José-Antonio Arias-Montaño

Histamine H3 receptor activation inhibits glutamate release from rat striatal synaptosomes.

The release of glutamate from striatal synaptosomes induced by depolarisation with 4-aminopyridine (4-AP) was studied by a method based on the fluorescent properties of the NAPDH formed by the metabolism of the neurotransmitter by glutamate dehydrogenase.Ca(2+)-dependent, depolarisation-induced glutamate release was inhibited in a concentration-dependent manner by the selective histamine H(3) agonist immepip. Best-fit estimates were: maximum inhibition 60+/-10% and IC(50) 68+/-10 nM. The effect of 300 nM immepip on depolarisation-evoked glutamate release was reversed by the selective H(3) antagonist thioperamide in a concentration-dependent manner (EC(50) 23 nM, K(i) 4 nM). In fura-2-loaded synaptosomes, the increase in the intracellular concentration of Ca(2+) ([Ca(2+)](i)) evoked by 4-AP-induced depolarisation (resting level 167+/-14 nM; Delta[Ca(2+)](i) 88+/-15 nM) was modestly, but significantly reduced (29+/-5% inhibition) by 300 nM immepip. The action of the H(3) agonist on depolarisation-induced changes in [Ca(2+)](i) was reversed by 100 nM thioperamide. Taken together, our results indicate that histamine modulates the release of glutamate from corticostriatal nerve terminals. Inhibition of depolarisation-induced Ca(2+) entry through voltage-dependent Ca(2+) channels appears to account for the effect of H(3) receptor activation on neurotransmitter release. Modulation of glutamatergic transmission in rat striatum may have important consequences for the function of basal ganglia and therefore for the control of motor behaviour.

Histamine H3-receptor activation inhibits dopamine synthesis in rat striatum.

Unilateral 6-hydroxydopamine lesion to rat substantia nigra pars compacta resulted in a modest, but significant, decrease in the specific binding of N-α-[methyl-3H]histamine (19 ± 5% reduction) to synaptosomal membranes from ipsilateral striata. Dopamine synthesis was assessed in striatal slices by determining [3H]DOPA accumulation after inhibition of DOPA decarboxylase. [3H]DOPA synthesis induced by 50 mM K+ (151 ± 4% of basal) was prevented by either Ca2+ removal or by Ni2+. Depolarization-stimulated [3H]DOPA accumulation was reduced by the selective H3-agonist immepip (100 nM; 68 ± 7% inhibition). The effect of immepip was reversed by thioperamide (100 nM), a selective H3-antagonist. Taken together, our results indicate that histamine modulates striatal dopamine synthesis by acting at H3-receptors located on dopaminergic nerve terminals.

Histamine H3 receptor-mediated inhibition of depolarization-induced, dopamine D1 receptor-dependent release of [3H]-γ-aminobutyric acid from rat striatal slices

A study was made of the regulation of [3H]‐γ‐aminobutyric acid ([3H]‐GABA) release from slices of rat striatum by endogenous dopamine and exogenous histamine and a histamine H3‐agonist. Depolarization‐induced release of [3H]‐GABA was Ca2+‐dependent and was increased in the presence of the dopamine D2 receptor family antagonist, sulpiride (10 μM). The sulpiride‐potentiated release of [3H]‐GABA was strongly inhibited by the dopamine D1 receptor family antagonist, SCH 23390 (1 μM). Neither antagonist altered basal release. The 15 mM K+‐induced release of [3H]‐GABA in the presence of sulpiride was inhibited by 100 μM histamine (mean inhibition 78±3%) and by the histamine H3 receptor‐selective agonist, immepip, 1 μM (mean inhibition 81±5%). The IC50 values for histamine and immepip were 1.3±0.2 μM and 16±2 nM, respectively. The inhibitory effects of histamine and immepip were reversed by the H3 receptor antagonist, thioperamide, 1 μM. The inhibition of 15 mM K+‐induced [3H]‐GABA release by immepip was reversed by the H3 receptor antagonist, clobenpropit, Kd 0.11±0.04 nM. Clobenpropit alone had no effect on basal or stimulated release of [3H]‐GABA. Elevated K+ caused little release of [3H]‐GABA from striatal slices from reserpinized rats, unless the D1 partial agonist, R(+)‐SKF 38393, 1 μM, was also present. The stimulated release in the presence of SKF 38393 was reduced by 1 μM immepip to the level obtained in the absence of SKF 38393. These observations demonstrate that histamine H3 receptor activation strongly inhibits the dopamine D1 receptor‐dependent release of [3H]‐GABA from rat striatum; primarily through an interaction at the terminals of GABA neurones.

Histamine H3 receptor activation inhibits dopamine D1 receptor-induced cAMP accumulation in rat striatal slices

In striatal membranes bearing significant levels of histamine H3 receptors (72 +/- 14 fmol/mg protein), the H3 agonist immepip (1 microM) increased [35S]GTPgammaS binding to 119 +/- 2% of basal, an effect prevented by the H3 antagonist clobenpropit and by pre-treatment with pertussis toxin. In slices labelled with [3H]adenine and in the presence of 1 mM isobutylmethylxantine (IBMX), the selective dopamine D1-like (D1/D5) receptor agonist SKF-81297 stimulated cyclic [3H]AMP ([3H]cAMP) accumulation (maximal stimulation 205 +/- 24% of basal, EC50 113 +/- 12 nM), an effect fully blocked by the D1/D5 antagonist SCH-23390. The accumulation of [3H]cAMP induced by 1 microM SKF-81297 was inhibited in a concentration-dependent manner by the selective H3 receptor agonist immepip (maximal inhibition 60+/-5%, IC50 13 +/- 5 nM). The inhibitory action of 100 nM immepip was reversed in a concentration-dependent manner by the H3 antagonist thioperamide (EC50 13 +/- 3 nM, Ki 1.4 +/- 0.3 nM). Forskolin-induced [3H]cAMP accumulation (726 +/- 57% of basal) was also reduced by H3 receptor activation, although to a lesser extent (19.1 +/- 3.2% inhibition), an action not affected by the absence of either IBMX or Ca2+ ions in the incubation medium. Neither the density of [3H]SCH-23390 binding sites (D1 receptors) nor the inhibition by SKF-81297 were affected by 1 microM immepip, ruling out a direct interaction between D1 and H3 receptors. These results indicate that through H3 receptors coupled to Galphai/o proteins, histamine modulates cAMP formation in striatal neurones that possess D1 receptors, most probably GABAergic striato-nigral neurones.

Histamine-induced Ca2+ entry in human astrocytoma U373 MG cells: Evidence for involvement of store-operated channels

Glial and glia‐derived cells express a variety of receptors for neurotransmitters and hormones, the majority of which evoke both Ca2+ release from intracellular stores and Ca2+ entry across the plasma membrane. We investigated the links between histamine H1 receptor activation, Ca2+ release from intracellular stores and Ca2+ influx in human astrocytoma U373 MG cells. Histamine, through a H1 receptor‐mediated effect, evoked an increase in cytoplasmic free calcium concentration ([Ca2+]i) that occurred in two phases: an initial, transient, increase owing to Ca2+ mobilization from intracellular pools, and a second, sustained increase dependent on both Ca2+ influx and continuous receptor occupancy. The characteristics of histamine‐induced increases in [Ca2+]i were similar to the capacitative entry evoked by emptying of the Ca2+ stores with thapsigargine, and different from that observed when Ca2+ influx was activated with OAG (1‐oleoyl‐2‐acetyl‐sn‐glycerol), a diacylglycerol (DAG) analog. OAG application or increased endogenous DAG, resulting from DAG kinase inhibition, reduced the histamine‐induced response. Furthermore, activation of the DAG target, protein kinase C (PKC), by TPA (12‐O‐tetradecanoyl 4β‐phorbol 13α‐acetate) resulted in inhibition of the histamine‐induced Ca2+ response, an action prevented by PKC inhibitors. By using reverse transcriptase–polymerase chain reaction analysis, mRNAs for transient receptor potential channels (TRPCs) 1, 4, and 6 as well as for STIM1 (stromal‐interacting molecule) and Orai1 were found to be expressed in the U373 MG cells, and confocal microscopy using specific antibodies revealed the presence of the corresponding proteins. Therefore, TRPCs may be candidate proteins forming store‐operated channels in the U373 MG cell line. Further, our results confirm the involvement of PKC in the regulation of H1 receptor‐induced responses and point out to the existence of a feedback mechanism acting via PKC to limit the increase in [Ca2+]i.

Histamine H1 receptors in rat dorsal raphe nucleus: pharmacological characterisation and linking to increased neuronal activity

In this work we studied the presence of histamine H(1) receptors in the rat dorsal raphe nucleus (DRN) and the effect of their activation on the activity of presumed serotonergic DRN neurones. [(3)H]-Mepyramine bound to DRN membranes with best-fit values of 107+/-13 fmol/mg protein for maximum binding (B(max)) and 1.2+/-0.4 nM for the equilibrium dissociation constant (K(d)). In DRN slices labelled with [(3)H]-inositol and in the presence of 10 mM LiCl, histamine stimulated the accumulation of [(3)H]-inositol phosphates ([(3)H]-IPs) with maximum effect 172+/-6% of basal and EC(50) 3.2+/-1.3 microM. [(3)H]-IPs accumulation induced by 100 microM histamine (162+/-5% of basal) was markedly, but not fully blocked by the selective H(1) antagonist mepyramine (300 nM; 64+/-6% inhibition). The simultaneous addition of mepyramine and the selective H(2) antagonist ranitidine (10 microM) abolished histamine-induced [(3)H]-IPs accumulation. The presence of H(2) receptors was confirmed by [(3)H]-tiotidine binding and by the determination of histamine-induced [(3)H]-cyclic AMP formation. Extracellular single-unit recording in brain stem slices showed that the exposure to histamine resulted in a marked increase in the firing rate of DRN presumed serotonergic neurones (471+/-10% of basal), that was dependent on the concentration of the agonist (EC(50) 4.5+/-0.3 microM). The action of histamine was not affected by the H(2) antagonist tiotidine (2 microM) but was fully prevented by 1 microM mepyramine. Taken together, our results indicate that histamine modulates the firing of DRN presumed serotonergic neurones through the activation of H(1) receptors coupled to phosphonositide hydrolysis.

Intranigral injection of the H3 agonist immepip and systemic apomorphine elicit ipsilateral turning behaviour in naive rats, but reduce contralateral turning in hemiparkinsonian rats

There is evidence that histamine H3 receptors co-localise with dopamine D1 receptors on the terminals of striato-nigral neurones. In this work we studied the effect of the local activation of H3 receptors present in substantia nigra pars reticulata (SNr) on turning behaviour following apomorphine administration to either naive or hemiparkinsonian rats. In naive rats the intranigral (SNr) injection of the H3 receptor agonist immepip (3.2 or 32 ng/1 microl) resulted in ipsilateral turning following systemic apomorphine (0.5 mg/kg, subcutaneous). The effect of immepip was related to the dose and prevented by the H3 antagonist thioperamide (5 mg/kg, intraperitoneal). Conversely, in rats with 6-hydroxydopamine (6-OHDA) lesions to either substantia nigra pars compacta or the medial forebrain bundle (mfb), apomorphine-induced contralateral turning was reduced by intranigral immepip, an effect prevented by systemic thioperamide. Our data show that H3 receptors present in SNr regulate the synaptic output of the basal ganglia, most likely by reducing GABA release from striato-nigral terminals. These results may be relevant for the understanding of the role of histamine and H3 receptors in the control of motor behaviour both in normal and pathophysiological conditions, such as Parkinsons disease in which histaminergic innervation and histamine levels in substantia nigra have been shown to increase.

Noradrenaline increases the firing rate of a subpopulation of rat subthalamic neurones through the activation of α1-adrenoceptors

In the rat subthalamic nucleus, which plays a critical role in the control of motor behaviour, specific binding of [3H]-prazosin was detected by radioligand binding to homogenates and by autoradiography in slices. [3H]-Prazosin binding to homogenates (Bmax 71 +/- 5 fmol/mg protein; Kd 0.27 +/- 0.05 nM) was competed for by alpha1-antagonists. In subthalamic nucleus slices and in the presence of 10 mM LiCl, noradrenaline (100 microM) produced a modest, but consistent, stimulation of [3H]-inositol phosphate accumulation (146 +/- 6% of basal), reversed by the alpha1-antagonist prazosin (1 microM). Extracellular single-unit recordings in slices showed that in a subpopulation (61 out of 94 cells) of rat subthalamic neurones with regular, single-spike firing pattern, noradrenaline induced a concentration-dependent increase in the firing rate (EC50 2.5 +/- 0.2 microM, maximum effect 272 +/- 33% of basal). The action of noradrenaline was mimicked by the selective alpha1-agonist phenylephrine but not by selective alpha2- or beta-agonists, and was blocked by the alpha1-antagonist prazosin but not by alpha2- or beta-antagonists. The excitatory effect of noradrenaline was not prevented by perfusion with low Ca2+/high Mg2+ solution. In four out of 11 neurones perfusion with 3 microM noradrenaline resulted in a shift from bursting to regular firing. Taken together, our results indicate that rat subthalamic neurones express alpha1-adrenoceptors responsible for noradrenaline-induced stimulation of the firing rate of a subpopulation of neurones. By modulating the spontaneous activity of STN neurones, noradrenergic pathways might have a significant role in regulating basal ganglia function and thus motor activity.

Histamine in brain development.

J. Neurochem. (2012) 122, 872–882.

Histamine H1 receptor activation stimulates mitogenesis in human astrocytoma U373 MG cells

In human astrocytoma U373 MG cells that express histamine H1 receptors (180 ± 6 fmol/mg protein) but not H2 or H3 receptors, histamine stimulated mitogenesis as assessed by [3H]-thymidine incorporation (173 ± 2% of basal; EC50, 2.5 ± 0.4 μM). The effect of 100 μM histamine was fully blocked by the selective H1 antagonist mepyramine (1 μM) and was markedly reduced (93 ± 4% inhibition) by the phospholipase C inhibitor U73122 (10 μM).The activator of protein kinase C (PKC) phorbol 12-tetradecanoyl-13-acetate (TPA, 100 nM) stimulated [3H]-thymidine incorporation (270 ± 8% of basal), and this response was not additive with that to 100 μM histamine. The incorporation of [3H]-thymidine induced by 100 μM histamine was partially reduced by the PKC inhibitor Ro 31-8220 (57 ± 7% inhibition at 300 nM) and by the compound PD 098,059 (30 μM, 62 ± 14% inhibition), an inhibitor of the mitogen-activated kinase (MAPK) kinases MEK1/MEK2.These results show that histamine H1receptor activation stimulates the proliferation of human astrocytoma U373 MG cells. The action of histamine appears to be partially mediated by PKC stimulation and MAPK activation.