Mechanisms of ischaemic damage to central white matter axons: a quantitative histological analysis using rat optic nerve

The mechanism of ischaemic injury to white matter axons was studied by transiently depriving rat optic nerves in vitro of oxygen and glucose. Light and electron microscopic analysis showed that increasing periods of oxygen/glucose deprivation (up to 1 h) caused, after a 90-min recovery period, the appearance of increasing numbers of swollen axons whose ultrastructure indicated that they were irreversibly damaged. This conclusion was supported by experiments showing that the damage persisted after a longer recovery period (3 h). To quantify the axonal pathology, an automated morphometric method, based on measurement of the density of swollen axons, was developed. Omission of Ca2+ from the incubation solution during 1 h of oxygen/glucose deprivation (and for 15 min either side) completely prevented the axonopathy (assessed following 90 min recovery). Omission of Na+ was also effective, though less so (70% protection). The classical Na+ channel blocker, tetrodotoxin (1 microM), provided 92% protection. In view of this evidence implicating Na+ channels in the pathogenesis of the axonal damage, the effects of three different Na+ channel inhibitors, with known neuroprotective properties towards gray matter in in vivo models of cerebral ischaemia, were tested. The compounds used were lamotrigine and the structurally-related molecules, BW619C89 and BW1003C87. All three compounds protected the axons to varying degrees, the maximal efficacies (observed at 30 to 100 microM) being in the order: BW619C89 (>95% protection) > BW1003C87 (70%) > lamotrigine (50%). At a concentration affording near complete protection (100 microM), BW619C89 had no significant effect on the optic nerve compound action potential. Experiments in which BW619C89 was added at different times indicated that its effects were exerted during two distinct phases, one (accounting for about 50% protection) was during the early stage of oxygen/glucose deprivation itself and the other (also about 50%) during the first 15 min of recovery in normal incubation solution. The results are consistent with a pathophysiological mechanism in which Na+ entry through tetrodotoxin-sensitive Na+ channels contributes to Na+ loading of the axoplasm which then results in a lethal Ca2+ overload through reversed Na(+)-Ca2+ exchange. The identification of BW619C89 as a compound able to prevent oxygen/glucose deprivation-induced injury to white matter axons without affecting normal nerve function opens the way to testing the importance of this pathway in white matter injury in vivo.

Lamotrigine for the treatment of bipolar disorder

OBJECTIVE

To describe the available data regarding the clinical efficacy of lamotrigine for the treatment of bipolar disorder.

SUMMARY

Anticonvulsants have emerged as alternative mood-stabilizing agents for patients with bipolar disorder who do not respond to lithium. Data regarding the efficacy of lamotrigine have been generated primarily from case reports, small open trials, and one large, randomized, placebo-controlled trial. These reports suggest that lamotrigine may be effective for the management of bipolar disorder.

CONCLUSIONS

Although current data are limited, treatment-refractory patients with bipolar disorder may benefit from lamotrigine therapy. Several studies are currently underway to determine the appropriate role of lamotrigine in the treatment of bipolar disorder.

Effects of some GABA and NMDA antagonists on a model of presynaptic hippocampal paired pulse inhibition

1. The effects of some NMDA antagonists (7-chlorokynurenic acid and CGS 19755) and of the GABA antagonist penicillin were tested in a model of presynaptic short-term paired-pulse inhibition elicited in rat hippocampal slice with high (+ 2 mM) calcium solutions subjected to paired (15 ms)-pulse stimulation paradigm. 2. In control condition a 15 ms paired-pulse stimulation delivered at the level of stratum radiatum, as revealed by the ratio between amplitudes of the conditioned and unconditioned CA1 population spikes (R2/R1), ranging from 1.27 to 2.57, a clear paired-pulse facilitation occurred. Slice perfusion with high (+ 2 mM) calcium shifted, within 30 min, as revealed by a significant (P<0.01) decrease in R2/R1 ratio, paired-pulse facilitation into inhibition. Further perfusion together to high (+ 2 mM) calcium with 0.5 mM penicillin or with 50 microM CGS 19755, but not with 50 microM 7-chlorokynurenic acid significantly decreases the degree of paired-pulse inhibition as revealed by a significative increase in the R2/R1 ratio. 3. The data, demonstrating an inhibitory influence of specific NMDA antagonists in a model a presynaptic paired-pulse inhibition, were discussed in relation with the specific psychodysleptic effects elicited by the drugs in animals and humans.

In vivo effects of adenosine A1 receptor agonist and antagonist on neuronal and astrocytic intermediary metabolism studied with ex vivo 13C NMR spectroscopy

Adenosine is a neuromodulator, and it has been suggested that cerebral acetate metabolism induces adenosine formation. In the present study the effects that acetate has on cerebral intermediary metabolism, compared with those of glucose, were studied using the adenosine A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA) and antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Fasted rats received an intravenous injection of CCPA, DPCPX, or vehicle. Fifteen minutes later either [1,2-13C]acetate or [1-13C]glucose was given intraperitoneally; after another 30 min the rats were decapitated. Cortical extracts were analyzed with 13C NMR spectroscopy and HPLC analysis. DPCPX affected neuronal and astrocytic metabolism. De novo synthesis of GABA from neuronal and astrocytic precursors was significantly reduced. De novo syntheses of glutamate and aspartate were at control levels, but their degradation was significantly elevated. In glutamine the anaplerotic activity and the amount of label in the position representing the second turn in the tricarboxylic acid cycle were significantly increased, suggesting elevated metabolic activity in astrocytes. CCPA did not influence GABA, aspartate, or glutamine synthesis. In glutamate the contribution from the astrocytic anaplerotic pathway was significantly decreased. In the present study the findings in the [1,2-13C]acetate and [1-13C]glucose control, CCPA, and DPCPX groups were complementary, and no adenosine A1 agonist effects arising from cerebral acetate metabolism were detected.

Caffeine during sleep deprivation: sleep tendency and dynamics of recovery sleep in rats

The adenosine antagonist caffeine disrupts sleep, but whether caffeine promotes wakefulness by interfering with the expression of sleep or by attenuating sleepiness is unknown. The ability of caffeine to reduce sleep tendency in rats was directly tested by quantifying the number of stimuli needed to maintain wakefulness during sleep deprivation for 6 h after systemic caffeine treatment. In addition, the influence of caffeine on the dynamics between nonrapid-eye-movement (NREM) and rapid-eye-movement (REM) sleep was investigated by comparing the magnitude and time course of the compensatory sleep responses for 42 h postsleep deprivation. Caffeine significantly reduced the attempts to sleep during sleep deprivation, F(1,9) 8.83, p = 0.0157; 44.9% of vehicle), but did not change compensatory slow-wave activity during recovery sleep. During the initial recovery phase, caffeine suppressed compensatory REM sleep and reduced, but did not block, compensatory NREM sleep duration and continuity. By 42 h postsleep deprivation, the amount of NREM recovered (70.0% of deficit) did not differ from vehicle. In contrast, the REM sleep deficit recovered after caffeine (100%) was more than after vehicle (43.9%). Thus, caffeine slowed the rate of compensatory sleep after sleep deprivation, as indexed by the duration of sleep states and sleep continuity.

Intravenous valproate in neuropsychiatry

Valproic acid (VPA) is administered for a variety of indications in neurology and psychiatry. The intravenous form of VPA, valproate, has been used extensively by neurologists since the 1980s for patients with status epilepticus, as serum levels can be achieved rapidly and telemetry is not required during administration. Psychiatrists have less experience with intravenous valproate, and little is documented in the literature regarding its nonepileptic indications. Patients who are unable or unwilling to take drugs orally, or for whom rapid treatment is clinically indicated, may benefit from VPA. Neuroleptics and benzodiazepines often are given parenterally; however, they may be accompanied by side effects. Intravenous valproate was administered successfully to three patients with neuropsychiatric disorders. It is hoped that this report will increase clinicians' awareness of this important and well-tolerated treatment option.

Adenosinergic modulation of rat basal forebrain neurons during sleep and waking: neuronal recording with microdialysis

1. The cholinergic system of the basal forebrain (BF) is hypothesized to play an important role in behavioural and electrocortical arousal. Adenosine has been proposed as a sleep-promoting substance that induces sleep by inhibiting cholinergic neurons of the BF and brainstem. However, adenosinergic influences on the activity of BF neurons in naturally awake and sleeping animals have not been demonstrated. 2. We recorded the sleep-wake discharge profile of BF neurons and simultaneously assessed adenosinergic influences on wake- and sleep-related activity of these neurons by delivering adenosinergic agents adjacent to the recorded neurons with a microdialysis probe. Discharge rates of BF neurons were recorded through two to three sleep-wake episodes during baseline (artificial cerebrospinal fluid perfusion), and after delivering an adenosine transport inhibitor (s-(p-nitrobenzyl)-6-thioinosine; NBTI), or exogenous adenosine, or a selective adenosine A1 receptor antagonist (8-cyclopentyl-1, 3-dimethylxanthine; CPDX). 3. NBTI and adenosine decreased the discharge rate of BF neurons during both waking and non-rapid eye movement (NREM) sleep. In contrast, CPDX increased the discharge rate of BF neurons during both waking and NREM sleep. These results suggest that in naturally awake and sleeping animals, adenosine exerts tonic inhibitory influences on BF neurons, supporting the hypothesized role of adenosine in sleep regulation. 4. However, in the presence of exogenous adenosine, NBTI or CPDX, BF neurons retained their wake- and sleep-related discharge patterns, i.e. still exhibited changes in discharge rate during transitions between waking and NREM sleep. This suggests that other neurotransmitters/neuromodulators also contribute to the sleep-wake discharge modulation of BF neurons.

The place of anticonvulsants and other putative mood stabilisers in the treatment of bipolar disorder

While lithium is an effective mood stabiliser still in widespread clinical use, a significant proportion of patients either respond poorly or are unable to tolerate its adverse effects. In the 1960s and 1970s preliminary reports of the possible effectiveness of carbamazepine and valproate began to appear, with confirmatory controlled studies being undertaken in the 1980s and 1990s. In recent years, further putative mood-stabilising agents have been described, in particular some of the newer anticonvulsants and the atypical antipsychotics. This paper critically evaluates the current evidential basis for claims for the efficacy of these compounds in bipolar disorder.

Frequency-dependent inhibition in the dentate gyrus is attenuated by the NMDA receptor blocker MK-801 at doses that do not yet affect long-term potentiation

The dual impairment of both long-term potentiation (LTP) in the dentate gyrus and spatial memory by N-methyl-D-aspartate (NMDA) blockers such as 2-aminophosphonovaleric acid (APV) or dizocilpine (MK-801) is considered supportive evidence for the hypothesis that LTP-like mechanisms are involved in spatial memory. However, several studies suggest that, at doses that affect aspects of behavior, LTP is not yet blocked. One possible explanation may be that the blockade of NMDA receptors affect processes other than LTP, which are required for learning. In the present study, we assessed in vivo the effects of the NMDA receptor antagonist MK-801 on LTP and on frequency-dependent inhibition, which has previously been shown to reflect activity of GABAergic interneurons in the rat dentate gyrus. We report here that NMDA receptors are instrumental in frequency-dependent inhibition. Furthermore, frequency-dependent inhibition was found to be more sensitive than LTP to the NMDA antagonist MK-801. Our findings indicate that, in addition to the blockade of LTP, the application of NMDA antagonists affects local circuit activity in the dentate gyrus. The results direct attention to the potential role of interneuronal activity in general and of frequency-dependent inhibition in particular in dentate gyrus related behaviors.

Adenosine and behavioral state control: adenosine increases c-Fos protein and AP1 binding in basal forebrain of rats

In several brain areas, extracellular adenosine (AD) levels are higher during waking than sleep and during prolonged wakefulness AD levels in the basal forebrain increase progressively. Similarly, c-Fos levels in several brain areas are higher during waking than sleep and remain elevated during prolonged wakefulness. In the present study, we investigated the effect of extracellular AD levels on c-Fos protein and activator protein-1 (AP1) binding in the basal forebrain of rats. Increased levels of extracellular AD were induced either by keeping the animals awake, or by local perfusion of AD into the basal forebrain. During prolonged wakefulness extracellular AD concentration was monitored using in vivo microdialysis. The effect of AD perfusion on the behavioral states was recorded using polysomnography. At the end of the perfusion period the basal forebrain tissue was analyzed for the levels of c-Fos protein and AP1 binding. In vivo microdialysis measurements showed an increase in AD levels with prolonged wakefulness. Unilateral perfusion of AD (300 microM) increased non-REM sleep and delta power (0.5 to 4 Hz) when compared to rats perfused with artificial CSF. The levels of c-Fos protein and the AP1 DNA binding were high in the basal forebrain of both sleep-deprived animals and in animals perfused with AD. The results suggest that AD might mediate, at least in part, the long term effects of sleep deprivation by inducing c-Fos protein and subsequent AP1 binding.

The anticonvulsant BW534U87 depresses epileptiform activity in rat hippocampal slices by an adenosine-dependent mechanism and through inhibition of voltage-gated Na+ channels

1. The cellular and molecular actions of BW534U87 were studied using intracellular and extracellular recordings from the CA1 region of rat hippocampal slices and whole-cell voltage-clamp recordings of recombinant human brain type IIA Na+ channels expressed in Chinese hamster ovary (CHO) cells. 2. Normal excitatory and inhibitory postsynaptic potentials evoked in hippocampal slices were unaffected by BW534U87 or the adenosine deaminase inhibitor EHNA. However, epileptiform activity was depressed by BW534U87 (50 micronM) and this inhibition was reversed by the adenosine receptor antagonist 8-phenyl theophylline (8-PT, 30 micronM). EHNA (10 micronM) mimicked the effects of BW534U87. Furthermore, BW534U87 enhanced the inhibitory effects of exogenous adenosine on evoked synaptic potentials. BW534U87 (50 micronM) also voltage- and use-dependently inhibited action potentials elicited by current injection, independent of the adenosine system, since it was not affected by 8-PT. 3. In CHO cells expressing the recombinant human brain Na+ channel, BW534U87 produced a concentration- and voltage-dependent inhibition of Na+ currents with a half-maximal inhibitory concentration of 10 micronM at a Vh of -60 mV. Use-dependent inhibition was evident at high-frequencies (20x20 ms pulse train at 10 Hz). 4 In conclusion, BW534U87 blocks hippocampal epileptiform activity by a dual mechanism. The first action is similar to that produced by EHNA and is dependent on endogenous adenosine probably by inhibition of adenosine deaminase. Secondly, BW534U87 directly inhibits voltage-gated Na+ channels in a voltage- and frequency-dependent manner. Both actions of BW534U87 are activity-dependent and may synergistically contribute to its overall anticonvulsant effects in animal models of epilepsy.

Gamma frequency-range abnormalities to auditory stimulation in schizophrenia

BACKGROUND

Basic science studies at the neuronal systems level have indicated that gamma-range (30-50 Hz) neural synchronization may be a key mechanism of information processing in neural networks, reflecting integration of various features of an object. Furthermore, gamma-range synchronization is thought to depend on the glutamatergically mediated interplay between excitatory projection neurons and inhibitory neurons utilizing gamma-aminobutyric acid (GABA), which postmortem studies suggest may be abnormal in schizophrenia. We therefore tested whether auditory neural networks in patients with schizophrenia could support gamma-range synchronization.

METHODS

Synchronization of the electroencephalogram (EEG) to different rates (20-40 Hz) of auditory stimulation was recorded from 15 patients with schizophrenia and 15 sex-, age-, and handedness-matched control subjects. The EEG power at each stimulation frequency was compared between groups. The time course of the phase relationship between each stimulus and EEG peak was also evaluated for gamma-range (40 Hz) stimulation.

RESULTS

Schizophrenic patients showed reduced EEG power at 40 Hz, but not at lower frequencies of stimulation. In addition, schizophrenic patients showed delayed onset of phase synchronization and delayed desynchronization to the click train.

CONCLUSIONS

These data provide new information on selective deficits in early-stage sensory processing in schizophrenia, a failure to support the entrainment of intrinsic gamma-frequency oscillators. The reduced EEG power at 40 Hz in schizophrenic patients may reflect a dysfunction of the recurrent inhibitory drive on auditory neural networks.

Comparison of brain metabolic activity patterns induced by ketamine, MK-801 and amphetamine in rats: support for NMDA receptor involvement in responses to subanesthetic dose of ketamine

Subanesthetic doses of NMDA receptor antagonists induce positive, negative and cognitive schizophrenia-like symptoms in healthy humans and precipitate psychotic reactions in stabilized schizophrenic patients. These findings suggest that defining neurobiologic effects induced by NMDA antagonists could guide the formulation of experimental models relevant to the pathophysiology of schizophrenia and antipsychotic drug action. Accordingly, the effects of subanesthetic doses of the non-competitive NMDA antagonists ketamine and MK-801 were examined on regional brain [14C]-2-deoxyglucose (2-DG) uptake in rats. The effects of these drugs were compared to those of amphetamine, in order to assess the potential role of generalized behavioral arousal, motor activity and dopamine release in brain metabolic responses to the NMDA antagonists. Subanesthetic doses of MK-801 and ketamine induced identical alterations in patterns of 2-DG uptake. The most pronounced increases in 2-DG for both NMDA antagonists were in the hippocampal formation and limbic cortical regions. By contrast, amphetamine treatment did not increase 2-DG uptake in these regions. In isocortical regions, ketamine and MK-801 reduced uptake in layers 3 and 4, creating a striking shift in the laminar pattern of 2-DG uptake in comparison to control conditions. After amphetamine, the fundamental laminar pattern of isocortical labeling was similar to saline-treated rats. Administration of ketamine and MK-801 decreased 2-DG uptake in the medial geniculate and inferior colliculus, whereas amphetamine tended to increase uptake in these regions. Since ketamine induced similar effects on regional 2-DG uptake as observed for the selective antagonists MK-801, the effects of ketamine are likely related to NMDA antagonistic properties of the drug. The distinct differences in brain 2-DG uptake induced by amphetamine and NMDA antagonists indicate that generalized behavioral arousal, and increased locomotor activity mediated by dopamine release, are not sufficient to account for the alterations in brain metabolic patterns induced by ketamine and MK-801. Thus, the dramatic alteration in regional 2-DG uptake induced by ketamine and MK-801 reflects a state selectively induced by reduced NMDA receptor function.

Antidepressant-induced bruxism successfully treated with gabapentin

BACKGROUND

Symptoms consistent with bruxism are a common chief complaint in dental practice. The authors describe a case of bruxism likely induced by the antidepressant venlafaxine and successfully treated with gabapentin.

CASE DESCRIPTION

A case of bruxism, anxiety, insomnia and tremor is reported in a man with bipolar disorder that developed a few days after he initiated venlafaxine therapy for depression. The patient's psychiatrist prescribed gabapentin for anxiety symptoms, and shortly thereafter the man experienced a complete resolution of the bruxism.

CLINICAL IMPLICATIONS

On the basis of this case and the available literature, the authors conclude that bruxism secondary to antidepressant therapy may be common. Thus, dentists should inquire about the use of these medications in patients who have bruxism. Gabapentin may offer promise in the treatment of this condition.

Modulatory effects of adenosine on inhibitory postsynaptic potentials in the lateral amygdala of the rat

1. Adenosine is a depressant in the central nervous system with pre- and postsynaptic effects. In the present study, intracellular recording techniques were applied to investigate the modulatory effects of adenosine on projection neurons in the lateral rat amygdala (LA), maintained as slices in vitro. 2. Adenosine reversibly reduced the amplitude of a fast inhibitory postsynaptic potential (IPSP) that was evoked by electrical stimulation of the external capsule and pharmacologically isolated by applying an N-methyl-D-aspartate and non-N-methyl-D-aspartate receptor antagonist, DL-(-)-2-amino-5-methyl-4-isoxazolepropionic acid and 6, 7-Dinitroquinoxaline-2,3-dione, respectively, and the gamma-aminobutyric acidB (GABAB) receptor antagonist CGP 35348. The postsynaptic potential that remained was abolished by locally applying bicuculline. 3. Adenosine reduced the amplitude of the fast IPSP on average by 40.3%. It had no significant effect on responses to exogenously applied GABA, on membrane potential or on input resistance, suggesting that the site of action was at presynaptic inhibitory interneurons in the LA. 4. The response to adenosine was mimicked by the selective adenosine A1 receptor agonist N6-cyclohexyladenosine and blocked by the selective adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine. 5. Neuronal responsiveness in the amygdala is largely controlled by inhibitory processes. Adenosine can presynaptically downregulate inhibitory postsynaptic responses and could exert dampening effects likely by depression of both excitatory and inhibitory neurotransmitter release.

Calcium channel blockers in psychiatric disorders: a review of the literature

OBJECTIVES

To review the published literature of the past 15 years regarding use of calcium channel blockers (CCBs) in psychiatric practice. These drugs, especially verapamil, have been recommended as possible treatments for mania and other disorders.

METHODS

The Cumulative Medical Index and other databases were searched and back-tracked to locate relevant articles. Sixty-one such articles were uncovered: 37 anecdotal reports, 7 partially controlled reports, and 17 controlled trials.

RESULTS

Most studies involved treatment of mania using verapamil. Although anecdotal reports were generally favourable, results from partially controlled reports or controlled clinical trials were mixed. Generally, verapamil was less effective than was lithium or placebo. Treatment of depression with CCBs was not very successful, regardless of the type of trial; the best trial was negative. The same was true for the treatment of schizophrenia, although the cases studied were extremely chronic and treatment-resistant. Evidence for efficacy in other illnesses, such as Alzheimer's disease or tardive dyskinesia was scanty but suggested that further trials might be in order.

CONCLUSIONS

CCBs do not at present have an established place in psychiatric treatment. Nonetheless, clinicians faced with a manic patient not responsive to other antimanic drugs, either alone or in combination, might consider adding verapamil as an adjunct. A study bearing on this specific issue is needed to determine whether or not such off-label use would really be justified.

Lamotrigine and the treatment of mania in bipolar disorder

Anticonvulsants, including valproate and carbamazepine, have established efficacy in the treatment of mania. The anticonvulsant, lamotrigine. has been reported to have antimanic and antidepressant efficacy, and mood-stabilising effects in case reports and preliminary open trials. The efficacy and tolerability of lamotrigine has been compared with olanzapine and lithium in a randomised, prospective, controlled fashion over a period of 4 weeks treatment in a total of 45 hospitalised patients with DSM-IV-defined mania. Significant improvements of a similar magnitude were observed for all treatment groups and lamotrigine was well tolerated. Mechanisms of action proposed to explain the antimanic activity of lamotrigine include inhibition of voltage-sensitive and use-dependent sodium channels, inhibition of glutamate release and calcium channel blockade. Platelet studies have indicated supersensitivity of glutamate receptors and increased intracellular calcium concentrations in patients with mania. Further clinical and mechanistic studies of lamotrigine use in mania are warranted.

Prophylaxis of bipolar disorder: how and who should we treat in the long term?

Bipolar disorder is a devastating and chronic mood disorder, which can require life-long treatment. The vast majority of patients will suffer relapse of symptoms in the absence of effective therapy. Of those patients receiving treatment, compliance to medication regimens is poor. Non-compliance, when associated with lithium treatment in particular, increases the risk of recurrence of illness. Problems associated with withdrawal serve as powerful stimuli to develop alternatives to lithium monotherapy. Conventional placebo-controlled studies of treatments are difficult in patients with bipolar disorder. Large-scale, pragmatic and clinically relevant trials should be employed to assess existing and novel treatments for bipolar disorder. These can only develop out of genuine clinician and patient uncertainty and the creation of a trial culture in everyday practice.

Electrophysiological correlates of language processing in schizotypal personality disorder

OBJECTIVE

This study examined whether the electrophysiological correlates of language processing found previously to be abnormal in schizophrenia are also abnormal in schizotypal individuals. The authors used the N400 component to evaluate language dysfunction in schizotypal individuals.

METHOD

Event-related potentials were recorded in 16 comparison subjects and 17 schizotypal individuals (who met full DSM-III-R criteria) to sentences presented both visually and aurally; half of the sentences ended with an expected word completion (congruent condition), and the other half ended with an unexpected word completion (incongruent condition).

RESULTS

In the congruent condition, the N400 amplitude was more negative in individuals with schizotypal personality disorder than in comparison subjects in both the visual and auditory modalities. In addition, in the visual modality, the N400 latency was prolonged in the individuals with schizotypal personality disorder.

CONCLUSIONS

The N400 was found to be abnormal in the individuals with schizotypal personality disorder relative to comparison subjects. The abnormality was similar to the abnormality the authors' laboratory reported earlier in schizophrenic subjects, in which the N400 amplitude was found to be more negative in both congruent and incongruent sentence completions. The N400 abnormality is consistent with the inefficient use of context.

Adenosine: a mediator of interleukin-1beta-induced hippocampal synaptic inhibition

Interleukin-1 (IL-1) is a pleotrophic cytokine implicated in a variety of central activities, including fever, sleep, ischemic injury, and neuromodulatory responses, such as neuroimmune, and neuroendocrine interactions. Although accumulating evidence is available regarding the expression pattern of this cytokine, its receptors in the CNS, and its mechanistic profile under pathological levels, it is unclear whether this substance modulates central neurons under physiological concentrations. Further, in light of the functional and spatial overlap between the adenosine and IL-1 systems, it is not known whether these two systems are coupled. We report here that, in rat brain slices, brief application of sub-femtomolar IL-1beta causes a profound decrease of glutamate transmission, but not GABAergic inhibition, in hippocampal CA1 pyramidal neurons. This decrease by IL-1beta is prevented by pharmacological blockade of adenosine A1 receptors. In addition, we show that IL-1beta failed to suppress glutamate transmission at room temperature. Because the production and release of adenosine in the CNS is thought to be metabolically dependent, this observation suggests that one of the functions of IL-1beta is to increase the endogenous production of adenosine. Together, these data suggest for the first time that sub-femtomolar levels of IL-1 can effectively modulate glutamate excitation in hippocampal neurons via an adenosine-dependent mechanism.

Adenosine: a mediator of interleukin-1beta-induced hippocampal synaptic inhibition

Interleukin-1 (IL-1) is a pleotrophic cytokine implicated in a variety of central activities, including fever, sleep, ischemic injury, and neuromodulatory responses, such as neuroimmune, and neuroendocrine interactions. Although accumulating evidence is available regarding the expression pattern of this cytokine, its receptors in the CNS, and its mechanistic profile under pathological levels, it is unclear whether this substance modulates central neurons under physiological concentrations. Further, in light of the functional and spatial overlap between the adenosine and IL-1 systems, it is not known whether these two systems are coupled. We report here that, in rat brain slices, brief application of sub-femtomolar IL-1beta causes a profound decrease of glutamate transmission, but not GABAergic inhibition, in hippocampal CA1 pyramidal neurons. This decrease by IL-1beta is prevented by pharmacological blockade of adenosine A1 receptors. In addition, we show that IL-1beta failed to suppress glutamate transmission at room temperature. Because the production and release of adenosine in the CNS is thought to be metabolically dependent, this observation suggests that one of the functions of IL-1beta is to increase the endogenous production of adenosine. Together, these data suggest for the first time that sub-femtomolar levels of IL-1 can effectively modulate glutamate excitation in hippocampal neurons via an adenosine-dependent mechanism.

Alcohol, slow wave sleep, and the somatotropic axis

When alcohol is a large proportion of daily nutrient energy, the network of signals for energy homeostasis appears to adapt with abnormal patterns of sleep and growth hormone (GH) release along with gradual acquisition of an addictive physical dependency on alcohol. Early relapse during treatment of alcoholism is associated with a lower GH response to challenge, perhaps reflecting an altered balance of somatostatin (SS) to somatropin releasing hormone (GHRH) that also affects slow wave sleep (SWS) in dependent patients. Normal patterns of sleep have progressively shorter SWS episodes and longer rapid eye movement (REM) episodes during the overall sleep period, but the early sleep cycles of alcoholics have truncated or non-existent SWS episodes, and the longer REM episodes occur in early cycles. During SWS delta wave activity, the hypothalamus releases GHRH, which causes the pituitary to release GH. Alcohol-dependent patients have lower levels of SWS power and GH release than normal subjects, and efforts to understand the molecular basis for this maladaptation and its relation to continued alcohol dependence merit encouragement. More needs to be learned about the possibility of decreasing alcohol dependency by increasing SWS or enhancing GHRH action.

Gabapentin: a review of published experience in the treatment of bipolar disorder and other psychiatric conditions

Successful therapy with valproate and carbamazepine in patients with psychiatric disorders led to investigation of other anticonvulsants for similar indications. Gabapentin is a relatively new anticonvulsant being investigated for potential use in the treatment of bipolar disorder (BD), anxiety disorders, behavioral dyscontrol, and substance use disorders. Its favorable side effect profile, absence of the need for therapeutic drug monitoring, and minimal drug interactions give gabapentin a potential role in these indications. Computer searches of the biomedical literature were undertaken to identify all pertinent case reports, case series, and studies of the drug as monotherapy or adjunctive therapy for BD; 10 reports were retrieved. In the treatment of various anxiety disorders, one study, one case report, and one case series were identified. At least one case series described gabapentin therapy for alcohol withdrawal and one case report of the drug for agitation associated with dementia. Published, well-designed studies evaluating the agent's effectiveness as monotherapy for BD are lacking. Its benefit as an adjunctive treatment with other mood stabilizers is also unestablished. Data regarding its efficacy in the treatment of anxiety disorders or manifestations of substance abuse are limited. These areas may deserve further investigation.

MRI anatomy of schizophrenia

Structural magnetic resonance imaging (MRI) data have provided much evidence in support of our current view that schizophrenia is a brain disorder with altered brain structure, and consequently involving more than a simple disturbance in neurotransmission. This review surveys 118 peer-reviewed studies with control group from 1987 to May 1998. Most studies (81%) do not find abnormalities of whole brain/intracranial contents, while lateral ventricle enlargement is reported in 77%, and third ventricle enlargement in 67%. The temporal lobe was the brain parenchymal region with the most consistently documented abnormalities. Volume decreases were found in 62% of 37 studies of whole temporal lobe, and in 81% of 16 studies of the superior temporal gyrus (and in 100% with gray matter separately evaluated). Fully 77% of the 30 studies of the medial temporal lobe reported volume reduction in one or more of its constituent structures (hippocampus, amygdala, parahippocampal gyrus). Despite evidence for frontal lobe functional abnormalities, structural MRI investigations less consistently found abnormalities, with 55% describing volume reduction. It may be that frontal lobe volume changes are small, and near the threshold for MRI detection. The parietal and occipital lobes were much less studied; about half of the studies showed positive findings. Most studies of cortical gray matter (86%) found volume reductions were not diffuse, but more pronounced in certain areas. About two thirds of the studies of subcortical structures of thalamus, corpus callosum and basal ganglia (which tend to increase volume with typical neuroleptics), show positive findings, as do almost all (91%) studies of cavum septi pellucidi (CSP). Most data were consistent with a developmental model, but growing evidence was compatible also with progressive, neurodegenerative features, suggesting a "two-hit" model of schizophrenia, for which a cellular hypothesis is discussed. The relationship of clinical symptoms to MRI findings is reviewed, as is the growing evidence suggesting structural abnormalities differ in affective (bipolar) psychosis and schizophrenia.

Region-dependent difference in the sleep-promoting potency of an adenosine A2A receptor agonist

The present study has demonstrated that the sleep-promoting potency of 2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamido adenosine (CGS21680), a selective agonist for the adenosine A2A receptor, varies depending on the location of the administration. CGS21680 was continuously administered to rats through a chronically implanted cannula for 6 h during their active phase. The tip of the cannula was located in the subarachnoid space or the brain ventricle neighbouring the established brain areas implicated in the regulation of sleep-wake phenomena, i.e. rostral basal forebrain, medial preoptic area, lateral preoptic area, posterior hypothalamus, and dorsal tegmentum of the pons and medulla. At an infusion rate of 2.0 pmol/min, the magnitude of increase in non-rapid eye movement sleep varied from 14 min (a 15% increase) to 96 min (a 103% increase), and those of rapid eye movement sleep varied from 6 min (a 40% increase) to 28 min (a 264% increase) from the respective baseline values. The largest increases in both types of sleep occurred when CGS21680 was administered to the subarachnoid space underlying the rostral basal forebrain. These findings were interpreted to mean that the major, if not the only, site responsible for the CGS21680-inducing sleep was located in or near the rostral basal forebrain. This interpretation was supported by the findings that the administration of CGS21680 to the rostral basal forebrain produced predominant expression of Fos within the shell of the nucleus accumbens and the medial portion of the olfactory tubercle, and that the microdialysis perfusion of CGS21680 into the shell of the nucleus accumbens also exhibited a sleep-promoting effect.

Mood stabilizers in children and adolescents

OBJECTIVE

The efficacy of mood stabilizers in children and adolescents has not been studied adequately. This article will review existing studies and highlight some important issues in designing future studies on these agents.

METHOD

Electronic databases including Medline, Psycholnfo, and CRISP were searched for data in children receiving compounds that have mood-stabilizing properties in adults.

RESULTS

Some open clinical data and an extremely modest amount of controlled research data suggest lithium, carbamazepine, and valproate may be effective mood stabilizers in children and adolescents. There are no controlled data on other potential mood stabilizers in children.

CONCLUSIONS

The disorders that may be responsive to mood stabilizers are among the most morbid in child psychiatry. More studies are needed to clarify the efficacy of these compounds in children and adolescents and to provide a rational basis for choosing among them.

Adenosine in sleep and wakefulness

Sleep propensity increases in the course of wakefulness: the longer the previous wakefulness period is, the longer and deeper (measured as delta power in EEG recordings) is the following sleep. The mechanisms that regulate the need of sleep at the cellular level are largely unknown. The inhibitory neuromodulator, adenosine, is a promising candidate for a sleep-inducing factor: its concentration is higher during wakefulness than during sleep, it accumulates in the brain during prolonged wakefulness, and local perfusions as well as systemic administration of adenosine and its agonists induce sleep and decrease wakefulness. Adenosine receptor antagonists, caffeine and theophylline, are widely used as stimulants of the central nervous system to induce vigilance and increase the time spent awake. Our hypothesis is that adenosine accumulates in the extracellular space of the basal forebrain during wakefulness, increasing the sleep propensity. The increase in extracellular adenosine concentration decreases the activity of the wakefulness-promoting cell groups, especially the cholinergic cells in the basal forebrain. When the activity of the wakefulness-active cells decreases sufficiently sleep is initiated. During sleep the extracellular adenosine concentrations decrease, and thus the inhibition of the wakefulness-active cells also decreases allowing the initiation of a new wakefulness period.

Long-term suppression of synaptic transmission by tetanization of a single pyramidal cell in the mouse hippocampus in vitro

1. The consequences of stimulating a single pyramidal cell in the CA1 area of the hippocampus for synaptic transmission in the stratum radiatum were investigated. 2. Tetanic activation of single pyramids caused by depolarizing current injection, but not an equal number of distributed action potentials, reduced excitatory transmission by 20 %, with a delayed onset, for more than 1 h. 3. EPSPs in the tetanized pyramidal cells were increased for equally long periods but this was not the cause of the field EPSP reduction. Spontaneous somatic IPSPs were not affected; evoked IPSPs were decreased in the tetanized cell. 4. Paired pulse facilitation of the field EPSPs was unchanged. 5. The field EPSP reduction was markedly diminished by a knife cut along the base of pyramidal cells in CA1. 6. The addition of antagonists of GABA, NMDA and metabotropic glutamate receptors blocked or diminished the field EPSP slope reduction evoked by intracellular stimulation. 7. Simultaneous recordings revealed long-lasting excitations of interneurons located in the outer oriens layer as a result of single pyramid tetanization. 8. Intense firing of small numbers of pyramidal cells can thus persistently inhibit mass transmission through the hippocampus. This effect involves activation of interneurons by glutamate receptors.

Differential induction of long-lasting potentiation of inhibitory postsynaptic potentials by theta patterned stimulation versus 100-Hz tetanization in hippocampal pyramidal cells in vitro

Tetanization of Schaffer collaterals, which induces long-term potentiation of excitatory transmission in the hippocampus of the rat, also affects local inhibitory circuits. Mechanisms controlling plasticity of early and late components of inhibitory postsynaptic potentials in CA1 pyramidal cells were studied using intracellular recordings and Ca2+ imaging in rat hippocampal slices. High-frequency stimulation (100 Hz/s) of Schaffer collaterals resulted in no change in the mean amplitude of early or late inhibitory postsynaptic potentials 30 min post-tetanus. However, intracellular injection of the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetate unmasked a significant increase in mean amplitude of both inhibitory postsynaptic potentials 30 min post-tetanus and the induction of this potentiation was blocked by the N-methyl-D-aspartate receptor antagonist(+/-)-2-amino-5-phosphopentanoic acid. In contrast to high-frequency tetanization, "theta-burst" stimulation in normal medium resulted in a significant potentiation of the mean amplitude of both early and late inhibitory postsynaptic potentials 30 min post-tetanus. This potentiation was blocked by the N-methyl-D-aspartate receptor antagonist. The more physiological tetanization pattern, which mimics the endogenous theta rhythm, therefore resulted in an N-methyl-D-aspartate-dependent increase in inhibition 30 min post-tetanus. Calcium imaging during whole-cell recordings from pyramidal cells revealed differences in the Ca2+ signal associated with high-frequency and theta-burst stimulations. During theta-burst stimulation of Schaffer collaterals, the mean time to peak of Ca2+ signals was significantly longer, and the mean peak amplitude and area under the Ca2+ response were larger than during high-frequency stimulation. These results indicate that tetanization induces long-lasting synaptic plasticity in hippocampal inhibitory circuits. This plasticity involves an interaction between a Ca2(+)-mediated postsynaptic depression and an N-methyl-D-aspartate-mediated potentiation of GABAA and GABAB inhibition, and these processes are differentially sensitive to tetanization parameters.

Selective suppression of forward and recurrent "rapid" inhibition by local application of picrotoxin in area CA1 of rat hippocampal slices

Living slices of rat hippocampus were used to study the possibility of suppressing forward and recurrent "rapid" inhibition in area CA1 by local application of picrotoxin, an antagonist of ionotropic gamma-aminobutyric acid (GABAA) receptors. Application of picrotoxin to the apical dendrites increased the duration of focal potentials recorded in the radial layer (143.0 +/- 7.5%, n = 5; here and subsequently, results are presented as mean +/- error of the mean and n is the number of experiments) but had no effect on the population peak in the pyramidal layer (103.0 +/- 19.6%, n = 5). This is evidence for the existence of suppression of direct, but not of recurrent inhibition. Application of picrotoxin to the cell body layer, on the other hand, significantly increased the population peak (654.5 +/- 245.1%, n = 4) and provoked convulsive activity in neurons, demonstrating suppression of recurrent inhibition. Local application of picrotoxin was further used to study the question of how completely antagonists of glutamate ionotropic receptors sensitive to alpha-amino-3-hydroxy-S-methyl-4-isoxazole propionic acid (AMPA) suppress inhibition in solutions with low magnesium contents. This question is important for interpreting experimental data obtained from measurements of the components of excitatory postsynaptic potentials (EPSP), which depend on activation of ionotropic glutamate receptors sensitive to N-methyl-d-aspartic acid (NMDA). A number of studies have suggested that even at low concentrations, AMPA receptor antagonists suppress forward inhibition to such an extent that it has no significant effect on measurements of the NMDA component of EPSP. Our data do not contradict this suggestion.

Adenosine release mediates cyanide-induced suppression of CA1 neuronal activity

The rapid suppression of CNS function produced by cyanide (CN) was studied by field, intracellular, and whole-cell recording in hippocampal slices (at 33-34 degrees C). Population spikes and field EPSPs were depressed by 4-5 min bath applications of 50-100 microM CN (IC50 was 18 miroM for spikes and 72 microM for EPSPs). The actions of CN were reversibly suppressed by the adenosine antagonists 8-sulfophenyltheophylline (8-SPT; 10 microM) and 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.2 microM), potentiated by the adenosine transport inhibitor dipyridamole (0.5 microM), but unaffected by the KATP channel blocker glyburide (10 microM). Therefore the CN-induced reductions of synaptic efficacy and postsynaptic excitability-demonstrated by synaptic input:output plots-are mediated mainly by adenosine. In whole-cell or intracellular recordings, CN depressed EPSCs and elicited an increase in input conductance and an outward current, the reversal potential of which was approximately -90 mV (indicating that K+ was the major carrier). These effects also were attenuated by 8-SPT. In the presence of 1 mM Ba, CN had no significant postsynaptic action; Cs (2 mM) also prevented CN-induced outward currents but only partly blocked the increase in conductance. Another 8-SPT-sensitive action of CN was to depress hyperpolarization-activated slow inward relaxations (Q current). At room temperature (22-24 degrees C), although it did not change holding current and slow inward relaxations, CN raised the input conductance; this effect also was prevented by 8-SPT (10 microM), but not by glyburide (10 microM). Adenosine release thus appears to be the major link between acute CN poisoning and early depression of CNS synaptic function.

Selective agonists of metabotropic glutamate receptors elicit significant EEG effects when infused in the nucleus accumbens of rats

The effect of intra-accumbens infusion of selective group I ((S)-3,5-dihydroxyphenylglycine, DHPG), group II ((2S,3S,4S)-CCG/(2S,1'S,2'S)-2-(carboxycyclopropyl)glycine, L-CCG-I) and group III ((L-(+)-2-amino-4-phosphonobutyric acid, L-AP4) metabotropic glutamate (mGlu) receptor agonists was studied in male Wistar rats. A computerised electroencephalographic (EEG) power spectral analysis was performed. While DHPG (400 nmoles) induced EEG and behavioural limbic seizures, L-CCG-I (400 nmoles) and L-AP4 (800 nmoles) induced a 'depressant' EEG with an increase in relative power in the slow-frequency bands and a decrease in relative power in the high-frequency bands) and behavioural effects. These results show for the first time that the stimulation of groups I, II and III mGlu receptors located in the nucleus accumbens significantly influences the EEG tracing in rats.

Human brain metabolic response to caffeine and the effects of tolerance

OBJECTIVE

Since there is limited information concerning caffeine's metabolic effects on the human brain, the authors applied a rapid proton echo-planar spectroscopic imaging technique to dynamically measure regional brain metabolic responses to caffeine ingestion. They specifically measured changes in brain lactate due to the combined effects of caffeine's stimulation of glycolysis and reduction of cerebral blood flow.

METHOD

Nine heavy caffeine users and nine caffeine-intolerant individuals, who had previously discontinued or substantially curtailed use of caffeinated products because of associated anxiety and discomforting physiological arousal, were studied at baseline and then during 1 hour following ingestion of caffeine citrate (10 mg/kg). To assess state-trait contributions and the effects of caffeine tolerance, five of the caffeine users were restudied after a 1- to 2-month caffeine holiday.

RESULTS

The caffeine-intolerant individuals, but not the regular caffeine users, experienced substantial psychological and physiological distress in response to caffeine ingestion. Significant increases in global and regionally specific brain lactate were observed only among the caffeine-intolerant subjects. Reexposure of the regular caffeine users to caffeine after a caffeine holiday resulted in little or no adverse clinical reaction but significant rises in brain lactate which were of a magnitude similar to that observed for the caffeine-intolerant group.

CONCLUSIONS

These results provide direct evidence for the loss of caffeine tolerance in the human brain subsequent to caffeine discontinuation and suggest mechanisms for the phenomenon of caffeine intolerance other than its metabolic effects on elevating brain lactate.

Multimodal imaging in psychiatry: the electroencephalogram as a complement to other modalities

The use of different imaging modalities provides the clinician and researcher with different views of anatomy and physiology at unprecedented levels of detail. Multimodal imaging allows for noninvasive measurement of structure and function in humans during complex behavior, and thus provides information about the inner workings of the brain previously unavailable. The present paper examines the various imaging techniques available, and describes their application to the clinic-in the case of epilepsy-and to research-in the case of schizophrenia. Because the electroencephalogram has a dynamic response in milliseconds, it provides the best temporal sensitivity of functional measures of brain activity. When coupled with high-resolution magnetic resonance imaging measures of brain structure, this multimodal approach provides a powerful tool for understanding brain activity. Clinically, the use of multimodal imaging has provided greater precision in localization of the epileptogenic focus. For researchers attempting to determine the underlying causes of schizophrenia, the use of multimodal imaging has helped lead the field away from a specific lesion view to a more distributed system abnormality view of this disorder.

Effects of (+/-)-kavain on voltage-activated inward currents of dorsal root ganglion cells from neonatal rats

Kava pyrones extracted from pepper Piper methysticum are pharmacologically active compounds. Since kava pyrones exhibit anticonvulsive, analgesic and centrally muscle relaxing properties, the influence of a synthetic kava pyrone, (+/-)-kavain, on voltage-dependent ion channel currents was studied. Effects of (+/-)-kavain on voltage-activated inward currents were analysed in cultured dorsal root ganglion cells derived from neonatal rats. Voltage-activated Ca2+ and Na+ currents were elicited in the whole-cell configuration of the patch clamp technique. Extracellularly applied (+/-)-kavain dissolved in hydrous salt solutions reduced voltage-activated Ca2+ and Na+ channel currents within 3-5 min. As the solubility of (+/-)-kavain in hydrous solutions is low, dimethyl sulfoxide (DMSO) was added to the saline as a solvent for the drug in most experiments. When (+/-)-kavain was dissolved in DMSO, the drug induced a fast and pronounced reduction of both Ca2+ and Na+ currents, which partly recovered within 2-5 min even in the presence of the drug. The present study indicates that (+/-)-kavain reduces currents through voltage-activated Na+ and Ca2+ channels.

Modulation of N-methyl-D-aspartate receptor function by glycine transport

The recent discovery of glycine transporters in both the central nervous system and the periphery suggests that glycine transport may be critical to N-methyl-D-aspartate receptor (NMDAR) function by controlling glycine concentration at the NMDAR modulatory glycine site. Data obtained from whole-cell patch-clamp recordings of hippocampal pyramidal neurons, in vitro, demonstrated that exogenous glycine and glycine transporter type 1 (GLYT1) antagonist selectively enhanced the amplitude of the NMDA component of a glutamatergic excitatory postsynaptic current. The effect was blocked by 2-amino-5-phosphonovaleric acid and 7-chloro-kynurenic acid but not by strychnine. Thus, the glycine-binding site was not saturated under the control conditions. Furthermore, GLYT1 antagonist enhanced NMDAR function during perfusion with medium containing 10 microM glycine, a concentration similar to that in the cerebrospinal fluid in vivo, thereby supporting the hypothesis that the GLYT1 maintains subsaturating concentration of glycine at synaptically activated NMDAR. The enhancement of NMDAR function by specific GLYT1 antagonism may be a feasible target for therapeutic agents directed toward diseases related to hypofunction of NMDAR.

Slow oscillations (</=1 Hz) mediated by GABAergic interneuronal networks in rat hippocampus

Perfusion of rat brain slices with low millimole CsCl elicits slow oscillations of </=1 Hz in hippocampal CA1 pyramidal neurons. These oscillations are GABAA receptor-mediated hyperpolarizations that permit a coherent fire-pause pattern in a population of CA1 neurons. They can persist without the activation of ionotropic glutamate receptors but require adenosine-dependent inhibition of glutamate transmission. In response to external Cs+, multiple interneurons in the CA1 region display rhythmic discharges that correlate with the slow oscillations in CA1 pyramidal neurons. The interneuronal discharges arise spontaneously from the resting potential, and their rhythmicity is regulated by periodic, GABAA receptor-mediated hyperpolarizations. In addition, interneurons show periodic partial spikes and neurobiotin coupling, and applications of known gap junctional uncouplers interrupt the Cs+-induced slow rhythm in both CA1 pyramidal neurons and interneurons. We propose that these slow oscillations originate from a GABAergic interneuronal network that interacts through reciprocal inhibition and possibly gap junctional connection.

Missing action of carbamazepine on postsynaptic GABA-responses of hippocampal CA3-neurons (slice, guinea pig)

Conflicting data exist concerning the interaction of carbamazepine (CBZ) and GABA-receptors involved in the pathophysiology of neuropsychiatric disorders. The present study reveals that CBZ failed to alter membrane potential fluctuations mediated by an activation of postsynaptic GABA(A)- and GABA(B)-receptors of hippocampal CA3-neurons even at a bath concentration of 500 microM (ca. 10-30 fold the therapeutic level, tested up to 90 min). Therefore, therapeutic effects of CBZ cannot be due to acute modulations of postsynaptic GABA-responses.