Unique prefrontal GABA and glutamate disturbances in co-occurring bipolar disorder and alcohol dependence

Bipolar disorder (BD) and alcohol dependence (AD) frequently co-occur, and co-occurring BD and AD are associated with devastating public health costs. Minimal neurobiological research exists to guide the development of effective treatments for this treatment-resistant population. We believe the present study represents the first investigation of prefrontal gamma-aminobutyric acid (GABA) and glutamate levels in co-occurring BD and current AD. The participants were 78 individuals who met DSM-IV criteria for BD I/II and current AD (n=20), BD I/II alone (n=19), current AD alone (n=20) or no diagnosis (n=19). The participants completed a baseline diagnostic visit, then returned approximately 4 days later for a two-dimensional J-resolved proton magnetic resonance spectroscopy (¹H-MRS) acquisition in dorsal anterior cingulate cortex (dACC). All participants were required to demonstrate ⩾1 week of abstinence from alcohol/drugs via serial biomarker testing before ¹H-MRS. A 2 × 2 factorial analysis of variance of cerebrospinal fluid (CSF)-corrected GABA/water concentrations demonstrated a significant BD × AD interaction (F=2.91, P<0.05), signifying uniquely low levels of GABA in BD+AD; this effect doubled when the sample was restricted to individuals who consumed alcohol within 2 weeks of ¹H-MRS. There were no overall effects of BD/AD on CSF-corrected glutamate/water levels. However, the BD × AD interaction, signifying uniquely low levels of glutamate in BD+AD, approached statistical significance (F=3.83, P=0.06) in individuals who consumed alcohol within 2 weeks of ¹H-MRS. The dACC GABA levels were significantly, negatively associated with Barratt Impulsiveness Scale (r=-0.28, P=0.02) and Obsessive Compulsive Drinking Scale (r=-0.35, P<0.01) scores. If replicated, these results may suggest that future treatment studies should preferentially evaluate therapeutics in BD+AD known to increase prefrontal GABA and glutamate levels.

Evidence for the continuous latent structure of mania and depression in out-patients with bipolar disorder: results from the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD)

BACKGROUND

Evidence supporting the continuous latent structure of mood phenomena has not been incorporated into psychiatric diagnostic systems, in part because the evidence has been incomplete. For example, no studies have investigated the boundary between 'sick' and 'well' periods in individuals with bipolar disorder, despite agreement that characterization of mood disorders as having a discrete episodic course is inaccurate. The present study examined the validity of mood episode symptom thresholds in out-patients with bipolar disorder using multiple methodologies: taxometrics and information-theoretic latent distribution modeling (ITLDM), to evaluate the continuity/discontinuity of mood symptoms; and structural equation mixture modeling (SEMM), to evaluate the continuity/discontinuity of associations between mood symptoms and general functioning.

METHOD

A total of 3721 out-patients with bipolar disorder from the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD) were available for analysis. Data were collected at participants' baseline STEP-BD visit. Taxometric [maximum covariance/means above minus below a cut (MAXCOV/MAMBAC) with simulated comparison data], ITLDM and SEMM methods were applied twice, once to the Montgomery-Åsberg Depression Rating Scale and again to the Young Mania Rating Scale.

RESULTS

Taxometric results unequivocally supported a continuous interpretation of the data. ITLDM results favored many valued 'discrete metrical' models, suggesting that mood symptoms have continuous, but potentially non-normally distributed, latent structures in out-patients with bipolar disorder. Finally, SEMM results demonstrated that latent associations between mood symptoms and general functioning were linear.

CONCLUSIONS

Results from the present study argue against the validity of DSM mood episode thresholds and argue for a graded continuum of care of bipolar symptom management.

The impact of clinical and demographic variables on cognitive performance in methamphetamine-dependent individuals in rural South Carolina

Inconsistencies in reports on methamphetamine (METH) associated cognitive dysfunction may be attributed, at least in part, to the diversity of study sample features (eg, clinical and demographic characteristics). The current study assessed cognitive function in a METH-dependent population from rural South Carolina, and the impact of demographic and clinical characteristics on performance. Seventy-one male (28.2%) and female (71.8%) METH-dependent subjects were administered a battery of neurocognitive tests including the Test of Memory Malingering (TOMM), Shipley Institute of Living Scale, Paced Auditory Serial Addition Test (PASAT), Symbol Digit Modalities Test (SDMT), Grooved Pegboard Test, California Verbal Learning Test (CVLT), and Wisconsin Card Sorting Test (WCST). Demographic and clinical characteristics (eg, gender, frequency of METH use) were examined as predictors of performance. Subjects scored significantly lower than expected on one test of attention and one of fine motor function, but performed adequately on all other tests. There were no predictors of performance on attention; however, more frequent METH use was associated with better performance for males and worse for females on fine motor skills. The METH-dependent individuals in this population exhibit very limited cognitive impairment. The marked differences in education, Intellectual Quotient (IQ), and gender in our sample when compared to the published literature may contribute to these findings. Characterization of the impact of clinical and/or demographic features on cognitive deficits could be important in guiding the development of treatment interventions.

Suppression of c-fos induction in the nucleus accumbens prevents acquisition but not expression of morphine-conditioned place preference

The c-fos immediate-early gene is induced by morphine and other drugs of abuse in the nucleus accumbens (NAc), a mesolimbic region implicated in drug abuse and reward. This study examined the role of c-fos in the acquisition and expression of the conditioned place paradigm (CPP) in the rat by suppressing Fos protein expression with c-fos antisense oligodeoxynucleotides (ODNs). CPP was completely prevented by c-fos antisense ODN infused bilaterally into the NAc prior to each systemic morphine injection, whereas sense and missense NAc injections had no effect on CPP. NAc administration of c-fos antisense ODN after the last systemic morphine conditioning session did not affect the expression of morphine-CPP. These results suggest that c-fos expression in NAc is necessary for the acquisition but not expression of morphine-CPP, and they have important implications for understanding conditioned behaviours and drug craving and addiction.

Bilateral blockade of NMDA receptors in anterior thalamus by dizocilpine (MK-801) injures pyramidal neurons in rat retrosplenial cortex

Non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists, ketamine, phencyclidine (PCP) and dizocilpine (MK-801), produce psychosis in people. In rodents they produce cytoplasmic vacuoles in injured retrosplenial cortical neurons that express HSP70 heat shock protein. This study examined possible circuits and receptors that mediate this neuronal injury. Bilateral, but not unilateral, injection of dizocilpine (5, 10, 15, 20 microg/microL per side) into the anterior thalamus induced HSP70 protein in pyramidal neurons in deep layer III of rat retrosplenial cortex 24 h later. In contrast, bilateral dizocilpine injections (5, 10, 15, 20 microg/microL per side) into the retrosplenial cortex or into the diagonal band of Broca did not induce HSP70. Bilateral injections of muscimol (0.1, 1, 10 microg/microL per side), a GABAA (gamma-aminobutyric acid) agonist, into the anterior thalamus blocked HSP70 induction in the retrosplenial cortex produced by systemic dizocilpine (1 mg/kg). Bilateral thalamic injections of baclofen (0.1, 1, 10 microg/microL per side), a GABAB agonist, were ineffective. Anterograde tracer studies confirmed that neurons in the anterior thalamus project to superficial layer III of the retrosplenial cortex where the dendrites of HSP70-immunostained neurons in deep layer III reside. Bilateral blockade of NMDA receptors on GABA neurons in the reticular nuclei of the thalamus is proposed to decrease GABA neuronal firing, decrease GABA release and decrease activation of GABAA receptors. This activates thalamic projection neurons that damage retrosplenial cortical neurons presumably via unblocked cortical glutamate alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) and kainate receptors. The increases of blood flow that occur in the thalamus and retrosplenial cortex of people that have psychosis produced by NMDA antagonists could be related to thalamic excitation of the retrosplenial cortex produced by these drugs.

Behavioral and neurochemical effects of the dopamine transporter ligand 4-chlorobenztropine alone and in combination with cocaine in vivo

The current studies evaluated the novel diphenylmethoxytropane analog 4-chlorobenztropine (4-Cl-BZT), cocaine, and combinations of the two drugs for their abilities to stimulate locomotor activity, produce cocaine-like discriminative stimulus effects, and elevate extracellular dopamine (DA) in the nucleus accumbens (NAc) as measured by in vivo microdialysis. Peripherally administered cocaine was approximately twice as efficacious as 4-Cl-BZT as a locomotor stimulant and was behaviorally active at a lower dose than was 4-Cl-BZT. Cocaine also was more efficacious than 4-Cl-BZT in producing discriminative-stimulus effects in rats trained to discriminate i.p. injections of 10 mg/kg cocaine from saline. The time course of behavioral activation differed markedly between the two drugs, with much shorter onset and duration of locomotor stimulant effects for cocaine relative to 4-Cl-BZT. Similarly, i.p. cocaine (10 and 40 mg/kg) induced a pronounced, rapid, and short-lived increase in DA in the NAc, whereas i.p. 4-Cl-BZT was effective only at the higher dose and produced a more gradual, modest, and sustained (>/=2 h) elevation in accumbens DA. In contrast to i.p. administration, local infusion of 4-Cl-BZT (1-100 microM) into the NAc through the microdialysis probe elevated extracellular DA to a much greater extent than did local cocaine (nearly 2000% of baseline maximally for 4-Cl-BZT versus 400% of baseline for cocaine) and displayed a much longer duration of action than cocaine. However, when microinjected bilaterally into the NAc at 30 or 300 nmol/side, cocaine remained a more efficacious locomotor stimulant than 4-Cl-BZT. Finally, pretreatment with i.p. 4-Cl-BZT dose dependently enhanced the locomotor stimulant, discriminative stimulus effects, and NAc DA response to a subsequent low-dose i.p. cocaine challenge. The diphenylmethoxytropane analog also facilitated the emergence of stereotyped behavior and convulsions induced by high-dose cocaine. The current results demonstrate that DA transporter ligands that do not share the neurochemical and behavioral profiles of cocaine nevertheless may enhance the effects of cocaine in vivo.

Necessary role for ventral tegmental area adenylate cyclase and protein kinase A in induction of behavioral sensitization to intraventral tegmental area amphetamine

In the present study, we investigated the effects of selective activation or inhibition of ventral tegmental area (VTA) adenylate cyclase (AC) and protein kinase A (PKA) on long-term sensitization induced by repeated intra-VTA or peripheral amphetamine (AMPH). Selective inhibition of AC by SQ 22,536 (9-(tetrahydro-2-furanyl)-9H-purin-6-amine; 100 nmol/side bilateral into VTA) had no effect on acute basal locomotion but attenuated the locomotor stimulation induced by acute i.p. AMPH (1.5 mg/kg). Coinjection of SQ 22,536 (100 nmol/side) fully blocked the sensitization induced by repeated intra-VTA AMPH (15 nmol/side) but had no detectable effect on the sensitization induced by repeated i. p. AMPH. Persistent activation of AC by intra-VTA cholera toxin (500 ng/side) modestly increased acute locomotion and induced a robust sensitization to i.p. AMPH challenge 10 days after the last of three repeated VTA microinjections. Selective inhibition of PKA by Rp-adenosine-3',5'-cyclic monophosphothioate triethylamine (Rp-cAMPS; 25 nmol/side) had no effect on acute basal or AMPH-stimulated locomotion. Coinjection of Rp-cAMPS (25 nmol/side) fully blocked the sensitization induced by repeated intra-VTA AMPH but had no effect on sensitization induced by repeated i.p. AMPH. Intra-VTA microinjection of the selective PKA activator Sp-adenosine-3',5'-cyclic monophosphothioate triethylamine (Sp-cAMPS; 25-100 nmol/side) dose-dependently stimulated acute locomotion and exerted synergistic effects on locomotor activity when coinfused into the VTA with AMPH but had no detectable effect on acute i.p. AMPH-induced locomotion. Repeated intra-VTA Sp-cAMPS did not induce sensitization to AMPH challenge but potentiated the sensitization induced by repeated i.p. AMPH. These results suggest that VTA cAMP signal transduction is necessary for the induction of persistent sensitization to intra-VTA amphetamine and that peripheral and intra-VTA AMPH may not induce behavioral sensitization by identical mechanisms.

Partial reversal of stress-induced behavioral sensitization to amphetamine following metyrapone treatment

Several studies indicate that blockade of stress-induced corticosterone secretion prevents the development of stress-induced sensitization to the behavioral effects of stimulants. The present study examined whether chronic blockade of corticosterone synthesis with metyrapone could reverse stress-induced amphetamine sensitization in rats. Restraint stress in cylindrical chambers, 2 times 30 min/day for 5 days over an 8-day schedule, was used as the stressor. Following completion of the stress protocol, animals were cannulated with microdialysis guide cannulae over the nucleus accumbens, and then treated with either metyrapone (50 mg/kg, i.p.) or vehicle (1 ml/kg) for 7 days. On the seventh day, animals were implanted with microdialysis probes in the nucleus accumbens, and on the following day, all animals were tested for their locomotor, stereotypy, and nucleus accumbens dopamine and DOPAC release responses to an injection of saline followed 60 min later by d-amphetamine (1.5 mg/kg, i.p.). Neither stress or metyrapone treatment had an effect on the behavioral or dopamine release response to saline. However, amphetamine-stimulated locomotion and stereotypy were strongly enhanced, while amphetamine-stimulated dopamine release response was slightly enhanced (significant only by drug x time interaction), in stressed animals. Metyrapone treatment reduced the stress-induced increase in the locomotor, but not stereotypy, response to amphetamine. In contrast, the dopamine release response to amphetamine was enhanced in metyrapone-treated animals, in both stressed and non-stressed groups, while DOPAC levels were unaffected by treatment group. This augmentation was particularly evident in the stressed-metyrapone-treated animals. Furthermore, non-stressed animals showed an increased locomotor and stereotypy response to amphetamine after treatment with metyrapone. These findings indicate that metyrapone treatment can reverse, or inhibit the expression of, stress-induced sensitization to the behavioral effects of amphetamine. However, the ability of metyrapone treatment to enhance the behavioral (in non-stressed animals) and dopamine release (in non-stressed and stressed animals) responses to amphetamine indicate that chronic metyrapone treatment will produce stimulant sensitization when given alone.

Evidence for dissociable mechanisms of amphetamine- and stress-induced behavioral sensitization: effects of MK-801 and haloperidol pretreatment

The present study examined the ability of pretreatment with MK-801 or haloperidol to block the induction of behavioral sensitization to amphetamine challenge by repeated immobilization stress in male Sprague-Dawley rats. Fifteen minutes before each of ten 30-min restraint sessions, rats were administered saline, MK-801 (0.01, 0.10 or 0.25 mg/kg i.p.) or haloperidol (0.10 or 0.25 mg/kg i.p.). Control rats received the same injection regimen without restraint. An additional experiment examined the ability of MK-801 to block the induction of sensitization by repeated d-amphetamine. In this experiment, rats were administered saline or MK-801 (0.25 mg/kg i.p.) 15 min before each of ten amphetamine injections (1.0 mg/kg i.p., administered under the same regimen as immobilization stress). Four days after the final immobilization or amphetamine injection, rats were tested for locomotor response to novelty, saline and d-amphetamine (1.5 mg/kg i.p.). Exposure to repeated immobilization stress significantly enhanced the locomotor response to amphetamine challenge but not to saline challenge whether rats were pretreated with saline, MK-801 or haloperidol. Secondary analysis of dose effects in each pretreatment group revealed that at 0.25 mg/kg, repeated MK-801 in itself induced sensitization to the response to amphetamine in control rats and potentiated stress-induced sensitization in restrained rats. In contrast, the sensitization induced by repeated amphetamine was attenuated by MK-801 pretreatment. Neither dose of haloperidol affected the locomotor response to saline or amphetamine in control or stressed rats. These results indicate that the effects of MK-801 on the induction of sensitization are complex and suggest that amphetamine- and stress-induced behavioral sensitization may arise through different mechanisms.

Evidence for involvement of ventral tegmental area cyclic AMP systems in behavioral sensitization to psychostimulants

The present study investigated the role of ventral tegmental area (VTA) cyclic AMP (cAMP) systems in the behavioral sensitivity to psychostimulants in male Sprague-Dawley rats. Bilateral microinjections of cholera toxin (CTX) into the VTA (50-500 ng/500 nl/side) dose-dependently sensitized animals to the locomotor stimulant effects of systemic d-amphetamine, cocaine and apomorphine, but were without effects on morphine-induced locomotion 24 hr after microinjection. The CTX-induced behavioral sensitization to amphetamine was even greater 72 hr after microinjection, but was no longer present 14 days after intra-VTA CTX pretreatment. Coadministration of the cAMP-dependent protein kinase inhibitor H8 into the VTA blocked CTX-induced sensitization to amphetamine, suggesting that the sensitization is dependent on phosphorylation events in the VTA mediated by cAMP-dependent protein kinase. Pretreatment with CTX did not enhance amphetamine-induced dopamine release in the nucleus accumbens relative to saline controls 24 hr after microinjection. A single bilateral injection of d-amphetamine into the VTA (5 micrograms/side) produced a significant sensitization to systemic amphetamine challenge 72 hr later, and this effect was also blocked by coadministration of H8 into the VTA. These results extend previous studies which have established the importance of the VTA in the development of behavioral sensitization and suggest that cAMP systems may play a crucial role in this neuroadaptive process.

Evidence for the involvement of phospholipase A2 mechanisms in the development of stimulant sensitization

Evidence suggests that phospholipase A2 (PLA2) activation is involved in numerous neuroplastic phenomena, including long-term potentiation. Considering the pharmacological similarities between long-term potentiation and stimulant sensitization, it seems possible that PLA2 inhibition activity also might have a role in the induction of stimulant sensitization. In this study, we have investigated whether PLA2 inhibition, by quinacrine, has any effects on stimulant-induced behavioral sensitization. Both locomotor and stereotypic behavioral sensitization were dose-dependently blocked in rats pretreated with quinacrine (8-25 mg/kg i.p.) 15 min before cocaine (30 mg/kg i.p.), when tested with cocaine (15 mg/kg i.p) 72 hr later. Similar results also were found with d-amphetamine (2 mg/kg i.p.) sensitization using a 10-day treatment regimen with testing on day 11. The ability of PLA2 activation, by melittin, to produce cocaine sensitization also was tested. Local injections of melittin (0.1 microgram/0.4 microliter) into the ventral tegmental area sensitized the subsequent stimulation of locomotor activity, stereotypy and nucleus accumbens dopamine release by cocaine, when tested 72 hr later. Local injections of melittin (0.1-1.0 microgram/0.8 microliter) into the nucleus accumbens had a moderate sensitizing effect on locomotion. Quinacrine (16 mg/kg) pretreatment 45 min before intraventral tegmental area melittin injection significantly decreased melittin-induced sensitization of the locomotor and stereotypy response to cocaine. These results indicate that PLA2 activation may play a role in the induction of stimulant sensitization. It is proposed that PLA2 activity in mesolimbic dopamine neurons, at the level of the cell bodies and perhaps the nerve terminals, is involved in the biochemical mechanisms mediating the development of stimulant sensitization.

Locomotor stimulant effects of cocaine and novel cocaine analogs in DBA/2J and C57BL/6J inbred mice

The current study compared the potencies of cocaine and a series of substituted phenyltropane analogs of cocaine in stimulating locomotor activity in two genetically distinct strains of mice previously shown to differ in their locomotor responsiveness to cocaine. In addition, these compounds were compared for their abilities to induce stereotyped behaviors in naive and cocaine-pretreated mice. All of the analogs tested were more potent locomotor stimulants than cocaine in both strains. Interstrain differences in the locomotor stimulant efficacy of RTI-31 and RTI-98 parallel those of cocaine, with DBA/2J mice being stimulated to a greater extent than C57BL/6J mice at maximally active doses. Significant differences exist in the onset and duration of action among cocaine and several analogs. Whereas the action of cocaine peaks in the first 10 min after injection and thereafter rapidly declines, the stimulant effects of RTI-31, RTI-98, and RTI-113 are maximal at 30-40 min and remain consistent through 60 min postinjection. The current results are discussed in the context of previously published reports of genotype-dependent differences in behavioral responsiveness to cocaine in the DBA/2J and C57BL/6J strains.

Genetic analysis of sensitization and tolerance to cocaine

The present study investigated the effects of acute and repeated administration of cocaine (1.0-56.0 mg/kg) on locomotor activity in the genetically distinct DBA/2J and C57BL/6J inbred strains of mice. In addition, quantitative trait loci analysis of the effects of acute and repeated cocaine in 16 BXD recombinant inbred strains was used to provisionally detect and map minor gene loci which associate with cocaine responsiveness. Whereas locomotor activity was elevated maximally in both strains by 32 mg/kg of cocaine, DBA/2J mice were stimulated to a much greater extent than C57BL/6J mice. The stimulant effects of cocaine were diminished to control levels in DBA/2J mice after repeated daily injections, whereas cocaine-induced locomotion remained consistent in C57BL/6J mice throughout the 7-day testing period. Emergence of stereotyped behavior with repeated daily injections of 32 mg/kg of cocaine was observed in DBA/2J but not C57BL/6J mice. No differences in brain cocaine levels were found between the DBA/2J and C57BL/6J strains after acute or repeated injections. Quantitative trait loci analysis indicated significant associations of differences in cocaine responsiveness with marker loci on several chromosomes in the BXD recombinant inbred series. Those marker loci associated with the acute cocaine response were in most cases different from those markers associated with long-term responses. The current results demonstrate that genotype-dependent variation exists in behavioral responsiveness to cocaine in mice and suggest that the acute and long-term responses to cocaine may be under the control of separate sets of genes.

Comparison of cocaine and GBR 12935: effects on locomotor activity and stereotypy in two inbred mouse strains

The current study compares the acute and long-term effects of GBR 12935 and cocaine on locomotor activity and stereotypy in two genetically distinct strains of mice. Although cocaine stimulated locomotor activity maximally in both strains at 32 mg/kg, a single injection of cocaine stimulated locomotion to a greater degree in DBA/2J mice than in C57BL/6J mice. In contrast, GBR 12935 elevated locomotion to a greater extent in C57BL/6J mice at the maximally active dose of 10 mg/kg. The stimulant effects of cocaine diminished to near control levels in DBA/2J mice upon repeated injections, whereas cocaine-induced locomotion remained relatively consistent in C57BL/6J mice. Locomotor stimulation by GBR 12935 remained consistent in both strains with repeated injections. DBA/2J mice became sensitized to cocaine-induced stereotypy with repeated injections. Cocaine induced no stereotypy in C57BL/6J mice on any test day. No stereotypies were induced by GBR 12935 in either strain on any test day. Moreover, no cross-sensitization between cocaine and GBR 12935 was observed. These results demonstrate differences in the behavioral effects of two dopamine uptake inhibitors, and suggest that genetically controlled factors other than dopamine uptake inhibition contribute to the acute and adaptive behavioral responses to cocaine.

Sensitization to stereotypy in DBA/2J but not C57BL/6J mice with repeated cocaine

The present study investigated the effects of seven repeated daily injections of 32 mg/kg cocaine on stereotyped behaviors (repetitive locomotion, rearing, and head bobbing) in two genetically distinct strains of mice. An initial injection of cocaine induced no stereotypy in either DBA/2J or C57BL/6J mice. Following the fourth daily injection, cocaine induced stereotypies in DBA/2J mice (11.33 +/- 4.40) compared to saline controls (2.67 +/- 1.54). Cocaine-induced stereotypy in DBA/2J mice was further enhanced following the seventh daily injection (19.83 +/- 4.39) as compared to saline controls (0.67 +/- 0.54). No cocaine-induced stereotypy was observed in C57BL/6J mice following any injection. Eighth day saline challenges of cocaine-sensitized mice did not induce stereotypy. Eighth day cocaine challenges of saline-treated mice induced no stereotypy in either strain. The current study demonstrates that sensitization to cocaine can be influenced by genotype and suggests that genetically defined animals may be useful in elucidating mechanisms underlying sensitization and tolerance to cocaine.