Arginine vasopressin gene expression changes within the nucleus accumbens during environment elicited cocaine-conditioned response in rats.

It is known that changes in gene expression within the nucleus accumbens (NAc) occur during cocaine dependence development. However, identification of specific genes involved in cocaine conditioning awaits further investigation. We conducted a high throughput gene expression profile analysis of the NAc, during different stages of the environment-elicited cocaine conditioning. Rats were assigned to two different environmental conditions. Cocaine conditioned group received a cocaine injection (10mg/kg, i.p.) prior to being placed in the activity chambers. Control rats received saline injections before being exposed to their environment. Both groups received a saline injection in their home cage. Conditioning training lasted for 10 days. Animals were then re-exposed to their previously paired environments only on day 12 (test session). We found that the gene for arginine vasopressin (AVP) was differentially expressed on experimental subjects during all stages of environment-elicited cocaine conditioning. To further validate our molecular results, biochemical and immunolocalization experiments were conducted. We found the presence of AVP within accumbal fibers and changes in AVP protein levels following cocaine conditioning. Moreover, we tested the effects of accumbal microinfusions of either AVP receptor V(1A) agonist [pGlu(4), Cyt6, Arg(8)] AVP 4-9 1.0 ng/0.5 microl, or V(1A) antagonist (CH2) 5[Tyr (Me) 2] AVP, 1.0 ng/0.5 microl or vehicle solution (0.9% saline solution) during different stages of the cocaine conditioning. Blockade of V(1A) receptors within the NAc during acquisition interrupted the expression of the conditioned response, while activation leads to an increase in this response. Our findings propose a new role for AVP in cocaine addiction.

Dissociation of the effect of spatial behaviors on the phosphorylation of cAMP-response element binding protein (CREB) within the nucleus accumbens.

Several studies have reported a role for the nucleus accumbens (NAcc) in learning and synaptic plasticity. Many of them suggest that the NAcc is involved in translating cortico-limbic information to the motor system mediating spatial learning and memory processes. Previous studies from our laboratory have shown that protein kinase C is activated following training in a food search spatial learning task. The present study further characterizes the molecular substrates associated with NAcc-dependent spatial behavior. The cyclic AMP-response element binding protein (CREB), a transcription factor implicated in the formation of long-term memory, was studied in the NAcc following spatial training in a food search spatial learning task. Western blots were performed to detect phosphorylated (activated) and total CREB protein levels. Our results show that CREB is significantly phosphorylated in the NAcc 48 h after habituation and at 5 min and 1 h after the first spatial training session in comparison with the naive animals that remained in their home cages. Since published data show that NAcc plays a role in novelty detection and reactivity, we conducted further experiments in order to dissociate the effect on CREB phosphorylation and expression of spatial novelty (single exposure), exploration, and spatial learning in the food search apparatus. Results show that CREB phosphorylation is significantly increased 48 h after exposure to a novel environment. The present study suggests that CREB phosphorylation observed in the NAcc during habituation and spatial training may be mainly triggered by detection of spatial novelty.

Effects of repeated GBR 12909 administration on brain stimulation reward.

Male rats were trained at three separate currents to bar press for intracranial self-stimulation. On days 1 and 15, all subjects were given 1-(2-bis(4-fluorophenyl)-methoxy)-ethyl-4-(3-phenylpropyl) piperazine, also known as GBR 12909 (10 mg/kg, i.p.), prior to test session. Between these days, the paired Chronic-before group was injected (every other day) with GBR 12909 prior to intracranial self-stimulation, while unpaired, Chronic-after group was given the drug just after the end of the session. A third group (Control) received saline injections (i.p.) 20 min following the session. Although GBR 12909 was found to be reward enhancing, neither sensitization nor tolerance developed to the rewarding and performance/motor effects regardless of the injection regimen. In addition, the rewarding effects of intracranial self-stimulation were found to be independent of both current and environment-specific pairing. The present data obtained for GBR 12909 agree with previous observations of the effects of repeated administration of drugs of abuse on intracranial self-stimulation.

Hippocampal expression of the orphan nuclear receptor gene hzf-3/nurr1 during spatial discrimination learning.

The immediate-early gene hzf-3, also known as nurr1, is a member of the inducible orphan nuclear receptor family and is one candidate in the search for genes associated with learning and memory processes. Here we report that acquisition of a spatial food search task is accompanied by elevated levels of hzf-3 mRNA in the hippocampus. Adult male Long-Evans rats were handled, food-restricted, and allowed to habituate to the maze prior to training. During acquisition, rats were given one training session per day for 5 days. Each training session consisted of five trials in which animals searched the maze for food located in 4 of 16 holes in the floor of the maze. Training resulted in spatial acquisition of the task. Northern blot analysis showed significant increases in hippocampal hzf-3 mRNA 3 h after training in the maze. Next, brains were obtained from Naive, Habituated, Day 1, Day 3, and Day 5 animals and processed for in situ hybridization. The results showed significant increases of hzf-3 mRNA in CA1 and CA3 subregions of the dorsal hippocampus during acquisition of the task. We conclude that expression of the hzf-3 gene in the brain is associated with long-term spatial memory processes. The present results are the first to implicate an orphan nuclear receptor in long-term information storage in the hippocampus.

Control of cocaine-seeking behavior by drug-associated stimuli in rats: effects on recovery of extinguished operant-responding and extracellular dopamine levels in amygdala and nucleus accumbens.

The conditioning of the pharmacological actions of cocaine with environmental stimuli is thought to be a critical factor in the long-term addictive potential of this drug. Cocaine-related stimuli may increase the likelihood of relapse by evoking drug craving, and brain-imaging studies have identified the amygdala and nucleus accumbens (NAcc) as putative neuroanatomical substrates for these effects of cocaine cues. To study the significance of environmental stimuli in the recovery of extinguished cocaine-seeking behavior, male Wistar rats were trained to associate discriminative stimuli (SDeltas) with response-contingent availability of intravenous cocaine vs. saline. The rats then were subjected to repeated extinction sessions during which cocaine, saline, and the respective SDeltas were withheld until the animals reached an extinction criterion of