Learning an operant conditioning task differentially induces gliogenesis in the medial prefrontal cortex and neurogenesis in the hippocampus

Behavioral Training Related Neurotransmitter Receptor Expression Dynamics in the Nidopallium Caudolaterale and the Hippocampal Formation of Pigeons

Learning and memory are linked to dynamic changes at the level of synapses in brain areas that are involved in cognitive tasks. For example, changes in neurotransmitter receptors are prerequisite for tuning signals along local circuits and long-range networks. However, it is still unclear how a series of learning events promotes plasticity within the system of neurotransmitter receptors and their subunits to shape information processing at the neuronal level. Therefore, we investigated the expression of different glutamatergic NMDA (GRIN) and AMPA (GRIA) receptor subunits, the GABAergic GABARG2 subunit, dopaminergic DRD1, serotonergic 5HTR1A and noradrenergic ADRA1A receptors in the pigeon's brain. We studied the nidopallium caudolaterale, the avian analogue of the prefrontal cortex, and the hippocampal formation, after training the birds in a rewarded stimulus-response association (SR) task and in a simultaneous-matching-to-sample (SMTS) task. The results show that receptor expression changed differentially after behavioral training compared to an untrained control group. In the nidopallium caudolaterale, GRIN2B, GRIA3, GRIA4, DRD1D, and ADRA1A receptor expression was altered after SR training and remained constantly decreased after the SMTS training protocol, while GRIA2 and DRD1A decreased only under the SR condition. In the hippocampal formation, GRIN2B decreased and GABARG2 receptor expression increased after SR training. After SMTS sessions, GRIN2B remained decreased, GABARG2 remained increased if compared to the control group. None of the investigated receptors differed directly between both conditions, although differentially altered. The changes in both regions mostly occur in favor of the stimulus response task. Thus, the present data provide evidence that neurotransmitter receptor expression dynamics play a role in the avian prefrontal cortex and the hippocampal formation for behavioral training and is uniquely, regionally and functionally associated to cognitive processes including learning and memory.

Neuroplastic Changes in the Superior Colliculus and Hippocampus in Self-rewarding Paradigm: Importance of Visual Cues

Coincident excitation via different sensory modalities encoding objects of positive salience is known to facilitate learning and memory. With a view to dissect the contribution of visual cues in inducing adaptive neural changes, we monitored the lever press activity of a rat conditioned to self-administer sweet food pellets in the presence/absence of light cues. Application of light cues facilitated learning and consolidation of long-term memory. The superior colliculus (SC) of rats trained on light cue showed increased neuronal activity, dendritic branching, and brain-derived neurotrophic factor (BDNF) protein and mRNA expression. Concomitantly, the hippocampus showed augmented neurogenesis as well as BDNF protein and mRNA expression. While intra-SC administration of U0126 (inhibitor of ERK 1/2 and long-term memory) impaired memory formation, lidocaine (local anaesthetic) hindered memory recall. The light cue-dependent sweet food pellet self-administration was coupled with increased efflux of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens shell (AcbSh). In conditioned rats, pharmacological inhibition of glutamatergic signalling in dentate gyrus (DG) reduced lever press activity, as well as DA and DOPAC secretion in the AcbSh. We suggest that the neuroplastic changes in the SC and hippocampus might represent memory engrams sculpted by visual cues encoding reward information.

Chimera RNA interference knockdown of γ-synuclein in human cortical astrocytes results in mitotic catastrophe

Elevated levels of γ-synuclein (γ-syn) expression have been noted in the progression of glioblastomas, and also in the cerebrospinal fluid of patients diagnosed with neurodegenerative diseases. γ-Syn can be either internalized from the extracellular milieu or expressed endogenously by human cortical astrocytes. Internalized γ-syn results in increased cellular proliferation, brain derived neurotrophic factor release and astroprotection. However, the function of endogenous γ-syn in primary astrocytes, and the relationship to these two opposing disease states are unknown. γ-Syn is expressed by astrocytes in the human cortex, and to gain a better understanding of the role of endogenous γ-syn, primary human cortical astrocytes were treated with chimera RNA interference (RNAi) targeting γ-syn after release from cell synchronization. Quantitative polymerase chain reaction analysis demonstrated an increase in endogenous γ-syn expression 48 hours after release from cell synchronization, while RNAi reduced γ-syn expression to control levels. Immunocytochemistry of Ki67 and 5-bromodeoxyuridine showed chimera RNAi γ-syn knockdown reduced cellular proliferation at 24 and 48 hours after release from cell synchronization. To further investigate the consequence of γ-syn knockdown on the astrocytic cell cycle, phosphorylated histone H3 pSer10 (pHH3) and phosphorylated cyclin dependent kinase-2 pTyr15 (pCDK2) levels were observed via western blot analysis. The results revealed an elevated expression of pHH3, but not pCDK2, indicating γ-syn knockdown leads to disruption of the cell cycle and chromosomal compaction after 48 hours. Subsequently, flow cytometry with propidium iodide determined that increases in apoptosis coincided with γ-syn knockdown. Therefore, γ-syn exerts its effect to allow normal astrocytic progression through the cell cycle, as evidenced by decreased proliferation marker expression, increased pHH3, and mitotic catastrophe after knockdown. In this study, we demonstrated that the knockdown of γ-syn within primary human cortical astrocytes using chimera RNAi leads to cell cycle disruption and apoptosis, indicating an essential role for γ-syn in regulating normal cell division in astrocytes. Therefore, disruption to γ-syn function would influence astrocytic proliferation, and could be an important contributor to neurological diseases.

Uncovering the complex genetics of human temperament

Experimental studies of learning suggest that human temperament may depend on the molecular mechanisms for associative conditioning, which are highly conserved in animals. The main genetic pathways for associative conditioning are known in experimental animals, but have not been identified in prior genome-wide association studies (GWAS) of human temperament. We used a data-driven machine learning method for GWAS to uncover the complex genotypic-phenotypic networks and environmental interactions related to human temperament. In a discovery sample of 2149 healthy Finns, we identified sets of single-nucleotide polymorphisms (SNPs) that cluster within particular individuals (i.e., SNP sets) regardless of phenotype. Second, we identified 3 clusters of people with distinct temperament profiles measured by the Temperament and Character Inventory regardless of genotype. Third, we found 51 SNP sets that identified 736 gene loci and were significantly associated with temperament. The identified genes were enriched in pathways activated by associative conditioning in animals, including the ERK, PI3K, and PKC pathways. 74% of the identified genes were unique to a specific temperament profile. Environmental influences measured in childhood and adulthood had small but significant effects. We confirmed the replicability of the 51 Finnish SNP sets in healthy Korean (90%) and German samples (89%), as well as their associations with temperament. The identified SNPs explained nearly all the heritability expected in each sample (37-53%) despite variable cultures and environments. We conclude that human temperament is strongly influenced by more than 700 genes that modulate associative conditioning by molecular processes for synaptic plasticity and long-term memory.

The complex genetics and biology of human temperament: a review of traditional concepts in relation to new molecular findings

Recent genome-wide association studies (GWAS) have shown that temperament is strongly influenced by more than 700 genes that modulate associative conditioning by molecular processes for synaptic plasticity and long-term learning and memory. The results were replicated in three independent samples despite variable cultures and environments. The identified genes were enriched in pathways activated by behavioral conditioning in animals, including the two major molecular pathways for response to extracellular stimuli, the Ras-MEK-ERK and the PI3K-AKT-mTOR cascades. These pathways are activated by a wide variety of physiological and psychosocial stimuli that vary in positive and negative valence and in consequences for health and survival. Changes in these pathways are orchestrated to maintain cellular homeostasis despite changing conditions by modulating temperament and its circadian and seasonal rhythms. In this review we first consider traditional concepts of temperament in relation to the new genetic findings by examining the partial overlap of alternative measures of temperament. Then we propose a definition of temperament as the disposition of a person to learn how to behave, react emotionally, and form attachments automatically by associative conditioning. This definition provides necessary and sufficient criteria to distinguish temperament from other aspects of personality that become integrated with it across the life span. We describe the effects of specific stimuli on the molecular processes underlying temperament from functional, developmental, and evolutionary perspectives. Our new knowledge can improve communication among investigators, increase the power and efficacy of clinical trials, and improve the effectiveness of treatment of personality and its disorders.

γ-Synuclein Induces Human Cortical Astrocyte Proliferation and Subsequent BDNF Expression and Release

γ-Synuclein (γ-syn) is expressed by astrocytes in the human nervous system, and increased extracellularly in the brain and cerebrospinal fluid of individuals diagnosed with Alzheimer's disease. Upregulation of γ-syn also coincides with proliferation of glioblastomas and other cancers. In order to better understand regulation and function of extracellular γ-syn, primary human cortical astrocytes were treated with γ-syn conditioned media at various physiological concentrations (50, 100, 150 nM) after cell synchronization. Additionally, extracellular brain-derived neurotrophic factor (BDNF), a neuroprotective growth factor released by astrocytes that has been shown to be decreased extracellularly in neurodegenerative disease, was observed in response to γ-syn treatment. Analysis of 5-bromodeoxyuridine (BrdU) and propidium iodide through flow cytometry 24 h after release from synchronization revealed an increase in G₂/M phase of the cell cycle with 100 nM γ-syn during initial cell division, an effect that was reversed at 48 h. However, increased extracellular BDNF was observed at 48 h with 100 nM and 150 nM γ-syn treatment with no difference between controls at 24 h. Further analysis of cell cycle markers with immunocytochemistry of BrdU and Ki67 after treatment with 100 nM γ-syn confirmed increased initial cell proliferation and decreased non-proliferating cells. Western blot analysis demonstrated increased γ-syn levels after 100 nM treatment at 24 and 48 h, and increased pro-BDNF, mature BDNF and cell viability at 48 h. The results demonstrate that γ-syn internalization by human cortical astrocytes causes upregulation of the cell cycle, followed by subsequent BDNF expression and release.

Voluntary exercise or systemic propranolol ameliorates stress-related maladaptive behaviors in female rats

Many people will experience at least one traumatic event in their lifetime, with up to 20% developing Post-Traumatic Stress Disorder (PTSD) or PTSD-like symptoms. In addition, the likelihood that females will develop PTSD after trauma is more than twice that of males. Despite its prevalence, current treatment strategies for trauma victims are limited and substantial portions of affected individuals remain resistant to treatment, suggesting that additional interventions are necessary. Using an animal model of traumatic stress, the present studies tested the hypothesis that either voluntary exercise and/or administration of the adrenergic beta-receptor antagonist propranolol, would ameliorate stress-related maladaptive behaviors. In Study 1 four groups of female rats were exposed to a sequence of stressors that included anesthesia, restraint, forced swim, exposure to predator scent and fear conditioning. Rats then underwent re-exposure sessions in which stress-related conditioned stimuli were presented. In addition to re-exposure, stressed rats were treated with propranolol (10 mg/kg) and/or given the opportunity to engage in voluntary wheel running intermittently for 4 weeks. Stress-associated maladaptive behavior was assessed using the elevated plus and open field mazes and fear memory tests. Cognitive ability was assessed using a novel odor recognition task. A main effect of exercise on behaviors related to anxiety and resilience was observed, but neither a main effect of propranolol nor a synergistic effect of propranolol and exercise were observed. Neither stress induction nor treatment influenced recognition memory. In contrast, in Study 2 in which the timing and dosage of propranolol (0.25-2.0 mg/kg), and the number and timing of re-exposure sessions were adjusted, propranolol produced both a reduction in anxiety-like behaviors as well as resilience to a subsequent stressor. These results are consistent with the notion that combining re-exposure therapy with additional interventions is beneficial for female trauma victims. Furthermore, the findings support the view that in pre-clinical models, voluntary exercise, which bolsters hippocampal function and propranolol, which affects amygdala-dependent memory reconsolidation and peripheral noradrenergic signaling, can ameliorate stress-related symptoms.

Glial markers and emotional memory in rats following acute cerebral radiofrequency exposures

The widespread mobile phone use raises concerns on the possible cerebral effects of radiofrequency electromagnetic fields (RF EMF). Reactive astrogliosis was reported in neuroanatomical structures of adaptive behaviors after a single RF EMF exposure at high specific absorption rate (SAR, 6 W/kg). Here, we aimed to assess if neuronal injury and functional impairments were related to high SAR-induced astrogliosis. In addition, the level of beta amyloid 1-40 (Aβ 1-40) peptide was explored as a possible toxicity marker. Sprague Dawley male rats were exposed for 15 min at 0, 1.5, or 6 W/kg or for 45 min at 6 W/kg. Memory, emotionality, and locomotion were tested in the fear conditioning, the elevated plus maze, and the open field. Glial fibrillary acidic protein (GFAP, total and cytosolic fractions), myelin basic protein (MBP), and Aβ1-40 were quantified in six brain areas using enzyme-linked immunosorbent assay. According to our data, total GFAP was increased in the striatum (+114 %) at 1.5 W/kg. Long-term memory was reduced, and cytosolic GFAP was increased in the hippocampus (+119 %) and in the olfactory bulb (+46 %) at 6 W/kg (15 min). No MBP or Aβ1-40 expression modification was shown. Our data corroborates previous studies indicating RF EMF-induced astrogliosis. This study suggests that RF EMF-induced astrogliosis had functional consequences on memory but did not demonstrate that it was secondary to neuronal damage.

Time-Course Analysis of Brain Regional Expression Network Responses to Chronic Intermittent Ethanol and Withdrawal: Implications for Mechanisms Underlying Excessive Ethanol Consumption

Long lasting abusive consumption, dependence, and withdrawal are characteristic features of alcohol use disorders (AUD). Mechanistically, persistent changes in gene expression are hypothesized to contribute to brain adaptations leading to ethanol toxicity and AUD. We employed repeated chronic intermittent ethanol (CIE) exposure by vapor chamber as a mouse model to simulate the cycles of ethanol exposure and withdrawal commonly seen with AUD. This model has been shown to induce progressive ethanol consumption in rodents. Brain CIE-responsive expression networks were identified by microarray analysis across five regions of the mesolimbic dopamine system and extended amygdala with tissue harvested from 0-hours to 7-days following CIE. Weighted Gene Correlated Network Analysis (WGCNA) was used to identify gene networks over-represented for CIE-induced temporal expression changes across brain regions. Differential gene expression analysis showed that long-lasting gene regulation occurred 7-days after the final cycle of ethanol exposure only in prefrontal cortex (PFC) and hippocampus. Across all brain regions, however, ethanol-responsive expression changes occurred mainly within the first 8-hours after removal from ethanol. Bioinformatics analysis showed that neuroinflammatory responses were seen across multiple brain regions at early time-points, whereas co-expression modules related to neuroplasticity, chromatin remodeling, and neurodevelopment were seen at later time-points and in specific brain regions (PFC or HPC). In PFC a module containing Bdnf was identified as highly CIE responsive in a biphasic manner, with peak changes at 0 hours and 5 days following CIE, suggesting a possible role in mechanisms underlying long-term molecular and behavioral response to CIE. Bioinformatics analysis of this network and several other modules identified Let-7 family microRNAs as potential regulators of gene expression changes induced by CIE. Our results suggest a complex temporal and regional pattern of widespread gene network responses involving neuroinflammatory and neuroplasticity related genes as contributing to physiological and behavioral responses to chronic ethanol.

Adult Astrogenesis and the Etiology of Cortical Neurodegeneration

As more evidence points to a clear role for astrocytes in synaptic processing, synaptogenesis and cognition, continuing research on astrocytic function could lead to strategies for neurodegenerative disease prevention. Reactive astrogliosis results in astrocyte proliferation early in injury and disease states and is considered neuroprotective, indicating a role for astrocytes in disease etiology. This review describes the different types of human cortical astrocytes and the current evidence regarding adult cortical astrogenesis in injury and degenerative disease. A role for disrupted astrogenesis as a cause of cortical degeneration, with a focus on the tauopathies and synucleinopathies, will also be considered.

A behavioral neuroenergetics theory of ADHD

Energetic insufficiency in neurons due to inadequate lactate supply is implicated in several neuropathologies, including attention-deficit/hyperactivity disorder (ADHD). By formalizing the mechanism and implications of such constraints on function, the behavioral Neuroenergetics Theory (NeT) predicts the results of many neuropsychological tasks involving individuals with ADHD and kindred dysfunctions, and entails many novel predictions. The associated diffusion model predicts that response times will follow a mixture of Wald distributions from the attentive state, and ex-Wald distributions after attentional lapses. It is inferred from the model that ADHD participants can bring only 75-85% of the neurocognitive energy to bear on tasks, and allocate only about 85% of the cognitive resources of comparison groups. Parameters derived from the model in specific tasks predict performance in other tasks, and in clinical conditions often associated with ADHD. The primary action of therapeutic stimulants is to increase norepinephrine in active regions of the brain. This activates glial adrenoceptors, increasing the release of lactate from astrocytes to fuel depleted neurons. The theory is aligned with other approaches and integrated with more general theories of ADHD. Therapeutic implications are explored.

Differential contribution of hippocampal circuits to appetitive and consummatory behaviors during operant conditioning of behaving mice

Operant conditioning is a type of associative learning involving different and complex sensorimotor and cognitive processes. Because the hippocampus has been related to some motor and cognitive functions involved in this type of learning (such as object recognition, spatial orientation, and associative learning tasks), we decided to study in behaving mice the putative changes in strength taking place at the hippocampal CA3-CA1 synapses during the acquisition and performance of an operant conditioning task. Mice were chronically implanted with stimulating electrodes in the Schaffer collaterals and with recording electrodes in the hippocampal CA1 area and trained to an operant task using a fixed-ratio (1:1) schedule. We recorded the field EPSPs (fEPSPs) evoked at the CA3-CA1 synapse during the performance of appetitive (going to the lever, lever press) and consummatory (going to the feeder, eating) behaviors. In addition, we recorded the local field potential activity of the CA1 area during similar behavioral displays. fEPSPs evoked at the CA3-CA1 synapse presented larger amplitudes for appetitive than for consummatory behaviors. This differential change in synaptic strength took place in relation to the learning process, depending mainly on the moment in which mice reached the selected criterion. Thus, selective changes in CA3-CA1 synaptic strength were dependent on both the behavior display and the learning stage. In addition, significant changes in theta band power peaks and their corresponding discrete frequencies were noticed during these behaviors across the sequence of events characterizing this type of associative learning but not during the acquisition process.

Increases in doublecortin immunoreactivity in the dentate gyrus following extinction of heroin-seeking behavior

Adult-generated neurons in the dentate gyrus (DG) of the hippocampus play a role in various forms of learning and memory. However, adult born neurons in the DG, while still at an immature stage, exhibit unique electrophysiological properties and are also functionally implicated in learning and memory processes. We investigated the effects of extinction of drug-seeking behavior on the formation of immature neurons in the DG as assessed by quantification of doublecortin (DCX) immunoreactivity. Rats were allowed to self-administer heroin (0.03 mg/kg/infusion) for 12 days and then subjected either to 10 days of extinction training or forced abstinence. We also examined extinction responding patterns following heroin self-administration in glial fibrillary acidic protein thymidine kinase (GFAP-tk) transgenic mice, which have been previously demonstrated to show reduced formation of immature and mature neurons in the DG following treatment with ganciclovir (GCV). We found that extinction training increased DCX immunoreactivity in the dorsal DG as compared with animals undergoing forced abstinence, and that GCV-treated GFAP-tk mice displayed impaired extinction learning as compared to saline-treated mice. Our results suggest that extinction of drug-seeking behavior increases the formation of immature neurons in the DG and that these neurons may play a functional role in extinction learning.

The effects of fetal and perinatal asphyxia on neuronal cytokine levels and ceramide metabolism in adulthood

In a rat model of global fetal and perinatal asphyxia, we investigated if asphyxia and long-lasting brain tolerance to asphyxia (preconditioning) are mediated by modifications in inflammatory cytokines and ceramide metabolism genes in prefrontal cortex, hippocampus and caudate-putamen at the age of 8months. Most significant changes were found in prefrontal cortex, with reduced LAG1 homolog ceramide synthase 1 expression after both types of asphyxia. Additionally, sphingosine kinase 1 was upregulated in those animals that experienced the combination of fetal and perinatal asphyxia (preconditioning), suggesting increased cell proliferation. While cytokine levels are normal, levels of ceramide genes were modulated both after fetal and perinatal asphyxia in the adult prefrontal cortex. Moreover, the combination of two subsequent asphyctic insults provides long-lasting neuroprotection in the prefrontal cortex probably by maintaining normal apoptosis and promoting cell proliferation. Better understanding of the effects of asphyxia on ceramide metabolism will help to understand the changes leading to brain tolerance and will open opportunities for the development of new neuroprotective therapies.

Cerebral antioxidant enzyme increase associated with learning deficit in type 2 diabetes rats

In this study, we examined alterations in the enzymatic antioxidant defenses associated with learning deficits induced by type 2 diabetes, and studied the effects of the peroxisome proliferator-activated receptor γ agonist pioglitazone on these learning deficits. Learning ability was assessed by visual discrimination tasks in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, as a model of spontaneous type 2 diabetes. Levels of the antioxidant enzymes glutathione peroxidase (GPx), Cu(2+)-Zn(2+) superoxide dismutase (CuZn-SOD) and manganese SOD were measured in the cortex, hippocampus and striatum. Half the rats received oral pioglitazone (20mg/kg/day) from the early stage of diabetes (22 weeks old) to 27 weeks old. OLETF rats showed learning deficits compared with control, Long-Evans Tokushima Otsuka (LETO) rats. GPx levels in the cortex and hippocampus were increased in OLETF rats compared with LETO rats, with an inverse correlation between GPx in the hippocampus and learning score. CuZn-SOD levels were also increased in the hippocampus in OLETF rats. Pioglitazone reduced blood glucose and increased serum adiponectin levels, but had no effect on learning tasks or antioxidant enzymes, except for CuZn-SOD. These results suggest that an oxidative imbalance reflected by increased brain antioxidant enzymes plays an important role in the development of learning deficits in type 2 diabetes. Early pioglitazone administration partly ameliorated diabetic symptoms, but was unable to completely recover cerebral oxidative imbalance and functions. These results suggest that diabetes-induced brain impairment, which results in learning deficits, may have occurred before the appearance of the symptoms of overt diabetes.

Contrasting hippocampal and amygdalar expression of genes related to neural plasticity during escape from social aggression

Social subjugation has widespread consequences affecting behavior and underlying neural systems. We hypothesized that individual differences in stress responsiveness were associated with differential expression of neurotrophin associated genes within the hippocampus and amygdala. To do this we examined the brains of hamsters placed in resident/intruder interactions, modified by the opportunity to escape from aggression. In the amygdala, aggressive social interaction stimulated increased BDNF receptor TrK(B) mRNA levels regardless of the ability to escape the aggressor. In contrast, the availability of escape limited the elevation of GluR(1) AMPA subunit mRNA. In the hippocampal CA(1), the glucocorticoid stress hormone, cortisol, was negatively correlated with BDNF and TrK(B) gene expression, but showed a positive correlation with BDNF expression in the DG. Latency to escape the aggressor was also negatively correlated with CA(1) BDNF expression. In contrast, the relationship between amygdalar TrK(B) and GluR(1) was positive with respect to escape latency. These results suggest that an interplay of stress and neurotrophic systems influences learned escape behavior. Animals which escape faster seem to have a more robust neurotrophic profile in the hippocampus, with the opposite of this pattern in the amygdala. We propose that changes in the equilibrium of hippocampal and amygdalar learning result in differing behavioral stress coping choices.

Depotentiation of hippocampal long-term potentiation depends on genetic background and is modulated by cocaine self-administration

Lewis (LEW) and Fischer 344 (F344) rats differ in their response to drugs and are frequently used as an experimental model to study vulnerability to drug addiction. We have previously reported that significant differences in hippocampal synaptic plasticity exist between LEW and F344 rats after non-contingent chronic cocaine administration. However, given the several biochemical differences between contingent and non-contingent administration of drugs, we have studied here the possible genetic differences in synaptic plasticity after contingent cocaine self-administration. LEW and F344 animals self-administered cocaine (1 mg/kg i.v.) or saline under a fixed ratio 1 schedule of reinforcement for 20 days. After self-administration, electrophysiological experiments were carried out in which hippocampal slices were tetanized with three high frequency pulses in order to induce long-term potentiation (LTP). After a 20 min period of LTP stabilization, a train of low frequency stimulation (LFS; 900 pulses, 1 Hz) was applied to induce depotentiation of LTP. Data showed no differences between cocaine self-administered LEW or F344 rats in the induction of saturated-LTP compared to saline animals. LEW saline self-administered rats showed normal LTP depotentiation whereas cocaine self-administration impaired depotentiation in this rat strain. In the F344 strain, depotentiation of saturated-LTP was impaired both in saline and cocaine self-administered rats. The present results corroborate previous findings showing differences in basal hippocampal synaptic plasticity between LEW and F344 rats. These differences seem to modulate cocaine effects in a manner independent of contingency of drug administration.

Oral administration of fluoxetine alters the proliferation/apoptosis balance of lymphoma cells and up-regulates T cell immunity in tumor-bearing mice

Antidepressants have a controversial role with regard to their influence on cancer and immunity. Recently, we showed that fluoxetine administration induces an enhancement of the T-cell mediated immunity in naïve mice, resulting in the inhibition of tumor growth. Here we studied the effects of fluoxetine on lymphoma proliferation/apoptosis and immunity in tumor bearing-mice. We found an increase of apoptotic cells (active Caspase-3(+)) and a decrease of proliferative cells (PCNA(+)) in tumors growing in fluoxetine-treated animals. In addition, differential gene expressions of cell cycle and death markers were observed. Cyclins D3, E and B were reduced in tumors from animals treated with fluoxetine, whereas the tumor suppressor p53 and the cell cycle inhibitors p15/INK4B, p16/INK4A and p27/Kip1 were increased. Besides, the expression of the antiapoptotic factor Bcl-2 and the proapoptotic factor Bad were lower and higher respectively in these animals. These changes were accompanied by increased IFN-γ and TNF-α levels as well as augmented circulating CD8(+) T lymphocytes in tumor-bearing mice treated with the antidepressant. Therefore, we propose that the up-regulation of T-cell mediated antitumor immunity may be contributing to the alterations of tumor cell proliferation and apoptosis thus resulting in the inhibition of tumor progression.