Gender differences in learned helplessness behavior are influenced by genetic background

Learned helplessness behavior was examined in female and male C57BL/6J (B6), 129/J (129) and (B6 x 129)F1 mice, common genetic backgrounds for the generation of knockout models, as well as in mice of a mixed genetic background (outbred mice). Both genotype and gender differences were observed in learned helplessness. Outbred males showed increased shuttle escape latencies following 60, 120, or 360 inescapable shocks compared to nonshocked controls, but outbred females showed no increase in escape latencies following inescapable shock pretreatment. B6 females showed increased escape latencies following 60, 120, or 360 inescapable shocks, whereas B6 males showed increased latencies only after 360 shocks. Female and male 129 and B6129F1 mice did not show an increase in escape latencies following inescapable shock, but this was most likely due to poor escape performance in nonshocked control mice. Differences in escape performance could not be explained by differences in pain thresholds between genotypes. These results support the idea that genetic background and gender are important to consider when using the learned helplessness model in genetically manipulated mice.

Effects of repeated nicotine administration and footshock stress on rat mesoprefrontal dopamine systems: Evidence for opioid mechanisms

We have examined the effects of nicotine pre-treatment on mesoprefrontal dopamine (DA) function in the presence and absence of acute stress, and the involvement of endogenous opiate peptide systems (EOPS). Acute electrical footshock stress preferentially increases DA utilization in medial prefrontal cortex (mPFC) compared to nucleus accumbens (NAS) and striatal terminal fields, and this is correlated with profound locomotor immobility. Our recent studies have demonstrated that repeated, but not acute, nicotine pre-treatment significantly reduced mPFC DA utilization and footshock stress-induced immobility responses. There is increasing evidence that the biochemical and behavioral effects of nicotine are mediated by EOPS, and we hypothesized that the stress-reducing effects of repeated nicotine administration in these studies were mediated by EOPS. Accordingly, rats pre-treated subcutaneously with repeated nicotine were given a single dose of the opiate receptor antagonist naloxone (0.1-10.0 mg/kg, i.p.) or saline as a co-treatment with nicotine or saline 10 min prior to acute footshock stress. Naloxone had no effects on non-stressed or acute footshock stress-induced mPFC DA utilization, but dose-dependently antagonized repeated nicotine's attenuation of stress-induced mesoprefrontal DA utilization and immobility responses. Furthermore, naloxone dose-dependently blocked repeated nicotine's augmentation of accumbal DA utilization. These results suggest that EOPS may be involved in mediating repeated nicotine administration effects on mesoprefrontal dopaminergic and immobility responses to acute footshock stress.

Disulfiram versus placebo for cocaine dependence in buprenorphine-maintained subjects: a preliminary trial

BACKGROUND

We examined the effects of disulfiram versus placebo on cocaine dependence in buprenorphine-maintained subjects.

METHODS

Opioid and cocaine dependent subjects (n = 20) were induced onto buprenorphine maintenance, then randomized to disulfiram (250 mg q.d. ; n = 11) or placebo (n = 9) treatment for 12 weeks.

RESULTS

Groups were comparable at baseline on demographic measures and on baseline measures of drug-use severity. Fifteen subjects completed the study, including 8 subjects randomized to disulfiram (72.7%) and 7 subjects randomized to placebo (77.8%). The total number of weeks abstinent from cocaine was significantly greater on disulfiram versus placebo (mean +/- SD: 7.8 +/- 2.6 vs. 3.3 +/- 0.5, p <.05) and the number of days to achieving 3 weeks (24.6 +/- 15.1 vs. 57.8 +/- 7.7, p <.01) of continuous cocaine abstinence was significantly lower in disulfiram compared with placebo. The number of cocaine-negative urine tests during the trial were also higher on disulfiram (14.7) than on placebo (8.6); furthermore, subjects in the disulfiram group achieved consistently higher rates of cocaine-negative urine tests in each 3-week interval and the increase over time was faster in the disulfiram compared with placebo.

CONCLUSIONS

This preliminary study suggests the potential efficacy of disulfiram versus placebo for treatment of cocaine dependence in buprenorphine-maintained patients.

Effects of repeated nicotine pre-treatment on mesoprefrontal dopaminergic and behavioral responses to acute footshock stress

The effects of acute and repeated nicotine administration on the stress response of rat mesoprefrontal dopaminergic pathways were examined. Rats were given daily injections of nicotine (0.15 or 0.60 mg/kg, s.c., freebase) or saline for 4 days, then challenged with either nicotine or saline. A regimen of inescapable electrical footshocks or no footshocks was then administered. Thirty minutes after final injection, rats were sacrificed, brains removed and dopamine (DA) and its metabolite dihydroxy-O-phenylacetic acid (DOPAC) were extracted from medial prefrontal cortex (mPFC), nucleus accumbens septi (NAS) and dorsolateral striatum and quantified by high performance liquid chromatography with electrochemical detection. Acute administration of low dose nicotine (0.15 mg/kg) produced an increase in DA utilization (increased DOPAC/DA ratio) in mPFC and NAS, but not striatum. High dose nicotine (0.60 mg/kg) produced activation in NAS, but not mPFC or striatum. Repeated low dose nicotine pre-treatment produced tolerance to the effects of nicotine challenge in the mPFC, and reduced its effects in NAS. Footshock stress preferentially increased DA utilization in mPFC and associated footshock stress-induced immobility responses, and these were reduced by low, but not high, dose repeated nicotine pre-treatment. Further, a single dose of the nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine (MCA) 30 min prior to nicotine challenge dose-dependently blocked the reduction of mesoprefrontal DA stress responsivity and immobility responses produced by repeated nicotine pre-treatment. These results indicate that: (1) there are dose-dependent differential effects of acute and repeated nicotine pre-exposure on regional DA utilization; (2) low, but not high, dose repeated nicotine reduces both the mesoprefrontal DA and behavioral effects of acute footshock stress; and (3) these effects of repeated nicotine may depend on mecamylamine-sensitive nAChR stimulation. These results may have relevance to acute stress and nicotine dependence, particularly in schizophrenic disorders, which have high prevalence rates of co-morbid nicotine dependence, stress-induced symptom exacerbation and prefrontal cortical dysfunction.

Schizophrenia and nicotine use: report of a pilot smoking cessation program and review of neurobiological and clinical issues

Nicotine use is a major public health problem that increases medical morbidity and mortality. Nicotine's action and the pathobiology of schizophrenic disorders have common neurobiological substrates. Tobacco smoking alters medication blood levels and effectiveness, modifies psychiatric symptoms, and is a clue for other substance abuse. This article presents an evaluation of a smoking cessation program for 24 smokers with schizophrenia. Fifty percent completed the program, 40 percent decreased use by 50 percent, and 13 percent remained abstinent (carbon monoxide verified) for 6 months. Nicotine replacement, motivational enhancement therapy, and relapse prevention behavioral therapy were important components of treatment. Pharmacotherapy strategies of a higher-dose nicotine patch, combining nicotine gum and a patch, and augmentation medication to nicotine replacement should be evaluated in future studies in this population.

Effects of clozapine on smoking in chronic schizophrenic outpatients

BACKGROUND

The effects of clozapine administration on smoking were examined in chronic schizophrenic outpatients.

METHOD

Twenty-nine of 30 schizophrenic outpatients enrolled in a university-affiliated Community Mental Health Center clozapine clinic were retrospectively surveyed by semistructured questionnaire regarding smoking before and after clozapine administration.

RESULTS

Smokers comprised 62% (N = 18) of patients, and within this group, there was a significant decrease in reported daily cigarette use during clozapine treatment compared with level of use when patients had been treated with typical neuroleptics (1.67 +/- 1.13 vs. 1.26 +/- 0.72 packs/day, p = .025).

CONCLUSION

Clozapine may alter smoking behaviors in chronic schizophrenics.

Inhibition of phosphatidylcholine and phosphatidylethanolamine biosynthesis by cytochalasin B in cultured glioma cells: potential regulation of biosynthesis by Ca(2+)-dependent mechanisms

The major route of phosphatidylcholine (PtdCho) biosynthesis in mammalian cells is the sequence: choline (Cho)----phosphocholine (PCho)----cytidinediphosphate choline (CDP-Cho)----PtdCho. Recently, we have found that intermediates of this pathway are not freely diffusible in cultured rat glioma (C6) cells but are channeled towards PtdCho biosynthesis (George et al. (1989). Biochim. Biophys. Acta. 1004, 283-291). Channeling of intermediates in other mammalian systems is thought to be mediated through adsorption of enzymes to membranes and cytoskeletal elements to form multienzyme complexes. In this study, agents which perturb the structure and function of cytoskeletal elements were tested for effects on phospholipid metabolism in glioma cells. The filament-disrupting agent cytochalasin B (CB), but not other cytochalasins or the microtubule depolymerizer colchicine inhibited PtdCho and phosphatidylethanolamine (PtdEtn) biosynthesis as judged by dose-dependent reduction of labeling from [3H]Cho and [14C]ethanolamine (Etn). 32Pi pulse-labeling indicated that CB selectively decreased PtdCho and PtdEtn biosynthesis without affecting synthesis of other phospholipids. Synthesis of water-soluble intermediates of PtdCho metabolism was unaffected but the conversion of phosphoethanolamine to CDP-ethanolamine was reduced by CB. Effects of CB on phospholipid biosynthesis were not due to inhibition of glucose uptake as shown by experiments with 2-deoxyglucose, glucose-starved cells and other cytochalasins. Experiments with Ca(2+)-EGTA buffers and digitonin-permeabilized cells, and the Ca(2+)-channel blocker verapamil suggest that effects of CB on PtdCho and PtdEtn biosynthesis are due to alteration of intracellular Ca2+. Taken together, these results suggest that CB acts at sites distinct from glucose transport and cellular microfilaments to specifically inhibit PtdCho and PtdEtn biosynthesis by mechanisms dependent on intracellular Ca2+.

Channeling of intermediates in the CDP-choline pathway of phosphatidylcholine biosynthesis in cultured glioma cells is dependent on intracellular Ca2+

The major route of phosphatidylcholine (Ptd-choline) biosynthesis in mammalian cells is the CDP-choline pathway which involves stepwise conversion of choline to phosphocholine (P-choline), cytidine diphosphate choline (CDP-choline), and Ptd-choline. Our previous studies with electropermeabilized (EP) rat glioma (C6) cells have indicated that the intermediates of this pathway are not freely diffusible in the cell but are channeled toward synthesis of Ptd-choline (George, T.P., Morash, S.C., Cook, H.W., Byers, D.M., Palmer, F. B. St.C., and Spence, M.W. (1989) Biochim. Biophys. Acta 1004, 283-291). In this study, Ca(2+)-[ethylene-bis(oxyethylenenitrilo)]tetraacetic acid buffers were used to investigate the role of intracellular free Ca2+ levels in functional organization of this pathway in EP glioma cells. In EP cells reduction of free Ca2+ in the medium from 1.8 mM to less than 200 nM resulted in 2-3-fold stimulation of exogenous [3H]choline and [14C]P-choline incorporation into Ptd-choline whereas incorporation of exogenous CDP-[14C]choline was augmented 100-fold; there was no uptake or incorporation of labeled P-choline or CDP-choline in intact cells. In EP cells incubated at 1.8 mM Ca2+ the water-soluble products of choline metabolism (choline, P-choline, CDP-choline, and glycerophosphocholine) were retained at 37 degrees C; in contrast, in the presence of 100 nM Ca2+ there was uniform leakage of these metabolites. Experiments with hemicholinium-3, an inhibitor of choline transport, and EP cells at 100 nM Ca2+ show that linkage of choline transport and Ptd-choline biosynthesis is also dependent on Ca2+. These results suggest that channeling of intermediates in the CDP-choline pathway of Ptd-choline biosynthesis in glioma cells is mediated by intracellular Ca2+ levels that may coordinately regulate the steps involved in conversion of choline to Ptd-choline.

Phosphatidylcholine biosynthesis in cultured glioma cells: evidence for channeling of intermediates

The major pathway of choline (Cho) incorporation into phosphatidylcholine (PtdCho) in mammalian cells is sequential conversion of Cho to phosphocholine (PCho), cytidinediphosphate choline (CDP-Cho) and PtdCho. In intact cells, this sequence is usually demonstrated using radiolabeled Cho since PCho and CDP-Cho do not enter the cell intact. We have studied the incorporation of radiolabeled Cho, PCho and CDP-Cho into rat glioma (C6) cells following electropermeabilization. C6 cells were permeable as judged by [U-14C]sucrose and Erythrosin B uptake and more rapid incorporation of [1,2,3-3H]glycerol into cell lipids, and viable as assessed by uptake and incorporation of [methyl-3H]Cho, [1-14C]oleate and [1,2,3-3H]glycerol into complex lipids. Despite rapid incorporation of [methyl-3H]Cho into PtdCho in permeabilized cells, there was no incorporation of [methyl-14C]PCho or CDP-[methyl-14C]Cho into PtdCho. PCho (300 microM) and CDP-Cho (300 microM) failed to significantly reduce incorporation of 28 microM [methyl-3H]Cho into PtdCho. Radioactivity in PtdCho of cells prelabeled with [methyl-3H]Cho prior to permeabilization could be chased with 4 mM Cho but not with 4 mM PCho or 4 mM CDP-Cho. The water-soluble products of Cho metabolism--PCho, CDP-Cho and glycerophosphocholine--were retained at 37 degrees C in permeabilized cells compared with controls while there was uniform leakage from permeabilized cells at 4 degrees C. Hemicholinium-3, an inhibitor of high-affinity Cho transport, decreased [methyl-3H]Cho incorporation into PtdCho in permeabilized cells, as in controls, suggesting that even in permeabilized cells, Cho incorporation into PtdCho is linked to the transport system. We propose that individual steps of the cytidine pathway of PtdCho biosynthesis are functionally linked and that reaction intermediates are not freely diffusible within the cell but are channeled to PtdCho biosynthesis.