The inflammatory response system and the availability of plasma tryptophan in patients with primary sleep disorders and major depression

BACKGROUND

It is now well established that major depression is accompanied by an immune-inflammatory system response and that indicators of the latter are inversely correlated with lower availability of plasma tryptophan in depression. Inflammation and infection can alter sleep architecture, whereas sleep disturbances can impair immune functions.

AIMS AND METHODS

The aims of the present study were to examine: (i) immune-inflammatory markers, i.e. serum interleukin-6 (IL-6), IL-8, IL-6 receptor (IL-6R), IL-1R antagonist (IL-1RA), gp130, and prostaglandin E2 (PGE2) production by mitogen-stimulated whole blood and the availability of plasma tryptophan in patients with primary sleep disorders, major depression and healthy volunteers; and (ii) the relationships between the availability of tryptophan and indicators of the immune-inflammatory response system.

RESULTS

Mitogen-stimulated release of PGE2, and serum IL-6 and IL-8, were significantly increased in both depressed and sleep disordered patients compared to normal controls. Serum IL-1RA was significantly higher in depressed patients than in normal controls. Patients with depression and sleep disorders had a significantly lower availability of tryptophan than normal controls. There were significant and inverse relationships between the availability of plasma tryptophan and serum IL-1RA, IL-6 and IL-8.

CONCLUSIONS

The results suggest that (i) there is an activation of the immune-inflammatory response system in primary sleep disorders and depression; and (ii) the decreased availability of plasma tryptophan may be related to the inflammatory system response.

Caffeine--an atypical drug of dependence

Caffeine has both positive effects that contribute to widespread consumption of caffeine-containing beverages and adverse unpleasant effects if doses are increased. Caffeine has weak reinforcing properties, but with little or no evidence for upward dose adjustment, possibly because of the adverse effects of higher doses. Withdrawal symptoms, although relatively limited with respect to severity, do occur, and may contribute to maintenance of caffeine consumption. Health hazards are small if any and caffeine use is not associated with incapacitation. Thus, although caffeine can be argued to fulfill regulatory criteria as a dependence-producing drug, the extensive use of caffeine-containing beverages poses little apparent risk to the consumer or to society. The positive stimulatory effects of caffeine appear in large measure to be due to blockade of A2A receptors that stimulate GABAergic neurons of inhibitory pathways to the dopaminergic reward system of the striatum. However, blockade of striatal A1 receptors may also play a role. The mechanisms underlying negative effects of higher doses of caffeine are as yet not well defined.

Isolation and expression of a rat brain cDNA encoding glutamate carboxypeptidase II

N-acetylated alpha-linked acidic dipeptidase (NAALADase) hydrolyzes acidic peptides, such as the abundant neuropeptide N-acetyl-alpha-L-aspartyl-L-glutamate (NAAG), thereby generating glutamate. Previous cDNA cloning efforts have identified a candidate rat brain NAALADase partial cDNA, and Northern analyses have identified a family of related RNA species that are found only in brain and other NAALADase-expressing cells. In this report, we describe the cloning of a set of rat brain cDNAs that describe a full-length NAALADase mRNA. Transient transfection of a full-length cDNA into the PC3 cell line confers NAAG-hydrolyzing activity that is sensitive to the NAALADase inhibitors quisqualic acid and 2-(phosphonomethyl)glutaric acid. Northern hybridization detects the expression of three similar brain RNAs approximately 3,900, 3,000, and 2,800 nucleotides in length. In situ hybridization histochemistry shows that NAALADase-related mRNAs have an uneven regional distribution in rat brain and are expressed predominantly by astrocytes as demonstrated by their colocalization with the astrocyte-specific marker glial fibrillary acidic protein.

Comparison of an adenosine A1 receptor agonist and antagonist on the rat EEG

The effects of the selective adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA; 1 and 0.1 mg/kg, i.p.) and the A1 selective antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX) have been examined on the electroencephalogram (EEG) of intact rats. From four EEG leads the EEG signal was subjected to Fast Fourier Transform and analysed both in narrow (0.01629638 Hz) and wide frequency bands. CPA tended to increase EEG power at low frequencies, and in several of the narrow frequency bands significantly shifted peak frequencies to lower values. The agonist also increased peak power in some frequency bands. The results are consistent with the view that A1 adenosine receptors mediate a generally depressant effect on neuronal activity in most brain regions, but may increase activity in areas with low resting rates of firing. The modest elevation of wave power by CPX indicates a limited control by resting endogenous adenosine, which is greatest in areas of highest activity, consistent with adenosine release being related to neuronal activity.

Piscicidal properties of piperovatine from Piper piscatorum (Piperaceae)

Extraction of the roots of the Amazonian medicinal plant, Piper piscatorum Trelease and Yuncker, with MeOH and subsequent bioassay guided fractionation using the guppy, Girardina guppii yielded the active amide, N-isobutyl-6-(p-methoxyphenyl) 2E, 4E-hexadieneamide (piperovatine) and a second inactive amide, N-isobutyl-(E)-7-(3,4-methylenedioxyphenyl)hept-2-enamide (pipercallosidine). The former displayed an LC50 of 115 ng/ml in toxicity tests and proved to be the constituent responsible for the dual ethnobotanical uses of this plant: that of fish stupefacient (barbasco) and oral local anesthetic.

Substance P regulates Ih via a NK-1 receptor in vagal sensory neurons of the ferret

Substance P (SP) hyperpolarizes approximately 80% of ferret vagal sensory neurons (nodose ganglion neurons) via NK-1 receptor-mediated activation of a potassium current (IK). A depolarizing current activated by membrane hyperpolarization could minimize the SP-induced hyperpolarization. Such a current exists in 65% of the nodose neurons (n = 264). In this study, we examine this current and how it can interact with SP-induced membrane hyperpolarizations. This slowly developing, noninactivating inward current, designated Ih, was activated maximally at about -120 mV and had a reversal potential value of -23 +/- 4.4 mV (n = 4). The time course of activation followed voltage-dependent, monoexponential kinetics. Steady-state activation curves derived from tail current analysis were well fit by a Boltzmann equation yielding a half-activation potential (V1/2) of-77 +/- 1.5 mV and a ks value of 18 +/- 0.5 (n = 8). In the presence of 1 mM cesium, the current was completely abolished. These parameters are consistent with those derived for Ih in other neurons. Substance P (200 nM) reduced the magnitude of Ih elicited by membrane hyperpolarizations to about -110 mV but did not affect the magnitude of Ih elicited by hyperpolarizations to more negative potentials. Tail current analysis revealed that this effect was the result of a SP-induced shift of the Ih activation curve to more negative membrane potentials. The V1/2 value for Ih was shifted by -20 +/- 1.4 mV in the presence of SP with no change in ks (18 +/- 0.7; n = 5). The SP effect on Ih, like its effect on IK, was blocked reversibly by 10 nM CP99,994, a NK-1 antagonist, and was mimicked by the NK-1 agonist Ac-[Arg6, Sar9, Met(O2)11]SP(6-11) (ASMSP; 200 nM). Ih was not affected by NK-2 or NK-3 selective agonists (n = 4 for each) nor was the effect of SP on Ih reduced by an NK-2 antagonist (n = 4). These results show that SP activates a NK-1 receptor coupled to the Ih channel. Thus NK-1 receptor activation in ferret vagal afferents not only leads to membrane hyperpolarization but it also can enhance synergistically this inhibitory effect by decreasing Ih.

Free recall and recognition in a network model of the hippocampus: simulating effects of scopolamine on human memory function

Free recall and recognition are simulated in a network model of the hippocampal formation, incorporating simplified simulations of neurons, synaptic connections, and the effects of acetylcholine. Simulations focus on modeling the effects of the acetylcholine receptor blocker scopolamine on human memory. Systemic administration of scopolamine is modeled by blockade of the cellular effects of acetylcholine in the model, resulting in memory impairments replicating data from studies on human subjects. This blockade of cholinergic effects impairs the encoding of new input patterns (as measured by delayed free recall), but does not impair the delayed free recall of input patterns learned before the blockade. The impairment is selective to the free recall but not the recognition of items encoded under the influence of scopolamine. In the model, scopolamine blocks strengthening of recurrent connections in region CA3 to form attractor states for new items (encoding impaired) but allows recurrent excitation to drive the network into previously stored attractor states (retrieval spared). Neuron populations representing items (individual words) have weaker recurrent connections than neuron populations representing experimental context. When scopolamine further weakens the strength of recurrent connections it selectively prevents the subsequent reactivation of item attractor states by context input (impaired free recall) without impairing the subsequent reactivation of context attractor states by item input (spared recognition). This asymmetry in the strength of attractor states also allows simulation of the list-strength effect for free recall but not recognition. Simulation of a paired associate learning paradigm predicts that scopolamine should greatly enhance proactive interference due to retrieval of previously encoded associations during storage of new associations.

Distribution of adenosine receptors in the postmortem human brain: an extended autoradiographic study

Whole-hemisphere sections from six subjects were used in a quantitative autoradiographic study to characterize and to investigate the distribution of adenosine receptors, using [3H]DPCPX, [3H]CGS 21680, and [3H]SCH 58261 as radioligands. [3H]DPCPX-binding showed the pharmacology expected for adenosine A1 receptors and is therefore taken to mirror adenosine A1 receptors. Adenosine A1 receptors were widely distributed, with the highest densities in the stratum radiatum/pyramidale of the hippocampal region CA1. Adenosine A1 receptors were nonhomogeneously distributed in nucleus caudatus, globus pallidus, and cortical areas: In the cingulate and frontal cortex the deep layers showed the highest labeling, while in the occipital, parietal, temporal, and insular cortex it was highest in the superficial layers. In addition, we found very high levels of adenosine A1 receptors in structures known to be important for cholinergic transmission, especially the septal nuclei. The Bmax values and KD values for [3H]DPCPX-binding in stratum radiatum/pyramidale of CA1 and the superficial layer of insular cortex were 598 and 430 fmol/mg gray matter and 9.9 and 14.2 nM, respectively. [3H]CGS 21680-binding was multiphasic, but showed the pharmacology expected for adenosine A2A receptors and was taken to represent them. Adenosine A2A receptors were abundant in putamen, nucleus caudatus, nucleus accumbens, and globus pallidus pars lateralis. Specific [3H]CGS 21680-binding was also found in certain thalamic nuclei and throughout the cerebral cortex. The adenosine A2A receptor antagonist radioligand [3H]SCH 58261 was also found to label these extrastriatal structures. Thus, adenosine A2A receptors seem to be more widely distributed in the human brain than previously recognized.

The nagging question of the function of N-acetylaspartylglutamate

N-Acetylaspartylglutamate (NAAG) is a neuropeptide found in millimolar concentrations in brain that is localized to subpopulations of glutamatergic, cholinergic, GABAergic, and noradrenergic neuronal systems. NAAG is released upon depolarization by a Ca(2+)-dependent process and is an agonist at mGluR3 receptors and an antagonist at NMDA receptors. NAAG is catabolized to N-acetylaspartate and glutamate primarily by glutamate carboxypeptidase II, which is expressed on the extracellular surface of astrocytes. The levels of NAAG and the activity of carboxypeptidase II are altered in a regionally specific fashion in several neuropsychiatric disorders.

N-acetylaspartylglutamate (NAAG) protects against rat striatal quinolinic acid lesions in vivo

We examined the effects of N-acetylaspartylglutamate (NAAG), an endogenous peptide thought to be involved in neurotransmission and neuromodulation, on striatal quinolinate lesions, a rodent model of Huntington's disease. We found that NAAG (500 and 1000 nmol) co-injected with quinolinic acid significantly reduced lesion volumes (by 50% and 65%, respectively). A 1000 nmol dose of the non-hydrolyzable analogue, beta-NAAG, also reduced quinolinic acid lesion volumes by 78.4%, indicating that the protection observed was not secondary to cleavage of NAAG into N-acetyl-aspartate (NAA) and glutamate. Likewise, co-injection of both NAA and glutamate (1000 nmol each) with quinolinic acid did not significantly alter the size of lesions. NAAG's protective effect may be mediated through actions on N-methyl-D-aspartate receptors or metabotropic glutamate receptors.

Glutamate in schizophrenia: clinical and research implications

The excitatory amino acids, glutamate and aspartate, are of interest to schizophrenia research because of their roles in neurodevelopment, neurotoxicity and neurotransmission. Recent evidence suggests that densities of glutamatergic receptors and the ratios of subunits composing these receptors may be altered in schizophrenia, although it is unclear whether these changes are primary or compensatory. Agents acting at the phencyclidine binding site of the NMDA receptor produce symptoms of schizophrenia in normal subjects, and precipitate relapse in patients with schizophrenia. The improvement of negative symptoms with agents acting at the glycine modulatory site of the NMDA receptor, as well as preliminary evidence that clozapine may differ from conventional neuroleptic agents in its effects on glutamatergic systems, suggest that clinical implications may follow from this model. While geriatric patients may be at increased risk for glutamate-mediated neurotoxicity, very little is known about the specific relevance of this model to geriatric patients with schizophrenia.

Distribution of N-acetylaspartylglutamate immunoreactivity in human brain and its alteration in neurodegenerative disease

The dipeptide N-acetylaspartylglutamate (NAAG) may be involved in the process of glutamatergic signaling by both acting at glutamate receptors and as a glutamate protransmitter. In the present study we determined the cellular localization and distribution of NAAG-like immunoreactivity (NAAG-LI) in normal human brain and in neurodegenerative disorders to ascertain the degree of NAAG's colocalization to putative glutamatergic pathways. Immunohistochemistry with an antibody against NAAG was performed on control, Huntington's disease (HD) and Alzheimer's disease (AD) human autopsy and biopsy brain sections from the cerebral cortex, hippocampus, amygdala, neostriatum, brainstem and spinal cord. In normal human brain, NAAG-LI was widespread localized to putative glutamatergic pyramidal neurons of the cerebral cortex and hippocampus. Punctate NAAG-LI was present in areas known to receive neuronal glutamatergic input, such as layer IV of the cerebral cortex, striatal neuropil, and the outer portion of the molecular layer of the hippocampal dentate gyrus. In the two pathologic brain regions examined, the HD neostriatum and the AD temporal cortex, we observed a widespread loss of NAAG-LI neurons. In addition NAAG-LI reactive microglia surrounding plaques were seen in AD temporal cortex but not in the HD striatum. Our results suggest that NAAG is substantially localized to putative glutamatergic pathways in human brain and that NAAG-LI neurons are vulnerable to the neurodegenerative process in HD and AD.

An immunocytochemical study on the distribution of two G-protein-gated inward rectifier potassium channels (GIRK2 and GIRK4) in the adult rat brain

G-protein-gated inward rectifier potassium channels mediate the synaptic actions of numerous neurotransmitters in the mammalian brain, and were recently shown to be candidates for genetic mutations leading to neuronal cell death. This report describes the localization of G-protein-gated inward rectifier potassium channel-2 and G-protein-gated inward rectifier potassium channel-4 proteins in the rat brain, as assessed by immunocytochemistry. G-protein-gated inward rectifier potassium channel-2 immunoreactivity was widely distributed throughout the brain, with the strongest staining seen in the hippocampus, septum, granule cell layer of the cerebellum, amygdala and substantia nigra pars compacta. In contrast, G-protein-gated inward rectifier potassium channel-4 immunoreactivity was restricted to some neuronal populations, such as Purkinje cells and neurons of the globus pallidus and the ventral pallidum. The presence of G-protein-gated inward rectifier potassium channel-2 immunoreactivity in substantia nigra pars compacta dopaminergic neurons was confirmed by showing its co-localization with tyrosine hydroxylase by double immunocytochemistry, and also by selectively lesioning dopaminergic neurons with the neurotoxin 6-hydroxydopamine. At the cellular level both proteins were localized in neuronal cell bodies and dendrites, but clear differences were seen in the degree of dendritic staining among neuronal groups. For some neuronal groups the staining of distal dendrites (notably dendritic spines) was strong, while for others the cell body and proximal dendrites were preferentially labelled. In addition, some of the results suggest that G-protein-gated inward rectifier potassium channel-2 protein could be localized in distal axonal terminal fields. A knowledge of the distribution of G-protein-gated inward rectifier potassium channel proteins in the brain could help to elucidate their physiological roles and to evaluate their potential involvement in neurodegenerative processes in animal models and human diseases.

Caffeine mimics the effect of a dopamine D2/3 receptor agonist on the expression of immediate early genes in globus pallidus

In order to evaluate the effect of caffeine on striatopallidal neurons we used in situ hybridization to examine the mRNA expression of the immediate early genes (IEGs), c-fos, fos B, c-jun, jun B, NGFI-A and NGFI-B in globus pallidus in rats given single or repeated administration of caffeine. A significant induction of c-fos mRNA, but not of any of the other IEGs, was found 2, 4 and 8 hr after a single injection of 50 mg/kg caffeine. Following repeated injections of caffeine for 2 weeks a single challenge with caffeine did not induce the expression of any of the studied genes. The ability of caffeine to increase pallidal c-fos mRNA expression was mimicked by the dopamine D2/3 receptor agonist quinpirole (1 or 3 mg/kg), whereas the dopamine D2/3 receptor antagonist raclopride (2 mg/kg) was ineffective. Caffeine and quinpirole did not have synergistic effects when given together. The caffeine-induced c-fos mRNA expression was not counteracted by concomitant treatment with raclopride. The present data provide evidence that acute treatment with caffeine reduces the activity of the striatopallidal neuron, and since this neuron is inhibitory the result is an increased activity in globus pallidus. The effect of blocking the striatal A2A receptors with caffeine is essentially identical to that observed after activation of dopamine D2 receptors, but is independent of these receptors. The fact that pallidal c-fos mRNA expression decreased upon repeated administration of caffeine may be related to the development of tolerance to locomotion stimulation that occurs following chronic caffeine ingestion.

Effects of clozapine on sleep: a longitudinal study

Polysomnographic studies on the effects of clozapine, an atypical antipsychotic agent with strong sedative properties, on night sleep report inconsistent results. Most of these studies did not include baseline recordings and were not controlled for clozapine-induced fever, which is known to alter nocturnal sleep. We conducted a 2-week longitudinal polysomnographic investigation in 10 long-term drug-free schizophrenic patients prior to and at the end of the first and second weeks of clozapine treatment. Rectal temperature was measured daily and patients with fever (> 37.9 degrees C) were excluded. Clozapine significantly improved sleep continuity. In addition, non-rapid eye movement (NREM) sleep and in particular stage 2 sleep increased significantly, while the amounts of stage 4 and slow-wave sleep decreased significantly. Clozapine increased significantly REM density, but it did not affect the amount of REM sleep. We conclude that in patients who do not experience clozapine-induced fever, clozapine has strong sleep consolidating effects resulting from an increase in stage 2 NREM sleep.

Role of adenosine in behavioral state modulation: a microdialysis study in the freely moving cat

There is considerable evidence to suggest that the activity of forebrain and mesopontine cholinergic neurons is intimately involved in electroencephalographic arousal. Furthermore, our previous in vitro investigation suggested that both cholinergic systems are under a powerful tonic inhibitory control by endogenous adenosine. We thus examined the in vivo effect, on electrographically defined behavioral states, of microdialysis perfusion of adenosine into the cholinergic zones of the substantia innominata of the basal forebrain and the laterodorsal tegmental nucleus of freely moving cats. Localized perfusion of adenosine into either the basal forebrain or the laterodorsal tegmental nucleus caused a marked alteration in sleep-wake architecture. Adenosine (300 microM) perfused into either the basal forebrain or laterodorsal tegmental nucleus produced a dramatic decrease in waking, to about 50% of the basal level. Perfusion into the basal forebrain resulted in a significant increase in rapid eye movement sleep, while slow wave sleep was unchanged. In contrast, adenosine perfusion into the laterodorsal tegmental nucleus produced an increase of both slow wave sleep and rapid eye movement sleep, the magnitude of which were proportional to the decrease in waking. Electroencephalographic power spectral analysis showed that adenosine perfusion into the basal forebrain increased the relative power in the delta frequency band, whereas higher frequency bands (theta, alpha, beta and gamma) showed a decrease. These data strongly support the hypothesis that adenosine might play a key role as an endogenous modulator of wakefulness and sleep. The decrease in wakefulness may be directly related to the inhibition of cholinergic neurons of the basal forebrain and the laterodorsal tegmentum. The increase in rapid eye movement sleep is a novel but robust effect whose origin, at present, is uncertain. The observation that local perfusion of adenosine into either the basal forebrain or the laterodorsal tegmental nucleus dramatically decreases wakefulness suggests that these areas might represent a major site of action of the xanthine stimulants (adenosine antagonists) found in coffee and tea.

Serotonergic dorsal raphe nucleus projections to the cholinergic and noncholinergic neurons of the pedunculopontine tegmental region: a light and electron microscopic anterograde tracing and immunohistochemical study

The serotonergic dorsal raphe nucleus is considered an important modulator of state-dependent neural activity via projections to cholinergic neurons of the pedunculopontine tegmental nucleus (PPT). Light and electron microscopic analysis of anterogradely transported biotinylated dextran, combined with choline acetyltransferase (ChAT) immunohistochemistry, were employed to describe the synaptic organization of mesopontine projections from the dorsal raphe to the PPT. In a separate set of experiments, we utilized immunohistochemistry for the serotonin transporter (SERT), combined with ChAT immunohistochemistry at the light and electron microscopic levels, to determine whether PPT neurons receive serotonergic innervation. The results of these studies indicate that: (1) anterogradely labeled and SERT-immunoreactive axons and presumptive boutons invest the PPT at the light microscopic level; (2) at the ultrastructural level, dorsal raphe terminals in the PPT pars compacta synapse mainly with dendrites and axosomatic contacts were not observed; (3) approximately 12% of dorsal raphe terminals synapse with ChAT-immunoreactive dendrites; and (4) at least 2-4% of the total synaptic input to ChAT-immunoreactive dendrites is of dorsal raphe and/or serotonergic origin. This serotonergic dorsal raphe innervation may modulate cholinergic PPT neurons during alterations in behavioral state. The role of these projections in the initiation of rapid eye movement (REM) sleep and the ponto-geniculo-occipital waves that precede and accompany REM sleep is discussed.

Adenosine: a mediator of the sleep-inducing effects of prolonged wakefulness

Both subjective and electroencephalographic arousal diminish as a function of the duration of prior wakefulness. Data reported here suggest that the major criteria for a neural sleep factor mediating the somnogenic effects of prolonged wakefulness are satisfied by adenosine, a neuromodulator whose extracellular concentration increases with brain metabolism and which, in vitro, inhibits basal forebrain cholinergic neurons. In vivo microdialysis measurements in freely behaving cats showed that adenosine extracellular concentrations in the basal forebrain cholinergic region increased during spontaneous wakefulness as contrasted with slow wave sleep; exhibited progressive increases during sustained, prolonged wakefulness; and declined slowly during recovery sleep. Furthermore, the sleep-wakefulness profile occurring after prolonged wakefulness was mimicked by increased extracellular adenosine induced by microdialysis perfusion of an adenosine transport inhibitor in the cholinergic basal forebrain but not by perfusion in a control noncholinergic region.

Effects of kawain and dihydromethysticin on field potential changes in the hippocampus

1. The kava-pyrones kawain and dihydromethysticin are constituents of Piper methysticum which exert anticonvulsant, analgesic and anxiolytic properties. 2. In the present study the effect of these kava-pyrones were tested on field potential changes (fp) induced by omission of the extracellular Mg2+, recorded from the area CA1 and CA3 of the hippocampal slice preparation of guinea pigs. These fp are generated by an activation of NMDA receptors and voltage dependent calcium channels. 3. Kawain and dihydromethysticin reduced reversibly the frequency of occurrence of fp in a concentration range from 5 to 40 mumol/l and 10 to 40 mumol/l, respectively. 4. Reduction of the fp frequency after addition of subthreshold concentrations of 5 mumol/l kawain and 10 mumol/l dihydromethysticin indicated additive actions of both drugs. 5. Since the serotonin-1A agonist ipsapirone also exerts anxiolytic effects, subthreshold concentrations of kawain or dihydromethysticin were combined with a subthreshold concentration of ipsapirone in another set of experiments. Combining kawain and ipsapirone or dihydromethysticin and ipsapirone caused a reduction of the rate of fp to 0.76 and 0.81 of the baseline value, respectively. 6. The findings suggest that (i) single constituents of Piper methysticum may have additive actions, (ii) that the two components kawain and dihydromethysticin may enhance the effects of the anxiolytic serotonin-1A agonist ipsapirone and (iii) that activation of NMDA receptors and/or voltage dependent calcium channels may be involved in the elementary mechanism of action of some kava-pyrones.

A calcium antagonistic effect of the new antiepileptic drug lamotrigine

The new antiepileptic drug lamotrigine (LTG; 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine) has been shown to be effective in the treatment of focal epilepsies with or without secondary generalization. Furthermore, some case reports indicate an efficacy in the treatment of bipolar affective disorders. It has been suggested that the main mechanism of action of LTG is the inhibition of glutamate release through blockade of voltage sensitive sodium channels and stabilisation of the neuronal membrane. Since some antidepressant drugs and the antiepileptic substance carbamazepine have calcium antagonistic properties, which may be of significance in the pathophysiology of epilepsies and affective disorders, the interaction of lamotrigine with carbamazepine and the organic calcium channel blocker verapamil was analyzed in the low Mg(2+)-induced model epilepsy which has been shown to be suppressed specifically by organic calcium antagonists. Lamotrigine reduced the frequency of occurrence of low-magnesium induced field potentials in CA1 and CA3 areas of the hippocampus slice preparation (guinea pigs) in a dose-dependent manner. The subthreshold concentrations which yielded no effect were 1 mumol/l for lamotrigine, 10 mumol/l for carbamazepine and 2 mumol/l for verapamil. Combinations of these subthreshold concentrations elicited a reduction in the repetition rate of field potentials. The results indicate that lamotrigine behaves additive with verapamil and carbamazepine what can be due to a common action on the same subtype of calcium channels. It can be assumed that lamotrigine may have besides its action on high-frequency sodium dependent action potentials also effects on calcium channels.

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.

Modulation of IH by 5-HT in neonatal rat motoneurones in vitro: mediation through a phosphorylation independent action of cAMP

The depolarization of adult and neonatal rat facial and spinal motoneurones by 5-hydroxytryptamine (5-HT) in part involves an enhancement of the hyperpolarization-activated, inward-rectifier, IH. Under experimental conditions which promote this action, 5-HT evokes an inward current which can be mimicked by intracellularly applied adenosine 3',5'-cyclic monophosphate (cAMP) and potentiated by the cAMP-specific phosphodiesterase inhibitor Ro 20-1724. In this study, we show that this action of 5-HT can be blocked by the adenylyl cyclase inhibitors 2'3'-dideoxyadenosine (2',3'-DDA). 5'-adenylimidodiphosphate (AMP-PNP) and SQ-22536 (9-(tetrahydro-2-furyl)adenine), but not by external or internal application of the protein kinase inhibitors H-7, staurosporine and chelerythrine. The most recently cloned 5-HT receptor subtypes, 5-HT4, 5-HT6 and 5-HT7, can all stimulate adenylyl cyclase when activated. In the presence of internal GTP-gamma-S, 5-HT irreversibly enhanced IH. The 5-HT-induced inward current could be reversibly blocked by methysergide, but not by the 5-HT4 receptor antagonist GR-113808A, the 5-HT6 and 5-HT7 antagonist clozapine and the 5-HT1A antagonist WAY-100365. 5-Methoxytryptamine (5-MeOT) and 5-carboxamidotryptamine (5-CT) mimicked the action of 5-HT with a rank order of potency of 5-HT = 5MeOT > 5-CT. Surprisingly, 8-hydroxy-2-(di-N-propylamino)-tetralin (8-OH DPAT), a 5-HT1A and 5-HT7 agonist was inactive on facial motoneurones unlike its reported agonist action on spinal motoneurones. It is proposed that cAMP produced by 5-HT-mediated stimulation of adenylyl cyclase acts in a phosphorylation-independent manner, possibly directly, on the IH channel. The 5-HT receptor subtype mediating this response cannot be correlated with any of the classified 5-HT receptor subtypes that stimulate adenylyl cyclase.

Alertness-enhancing drugs as a countermeasure to fatigue in irregular work hours

Irregular work/rest patterns frequently cause disturbed sleep and excessive sleepiness and accidents. This review is focused on four pharmacological countermeasures-the "new" drugs modafinil and pemoline, the traditional caffeine, and, as a reference, amphetamine. It is concluded that there is still too little data available to decide whether systematic use of alertness-enhancing drugs is feasible in occupational settings. D-Amphetamine is ruled out because of its abuse potential and mood effects. Modafinil and pemoline have not been tested in field situations, whereas caffeine certainly is used to improve alertness during work, but the use is spontaneous/ad hoc, and there is still a lack of data on its systematic application. Particularly, the optimal amount and pattern of administration need elucidation.

[125I]4-aminobenzyl-5'-N-methylcarboxamidoadenosine (125I)AB-MECA) labels multiple adenosine receptor subtypes in rat brain

Adenosine modulates neuronal activity and neurotransmitter release through interaction with cell surface receptors. Four adenosine receptor subtypes, A1, A2A, A2B, and A3 receptors, have been cloned and characterized. The agonist ligand, [125I]AB-MECA ([125I]4-aminobenzyl-5'N-methylcarboxamidoadenosine) has high affinity for recombinant A1 and A3 receptors [Olah et al., Mol. Pharmacol, 45 (1994) 978-982]. Rodent A3 receptors are relatively insensitive to xanthines; inhibition of A1 receptors with xanthines allows selective detection of A3 receptors despite the lack of selectivity of the ligand. We studied whether [125I]AB-MECA is useful for localization and characterization of A3 receptors in rat brain. The autoradiographic distribution of total [125I]AB-MECA (400 pM) binding closely resembled the pattern of A1 receptor binding, with highest levels in cerebellum, hippocampus, and thalamus, and moderate levels in cortex and striatum. Drug competition studies confirmed that almost all [125I]AB-MECA binding could be attributed to labeling of A1 receptors. Xanthine amine congener (1 microM) reduced specific [125I]AB-MECA binding by > 95%, indicating that xanthine-resistant A3 receptors represent a quantitatively minor subtype. Despite the use of a radioligand with high affinity and high specific activity, the low density of A3 receptors in rat brain appears insufficient to allow localization, or even consistent detection, of this receptor subtype. In the presence of DPCPX (50 nM, to block A1 receptors), residual [125I]AB-MECA binding to A2A receptors was observed in the striatum. Thus [125I]AB-MECA labels primarily A1 and A2A adenosine receptors in rat brain.

Stress-like adrenocorticotropin responses to caffeine in young healthy men

The effects of oral caffeine (3.3 mg/kg, equivalent to 2-3 cups of coffee) on plasma adrenocorticotropin (ACTH) and cortisol (CORT) were tested in 47 healthy young men at rest in a double-blind, placebo-controlled, crossover study. Following caffeine, ACTH was significantly elevated at all times from 30 min to 180 min, and CORT was elevated from 60 min to 120 min (Fs > or = 8.4, ps < 0.01). Peak increases relative to placebo were: ACTH, 33% (+5.2 pg/ml) and CORT, 30% (+2.7 micrograms/dl) at 60 min postcaffeine. The results suggest that caffeine can activate important components of the pituitary-adrenocortical response in humans during the resting state. Caffeine's known ability to increase CORT production appears at least partly due to an increase in ACTH release at the pituitary.

Antipsychotic drugs block IP3-dependent Ca(2+)-release from rat brain microsomes

Cellular Ca(2+)-dysregulation has been proposed as an important mechanism in certain diseases such as bipolar affective disorder (BPAD) and malignant hyperthermia. Recently it has been found that in BPAD, the plasma membrane Ca(2+)-channel blockers verapamil and nimodipine are useful substitutes in Li(+)-treatable patients. We have investigated the effects of these drugs and the antipsychotic drugs (clozapine, fluspirilene, and haloperidol) on IP3-induced Ca(2+)-release from Ca(2+)-loaded rat brain microsomes. In the presence of either the Ca(2+)-channel blockers or the neuroleptic drugs, Ca(2+)-release was blocked in a dose-dependent fashion. For the neuroleptics, the EC50 ranged from 22 microM for fluspirilene to 145 microM for haloperidol. The EC50 for nimodipine was 160 microM and 450 microM for verapamil. Carbamazapine and valproic acid, anticonvulsants recently used for treating BPAD, were relatively ineffective, as were various haloperidol metabolites. The research described in this paper establishes for the first time that antipsychotic drugs, as well as certain Ca(2+)-channel blockers, directly block the IP3-induced Ca(2+)-release in a rat brain microsome assay.

Characterization of ATP transport into chromaffin granule ghosts. Synergy of ATP and serotonin accumulation in chromaffin granule ghosts

ATP is an excitatory neurotransmitter that is stored and cosecreted with catecholamines from cells of the adrenal medulla. While the transport of catecholamines into chromaffin granule ghosts has been extensively characterized, there is little information on the mechanism of ATP transport into these structures. Here we show that ATP transport is driven by the electrical component of the electrochemical proton gradient created by the chromaffin granule membrane H+-ATPase, and that the accumulated nucleotide is released from the vesicles by inhibition of the H+-ATPase. GTP and UTP are also substrates for this transporter, distinguishing it from the mitochondrial ADP/ATP exchanger. Accumulation of ADP and ATP (rather than exchange with intravesicular ATP) is demonstrated by high pressure liquid chromatography measurements. The anion transport inhibitor 4,4-diisothiocyanatostilbene-2,2-disulfonic acid (Ki = 27 microM) inhibits ATP transport, while atractyloside, the inhibitor of the mitochondrial ATP/ADP exchanger, is a very poor inhibitor. Finally, we have demonstrated a synergy between the accumulation of ATP and that of serotonin (i.e. more of each solute accumulates when the two are accumulated together), supporting the view that there is an interaction between serotonin and ATP that reduces their effective concentration within the ghosts.

Extracellular adenosine levels in neostriatum and hippocampus during rest and activity periods of rats

Adenosine is an inhibitory modulator in the mammalian brain with a possible role in sleep regulation, which is mainly indicated by pharmacological studies showing that adenosine or its analogs can induce sedation and sleep, whereas adenosine antagonists, like caffeine and theophylline, are potent behavioral and neuronal stimulants. In contrast to these pharmacological findings, data on endogenous adenosine in relation to sleep and waking are sparse. Therefore, we have now used in vivo microdialysis to investigate the extracellular levels of adenosine in the neostriatum and hippocampus of freely moving rats. Adenosine was monitored over a time course of 24 h, during which the animals were exposed to a 12 h day/night rhythm with lights-off from 19.00 to 07.00. In this lights-off period, i.e. the rats' active period, the maximal levels of neostriatal and hippocampal extracellular adenosine were higher than during the lights-on period. In contrast to the neostriatum, extracellular levels of hippocampal adenosine tended to increase towards the end of the lights-off period, reaching its maximal level at 07.00, and decreasing again within the following hour. The changes of hippocampal adenosine levels were related to behavior, since significant increases in "sleep-like" behavior, as well as decreases in overall movements and consummatory behavior, were observed when adenosine levels had reached their maxima in the hippocampus; no such relationship was found with respect to the neostriatum. These results are in keeping with a role of endogenous adenosine in the regulation of sleep and wakefulness, and point to a specific role of adenosine in the hippocampus. They also raise the possibility that adenosine may be involved in different behavioral processes dependent on the area of the brain, as well as the type of adenosine receptor involved. Finally, given the known evidence for neuroprotective actions of adenosine, its accumulation in the hippocampus as a function of behavioral activity may serve to prevent or repair the neural degenerative consequences of such activity. It is proposed that adenosine's sleep-promoting effects result from its signalling to cease behavioral activity in order to prevent excessive activity-related changes, and thus allow other restorative sleep-related processes to take over.

Promotion of sleep mediated by the A2a-adenosine receptor and possible involvement of this receptor in the sleep induced by prostaglandin D2 in rats

A 6-hr continuous infusion of 2-[p-(2-carboxyethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenos ine (CGS21680), a selective A2a-adenosine agonist, into the subarachnoid space underlying the ventral surface region of the rostral basal forebrain, which has been defined as the prostaglandin (PG) D2-sensitive sleep-promoting zone, at rates of 0.02, 0.2, 2.0, and 12 pmol/min increased slow-wave sleep (SWS) and paradoxical sleep (PS) in a dose-dependent manner up to 183% and 202% of their respective baseline levels. The increments produced by the infusion of CGS21680 at 0.2 and 2.0 pmol/min were totally diminished when the rats had been pretreated with an i.p. injection of (E)-1,3-dipropyl-7-methyl-8-(3,4-dimethoxystyryl)xanthine (KF17837; 30 mg/kg of body weight), a selective A2-adenosine antagonist. In contrast, the infusion of N6-cyclohexyladenosine (CHA), a selective A1-adenosine agonist, at 2 pmol/min significantly suppressed SWS before causing an increase in SWS, and a decrease in PS was also markedly visible. Essentially the same effects of CGS21680 and CHA were observed when these compounds were administered to the parenchymal region of the rostral basal forebrain through chronically implanted microdialysis probes. Thus, we clearly showed that stimulation of A2a-adenosine receptors in the rostral basal forebrain promotes SWS and PS. Furthermore, i.p. injections of KF17837 at 30 and 100 mg/kg of body weight dose-dependently attenuated the magnitude of the SWS increase produced by the infusion of PGD2 into the subarachnoid space of the sleep-promoting zone, thus indicating that the A2a-adenosine receptors are crucial in the sleep-promoting process triggered by PGD2.

Stimulation of adenosine A1 receptors prevents the EEG arousal due to dopamine D1 receptor activation in rabbits

The influence of adenosine A1 (N6-cyclopentyladenosine, CPA) and A2 (2-[4-(2-carboxylethyl)phenethylamino]-5'-N-ethylcarboxamido -adenosine hydrochloride, CGS 21680) receptor agonists on SKF 38393-induced electroencephalographic (EEG) arousal was studied in rabbits. While CPA (0.1 mg/kg i.v.) significantly prevented the EEG effects of SKF 38393, CGS 21680 (0.2 mg/kg i.v.) did not affect them. These results demonstrate that adenosine A1 receptors can modulate dopamine D1 receptor-induced EEG arousal and show, for the first time, that adenosine-dopamine interactions are involved in brain functions other than motor activity.

Effects of N6-cyclopentyladenosine and caffeine on sleep regulation in the rat

To study the role of adenosine in sleep regulation, the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) and the antagonist caffeine were administered to rats. Intraperitoneal (i.p.) CPA 1 mg/kg but not 0.1 mg/kg, suppressed rapid-eye-movement (REM) sleep and enhanced electroencephalographic (EEG) slow-wave activity (power density 0.75-4.0 Hz) in non-REM sleep. The latter effect was remarkably similar to the response to 6-h sleep deprivation. The effects persisted when CPA-induced hypothermia was prevented. Caffeine (10 and 15 mg/kg i.p.) elicited a dose-dependent increase in waking followed by a prolonged increase of slow-wave activity in non-REM sleep. The combination of caffeine (15 mg/kg) and sleep deprivation caused less increase in slow-wave activity than sleep deprivation alone, indicating that caffeine may reduce the buildup of sleep pressure during waking. The results are consistent with the involvement of adenosine in the regulation of non-REM sleep.

Combined treatment with lithium and nimodipine in a bipolar I manic syndrome

1. The benefit of a combined treatment with the calcium antagonist nimodipine and lithium in a bipolar I disorder (currently manic, DSM IV 296.44, ICD 10 F 31.1) was explored and documented in a longitudinal single case study. 2. Nimodipine (270 mg/d) was added to lithium (900 mg/d), substituting for previously administered neuroleptics, in an up to then unsatisfactorily treated manic patient. 3. A clear-cut improvement in the patient's condition was achieved within a fortnight, and lasted over the continuation period of this drug regimen. This combined treatment was discontinued after eight weeks and lithium alone was then administered. Within three months another manic episode appeared. 4. Side-effects and changes of lithium blood levels were not observed during the combined treatment with nimodipine and lithium. 5. Further research on the benefits of adding a calcium antagonist, instead of neuroleptics, to lithium therapy for bipolar manic disorder patients who do not respond sufficiently to lithium is recommended. In addition, the benefits of a long term prophylaxis of nimodipine alone or in combination with lithium should be evaluated in those bipolar patients who still show a high relapse frequency on lithium alone.

Evidence that direct binding of G beta gamma to the GIRK1 G protein-gated inwardly rectifying K+ channel is important for channel activation

Activation of G protein-gated K+ channels by G protein-coupled receptors contributes to parasympathetic regulation of heart rate in the atrium and inhibitory postsynaptic potentials in the peripheral and central nervous system. Having found that G beta gamma activates the cloned GIRK1 channel, we now report evidence for direct binding of G beta gamma to both the N-terminal hydrophilic domain and amino acids 273-462 of the C-terminal domain of GIRK1. These direct interactions are physiologically important because synthetic peptides derived from either domain reduce the G beta gamma binding as well as the G beta gamma activation of the channel. Moreover, the N-terminal domain may also bind trimeric G alpha beta gamma, raising the possibility that physical association of G protein-coupled receptors, G proteins, and K+ channels partially accounts for their compartmentalization and hence rapid and specific channel activation by receptors.

Action of GP 47779, the active metabolite of oxcarbazepine, on the corticostriatal system. I. Modulation of corticostriatal synaptic transmission

Oxcarbazepine (OCBZ) is the keto-analogue of carbamazepine (CBZ). In humans, OCBZ is rapidly and almost completely metabolized to 10, 11-dihydro-10-hydroxy-CBZ (GP 47779), the main metabolite responsible for the drug's antiepileptic activity. The corticostriatal pathway is involved in the propagation of epileptic discharges. We characterized the electrophysiological effects of GP 47779 on striatal neurons by making intracellular recordings from corticostriatal slices. GP 47779 (3-100 microM) produced a dose-dependent inhibition of glutamatergic excitatory postsynaptic potentials (EPSPs). This effect was not coupled either with changes of the membrane potential of these cells or with alterations of their postsynaptic sensitivity to excitatory amino acids (EAA) suggesting a presynaptic site of action. GP 47779 reduced the current-evoked firing discharge only at concentrations > 100 microM. GP 47779 did not affect the presynaptic inhibitory action of adenosine, showing that presynaptic adenosine receptors were not implicated in the GP 47779-mediated reduction of corticostriatal EPSPs. Our data indicate that GP 47779 apparently acts directly on corticostriatal terminals to reduce the release of EAA, probably by inhibiting high-voltage-activated (HVA) calcium (Ca2+) currents (described in the accompanying article). The inhibitory action of GP 47779 on corticostriatal transmission may contribute to the antiepileptic effects of this drug.

EEG slow waves and sleep spindles: windows on the sleeping brain

Slow waves and sleep spindles are prominent features of the EEG in non-REM sleep and some of the neurophysiological mechanisms underlying their genesis have been elucidated. In humans, slow-wave activity in non-REM sleep increases and EEG activity in the frequency range of sleep spindles decreases when wakefulness prior to sleep is varied from 2 to 40 h. The opposite changes are observed in the course of sleep, even when sleep is scheduled out of phase with the circadian rhythm of sleep propensity. Within non-REM sleep episodes the association between slow waves and sleep spindles is bi-phasic: both activities are correlated positively at the beginning and end of non-REM sleep episodes whereas in the middle part of non-REM sleep episodes high values of slow-wave activity coincide with low levels of spindle activity. An extension of wakefulness enhances the rise rate of slow-wave and spindle activity at the onset of sleep. Since macroscopic slow waves and sleep spindles both are dependent on hyperpolarization and synchronization of neurons in thalamo-cortical and cortical circuits, the sleep deprivation induced changes in these EEG activities may be related to reduced activating input to thalamo-cortical and cortical neurons, local facilitation of their hyperpolarization or facilitation of their synchronization. The precise regulation of slow-wave and spindle activity as a function of the duration and intensity of prior sleep and wakefulness demonstrates that these EEG oscillations are accurate indicators of non-REM-sleep homeostasis and suggests that they are fundamental to the sleeping brain.

Effects of caffeine on cognition and mood without caffeine abstinence

The objective of this study was to evaluate the effects of low doses (75 mg and 150 mg) of caffeine on mood and cognition in healthy people, with minimal abstinence of 1 h from caffeine. Improvements were obtained in cognition for attention, problem solving and delayed recall, but not immediate recall or working memory, but performance in the placebo condition was close to the maximum, giving little margin for improvement. For mood, there were statistically significant increase in clearheadedness, happiness and calmness and decreases in tenseness. These mood and performance-enhancing effects of caffeine cannot be seen as representing an alleviation of deficits induced by caffeine abstinence, because there was only minimal deprivation from caffeine.

Influence of BAY k-8644, a calcium channel agonist, on the anticonvulsant activity of conventional anti-epileptics against electroconvulsions in mice

BAY k-8644, an agonist at the dihydropyridine binding site of the L-type voltage dependent calcium channel, at the dose of 5 mg/kg (s.c.) did not significantly affect the threshold for electroconvulsions, but impaired the protective efficacy of flunarizine (15 and 20 mg/kg, i.p.) in the electroconvulsive test. Interestingly, the calcium channel agonist (at 1 and 5 mg/kg) distinctly diminished the protection offered by conventional anti-epileptic drugs (carbamazepine, diphenylhydantoin and phenobarbital) against maximal electroshock-induced seizures in mice. A pharmacokinetic interaction does not seem to be involved in the effect of BAY k-8644, since total plasma levels of these anti-epileptics (measured by immunofluorescence) were not affected by the calcium channel agonist. The only anti-epileptic drug resistant to BAY k-8644 (up to 5 mg/kg) was valproate, whose ED50 (in mg/kg) was not changed in the presence of the calcium channel agonist. Further, BAY k-8644 (5 mg/kg) did not influence the flunarizine (a calcium channel blocker)-induced potentiation of the protective action of valproate against maximal electroshock-induced convulsions. The calcium channel agonist (5 mg/kg) reversed the flunarizine-induced augmentation of the anticonvulsive activity of carbamazepine. It may be concluded that carbamazepine, diphenylhydantoin and phenobarbital partially exert their anticonvulsive effects via blockade of calcium influx whilst valproate does not seem to. In this context, the flunarizine-induced potentiation of the anticonvulsive activity of valproate is probably independent of calcium channel blockade.

Caffeine intake (200 mg) in the morning affects human sleep and EEG power spectra at night

Adenosine has been implicated in the physiological regulation of sleep propensity. The adenosine-receptor-antagonist, caffeine (100 mg), administered immediately prior to a nocturnal sleep episode, has previously been shown to lower sleep propensity as indexed by a reduced sleep efficiency, a reduced EEG power density in low delta frequencies and enhanced power density in the frequency range of sleep spindles. To further investigate the role of adenosine in sleep regulation we administered 200 mg of caffeine at 07.10 h and analyzed the sleep stages and EEG power spectra during the subsequent night in nine healthy men. Caffeine levels in saliva decreased from a maximum of 17 mumol/l one hour after intake, to 3 mumol/l immediately prior to the sleep episode starting at 23.00 h. Compared to placebo, sleep efficiency and total sleep time were significantly reduced. EEG power density in nonREM sleep was suppressed in the 0.25-0.5 Hz band and enhanced in the frequency range of sleep spindles (11.25-12.0 Hz and 13.25-14.0 Hz). In REM sleep EEG power density was suppressed in the frequency range of 0.75-4.5 and 5.25-6.0 Hz. The data indicate that a saliva level of caffeine as low as 3 mumol/l directly affects sleep propensity or, alternatively, that the presence of caffeine in the central nervous system during the waking episode reduces the progressive increase of sleep propensity associated with wakefulness.

Astra Award Lecture. Adenosine, adenosine receptors and the actions of caffeine

Of the known biochemical actions of caffeine, only inhibition of adenosine receptors occurs at concentrations achieved during normal human consumption of the drug. Under normal physiological conditions, adenosine is present in sufficient concentrations to activate A1 and A2a receptors. Via actions on A1 receptors, adenosine decreases neuronal firing and the release of neurotransmitters. The exact mechanisms are not known, but several possibilities are discussed. Via actions on A2a receptors, adenosine--and hence caffeine--can influence dopaminergic neurotransmission. Caffeine can induce rapid changes in gene expression and, somewhat later, marked adaptive changes. These include antiepileptic and neuroprotective changes. Thus, caffeine has a number of central effects directly or indirectly related to adenosine receptors. Some of these are potentially useful, and drug development based on the actions of caffeine should be interesting.

Clozapine therapy in patients with neurologic illness

OBJECTIVE

This review will analyze the use of clozapine in patients with neurologic illness.

METHODS

A review of the literature was performed. Attention is focused particularly on patients with seizure disorder, head injury, mental retardation, Parkinson's disease, Huntington's disease, tardive dyskinesia, and selected other neurological disorders.

RESULTS

This review discusses clinical difficulties/issues associated with clozapine therapy in patients with a variety of neurological disorders.

CONCLUSION

Although clozapine therapy should be reserved for those patients who are refractory to conventional psychotropic medications, when used appropriately it may offer a safe and effective way of improving quality of life for patients with behavioral symptoms and neurologic illness.

A calcium antagonist for the treatment of depressive episodes: single case reports

Preclinical studies indicate that a disturbed intracellular calcium ion homeostasis is involved in the pathophysiology of affective disorders. Therefore some calcium antagonists were investigated, especially in the treatment of the manic syndrome. In the present study the calcium antagonist nimodipine was used in 10 out-patients with single or recurrent depressive episodes. As a result the mean HAMD scores changed from 26.5 to 9.9 after the individual nimodipine administration. These single case reports suggest an effective new therapy strategy for the treatment of affective dysregulations and give rise to controlled clinical studies with calcium antagonists.