Unique gene alterations are induced in FACS-purified Fos-positive neurons activated during cue-induced relapse to heroin seeking.

Cue-induced heroin seeking after prolonged withdrawal is associated with neuronal activation and altered gene expression in prefrontal cortex (PFC). However, these previous studies assessed gene expression in all neurons regardless of their activity state during heroin seeking. Using Fos as a marker of neural activity, we describe distinct molecular alterations induced in activated versus non-activated neurons during cue-induced heroin seeking after prolonged withdrawal. We trained rats to self-administer heroin for 10 days (6 h/day) and assessed cue-induced heroin seeking in extinction tests after 14 or 30 days. We used fluorescent-activated cell sorting (FACS) to purify Fos-positive and Fos-negative neurons from PFC 90 min after extinction testing. Flow cytometry showed that Fos-immunoreactivity was increased in less than 10% of sparsely distributed PFC neurons. mRNA levels of the immediate early genes fosB, arc, egr1, and egr2, as well as npy and map2k6, were increased in Fos-positive, but not Fos-negative, neurons. In support of these findings, double-label immunohistochemistry indicated substantial coexpression of neuropeptide Y (NPY)- and Arc-immunoreactivity in Fos-positive neurons. Our data indicate that cue-induced relapse to heroin seeking after prolonged withdrawal induces unique molecular alterations within activated PFC neurons that are distinct from those observed in the surrounding majority of non-activated neurons.

Deep brain stimulation reveals a dissociation of consummatory and motivated behaviour in the medial and lateral nucleus accumbens shell of the rat.

Following the successful application of deep brain stimulation (DBS) in the treatment of Parkinson's disease and promising results in clinical trials for obsessive compulsive disorder and major depression, DBS is currently being tested in small patient-populations with eating disorders and addiction. However, in spite of its potential use in a broad spectrum of disorders, the mechanisms of action of DBS remain largely unclear and optimal neural targets for stimulation in several disorders have yet to be established. Thus, there is a great need to examine site-specific effects of DBS on a behavioural level and to understand how DBS may modulate pathological behaviour. In view of the possible application of DBS in the treatment of disorders characterized by impaired processing of reward and motivation, like addiction and eating disorders, we examined the effect of DBS of the nucleus accumbens (NAcc) on food-directed behavior. Rats were implanted with bilateral stimulation electrodes in one of three anatomically and functionally distinct sub-areas of the NAcc: the core, lateral shell (lShell) and medial shell (mShell). Subsequently, we studied the effects of DBS on food consumption, and the motivational and appetitive properties of food. The data revealed a functional dissociation between the lShell and mShell. DBS of the lShell reduced motivation to respond for sucrose under a progressive ratio schedule of reinforcement, mShell DBS, however, profoundly and selectively increased the intake of chow. DBS of the NAcc core did not alter any form of food-directed behavior studied. DBS of neither structure affected sucrose preference. These data indicate that the intake of chow and the motivation to work for palatable food can independently be modulated by DBS of subregions of the NAcc shell. As such, these findings provide important leads for the possible future application of DBS as a treatment for eating disorders such as anorexia nervosa.

FACS identifies unique cocaine-induced gene regulation in selectively activated adult striatal neurons.

Numerous studies with the neural activity marker Fos indicate that cocaine activates only a small proportion of sparsely distributed striatal neurons. Until now, efficient methods were not available to assess neuroadaptations induced specifically within these activated neurons. We used fluorescence-activated cell sorting (FACS) to purify striatal neurons activated during cocaine-induced locomotion in naive and cocaine-sensitized cfos-lacZ transgenic rats. Activated neurons were labeled with an antibody against ß-galactosidase, the protein product of the lacZ gene. Cocaine induced a unique gene expression profile selectively in the small proportion of activated neurons that was not observed in the nonactivated majority of neurons. These genes included altered levels of the immediate early genes arc, fosB, and nr4a3, as well as genes involved in p38 MAPK signaling and cell-type specificity. We propose that this FACS method can be used to study molecular neuroadaptations in specific neurons encoding the behavioral effects of abused drugs and other learned behaviors.