EPINASTINE, A HIGHLY SPECIFIC ANTAGONIST OF INSECT NEURONAL OCTOPAMINE RECEPTORS

The tetracyclic compound epinastine (3-amino-9, 13b-dihydro-1H-dibenz( c,f)imidazo(l,5a)azepine hydrochloride) that was recently introduced a s a vertebrate histamine H, receptor antagonist has also high affinity for insect neuronal octopamine receptors. This holds true for the neu ronal octopamine receptor from the locust (K-i = 2 Nm) as well as from the honey bee nervous system (K-i = 1.1 Nm). In addition to its high affinity, it has a high degree of specificity. Its affinity for other insect receptors for biogenic amines, such as 5-hydroxytryptamine, dop amine, histamine, and tyramine, is at least four orders of magnitude l ower. Therefore, epinastine could serve as a highly specific antagonis t of octopamine receptors that enables physiological dissection of oct opaminergic neurotransmission within the nervous system of insects. To demonstrate these abilities, epinastine was used to inhibit the visua lly evoked activity of an identified interneuron in the visual pathway which is known to be modulated by octopamine. (C) 1998 Elsevier Scien ce B.V. All rights reserved.