The phenolamines tyramine and octopamine are decarboxylation products of the amino acid tyrosine. Although tyramine is the biological precursor of octopamine, both compounds are independent neurotransmitters, acting through various G-protein coupled receptors. Especially, octopamine modulates a plethora of behaviors, peripheral and sense organs. Both compounds are believed to be homologues of their vertebrate counterparts adrenaline and noradrenaline. They modulate behaviors and organs in a coordinated way, which allows the insects to respond to external stimuli with a fine tuned adequate response. As these two phenolamines are the only biogenic amines whose physiological significance is restricted to invertebrates, the attention of pharmacologists was focused on the corresponding receptors, which are still believed to represent promising targets for new insecticides. Recent progress made on all levels of octopamine/tyramine research enabled us to better understand the molecular events underlying the control of complex behaviors.

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1 Honey bees are perhaps the most versatile models to study the cellular and pharmacological basis underlying behaviours ranging from learning and memory to sociobiology. For both aspects octopamine (OA) is known to play a vital role. 2 The neuronal octopamine receptor of the honey bee shares pharmacological similarities with the neuronal octopamine receptor of the locust. Both, agonists and antagonists known to have high anities for the locust neuronal octopamine receptor have also high anities for the bee neuronal octopamine receptor. 3 The distribution of receptors is more or less congruent between locusts and bees. Optic lobes and especially the mushroom bodies are areas of greatest octopamine receptor expression in both species, which mirrors the physiological signi®cance of octopamine in the insect nervous system. 4 The neuronal octopamine receptor of insects served as a model to study the pharmacological similarity of homologous receptors from distantly related species, because bees and locusts are separated by at least 330 million years of evolution.

Histamine-gated chloride channels, members of the ligandgated ion channel superfamily, are thought to be peculiar for arthropods. Their cognate ligand, histamine, is the transmitter of all arthropod photoreceptors and of thoracic mechanoreceptors. To identify putative histamine-gated chloride channel subunits we scanned the Drosophila genome for putative ligand-gated chloride channel subunits and found 12 candidate genes. We found four groups of transcripts based on their expression pattern. Only members of the last group show an expression pattern that is consistent with our knowledge about histamine-gated chloride channels in insects. In the brain these transcripts (Dm HA-Cl I and II) are exclusively present in interneurones postsynaptic to photoreceptors.Within the lamina (the first visual ganglion) only the L1-L3 neurones are labelled. The lack of non-photoreceptor dependent staining in the brain indicates that mechanosensory transmission differs between the head and the thorax/abdomen, and that the receptors responding to brain-intrinsic histaminergic cells use different signalling pathways. The putative histamine-gated chloride channels show the greatest homology mammalian glycine receptors. These ion-channels are the first specific molecular markers for postsynaptic cells in the insect visual system, thus representing ideal tools to study its physiology and development.

Summary. 1. Several flight parameters, the wing-beat frequency, the wing-stroke angles, the lift and the flight speed, were measured simultaneously by means of a pendulum or a transducer apparatus (Figs. 1, 2) in tethered flying Locusta migratoria ( 2 ~).2. In normal locusts all these parameters decrease with increasing duration of flight , i.e., they are positively correlated (Figs. 8, 9). The wing-beat frequency seems to be the primary factor in governing flight speed and lift.3. It is demonstrated by elimination experiments that all measured flight parameters are controlled in part by the air-current sense organs of the head, i.e., the hair patches and the antelmae. After immobilization of the wind sensitive hairs the wing-beat frequency and the flight speed are reduced with respect to normal animals (Figs. 3c, 4c). If the antennae are eliminated, however, the wing-beat frequency, the wing-stroke angle and the flight speed are increased (Figs. 3b, 4b, 5a, e, 6a). These findings suggest that in free flying locusts the air-current sense organs affect the flight speed in opposite ways: the hair patches stimulate it and the antennae reduce it, they being the sensory units of a negative feedback mechanism.4. Since the flight speed is increased and the lift decreased in flagella-less locusts in relation to normal ones, it is clear that the antennae govern the direction of the "resulting force" of these tethered flying locusts (Fig. 10b).5: The maintenance of flight is enhanced by both the hair patches and the antennae.