New technologies for examining the role of neuronal ensembles in drug addiction and fear

Abstract

Correlational data suggest that learned associations are encoded within neuronal ensembles. However, it has been difficult to prove that neuronal ensembles mediate learned behaviours because traditional pharmacological and lesion methods, and even newer cell type-specific methods, affect both activated and non-activated neurons. Additionally, previous studies on synaptic and molecular alterations induced by learning did not distinguish between behaviourally activated and non-activated neurons. Here, we describe three new approaches—Daun02 inactivation, FACS sorting of activated neurons and c-fos-GFP transgenic rats — that have been used to selectively target and study activated neuronal ensembles in models of conditioned drug effects and relapse. We also describe two new tools — c-fos-tTA mice and inactivation of CREB-overexpressing neurons — that have been used to study the role of neuronal ensembles in conditioned fear.

Counterconditioning During Reconsolidation Prevents Relapse of Cocaine Memories

“…Moreover, our findings support the possibility that rather than forming a new memory trace as in the regular counterconditioning procedure, counterconditioning administered during reconsolidation led to incorporation of the aversive information into the original memory trace, so that the retrieved cue-cocaine memory was reconsolidated as a cue-aversion memory, and therefore the reinstatement of cocaine-seeking behavior was prevented. Nonetheless, the notion that the memory was replaced is yet to be shown Prevention of drug relapse by memory replacement K Goltseker et al directly in the future using ensemble/engram procedures (Cruz et al, 2013;Pfarr et al, 2015). Interestingly, several studies have recently shown that flipping the order of events in the retrieval-extinction procedure, that is, retrieving the memory after, rather than before extinction training, can prevent relapse in a similar manner to post-retrieval extinction (Baker et al, 2013;Millan et al, 2013), suggesting that the mechanisms underlying this procedure are not necessarily reconsolidation mechanisms.…”

The Nucleus Accumbens: Mechanisms of Addiction across Drug Classes Reflect the Importance of Glutamate Homeostasis

“…Given that expression of c-Fos coincides with neuronal activity, only activated neurons express the LacZ transgene in the c-Fos-LacZ rat model. After the behavior of choice, the Daun02 reagent is infused intracranially into the brain region of choice, resulting in the selective inactivation of the neurons that express LacZ due to b-galactosidasemediated processing of Daun02 to daunoribicin (Cruz et al, 2013). Similar to the methods described above, neurons activated by a discrete stimulus can be functionally silenced to assess their role in a particular behavior.…”

“…Recent studies have begun to elucidate the role of specific prefrontal inputs to the NAshell in addiction-related behaviors. Although neither the ILC or NAshell appears to be important for drug-seeking behavior guided by cues, it is crucial for drug-primed and contextinduced reinstatement of cocaine seeking (McFarland and Kalivas, 2001;Anderson et al, 2003;Cruz et al, 2013). In addition, the ILC-to-NAshell pathway is necessary for context-induced heroin seeking (Bossert et al, 2007(Bossert et al, , 2012.…”

Daun02 Inactivation of Behaviorally Activated Fos‐Expressing Neuronal Ensembles

“…After several conditioning sessions, the rats form a learned association (e.g. drug and drug context), and it is thought that this association is stored in neuronal ensembles in various brain areas (Cruz et al, 2013). On 'induction day', some day following the last training session, the rats are exposed to the conditioned stimulus (e.g.…”