor function and expression Drugs of abuse and plasticity activate common signal transduction cascades (kinases & phosphatases, transcriptional regulators, neurotrophins, etc) Drugs of abuse influence LTP and LTD in reward-related pathways
Glutamate and glutamate receptors Glutamate: major excitatory transmitter in the brain, activates ionotropic receptors and GPCRs Ionotropic receptors AMPA receptors – bulk of fast excitatory transmission NMDA receptors – slower synaptic potentials, enable plasticity (and excitotoxicity) Kainate receptors – less understood Metabotropic receptors (GPCRs) at least 8 subtypes (mGluR1-8) important in normal synaptic transmission and plasticity
Long-term potentiation (LTP) LTP Strong NMDAR activation Large postsynaptic Ca increase Preferential activation of kinases Potentiation of AMPAR currents LTD More modest NMDAR activation Less robust postsynaptic Ca increase Preferential activation of phosphatases Depression of AMPAR currents LTP in NAc (Julie Kauer, Brown Univ) stimulaterecord
Functional significance of LTP in addiction-related pathways? Wolf, Molecular Interventions 2002
How do drugs that initially target monoamine transporters influence glutamate transmission and glutamate- dependent processes such as LTP and LTD?
Drugs may modulate LTP via actions on neuronal circuits Everitt and Wolf, J Neurosci 2002
Dendritic spine (postsynaptic) Glutamate Dopamine Drugs may modulate LTP at the single cell level
Two inter-related mechanisms for regulating AMPA receptor transmission during LTP and LTD a)GluR1 is phosphorylated during LTP, and dephosphorylated during LTD b)GluR1-containing AMPA receptors are inserted into synapses during LTP and removed during LTD Song & Huganir, TINS 2002
Link to dopamine? D1 receptors are coupled to PKA PKA is involved in both mechanisms for regulating AMPA receptor function during LTP Hypothesis: D1 receptors modulate AMPA receptor phosphorylation and trafficking through PKA-dependent mechanisms, and thereby influence LTP and LTD. Song & Huganir, TINS 2002
Nucleus accumbens Dopamine afferents Glutamate afferents (cortex, hippocampus, amygdala) Medium spiny projection neuron Do D1 receptors regulate AMPA receptor trafficking in NAc neurons?
~80% medium spiny neurons and 20% interneurons Almost all neurons are GABAergic GluR1 is expressed by all neurons D1 receptors are expressed by ~80% of neurons D2 receptors are expressed by ~80% of neurons Postnatal NAc cultures reproduce many features of the intact NAc Chao et al, J Neurochem 83:704-12, 2002
D1 receptor stimulation increases GluR1 surface expression in NAc neurons Control 1 M SKF Chao et al, J Neurochem 83:704-12, 2002
Pre-blocking protocol for selectively detecting newly externalized GluR1 Lu, Man, Ju, Trimble, MacDonald, & Wang, Neuron, 2001 Pre-block GluR1 on the surface of live cells with N-GluR1 antibody and unlabeled secondary antibody Incubate at room temperature to allow GluR1 externalization Second round of immunostaining, under non-permeant conditions, with N-GluR1 antibody and Cy3 secondary antibody 1 o Ab 2 o Ab Cy3 2 o Ab
Media SCH10uM SCH + SKF 1uM SKF 20um Control D1 receptor stimulation increases the rate of GluR1 externalization Mangiavacchi & Wolf J Neurochem 88: , 2004
Requires PKA activation (Mangiavacchi & Wolf, J Neurochem 88: , 2004) GluR1 may be the relevant substrate because D1 agonists also stimulate phosphorylation of GluR1 at the PKA site in NAc cultures (Chao et al, J Neurochem 81: , 2002) Consistent with results in hippocampus indicating that PKA phosphorylation of GluR1 promotes its trafficking to the cell surface (Ehlers, Neuron 28: , 2000; Esteban et al, Nat Neurosci 6:136-43,2003)
Medium spiny neurons Interneurons Control 50µM GluControl 50μM Glu Glutamate agonists produce rapid internalization of GluR1 Mangiavacchi & Wolf, Eur J Neurosci, submitted
D1 NAc Prefrontal cortex, BLA, HPC VTA Dopamine inputs increase rate of AMPAR externalization Glutamate inputs increase rate of AMPAR internalization Changes in afferent activity result in minute-by-minute modulation of AMPAR surface expression on NAc neurons? DA Glu AMPA
Do D1 receptors drive GluR1 all the way into the synapse? Modified from Bredt & Nicoll, Neuron 2003 D1R PKA ???
Prefrontal Cortex D1R NMDAR CB1R
Synaptic and extrasynaptic AMPA receptors in PFC cultures Red = GluR1 Green = SB Yellow = overlay Sun & Wolf, unpublished
Summary of unpublished results presented at APA meeting but not provided on NIDA website D1 receptor stimulation increases GluR1 externalization at extrasynaptic sites, facilitating synaptic insertion as a result of subsequent NMDA receptor stimulation (Sun et al., Soc Neurosci Abstr 30, in press)
D1R (PKA) NMDAR D1 receptor stimulation externalizes AMPAR at extrasynaptic sites, increasing the pool available for synaptic insertion during LTP DA input Glutamate input Modified from Bredt & Nicoll, Neuron 2003
DA facilitates LTP induction in prefrontal cortex (Gurden et al, Neurosci 94: , 1999; Blond et al, Eur J Pharmacol 438: , 2002) The facilitation is mediated by D1 receptors and PKA (Jay et al, Eur J Neurosci 10: ,1998; Gurden et al, J Neurosci 20:RC106, 2000) Our results are consistent with studies showing that:
D1 receptor stimulation increases GluR1 surface expression through a PKA-dependent pathway at extrasynaptic sites. By increasing extrasynaptic GluR1, D1 receptors increase the pool available for synaptic insertion as a result of NMDA receptor stimulation. This may facilitate the induction of LTP. These findings suggest a mechanism by which drugs of abuse can directly “tap into” fundamental mechanisms for regulating synaptic strength. Summary
D1 NAc Prefrontal cortex, BLA, HPC VTA D1 and glutamate inputs normally regulate AMPA receptor trafficking Chronic drug exposure: adaptations in D1 receptor and PKA signaling Compensatory changes in AMPA receptor trafficking Inappropriate synaptic plasticity, rewiring of motivational circuitry, and formation of new habits focused on drug seeking DA Glu AMPA Cocaine Amphetamine Relevance to addiction?
Proposed sequence of mechanisms for long-term plasticity Luscher, Nicoll, Malenka & Muller (Nature Neurosci 2000)
Steven Chao Amy Bluestein Marjorie Ariano Dan Peterson Kathy Steece-Collier Robert Malenka Reed Carroll Richard Huganir Hey-Kyoung Lee National Institute on Drug Abuse Simona Mangiavacchi Xiu Sun