Identification of two novel diurnal genes by screening of a rat brain cDNA library

While the hypothalamus is fundamental for sleep and circadian regulation, the molecular mechanisms involved are poorly understood. We have used a differential gene expression technique to identify hypothalamic genes which have altered expression in rat sleep periods. Complex cDNA probes from rat hypothalami removed at Zeitgeber times 4 and 15 were hybridised to rat brain cDNA library girds. From 30 differentially expressed clones, six were further analysed and two were confirmed to exhibit increased expression at Zeitgeber time 4. A Northern blot hybridization of brain, heart, kidney, lung, testis and skin mRNA showed that both clones were brain specific. Therefore, we have identified two novel brain specific diurnally expressed hypothalamic genes. Both genes may have roles in sleep or circadian regulation.

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.

Immunohistochemical localization of caffeine-induced c-Fos protein expression in the rat brain

Although caffeine is the most widely used central nervous system stimulant, the neuronal populations and pathways mediating its stimulant effects are not well understood. Using c-Fos protein as a marker for neuronal activation, the present study investigated the pattern of c-Fos induction at 2 hours after low locomotor-stimulant doses (1, 5, 10, and 30 mg/kg, i.p.) of caffeine and compared them with those after a higher dose (75 mg/kg, i.p.) or saline injection in adult male rats. Fos-immunoreactive neurons were counted in selected nuclei across the entire brain. Caffeine induced an increase in locomotor activity in a dose-dependent manner up to doses of 30 mg/kg and a decline at 75 mg/kg. Quantitative analysis of Fos-immunoreactive neurons indicated that no structures showed significant Fos expression at doses below 75 mg/kg or a biphasic pattern of Fos expression, as in locomotion. In contrast, caffeine at 75 mg/kg induced a significant increase compared with the saline condition in the number of Fos-immunoreactive neurons in the majority of structures examined. The structures included the striatum, nucleus accumbens, globus pallidus, and substantia nigra pars reticulata and autonomic and limbic structures including the basolateral and central nuclei of the amygdala, paraventricular and supraoptic hypothalamic nuclei, periventricular hypothalamus, paraventricular thalamic nuclei, parabrachial nuclei, locus coeruleus, and nucleus of the solitary tract. The locomotor-enhancing effects of low doses of caffeine did not appear to be associated with significant Fos expression in the rat brain.

Recovery of cable properties through active and passive modeling of subthreshold membrane responses from laterodorsal tegmental neurons

The laterodorsal tegmental nucleus (LDT) is located in the dorsolateral pontine reticular formation. Cholinergic neurons in the LDT and the adjacent pedunculopontine tegmental nucleus (PPT) are hypothesized to play a critical role in the generation of the electroencephalographic-desynchronized states of wakefulness and rapid eye movement sleep. A quantitative analysis of the cable properties of these cells was undertaken to provide a more detailed understanding of their integrative behavior. The data used in this analysis were the morphologies of intracellularly labeled guinea pig LDT neurons and the voltage responses of these cells to somatic current injection. Initial attempts to model the membrane behavior near resting potential and in the presence of tetrodotoxin (TTX, 1 microM) as purely passive produced fits that did not capture many features of the experimental data. Moreover, the recovered values of membrane conductance or intracellular resistivity were often very far from those reported for other neurons, suggesting that a passive description of cell behavior near rest was not adequate. An active membrane model that included a subthreshold A-type K+ current and/or a hyperpolarization-activated cation current (H-current) then was used to model cell behavior. The voltage traces calculated using this model were better able to reproduce the experimental data, and the cable parameters determined using this methodology were more consistent with those reported for other cells. Additionally, the use of the active model parameter extraction methodology eliminated a problem encountered with the passive model in which parameter sets with widely varying values, sometimes spanning an order of magnitude or more, would produce effectively indistinguishable fits to the data. The use of an active model to directly fit the experimentally measured voltage responses to both long and short current pulses is a novel approach that is of general utility.

Glutamatergic neurotransmission involves structural and clinical deficits of schizophrenia

BACKGROUND

Phencyclidine and ketamine induce a syndrome closely resembling schizophrenia due to their blockade of N-methyl-D-aspartate (NMDA) receptor. These findings suggested that some aspects of schizophrenia are associated with decreased NMDA--glutamatergic function. We hypothesized that structural and symptomatic deficits in schizophrenia are related to glutamatergic neurotransmission.

METHODS

We studied the relationships among cerebrospinal fluid (CSF) glutamatergic markers, clinical presentation of schizophrenia, and CT parameters of brain structure in drug-free schizophrenics.

RESULTS

We found no significant differences between patients with schizophrenia and controls in CSF glutamatergic markers. When patients with schizophrenia were considered as a group, significant negative correlations between glutamatergic markers and brain structural measures as well as clinical measures were observed. Cluster analysis reveals a group of lower indices of glutamatergic neurotransmission, and more prominent thought disorder as well as ventricular enlargement, and a group with increased glutamate level.

CONCLUSIONS

The findings support the hypothesis that altered glutamatergic neurotransmission plays a role in the brain structure and the clinical symptoms of schizophrenia.

Opioid inhibition of hippocampal interneurons via modulation of potassium and hyperpolarization-activated cation (Ih) currents

The actions of mu- and delta-opioid agonists (DAMGO and DPDPE, respectively) on GABAergic interneurons in stratum oriens of area CA1 of the hippocampus were examined by using whole-cell voltage-clamp recordings in brain slices. Both agonists consistently generated outward currents of similar magnitude (15-20 pA) in the majority of cells. However, under control conditions, current-voltage (I/V) relationships revealed that only a small number of these cells (3 of 77) demonstrated clear increases in membrane conductance, associated with the activation of the potassium current known as Girk. These interneurons also exhibited a slowly activating, inwardly rectifying current known as Ih on hyperpolarizing step commands. Ih was blocked by the extracellular application of cesium (3-9 mM) or ZD 7288 (10-100 microM) but was insensitive to barium (1-2 mM). In an effort to determine whether the holding current changes were attributable to the modulation of Girk and/or Ih, we used known blockers of these ion channels (barium or cesium and ZD 7288, respectively). Extracellular application of cesium (3-9 mM) or ZD 7288 (25-100 microM) blocked Ih and significantly reduced the opioid-induced outward currents by 58%. Under these conditions the opioid agonists activated a potassium current with characteristics similar to Girk. Similarly, during barium (1-2 mM) application the opioid-induced outward currents were reduced by 46%, and a clear reduction in Ih and the whole-cell conductance was revealed. These data suggest that the opioids can modulate both Ih and Girk in the same population of stratum oriens interneurons and that the modulation of these ion channels can contribute to the inhibition of interneuron activity in the hippocampus.

Modulation of calcium and potassium currents by lamotrigine

Actions of the new antiepileptic drug lamotrigine (LTG) were characterized using extracellular and whole cell patch clamp recordings from rat CA1 and CA3 pyramidal cells in vitro. The results suggest that LTG, beside its previously described effect on the fast sodium inward current, also modulates - presumably voltage-gated - calcium currents and the transient potassium outward current ID. These may be effective mechanisms to inhibit pathological excitation in epilepsy and may be of potential benefit in treating underlying cellular disturbances in bipolar disorder.

Effect of kava extract and individual kavapyrones on neurotransmitter levels in the nucleus accumbens of rats

1. Kavapyrones have well-known psychotropic properties. The most common actions of the extract are relaxation and euphoria, depending on the circumstances of ingestion, whereas higher doses cause sleepiness and skeletal muscle relaxation. Several other actions have been reported such as anticonvulsant properties, neuroprotection and analgesia. No interactions with neuroreceptors have yet been found that would explain the multiple actions. 2. To reveal neuronal functions affected by the kavapyrones the authors studied their actions on the mesolimbic reward system using in vivo microdialysis. 3. A small dose of kava extract (20 mg/kg body weight i.p.) caused changes in rat behaviour and concentrations of dopamine in the nucleus accumbens. Higher doses (120 mg/kg i.p.) increased the levels of dopamine. With respect to the individual compounds, D,L-kawain induced in low doses a decrease in dopamine levels and in higher amounts either an increase or no change in dopamine concentrations. Yangonin resulted in a decrease of dopamine levels to below the detection limit and desmethoxyyangonin in an increase of dopamine levels. Dihydrokawain, methysticin and dihydromethysticin did not produce any significant changes of dopamine levels. D,L-kawain caused a decrease in 5-HT concentrations. Some of the other kavapyrones affected 5-HT levels as well. 4. The results suggest that the relaxing and slightly euphoric actions may be caused by the activation of the mesolimbic dopaminergic neurones. Changes of the activity of 5-HT neurones could explain the sleep-inducing action.

Nimodipine monotherapy and carbamazepine augmentation in patients with refractory recurrent affective illness

Of 30 patients with treatment-refractory affective illness, 10 showed a moderate to marked response to blind nimodipine monotherapy compared with placebo on the Clinical Global Impressions Scale. Fourteen inadequately responsive patients (3 unipolar [UP], 11 bipolar [BP]) were treated with the blind addition of carbamazepine. Carbamazepine augmentation of nimodipine converted four (29%) of the partial responders to more robust responders. Patients who showed an excellent response to the nimodipine-carbamazepine combination included individual patients with patterns of rapid cycling, ultradian cycling, UP recurrent brief depression, and one with BP type II depression. When verapamil was blindly substituted for nimodipine, two BP patients failed to maintain improvement but responded again to nimodipine and remained well with a blind transition to another dihydropyridine L-type calcium channel blocker (CCB), isradipine. Mechanistic implications of the response to the dihydropyridine L-type CCB nimodipine alone and in combination with carbamazepine are discussed.

Opioid inhibition of hippocampal interneurons via modulation of potassium and hyperpolarization-activated cation (Ih) currents

The actions of mu- and delta-opioid agonists (DAMGO and DPDPE, respectively) on GABAergic interneurons in stratum oriens of area CA1 of the hippocampus were examined by using whole-cell voltage-clamp recordings in brain slices. Both agonists consistently generated outward currents of similar magnitude (15-20 pA) in the majority of cells. However, under control conditions, current-voltage (I/V) relationships revealed that only a small number of these cells (3 of 77) demonstrated clear increases in membrane conductance, associated with the activation of the potassium current known as Girk. These interneurons also exhibited a slowly activating, inwardly rectifying current known as Ih on hyperpolarizing step commands. Ih was blocked by the extracellular application of cesium (3-9 mM) or ZD 7288 (10-100 microM) but was insensitive to barium (1-2 mM). In an effort to determine whether the holding current changes were attributable to the modulation of Girk and/or Ih, we used known blockers of these ion channels (barium or cesium and ZD 7288, respectively). Extracellular application of cesium (3-9 mM) or ZD 7288 (25-100 microM) blocked Ih and significantly reduced the opioid-induced outward currents by 58%. Under these conditions the opioid agonists activated a potassium current with characteristics similar to Girk. Similarly, during barium (1-2 mM) application the opioid-induced outward currents were reduced by 46%, and a clear reduction in Ih and the whole-cell conductance was revealed. These data suggest that the opioids can modulate both Ih and Girk in the same population of stratum oriens interneurons and that the modulation of these ion channels can contribute to the inhibition of interneuron activity in the hippocampus.

Lipopolysaccharide-induced expression of IP-10 mRNA in rat brain and in cultured rat astrocytes and microglia

Using mRNA differential display technique, we have found a differentially expressed band in rat brain, designated HAP2G1, which was the strongest one induced in response to peripheral administration of lipopolysaccharide (LPS). Sequence analysis showed that HAP2G1 cDNA is the rat homologue of the human alpha-chemokine IP-10. Using RT-PCR technique and in situ hybridization, we demonstrate that IP-10 mRNA was expressed only in brain tissue of rats treated with LPS and not in control brain tissue. Using semi-quantitative PCR, we found that both cultured astrocytes and microglia express IP-10 mRNA after treatment with LPS. LPS-induced IP-10 mRNA reached peak levels in rat brain and in cultured microglia at approximately 3 h after treatment with LPS. At 10 h, IP-10 mRNA was markedly decreased, and at 24 h it was low but still detectable by PCR or in situ hybridization. In contrast to unstimulated microglia, unstimulated astrocytes constitutively expressed IP-10 mRNA at a low level. Increased IP-10 expression could possibly be involved in the microglia response to inflammatory stimuli in vivo.

Effects of the atypical antidepressant trimipramine on field potentials in the low Mg2+-model in guinea pig hippocampal slices

Trimipramine has been classified as an atypical tricyclic antidepressant, because only weak inhibitory effects on serotonin and/or noradrenaline reuptake have been found. Since some antidepressive drugs (e.g. imipramine) and other agents used in the treatment of affective disorders (e.g. carbamazepine) modulate neuronal calcium channels, trimipramine was tested on field potential changes (fp) in the low Mg2+-model of epilepsy which has been shown to be affected by calcium antagonists. Trimipramine reduced the frequency of occurrence of fp in a dose dependent manner (5-100 microM). The threshold concentration of trimipramine which did not decrease the firing rate was approximately 1 microM. Simultaneous application of subthreshold concentrations (2 microM) of the organic calcium antagonist verapamil with trimipramine decreased the firing rate to 37.0+/-22.7% (means+/-SEM, n=7) with respect to baseline values. In contrast, no additive effects of N-methyl-D-aspartate antagonists and trimipramine were observed. In conclusion, the data suggests that the antidepressive effects observed with trimipramine treatment may be due to its inhibitory action on neuronal calcium channels.

New perspectives in the treatment of acute mania: a single case report

1. There is increasing evidence that standard treatment of mania with lithium or neuroleptics fails in many subtypes of mania, e.g. dysphoric mania or rapid cycling, and new strategies are needed. 2. This single case report reports on possibilities and pitfalls in alternative attempts to tackle a severe manic syndrome successfully. 3. In this patient, lamotrigine and valproate, the latter only in an i.v. formulation, led to a relief from mania. 4. It is concluded that the success of this treatment may be due to a common underlying mechanism of action of these drugs, most likely on the level of ion channel regulation, and that further experience with alternative formulations of standard treatments such as valproate i.v. should be collected.

Calcium-dependent spike-frequency accommodation in hippocampal CA3 nonpyramidal neurons

Interneurons of the hippocampal formation are traditionally identified electrophysiologically as those cells that fire trains of weakly accommodating action potentials in response to depolarizing current injection. We studied the firing properties of nonpyramidal neurons in the five substrata of the CA3b region of hippocampus. With the use of whole cell recording methods we found that nonpyramidal neurons fired in a range from weak to strong spike-frequency accommodation (SFA) that was calcium dependent. Slow afterhyperpolarizations were not associated with strong SFA. In addition a subset of interneurons ( approximately 20%) fired with an irregular firing pattern that was generally calcium independent. These results suggest a calcium-dependent mechanism for SFA in nonpyramidal neurons that is distinct from pyramidal cells and further demonstrates the heterogeneity of hippocampal interneurons.

Effects of GABA(A) inhibition on the expression of long-term potentiation in CA1 pyramidal cells are dependent on tetanization parameters

Long-term potentiation (LTP) of excitatory synaptic responses of principal neurons in the hippocampus is accompanied by changes in GABAergic inhibition mediated by interneurons. The impact of inhibition on LTP of excitatory postsynaptic responses in CA1 pyramidal cells was assessed by monitoring changes in field potentials evoked by Schaffer collateral stimulation in hippocampal slices in vitro. First, to determine the effect of inhibition on population EPSPs, slices were exposed to the GABA(A) receptor antagonist bicuculline (10 microM). Both the slope and amplitude of field EPSPs (fEPSPs) were significantly enhanced by bicuculline indicating that inhibition modulates excitatory postsynaptic responses of pyramidal cells. To assess if stimulation-dependent changes in inhibition influence LTP of excitatory responses of pyramidal cells, LTP was examined in the presence and absence of bicuculline (20 microM) following either 100 Hz tetanization, or theta-patterned stimulation (short bursts delivered at 5 Hz). In normal medium, 100 Hz stimulation produced marked short-term potentiation that decayed 5-10 min post-tetanus and both stimulation paradigms produced similar LTP at 30 min post-tetanus. In comparison, LTP of the fEPSP slope and amplitude was significantly enhanced after theta-patterned stimulation, but not after 100 Hz stimulation, in bicuculline. The greater potentiation of field responses following theta-patterned stimulation in the presence of bicuculline indicates that a larger potentiation of excitatory responses was unmasked during suppression of inhibitory inputs. These results suggest that a long-lasting enhancement of inhibition in pyramidal cells was also induced following theta-patterned stimulation in normal ACSF. Since suppression of inhibition did not uncover a significantly larger potentiation following 100 Hz tetanization, the influence of inhibition on LTP of excitatory responses appears to be stimulation-dependent. In conclusion, theta-patterned stimulation appears to be more effective at inducing plasticity within inhibitory circuits, and this plasticity may partially offset concurrent increases in the excitability of the CA1 network.

Involvement of adenosine A2A receptor in sleep promotion

We examined the sleep-modulatory effects of four adenosine agonists, namely, (1) 2-(4-(2-carboxyethyl)phenylethylamino)adenosine-5'-N-ethylcarbo xamideadenosine (CGS21680), a highly selective adenosine A2A receptor agonist; (2) 2-(4-(2-(2-aminoethylaminocarbonyl)ethyl)phenylethylamino)-5 '-N-ethylcarboxamidoadenosine (APEC), a selective adenosine A2A receptor agonist; (3) 5'-N-ethylcarboxamidoadenosine (NECA), a nonselective adenosine A1/A2 receptor agonist, and (4) N6-cyclopentyladenosine (CPA), a selective adenosine A1 receptor agonist. Each agonist was administered in the subarachnoid space underlying the rostral basal forebrain of rats through chronically implanted cannulae at the rate of 0.02, 0.2, 2.0, 12.0, or 20.0 pmol/min over a 6-h period starting from 2300 h, which period is the active phase of the animals. CGS21680, APEC, and NECA produced significant increases in the total amounts of non-rapid-eye-movement (NREM) sleep and rapid-eye-movement (REM) sleep after at least one dose within the range of administration rates. CPA did not produce any significant increase in the total amount of either type of sleep at any of the above administration rates, but instead suppressed REM sleep at the administration rates of 12.0 and 20.0 pmol/min. These results indicate that the activities of adenosine A2A receptors are crucially involved in the promotion of sleep.

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.

Antagonism of adenosine A2A receptors underlies the behavioural activating effect of caffeine and is associated with reduced expression of messenger RNA for NGFI-A and NGFI-B in caudate-putamen and nucleus accumbens

Caffeine, the most widely consumed of all psychostimulant drugs, exerts its action by antagonizing adenosine receptors. To study the arousing properties of caffeine, we injected rats intraperitoneally with vehicle, caffeine (7.5, 15 or 30mg/kg), the selective adenosine A2A receptor antagonist, SCH 58261 (3.75 mg/kg) or the selective adenosine A1 receptor selective antagonist DPCPX (7.5 mg/kg). In a behavioural test it was found that administration of caffeine and SCH 58261 significantly increased locomotion and rearing, whereas DPCPX did not alter locomotion and reduced rearing. After the behavioural session the rats were killed, their brains were cut at several levels along a rostrocaudal axis and in situ hybridization against NGFI-A messenger RNA and NGFI-B messenger RNA was performed. A reduction of NGFI-A messenger RNA was found in several subregions of both caudate putamen and nucleus accumbens in caffeine-treated animals. Similarly, animals that had received SCH 58261 showed significant decreases of NGFI-A messenger RNA in the rostral part of caudate putamen and in the shell part of nucleus accumbens. By contrast, DPCPX treatment caused an increase in the expression of NGFI-A messenger RNA and a smaller increase in NGFI-B messenger RNA in the lateral parts of caudate putamen. In addition, it was found that caffeine, but not SCH 58261 or DPCPX, elevated the expression of NGFI-A and NGFI-B messenger RNA in the cerebral cortex, especially in its parietal part. Thus, these results provide evidence that endogenous adenosine, via adenosine A2A receptors, causes a tonic activation of striatopallidal neurons. By blocking this adenosine effect, caffeine causes behavioural activation.

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.

Receptor-regulated ion channels

Recent advances in the study of receptor-regulated ion channels include the cloning of the genes encoding three types of potassium channel that are favorite targets of receptors for transmitters and hormones. Studies of these channels have also provided a strong indication that G-protein betagamma subunits may gate ion channels via direct protein-protein interactions. Similarities between channel regulation by natriuretic peptides and channel regulation by secreted peptide products of the Alzheimer's beta-amyloid precursor protein offer hints for the existence of a receptor for the latter. There are also other novel examples of channel regulation in excitable and nonexcitable cells, including liver cells and blood cells.

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.

Quantitative morphology of physiologically identified and intracellularly labeled neurons from the guinea-pig laterodorsal tegmental nucleus in vitro

Mesopontine cholinergic neurons have been implicated in the initiation and maintenance of rapid eye movement sleep via their efferent connections to the thalamus and the medial pontine reticular formation. As a first step toward understanding how these modulatory neurons integrate synaptic input, we have investigated the dendritic architecture of laterodorsal tegmental nucleus neurons. The principal cells of the guinea-pig laterodorsal tegmental nucleus were identified electrophysiologically in a brain slice preparation, then were intracellularly injected with biocytin and reconstructed using a computer-aided tracing system. The somata were large (27 +/- 3 microns; n = 11) and gave rise to an average of 4.8 primary dendrites which, in most cases, emerged from the soma in a pattern that was radially symmetric in the plane of the slice. Primary dendrites had an average of 3.7 endings. A single axon arose from either the soma or a proximal dendrite and exited the nucleus with a medial and/or lateral trajectory. Some axons also gave rise to a local terminal plexus composed of fine fibers bearing numerous punctate swellings that ramified profusely within the neuron's dendritic field. Total dendritic area averaged about 10(5) microns2, and therefore the average contribution of the soma to the total surface area (20%) was significantly larger than the values reported for many other cell types. Dendritic diameters were non-uniform in three respects. Some processes were sparsely spiny. Most processes were varicose, with the degree of varicosity increasing substantially in secondary and tertiary dendritic segments. There was also a large degree of taper in dendritic processes; those processes with a non-negative taper had an average diameter decrease of 40 +/- 25%. Dendritic processes deviated from the criteria necessary for a Rall equivalent cylinder approximation due to non-uniformity in morphotonic path length, failure to conform to the Rall 3/2 branching rule and non-uniformity of dendritic diameter. An analysis was done to assess the impact of dendritic varicosities on the extraction of cable parameters for these cells. Voltage traces were simulated by solving the cable equation for a varicose dendrite and then membrane parameters were recovered using an equivalent cylinder model. Errors in the extracted values of specific membrane conductance and specific membrane capacitance were quite small (< or = 5%), while larger errors were seen for electrotonic length (< or = 21%) and intracellular resistivity (< or = 5%). These data indicate that the principal cells of the laterodorsal tegmental nucleus, while possessing a relatively simple dendritic structure in terms of number and branchiness of dendrites, display a heterogeneity of dendritic process types. Processes range from smooth to markedly varicose, and can be aspiny or sparsely spiny. The possibility that the dendritic varicosities function as sites of either electrical or chemical compartmentalization is discussed. The degree of error resulting from a Rall equivalent cylinder approximation in light of these varicosities indicated that a generalized cable model approach may prove more effective in estimating their cable parameters.