Anxiety and cognition in histamine H3 receptor-/- mice

Histamine H(3) receptors (H3Rs) were first characterized as autoreceptors modulating histamine release and synthesis via negative feedback. Acute H3R stimulation or blockade with selective agonists and antagonists suggests a role for H3R in anxiety and cognition. However, little is known about the long-term effects of H3R blockade on brain function. In the current study, mice lacking H3 receptors (H3R(-/-)) were used to investigate the role of H3R-mediated signalling in anxiety and cognition. H3R(-/-) mice showed enhanced spatial learning and memory in the Barnes maze. In addition, H3R(-/-) mice showed reduced measures of anxiety in the elevated plus and zero mazes involving exploratory behaviour and avoidable anxiety-provoking stimuli, but enhanced acoustic startle responses involving unavoidable anxiety-provoking stimuli. These behavioural alterations were associated with higher arginine vasopressin levels in the central and basolateral nuclei of the amygdala. These findings support a role for H3Rs in mediating histamine effects on spatial learning and memory and measures of anxiety.     

Effects of histamine H3 receptor agonist and antagonist on histamine co-transmitter expression in rat brain

Summary. The histaminergic H₃-receptor (H₃R) controls histamine synthesis and release in the tuberomamillary nucleus. We evaluated the effects of stimulating or blocking of H₃R on glutamate-decarboxylase 67 kDa (GAD-67) and galanin mRNA expression, two histamine co-transmitters. After in situ hybridization histochemistry (ISHH), we observed a colocalization of 100% between histidine decarboxylase (HDC) and GAD-67 or H₃R and of 80 to 97% with galanin. Adult rats received an H₃R agonist ((R)α-Methylhistamine) or antagonist (ciproxifan) and were sacrificed 1 or 3 hours later. Treatment effects on HDC, galanin and GAD-67 mRNA were studied by quantitative ISHH on serial sections. Treatment with the H₃R agonist known to decrease histamine neuron activity initially reduced HDC and galanin gene expression but an inverse change, presumably reflecting a compensatory mechanism, was observed after 3 h on both markers. In contrast, the H₃R antagonist known to activate histamine neurons, had opposite effects on the two markers, suggesting that co-transmitters are submitted to independent control mechanisms. Furthermore, GAD-67 mRNA levels were not significantly modified by these treatments. Received November 12, 2001; accepted November 16, 2001     

Chemical kindling induced by pentylenetetrazol in histamine H(1) receptor gene knockout mice (H(1)KO), histidine decarboxylase-deficient mice (HDC(-/-)) and mast cell-deficient W/W(v) mice

The role of brain histamine on seizure development of pentylenetetrazol (PTZ)-induced kindling was examined in H(1)-receptor gene knockout (H(1)KO), histidine decarboxylase-deficient (HDC(-/-)) and mast cell-deficient (W/W(v)) mice. All H(1)KO, HDC(-/-) and W/W(v) mice had accelerated seizure development of PTZ-induced kindling when compared to their respective wild-type mice. The daily PTZ-kindling increased histamine content in the cortex and diencephalon of H(1)KO mice, whereas the histamine content in the diencephalon of W/W(v) mice was decreased. The present study indicates that histamine plays a suppressive role in seizure development through H(1)-receptors.     

Effects of pitolisant,a histamine H3 inverse agonist,in drug-resistant idiopathic and symptomatic hypersomnia: a chart review

ObjectiveTo evaluate the benefits and risks of pitolisant (a wake-enhancing drug that increases the histamine release in the brain by blocking presynaptic H3 histamine reuptake) in patients with idiopathic (IH) and symptomatic (SH) hypersomnia plus sleepiness refractory to available stimulants (modafinil, methylphenidate, mazindol, sodium oxybate, and d-amphetamine).MethodsThrough retrospective analyses of patient files, the benefit (the score from the Epworth Sleepiness Scale [ESS], authorization renewal) and tolerance (side-effects) of pitolisant were assessed.ResultsA total of 78 patients with IH (n = 65%, 78% women) and SH (n = 13%, 54% women) received pitolisant 5–50 mg once per day over the course of five days to 37 months. The median (interquartile range) ESS scores of patients with IH decreased from 17 (15.5–18.5) to 14 (12–17). There were 36% responders (ESS fall of ⩾3). The improvement in ESS score (−1.9 ± 2.6) was different from 0 in IH without long sleep time (P < 0.002) and in IH with a long sleep time (P < 0.0001), but not in SH. Forty-four (63%) patients with IH and 12 (77%) patients with SH stopped pitolisant, mostly due to a lack of efficacy. Side-effects included gastrointestinal pain (15.4%), increased appetite and weight gain (14.1%), headache (12.8%), insomnia (11.5%), and anxiety (9%), as well as exceptional reports of depression and persistent genital arousal.ConclusionPitolisant had a long-term favorable benefit/risk ratio in 23–38% of drug-resistant patients with IH and SH, suggesting that histamine neurons can be stimulated in severe idiopathic and symptomatic hypersomnia.     

Pilot randomized controlled study of a histamine receptor inverse agonist in the symptomatic treatment of AD

We performed a clinical trial to evaluate the effects of the histamine subtype-3 receptor inverse agonist MK- 0249 on cognition in AD patients. Mild-to-moderate AD patients were randomized 1:1 to 4 weeks of double-blind daily treatment with oral MK-0249 5-mg or placebo. Pharmacokinetic and PET data suggested that MK-0249 5-mg daily would achieve approximately 85% brain receptor occupancy at Cmax in elderly patients. Primary efficacy measures were the short Computerized-Neuropsychological-Test-Battery (CNTB) summary score and ADAS-Cog score. A secondary efficacy measure was a Cognition Summary Score summarizing results from 7 cognitive tests. Of 144 patients randomized, 132 completed 4 weeks (MK-0249 = 65, placebo = 67). Most patients (88.2%) were on concomitant symptomatic AD treatment. There were no significant differences between treatments on primary and secondary endpoints at week 4: short CNTB summary score = 0.89 (95% CI: -0.74,2.52); ADAS-Cog score s -0.25 (95% CI: -1.61,1.11); Cognition Summary Score = 1.38 (95% CI: -0.64,3.40). MK-0249 was generally well tolerated but was associated with an increased percentage of patients with adverse events (41/73; 56.2) versus placebo (18/70; 25.7%). Adverse events in > 5% of patients on MK-0249 were diarrhea (8.2% vs. 2.9%), headache (8.2% vs. 1.4%), muscle spasms (5.5% vs. 0%), insomnia (5.5% vs. 0%) and stomach discomfort (5.5% vs. 0%). MK-0249 5-mg once daily over 4 weeks was not effective in improving cognitive function in mild to moderate AD patients who were on concomitant symptomatic AD treatment. (ClinicalTrials.gov trial registration, NCT00420420).     

Ciproxifan,a histamine H3-receptor antagonist/inverse agonist,modulates the effects of methamphetamine on neuropeptide mRNA expression in rat striatum

We have explored the effect of histamine H3-receptor ligands on the regulation of neuropeptide mRNA expression in the striatum by using in situ hybridization performed with proenkephalin, prodynorphin, substance P and proneurotensin riboprobes. Acute administration of ciproxifan, an H3-receptor antagonist/inverse agonist, or (R)-alpha-methylhistamine, an H3-receptor agonist, did not modify the striatal expression of the neuropeptides by itself. However, ciproxifan strongly and differentially modulated the effect of a single administration of 3 mg/kg methamphetamine on neuropeptide mRNA expression. This modulation was suppressed by the administration of (R)-alpha-methylhistamine and occurred in both the caudate-putamen and nucleus accumbens. Ciproxifan strongly potentiated the decrease of proenkephalin mRNA expression induced by methamphetamine. In contrast, it suppressed the increase in prodynorphin and substance P mRNA expression induced by methamphetamine. Methamphetamine alone or with ciproxifan did not modify proneurotensin mRNA expression. These neurochemical findings indicate that ciproxifan differentially regulates the effect of methamphetamine on the neuropeptides contained in striatonigral and striatopallidal neurons. They suggest that endogenous histamine and dopamine cooperate to modulate the activity of striatal projection neurons and strengthen the interest of H3-receptors as new targets for the treatment of psychotic disorders and drug abuse.     

Comparison of the effect of an H(3)-inverse agonist on energy intake and hypothalamic histamine release in normal mice and leptin resistant mice with high fat diet-induced obesity

Leptin is a key signal linking peripheral adiposity levels to the regulation of energy homeostasis in the brain. The injection of leptin decreases body weight and food intake in lean rodents; however, in a rodent model of high fat diet-induced obesity (DIO), the exogenous leptin cannot improve adiposity. This ineffectiveness is known as leptin resistance, and the factors downstream of leptin signaling have received attention as viable targets in the treatment of obesity. We previously reported that the histaminergic system is one of the targets of leptin. In the present study, the effect of an H(3)-receptor inverse agonist on hypothalamic histamine release and energy intake was investigated in normal and DIO mice. Leptin (1.3 mg/kg, i.p.) significantly increased hypothalamic histamine release and reduced 12 h-energy intake in normal mice, but had no such effects in DIO mice. In contrast, clobenpropit (5 mg/kg, i.p.), an H(3)-inverse agonist, elicited a significant increase in histamine release in both types of mice. Clobenpropit did not reduce 12 h-energy intake; however, it decreased 3 h-energy intake in both types of mice. These results suggest that lack of the activation of the histaminergic system partly contributes to obesity in DIO mice and direct activation of the histaminergic system circumvents leptin resistance.     

Structure of the human histamine H3 receptor gene (HRH3) and identification of naturally occurring variations

Summary. Neurotransmitter release is modulated by presynaptic histamine H₃ receptors located on histaminergic, noradrenergic and other nonhistaminergic neurons of the central and peripheral nervous system. Here, we report the determination of the structure of the human histamine H₃ receptor gene (HRH3) and the identification of a missense mutation (Ala280Val) in a patient with Shy-Drager syndrome. The coding region of the gene consists of three exons interrupted by two introns of approximately 1 kb in size. Exon boundaries only partly correspond to transmembrane domain organization. The homozygous Ala280Val variation in the third intracellular loop of the histamine H₃ receptor of a patient with Shy-Drager syndrome may be related to the etiology of the illness due to altered norepinephrine release. Furthermore, knowledge of the gene structure allows the verification of alternative splicing of the receptor. The corresponding histamine H₃ receptor isoforms as reported for the guinea pig and rat histamine H₃ receptor in different brain regions are not found in the human brain. Received July 11, 2001; accepted November 30, 2001     

In vitro characterization of SLV308 (7-[4-methyl-1-piperazinyl]-2(3H)-benzoxazolone, monohydrochloride): a novel partial dopamine D2 and D3 receptor agonist and serotonin 5-HT1A receptor agonist

Present Parkinson's disease treatment strategies are far from ideal for a variety of reasons; it has therefore been suggested that partial dopamine receptor agonism might be a potential therapeutic approach with potentially fewer side effects. In the present study, we describe the in vitro characterization of the nonergot ligand SLV308 (7-[4-methyl-1-piperazinyl]-2(3H)-benzoxazolonemonohydrochloride). SLV308 binds to dopamine D(2), D(3), and D(4) receptors and 5-HT(1) (A) receptors and is a partial agonist at dopamine D(2) and D(3) receptors and a full agonist at serotonin 5-HT(1) (A) receptors. At cloned human dopamine D(2,L) receptors, SLV308 acted as a potent but partial D(2) receptor agonist (pEC(50) = 8.0 and pA(2) = 8.4) with an efficacy of 50% on forskolin stimulated cAMP accumulation. At human recombinant dopamine D(3) receptors, SLV308 acted as a partial agonist in the induction of [(35)S]GTPgammaS binding (intrinsic activity of 67%; pEC(50) = 9.2) and antagonized the dopamine induction of [(35)S]GTPgammaS binding (pA(2) = 9.0). SLV308 acted as a full 5-HT(1) (A) receptor agonist on forskolin induced cAMP accumulation at cloned human 5-HT(1) (A) receptors but with low potency (pEC(50) = 6.3). In rat striatal slices SLV308 concentration-dependently attenuated forskolin stimulated accumulation of cAMP, as expected for a dopamine D(2) and D(3) receptor agonist. SLV308 antagonized the inhibitory effect of quinpirole on K(+)-stimulated [(3)H]-dopamine release from rat striatal slices (pA(2) = 8.5). In the same paradigm, SLV308 had antagonist properties in the presence of quinpirole (pA(2) = 8.5), but the partial D(2) agonist terguride had much stronger antagonistic properties. In conclusion, SLV308 combines high potency partial agonism at dopamine D(2) and D(3) receptors with full efficacy low potency serotonin 5-HT(1) (A) receptor agonism and is worthy of profiling in in vivo models of Parkinson's disease.     

Dopamine (D2/3) receptor agonist positron emission tomography radiotracer [11C]-(+)-PHNO is a D3 receptor preferring agonist in vivo

[11C]PHNO is a recently introduced agonist to image DA D2-like receptors with Positron Emission Tomography (PET). In cats and humans, [11C]PHNO revealed an atypical distribution compared to radiolabeled D2-like antagonists (such as [11C]raclopride) or other D2-like agonists (such as [11C]NPA), as it displayed unusual high binding in the globus pallidus (GP). The goal of this study was to assess the pharmacological nature of the binding of [11C]PHNO in the GP in nonhuman primates. As previously reported in humans, [11C]PHNO equilibrium specific to nonspecific equilibrium partition coefficients (V3') in baboons was much higher in GP (3.88 +/- 1.15) than in the dorsal striatum (DST, 2.07 +/- 0.43), whereas the reverse was true for [11C]raclopride (1.48 +/- 0.41 in GP, 2.56 +/- 0.91 in DST) and [11C]NPA (0.87 +/- 0.19 in GP, 1.02 +/- 0.13 in DST). Administration of unlabeled raclopride resulted in similar reductions of [11C] PHNO V3' and [11C]raclopride V3' in both the GP and the DST. This observation demonstrated that the [11C]PHNO binding in the GP was specific to D2-like receptors. To evaluate the respective contribution of D3 and D2 receptors to the binding potential (BP) of [11C]PHNO and [11C]raclopride, experiments were carried out with the selective D3 partial agonist 1-(4(2-Napthoylamino)butyl)-4-(2-methoxyphenyl)-1A-piperazine HCL (BP897). BP897 reduced [11C]raclopride V3' by 29% +/- 9%, 19% +/- 8%, and 10% +/- 7% in GP, VST, and DST, respectively, a result consistent with expectation from postmortem studies (D3/D2 ratio in GP > VST > DST). BP897 reduced [11C]PHNO V3' by 57% +/- 11%, 30% +/- 11%, and 13% +/- 8% in GP, VST, and DST, respectively, indicating that the D3 receptor contribution to [11C]PHNO signal is higher than that of [11C]raclopride. From these experiments we conclude that [11C]PHNO is a D3 preferring agonist, and that this property explains the high GP signal not observed with [11C]raclopride or [11C]NPA. This property might contribute to its higher vulnerability to endogenous DA compared to [11C]raclopride and [11C]NPA.     

Effects of H1- and H2-histamine receptor agonists and antagonists on sleep and wakefulness in the rat

Summary The H 1-receptor agonist 2-thiazolylethylamine (2-TEA) given by i.c.v. route dose-dependently increased wakefulness (W) and decreased NREM sleep (NRMS) and REM sleep (REMS) in rats prepared for chronic sleep recordings. The H 1-receptor antagonists pyrilamine and diphenhydramine given by i.p. route decreased W and increased NREMS. Pyrilamine prevented the increase of W and decrease of NREMS produced by 2-TEA. However, REMS reduction was not antagonized, what tends to suggest that two different mechanisms could be involved in the 2-TEA-induced effects on NREMS and REMS.Cimetidine which blocks H 2-receptors, when given by i.p. route showed no significant effects on sleep and W. Administration of the H 2-receptor agonist dimaprit and the H 2-receptor antagonists cimetidine, metiamide and ramtidine by i.c.v. route induced the appearance of high voltage spikes at cortical leads, thus leaving inconclusive the matter of their effects on sleep and wakefulness.Our results tend to support the proposal that the H 1-receptor intervenes in sleep-wakefulness regulation. Limitations in the available H 2-receptor agonists and antagonists presently preclude a more detailed analysis of the role of H 2-receptors on sleep and W.     

Histamine responses of large neostriatal interneurons in histamine H1 and H2 receptor knock-out mice

Histamine (HA) is an important neuro-modulator, contributing to a variety of physiological responses in the mammalian central nervous system (CNS). However there is little information about the cell/signaling mechanism underlying its role. In the present study, we characterized HA responses in single large neostriatal neurons acutely dissociated from wild type (WT) and HA receptor knock-out (KO) mice, with a particular emphasis on identifying the role of HA receptor subtypes. HA (10 μM) and a selective H₂ receptor agonist dimaprit (1 μM) both evoked an inward current in H₁-KO mice, and HA and a selective H₁ receptor agonist HTMT (10 μM) both evoked an inward current in H₂-KO mice. In the H₁ and H₂ double (H_1/2) KO mice, there was no response to either the application of HA or the selective H₁, H₂ receptor agonists. Hence we have confirmed that the targeted genes were indeed absent in these KO mice and that both receptor subtypes contribute to HA's excitatory actions. Furthermore the HA-induced inward currents were mediated by a decrease in current through K⁺ channels. In addition, we observed the effects of methamphetamine (METH) on the locomotor activity of WT and HA receptor KO mice, and found that METH-induced behavioral sensitization is evident in H_1/2-KO mice, but not in H₁- or H₂-KO mice. These observations suggest that suppressive roles of HA on methamphetamine-induced behavioral sensitization would be mediated through both H₁ and H₂ receptors in the CNS including neostriatum.     

Improvement of spatial memory by (R)-alpha-methylhistamine, a histamine H(3)-receptor agonist, on the Morris water-maze in rat.

This work aims to clarify the role of histamine in learning and memory. This is done by studying the effect of administration of the histamine precursor, L-histidine (His), and the agonist of the H(3) receptor (R)-alpha-methylhistamine (RAMH), on acquisition and retention of spatial reference memory in rats. Treatment with RAMH (10 mg/kg i.p.) facilitates recovery of spatial memory. In contrast, administration of His (500 mg/kg i.p.) does not affect the performance of this task. Moreover, pharmacological modulation of the cerebral histaminergic system does not impair the animal's behavioral flexibility, i.e. their ability to adapt to a new learning task in the same stimular context. Improved retention of spatial memory after a reduction in cerebral histamine confirms the modulating role of this neurotransmitter in memory processes.     

Chromosomal mapping and organization of the human histamine H3 receptor gene

The histamine H3 receptor (H3R) was recently cloned, and two isoforms, termed H3L and H3S, differing in the third intracytosolic loop, were isolated but the chromosomal mapping and organization of its gene remained unknown. PCR analysis of a human x rodent cell hybrid panel indicated that the H3R gene is located in the telomeric region of chromosome 20q. Alignment of human H3R cDNA sequences with DNA sequences of this chromosome revealed that its coding region comprises three exons interrupted by two introns located in the second transmembrane domain (TM2) and second intracytosolic loop, respectively. Thus the organization of the H3R gene indicates that the H3L and H3S isoforms, that we characterized not only in rodents but also in humans, are generated by retention and deletion, respectively, of a pseudo-intron located in the third intracytosolic loop.     

Decreased histamine H1 receptor binding in the brain of depressed patients

The central histaminergic neuron system modulates the wakefulness, sleep-awake cycle, appetite control, learning and memory, and emotion. Previous studies have reported changes in neuronal histamine release and its metabolism under stress conditions in the mammalian brain. In this study, we examined, using positron emission tomography (PET) and [(11)C]-doxepin, whether the histaminergic neuron system is involved in human depression. Cerebral histamine H1 receptor (H(1)R) binding was measured in 10 patients with major depression and in 10 normal age-matched subjects using PET and [(11)C]-doxepin. Data were calculated by a graphical analysis on voxel-by-voxel and ROI (region of interests) basis. Binding potential (BP) values for [(11)C]-doxepin binding in the frontal and prefrontal cortices, and cingulate gyrus were significantly lower in the depressed patients than those in the normal control subjects. There was no area of the brain where [(11)C]-doxepin binding was significantly higher in the depressed patients than in the controls. ROI-based analysis also revealed that BP values for [(11)C]-doxepin binding in the frontal cortex and cingulate gyrus decreased in proportion to self-rating depressive scales scores. The results of this study demonstrate that depressed patients have decreased brain H(1)R binding and that this decrease correlates with the severity of depression symptoms. It is therefore suggested that the histaminergic neuron system plays an important role in the pathophysiology of depression and that its modulation may prove to be useful in the treatment of depression.     

Immunological identification of the mammalian H3 histamine receptor in the mouse brain

Affinity-purified antibodies raised against the peptide sequence H3 (349-358) receptor specifically recognized two protein species with Mr 62,000 and 93,000 in adult mouse forebrain membranes. Both immunoreactive species were suppressed greatly by preincubation of the antibody with the respective peptide. Immunohistochemical analysis using affinity-purified anti-H3 (349-358) antibodies yielded a high degree of coincidence with ligand-autoradiographical information, with high levels detected in the CA3 and dentate gyrus of the hippocampus, laminae V of the cerebral cortex, the olfactory tubercle, Purkinje cell layer of the cerebellum, substantia nigra, globus pallidus, thalamus and striatum. This study suggests further biochemical evidence for multiple H3 receptor subtypes and the widespread distribution of the H3 receptor in the mammalian brain.     

Effects of the 5-HT3 receptor agonist 1-(m-chlorophenyl)-biguanide in the rat kindling model of epilepsy

The present study was conducted to identify serotonin (5-HT) receptor subtypes involved in the development of amygdala (AM) kindling. We used 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), a 5-HT_1A agonist, and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), a 5-HT₂ agonist, both of which were injected subcutaneously 15 min prior to each daily electrical stimulation to the rat AM. Treatment with 8-OH-DPAT (1 mg/kg) slightly suppressed behavioral and electrographic seizure development during the course of kindling. In contrast, DOI (1 mg/kg) strongly facilitated kindling development and reduced the number of stimulations needed to produce generalized seizures. These facilitatory effects of DOI were completely blocked by pretreatment with a 5-HT₂ antagonist ketanserin. The present results suggest that the activation of 5-HT_1A receptors can retard the development of AM kindling, whereas 5-HT₂ receptors play a facilitatory role in this developmental seizure process.