Deep androgen receptor suppression in prostate cancer exploits sexually dimorphic renal expression for systemic glucocorticoid exposure.

BACKGROUND: Enzalutamide and apalutamide are potent next-generation androgen receptor (AR) antagonists used in metastatic and non-metastatic prostate cancer. Metabolic, hormonal and immunologic effects of deep AR suppression are unknown. We hypothesized that enzalutamide and apalutamide suppress 11ß-hydroxysteroid dehydrogenase-2 (11ß-HSD2), which normally converts cortisol to cortisone, leading to elevated cortisol concentrations, increased ratio of active to inactive glucocorticoids and possibly suboptimal response to immunotherapy. On-treatment glucocorticoid changes might serve as an indicator of active glucocorticoid exposure and resultant adverse consequences. PATIENTS AND METHODS: Human kidney tissues were stained for AR and 11ß-HSD2 expression. Patients in three trials [neoadjuvant apalutamide plus leuprolide, enzalutamide ± PROSTVAC (recombinant poxvirus prostate-specific antigen vaccine) for metastatic castration-resistant prostate cancer (CRPC) and enzalutamide ± PROSTVAC for non-metastatic castration-sensitive prostate cancer] were analyzed for cortisol and its metabolites using liquid chromatography-mass spectrometry (LC-MS/MS). Progression-free survival was determined in the metastatic CRPC study of enzalutamide ± PROSTVAC for those with glucocorticoid changes above and below the median. RESULTS: Concurrent AR and 11ß-HSD2 expression occurs only in the kidneys of men. A statistically significant rise in cortisol concentration, cortisol/cortisone ratio and tetrahydrocortisol/tetrahydrocortisone ratio with AR antagonist treatment occurred uniformly across all three trials. In the trial of enzalutamide ± PROSTVAC for metastatic CRPC, high cortisol/cortisone ratio in the enzalutamide arm was associated with significantly improved progression-free survival. However, in the enzalutamide + PROSTVAC arm, the opposite trend was observed. CONCLUSION: Enzalutamide and apalutamide treatment toggles renal 11ß-HSD2 and significantly increases indicators of and exposure to biologically active glucocorticoids, which is associated with clinical outcomes.

Avelumab for the treatment of metastatic Merkel cell carcinoma.

Avelumab is a promising new therapeutic agent for patients with metastatic Merkel cell carcinoma, a rare and aggressive type of neuroendocrine tumor of the skin. Until the recent approval of avelumab (Bavencio), no therapies were approved by the U.S. Food and Drug Administration for the treatment of metastatic Merkel cell carcinoma. In a recent trial, avelumab, an anti-programmed death ligand-1 antibody, demonstrated an objective response in 28 of 88 patients (31.8% [95.9% CI, 21.9-43.1]) with advanced, chemotherapy-refractory Merkel cell carcinoma. Overall, avelumab was well tolerated at a dose of 10 mg/kg administered intravenously every 2 weeks. Serious treatment-related adverse events were reported in 5 patients (6%), but no grade 4 adverse events or treatment-related deaths were reported. Preliminary data evaluating avelumab in chemotherapy-naive patients is also encouraging.

D1 receptor-mediated inhibition of medial prefrontal cortex neurons is disrupted in adult rats exposed to amphetamine in adolescence.

Amphetamine (AMPH) exposure leads to changes in behavior and dopamine receptor function in the prefrontal cortex (PFC). Since dopamine plays an important role in regulating GABAergic transmission in the PFC, we investigated if AMPH exposure induces long-lasting changes in dopamine's ability to modulate inhibitory transmission in the PFC as well as whether the effects of AMPH differed depending on the age of exposure. Male Sprague-Dawley rats were given saline or 3 mg/kg AMPH (i.p.) repeatedly during adolescence or adulthood and following a withdrawal period of up to 5 weeks (Experiment 1) or up to 14 weeks (Experiment 2), they were sacrificed for in vitro whole-cell recordings in layer V/VI of the medial PFC. We found that in brain slices from either adolescent- or adult-exposed rats, there was an attenuation of dopamine-induced increases in inhibitory synaptic currents in pyramidal cells. These effects did not depend on age of exposure, were mediated at least partially by a reduced sensitivity of D1 receptors in AMPH-treated rats, and were associated with an enhanced behavioral response to the drug in a separate group of rats given an AMPH challenge following the longest withdrawal period. Together, these data reveal a prolonged effect of AMPH exposure on medial PFC function that persisted for up to 14 weeks in adolescent-exposed animals. These long-lasting neurophysiological changes may be a contributing mechanism to the behavioral consequences that have been observed in those with a history of amphetamine abuse.

The effects of abused drugs on adolescent development of corticolimbic circuitry and behavior.

Adolescence is a period of significant neurobiological change that occurs as individuals transition from childhood to adulthood. Because the nervous system is in a relatively labile state during this stage of development, it may be especially sensitive to experience-induced plasticity. One such experience that is relatively common to adolescents is the exposure to drugs of abuse, particularly alcohol and psychostimulants. In this review, we highlight recent findings on the long-lasting effects of exposure to these drugs during adolescence in humans as well as in animal models. Whenever possible, our focus is on studies that use comparison groups of adolescent- and adult-exposed subjects as this is a more direct test of the hypothesis that adolescence represents a period of enhanced vulnerability to the effects of drug-induced plasticity. Lastly, we suggest areas of future investigation that are needed and methodological concerns that should be addressed.

Effects of ethanol during adolescence on the number of neurons and glia in the medial prefrontal cortex and basolateral amygdala of adult male and female rats.

Human adolescents often consume alcohol in a binge-like manner at a time when changes are occurring within specific brain structures, such as the medial prefrontal cortex (mPFC) and the basolateral nucleus of the amygdala (BLN). In particular, the number of neurons and glia is changing in both of these areas in the rat between adolescence and adulthood (Markham et al., 2007; Rubinow and Juraska, 2009). The current study investigated the effects of ethanol exposure during adolescence on the number of neurons and glia in the adult mPFC and BLN in Long-Evans male and female rats. Saline or 3g/kg ethanol was administered between postnatal days (P) 35-45 in a binge-like pattern, with 2days of injections followed by 1 day without an injection. Stereological analyses of the ventral mPFC (prelimbic and infralimbic areas) and the BLN were performed on brains from rats at 100 days of age. Neuron and glia densities were assessed with the optical disector and then multiplied by the volume to calculate the total number of neurons and glia. In the adult mPFC, ethanol administration during adolescence resulted in a decreased number of glia in males, but not females, and had no effect on the number of neurons. Adolescent ethanol exposure had no effects on glia or neuron number in the BLN. These results suggest that glia cells in the prefrontal cortex are particularly sensitive to binge-like exposure to ethanol during adolescence in male rats only, potentially due to a decrease in proliferation in males or protective mechanisms in females.

Long-term follow-up of prostate cancer patients treated with vaccine and definitive radiation therapy.

BACKGROUND: Vaccine therapy in combination with radiation therapy may improve distant and/or local control in prostate cancer. We present long-term follow-up data on the secondary and exploratory endpoints of safety and biochemical failure, respectively, from patients with clinically localized prostate cancer treated definitively with a poxviral vector-based therapeutic vaccine combined with external beam radiation therapy (EBRT). METHODS: Thirty-six prostate cancer patients received definitive EBRT plus vaccine. A total of 18 patients were treated with adjuvant standard-dose interleukin-2 (S-IL-2) (4 MIU m(-2)) and 18 were treated with very low-dose IL-2 (M-IL-2) (0.6 MIU m(-2)). Seven patients were treated with EBRT alone. Twenty-six patients treated with EBRT plus vaccine returned for follow-up, and we reviewed the most recent labs and clinical notes of the remaining patients. RESULTS: Median follow-up for the S-IL-2, M-IL-2 and EBRT-alone groups was 98, 76 and 79 months, respectively. Actuarial 5-year PSA failure-free probability was 78%, 82% and 86% (P=0.58 overall), respectively. There were no significant differences between the actuarial overall survival and the prostate cancer-specific survival between the two vaccine arms. Of the 26 patients who returned for follow-up, Radiation Therapy Oncology Group grade ≥2 genitourinary (GU) and gastrointestinal (GI) toxicity was seen in 19% and 8%, respectively, with no difference between the arms (P=1.00 and P=0.48 for grade ≥2 GU and GI toxicity, respectively). In all, 12 patients were evaluated for PSA-specific immune responses, and 1 demonstrated a response 66 months post-enrollment. CONCLUSIONS: We demonstrate that vaccine combined with EBRT does not appear to have significant differences with regard to PSA control or late-term toxicity compared with standard treatment. We also found limited evidence of long-term immune response following vaccine therapy.

Impact of tumour volume on the potential efficacy of therapeutic vaccines.

With the recent approval by the U.S. Food and Drug Administration of the first therapeutic vaccine for cancer, the long-awaited goal of harnessing a patient's immune system to attack cancer through this modality is finally realized. However, as researchers in the field of cancer immunotherapy continue to perform randomized definitive studies, much remains to be learned about potential surrogate endpoints and appropriate patient populations for therapeutic vaccines. The present review addresses available data from clinical trials of immunotherapeutic agents relevant to the selection of appropriate patient populations. We believe that the weight of evidence supports the use of immunotherapy earlier in the disease course and in patients with less aggressive disease, and that the relevant findings have important implications for the design of clinical trials with therapeutic vaccines.

Adaptations in medial prefrontal cortex function associated with amphetamine-induced behavioral sensitization.

Neuroadaptations in the prefrontal cortex (PFC) are hypothesized to play an important role in the behavioral changes associated with repeated psychostimulant exposure, but there are few published studies that measure neuronal activity during the development and expression of sensitization. To address this, we recorded single neuron activity in the medial PFC (mPFC) of male rats that were exposed for 5 days to saline or amphetamine (AMPH; 1.0 mg/kg i.p.) and then given saline or AMPH challenges following a three-day withdrawal. We found that rats exposed to AMPH developed locomotor sensitization to the drug that emerged on the fifth treatment session and became statistically significant at AMPH challenge. This was associated with no change in baseline (i.e., pre-injection) activity of mPFC neurons across the treatment or challenge sessions. Following the first AMPH injection, mPFC neurons responded primarily with reductions in firing, with the overall pattern and magnitude of responses remaining largely similar following repeated treatment. The exception was in the minority of cells that respond to AMPH with increases in firing rate. In this population, the magnitude of excitations peaked during the fifth AMPH exposure and was still relatively elevated at the AMPH challenge. Furthermore, these units increased firing during a saline challenge that was given to assess associative conditioning. These results suggest that AMPH-induced adaptations in mPFC function are not as apparent as AMPH-induced adaptations in behavior. When mPFC adaptations do occur, they appear limited to the population of neurons that increase their firing in response to AMPH.

Long-term survival and PSA control with radiation and immunotherapy for node positive prostate cancer.

We describe a patient with node positive prostate cancer treated with radiation, androgen deprivation, and immunotherapy with long-term overall survival and PSA control. ELISPOT immunoassay studies demonstrated PSA specific T-cells prior to starting vaccine therapy suggesting that this positive response may be related to an improved antitumor immune response of the patient, increased immunogenicity of the tumor, or decreased activation of immune escape pathways. Further evaluation of therapeutic cancer vaccines in combination with radiation and hormonal therapy in the definitive management of prostate cancer is warranted.

Role of vaccine therapy in cancer: biology and practice.

Vaccines constitute a potential new therapeutic approach for a range of human cancers. Unlike other therapeutics, vaccines initiate a dynamic process in the host immune system that can be exploited with subsequent therapies. Indeed, recent preclinical and clinical studies with cancer vaccines have provided evidence that this unique therapeutic modality should lead to consideration of new paradigms in both clinical trial design and endpoints and in combination therapies. The present article reviews and sets out a rationale for these new paradigms, with a focus on prostate cancer.

Behavior-related modulation of substantia nigra pars reticulata neurons in rats performing a conditioned reinforcement task.

Motor-control models of basal ganglia function have emphasized disinhibition through reduction of tonic, inhibitory output. Although these models have shed important light on basal ganglia operations, evidence emerging from electrophysiological studies of behaving primates suggests that disinhibition alone may not adequately explain the role of the basal ganglia in movement. To assess this role in the rat, the most frequently used subject in studies of basal ganglia function, we recorded neuronal activity in the primary output nucleus, the substantia nigra pars reticulata, during an operant task. After rats were trained to nosepoke into an illuminated hole for access to a 10% sucrose solution delivered through a spout, single- and multiple-unit activity was recorded during 60-120 nosepoke trials. Compared to the period 60 s before the start of the first trial in the task, 110 of 225 reticulata units increased firing >200% while 17 of 225 decreased to 40% of baseline. Of these 225 units, >60% responded coincident with specific task events such as nosepokes and spout licking. Most nosepoke-responsive units showed either excitation (>50%) or a combination of excitation and inhibition (>25%) rather than inhibition alone (>20%). Increases in firing were also common during approach and licking at the spout, with inhibitions alone comprising 30% of responses. In some units, there was evidence of reward-related responding, with changes occurring in anticipation of reward delivery or during the delivery of sucrose, but not the persistent licking that continued for several seconds after its offset. While 70% of units responded during both nosepokes and spout licking, changes in firing were typically unique depending on the motor behavior required (i.e. nosepoking vs. licking). Our results, which indicate a prominent role for increases in nigra reticulata activity during movement, add to growing evidence that although inhibitions may allow desired motor responses to emerge, excitations may help shape behavioral output by suppressing competing motor programs.

A randomized phase II trial of docetaxel (taxotere) plus thalidomide in androgen-independent prostate cancer.

New therapeutic alternatives are needed to improve outcomes in patients with androgen-independent prostate cancer (AIPC). For several years, researchers at the National Cancer Institute have been interested in elucidating the importance of angiogenesis in the pathogenesis of prostate cancer and in identifying inhibitors of this process. Thalidomide has been shown to inhibit the ability of tumors to recruit new blood vessels. In a recent phase II trial of thalidomide in AIPC, 28% of patients achieved a prostate-specific antigen (PSA) decrease of >40%. The taxane docetaxel also produces PSA and measurable disease responses when used as monotherapy or as a component of combination chemotherapy for AIPC. Thus, based on the single-agent activity of thalidomide and docetaxel, we initiated a randomized phase II study of weekly docetaxel with or without thalidomide, 200 mg at bedtime, in patients with chemotherapy-naive metastatic AIPC. Docetaxel, 30 mg/m(2) intravenously, was administered every 7 days for 3 weeks, followed by a 1-week rest period. Both regimens have been well tolerated among the first 59 treated patients, with a near absence of grade (3/4) myelosuppression. Fatigue, hyperglycemia, and pulmonary toxicity were seen in both groups. Thrombotic events have been seen in the combination arm. Thirty-five percent (6 of 17) of the patients receiving docetaxel alone and 53% (19 of 36) of those receiving docetaxel and thalidomide have had a PSA decrease of at least 50%. Combining a cytotoxic agent with an angiogenesis inhibitor is a promising area of investigation for prostate cancer management.

The infection of human dendritic cells with recombinant avipox vectors expressing a costimulatory molecule transgene (CD80) to enhance the activation of antigen-specific cytolytic T cells.

Human dendritic cells (DCs) express MHC class I and II molecules and several T-cell costimulatory molecules that contribute to their efficiency as antigen-presenting cells (APCs). Whereas most human DC populations uniformly express some costimulatory molecules such as B7-2 (CD86), previous studies have shown a wide variation in the expression of B7-1 (CD80) among different human DC preparations. In the studies reported here, we demonstrate that replication-defective avipox vectors expressing B7-1 can be used to rapidly and efficiently infect human DCs and can enhance the efficacy of human DCs to activate specific human T-cell populations. This has been demonstrated both in systems using peptide as a source of signal 1 and in systems using recombinant avipox vector to deliver signal 1. The antigen used in these studies was the tumor-associated human carcinoembryonic antigen (CEA). An immunodominant 9-mer CTL epitope for CEA (designated CAP-1) has been previously characterized (K. Y. Tsang et al., J. Natl. Cancer Inst. (Bethesda), 87: 982-990, 1995). The source of signal 1 used in these studies was (a) the CAP-1 peptide; (b) recombinant avipox-CEA; or (c) the dual transgene recombinant avipox-CEA/B7-1. These studies demonstrate that CEA-specific T cells are more efficiently activated using as APCs peptide-pulsed DCs infected with avipox-B7-1, as compared with peptide-pulsed DCs infected with wild-type vector, or with uninfected peptide-pulsed DCs. Greater activation of CEA-specific T cells was also obtained using as APCs DCs that were infected with avipox-CEA/B7-1 as compared with the use of DCs infected with avipox-CEA. A CEA tetramer was also used to isolate high- and low-tetramer-binding CEA-specific T-cell populations. Although both high- and low-tetramer-binding T cells had the ability to lyse CEA peptide-pulsed targets, only the high-tetramer-binding T cells had the ability to lyse colon carcinoma cells expressing CEA, which suggests the existence of tetramer-binding populations with different T-cell receptor (TCR) affinities. The demonstrated safety of recombinant avipox vectors in humans and the previously demonstrated ability to administer them multiple times without host immune response limitations indicate that these vectors expressing B7-1 have a potential use in enhancing the efficacy of human DC immunotherapy protocols using either peptide or recombinant vector to deliver signal 1.

The influence of granulocyte macrophage colony-stimulating factor and prior chemotherapy on the immunological response to a vaccine (ALVAC-CEA B7.1) in patients with metastatic carcinoma.

Granulocyte macrophage colony-stimulating factor (GM-CSF) has been shown to be an effective vaccine adjuvant because it enhances antigen processing and presentation by dendritic cells. ALVAC-CEA B7.1 is a canarypox virus encoding the gene for the tumor-associated antigen carcinoembryonic antigen (CEA) and for a T-cell costimulatory molecule, B7.1. After an initial dose escalation phase, this study evaluated vaccination with 4.5 x 10(8) plaque-forming units ALVAC-CEA B7.1 alone (n = 30) or with GM-CSF (n = 30) in patients with advanced CEA-expressing tumors to determine whether the addition of the adjuvant GM-CSF enhances induction of CEA-specific T-cells. Patients were vaccinated with vaccine intradermally every other week for 8 weeks. GM-CSF was given s.c. for 5 days beginning 2 days before vaccination. Patients with stable or responding disease after four immunizations received monthly boost injections alone or with GM-CSF. Biopsies of vaccine sites were obtained 48 h after vaccination to evaluate leukocytic infiltration and CEA expression. Induction of peripheral blood CEA-specific T-cell precursors was assessed in HLA-A2 positive patients by an ELISPOT assay looking for the production of IFN-gamma. Therapy was well tolerated. All of the patients had evidence of leukocytic infiltration and CEA expression in vaccine biopsy sites. In the patients receiving GM-CSF, leukocytic infiltrates were greater in cell number but were less likely to have a predominant lymphocytic infiltrate compared with patients receiving vaccine in the absence of the cytokine adjuvant. After four vaccinations, CEA-specific T-cell precursors were statistically increased in HLA-A2 positive patients who received vaccine alone. However, the GM-CSF plus vaccine cohort of HLA-A2 positive did not demonstrate a statistically significant increase in their CEA-specific T-cell precursor frequencies compared with baseline results. The number of prior chemotherapy regimens was negatively correlated with the generation of a T-cell response, whereas there was a positive correlation between the number of months from the last chemotherapy regimen and the T-cell response. ALVAC-CEA B7.1 is safe in patients with advanced, recurrent adenocarcinomas that express CEA, is associated with the induction of a CEA-specific T-cell response in patients treated with vaccine alone but not with vaccine and GM-CSF, and can lead to disease stabilization for up to 13 months.

Enhanced activation of human T cells via avipox vector-mediated hyperexpression of a triad of costimulatory molecules in human dendritic cells.

T-cell activation usually requires at least two signals. The first signal is antigen-specific, and the second signal(s) involves the interaction of a T-cell costimulatory molecule(s) on the antigen-presenting cell (APC) with its ligand on the T cell. Dendritic cells (DCs) are the most potent APCs, attributable, in part, to their expression of several T-cell costimulatory molecules. Human DCs generated in vitro, however, will vary in methods of generation and maturation and in terms of expression of different phenotypic markers-including costimulatory molecules-among different donors. We report here that a recombinant avipox (fowlpox, rF) vector has been constructed that can efficiently express the transgenes for three human T-cell costimulatory molecules (B7-1, ICAM-1, and LFA-3) as a result of individual early avipox promoters driving the expression of each transgene. This triad of costimulatory molecules (designated TRICOM) was selected because each has an individual ligand on T cells and each has been shown previously to prime a unique signaling pathway in T cells. We report here that rF-TRICOM can efficiently infect human DCs of different states of maturity and hyperexpress each of the three costimulatory molecules on the DC surface without affecting other DC phenotypic markers. Infection of influenza or human papilloma virus 9-mer peptide-pulsed DCs from different individuals, or at different stages of maturity with rF-TRICOM, resulted in enhanced activation of T cells from peripheral blood mononuclear cells of autologous donors after 24 h of incubation with DCS: This enhanced activation was analyzed by both titrating the peptide and differing the DC:effector cell ratios. No effect was observed using the control wild-type avipox vector. No increase in apoptosis was observed in T cells hyperstimulated with the TRICOM vector, and no decrease in interleukin-12 production was seen in lipopolysaccharide-stimulated DCs infected with rF-TRICOM. Antibody-blocking experiments demonstrated that enhanced T-cell activation by TRICOM was attributed to each of the three costimulatory molecules. Peptide-pulsed, rF-TRICOM-infected DCs were also shown to be more effective than peptide-pulsed DCs in activating T cells to 9-mer peptides derived from two relatively weak "self" immunogens, i.e., human prostate-specific antigen and human carcinoembryonic antigen. These studies thus demonstrate for the first time that a vector that can simultaneously hyperexpress three costimulatory molecules can be used to efficiently infect human DCs, leading to enhanced peptide-specific T-cell activation. The use of this approach for in vitro studies and clinical applications in immunotherapy is discussed.

Operant-self-administration of ethanol in mice prenatally exposed to cocaine.

Prenatal drug exposure may affect postnatal response to the reinforcing effects of a broad array of drugs. This study investigated the effects of prenatal cocaine exposure on operant self-administration of ethanol. Eighteen male, C57BL/6J mice were divided into three groups. The first had been prenatally exposed to 30 mg/kg of cocaine twice per day while the other groups were offspring of mothers which were either pair fed and saline intubated or untreated. Once adults, the mice were trained and subsequently tested for reinforcement from ethanol. The prenatal cocaine group responded less than the two control groups, with the largest decrease during a progressive ratio schedule of reinforcement. There were no differences in responding as a function of ethanol concentrations. These findings suggest that prenatal exposure to cocaine may not affect reinforcement per se, but may decrease motivation, drive state or propensity to work for ethanol.

Behavior-related changes in the activity of substantia nigra pars reticulata neurons in freely moving rats.

As one of the primary targets of the striatum, the substantia nigra pars reticulata (SNr) has been hypothesized to play a role in normal motor behavior. Specifically, inhibition of usually high, tonic SNr output is predicted to correlate with motor activation. While support for this has come primarily from electrophysiological studies in primates performing goal-directed movements, we tested this hypothesis in rats behaving in an open-field arena. SNr single-unit activity was recorded during spontaneous bouts of open-field behavior (e.g., head and body movements, locomotion) and after rats were given D-amphetamine (1.0 mg/kg, s.c.), which reliably increases motor activity and elevates the firing of motor-related striatal neurons. Prior to drug administration, SNr neurons had either regular, slightly irregular or irregular firing patterns when animals rested quietly. During movement, some inhibitions were observed, but the majority ( approximately 79%) of analyzed units increased firing by as much as 38%. Regardless of the predrug behavioral response of the cell, amphetamine strongly inhibited firing rate ( approximately 90% below nonmovement baseline) and changed firing pattern such that all cells fired irregularly. Subsequent injection with the dopamine antagonist haloperidol (1.0 mg/kg, s.c.) reversed amphetamine-induced inhibitions in all tested cells, which supports a role for dopamine in this effect. These results suggest that the pattern of striatal activity established by amphetamine, which may be critical for determining the drug-induced behavioral pattern, is represented in the SNr regardless of the predrug behavioral response of the cell.

Modulatory effects of ascorbate, alone or with haloperidol, on a lever-release conditioned avoidance response task.

Pretreatment with ascorbate, a modulator of dopamine transmission in the striatum, enhances the ability of haloperidol, a dopamine antagonist, to induce catalepsy and block the motor-activating effects of amphetamine. The present study extended this line of work to a lever-release version of the conditioned avoidance response (CAR) task, which is highly sensitive to changes in striatal dopamine. Adult male rats were trained to avoid footshock by releasing a lever within 500 ms of tone onset. Ascorbate (100 and 1000 mg/kg, IP) or vehicle was tested either alone or in conjunction with haloperidol (0.01 and 0.05 mg/kg, SC). Compared to vehicle pretreatment, 1000 mg/kg ascorbate alone or in combination with haloperidol impaired CAR performance by increasing avoidance latency. Latency to escape footshock was not impaired, ruling out a generalized motor deficit. In contrast, 100 mg/kg ascorbate alone or in combination with haloperidol had no consistent effects on CAR performance, even at a haloperidol dose (0.005 mg/kg, SC) known to potentiate dopamine transmission by preferentially blocking autoreceptors. Collectively, these results support an antidopaminergic action of ascorbate on striatal function, but suggest that this effect requires relatively high systemic doses.

Selective serotonin reuptake inhibitors: effects of chronic treatment on ethanol-reinforced behavior in mice.

Several lines of evidence suggest that aspects of ethanol drinking are mediated, at least in part, by serotonergic (5-HT) neurotransmitter systems. Ethanol-preferring animals show decreases in serotonin function and receptor densities. In addition, serotonin uptake inhibitors have been shown to decrease ethanol consumption in animal models and in humans. However, the time course of these effects and their duration remain undetermined. In the present studies, C57BL/6J male mice were treated with one of three selective 5-HT reuptake inhibitors (SSRIs): fluoxetine, sertraline, or paroxetine. All three drugs produced initial decreases in operant lever pressing behavior for ethanol followed by a return to baseline on subsequent days. Immediately following 14 days of this initial treatment, subsequent treatment with higher SSRI doses was ineffective in decreasing ethanol-reinforced behavior. However, after a several week "washout period," SSRI pretreatment again produced an initial decrease in responding for ethanol, again followed by a return to baseline. Thus, suppression of ethanol drinking may be related to immediate changes in 5-HT function following treatment with SSRIs, and tolerance to this effect appears to develop rapidly.