Abstract
Publisher Summary This chapter discusses the new histamine H 3 receptor ligands as pharmacological tools. In various brain areas, neuronal histamine release and synthesis is regulated presynaptically by histamine H 3 receptors. Recent studies reveal that H 3 receptors not only act as autoreceptors to regulate the release and synthesis of histamine, but also modulate the release of other neurotransmitters, like acetylcholine, serotonin, dopamine, and noradrenaline. Potent agonists for the H 3 receptor are obtained by simple modifications of the histamine molecule. The imidazole ring is very important for H 3 agonistic activity. Methylation of one of the nitrogens or replacements with other aromatic ring systems is not tolerated. It is apparent on comparing the structures of histamine and imetit that the distance between the imidazole ring and the protonated group on the sidechain are different. Decreasing or increasing the alkyl sidechain of histamine with one methyl group completely eliminates the H 3 agonistic activity at the guinea-pig jejunum. The chapter identifies several H 3 receptor ligands with different pharmacological characteristics. However, before a definite subclassification of the H 3 receptor can be accepted, a careful investigation of the pharmacological profile of several impentamine analogues is needed.
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