Abstract
This article describes the cellular sources for tyramine and the cellular targets of tyramine via the Tyramine Receptor 1 (AmTyr1) in the olfactory learning and memory neuropils of the honey bee brain. Clusters of approximately 160 tyramine immunoreactive neurons are the source of tyraminergic fibers with small varicosities in the optic lobes, antennal lobes, lateral protocerebrum, mushroom body (calyces and gamma lobes), tritocerebrum and subesophageal ganglion (SEG). Our tyramine mapping study shows that the primary sources of tyramine in the antennal lobe and calyx of the mushroom body are from at least two Ventral Unpaired Median neurons (VUMmd and VUMmx) with cell bodies in the SEG. To reveal AmTyr1 receptors in the brain, we used newly characterized anti-AmTyr1 antibodies. Immunolocalization studies in the antennal lobe with anti-AmTyr1 antibodies showed that the AmTyr1 expression pattern is mostly in the presynaptic sites of olfactory receptor neurons (ORNs). In the mushroom body calyx, anti-AmTyr1 mapped the presynaptic sites of uniglomerular Projection Neurons (PNs) located primarily in the microglomeruli of the lip and basal ring calyx area. Release of tyramine/octopamine from VUM (md and mx) neurons in the antennal lobe and mushroom body calyx would target AmTyr1 expressed on ORN and uniglomerular PN presynaptic terminals. The presynaptic location of AmTyr1, its structural similarity with vertebrate alpha-2 adrenergic receptors, and previous pharmacological evidence suggests that it has an important role in the presynaptic inhibitory control of neurotransmitter release.
Highlights
The biogenic amines tyramine and octopamine are neuroactive compounds that are involved in a large repertoire of invertebrate behaviors, including locomotion, sensory processing, learning and memory (Roeder, 2005; Scheiner et al, 2006; Lange, 2009)
When the same working dilution of anti-tyramine antibodies was preincubated with octopamine-G-bovine serum albumin (BSA), the tyramine immunoreactive staining in the cell bodies and processes was still present (Figure 1C)
One of the important findings in our studies is that tyramine could originate from VUMmx and VUMmd neurons in the antennal lobe, lateral protocerebrum and mushroom body calyx
Summary
The biogenic amines tyramine and octopamine are neuroactive compounds that are involved in a large repertoire of invertebrate behaviors, including locomotion, sensory processing, learning and memory (Roeder, 2005; Scheiner et al, 2006; Lange, 2009). Since Erspamer and Boretti (1951a,b) first described octopamine in the salivary gland of the octopus as having ‘‘adrenaline-like’’ action, many studies have demonstrated the important role octopamine and its biosynthetic precursor tyramine play in invertebrate physiology and behavior. The source of octopamine was mostly allocated to the paracrine cells, the so-called dorsal (ventral) unpaired median (DUM/VUM) neurons, first described by Plotnikova (1969). Due to their location on Tyramine Receptor in Insect Brain the midline of the ventral nerve cord and brain, and to their unique morphology, Hoyle (1974) proposed that these octopaminergic neurons are involved in the modulation of many types of behavior. Studies in the fruit fly larval central nervous system reported the presence of tyramine-containing neurons that are distinct from octopaminergic neurons (Nagaya et al, 2002)
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