Discovery of (1R,6S)-5-[4-(1-cyclobutyl-piperidin-4-yloxy)-phenyl]-3,4-diaza-bicyclo[4.1.0]hept-4-en-2-one (R,S-4a): histamine H(3) receptor inverse agonist demonstrating potent cognitive enhancing and wake promoting activity

Short- and Long-Term Social Recognition Memory Are Differentially Modulated by Neuronal Histamine

The ability of recognizing familiar conspecifics is essential for many forms of social interaction including reproduction, establishment of dominance hierarchies, and pair bond formation in monogamous species. Many hormones and neurotransmitters have been suggested to play key roles in social discrimination. Here we demonstrate that disruption or potentiation of histaminergic neurotransmission differentially affects short (STM) and long-term (LTM) social recognition memory. Impairments of LTM, but not STM, were observed in histamine-deprived animals, either chronically (Hdc^−/− mice lacking the histamine-synthesizing enzyme histidine decarboxylase) or acutely (mice treated with the HDC irreversible inhibitor α-fluoromethylhistidine). On the contrary, restriction of histamine release induced by stimulation of the H₃R agonist (VUF16839) impaired both STM and LTM. H₃R agonism-induced amnesic effect was prevented by pre-treatment with donepezil, an acetylcholinesterase inhibitor. The blockade of the H₃R with ciproxifan, which in turn augmented histamine release, resulted in a procognitive effect. In keeping with this hypothesis, the procognitive effect of ciproxifan was absent in both Hdc^−/− and αFMH-treated mice. Our results suggest that brain histamine is essential for the consolidation of LTM but not STM in the social recognition test. STM impairments observed after H₃R stimulation are probably related to their function as heteroreceptors on cholinergic neurons.

Central Histamine Boosts Perirhinal Cortex Activity and Restores Forgotten Object Memories

BACKGROUND

A method that promotes the retrieval of lost long-term memories has not been well established. Histamine in the central nervous system is implicated in learning and memory, and treatment with antihistamines impairs learning and memory. Because histamine H₃ receptor inverse agonists upregulate histamine release, the inverse agonists may enhance learning and memory. However, whether the inverse agonists promote the retrieval of forgotten long-term memory has not yet been determined.

METHODS

Here, we employed multidisciplinary methods, including mouse behavior, calcium imaging, and chemogenetic manipulation, to examine whether and how the histamine H₃ receptor inverse agonists, thioperamide and betahistine, promote the retrieval of a forgotten long-term object memory in mice. In addition, we conducted a randomized double-blind, placebo-controlled crossover trial in healthy adult participants to investigate whether betahistine treatment promotes memory retrieval in humans.

RESULTS

The treatment of H₃ receptor inverse agonists induced the recall of forgotten memories even 1 week and 1 month after training in mice. The memory recovery was mediated by the disinhibition of histamine release in the perirhinal cortex, which activated the histamine H₂ receptor. Histamine depolarized perirhinal cortex neurons, enhanced their spontaneous activity, and facilitated the reactivation of behaviorally activated neuronal ensembles. A human clinical trial revealed that treatment of H₃ receptor inverse agonists is specifically more effective for items that are more difficult to remember and subjects with poorer performance.

CONCLUSIONS

These results highlight a novel interaction between the central histamine signaling and memory engrams.

Brain histamine modulates recognition memory: possible implications in major cognitive disorders

Several behavioural tests have been developed to study and measure emotionally charged or emotionally neutral memories and how these may be affected by pharmacological, dietary or environmental manipulations. In this review, we describe the experimental paradigms used in preclinical studies to unravel the brain circuits involved in the recognition and memorization of environmentally salient stimuli devoid of strong emotional value. In particular, we focus on the modulatory role of the brain histaminergic system in the elaboration of recognition memory that is based on the judgement of the prior occurrence of an event, and it is believed to be a critical component of human declarative memory. The review also addresses questions that may help improve the treatment of impaired declarative memory described in several affective and neuropsychiatric disorders such as ADHD, Alzheimer's disease and major neurocognitive disorder. LINKED ARTICLES: This article is part of a themed section on New Uses for 21st Century. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.3/issuetoc.

3-(1'-Cyclobutylspiro[4H-1,3-benzodioxine-2,4'-piperidine]-6-yl)-5,5-dimethyl-1,4-dihydropyridazin-6-one (CEP-32215), a new wake-promoting histamine H3 antagonist/inverse agonist

CEP-32215 is a new, potent, selective, and orally bioavailable inverse agonist of the histamine H3 receptor (H3R) with drug-like properties. High affinity in human (hH3R Ki = 2.0 ± 0.2 nM) and rat (rH3R Ki = 3.6 ± 0.7 nM) H3R radioligand binding assays was demonstrated. Potent functional antagonism (Kb = 0.3 ± 0.1 nM) and inverse agonism (EC50 = 0.6 ± 0.2 nM) were demonstrated in [(35)S]guanosine 5(')-O-(γ-thio)-triphosphate binding assays. Oral bioavailability and dose-related exposure was consistent among rat, dog, and monkey. After oral dosing, occupancy of H3R by CEP-32215 was estimated by the inhibition of ex vivo binding in rat cortical slices (ED50 = 0.1 mg/kg p.o.). Functional antagonism in brain was demonstrated by the inhibition of R-α-methylhistamine-induced drinking in the rat dipsogenia model (ED50 = 0.92 mg/kg). CEP-32215 significantly increased wake duration in the rat EEG model at 3-30 mg/kg p.o. Increased motor activity, sleep rebound or undesirable events (such as spike wave or seizure activity) was not observed following doses up to 100 mg/kg p.o., indicating an acceptable therapeutic index. CEP-32215 may have potential utility in the treatment of a variety of sleep disorders. This article is part of the Special Issue entitled 'Histamine Receptors'.