EFhd2/Swiprosin-1 is a common genetic determinator for sensation-seeking/low anxiety and alcohol addiction.

In many societies, the majority of adults regularly consume alcohol. However, only a small proportion develops alcohol addiction. Individuals at risk often show a high sensation-seeking/low-anxiety behavioural phenotype. Here we asked which role EF hand domain containing 2 (EFhd2; Swiprosin-1) plays in the control of alcohol addiction-associated behaviours. EFhd2 knockout (KO) mice drink more alcohol than controls and spontaneously escalate their consumption. This coincided with a sensation-seeking and low-anxiety phenotype. A reversal of the behavioural phenotype with ß-carboline, an anxiogenic inverse benzodiazepine receptor agonist, normalized alcohol preference in EFhd2 KO mice, demonstrating an EFhd2-driven relationship between personality traits and alcohol preference. These findings were confirmed in a human sample where we observed a positive association of the EFhd2 single-nucleotide polymorphism rs112146896 with lifetime drinking and a negative association with anxiety in healthy adolescents. The lack of EFhd2 reduced extracellular dopamine levels in the brain, but enhanced responses to alcohol. In confirmation, gene expression analysis revealed reduced tyrosine hydroxylase expression and the regulation of genes involved in cortex development, Eomes and Pax6, in EFhd2 KO cortices. These findings were corroborated in Xenopus tadpoles by EFhd2 knockdown. Magnetic resonance imaging (MRI) in mice showed that a lack of EFhd2 reduces cortical volume in adults. Moreover, human MRI confirmed the negative association between lifetime alcohol drinking and superior frontal gyrus volume. We propose that EFhd2 is a conserved resilience factor against alcohol consumption and its escalation, working through Pax6/Eomes. Reduced EFhd2 function induces high-risk personality traits of sensation-seeking/low anxiety associated with enhanced alcohol consumption, which may be related to cortex function.

Induction of activin A is essential for the neuroprotective action of basic fibroblast growth factor in vivo.

Exogenous application of neurotrophic growth factors has emerged as a new and particularly promising approach not only to promote functional recovery after acute brain injury but also to protect neurons against the immediate effect of the injury. Among the various growth factors and cytokines studied so far, the neuroprotective and neurotrophic profile of basic fibroblast growth factor (bFGF) is the best documented. Using an animal model of acute excitotoxic brain injury, we report here that the neuroprotective action of bFGF, which is now being tested in stroke patients, depends on the induction of activin A, a member of the transforming growth factor-beta superfamily. Our evidence for this previously unknown mechanism of action of bFGF is that bFGF strongly enhanced lesion-associated induction of activin A; in the presence of the activin-neutralizing protein follistatin, bFGF was no longer capable of rescuing neurons from excitotoxic death; and recombinant activin A exerted a neuroprotective effect by itself. Our data indicate that the development of substances influencing activin expression or receptor binding should offer new ways to fight neuronal loss in ischemic and traumatic brain injury.

Activin tunes GABAergic neurotransmission and modulates anxiety-like behavior.

Activin, a member of the transforming growth factor-beta superfamily, affords neuroprotection in acute brain injury, but its physiological functions in normal adult brain are largely unknown. Using transgenic (tg) mice expressing a dominant-negative activin receptor mutant under the control of the CaMKIIalpha promoter in forebrain neurons, we identified activin as a key regulator of gamma-aminobutyric acid (GABA)ergic synapses and anxiety-like behavior. In the open field, wild-type (wt) and tg mice did not differ in spontaneous locomotion and exploration behavior. However, tg mice visited inner fields significantly more often than wt mice. In the light-dark exploration test, tg mice made more exits, spent significantly more time on a well-lit elevated bar and went farther away from the dark box as compared to wt mice. In addition, the anxiolytic effect of diazepam was abrogated in tg mice. Thus the disruption of activin receptor signaling produced a low-anxiety phenotype that failed to respond to benzodiazepines. In whole-cell recordings from hippocampal pyramidal cells, enhanced spontaneous GABA release, increased GABA tonus, reduced benzodiazepine sensitivity and augmented GABA(B) receptor function emerged as likely substrates of the low-anxiety phenotype. These data provide strong evidence that activin influences pre- and postsynaptic components of GABAergic synapses in a highly synergistic fashion. Given the crucial role of GABAergic neurotransmission in emotional states, anxiety and depression, dysfunctions of activin receptor signaling could be involved in affective disorders: and drugs affecting this pathway might show promise for psychopharmacological treatment.

Disinhibition of hippocampal CA3 neurons induced by suppression of an adenosine A1 receptor-mediated inhibitory tonus: pre- and postsynaptic components.

Intracellular recordings were performed on hippocampal CA3 neurons in vitro to investigate the inhibitory tonus generated by endogenously produced adenosine in this brain region. Bath application of the highly selective adenosine A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine at concentrations up to 100 nM induced both spontaneous and stimulus-evoked epileptiform burst discharges. Once induced, the 1,3-dipropyl-8-cyclopentylxanthine-evoked epileptiform activity was apparently irreversible even after prolonged superfusion with drug-free solution. The blockade of glutamatergic excitatory synaptic transmission by preincubation of the slices with the amino-3-hydroxy-5-methyl-4-isoxazolpropionic acid receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (10 microM), but not with the N-methyl-D-aspartate receptor antagonist D-2-amino-5-phosphonovaleric acid (50 microM), prevented the induction of epileptiform activity by 1,3-dipropyl-8-cyclopentylxanthine. The generation of the burst discharges was independent of the membrane potential, and the amplitude of the slow component of the paroxysmal depolarization shift increased with hyperpolarization, indicating that the 1,3-dipropyl-8-cyclopentylxanthine-induced bursts were synaptically mediated events. Recordings from tetrodotoxin-treated CA3 neurons revealed a strong postsynaptic component of endogenous adenosinergic inhibition. Both 1,3-dipropyl-8-cyclopentylxanthine and the adenosine-degrading enzyme adenosine deaminase produced an apparently irreversible depolarization of the membrane potential by about 20 mV. Sometimes, this depolarization attained the threshold for the generation of putative calcium spikes, but no potential changes resembling paroxysmal depolarization shift-like events were observed. At the concentrations used in electrophysiological experiments (30-100 nM), 1,3-dipropyl-8-cyclopentylxanthine displayed only a negligible inhibitory action on total cyclic nucleotide phosphodiesterase activity measured by means of a radiochemical assay in a homogenate of the rat cerebral cortex. Furthermore, even high concentrations of the selective phosphodiesterase inhibitor rolipram (10 microM), which displays no affinity to adenosine receptors, did not mimic the electrophysiological actions of 1,3-dipropyl-8-cyclopentylxanthine, thus excluding the possibility that the effects of the A1 receptor antagonist on neuronal discharge behavior can be ascribed to an inhibition of phosphodiesterases. The present data demonstrate that endogenously released adenosine exerts a vigorous control on the excitability of hippocampal CA3 neurons on both the pre- and postsynaptic sites. The long-lasting disinhibition following a transient suppression of adenosinergic inhibition strongly suggests that, besides its well-known short-term effects on neuronal activity, adenosine might also contribute to the long-term control of hippocampal excitability.

A special blocker reveals the presence and function of the hyperpolarization-activated cation current IH in peripheral mammalian nerve fibres.

Electrotonic responses recorded extra- or intracellularly from peripheral nerve preparations show a "sag" to hyperpolarizing current pulses. The biophysical nature of this "inward rectification" is still under discussion since the phenomenon has not been noted at voltage-clamped single nerve fibres, and since Cs+, which reduces inward rectification, is not a specific ion channel blocker. In this study, we found that low micromolar concentrations of ZD 7288, a specific blocker of the hyperpolarization-activated cationic current (Ih) in the soma of central mammalian neurons, result in a complete block of inward rectification in the electrotonic responses of isolated rat spinal dorsal roots. In addition, ZD 7288 enhanced the activity-dependent slowing of conduction seen in compound C fibre action potentials of isolated rat vagus nerves and augmented the post-tetanic hyperpolarization following trains of action potentials in unmyelinated and myelinated axons. The data suggest that ZD 7288 is a potent blocker and a useful research tool for the study of hyperpolarization-activated inward rectification (Ih) of peripheral nerve preparations.

The roles of activins in repair processes of the skin and the brain.

A recent study from our laboratory demonstrated a strong upregulation of activin expression during cutaneous wound healing. To further analyze the role of activin A in skin morphogenesis and wound repair, we generated transgenic mice that overexpress activin A under the control of the keratin 14 promoter. The latter targets expression of transgenes to the basal, proliferating layer of the epidermis. Hetero- as well as homozygous transgenic animals were viable and fertile. However, they were smaller than non-transgenic littermates and they had smaller ears and shorter tails. Histological analysis of their skin revealed dermal hyperthickening, mainly due to the replacement of fatty tissue by connective tissue, and an increase in suprabasal, partially differentiated epidermal layers. After cutaneous injury, a strong enhancement of granulation tissue formation was observed. Furthermore, the extent of re-epithelialization was increased in some of the wounds. These data demonstrate that activin A is a potent stimulator of the wound healing process. Using an in vivo model of local brain injury, we found that activin A also plays a significant role in the early cellular response to neuronal damage. Expression of activin mRNA and protein is markedly upregulated within a few hours of injury. If applied exogenously, recombinant activin A is capable of rescuing neurons from acute cell death. Studying the interaction between bFGF, a well-established neuroprotective agent, which is currently being tested in stroke patients, and activin A, we arrived at the unexpected conclusion that it is the strong induction of activin A by bFGF which endows the latter with its beneficial actions in patients. These findings suggest that the development of substances directly targeting activin expression or receptor binding should offer new possibilities in the acute treatment of stroke and brain trauma.

Activin: a novel player in tissue repair processes.

Recent studies have demonstrated a strong expression of activin in repair processes of various tissues and organs, including the skin, the lung, the intestine, the cardiovascular system, and even the brain. Although little is as yet known about the function of activin in tissue repair, first results suggest a role of activin in epithelial differentiation, fibroblast proliferation and expression of matrix molecules by these cells, and also in neuroprotection. Whereas a transient overexpression of activin after tissue injury might be beneficial for the repair process, sustained expression of activin could lead to fibrotic processes. Therefore, the modulation of the availability or biological activity of activin could be of particular importance for the treatment of impaired tissue repair on the one hand and tissue fibrosis on the other hand.

Effects of phenytoin on the persistent Na+ current of mammalian CNS neurones.

Whole-cell recordings in voltage-clamp mode were performed on acutely isolated neurones from rat neocortex and neostriatum to examine the effects of the anticonvulsant phenytoin on a non-inactivating (persistent) Na+ current (INaP). INaP was chosen because it enhances neuronal excitability near firing threshold, which makes it a potential target for anticonvulsant drugs. In both preparations, phenytoin (10-100 microM) inhibited INaP in a dose-dependent fashion without altering the voltage-dependence of current activation. On average, half-block of INaP was produced by 34 microM phenytoin suggesting that therapeutic drug concentrations are likely to affect INaP. Inhibition of INaP might represent a novel mechanism contributing to the anticonvulsant profile of phenytoin.

Strong induction of activin expression after hippocampal lesion.

We studied the temporal and spatial mRNA expression pattern of activin/inhibin beta A, beta B and alpha subunits after unilateral kainic acid lesions of the hippocampal CA3 region. We found a strikingly increased expression of beta A mRNA in the ipsilateral hippocampus 6-24 h after injury. By contrast, the beta B and alpha mRNAs were expressed at equally low levels in normal and injured hippocampi, suggesting that the beta A transcripts give rise to activin A, but not to activin AB or inhibin. In situ hybridization demonstrated the presence of beta A mRNA in neurones near the site of lesion. Expression of all known types of activin receptors could be demonstrated in normal and injured hippocampi by RT-PCR. These findings suggest a role of activin in brain injury.

Adenosine depresses induction of LTP at the mossy fiber-CA3 synapse in vitro.

Using the hippocampal slice preparation, extracellular recordings of CA3 field excitatory postsynaptic potentials (fEPSPs) were performed to assess the effects of adenosine on the induction of mossy fiber long-term potentiation (LTP). When present during tetanization, adenosine (50 microM) significantly suppressed mossy fiber LTP whereas it failed to inhibit LTP when applied immediately after high-frequency stimulation. Based on the hypothesis that mossy fiber LTP is presynaptic in origin, our data thus provide first evidence that adenosine's presynaptic action alone is sufficiently powerful to interfere with synaptic plasticity.

Adenosinergic inhibition in hippocampus is mediated by adenosine A1 receptors very similar to those of peripheral tissues.

The amplitude of the orthodromically evoked population spike (PS) of CA1 neurons was used to investigate quantitatively adenosine receptor antagonism in guinea pig hippocampal slices. Increasing concentrations of the highly selective adenosine A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 3-100 nM) produced parallel, rightward shifts of the dose-response curve for the N6-cyclopentyladenosine (CPA)-induced decrease in PS amplitude. Schild plot analyses of the respective antagonism data obtained in both the presence and virtual absence of endogenous adenosine yielded apparent dissociation constants (KD) of DPCPX at the hippocampal A1 receptor of 3.3 and 3.6 nM, respectively. This indicates that the inhibitory tonus generated by endogenously produced adenosine is due to tonic activation of A1 receptors. The KD values agree well with the binding affinity of DPCPX to A1 receptors determined in brain tissue sections. Since, in our preparation, Schild plot analyses of DPCPX antagonism revealed KD values close to those reported for other tissues, it is concluded that the central A1 receptor mediating adenosinergic inhibition is pharmacologically not distinct from A1 receptors identified in peripheral tissues.

Transient and selective blockade of adenosine A1-receptors by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) causes sustained epileptiform activity in hippocampal CA3 neurons of guinea pigs.

The effects of endogenously released adenosine on the excitability of hippocampal neurons were studied using the novel and highly selective adenosine A1-receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Extra- and intracellular recordings performed in area CA1 and CA3 of the guinea pig hippocampal slice preparation revealed that a transient suppression of an inhibitory purinergic tonus by DPCPX leads to sustained interictal-like epileptiform activity arising in area CA3. Once induced, the spontaneous burst discharges were apparently irreversible within the observation period, even after prolonged washout (2-3 h) in normal solution. In contrast, the hyperpolarizing action of exogenous adenosine, which was substantially reduced by DPCPX, recovered within 30-60 min of drug washout, indicating that DPCPX was not irreversibly bound to the A1-receptor.

Stimulus-evoked dopamine overflow in the rat nucleus accumbens is decreased following chronic haloperidol administration: an in vivo voltammetric study.

Fast cyclic voltammetry was used to investigate the effects of chronic haloperidol (HAL) treatment on electrically evoked dopamine (DA) overflow in the nucleus accumbens of the anaesthetized rat in vivo. Evoked DA efflux was significantly reduced in rats treated with 1.0 mg/kg per day HAL for 21 days. In rats treated with 0.5 mg/kg per day, evoked DA overflow was reduced, but did not differ significantly from control values. In untreated animals, injection of a single dose of HAL resulted in a significant increase in the DA overflow evoked by subsequent stimulus trains. In contrast, this HAL challenge did not produce a significant enhancement in evoked DA overflow in any of the HAL-treated groups. These results are consistent with the previous reports that basal DA release is reduced after chronic HAL treatment, and show for the first time that chronic HAL administration decreases stimulus-evoked DA overflow in the rat nucleus accumbens in vivo.

Actions of BRL 34915 (Cromakalim) upon convulsive discharges in guinea pig hippocampal slices.

The effects of the purported K+ channel opener BRL 34915 upon CNS neurons were examined in guinea pig hippocampal slices. Both the EPSP component and the population spike of field potentials recorded in the CA1 area were reduced in amplitude by BRL 34915 (EC50 about 100 mumol/l). In the same concentration range, BRL 34915 also slowed down the bursting rate of pacemaker neurons in the CA3 region. In order to test a possible anticonvulsant efficacy of the drug, the excitability of hippocampal neurons was increased experimentally by changing the ionic composition of the perfusion medium (omission of Ca2+ or Mg2+, elevation of K+). In all three conditions, epileptiform neuronal activity occurred, which was depressed by BRL 34915. The similarity of the effects of BRL 34915 in normal and convulsive slices indicates that the compound acts upon intrinsic nonsynaptic processes controlling neuronal excitability and cell firing.

Effects of cromakalim (BRL 34915) on potassium conductances in CA3 neurons of the guinea-pig hippocampus in vitro.

The action of the potassium channel activator, cromakalim (BRL 34915), on membrane potential, input resistance and current-voltage-relationship of CA3 neurons in a slice preparation of the guinea-pig hippocampus was investigated by means of intracellular recordings. In the presence of tetrodotoxin, cromakalim (30-100 mumol/l) produced a hyperpolarization up to 4 mV associated with a decrease in input resistance up to 10 MOhms. Determination of the equilibrium potential of the cromakalim action revealed that the hyperpolarization is due to the activation of a potassium conductance. This cromakalim-activated potassium conductance was voltage-dependent, i.e. it increased with hyperpolarization. Among a number of potassium channel blockers tested, only Cs+ (2 mmol/l) and Ba2+ (0.5 mmol/l) were able to inhibit the cromakalim-induced effects. Simultaneously, both cations suppressed the hyperpolarizing inward rectification (anomalous rectification) in these neurons, indicating that cromakalim activated or potentiated an inwardly rectifying potassium conductance. In addition, cromakalim slightly enhanced both amplitude and duration of afterhyperpolarizations following single calcium-dependent action potentials, suggesting that cromakalim might have a weak facilitatory effect on calcium-dependent potassium conductances.

The low KM-phosphodiesterase inhibitor denbufylline enhances neuronal excitability in guinea pig hippocampus in vitro.

The actions of the phosphodiesterase inhibitor denbufylline on the excitability of hippocampal neurons were investigated by means of extracellular and intracellular recordings. Denbufylline, which has been shown to selectively inhibit a low KM, Ca2+/calmodulin-independent phosphodiesterase isozyme, concentration-dependently increased the amplitude of the extracellularly recorded CA1 population spike evoked by electrical stimulation of the Schaffer collateral/commissural pathway. Concentration-response-curves yielded an EC50 for denbufylline of 0.76 microM. In comparison, the non-selective phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) also produced an increase in the amplitude of the population spike. From the concentration-response-curve, which was steeper than that of denbufylline, an EC50 for IBMX of 1.04 microM was obtained. However, despite their similar EC50 values, denbufylline was found to be significantly more potent at lower concentrations (less than or equal to 300 nM) than IBMX. Intracellular recordings from CA1 pyramidal cells revealed postsynaptic actions of denbufylline (300 nM) as indicated by a small drug-induced depolarization (2-5 mV) associated with an increase in membrane input resistance by 10-20%. In addition, denbufylline blocked the accommodation of trains of action potentials evoked by the injection of depolarizing current pulses. The results suggest i) that accumulation of adenosine-3',5'-monophosphate (cAMP) in the postsynaptic cell and/or in the presynaptic terminal produced by blockade of phosphodiesterases leads to enhanced synaptic transmission in the CA1 area of the hippocampus and ii) that a low KM, Ca2+/calmodulin-independent cAMP-phosphodiesterase is an important component involved in the regulation of the intracellular cAMP level at synapses of central nervous system neurons.

Chronic clozapine versus chronic haloperidol treatment: differential effects on electrically evoked dopamine efflux in the rat caudate putamen, but not in the nucleus accumbens.

Fast cyclic voltammetry at carbon-fibre micro-electrodes was used to investigate the effects of chronic clozapine or haloperidol administration on electrically evoked dopamine efflux in the nucleus accumbens and caudate putamen of the anaesthetized rat. Stimulation trains were delivered to the median forebrain bundle (60 pulses, 350 microns duration) every 5 min, and the evoked dopamine efflux measured as a function of a) the applied stimulus intensity (range 0.2 mA-1.0 mA), and b) the applied stimulus frequency (range 10 Hz-250 Hz). Chronic administration of either clozapine (20 mg/kg x 21 days, p.o.) or haloperidol (1 mg/kg x 21 days, p.o.) significantly reduced electrically evoked dopamine efflux in the nucleus accumbens over the range of stimulus intensities and frequencies tested. The reduction in evoked dopamine efflux observed in the nucleus accumbens of clozapine- and haloperidol-treated rats showed no statistically significant difference. In contrast, only chronic haloperidol treatment significantly reduced evoked dopamine efflux in the caudate putamen. These findings demonstrate that chronic treatment with either the atypical neuroleptic, clozapine, or the typical neuroleptic, haloperidol, produce long-term changes in mesolimbic dopamine function; actions which may underlie their antipsychotic efficacy. They also provide further evidence that the sparing action of clozapine on nigrostriatal dopamine activity may underlie the lower incidence of extrapyramidal side effects associated with its long-term administration.

A novel voltage-dependent cation current in rat neocortical neurones.

1. Using the whole-cell configuration of the patch-clamp technique, an unexpected voltage-dependent cation current (Icat) was recorded from acutely isolated rat neocortical neurones, the Na+, K+ and Ca2+ currents of which were pharmacologically suppressed. 2. Icat was activated at potentials more positive than -45 mV, displayed outward rectification, and deactivated with a slow voltage-dependent time course causing prominent inward tail currents. 3. Activation of Icat was not dependent on Ca2+ influx or increases in cytosolic Ca2+, since it was not abolished by inorganic Ca2+ channel blockers or by internal Ca2+ chelators. 4. Icat was reduced by tetraethylammonium at high concentrations, but not by 4-amino-pyridine, and proved to be insensitive to cation channel blockers such as Cs+, amiloride or gadolinium. 5. Ion substitution experiments revealed that the channel producing Icat was permeable to a number of monovalent cations, including K+, Cs+, Na+ and choline+, but not to the Cl-anion. 6. The features of Icat suggest that, in electrically active neurones, it should play a role in both the initial repolarization of membrane potential after strong depolarization and the generation of depolarizing after-potential.

Expression and biological significance of Ca2+-activated ion channels in human keratinocytes.

In whole-cell recordings from HaCaT keratinocytes, ATP, bradykinin, and histamine caused a biphasic change of the membrane potential consisting of an initial transient depolarization, followed by a pronounced and long-lasting hyperpolarization. Flash photolysis of caged IP3 mimicked the agonist-induced voltage response, suggesting that intracellular Ca2+ release and subsequent opening of Ca2+-activated ion channels serve as the common transduction mechanism. In contrast, cAMP- and PKC-dependent pathways were not involved in the electrophysiological effects of the extracellular signaling molecules. The depolarization was predominantly mediated by a DIDS- and niflumic acid-sensitive Cl- current, whereas a charybdotoxin- and clotrimazole-sensitive K+ current underlay the prominent hyperpolarization. Consistent with the electrophysiological data, RT-PCR showed that HaCaT keratinocytes express two types of Ca2+-activated Cl- channels, CaCC2 and CaCC3 (CLCA2), as well as the Ca2+-activated K+ channel hSK4. That the pronounced hSK4-mediated hyperpolarization bears significance on the growth and differentiation properties of keratinocytes is suggested by RNase protection assays showing that hSK4 mRNA expression is strongly down-regulated under conditions that allow keratinocyte differentiation. hSK4 might thus play a role in linking changes in membrane potential to the biological fate of keratinocytes.