Glutamate and GABA modulate dopamine in the pedunculopontine tegmental nucleus

Multimodal Investigations of Reward Circuitry and Anhedonia in Adolescent Depression

Depression is a highly prevalent condition with devastating personal and public health consequences that often first manifests during adolescence. Though extensively studied, the pathogenesis of depression remains poorly understood, and efforts to stratify risks and identify optimal interventions have proceeded slowly. A major impediment has been the reliance on an all-or-nothing categorical diagnostic scheme based solely on whether a patient endorses an arbitrary number of common symptoms for a sufficiently long period. This approach masks the well-documented heterogeneity of depression, a disorder that is highly variable in presentation, severity, and course between individuals and is frequently comorbid with other psychiatric conditions. In this targeted review, we outline the limitations of traditional diagnosis-based research and instead advocate an alternative approach centered around symptoms as unique dimensions of clinical dysfunction that span across disorders and more closely reflect underlying neurobiological abnormalities. In particular, we highlight anhedonia-the reduced ability to anticipate and experience pleasure-as a specific, quantifiable index of reward dysfunction and an ideal candidate for dimensional investigation. Anhedonia is a core symptom of depression but also a salient feature of numerous other conditions, and its severity varies widely within clinical and even healthy populations. Similarly, reward dysfunction is a hallmark of depression but is evident across many psychiatric conditions. Reward function is especially relevant in adolescence, a period characterized by exaggerated reward-seeking behaviors and rapid maturation of neural reward circuitry. We detail extensive work by our research group and others to investigate the neural and systemic factors contributing to reward dysfunction in youth, including our cumulative findings using multiple neuroimaging and immunological measures to study depressed adolescents but also trans-diagnostic cohorts with diverse psychiatric symptoms. We describe convergent evidence that reward dysfunction: (a) predicts worse clinical outcomes, (b) is associated with functional and chemical abnormalities within and beyond the neural reward circuitry, (c) is linked to elevated peripheral levels of inflammatory biomarkers, and (d) manifests early in the course of illness. Emphasis is placed on high-resolution neuroimaging techniques, comprehensive immunological assays, and data-driven analyses to fully capture and characterize the complex, interconnected nature of these systems and their contributions to adolescent reward dysfunction.

Anti-Inflammatory Diets and Schizophrenia

Schizophrenia is a mental illness characterized by symptoms such as hallucinations, delusions, disorganized speech, disorganized or catatonic behavior, and negative symptoms (emotional flatness, apathy, and lack of speech). It causes social and economic burdens to patients and their family. Although etiology of schizophrenia is still uncertain, dopamine dysregulation is traditionally considered as a main etiological factor of schizophrenia, which has been utilized to develop drugs for treating schizophrenia. Recently, inflammation has presented being a risk factor for schizophrenia in that neuroinflammation contributes to the pathophysiology of schizophrenia and the exacerbation of symptom severity. Various factors including diet can regulate inflammatory state. Specific foods or dietary patterns have anti- or pro-inflammatory potentials. Increased levels of pro-inflammatory cytokines and microglia activation have been reported in schizophrenia populations and were related to the pathogenesis of schizophrenia. Omega-3 fatty acids were often recommended to schizophrenia patients because of their anti-inflammatory activities. In this review, we investigate the inflammation-related pathogenesis of schizophrenia and summarize potential nutritional approaches to inhibit the manifestation of symptoms and to alleviate symptom severity using anti-inflammatory nutrients or functional components.

NMDA receptor modulation of the pedunculopontine tegmental nucleus underlies the motivational drive for feeding induced by midbrain dopaminergic neurons

The mesolimbic system, particularly the somatodendritic ventral tegmental area (VTA), is responsible for the positive reinforcing aspects of various homeostatic stimuli. In turn, the pedunculopontine tegmental nucleus (PPN) is anatomically and functionally connected with the VTA and substantia nigra (SN). In the present study, we investigated the role of glutamate receptors in the PPN in motivated behaviors by using a model of feeding induced by electrical stimulation of the VTA in male Wistar rats (n = 80). We found that injection of 2.5/5 µg dizocilpine (MK-801; NMDA receptor antagonist) to the PPN significantly reduced the feeding response induced by unilateral VTA-stimulation. This reaction was significantly impaired after local injection of MK-801 into the PPN in the ipsilateral rather than the contralateral hemisphere. After NMDA injection (2/3 µg) to the PPN we did not observe behavioral changes, only a trend of a lengthening/shortening of the latency to a feeding reaction at the highest dose of NMDA (3 µg). Immunohistochemical TH+/c-Fos+ analysis revealed a decrease in the number of TH+ cells in the midbrain (VTA-SN) in all experimental groups and altered activity of c-Fos+ neurons in selected brain structures depending on drug type (MK-801/NMDA) and injection site (ipsi-/contralateral hemisphere). Additionally, the pattern of TH+/c-Fos+ expression showed lateralization of feeding circuit functional connectivity. We conclude that the level of NMDA receptor arousal in the PPN regulates the activity of the midbrain dopaminergic cells, and the PPN-VTA circuit may be important in the regulation of motivational aspects of food intake.

Parallel descending dopaminergic connectivity of A13 cells to the brainstem locomotor centers

The mesencephalic locomotor region (MLR) is an important integrative area for the initiation and modulation of locomotion. Recently it has been realized that dopamine (DA) projections from the substantia nigra pars compacta project to the MLR. Here we explore DA projections from an area of the medial zona incerta (ZI) known for its role in motor control onto the MLR. We provide evidence that dopaminergic (DAergic) A13 neurons have connectivity to the cuneiform nucleus (CnF) and pedunculopontine tegmental nucleus (PPTg) of the MLR. No ascending connectivity to the dorsolateral striatum was observed. On the other hand, DAergic A13 projections to the medullary reticular formation (MRF) and the lumbar spinal cord were sparse. A small number of non-DAergic neurons within the medial ZI projected to the lumbar spinal cord. We then characterized the DA A13 cells and report that these cells differ from canonical DA neurons since they lack the Dopamine Transporter (DAT). The lack of DAT expression, and possibly the lack of a dopamine reuptake mechanism, points to a longer time of action compared to typical dopamine neurons. Collectively our data suggest a parallel descending DAergic pathway from the A13 neurons of the medial ZI to the MLR, which we expect is important for modulating movement.

Anterior cingulate cortex γ-aminobutyric acid deficits in youth with depression

Abnormally low γ-aminobutyric acid (GABA) levels have been consistently reported in adults with major depressive disorder (MDD). Our group extended this finding to adolescents, and documented that GABA deficits were associated with anhedonia. Here we aimed to confirm our prior finding of decreased brain GABA in youth with depression and explore its associations with clinical variables. Forty-four psychotropic medication-free youth with MDD and 36 healthy control (HC) participants (12-21 years) were studied. Participants represent a combined sample of 39 newly recruited youth (MDD=24) and 41 youth from our previously reported study (MDD=20). GABA levels and the combined resonances of glutamate and glutamine (Glx) were measured in vivo in the anterior cingulate cortex using proton magnetic resonance spectroscopy. Youth with depression exhibited significantly lower GABA levels than HC in both the newly reported (P=0.003) and the combined (P=0.003) samples. When depressed participants were classified based on the presence of anhedonia, only the anhedonic MDD subgroup showed reduced GABA levels compared to HC (P=0.002). While there were no associations between any clinical measures and GABA or Glx levels in the new sample, GABA was negatively correlated with only anhedonia severity in the combined MDD group. Furthermore, in the combined sample, hierarchical regression models showed that anhedonia, but not depression severity, anxiety or suicidality, contributed significant variance in GABA levels. This report solidifies the evidence for a GABA deficit early in the course of MDD, which correlates specifically with anhedonia in the disorder.

Efficacy of lurasidone in the treatment of agitation: A post hoc analysis of five short-term studies in acutely ill patients with schizophrenia

OBJECTIVE

This post hoc analysis evaluated the effect of lurasidone on agitation in acutely ill patients with schizophrenia.

METHOD

Patient-level data were pooled from five 6-week, randomized, double-blind, placebo-controlled studies of fixed-dose, once-daily, oral lurasidone (40, 80, 120, or 160 mg/d). Agitation was assessed with the Positive and Negative Syndrome Scale-Excited Component (PANSS-EC) score, utilizing a mixed model for repeated measurement analysis.

RESULTS

In patients with higher levels of agitation at baseline (PANSS-EC score≥14; n=773), lurasidone was associated with significantly greater improvement in least-squares (LS) mean PANSS-EC scores versus placebo at Day 3/4 (-1.6 vs -1.0; p<0.05), Day 7 (-2.3 vs -1.6; p<0.05), and at Week 6 endpoint (-5.5 vs -3.8; p<0.001; effect size=0.43). In patients with lower agitation at baseline (PANSS-EC score<14; n=754), LS mean PANSS-EC score change was significantly greater for lurasidone compared with placebo at Day 7 (-0.8 vs -0.1; p<0. 01) through Week 6 endpoint (-1.9 vs -0.9; p<0.001; effect size=0.31). Higher doses of lurasidone were notably more effective than lower doses in patients with more severe agitation at study baseline.

CONCLUSION

In this pooled analysis of 5 short-term studies, lurasidone provided early and sustained reduction in agitation, assessed using the PANSS-EC score, in patients with an acute exacerbation of schizophrenia. Higher doses of lurasidone were particularly effective in patients with more severe agitation at study baseline. Overall, these results suggest that lurasidone may be a useful treatment option for patients exhibiting agitation associated with acute psychotic symptoms of schizophrenia. ClinicalTrials.gov Identifiers: NCT00088634 (Study D1050196); NCT00549718 (Study D1050229), NCT00615433 (Study D1050231); NCT00790192 (Study D1050233). Study D1050006 was completed prior to the requirement to register trials.

Dopamine and the Brainstem Locomotor Networks: From Lamprey to Human

In vertebrates, dopamine neurons are classically known to modulate locomotion via their ascending projections to the basal ganglia that project to brainstem locomotor networks. An increased dopaminergic tone is associated with increase in locomotor activity. In pathological conditions where dopamine cells are lost, such as in Parkinson's disease, locomotor deficits are traditionally associated with the reduced ascending dopaminergic input to the basal ganglia. However, a descending dopaminergic pathway originating from the substantia nigra pars compacta was recently discovered. It innervates the mesencephalic locomotor region (MLR) from basal vertebrates to mammals. This pathway was shown to increase locomotor output in lampreys, and could very well play an important role in mammals. Here, we provide a detailed account on the newly found dopaminergic pathway in lamprey, salamander, rat, monkey, and human. In lampreys and salamanders, dopamine release in the MLR is associated with the activation of reticulospinal neurons that carry the locomotor command to the spinal cord. Dopamine release in the MLR potentiates locomotor movements through a D1-receptor mechanism in lampreys. In rats, stimulation of the substantia nigra pars compacta elicited dopamine release in the pedunculopontine nucleus, a known part of the MLR. In a monkey model of Parkinson's disease, a reduced dopaminergic innervation of the brainstem locomotor networks was reported. Dopaminergic fibers are also present in human pedunculopontine nucleus. We discuss the conserved locomotor role of this pathway from lamprey to mammals, and the hypothesis that this pathway could play a role in the locomotor deficits reported in Parkinson's disease.

GABAA and GABAB receptor dysregulation in superior frontal cortex of subjects with schizophrenia and bipolar disorder

Schizophrenia and bipolar disorder are complex psychiatric disorders that affect millions of people worldwide. Evidence from gene association and postmortem studies has identified abnormalities of the gamma-aminobutyric acid (GABA) signaling system in both disorders. Abnormal GABAergic signaling and transmission could contribute to the symptomatology of these disorders, potentially through impaired gamma oscillations which normally occur during cognitive processing. In the current study, we examined the protein expression of 14 GABA_A and two GABA_B receptor subunits in the superior frontal cortex of subjects with schizophrenia, bipolar disorder, and healthy controls. Analyses of Variance (ANOVAs) identified significant group effects for protein levels for the α1, α6, β1, β3, δ, ɛ, and π GABA_A receptor subunits and R1 and R2 GABA_B receptor subunits. Follow-up t tests confirmed changes for these subunits in subjects with schizophrenia, subjects with bipolar disorder, or both groups. Alterations in stoichiometry of GABA receptor subunits could result in altered ligand binding, transmission, and pharmacology of GABA receptors in superior frontal cortex. Thus, impaired GABAergic transmission may negatively contribute to symptoms such as anxiety or panic as well as impaired learning and information processing, all of which are disrupted in schizophrenia and bipolar disorder. Taken together, these results provide additional evidence of GABAergic receptor abnormalities in these disorders.

Hyperactivity and impaired attention in Gamma aminobutyric acid transporter subtype 1 gene knockout mice

OBJECTIVES

Attention-deficit hyperactivity disorder (ADHD) is a common neurobehavioural disorder. It is conceivable that Gamma aminobutyric acid (GABA) neurotransmission is implicated in the pathophysiology of ADHD. This study investigated the effect of GABA transporter 1 (GAT-1) on the anxiety-like behaviours and cognitive function in knockout mice.

METHODS

In all, 20 adult male mice were divided into two groups: wild-type (WT) group and GAT-1-/- group. The open field test, elevated O-maze (EZM) and Morris water maze were used to evaluate behavioural traits relevant to ADHD.

RESULTS

Compared with WT mice, the GAT-1-/- mice travelled longer and displayed an enhanced kinematic velocity with the significant reduction of rest time in the open field test (p<0.05). The EZM showed that GAT-1-/- mice displayed a significant increase in total entries into the open sectors and the closed sectors compared with the WT mice. The WT mice showed shorter latencies after the training session (p<0.01), whereas the GAT-1-/- mice made no difference during probe test, the GAT-1-/- mice spent less time in the target quadrant (p<0.01).

CONCLUSION

Our results demonstrated that GAT-1-/- mice have phenotypes of hyperactivity, impaired sustained attention and learning deficiency, and the performance of GAT-1-/- mice is similar to ADHD symptoms. So, the study of the GAT-1-/- mice may provide new insights into the mechanisms and the discovery of novel therapeutics for the treatment of ADHD.

The effect of low frequency stimulation of the pedunculopontine tegmental nucleus on basal ganglia in a rat model of Parkinson's disease

The pedunculopontine nucleus (PPN) has recently been introduced as an alternative target to the subthalamic nucleus (STN) or globus pallidus internus (GPi) for the treatment of advanced Parkinson's disease with severe and medically intractable axial symptoms such as gait and postural impairment. However, it is little known about how electrical stimulation of the PPN affects control of neuronal activities between the PPN and basal ganglia. We examined how low frequency stimulation of the pedunculopontine tegmental nucleus (PPTg) affects control of neuronal activities between the PPN and basal ganglia in 6-OHDA lesioned rats. In order to identify the effect of low frequency stimulation on the PPTg, neuronal activity in both the STN and substantia nigra par reticulata (SNr) were recorded and subjected to quantitative analysis, including analysis of firing rates and firing patterns. In this study, we found that the firing rates of the STN and SNr were suppressed during low frequency stimulation of the PPTg. However, the firing pattern, in contrast to the firing rate, did not exhibit significant changes in either the STN or SNr of 6-OHDA lesioned rats during low frequency stimulation of the PPTg. In addition, we also found that the firing rate of STN and SNr neurons displaying burst and random pattern were decreased by low frequency stimulation of PPTg, while the neurons displaying regular pattern were not affected. These results indicate that low frequency stimulation of the PPTg affects neuronal activity in both the STN and SNr, and may represent electrophysiological efficacy of low frequency PPN stimulation.

Change in Brainstem Gray Matter Concentration Following a Mindfulness-Based Intervention is Correlated with Improvement in Psychological Well-Being

Individuals can improve their levels of psychological well-being (PWB) through utilization of psychological interventions, including the practice of mindfulness meditation, which is defined as the non-judgmental awareness of experiences in the present moment. We recently reported that an 8-week-mindfulness-based stress reduction (MBSR) course lead to increases in gray matter concentration in several brain areas, as detected with voxel-based morphometry of magnetization prepared rapid acquisition gradient echo MRI scans, including the pons/raphe/locus coeruleus area of the brainstem. Given the role of the pons and raphe in mood and arousal, we hypothesized that changes in this region might underlie changes in well-being. A subset of 14 healthy individuals from a previously published data set completed anatomical MRI and filled out the PWB scale before and after MBSR participation. PWB change was used as the predictive regressor for changes in gray matter density within those brain regions that had previously shown pre- to post-MBSR changes. Results showed that scores on five PWB subscales as well as the PWB total score increased significantly over the MBSR course. The change was positively correlated with gray matter concentration increases in two symmetrically bilateral clusters in the brainstem. Those clusters appeared to contain the area of the pontine tegmentum, locus coeruleus, nucleus raphe pontis, and the sensory trigeminal nucleus. No clusters were negatively correlated with the change in PWB. This preliminary study suggests a neural correlate of enhanced PWB. The identified brain areas include the sites of synthesis and release of the neurotransmitters, norepinephrine and serotonin, which are involved in the modulation of arousal and mood, and have been related to a variety of affective functions as well as associated clinical dysfunctions.

Activity in mouse pedunculopontine tegmental nucleus reflects action and outcome in a decision-making task

Recent studies across several mammalian species have revealed a distributed network of cortical and subcortical brain regions responsible for sensorimotor decision making. Many of these regions have been shown to be interconnected with the pedunculopontine tegmental nucleus (PPTg), a brain stem structure characterized by neuronal heterogeneity and thought to be involved in several cognitive and behavioral functions. However, whether this structure plays a general functional role in sensorimotor decision making is unclear. We hypothesized that, in the context of a sensorimotor task, activity in the PPTg would reflect task-related variables in a similar manner as do the cortical and subcortical regions with which it is anatomically associated. To examine this hypothesis, we recorded PPTg activity in mice performing an odor-cued spatial choice task requiring a stereotyped leftward or rightward orienting movement to obtain a reward. We studied single-neuron activity during epochs of the task related to movement preparation, execution, and outcome (i.e., whether or not the movement was rewarded). We found that a substantial proportion of neurons in the PPTg exhibited direction-selective activity during one or more of these epochs. In addition, an overlapping population of neurons reflected movement direction and reward outcome. These results suggest that the PPTg should be considered within the network of brain areas responsible for sensorimotor decision making and lay the foundation for future experiments to examine how the PPTg interacts with other regions to control sensory-guided motor output.

Parallels between behavioral and neurochemical variability in the rat vacuous chewing movement model of tardive dyskinesia

The widely accepted rat vacuous chewing movement model for tardive dyskinesia could be more fully mined through greater focus on individual variability in vulnerability to this neuroleptic-induced behavior. We have examined parallels between behavioral and neurobiological variability within a cohort in order to evaluate the role that neurobiological factors might play in determining susceptibility to tardive dyskinesia. Inter-observer reliability and individual consistency across time, in both spontaneous and neuroleptic-induced vacuous chewing movements, were empirically demonstrated. While this behavior increased across 8 months of observation in both vehicle controls and haloperidol-treated rats, pre-treatment baselines were predictive of final levels across individuals only in the vehicle control group, not the haloperidol-treated group. Haloperidol-induced elevations in neostriatal D2 and GAD(67) mRNA were not correlated with individual variability in haloperidol-induced vacuous chewing movements. Ambient noise during the observations was found to exacerbate chronic haloperidol-induced, but not spontaneous vacuous chewing movements. Significant correlations were found among the haloperidol-treated rats between nigral and tegmental GAD(67) and tegmental α7 mRNA levels, measured by in situ hybridization histochemistry, and vacuous chewing movements, specifically in the noisy conditions. Variability in these secondary responses to primary striatal dopamine and GABA perturbations may play a role in determining vulnerability to vacuous chewing movements, and by analogy, tardive dyskinesia. Both the differential predictive value of baseline vacuous chewing movements and the differential effect of noise, between controls and haloperidol-treated rats, add to evidence that haloperidol-induced vacuous chewing movements are regulated, in part, by different mechanisms than those mediating spontaneous vacuous chewing movements.

Anterior cingulate cortex γ-aminobutyric acid in depressed adolescents: relationship to anhedonia

CONTEXT

Anhedonia, a core symptom of major depressive disorder (MDD) and highly variable among adolescents with MDD, may involve alterations in the major inhibitory amino acid neurotransmitter system of γ-aminobutyric acid (GABA).

OBJECTIVE

To test whether anterior cingulate cortex (ACC) GABA levels, measured by proton magnetic resonance spectroscopy, are decreased in adolescents with MDD. The associations of GABA alterations with the presence and severity of anhedonia were explored.

DESIGN

Case-control, cross-sectional study using single-voxel proton magnetic resonance spectroscopy at 3 T.

SETTING

Two clinical research divisions at 2 teaching hospitals.

PARTICIPANTS

Twenty psychotropic medication-free adolescents with MDD (10 anhedonic, 12 female, aged 12-19 years) with episode duration of 8 weeks or more and 21 control subjects group matched for sex and age.

MAIN OUTCOME MEASURES

Anterior cingulate cortex GABA levels expressed as ratios relative to unsuppressed voxel tissue water (w) and anhedonia scores expressed as a continuous variable.

RESULTS

Compared with control subjects, adolescents with MDD had significantly decreased ACC GABA/w (t = 3.2; P < .003). When subjects with MDD were categorized based on the presence of anhedonia, only anhedonic patients had decreased GABA/w levels compared with control subjects (t = 4.08; P < .001; P(Tukey) < .001). Anterior cingulate cortex GABA/w levels were negatively correlated with anhedonia scores for the whole MDD group (r = -0.50; P = .02), as well as for the entire participant sample including the control subjects (r = -0.54; P < .001). Anterior cingulate cortex white matter was also significantly decreased in adolescents with MDD compared with controls (P = .04).

CONCLUSIONS

These findings suggest that GABA, the major inhibitory neurotransmitter in the brain, may be implicated in adolescent MDD and, more specifically, in those with anhedonia. In addition, use of a continuous rather than categorical scale of anhedonia, as in the present study, may permit greater specificity in evaluating this important clinical feature.

Deficits in GABA(B) receptor system in schizophrenia and mood disorders: a postmortem study

Postmortem and genetic studies have clearly demonstrated changes in GABA(B) receptors in neuropsychiatric disorders such as autism, bipolar disorder, major depression, and schizophrenia. Moreover, a number of recent studies have stressed the importance of cerebellar dysfunction in these same disorders. In the current study, we examined protein levels of the two GABA(B) receptor subunits GABBR1 and GABBR2 in lateral cerebella from a well-characterized cohort of subjects with schizophrenia (n=15), bipolar disorder (n=14), major depression (n=13) and healthy controls (n=12). We found significant reductions in protein for both GABBR1 and GABBR2 in lateral cerebella from subjects with schizophrenia, bipolar disorder and major depression when compared with controls. These results provide further evidence of GABAergic dysfunction in these three disorders as well as identify potential targets for therapeutic intervention.

Effects of scopolamine on dopamine neurons in the substantia nigra: role of the pedunculopontine tegmental nucleus

Previous neurochemical and behavioral studies suggest that muscarinic receptor antagonism has an excitatory effect on the nigrostriatal dopamine (DA) system. Using in vivo extracellular single unit recording, this study examined whether blockade of the muscarinic receptor by scopolamine alters the firing properties of DA neurons in the substantia nigra (SN). Scopolamine was administered either systemically or locally to DA neurons using microiontophoresis. Surprisingly, scopolamine did not cause any significant change in either the firing rate or pattern of the spontaneously active DA neurons. However, systemic injection of scopolamine significantly increased the number of active DA neurons in the SN. Local infusion of scopolamine into the pedunculopontine tegmental nucleus (PPT) mimicked the effect induced by systemically administered scopolamine, significantly increasing the number of active DA neurons without altering the firing rate and pattern. These results suggest that the reported increase in striatal DA release induced by scopolamine is in part mediated by activation of silent nigral DA neurons. The experiments with PPT local infusion further suggest that part of the effect of scopolamine may be due to its blockade of the inhibitory muscarinic autoreceptors on PPT cholinergic cells. The latter effect may lead to activation of quiescent DA neurons by increasing acetylcholine (ACh) release in the SN or in other brain areas providing inputs to DA neurons. Further understanding of the mechanism of action of scopolamine may help us further understand the role of ACh in both the pathophysiology and treatment of DA-related disorders including schizophrenia and Parkinson's disease.

Structural basis of the involvement of the striopallidum and pedunculopontine tegmental nucleus in the organization of adaptive behavior

Retrograde axonal transport was used to study the organizational characteristics of the afferent and efferent projection systems of individual substructures of the pedunculopontine tegmental nucleus and the functionally diverse (motor, limbic) areas of structures in the striopallidum. The structural bases of the conduction of functionally diverse information and its integration in the basal ganglia system and tegmental area were evaluated. The morphological data obtained here aid our understanding of the morphofunctional bases of the interaction of these structures and their involvement in adaptive behavior.

Further evidence that the delayed temporal dopaminergic effects of LSD are mediated by a mechanism different than the first temporal phase of action

Activation of 5-HT(2A) receptors is thought to mediate the hallucinogenic effects of LSD. Nevertheless, in a previous report we provided evidence that a delayed temporal phase of the behavioral pharmacology of LSD is mediated by D(2)-like dopamine receptor stimulation. In this study rats were trained to discriminate LSD with either a 30 min preinjection time (LSD-30, N=12) or a 90 min preinjection time (LSD-90, N=13) from saline, using a two-lever, food-reinforced operant conditioning task. We then tested a large number of agonists and antagonists belonging to distinct pharmacological classes in these animals. As anticipated, classical hallucinogens such as psilocin and mescaline substituted only in LSD-30 rats, and not in LSD-90 rats. The dopamine receptor agonists ABT-724, aripiprazole, dihydrexidine, WAY 100635, and SKF 38393, fully or partially mimicked LSD-90, but not LSD-30. The results reported here support and extend our previous conclusion that the delayed temporal effects of LSD are mediated by activation of a dopaminergic system.

Noradrenaline transmission within the ventral bed nucleus of the stria terminalis is critical for fear behavior induced by trimethylthiazoline, a component of fox odor

The bed nucleus of the stria terminalis (BNST) is involved in the mediation of fear behavior in rats. A previous study of our laboratory demonstrated that temporary inactivation of the BNST blocks fear behavior induced by exposure to trimethylthiazoline (TMT), a component of fox odor. The present study investigates whether noradrenaline release within the BNST is critical for TMT-induced fear behavior. First, we confirmed previous studies showing that the ventral BNST is the part of the BNST that receives the densest noradrenaline innervation. Second, using in vivo microdialysis, we showed that noradrenaline release within the BNST is strongly increased during TMT exposure, and that this increase can be blocked by local infusions of the alpha2-receptor blocker clonidine. Third, using intracerebral injections, we showed that clonidine injections into the ventral BNST, but not into neighboring brain sites, completely blocked TMT-induced potentiation of freezing behavior. The present data clearly show that the noradrenergic innervation of the ventral BNST is important for the full expression of behavioral signs of fear to the predator odor TMT.

Pharmacological management of acute agitation

Acute agitation occurs in a variety of medical and psychiatric conditions, and when severe can result in behavioural dyscontrol. Rapid tranquillisation is the assertive use of medication to calm severely agitated patients quickly, decrease dangerous behaviour and allow treatment of the underlying condition. Intramuscular injections of typical antipsychotics and benzodiazepines, given alone or in combination, have been the treatment of choice over the past few decades. Haloperidol and lorazepam are the most widely used agents for acute agitation, are effective in a wide diagnostic arena and can be used in medically compromised patients. Haloperidol can cause significant extrapyramidal symptoms, and has rarely been associated with cardiac arrhythmia and sudden death. Lorazepam can cause ataxia, sedation and has additive effects with other CNS depressant drugs.Recently, two fast-acting preparations of atypical antipsychotics, intramuscular ziprasidone and intramuscular olanzapine, have been developed for treatment of acute agitation. Intramuscular ziprasidone has shown significant calming effects emerging 30 minutes after administration for acutely agitated patients with schizophrenia and other nonspecific psychotic conditions. Intramuscular ziprasidone is well tolerated and has gained widespread use in psychiatric emergency services since its introduction in 2002. In comparison with other atypical antipsychotics, ziprasidone has a relatively greater propensity to increase the corrected QT (QTc) interval and, therefore, should not be used in patients with known QTc interval-associated conditions. Intramuscular olanzapine has shown faster onset of action, greater efficacy and fewer adverse effects than haloperidol or lorazepam in the treatment of acute agitation associated with schizophrenia, schizoaffective disorder, bipolar mania and dementia. Intramuscular olanzapine has been shown to have distinct calming versus nonspecific sedative effects. The recent reports of adverse events (including eight fatalities) associated with intramuscular olanzapine underscores the need to follow strict prescribing guidelines and avoid simultaneous use with other CNS depressants. Both intramuscular ziprasidone and intramuscular olanzapine have shown ease of transition to same-agent oral therapy once the episode of acute agitation has diminished. No randomised, controlled studies have examined either agent in patients with severe agitation, drug-induced states or significant medical comorbidity. Current clinical experience and one naturalistic study with intramuscular ziprasidone suggest that it is efficacious and can be safely used in such populations. These intramuscular atypical antipsychotics may represent a historical advance in the treatment of acute agitation.

Different function of pedunculopontine GABA and glutamate receptors in nucleus accumbens dopamine, pedunculopontine glutamate and operant discriminative behavior

The nucleus accumbens, as the main input structure of the ventral basal ganglia loop, is described as a limbic-motor interface. Dopamine input to nucleus accumbens modulates processing of concurrent glutamate input from limbic structures carrying motor and motivational information. There is evidence that these dopamine/glutamate interactions are fundamentally involved in response selection processes. However, the pedunculopontine tegmental nucleus (PPTg) in the brainstem is connected with limbic structures as well as dopaminergic midbrain areas, which also project to the nucleus accumbens. Furthermore, behavioral studies implicate the PPTg in complex, motivated behavior. Thus, the PPTg might be involved in motivated behavior by influencing response selection processes in the nucleus accumbens. In this study we used in vivo microdialysis in freely moving rats in order to inhibit (100, 200, 300 and 400 microm baclofen) or stimulate [5, 12.5, 25 or 50 micromalpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA)] the PPTg in animals that are performing an operant discrimination task for food reward. The behavioral consequences were correlated with dopamine and glutamate levels in nucleus accumbens and PPTg, respectively. PPTg inhibition by local GABAB receptors impaired the response rate and accuracy of performance in the operant discrimination task. PPTg stimulation by local AMPA receptors exclusively impaired the response rate. Both treatments blocked the performance-driven dopamine signal in nucleus accumbens, whereas glutamate in PPTg was enhanced after AMPA administration only. The data indicate that the PPTg functionally participates in a network of subcortical and cortical structures, which is responsible for the execution of motivated behavior and response selection processes.

Attenuation of d-amphetamine self-administration by baclofen in the rat: behavioral and neurochemical correlates

RATIONALE

Recent reports have demonstrated that gamma-aminobutyric acid (GABA)-ergic compounds attenuate the reinforcing effects of cocaine in rats. Baclofen, a GABA(B) receptor agonist, appears to be particularly effective in this respect, suggesting that GABA(B) receptor activation is critically involved in mediating anti-cocaine effects. Amphetamine, like cocaine, is a psychomotor stimulant with high abuse potential in humans.

OBJECTIVES

The purpose of the present investigation was to determine whether baclofen may attenuate the reinforcing effects of d-amphetamine (dAMPH) in rats. Dose-response curves were generated to examine the effect of three doses of baclofen (1.8, 3.2 or 5.6 mg/kg, IP) on dAMPH intravenous self-administration (IVSA). Separate groups were trained to self-administer two doses of dAMPH (0.1 mg/kg or 0.2 mg/kg per injection) under either a fixed-ratio (FR) or progressive ratio (PR) schedule of reinforcement. Microdialysis was performed in an additional group of rats to examine the effect of baclofen on dAMPH-induced increases in dopamine (DA) efflux in the nucleus accumbens (NAc).

RESULTS

Pretreatment with baclofen produced dose-dependent reductions in responding for dAMPH under both the FR and PR schedules, and attenuated dAMPH-induced increases in DA levels in the NAc.

CONCLUSION

These results add to previous findings showing that baclofen attenuates the reinforcing effects of psychostimulant drugs, and suggest that further investigation into the effects of GABA(B) receptor agonists on drug self-administration is warranted.